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060884185 | claims | 1. A method of mitigating pressure disturbances resulting from venting gas through a series of spargers submerged in a liquid coolant that is contained in a suppression pool, the method comprising the steps of: obtaining fundamental frequencies of the pressure disturbances arising at each of the spargers; adjusting the time delay between the start of gas venting of two successive spargers so as to substantially satisfy the relation ##EQU19## wherein .tau. represents the time delay and .function.represents the fundamental frequency of the disturbance at the later venting sparger; and repeating the adjusting step for every pair of successive spargers in the series of spargers. obtaining fundamental frequencies of the pressure disturbances arising at each of the spargers; adjusting phase angles of the disturbances at two successive spargers so that the phase angles substantially satisfy the relation ##EQU20## wherein .phi..sub.i and .phi..sub.i-1 represent the phase angles of the disturbances at two successive spargers, i is an integer greater than one and less than or equal to N and denotes the serial position of the sparger, and m is a positive integer greater than or equal to zero; and repeating the adjusting step for every pair of successive spargers in the series of spargers. a series of spargers submerged in the suppression pool, wherein the total number of spargers equals N; and a header sequentially connecting each of the spargers; wherein the spargers are configured in such a way that when steam is vented into the header from the nuclear reactor, pressure disturbances arising at any two successive spargers substantially satisfy the relation ##EQU21## wherein .phi..sub.i and .phi..sub.i-1 represent phase angles of the disturbances at two successive spargers, i is an integer greater than one and less than or equal to N and denotes the serial position of the sparger, and m is a positive integer greater than or equal to zero. 2. The method of claim 1, wherein the adjusting step, the time delay between the start of gas venting of two successive spargers is about one-half the reciprocal of the fundamental frequency of the pressure disturbance at the later venting sparger. 3. The method of claim 1, wherein the adjusting step, the requisite time delay is achieved by providing an appropriate separation distance along a header connecting successive spargers. 4. The method of claim 3, wherein the adjusting step, the appropriate separation distance is found by obtaining the velocity of fluid in the header prior to gas venting through the spargers. 5. The method of claim 4, wherein the adjusting step, the velocity of the fluid is obtained by determining the gas velocity behind a shock wave traveling in the header. 6. The method of claim 4, wherein the adjusting step, the velocity of the fluid is obtained by determining the liquid coolant flow rate out of the spargers. 7. The method of claim 1, wherein the adjusting step, the requisite time delay is achieved by providing successive spargers that vent gas at different depths in the suppression pool. 8. The method of claim 1, further comprising the step of modifying the spargers so that the disturbance frequencies of successive spargers are about the same. 9. The method of claim 8, wherein the modifying step comprises arranging successive spargers so that they vent gas at different depths in the suppression pool. 10. The method of claim 8, wherein the modifying step comprises providing successive spargers with different flow areas for venting gas. 11. A method of mitigating pressure disturbances resulting from venting gas through a series of spargers submerged in a liquid coolant that is contained in a suppression pool, wherein the total number of spargers equals N, the method comprising the steps of: 12. The method of claim 11, wherein the adjusting step, the absolute value of the difference in phase angle between the successive spargers is about .pi. radians. 13. The method of claim 11, wherein the adjusting step, the requisite relation between the phase angles of successive spargers is achieved by providing an appropriate separation distance along a header connecting successive spargers. 14. The method of claim 13, wherein the adjusting step, the appropriate separation distance is found by obtaining the velocity of fluid in the header prior to gas venting through the spargers. 15. The method of claim 14, wherein the adjusting step, the velocity of the fluid is obtained by determining the gas velocity behind a shock wave traveling in the header. 16. The method of claim 14, wherein the adjusting step, the velocity of the fluid is obtained by determining the liquid coolant flow rate out of the spargers. 17. The method of claim 11, wherein the adjusting step, the requisite relation between the phase angles is achieved by providing successive spargers that vent gas at different depths in the suppression pool. 18. The method of claim 11, further comprising the step of modifying the spargers so that the disturbance frequencies of successive spargers are about the same. 19. The method of claim 18, wherein the modifying step comprises arranging successive spargers so that they vent gas at different depths in the suppression pool. 20. The method of claim 18, wherein the modifying step comprises providing successive spargers with different flow areas for venting gas. 21. An apparatus for mitigating pressure disturbances resulting from venting steam from a nuclear reactor into a suppression pool, the apparatus comprising: 22. The apparatus of claim 21, wherein the absolute value of the difference in phase angle between any two successive spargers is about .pi. radians. 23. The apparatus of claim 21, wherein distances between each of the spargers along the header are dimensioned so as to satisfy the relation between the phase angles of disturbances at any two successive spargers. 24. The apparatus of claim 21, wherein the header is filled with a stagnant gas prior to venting steam. 25. The apparatus of claim 21, wherein the header is filled with a liquid coolant prior to venting steam. 26. The apparatus of claim 21, wherein each of the spargers are substantially the same. 27. The apparatus of claim 21, wherein venting depths of the spargers are chosen so that they satisfy the relation between the phase angles of the disturbances at any two successive spargers. 28. The apparatus of claim 21, wherein the spargers are configured in such a way that when steam is vented into the header from the nuclear reactor, pressure disturbances arising at each of the spargers have about the same frequency. 29. The apparatus of claim 28, wherein venting depths of the spargers are chosen so that the pressure disturbances arising at each of the spargers have about the same frequency. 30. The apparatus of claim 28, wherein flow areas for venting steam from the spargers are sized so that the pressure disturbances arising at each of the spargers have about the same frequency. |
039430375 | claims | 1. A system for the wet exchange of fuel elements in a nuclear reactor housed in a round reactor building having a generally circularly extending vertical wall surrounding the nuclear reactor; the nuclear reactor being of the type having a safety pressure vessel containing nuclear fuel elements in use, a reactor pool situated above the pressure vessel, a fuel element storage pool of arcuate outline, a gate-controlled channel connecting the reactor pool with the storage pool, and an operating platform situated adjacent the pools; comprising in combination: a. a support column disposed within and substantially centrally with respect to said reactor building; b. a first fuel element exchange gantry including a bridge disposed above the level of said operating platform and having two opposite ends, one of said ends being supported on said column; c. an arcuately extending rail held in said vertical wall above the level of said operating platform and supporting the other of said ends of said bridge; d. a second fuel element exchange gantry having a cantilever bridge; e. means for supporting said second gantry below said first gantry and providing for said second gantry a free, unobstructed passage under said first gantry; and f. at least one fuel element box-stripping machine disposed at said storage pool immediately across from said channel within the operational range of said first and second gantries. 2. A system as defined in claim 1, wherein said one end of the bridge of said first gantry is supported for rotation about a vertical axis extending centrally with respect to the reactor building. 3. A system as defined in claim 1, including at least one tool storing device disposed immediately laterally adjacent said box-stripping machine. 4. A system as defined in claim 1, wherein the reactor building has a roof, said column is connected to the roof for serving as a roof support. 5. A system as defined in claim 1, wherein said column includes means for supporting a building gantry situated above said first gantry. 6. A system as defined in claim 1, wherein said means for supporting said second gantry includes two additional, vertically spaced parallel rails supported in said wall below the rail associated with said first gantry. 7. A system as defined in claim 6, wherein the rail associated with said first gantry defines a travelling path for said first gantry for carrying fuel elements between the pressure vessel and the box-stripping machine through the reactor pool, the channel and the storage pool; the additional rails associated with said second gantry define a travelling path for said second gantry for carrying fuel elements through the storage pool between the box-stripping machine and their location of storage in the storage pool. |
059498374 | summary | TECHNICAL FIELD The present invention relates in general to light water nuclear reactor designs which employ thorium as a fuel. The reactors can burn with the thorium, nonproliferative enriched uranium, weapons grade plutonium or reactor grade plutonium. BACKGROUND ART Nuclear power remains an important energy resource throughout the world today. Many countries without sufficient indigenous fossil fuel resources rely heavily on nuclear power for the production of electricity. For many other countries, nuclear energy is used as a competitive electricity producer that also diversifies their energy mix. Further, nuclear power also makes a very important contribution to the goals of controlling fossil fuel pollution (e.g., acid rain, global warming), and conservation of fossil fuels for future generations. In terms of numbers, nuclear power provides approximately 11% of the world's electricity. At the end of 1994, there were 424 nuclear power plants in 37 countries. Plants under construction will bring this number to approximately 500 plants by the end of the decade. Although safety is certainly a major concern in the design and operation of nuclear reactors, another major concern is the threat of proliferation of materials which could be used in nuclear weapons. This is of particular concern in countries with unstable governments whose possession of nuclear weapons could pose a significant threat to world security. Nuclear power must therefore be designed and used in a manner which does not cause proliferation of nuclear weapons, and the resulting risk of their use. Unfortunately, all present nuclear power reactors create large amounts of what is known as reactor grade plutonium. For example, a typical 1,000 MWe reactor creates on the order of 200-300 kg per year of reactor grade plutonium. It is not difficult to reprocess this discharged reactor grade plutonium into weapons grade plutonium, and only approximately 7.5 kg of reactor grade plutonium is required to manufacture a single nuclear weapon. Accordingly, the fuel discharged from the cores of conventional reactors is highly proliferative, and safeguards are required to insure that the discharged fuel is not acquired by unauthorized individuals. A similar security problem exists with the vast stockpiles of weapons grade plutonium which have been created as the U.S. and the countries of the former U.S.S.R. have dismantled their nuclear weapons. Other problems involved with the operation of conventional nuclear reactors concern permanent disposal of long term radioactive waste products, as well as the quickly diminishing worldwide supply of natural uranium ore. Regarding the former, government owned repository spaces are virtually nonexistent and the Yucca Flats project located in the United States has now been delayed by Congress. As to the latter, significant problems with supplies of natural uranium ore are foreseen within the next 50 years. As a result of the foregoing problems, attempts have been made in the past to construct nuclear reactors which operate on relatively small amounts of nonproliferative enriched uranium (enriched uranium having a U-235 content of 20% or less), and do not generate substantial amounts of proliferative materials, such as plutonium. Examples of such reactors are disclosed in my two previous international applications, Nos. PCT/US84/01670, published on 25 Apr. 1985 under International Publication No. WO 85/01826, and PCT/US93/01037, published on 19 Aug. 1993 under International Publication No. WO 93/06477. The '826 and '477 applications both disclose seed-blanket reactors which derive a substantial percentage of their power from thorium fueled blankets. The blankets surround an annular seed section which contains fuel rods of nonproliferative enriched uranium. The uranium in the seed fuel rods releases neutrons which are captured by the thorium in the blankets, thereby creating fissionable U-233 which burns in place, and generates heat for powering the reactor. The use of thorium as a nuclear reactor fuel in the foregoing manner is attractive because thorium is considerably more abundant in the world than is uranium. In addition, both of the reactors disclosed in the '826 and '477 applications claimed to be nonproliferative in the sense that neither the initial fuel loading, nor the fuel discharged at the end of each fuel cycle, is suitable for use in the manufacture of nuclear weapons. This is accomplished by employing only nonproliferative enriched uranium as the seed fuel, selecting moderator/fuel volume ratios which minimize plutonium production and adding a small amount of nonproliferative enriched uranium to the blanket whose U-238 component uniformly mixes with the residual U-233 at the end of the blanket cycle, and "denatures" the U-233, thereby rendering it useless for manufacture of nuclear weapons. Unfortunately, Applicant has discovered through continued research that neither of the reactor designs disclosed in the aforementioned international applications is truly nonproliferative. In particular, it has now been discovered that both of these designs result in a higher than minimum production of proliferative plutonium in the seed due to the annular seed arrangement. The use of the annular seed with both an inner, central blanket section and an outer, surrounding blanket section cannot be made nonproliferative because the thin, annular seed has a correspondingly small "optical thickness" which causes the seed spectrum to be dominated by the much harder spectrum of the inner and outer blanket sections. This results in a greater fraction of epithermal neutrons and a higher than minimum production of proliferative plutonium in the seed. Both of these previous reactor designs are also not optimized from an operational parameter standpoint. For example, moderator/fuel volume ratios in the seed and blanket regions are particularly crucial to minimize plutonium production in the seed, permit adequate heat removal from the seed fuel rods and insure optimum conversion of thorium to U-233 in the blanket. Further research indicates that the preferred moderator/fuel ratios disclosed in these international applications were too high in the seed regions and too low in the blanket regions. The previous reactor core designs were also not particularly efficient at consuming the nonproliferative enriched uranium in the seed fuel elements. As a result, the fuel rods discharged at the end of each seed fuel cycle contained so much residual uranium that they needed to be reprocessed for reuse in another reactor core. The reactor disclosed in the '477 application also requires a complex mechanical reactor control arrangement which makes it unsuitable for retrofitting into a conventional reactor core. Similarly, the reactor disclosed in the '826 application cannot be easily retrofitted into a conventional core either because its design parameters are not compatible with the parameters of a conventional core. Finally, both of the previous reactor designs were designed specifically to burn nonproliferative enriched uranium with the thorium, and are not suitable for consuming large amounts of plutonium. Thus, neither of these designs provides a solution to the stockpiled plutonium problem. DISCLOSURE OF INVENTION In view of the foregoing, it is an object of the present invention to provide improved seed-blanket reactors which provide optimum operation from both an economic and a nonproliferative standpoint. It is a further object of the present invention to provide seed-blanket reactors which can be easily retrofitted into conventional reactor cores. It is another object of the present invention to provide a seed-blanket reactor which can be utilized to consume large quantities of plutonium with thorium, without generating proliferative waste products. A still further object of the present invention is to provide seed-blanket reactors which produce substantially reduced amounts of high level radioactive wastes, thereby resulting in a significant reduction in long term waste storage space requirements. The foregoing and other objects of the invention are achieved through provision of improved seed-blanket reactors which utilize thorium fuel in combination with either uranium or plutonium fuel. The first preferred embodiment of the present invention comprises an improved version of the nonproliferative reactor disclosed in the '477 application. Through the use of specific moderator to fuel ratios and a novel refueling scheme, this embodiment of the invention achieves a fuel burn up efficiency which has heretofore been impossible to achieve in any known reactors, and generates only nuclear wastes that are incapable of being used for formation of nuclear weapons. A second preferred embodiment of the invention is designed specifically for consuming large quantities of both reactor grade discharge plutonium and weapons grade plutonium in a fast, efficient manner. Again, the waste material generated thereby cannot be employed for forming nuclear weapons. The first embodiment of the invention is known as the nonproliferative light water thorium reactor, and is so named because neither its fuel nor its waste products can be employed for forming nuclear weapons. The nonproliferative reactor's core is comprised of a plurality of seed-blanket units (SBUs), each of which includes a centrally located seed region and a surrounding, annular blanket region. The SBUs are specifically designed to be easily retrofitted in place of fuel assemblies of a conventional reactor core. The seed regions in the SBUs have a multiplication factor greater than 1, and contain seed fuel elements of enriched uranium with a ratio of U-235 to U-238 equal to or less than 20% U-235 to 80% U-238, this being the maximum ratio which is considered to be nonproliferative. The enriched uranium is preferably in the form of rods and/or plates consisting of uranium-zirconium alloy (uranium-zircalloy) or cermet fuel (uranium oxide particles embedded in a zirconium alloy matrix). The blanket regions have a multiplication factor less than 1, and contain blanket fuel elements essentially comprising Th-232 with a small percentage of enriched uranium (again enriched as high as 20% U-235) to assist the seed in providing reactor power during the initial stages of operation when the thorium is incapable of providing power on its own. By adding enriched uranium to the blanket, the blanket can generate approximately the same fraction of power at start up that it does later when a large number of neutrons released by the seed fuel elements have been absorbed by the thorium fuel elements in the blanket. This absorption generates fissionable U-233 which is burned in place, and provides power from the blanket once the reactor is up and running. The 20% enriched uranium oxide in the blanket also serves to denature any residual U-233 left in the blanket at the end of its lifetime by uniformly mixing the U-233 with nonfissionable uranium isotopes including U-232, U-234, U-236 and U-238. This denaturing is important because it is nearly impossible to separate the residual U-233 from the nonfissile isotopes thus making the residual U-233 unsuitable for use in the formation of nuclear weapons. Light water moderator is employed in both the seed and blanket regions of each SBU to control reactivity. Unlike in conventional uranium cores, boron is not dissolved in the water moderator during power operation because this would unacceptably lower the multiplication factor of the blanket, thus resulting in a drastically lower blanket power fraction. The volume ratios of the water moderator to fuel in each region are crucial. In the seed region, to insure that the reactor will not generate sufficient amounts of plutonium waste to be considered proliferative, the moderator/fuel ratio must be as high as practicable to slow down the neutrons in the seed, and decrease the likelihood that they will be absorbed by the uranium-238 in the seed, thereby generating plutonium. Unfortunately, to increase the moderator volume in the seed naturally implies that the fuel volume must be correspondingly decreased, and this increases the power density which, if increased too far, will generate too much heat. Both of these factors must therefore be taken into consideration in order to determine the optimum moderator/fuel ratio in the seed region. Use of uranium/zirconium alloy for the seed fuel permits a higher moderator/fuel ratio because of its higher thermal conductivity compared to that of oxide fuel. Using these types of fuel elements, the moderator/fuel ratio in the seed region should be between 2.5 and 5.0, and preferably between 3.0 and 3.5. Another benefit of the use of the high moderator/fuel ratio in the seed is that it results in a substantial reduction in the generation of high level radioactive wastes, particularly transuranic actinides. This, combined with the fact that the blanket fuel rods remain in the core for approximately 10 years, results in a substantial reduction in long term waste storage space requirements. The moderator/fuel volume ratio in the blanket region should be considerably lower than that in the seed region because it is desirable that the thorium fuel in the blanket absorb as many neutrons as possible. These are necessary to convert the thorium into fissionable U-233 which is burned in place, and supplies a substantial portion of the reactor power. Research has established that the optimum moderator/fuel volume ratio in the blanket region should be in the range of approximately 1.5-2.0, and preferably approximately 1.7. If the ratio is higher than 2.0, too many thermal neutrons will be absorbed by the water, while if the ratio is below 1.5, too much protactinium will be formed in the blanket region which will also interfere with the formation of U-233. A once-through fuel cycle is employed with the first preferred embodiment which eliminates the need for reprocessing spent fuel assemblies for future use. In addition, a novel refueling scheme is employed which maximizes fuel consumption in both the seed and blanket regions, and further reduces the likelihood that any of the fuel remaining in the spent fuel elements can be reprocessed and employed in the manufacture of nuclear weapons. In this refueling scheme, the seed fuel elements are replaced in a staggered manner in which a portion, preferably 1/3, of the total seed fuel elements is replaced at the end of each fuel cycle, and each seed fuel element remains in the core for more than one, preferably three, fuel cycles. Each fuel cycle is approximately 13 months in length. The blanket fuel elements, because they are comprised predominantly of thorium, can remain in the core for up to nine fuel cycles, or approximately 10 years. However, shuffling of the SBUs in the core is performed at the end of each fuel cycle to improve power distribution throughout the core. This refueling scheme enables the enriched uranium seed fuel rods to be depleted down to less than 20% of their original U-235 content. In addition, the long residency time in the core of the seed fuel elements increases the generation of Pu-238 to the point where it denatures the relatively small amount of Pu-239 which is generated by the seed fuel elements. As a result, the spent seed fuel elements are effectively rendered useless for the formation of nuclear weapons. The second preferred embodiment of the present invention uses the same basic seed-blanket core arrangement as the first preferred embodiment with a plurality of SBUs that can be retrofitted into a conventional reactor core. However, this embodiment of the invention is designed specifically for consuming very large amounts of plutonium, either weapons grade or reactor discharge grade, with the thorium in the blanket. Thus, the thorium oxide is mixed with plutonium in the blanket fuel rods, while the seed fuel rods are formed predominantly of plutonium-zirconium alloy. Unlike the first embodiment whose goal is to maximize the amount of power generated by the thorium in the blanket, the goal of the second embodiment is to maximize the consumption of plutonium without generating large amounts of new plutonium as typically occurs in a conventional reactor. The plutonium incinerator embodiment also employs a high water moderator/fuel volume ratio, preferably between approximately 2.5 and 3.5. However, the reason for the high ratio is different than that for the first embodiment. In particular, the high water to fuel volume ratio provides a very thermal spectrum in the seed regions. This simplifies core control since all control is concentrated in the seed regions, and control can thereby be effected without boron chemical control or increased use of control rods. In the blanket region, the only notable difference in the plutonium incinerator embodiment is that the thorium oxide in the blanket fuel rods is mixed with a small percentage of plutonium oxide to assist during initial reactor operation. In addition, it is very important that approximately 2-5% by volume uranium tailings (natural uranium with its U-235 content reduced to approximately 0.2%) are added to the blanket fuel rods. These tailings serve to denature (render useless for use in the manufacture of nuclear weapons) the U-233 which is formed in the blanket during reactor operation. The moderator/fuel ratio in the blanket region is preferably between approximately 1.5 and 2.0 to satisfy neutronic and thermal hydraulic constraints. |
summary | ||
claims | 1. A storage system comprising: a container having a wall with an outer surface and an inner surface and a first open end, said container defining an interior; a closure lid configured to be inserted within said open end and adapted to engage in a sealing relationship with said inner surface; and a compression link having a container engagement surface and a closure lid engagement surface, said compression link being configured to engage between said closure lid and said inner surface to retain said closure lid in sealing engagement with said container, said container engagement surface and said closure lid engagement surface being configured to extend outwardly from each other, said container engagement surface being adapted to contact said inner surface and said closure lid engagement surface being adapted to engage said closure lid such that, said closure lid is retained in sealing engagement with said inner surface. 2. The storage system of claim 1 , wherein said inner surface has a closure lid retention ledge formed thereon, and wherein said container engagement surface of said compression link is adapted to engage said closure lid retention ledge. claim 1 3. The storage system of claim 1 , wherein said closure lid has a stepped outer surface defining an annular region, and wherein said compression link is adapted to be received within said annular region. claim 1 4. The storage system of claim 1 , wherein said inner surface has a recess formed therein for receiving at least a portion of said compression link. claim 1 5. The storage system of claim 1 , further comprising a backing member adapted to be inserted between said closure lid and said compression link such that insertion therebetween urges said compression link radially outwardly from said closure lid and positions said container engagement surface of said compression link for engagement with said inner surface. claim 1 6. The storage system of claim 1 , further comprising: claim 1 an outer lid configured for engaging a distal end of said container such that said closure lid is disposed between said outer lid and said interior. 7. The storage system of claim 6 , wherein said outer lid has a lid hold-down member associated therewith for retaining said outer lid in sealing engagement with said container. claim 6 8. The storage system of claim 7 , wherein said outer surface has a recess formed therein, and wherein said hold-down member has a retention ledge configured to engage said recess. claim 7 9. The storage system of claim 1 , further comprising: claim 1 a bearing member configured to fit between said closure lid engagement surface and said container engagement surface of said compression link, wherein said bearing member engages said closure lid. 10. The storage system of claim 9 , wherein said closure lid has a stepped outer surface, said stepped outer surface being adapted to engage said bearing member. claim 9 11. The storage system of claim 10 , wherein said stepped outer surface is made of a surface harder than said bearing member. claim 10 12. The storage system of claim 1 , further comprising: claim 1 an exothermic material, wherein said exothermic material has been inserted within said container and sealed therein. 13. The storage system of claim 12 , wherein said exothermic material is spent nuclear fuel. claim 12 14. The storage system of claim 1 , wherein said closure lid lacks holes for mechanical fasteners. claim 1 15. A method for storing a material comprising: providing a container having a single wall with an inner surface and an outer surface, and a first open end, said container defining an interior; providing a closure lid adapted to be received within the open end and adapted to engage in a sealing relationship with said inner surface; providing a compression link having a container engagement surface and a closure lid engagement surface; and engaging said compression link between said closure lid and said inner surface such that said closure lid is retained by placing a portion of the closure lid under compression and a corresponding portion of inner surface under tension with said compression link contacting both said closure lid and said inner surface. 16. The method of claim 15 , further comprising the steps of: claim 15 providing an outer lid configured for engaging a distal end of the container such that the closure lid is disposed between the outer lid and the interior; and retaining the outer lid in sealing engagement with the container. 17. The method of claim 15 , further comprising the steps of: providing a backing member; and claim 15 inserting the backing member between the closure lid and the compression link such that insertion therebetween urges the compression link radially outwardly from the closure lid. 18. The method of claim 15 , further comprising the steps of: claim 15 providing a bearing member; inserting the bearing member between a portion of the compression link; and engaging said bearing member with said closure lid. 19. The method of claim 15 , further comprising the step of: claim 15 inserting an exothermic material within the container prior to sealing the closure lid. 20. The method of claim 19 , wherein the exothermic material is spent nuclear fuel. claim 19 21. A storage system comprising: a container having a wall and a first open end, said wall having an inner surface and an outer surface; a closure lid configured to be inserted within said open end and adapted to engage in a sealing relationship with said inner surface; a compression link having a container engagement surface and a closure lid engagement surface, said compression link being configured to engage between and contact said closure lid and said inner surface to retain said closure lid in sealing engagement with said container; and an outer lid configured to engage a distal end of said container, wherein said outer lid has a lid hold-down member associated therewith for retaining said outer lid by exerting force on said outer surface of said wall of said container. 22. The storage system of claim 21 , wherein said container is a single-walled container. claim 21 23. The storage system of claim 21 , further comprising a backing member adapted to be inserted between said closure lid and said compression link such that insertion therebetween urges said compression link radially outwardly from said closure lid and positions said container engagement surface of said compression link for engagement with said inner surface. claim 21 24. The storage system of claim 21 , wherein said inner surface has a recess formed therein for receiving at least a portion of said compression link. claim 21 25. The storage system of claim 21 , further comprising: claim 21 a bearing member configured to fit between said closure lid engagement surface and said closure lid engagement surface, wherein said bearing member engages said closure lid. 26. The storage system of claim 21 , wherein said closure lid has a stepped outer surface for receiving said bearing member. claim 21 27. The storage system of claim 21 , wherein said outer surface has a recess formed therein, and wherein said lid hold-down member has a retention ledge configured to engage said recess. claim 21 28. The storage system of claim 21 , further comprising: claim 21 an exothermic material, wherein said exothermic material has been inserted within said container and sealed therein. 29. The storage system of claim 28 , wherein said exothermic material is spent nuclear fuel. claim 28 30. The storage system of claim 28 , further comprising: claim 28 a basket configured to be inserted within said container for storing said exothermic material, wherein said basket is comprised of a neutron absorbing material. 31. A storage system comprising: a container defining an interior and having an open end and a wall, the wall having an outer surface and an inner surface; the inner surface of the container having a first annular ledge and a first annular recess, the first annular ledge extending into the interior of the container, the first annular recess being located about a circumference of the inner surface and between the first annular ledge and the open end, the first annular recess having an upper surface; a closure lid sized and shaped to be inserted within the open end of the container and to engage in a sealing relationship with the inner surface of the wall, the closure lid having a second annular recess formed about an outer periphery thereof, the second annular recess being defined by a lower surface, the closure lid being movable between an open position, in which the closure lid is disengaged from a sealing relationship with the container, and a closed position, in which the closure lid is inserted within the open end of the container and contacts and is supported by the first annular ledge, the first annular ledge preventing further movement of the closure lid into the interior of the container; and a compression link sized and shaped to engage between and contact the closure lid and the inner surface to retain said closure lid in sealing engagement with said container, the compression link having a container engagement surface and a closure lid engagement surface, the container engagement surface and said closure lid engagement surface being operative to extend outwardly from each other such that, when the closure lid is in the closed position and the compression link is positioned to retain the closure lid in the sealing relationship with the container, said container engagement surface contacts the upper surface of the first annular recess of the inner wall and the closure lid engagement surface contacts the lower surface of the second annular recess of the closure lid. 32. The storage system of claim 31 , further comprising: claim 31 a second annular recess located about a circumference of the outer wall of the container; an outer lid sized and shaped to contact and engage in a sealing relationship with a distal end of the container, the outer lid being movable between an open position, in which the outer lid is disengaged from a sealing relationship with the container, and a closed position, in which the outer lid is engaged in the sealing relationship with the distal end of said container such that, when the closure lid and the outer lid are in respective closed positions, the closure lid is disposed between said outer lid and said interior of the container; and a hold-down member operative to retain the outer lid in the sealing engagement with the container, the hold-down member having a ring, an arcuate segment and a connector extending between the ring and the arcuate segment, the ring having an annular ledge extending radially inwardly therefrom, the arcuate segment having an arcuate ledge extending inwardly therefrom, the connector being operative to selectively urge the ring and arcuate segment toward each other or away from each other; wherein, when the outer lid is in the closed position and the hold-down member is retaining the outer lid in the sealing engagement with the container, the annular ledge of the ring contacts the outer lid, and the arcuate ledge of the arcuate segment contacts the second annular recess of the outer wall of the container. 33. The storage system of claim 31 , further comprising: claim 31 a backing member sized and shaped to be inserted between the closure lid and the compression link such that insertion therebetween urges the compression link radially outwardly from the closure lid and positions the container engagement surface of the compression link for engagement with the inner surface such that at least a portion of the compression ink is located within the first annular recess of the inner surface of the container. 34. The storage system of claim 31 , further comprising: claim 31 a ring-shaped bearing member configured to be positioned between the closure lid engagement surface and the container engagement surface of the compression link, the ring-shaped bearing member being formed of a harder material than the closure lid, the ring-shaped bearing member having a recess such that, when the ring-shaped bearing member is positioned between the closure lid engagement surface and the container engagement surface of the compression link, the closure lid engagement surface contacts the ring-shaped bearing member within the recess. 35. The storage system of claim 31 , further comprising: claim 31 an exothermic material inserted within the container. |
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055639259 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a radiation emitting device, and particularly to a system and a method for adjusting the radiation delivered to an object in a radiation treatment device. 2. Description of the Related Art Radiation-emitting devices are generally known and used, for instance as radiation therapy devices for the treatment of patients. A radiation therapy device generally comprises a gantry which can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment. A linear accelerator is located in the gantry for generating a high-energy radiation beam for therapy. This high energy radiation beam can be an electron radiation or photon (X-ray) beam. During treatment, this radiation beam is trained on one zone of a patient lying in the isocenter of the gantry rotation. In order to control the radiation emitted toward an object, a beam-shielding device such as a plate arrangement or collimator is usually provided in the trajectory of the radiation beam between the radiation source and the object. This beam-shielding device defines a field on the object to which a prescribed amount of radiation is to be delivered. The radiation delivered to an object may be analyzed into primary and scattered components. The primary radiation is made up of the initial or original photons emitted from the radiation source, and the scattered radiation is the result of the photons scattered by the plate arrangement itself. The beam's radiation output in free space increases because of the increased collimator scatter, which is added to the primary beam. In other words, a point in the field is subjected not only to direct radiation, that is the primary component, but also to radiation that is scattered from the plate arrangement. The ratio of the radiation output in air with the scatterer to the radiation output without the scatterer for a reference field (for instance 10.times.10 cm) is commonly called the "output factor" or the collimator scatter factor. The concept and definition of the output factor are well understood in the art. Thus, due to these scattered photons, the dose rate applied to the surface of the object changes dependent on the size of the opening in the plate arrangement, that is, on the field size. This means that the radiation emitted to the same spot, for instance in the center of the radiation beam onto the object, changes according to the size of the opening in the plate arrangement. When the plate arrangement shows only a small opening, then the accumulated dose at the same spot is less than the accumulated dose at the same spot when the opening is big. Frequently, special filters or absorbing blocks are located in the trajectory of the radiation beam to modify its isodose distribution. A most commonly used filter is the wedge filter. This is a wedge-shaped absorbing block which causes a progressive decrease in the intensity across the beam, resulting in isodose curves that are modified relative to their normal positions. Such wedge filters are usually made of dense material, such as lead or steel, or other absorbing material. The presence of a wedge filter decreases the output of the radiation-emitting device and this decrease must be taken into account in treatment calculations. This effect is characterized by the so-called "wedge factor", defined as the ratio of doses with and without the wedge at a point in the object along the central axis of the radiation beam. The wedge factor depends on the material, size and angle of the wedge. Wedges, and particular the wedge factor, are described in Faiz M. Khan, Ph.D, "The Physics of Radiation Therapy", Williams & Wilkins, pages 234 to 238. The delivery of radiation by such a radiation therapy device is prescribed and approved by an oncologist. Actual operation of the radiation equipment, however, is normally done by a therapist. When the therapist administers the actual delivery of the radiation treatment as prescribed by the oncologist, the device is programmed to deliver that specific treatment. When programming the treatment, the therapist has to take into consideration the output factor and has to adjust the dose delivery based on the plate arrangement opening in order to achieve the prescribed radiation output on the surface of the object. This adjustment can be made according to known calculations, but the therapist normally has to do them manually, which can easily lead to errors. In the context of radiation therapy, a miscalculation can lead to either a dose that is too low and is ineffective, or that is too high and dangerous; a large error, for example, a misplaced decimal point, can be lethal. U.S. Pat. No. 5,148,032 discloses a radiation treatment device in which isodose curves in the object are adjusted both by a plate arrangement, which includes at least one movable plate that is controlled during irradiation, and by varying the radiation output of the radiation beam during irradiation, so that a wide range of variations in the possible isodose curves is obtained. A wedge-shaped isodose distribution is established, for example, by moving one plate at a constant speed while simultaneously changing the radiation output of the radiation beam. In this radiation treatment device there is no physical absorbing block in the trajectory of the radiation beam, and the therapist has to take this into account. What is needed is a method, and corresponding system, for adjusting the delivery of radiation to the object in order to make sure that the actually delivered radiation output is exactly the same as the desired radiation output, independent of the use of a wedge function. SUMMARY OF THE INVENTION According to the invention, radiation output delivered to an object from a radiation source is adjusted by generating a radiation beam having a variable radiation output and a substantially lossless beam path from a radiation source to the object. The beam path is delimited by moving at least one beam-shielding device such as a movable plate. An irradiated field of the object is defined. The radiation output of the beam is varied as a predetermined function of the position of the beam-shielding device, a wedge factor of the radiation output thereby varying according to a predetermined profile, in which the wedge factor is defined as the ratio between a reference radiation output along a reference axis of the beam with a predetermined physical wedge in the beam path and an actual radiation output of the beam in a substantially lossless beam path. The radiation output is varied such that the wedge factor is constant regardless of the size of the irradiated field, and is preferably equal to unity. |
044903286 | abstract | A gas cooled, high temperature nuclear reactor is provided with a base plate arranged under the reactor core and over the bottom of the prestressed concrete pressure vessel serving as the bottom shield. The bottom shield comprises at least two plates arranged coaxially with respect to each other, one above the other. Each plate comprises several partially interconnected parts with the lower plate being placed at an axial and vertical distance from the bottom liner of the prestressed concrete pressure vessel and also from the upper plate. |
claims | 1. An illumination system comprising: a light source that emits light rays; a grating element having a plurality of gratings; and a diaphragm that is arranged after said grating element in a beam path from an object plane to a field plane, wherein said light rays in said beam path after said diaphragm have a wavelength in a range of 7-26 nm. 2. The illumination system according to claim 1 , claim 1 wherein said beam path impinges said grating element, and wherein said plurality of gratings have a first grating arranged above a second grating with respect to a direction of said beam path. 3. The illumination system according to claim 2 , wherein said first grating and said second grating are parallel to each other. claim 2 4. The illumination system according to claim 2 , wherein said first grating and said second grating are at a tilt relative to each other. claim 2 5. The illumination system according to claim 1 , claim 1 wherein said beam path impinges said grating element, and wherein said plurality of gratings have a first grating arranged after a second grating with respect to a direction of said beam path. 6. The illumination system according to claim 5 , wherein said first grating and said second grating are in a plane defined by said grating element. claim 5 7. The illumination system according to claim 5 , wherein said first grating and said second grating are at a tilt relative to a plane defined by said grating element. claim 5 8. The illumination system according to claim 1 , further comprising a cooling device on a side of said grating element facing away from an incident ray. claim 1 9. The illumination system according to claim 1 , wherein said plurality of gratings comprise a flat grating. claim 1 10. The illumination system according to claim 1 , claim 1 wherein said plurality of gratings have a first grating having a first grating period and a second grating having a second grating period, and wherein said first grating period is different from said second grating period. 11. The illumination system according to claim 10 , claim 10 wherein said first grating has a first mean angle of incidence of rays impinging thereon, wherein said second grating has a second mean angle of incidence of said rays impinging thereon, wherein said first mean angle of incidence is a larger angle than said second mean angle of incidence, and wherein said first grating period is smaller than said second grating period. 12. The illumination system according to claim 1 , wherein said plurality of gratings comprises a Blaze grating. claim 1 13. The illumination system according to claim 1 , wherein said grating element has a surface material selected from the group consisting of ruthenium, palladium, rhodium, and gold. claim 1 14. The illumination system according to claim 1 , further comprising a collector unit for generating a convergent light bundle, wherein said convergent light bundle impinges on said grating element. claim 1 15. The illumination system according to claim 14 , claim 14 wherein said light bundle has a focus, and wherein said focus of said light bundle of n th diffraction order of said grating element lies at or near said diaphragm, where|n|xe2x89xa71. 16. The illumination system according to claim 1 , further comprising a primary light source in said object plane, wherein said primary light source is imaged in a secondary light source at said diaphragm. claim 1 17. The illumination system according to claim 1 , further comprising an optical component for forming and illuminating a field in said field plane. claim 1 18. The illumination system according to claim 17 , wherein said optical component homogeneously illuminates said field. claim 17 19. The illumination system according to claim 17 , claim 17 wherein said field is a segment of an annular field, and wherein said optical component has a field-forming element. 20. The illumination system according to claim 1 , further comprising an additional diaphragm in said beam path between said object plane and said field plane. claim 1 21. An illumination system comprising: a light source that emits light rays having a wavelength of xe2x89xa6100 nm; a grating element having a plurality of gratings; and a diaphragm that is arranged after said grating element in a beam path from an object plane to a field plane, wherein said diaphragm admits said light rays of an n th diffraction order of said grating element, where |n|xe2x89xa71, and substantially blocks all said light rays of an m th diffraction order by more than 90%, where mxe2x89xa0n. 22. The illumination system according to claim 21 , claim 21 wherein said beam path impinges said grating element, and wherein said plurality of gratings have a first grating arranged above a second grating with respect to a direction of said beam path. 23. The illumination system according to claim 22 , wherein said first grating and said second grating are parallel to each other. claim 22 24. The illumination system according to claim 22 , wherein said first grating and said second grating are at a tilt relative to each other. claim 22 25. The illumination system according to claim 21 , claim 21 wherein said beam path impinges said grating element, and wherein said plurality of gratings have a first grating arranged after a second grating with respect to a direction of said beam path. 26. The illumination system according to claim 25 , wherein said first grating and said second grating are in a plane defined by said grating element. claim 25 27. The illumination system according to claim 25 , wherein said first grating and said second grating are at a tilt relative to a plane defined by said grating element. claim 25 28. The illumination system according to claim 21 , further comprising a cooling device on a side of said grating element facing away from an incident ray. claim 21 29. The illumination system according to claim 21 , wherein said plurality of gratings comprise a flat grating. claim 21 30. The illumination system according to claim 21 , claim 21 wherein said plurality of gratings have a first grating having a first grating period and a second grating having a second grating period, and wherein said first grating period is different from said second grating period. 31. The illumination system according to claim 30 , claim 30 wherein said first grating has a first mean angle of incidence of rays impinging thereon, wherein said second grating has a second mean angle of incidence of said rays impinging thereon, wherein said first mean angle of incidence is a larger angle than said second mean angle of incidence, and wherein said first grating period is smaller than said second grating period. 32. The illumination system according to claim 21 , wherein said plurality of gratings comprises a Blaze grating. claim 21 33. The illumination system according to claim 21 , wherein said grating element has a surface material selected from the group consisting of ruthenium, palladium, rhodium, and gold. claim 21 34. The illumination system according to claim 21 , further comprising a collector unit for generating a convergent light bundle, wherein said convergent light bundle impinges on said grating element. claim 21 35. The illumination system according to claim 34 , claim 34 wherein said light bundle has a focus, and wherein said focus of said light bundle of an n th diffraction order of said grating element lies at or near said diaphragm, where |n|xe2x89xa71. 36. The illumination system according to claim 21 , further comprising a primary light source in said object plane, wherein said primary light source is imaged in a secondary light source at said diaphragm. claim 21 37. The illumination system according to claim 21 , further comprising an optical component for forming and illuminating a field in said field plane. claim 21 38. The illumination system according to claim 37 , wherein said optical component homogeneously illuminates said field. claim 37 39. The illumination system according to claim 37 , claim 37 wherein said field is a segment of an annular field, and wherein said optical component has a field-forming element. 40. The illumination system according to claim 21 , further comprising an additional diaphragm in said beam path between said object plane and said field plane. claim 21 41. A projection exposure system for the production of a microelectronic component, comprising: an illumination system having: (a) a light source that emits radiation; (b) a grating element having a plurality of gratings; and (c) a diaphragm that is arranged downstream of said grating element in a light path from said light source to a field plane, wherein said radiation in said light path downstream of said diaphragm has a wavelength in a range from about 7 to 26 nm; and a projection objective, wherein said illumination system illuminates a pattern-bearing mask situated in a field of said field plane, and wherein said projection objective images said pattern-bearing mask onto a light sensitive object. 42. A method for production of a microelectronic component, comprising: employing a projection exposure system having: an illumination system having: (a) a light source that emits radiation; (b) a grating element having a plurality of gratings; and (c) a diaphragm that is arranged downstream of said grating element in a light path from said light source to a field plane, wherein said radiation in said light path downstream of said diaphragm has a wavelength in a range from about 7 to 26 nm; and a projection objective, wherein said illumination system illuminates a pattern-bearing mask situated in a field of said field plane, and wherein said projection objective images said pattern-bearing mask onto a light sensitive object. 43. An illumination system comprising: a light source that emits radiation; a grating element having a plurality of gratings; and a diaphragm that is arranged downstream of said grating element in a light path from said light source to a field plane, wherein said radiation in said light path downstream of said diaphragm has a wavelength in a range of about 7 nm to about 26 nm. 44. An illumination system comprising: a light source that emits radiation; a grating element having a plurality of gratings; and a diaphragm that is arranged downstream of said grating element in a light path from said light source to a field plane, wherein said diaphragm admits radiation wavelengths xe2x89xa6100 nm that are of an n th diffraction order of said grating element, where |n|xe2x89xa71, and substantially blocks all radiation of an m th diffraction order by more than about 90%, where mxe2x89xa0n. 45. A projection exposure system for the production of a microelectronic component, comprising: an illumination system having: (a) a light source that emits radiation; (b) a grating element having a plurality of gratings; and (c) a diaphragm that is arranged downstream of said grating element in a light path from said light source to a field plane, wherein said diaphragm wavelengths xe2x89xa6100 nm that are of an n th diffraction order of said grating element, where |n|xe2x89xa71, and substantially blocks all said radiation of an m th diffraction order by more than 90 %, where mxe2x89xa0n; and a projection objective, wherein said illumination system illuminates a pattern-bearing mask situated in said field plane, and wherein said projection objective images said pattern-bearing mask onto a light sensitive object. 46. A method for production of a microelectronic component, comprising: employing a projection exposure that has: an illumination system having: (a) a light source that emits radiation; (b) a grating element having a plurality of gratings; and (c) a diaphragm that is arranged downstream of said grating element in a light path from said light source to a field plane, wherein said diaphragm admits radiation wavelengthsxe2x89xa6100 nm that are of an n th diffraction order of said grating element, where |n|xe2x89xa71, and substantially blocks all radiation of an m th diffraction order by more than 90%, where mxe2x89xa0n; and a projection objective, wherein said illumination system illuminates a pattern-bearing mask situated in said field plane, and wherein said projection objective images said pattern-bearing mask onto a light sensitive object. |
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claims | 1. A reactivity control device for storing nuclear fuel, the device comprising:a top tube sheet;an array comprising a plurality of vertically elongated neutron absorber rods fixedly attached to the top tube sheet, the absorber rods arranged parallel to each other; anda floating guide plate slideably mounted on the absorber rods for upward and downward movement along the absorber rods, the floating guide plate movable between a lower position proximate to bottom ends of the absorber rods and an upper position abuttingly engaging the top tube sheet. 2. The reactivity control device according to claim 1, wherein the top tube sheet and floating guide plate have the same shape in top plan view. 3. The reactivity control device according to claim 1, wherein the floating guide plate has a substantially rectilinear shape in top plan view including a plurality of straight lateral peripheral edges and arcuately rounded corners formed between adjoining peripheral edges. 4. The reactivity control device according to claim 3, wherein the top tube sheet has a substantially rectilinear shape in top plan view including a plurality of straight lateral peripheral edges and arcuately rounded corners formed between adjoining peripheral edges. 5. The reactivity control device according to claim 1, wherein the floating guide plate includes guide holes which slideably receive the absorber rods therethrough and allow the plate to slide upwards and downwards along a length of the absorber rods. 6. The reactivity control device according to claim 1, wherein the top tube sheet and floating guide plate each include a plurality of flow apertures, each flow aperture in the top tube sheet being concentrically aligned with a corresponding flow aperture in the floating guide plate. 7. The reactivity control device according to claim 1, wherein the absorber rods each comprise a solid ductile neutron-absorbing material or a hollow ductile tube containing a neutron absorber material. 8. The reactivity control device according to claim 1, wherein the absorber rods each include a fixed top end mounted to the top tube sheet and a free bottom end. 9. The reactivity control device according to claim 8, wherein the free bottom end of each absorber rod is tapered. 10. The reactivity control device according to claim 1, further comprising at least one end stop formed on at least one absorber rod proximate to a bottom end of the at least one absorber rod, the at least one and stop engaging and preventing the floating guide plate from sliding off of the absorber rod array. 11. The reactivity control device according to claim 10, wherein the end stop is formed by a stepped shoulder formed by a reduced diameter portion of the at least one absorber rod that engages and captures the floating guide plate. 12. The reactivity control device according to claim 1, further comprising a lifting coupling element mounted on the top tube sheet for filling the reactivity control device, the coupling element configured for engagement by a lifting tool. 13. A reactivity control system for storing nuclear fuel, the system comprising:a nuclear fuel assembly comprising a bottom nozzle box, a top nozzle box, a plurality of fuel rods extending vertically between the nozzle boxes, and a plurality of guide tubes extending vertically between the nozzle boxes;a reactivity control device comprising a top tube sheet, a plurality of neutron absorber rods fixedly attached to the top tube sheet, and a floating guide plate slideably mounted on the absorber rods for upward and downward movement along the absorber rods, the absorber rods removably insertable into the guide tubes of the fuel assembly;wherein the reactivity control device has a first uninstalled, position prior to insertion of the absorber rods into the fuel assembly in which the floating guide plate is spatially separated from the top tube sheet, and a second installed position after insertion of the absorber rods into the guide tubes of the fuel assembly in which the floating guide plate is abuttingly engaged with the top tube sheet. 14. The reactivity control device according to claim 13, wherein the top nozzle box includes an upwardly open top recess, the top tube sheet and floating guide plate being positioned inside the top recess when the reactivity control device is in the installed position. 15. The reactivity control device according to claim 13, wherein the floating guide plate includes arcuately rounded corners which are positioned inside truncated corner regions of the top nozzle box. 16. The reactivity control device according to claim 15, wherein the truncated corner regions are formed by inward facing angled inner corner surfaces formed adjacent to an upwardly open top recess defined by the top nozzle box. 17. The reactivity control device according to claim 13, wherein each of the guide tubes in the fuel assembly is accessible to the absorber rods of the reactivity control device through penetrations in top nozzle box, the penetrations arranged in a pattern that is the same as a pattern of the absorber rods on the reactivity control device. 18. The reactivity control device according to claim 13, further comprising a spent fuel pool containing water, the fuel assembly submerged in the pool with the reactivity control device inserted in the fuel assembly. 19. The reactivity control device according to claim 13, further comprising a canister including a fuel basket comprising a plurality of open cells, the fuel assembly disposed in one of the cells with the reactivity control device inserted in the fuel assembly. 20. A method for controlling reactivity in a spent nuclear fuel assembly removed from a nuclear reactor core, the method comprising:removing a spent fuel assembly from a nuclear reactor core;positioning a reactivity control device above the spent fuel assembly, the device comprising a top tube sheet, a plurality of absorber rods fixedly attached to the top tube sheet, and a floating guide plate slideably mounted on the absorber rods for upward and downward movement along the absorber rods, the top tube sheet and floating guide plate being spatially separated;aligning each of the absorber rods with a corresponding one of a plurality of guide tubes disposed in the spent fuel assembly;lowering the reactivity control device toward the spent fuel assembly;inserting the absorber rods into the guide tubes;abuttingly engaging firstly the floating guide plate with a top of the fuel assembly;sliding the absorber rods through the floating guide plate while continuing to lower the reactivity control device toward the spent fuel assembly; andabuttingly engaging secondly the top tube sheet with the floating guide plate, wherein the absorber rods are fully inserted in the guide tubes. 21. The method according to claim 20, wherein the aligning step includes angularly rotating the reactivity control device about its centerline until straight peripheral edges of the floating guide plate are oriented parallel to straight peripheral sidewalls of a top nozzle box mounted on the spent fuel assembly. 22. The method according to claim 21, wherein the aligning step includes vertically aligning arcuately shaped corners of the floating guide plate with truncated corner regions of the top nozzle box on the spent fuel assembly. 23. The method according to claim 20, wherein the abuttingly engaging firstly step includes positioning the floating guide plate against a floor plate of a top nozzle box of the fuel assembly that recessed below a top edge of the top nozzle box. 24. The method according to claim 23, wherein the floating guide plate and top tube sheet are recessed below the top edge of the top nozzle box. |
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claims | 1. A method of fabricating a neutronic fuel element comprising an elongated fuel matrix penetrated longitudinally by a multiplicity of metal coolant tubes, wherein said fuel matrix is metallurgically bonded to said metal coolant tubes, said method comprising the steps of: (a) providing oversize coolant channels through said fuel matrix; (b) disposing oversize metal coolant tubes within said coolant channels, each of said tubes having an outside diameter substantially equal to the diameter of said oversize coolant channels, and an oversize inside diameter; (c) placing cylindrical pins within the bores of said coolant tubes, said pins having diameters substantially equal to the final desired inside diameter of said coolant tubes; (d) applying pressure transversely to said fuel matrix at high temperature to establish a metallurgical bond between said fuel matrix and said coolant tubes and to squeeze said coolant tubes onto said pins; and (e) selectively leaching said pins from said coolant tubes. 2. The method of claim 1 wherein molybdenum pins are placed within tantalum coolant tubes. claim 1 3. The method of claim 2 wherein a dilute solution of nitric and sulfuric acid is used to leach said pins from said coolant tubes. claim 2 4. The method of claim 1 wherein high temperature and pressure gas is used to apply pressure to said fuel matrix. claim 1 5. The method of claim 1 wherein said fuel matrix comprises uranium fuel disposed within a tungsten matrix. claim 1 6. A method for providing a leak-tight metal enclosure to a fuel matrix penetrated by coolant channels, wherein the mutually contacting surfaces of said metal enclosure and said fuel matrix are metallurgically bonded, said method comprising the steps of: (a) placing a metal cladding about the lateral surface of said fuel matrix; (b) disposing oversize metal coolant tubes within said coolant channels, each of said tubes having an outside diameter substantially equal to the diameter of said coolant channels, and an oversize inside diameter; (c) placing cylindrical pins within the bores of said coolant tubes, said pins having diameters substantially equal to the final desired inside diameter of said coolant tubes; (d) placing perforated metal header plates at each end of said fuel matrix, said coolant tubes passing through said header plates; (e) welding, under vacuum, the ends of said cladding to said header plates; (f) welding, under vacuum, metal closure plates over said header plates to seal the ends thereof and complete a leak-tight metal enclosure about said fuel matrix; (g) exposing the assembly comprising the fuel matrix and metal enclosure to a gas at high temperature and pressure; (h) machining said closure plates and header plates to expose the ends of said pins; and (i) selectively leaching said pins from said coolant tubes. 7. The method of claim 6 wherein molybdenum pins are placed within tantalum coolant tubes. claim 6 8. The method of claim 6 wherein said fuel matrix comprises a uranium fuel disposed within a tungsten matrix. claim 6 9. The method of claim 6 wherein tantalum cladding, header plates and coolant tubing are used to provide a leak-tight enclosure to a fuel matrix comprising uranium fuel disposed within a tungsten matrix. claim 6 |
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056339046 | abstract | A dry transfer system for spent nuclear fuel (SNF) assemblies includes a transfer container with a sliding sleeve for vertical translation therein. The sliding sleeve includes a number of compartments for receiving a corresponding number of fuel assemblies. The container includes an integral and remotely controllable hoist with a number of individually actuated grapples for latching onto a corresponding number of fuel assemblies. The system further includes a loading stand with an elevator for raising and lowering a fuel basket that also includes a number of compartments for moving fuel assemblies up to and in alignment with the sleeve of the transfer container that is landed on the loading stand. |
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046997610 | description | DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like are words of convenience and are not to be construed as limiting terms. IN GENERAL Referring now to the drawings, and particularly to FIG. 1, there is shown an elevational view of a reconstitutable nuclear reactor fuel assembly, represented in vertically foreshortened form and being generally designated by the numeral 10. Basically, the fuel assembly 10 includes a lower end structure or bottom nozzle 12 for supporting the assembly on the lower core plate (not shown) in the core region of a reactor (not shown), and a number of longitudinally extending guide tubes or thimbles 14 which project upwardly from the bottom nozzle 12. The assembly 10 further includes a plurality of transverse grids 16 axially spaced along the guide thimbles 14 and an organized array of elongated fuel rods 18 transversely spaced and supported by the grids 16. Also, the assembly 10 has an instrumentation tube 20 located in the center thereof and an upper end structure or top nozzle 22 attached to the upper end portions 24 of the guide thimbles 14 which together incorporate certain locking features in accordance with the present invention which will be fully described below. With such arrangement of parts, the fuel assembly 10 forms an integral unit capable of being conventionally handled without damaging the assembly parts. As mentioned above, the fuel rods 18 in the array thereof in the assembly 10 are held in spaced relationship with one another by the grids 16 spaced along the fuel assembly length. Each fuel rod 18 includes nuclear fuel pellets (not shown) and is closed at its opposite ends by upper and lower end plugs 26,28. The fuel pellets composed of fissile material are responsible for creating the reactive power of the reactor. A liquid moderator-coolant such as water, or water containing boron, is pumped upwardly through the guide thimbles 14 and along the fuel rods 18 of the fuel assembly 10 in order to extract heat generated therein for the production of useful work. To control the fission process, a number of control rods (not shown) are reciprocally movable in the guide thimbles 14 located at predetermined positions in the fuel assembly 10. Since the control rods are inserted into the guide thimbles 14 from the top of the fuel assembly 10, the placement of the components forming the top nozzle 22 and their attachment to the upper end portions 24 of the guide thimbles 14, along with the integral locking features of the present invention, must accommodate the movement of the control rods into the guide thimbles 14 from above the top nozzle 22. TOP NOZZLE REMOVABLY MOUNTED ON GUIDE THIMBLES Turning now to FIGS. 2 and 3, as well as Fig. 1, there is shown in greater detail the separate components making up the top nozzle 22 which is removably mounted on the upper end portions 24 of the guide thimbles 14 of the fuel assembly 10. The top nozzle 22 basically includes an upper hold-down plate 30, an enclosure 32 having a lower adapted plate 34 and an upstanding discontinuous sidewall 36 formed by a plurality of spaced upstanding wall portions 38 surrounding and attached to the periphery of the adapter plate, a plurality of tubular alignment sleeves 40 disposed between the upper and lower plates 30,34, and a plurality of hold-down coil springs 42 extending between the upper and lower plates 30,34 and about the respective sleeves 40. The upper hold-down plate 30 has a plurality of passageways 44 defined therethrough, while the lower adapter plate has a plurality of openings 46, the passageways 44 and openings 46 being arranged in respective patterns which are matched to that of the guide thimbles 14 of the fuel assembly 10. More particularly, the upper end portions 24 of the guide thimbles 14 extend upwardly through the openings 46 in the lower adapter plate 34 and above the upper surface 48 thereof. A plurality of lower retainers 50 are attached, such as by brazing, to the guide thimbles 14 below the lower adapter plate 34 for limiting downward slidable movement of the adapter plate 34 relative to the guide thimbles 14 and thereby supporting the adapter plate on the guide thimbles with the upper end portions 26 thereof extending above the adapter plate. Each lower retainer 50 on one guide thimble 14 has a series of scallops 52 formed on its periphery which are aligned with those of the fuel rods 18 grouped about the respective one guide thimble so that the fuel rods may be removed and replaced during reconstitution of the fuel assembly 10. Furthermore, the top nozzle 22 includes a plurality of upstanding bosses 54 having respective central bores 56 defined therethrough. The bosses 54 are disposed above the upper hold-down plate 30, and each boss is attached to the hold-down plate 30 such that its central bore 56 is aligned with a respective one of the passageways 44 of the hold-down plate. Additionally, each boss 54 is of a cross-sectional size adapted to interfit within one of a plurality of holes 58 (only one of which is seen in FIG. 5) formed in the upper core plate 60 which opens at a lower side 62 of the core plate. The upper circumferential edge 64 of each boss 54 is chamfered for mating with a complementarily chamfered edge 66 on the lower side 62 of the upper core plate 60 at the entrance to each of the holes 58 defined therein. Edges having such shapes act as guiding surfaces which facilitate alignment and insertion of the respective bosses 54 into the corresponding holes 58 in the upper core plate 60 during installation of the fuel assembly 10 within the reactor core. As mentioned above, the hold-down coil springs 42 are disposed about the respective elongated alignment sleeves 40 within the enclosure 32. Further, the springs 42 extend between the lower adapter plate 34 and the upper hold-down plate 30 and support the upper plate in a spaced relation above the lower plate at a stationary position in which the upper plate abuts the lower side 62 of the upper core plate 60 with the upstanding bosses 54 interfitted within the holes 58 of the upper core plate 60. Also, the upper hold-down plate 30 is composed of an array of hubs 68 and ligaments 70 which extend between and interconnect the hubs. Each of the hubs 68 has one of the passageways 44 defined therethrough. Furthermore, one boss 54 is disposed above and connected to each of the hubs 68 with the bore 56 of the boss aligned with the respective passageway 44 of the hub. Finally, the top nozzle 22 includes means interconnecting the spaced upper and lower plates 30,34 so as to accommodate movement of the lower plate 34 toward and away from the upper plate 30 upon axial movement of the guide thimbles 14 of the fuel assembly 10, such as due to thermal growth, toward and away from the upper core plate 60. Also, the interconnecting means is effective to limit movement of the lower adapter plate 34 away from the upper hold-down plate 30 so as to maintain the springs 42 in a state of compression therebetween. In particular, the interconnecting means includes a plurality of lugs 72 connected to and extending downwardly from peripheral ones of the ligaments 70. The lugs 72 are respectively coupled to the upstanding wall portions 38 of the discontinuous sidewall 36 of the enclosure 32. Specifically, a generally vertical slot 74 is formed in each wall portion 38 and opens at the upper end thereof. A removable locking pin 76 is inserted horizontally into the upper end of the wall portion 38 to close the upper end of the slot 74 and a pin 78 mounted in the lower end of each lug 72 extends into the slot 74 below the locking pin 76 for slidable movement therealong as the upper and lower plates 30,34 move relative to one another. In such arrangement, the locking pin 76 and the lower end of the slot 74 respectively define the limits of movement of the lower adapter plate 34 toward and away from the upper hold-down plate 30. Integral Reusable Locking Arrangement for Top Nozzle Referring now to FIGS. 4 and 5, there is shown one of the elongated tubular alignment sleeves 40 extending through one of the hold-down coil springs 42 between the upper and lower plates 30,34 and the threaded features on the sleeve 40 and on the upper end portion 24 of the one guide thimble 14 illustrated in the figures for attaching the sleeve and guide thimble together. Also illustrated in these figures is the reusable locking arrangement, generally designated as 80, integrally associated with both the sleeve 40 and the guide thimble upper end portion 24 for locking the attached sleeve and guide thimble together. With respect to the threaded features on the guide thimble 14 and sleeve 40, the upper end portion 24 of the guide thimble 14 has an annular externally threaded section 82, whereas the tubular alignment sleeve 40 has a lower annular internally threaded section 84. The sleeve 40 is mounted through the passageway 44 and bore 56 of the hold-down plate hub 68 and boss 54 for rotatable movement relative to the guide thimble upper end portion 24 between lowered and raised positions, as depicted respectively in FIGS. 5 and 4, for threading and unthreading its internally threaded section 84 onto and from externally threaded section 82 of the guide thimble upper end portion 24 in order to attach and detach the top nozzle 22 onto and from the guide thimble 14. The sleeve 40 is hollow so that, in addition to accommodating insertion of a control rod through it, a suitable tool (not shown) can be inserted into the sleeve for gripping it internally to rotate it in either direction for threading on and unthreading from the upper end portion 24 of the guide thimble 14. When threaded on the guide thimble upper end portion 24, the sleeve 40 cooperates with the lower retainer 50 to clamp the adapter plate 34 therebetween. The integral reusable locking arrangement 80 for the top nozzle 22 includes inner means in the form of a thin-walled tubular section 86 on the guide thimble upper end portion 24 above its externally threaded section 82 and outer means in the form of an axial section 88 on the alignment sleeve 40 above its internally threaded section 84. The tubular section 86 has an enlarged region in the form of an annular circumferential protrusion 90 defined thereon. The protrusion 90 has an external diametric size which is greater than the external diametric size of the remainder of the tubular section 86. The protrusion 90 can be machined around the entire tubular section 86, or can alternately be formed by an expansion (or bulge) operation or take the form of local dimples. The axial section 88 on the alignment sleeve 40 has an internal diametric size which is greater than that of the tubular section 86 but less than that protrusion 90 on the tubular section. With such diametric relationships between the axial section 88 and the protrusion 90, rotational movement of the alignment sleeve 40 relative to the guide thimble upper end portion 24 from its raised toward its lowered position causes interference contact of the axial section 88 with the tubular section protrusion 90 so as to produce a locking force. Additionally, it will be noticed in FIG. 4 that diametric sizes of the tubular section 86 and protrusion 90 are less than that of the exterior diametric size of the externally threaded section 82 of the guide thimble upper end portion 24, and, similarly, the diametric size of the axial section 88 is less than that of the interior diametric size of the internally threaded section 84 of the alignment sleeve 40. Thus, the protrusion 90 on the tubular sleeve 40 coacts with the interior surface 92 of the axial section 88 on the alignment sleeve 40 by creating an interference fit therewith as the internally threaded section 80 of the sleeve 40 is threaded on the externally threaded section 82 of the guide thimble upper end portion 24 when attaching the top nozzle 22 to the guide thimble 14. The interference fit causes the locking force which must be overcome in order to unthread the internally threaded section 84 of the alignment sleeve 40 from the externally threaded section 82 of the guide thimble upper end portion 24 and detach the top nozzle 22 from the guide thimble 14. The locking force takes the form of a constant torsional drag produced between the tubular section protrusion 90 and the axial section interior surface 92 as the alignment sleeve 40 is rotatably moved relative to the guide thimble upper end portion 24 between its lowered and raised positions. During in-core operation there are no appreciable loads acting on these threaded joints. Hence, the drag force, which prevents loosening of the sleeve 40, can be relatively low. It will be noted that unlike a lock washer where total loosening occurs upon small rotation, the interference drag force will act throughout the unthreading operation. An examination of FIG. 4 reveals that the circumferential protrusion 90 on the tubular section 86 is axially displaced from the axial section 88 when the internally threaded section 84 on the alignment sleeve 40 is initially rotatably moved into threaded engagement with the externally threaded section 82 on the guide thimble upper end portion 24. In such arrangement where engagement between the threaded ends of the sleeve 40 and guide thimble 14 leads interference contact between the protrusion 90 and the interior surface 92 of the axial section 88, the mechanical advantage produced by threading the internally threaded section 84 of the sleeve 40 on the externally threaded section 82 of the guide thimble 14 can be used to overcome the torsional drag and force the sleeve onto the guide thimble. When all of the sleeves 40 are unthreaded from the upper end portions 24 of the respective guide thimbles 14, the top nozzle 22 is in condition for removal from the remainder of the fuel assembly 10 for reconstitution thereof. However, due to the cross-sectional size of each of the sleeves 40, it stays in place between the upper and lower plates 30,34 of the top nozzle. Particularly, each sleeve 40 has a lower portion 94 of a cross-sectional diameter that is greater than that of an upper portion 96 thereof and also greater than the size of the diameter of the one passageway 44 of the upper hold-down plate 30. Thus, the sleeve 40 cannot be withdrawn through the passageway 44 and so it remains captured between the upper and lower plates 30,34, as also does the respective hold-down coil spring 42 encompassing the sleeve 40, when each sleeve is released from its threaded connection with its respective guide thimble 14. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention of sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof. |
055725600 | description | DETAILED DESCRIPTION Referring to FIG. 1, a boiling water reactor nuclear fuel assembly is generally shown at 10 having elongated fuel rods 12 each of which generally includes a zirconium alloy tube 12a within which are nuclear fuel pellets 12b. Fuel rods 12 have a uniform diameter along their length. The fuel rods are supported between a lower tie plate 14 and upper tie plate 16. The lower and upper tie plates can also or alternatively function to position the ends of the fuel rods in a spaced relationship. Fuel rods 12 pass through apertures or support cells in spacer grids 18, only two of which are shown in this fragmentary view. Spacer grids 18 provide intermediate support of fuel rods 12 over the length of fuel assembly 10 and position them in a spaced relationship while restraining them from lateral vibration. The fuel rod pitch or distance between the centerlines of adjacent fuel rods is maintained by the spacers. Outer square channel 11 is shown around the fuel rods 12 and spacers 18. Although a central water channel 44 is shown disposed in the center of the array of fuel rods 12 and replaces in this example the innermost three by three array of fuel rods, the present invention is not limited to fuel assemblies with central water channel(s) or water rod(s). Assembly 10 houses an 11.times.11 fuel array although most of the fuel rods 12 are not shown for clarity of illustration. Although reference is made in the specification to an 11.times.11 fuel rod array with each fuel rod having an equal diameter, such an array has been selected for illustrative purposes only. The present invention can be used with other arrays including, but not limited to 8.times.8, 9.times.9, and 10.times.10. Central water channel 44 is shown in this example with a square cross-sectional area which varies along the height of the fuel assembly. In accordance with the present invention, in order to accommodate the changing cross-sectional area of central water channel 44 but without changing the diameter of fuel rods 12 and without increasing the size of outer channel 11, the position and the distance between fuel rods 12 in the example shown in FIG. 1 varies along the height of the fuel assembly. Referring to FIG. 2 which is a cross-sectional view taken along line 2--2 of fuel assembly 10 shown in FIG. 1, central water channel 44 is at the center of the fuel assembly and the arrangement of the fuel rods is square with the distance between each fuel rod being the same. The pitch or distance between the centerlines of each fuel rod at the elevation shown in FIG. 2 is uniform and is designated by "P". Referring to FIG. 3 which is a cross-sectional view taken along line 3--3 of fuel assembly 10 shown in FIG. 1, the cross-sectional area of central water channel 44 is enlarged from that shown in FIG. 2. The cross-sectional area of central water channel 44 varies along the height of the fuel assembly and in the view shown in FIG. 3 has increased from its position in the lower portion of the fuel assembly (FIG. 2) toward the top of the fuel assembly where it achieves in this particular example its maximum cross-sectional area. Each of the four corner areas of the assembly shown in FIG. 3 has a 4.times.4 square array of fuel rods with a fuel rod pitch of P.sub.1. Between each of the four corner areas are regions called flats where the fuel rods are arranged in a 3.times.4 or 4.times.3 rectangular array with fuel rod pitches of P.sub.2 and P.sub.3. In an array of fuel rods other than a square array such as the 3.times.4 or 4.times.3 rectangular array shown in FIG. 3., the pitch or distance between the centerlines of two adjacent fuel rods which extend in the radial direction away from the center of the fuel assembly is referred to as a radial pitch. In the 3.times.4 or 4.times.3 array, the four fuel rods in a row extend in the radial direction. An example of radial pitch is shown in FIG. 3 as P.sub.3. Similarly, in an array of fuel rods other than a square array, the pitch or distance between the centerlines of two adjacent fuel rods which extend tangentially or circumferentially from the center of the fuel assembly is referred to as a tangential pitch. In the 3.times.4 or 4.times.3 array, the 3 fuel rods in a row extend tangentially. An example of a tangential pitch is shown in FIG. 3 as P.sub.2. In order to accommodate the larger cross-sectional area of the central water channel but without decreasing the fuel rod diameter and without using short or part length fuel rods, the fuel rod pitch changes from the lower elevation (FIG. 2) to the upper elevation (FIG. 3) of the fuel assembly. The pitch P.sub.1 of each of the fuel rods in the 4.times.4 array of fuel rods in each of the four corner areas of fuel assembly 10 shown in FIG. 3 is smaller than the pitch P of the fuel rods in the corners at the elevation shown in FIG. 2. of the fuel assembly. The complete array shown in Fig. 3 is a combination square/rectangular array in which P.sub.1 has been chosen to equal P.sub.3, and P.sub.2 has been chosen to be greater than P.sub.1 Other values of the pitches P.sub.1, P.sub.2 and P.sub.3 can be chosen. In the embodiment shown in FIGS. 1-3, the fuel rod pitch at each of the intermediate elevations between the view shown in Fig. 2 and that in FIG. 3 varies from the pitch at the lower tie plate to the pitch of the upper spacer. Thus, the fuel rods extend from their positions in the uniform square array in the view shown in FIG. 2 to their positions in the combination square/rectangular array shown in FIG. 3. More particularly, the 4.times.4 square array in each of the corners of fuel assembly 10 and the 3.times.4 and 4.times.3 rectangular arrays in the flats of the assembly shown in FIG. 3 progress from the uniform square array in the view shown in FIG. 2. Thus, the pitch of the fuel rods in fuel assembly 10 can vary in the radial direction and/or in the tangential direction at each elevation of the fuel assembly (e.g. the corners and the flats) and can thus vary vertically or axially along the height of the fuel assembly. Although in the embodiment of the present invention shown in FIGS. 1-3 the fuel rod pitch varies from the lower portion of the assembly to the upper portion of the assembly, the pitch(es) could vary abruptly or may alternate from an increasing to a decreasing pitch (or vice versa) at selected elevations determined by the position of a spacer (or spacers) as shown for example in the region above the uppermost spacer in FIG. 1. Varying the fuel rod pitch along the fuel assembly height permits positioning the fuel rods to take advantage of local moderator distribution so as to provide closer to the optimum local water to fuel ratios at different axial locations. In addition to improvements in local water to fuel ratio, rod positioning and pitch may be varied along the fuel assembly height to accommodate fuel assembly geometry changes which in turn enables selective control of the water to fuel ratio or the coolant flow areas. Such modifications could include increases or decreases in the center water channel cross-sectional area along the height of the assembly, or increases in the flow area within the outer channel which is accomplished by adjusting the rod pitch at selected axial locations. As the coolant density decreases as a function of the height of the fuel assembly, there is an associated velocity increase which causes a proportionately higher pressure drop in the two phase flow region of the fuel assembly. A high two phase to single phase pressure drop ratio can be detrimental to core stability. For this reason strategies to increase coolant flow area and reduce pressure drop at the top of the assembly are sometimes employed. A change in the lateral rod positioning toward the top of the assembly may be beneficial, for example, by more effectively using the water channel exit flow or the flow from part length rods to improve the cooling of fuel rods at the top of the assembly. The changes in fuel rod pitch may be accomplished by flexing the fuel rods laterally in the spans between grid spacers. Flexure of the fuel rod, for example, from one cell position in a square array in one span to an adjacent cell in the next span can be achieved without exceeding the yield strength of the fuel rod cladding. Such flexure can also be achieved without interference from the pellets as the relatively short pellet length and large pellet to clad diametral gap can accommodate the necessary clad curvature without pellet-clad interference. By varying the fuel rod pitch radially, tangentially and axially in the fuel assembly, one can accommodate an inner or central water channel that varies in cross-sectional area as well as shape along the height of the fuel assembly without having to remove any fuel rod from the assembly. Furthermore, according to the invention, the size of the center water channel can be optimized axially by selectively changing its cross-sectional area as a function of the height of the assembly which can be accomplished by selectively changing the pitch of the fuel rods as a function of the height of the assembly. With prior art fuel assemblies having uniform fuel rod pitch, increasing the size of the central water channel necessitates the removal of those fuel rods which occupy the space or volume into which the enlarged center water channel would extend, thereby decreasing the number of fuel rods in the fuel assembly. With non-uniform pitch, the center water channel size can be increased without necessarily removing any fuel rod. With prior art fuel assemblies having uniform pitch, if the fuel rods were not removed, then the shape of the central water channel which could be accommodated would have to be changed because of the physical position of the fuel rods. Referring to FIG. 4, an alternative embodiment of the present invention is shown in which a boiling water reactor nuclear fuel assembly is shown at 110 having elongated fuel rods 112 each of which generally includes a zirconium alloy tube 112a within which are nuclear fuel pellets 112b. Fuel rods 112 have a uniform diameter along their length with each fuel rod having an equal diameter. The fuel rods are supported between a lower tie plate 114 and an upper tie plate 116 and pass through apertures or support cells in spacer grids 118, only two of which are shown in this fragmentary view. The lower and upper tie plates can also or alternatively function to position the ends of the fuel rods in a spaced relationship. Spacer grids 118 provide intermediate support of fuel rods 112 over the length of fuel assembly 110 and position them in a spaced relationship while restraining them from lateral vibration. The fuel rod pitch is maintained by the spacers. A central water channel 144 is disposed toward the center of the array of fuel rods 112 and replaces a three by three fuel rod array disposed toward the center of the fuel assembly. Outer channel 111 is shown around the fuel rods 112 and spacers 118. In those reactor assembly designs in which a structural connection is formed by the inner or central water channel to the upper and the lower tie plates, the spacers provide support for the fuel rods over the length of the assembly and position the fuel rods in an array with the fuel rods having a predetermined pitch or pitches. Although assembly 110 houses a 10.times.10 fuel array, such an array has been selected for purposes of illustration only. The embodiment shown in FIG. 4 can be used with other arrays including, but not limited to 8.times.8, 9.times.9, and 11.times.11. Referring to FIG. 5 which is a cross-sectional view taken along line 5--5 of fuel assembly 110 shown in FIG. 4, the array of fuel rods is uniform and square, and their pitch is constant and designated by P.sub.4. Referring to FIG. 6 which is a cross-sectional view taken along line 6--6 of fuel assembly shown 10 in FIG. 4, central water channel 144 is enlarged from that shown in FIG. 5. The cross-sectional area of central water channel 144 has increased eccentrically from its position in the lower portion of fuel assembly 110 (FIG. 5) toward the top of the fuel assembly. The eccentrically expanding 3.times.3 central water channel 144 is more centrally located within the interior of the fuel assembly thereby enabling the selective positioning of increased moderation in the center as well as the upper portions of the fuel assembly. In order to accommodate the larger cross-sectional area of the eccentrically expanded central water channel 144 but without decreasing the diameter of the fuel rods and without substituting short or part length fuel rods, the fuel rod pitch changes from a uniform pitch p.sub.4 at a lower elevation of the fuel assembly (FIG. 5) to non-uniform pitches P.sub.i, P.sub.j, P.sub.k, P.sub.L, etc. at a higher elevation of the fuel assembly (FIG. 6). The non-uniform pitches of the fuel rods shown in FIG. 6 varies from a square pitch P.sub.i in the bottom right corner of the assembly to smaller pitches (e.g. P.sub.j, P.sub.k) of combination square/rectangular arrays of fuel rods, to an even smaller pitch (P.sub.L) of the square array of fuel rods shown in the opposite top left diagonal corner of the fuel assembly. In this example, P.sub.i has been chosen to equal p.sub.4. Although the non-uniform pitches shown in FIG. 6 are shown to vary substantially continuously from one corner of the fuel assembly to the diagonally opposite corner, the variation and degree of variation can depend upon other factors or design choices. For example, selecting the radial pitch of the rods closest to the inner and/or outer channels to be smaller than the radial pitch of the intermediate rows of fuel rods results in a more uniform moderator to fuel ratio for all the rods in the assembly at the upper more voided region of the fuel assembly. Stated more broadly, since moderation is a function of the ratio of the amount of fuel to the amount of moderator, changing the fuel rod pitch changes the moderation. Thus, selectively changing the fuel rod pitch while maintaining uniform rod size allows changing or tailoring the moderation along the axial position of the fuel assembly. While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the true spirit and scope of the present invention. |
040452867 | abstract | In a molten-salt reactor, a common vessel contains the reactor core, a neutron-moderating mass pierced by passages for the circulation of the fuel salt, at least one primary heat exchanger which is located close to the reactor core and through which the hot fuel salt passes after discharge from the core, pumps for circulating the cold fuel salt from the heat exchangers back into the reactor core. The free spaces defined within the reactor vessel between the core, the heat exchangers and the pumps except for the passages in which the molten fuel salt is circulated are packed with material which is compatible with the fuel salt. |
claims | 1. An x-ray/gamma-ray imaging apparatus, the apparatus including a pulse mode x-ray/gamma-ray detector having a dynamic range and comprising a member that is pixelated and configured to convert incident x-ray/gamma-ray wavelength photons directly into an electronic signal, a position for a material under test, an x-ray/gamma-ray source, and a structure configured to perturb an x-ray/gamma-ray energy spectrum, each lying on a common axis, wherein the structure comprises at least three regions adjacent and to the side of each other, each different from each other and having a different x-ray perturbing characteristic, and wherein said structure lies between the x-ray/gamma-ray source and the member and to one side of the position for material under test, the said structure intersecting the common axis such that x-ray/gamma-ray photons perturbed differently by respective regions of the at least three regions of said structure impinge upon different pixels of the pixelated detector substantially simultaneously, and wherein by means of the different perturbation characteristics of the at least three regions of the structure at least some of the pixels of the pixelated detector are impinged upon by x-ray/gamma-ray photons that are within the dynamic range of the detector. 2. An x-ray/gamma-ray imaging apparatus according to claim 1, wherein the at least three regions lie laterally of one another. 3. An x-ray/gamma-ray imaging apparatus according to claim 2, wherein the at least three regions lie laterally of one another in two orthogonal directions. 4. An x-ray/gamma-ray imaging apparatus according to claim 1, wherein at least three regions of the structure are formed in an array. 5. An x-ray/gamma-ray imaging apparatus according to claim 4, wherein the array comprises an x by y array wherein the multiple of x and y is greater than or equal to three. 6. An x-ray/gamma-ray imaging apparatus according to claim 4, wherein the array repeats itself in the structure. 7. An x-ray/gamma-ray imaging apparatus according to claim 4, wherein the structure includes a multiplicity of arrays. 8. An x-ray/gamma-ray imaging apparatus according to claim 1, wherein individual regions each include one or more x-ray/gamma-ray perturbation elements. 9. An x-ray/gamma-ray imaging apparatus according to claim 8, wherein the x-ray/gamma-ray perturbation elements are one of the same and different. 10. An x-ray/gamma-ray imaging apparatus according to claim 1, wherein the structure is one of planar and non-planar. 11. An x-ray/gamma-ray imaging apparatus according to claim 10, wherein the structure is curved in at least one plane. 12. X-ray/gamma-ray imaging apparatus according to claim 1, wherein the structure is configured to perturb both the energy distribution and the intensity of the x-ray/gamma-ray energy spectrum. 13. An x-ray/gamma-ray imaging apparatus according to claim 1, wherein the difference between adjacent regions of the structure includes the thickness of the material of the structure in adjacent regions. 14. An x-ray/gamma-ray imaging apparatus according to claim 13, wherein the thickness of the region changes continuously across the structure in at least one direction. 15. An x-ray/gamma-ray imaging apparatus according to claim 14, wherein the thickness of the region changes continuously across the structure in two orthogonal directions. 16. An x-ray/gamma-ray imaging apparatus according to claim 1, wherein the difference between adjacent regions includes the material from which the individual adjacent regions of the structure are formed. 17. An x-ray/gamma-ray imaging apparatus according to claim 13, wherein the individual regions of the structure include discrete layers. 18. An x-ray/gamma-ray imaging apparatus according to claim 17, wherein the discrete layers differ and the difference between discrete layers is selected from the group comprising the thickness of the discrete layers between regions; the thickness of the discrete layers within a region; the material from which the discrete layers are formed differs between regions; the material from which the discrete layers are formed differs within a region; the number of discrete layers differs between regions; and the number of discrete layers differs within a region. 19. An x-ray/gamma-ray imaging apparatus according to claim 17, wherein the structure includes a plurality of discrete layers and at least one of the discrete layers includes at least one aperture. 20. An x-ray/gamma-ray imaging apparatus according to claim 19, wherein a plurality of the discrete layers include at least one aperture and wherein apertures of different layers within the structure are of different dimensions. 21. An x-ray/gamma-ray imaging apparatus according to claim 19, wherein the discrete layers are formed of foil. 22. An x-ray/gamma-ray imaging apparatus according to claim 1, wherein the structure is configured to perturb the count rate whilst preserving the energy distribution of the x-ray/gamma-ray energy spectrum. 23. An x-ray/gamma-ray imaging apparatus according to claim 22, wherein the structure is a collimator, each of the at least three regions of the structure comprises an aperture of a different size to an aperture of an immediately adjacent region, wherein adjacent apertures are separated by an x-ray/gamma-ray absorbing material and the structure providing at least two different sizes of aperture. 24. An x-ray/gamma-ray imaging apparatus according to claim 23, wherein the structure comprises a plate of x-ray/gamma-ray absorbing materials have said apertures formed therein. 25. An x-ray/gamma-ray imaging apparatus according to claim 22, wherein the structure is formed from a selected one of tungsten, gold or lead. 26. An x-ray/gamma-ray imaging apparatus according to claim 22, wherein the said apertures are formed in the structure by spark erosion. 27. An x-ray/gamma-ray imaging apparatus according to claim 1, further including means for generating absorption edges and fluorescence peaks in the x-ray/gamma-ray energy spectrum. 28. An x-ray/gamma-ray imaging apparatus according to claim 27, wherein the means for generating absorption edges and fluorescence peaks in the x-ray/gamma-ray energy spectrum is comprised in the structure. 29. An x-ray/gamma-ray imaging apparatus according to claim 28, wherein the at least three regions of the structure each have a different absorption edge and fluorescence peak. 30. A structure suitable for use in an x-ray/gamma-ray detector according to claim 1, the structure configured to perturb an x-ray/gamma-ray energy spectrum incident thereon, the structure comprising at least three regions adjacent each other lying on a common plane, wherein each region is different from each other, each adjacent region configured to perturb the x-ray/gamma-ray energy spectrum differently. 31. A structure according to claim 30, wherein the structure includes a plurality of protrusions or depressions, the thickness of said protrusions or depressions changing in at least one direction thereof, each protrusion or depression providing at least three adjacent regions configured to perturb the x-ray/gamma-ray energy spectrum. 32. A structure according to claim 31, wherein the protrusions or depressions are pyramidal in shape. 33. A structure according to claim 31, wherein the structure comprises a non-metallic layer having a multiplicity of depressions formed therein, each depression filled with metal. 34. A structure according to claim 33, wherein the structure comprises a first non-metallic layer having a multiplicity of depressions formed therein and a second metallic layer including a corresponding number of protrusions each protrusion filling a corresponding depression. 35. A structure according to claim 34, wherein the second layer covers the surface of the first layer in which the openings to the depressions are situated. 36. A structure according to claim 31, wherein adjacent depressions or protrusions are separated from one another by x-ray/gamma-ray perturbing material and wherein the material separating adjacent depressions or protrusions constitute one of the at least three regions. 37. A structure according to claim 33, wherein the non-metallic layer is formed of silicon. 38. A method of determining a material property of a substance comprising the steps of:a) positioning the substance in an x-ray/gamma-ray imaging apparatus as claimed in claim 1;b) causing the x-ray/gamma-ray source to direct an x-ray/gamma-ray energy spectrum along the common axis;c) analyzing electronic signals emitted by the member configured to convert incident x-ray/gamma-ray wavelength photons into electronic signals; andd) deleting those electronic signals outwith the dynamic range of the member. 39. A method according to claim 38, wherein the member is pixilated, the method comprising the further step of analyzing the electronic signal for each pixel; and deleting those electronic signals outwith the dynamic range of the member. 40. A method according to claim 39, comprising the further step of assigning to each pixel of the member where the electronic signal has been deleted, the electronic signal of an adjacent pixel that is within the dynamic range of the member. 41. A method according to claim 39, comprising the further step of assigning to each pixel of the member where the electronic signal has been deleted, an electronic signal that is one of: interpolated and extrapolated, from the electronic signals of surrounding pixels. 42. A method according to claim 40, wherein the pixel from which an electronic signal is selected, interpolated or extrapolated is a nearest neighbor or nearest neighbor associated with a region having the same material properties. 43. An x-ray/gamma-ray imaging apparatus, the apparatus including a pulse mode x-ray/gamma-ray detector having a dynamic range and comprising a member that is pixelated and configured to convert incident x-ray/gamma-ray wavelength photons directly into an electronic signal, a position for a material under test, an x-ray/gamma-ray source, and a structure configured to perturb an x-ray/gamma-ray energy spectrum, each lying on a common axis, wherein the structure comprises at least three regions adjacent and to the side of each other, each different from each other and having a different x-ray perturbing characteristic, and wherein said structure lies between the x-ray/gamma-ray source and the member and to one side of the position for material under test, the said structure intersecting the common axis such that x-ray/gamma-ray photons perturbed differently by respective regions of the at least three regions of said structure impinge upon different pixels of the pixelated detector substantially simultaneously, and wherein by means of the different perturbation characteristics of the at least three regions of the structure at least some of the pixels of the pixelated detector are impinged upon by x-ray/gamma-ray photons that are within the dynamic range of the detector further comprising image processing software and a data processor, the image processing software configured to perform the method steps of:a) positioning the substance in the x-ray/gamma-ray imaging apparatus;b) causing the x-ray/gamma-ray source to direct an x-ray/gamma-ray energy spectrum along the common axis;c) analyzing electronic signals emitted by the member configured to convert incident x-ray/gamma-ray wavelength photons into electronic signals; andd) deleting those electronic signals outwith the dynamic range of the member. 44. An x-ray/gamma-ray imaging apparatus according to claim 43, further including a database. 45. An x-ray/gamma-ray imaging apparatus according to claim 43, further including a data recording means. |
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description | The United States Government has rights in this invention pursuant to Contract No. DE-AC52-06NA25396 between the United States Department of Energy/National Nuclear Security Administration and the Los Alamos National Security LLC for the operation of the Los Alamos National Laboratory. 1. Field of the Invention The present invention relates generally to X-ray radiography, and more particularly relates to radiation inspection devices and methods for detecting the presence of high-z materials in containers. 2. Related Art The detonation of a nuclear weapon in a major city is perhaps the worst terrorist threat imaginable, with casualties and property damage likely exceeding those of past terrorist attacks by a factor of ten or a hundred or even more. The shipping and transportation industry is considered at risk for terrorist activity due to the high volume of containers that moved across borders and low inspection rates. For example in the United States, approximately 7,000,000 cargo containers enter the country by sea each year and about 9,000,000 by land, in addition to the thousands of cargo containers that enter the country by air. Since existing inspection methods are insufficient in detecting the presence of nuclear weapons, each of the containers must be opened and inspected manually. Inspecting each container manually would be time consuming and cause major delays. Thus, of these millions of containers only a comparatively few are opened for inspection, thereby offering a terrorist a potential opening for smuggling a nuclear weapon into a country. According to a first broad aspect of the present invention, there is provided an inspection method comprising: generating a radiographic image based on a detected attenuation corresponding to a plurality of pulsed beams of radiation transmitted through a voluminous object; and determining that there is a high-z material in the voluminous object based on a localized high attenuation in the generated radiographic image, wherein the plurality of pulsed beams of radiation are transmitted substantially downward along an incident angle to a vertical axis extending through the voluminous object. According to a second broad aspect of the invention, there is provided an inspection device for inspecting a voluminous object comprising: a high-energy source for generating a first set of pulsed beams of radiation, wherein the plurality of pulsed beams of radiation are transmitted substantially downward along an incident angle to a vertical axis extending through the voluminous object; means for discriminating against scattered radiation from the plurality of pulsed beams of radiation that are transmitted through the voluminous object; means for generating a radiographic image based on detected attenuation corresponding to the plurality of pulsed beams of radiation transmitted through the voluminous object; and means for determining that a high-z material exists in the voluminous object based a localized high attenuation in the radiographic image. According to a third broad aspect of the invention, there is provided an inspection device comprising a high-energy source for producing a plurality of pulsed beams of radiation at an incident angle to a vertical axis extending through the voluminous object; one or more upper collimators for filtering the plurality of pulsed beams of radiation into a fan beam of radiation having a width approximate to the width of the voluminous object; one or more lower collimators for shielding scattered radiation from the fan beam of radiation that is scattered within the voluminous object; and a detector array for generating an attenuation signal based on radiation transmitted through the lower collimator, wherein the high-energy source is positioned above the voluminous object, the one or more upper collimators being positioned between the high-energy source and the voluminous object, the one or more lower collimators being positioned directly below the voluminous object and the detector array is positioned below the one or more lower collimators. The one or more lower collimators may include a “Bucky” collimator consisting of narrow hollow tubes in a block of absorbing material, where the tubes are aligned along straight rays from the source of radiation to each element of the detector array. It is advantageous to define several terms before describing the invention. It should be appreciated that the following definitions are used throughout this application. Where the definition of terms departs from the commonly used meaning of the term, applicant intends to utilize the definitions provided below, unless specifically indicated. For the purposes of the present invention, a step, method or information is “based” on a particular step, method, or information, if that step, method or information is derived by performing a mathematical calculation or logical decision using that step, method, or information. For the purposes of the present invention, the term “downward” refers to a direction that is towards the ground, i.e. floor, earth, pavement, etc. For the purposes of the present invention, the term “high-z” refers to a material, element, alloy or compound with a high atomic number. Such elements include those that are used in nuclear weapons, such as uranium and plutonium and their compounds and alloys. For the purposes of the present invention, the term “incident angle” refers to the angle from a vertical axis at which radiation enters the container under inspection. FIG. 3B illustrates different incident angles. For the purposes of the present invention, the term “voluminous container” refers to a container that is used in transporting and shipping goods and products. The containers may be shipped by land, air or sea. An exemplary voluminous container is an intermodal container or cargo container having the approximate dimensions of 2.6 meters height by 2.6 meters wide by 12 meters long. This type of voluminous container may hold a load of up to 30 metric tons. It should be appreciated that different sizes of containers that can hold different load amounts may also be inspected using embodiments of the present invention. Aspects of the present invention provide inspection methods, devices and systems for detecting a high-z material in a voluminous container using pulsed radiation from a high-energy source. The high-z material may be detected as a localized high attenuation in a radiographic image generated from an array of detectors. To determine the presence of high-z material, radiation is emitted substantially downward along an incident angle from the high-energy source and filtered through a series of collimators above the voluminous container. These collimators produce a fan beam of radiation. The fan beam of radiation is as wide as width of the voluminous container under inspection. To enhance the attenuation and reduce scattering detected by the detector array, a second set of lower collimators may be placed between the detector array and voluminous container. Using such methods, devices and systems, embodiments of the present invention allow non-invasive detection of potentially dangerous object that may enter a country. X-ray radiography is the traditional method of looking inside opaque objects. It works very well for comparatively small objects, but the dimensions of a standard intermodal container (2.6 m×2.6 m×12 m) and heavy and spatially complex loading of such container presents serious obstacles. At a mean density of 300 kg/m3, such a container has column density across its shortest dimension of about 780 kg/m2. The scattering of X-rays of energies less than a few hundred KeV is well described by the Thomson cross-section as giving an opacity of about 0.02 m2/kg for most materials. This leads to 15.6 e-folds (a factor of 1.7×10−7) of beam attenuation, which precludes use of these lower energy X-rays for such intermodal containers. At higher energies the scattering cross-section is described by the Klein-Nishina formula, and declines nearly as the reciprocal of the energy. For high-Z materials such as uranium and plutonium another absorption process, electron-positron pair production, whose cross-section increases with energy, dominates the attenuation above about 3 MeV. Pair production is less important for lower-Z materials, so their opacities flatten out or continue to decrease as the energy increases, as shown in FIG. 1. FIG. 1 is a graph showing the cross-section of plutonium 102 (z=94) increases with energy while iron 104 (z=26) flattens out and carbon 106 (z=8) continues to decrease. This makes the use of higher energy (3-10 MeV) X-rays particularly advantageous for discriminating high-Z materials from dense bodies of intermediate-Z materials such as iron that are frequently present in innocent cargo. At energies of several MeV, the beam attenuation across a container filled with 300 kg/m3 of low or medium-Z material is about 2 e-folds (a factor of 0.14), so that X-ray radiography becomes possible. Further, because the opacity (in m2/kg) is larger for high-Z materials, these materials will stand out even more strongly in radiographs than indicated by the material's density alone. Prior X-ray non-invasive techniques use side vertical illumination. One problem with vertical illumination is that a terrorist could hide his fissionable cargo in the shadow of a larger and deep absorber (such as a 30 MT cube of solid iron). Such a threat could be found by opening the very few containers which show absorption too deep to see through. The innocent shipper can avoid false-positive detection (and the opening of his container) by ensuring that his cargo does not present a deep, spatially localized, absorption maximum in the known direction of irradiation. Embodiments of the present invention use radiation at an oblique downward angle to detect high-z materials. This allows the radiography generated by embodiments of the present invention to identify all containers that might contain a threat, and thus saving the resources required to open and manually inspect the container. Another existing X-ray detection uses side elevation illumination as shown in U.S. Pat. No. 6,347,132 to Annis. The detection method in the Annis patent uses a low energy source. By using a substantially downward illumination, embodiments of the present invention permit the use of higher energy and more powerful X-ray sources and reduce or eliminate the transmitted and scattered radiation dose and hazard to bystanders and operators because downward radiation will be absorbed by the earth. Similarly to vertical illumination, side illumination may not detect high-z materials in cluttered environments. Because dense innocent cargo is generally placed on the floors or bottoms of containers, and long objects such as ingots, rod stock, axles, beams and shafts are generally placed with their long axes horizontal, such cargo may block near-horizontal (side) radiography, requiring manual unloading and/or inspection. Such cargo is much less likely to block near-vertical radiography. Use of two distinct near-vertical X-ray beam angles ensures that innocent but strongly absorbing long objects do not block high energy X-rays in at least one of the beam directions, in contrast to dense blocks of threat high-Z material that strongly absorb high energy X-rays in any direction, thus permitting effective discrimination of threat from innocent cargo. Various other embodiments of the present invention are an improvement over the Annis patent. Embodiments of the present invention may scan and inspect a voluminous container according the exemplary method shown in FIG. 2. Prior to scanning, the high energy x-ray source and components are fixed into the desired position along an incident angle. In some alternative embodiments these components may have moveable pieces that allow the components to align along multiple incident angles. The voluminous container is moved through the radiation and scanned in 202. When a pulsed X-ray source is used, multiple scans may be used as the voluminous container moves through the radiation. The detectors in 204 detect the attenuation of the radiation and send the data to a computer system to be processed. The computer in 206 processes the data to produce a radiographic image. In 208 the radiographic image is analyzed to determine the presence of high-z materials. When such materials are detected, the system flags the container to be manually opened in 210. When no high-z materials are detected, the system ends in 212 and the process may be repeated for the next voluminous container. The multiple physical processes and complex geometries required to model X-ray radiography imply that quantitative results may be obtained from Monte Carlo calculations. In making such calculation, it is necessary to include electron and positron elastic scattering, bremsstrahlung, collisional ionization and Coulomb pair production, pair annihilation, photon Compton and coherent scattering, photoionization and photopair production and radiative recombination. The spatial, angular and energy distribution of photons, electrons and positrons must be tracked. In auxiliary calculations photoneutron processes and neutron transport and capture must be calculated as well. In order to handle these computationally formidable tasks, the Monte Carlo radiation transport (MCNPX) code may be used. FIGS. 3A and 3B illustrate front and side views, respectively, of an exemplary diagram showing a voluminous container 300 under inspection according to various embodiments of the present invention. X-ray source 302 comprises an accelerator (not shown) that produces a beam of electrons 304 which radiate bremsstrahlung when stopped by a converter slab 306. X-ray source 302 is positioned a distance d1 above container 300. X-ray source 302 emits radiation substantially downward. A series of collimators 308, 310 filter the radiation into a fan beam of radiation 312. Fan beam 312 enters container 300 at an incident angle θ1 and travels through contents, which may include high-z objects 314 and low to medium-z objects 316. Below container 300 is a “Bucky” collimator 318 and detector 320. Detectors 320 may be high-z scintillator detectors. Such high-z scintillator detectors may maximize detector efficiency and permit use of smaller detectors, thus increasing spatial resolution of the system and permitting narrower collimation to minimize scattered radiation background. Behind detector 320 is an absorbing slab 322. The absorbing slab 322 may reduce background scattering from the ground. A computer 324 may control X-ray source 302 and receive data from detector 322. The radiographic image generated by the processing of the data may be displayed on screen 324. A vertical axis 330 is defined to extend downwardly through container 300. The angle θ may be approximately 1° to 30° from vertical axis 330 to allow the emitted radiation to travel substantially downward through container 300. In some embodiments this angle θ1 may be approximately 10° to 15° from vertical axis 330. Such an incident angle may be taken in either direction from the vertical axis. Note that one or more radiographic images may be generated using multiple X-ray detectors positioned at various angles as shown in FIG. 3B. In FIG. 3B there is X-ray source 302 produces radiation for a second series of collimators 308′, 310′ that create an additional fan beam of radiation 312′, “Bucky” collimator 318′, and detector 320′. The angles θ1 and θ2 shown in FIG. 3B may be different. It should be appreciated that various combinations of X-ray sources and angles that are offset from the vertical axis 330, 330′ may be used to inspect container 300. Container 300 moves through the fan beams of radiation as shown by arrow 340 in a direction that is orthogonal to vertical axis 330. Any suitable mechanisms may move the container such as a conveyer belt, crane, lift, track, slide, trolley, etc. Inspection methods and devices of the present invention may non-invasively scan the container when or after being unloaded from a ship or other mode of transportation or when or before being loaded on a ship or other mode of transportation. For example, the entire longitudinal length of a 40-foot intermodal cargo container may be scanned using 1200 exposures as the container is continuously moved through a pulsed X-ray beam. MeV electron accelerators in the high energy X-ray source may produce micro-second pulses at a rate of several hundred per second thus requiring a scanning time of only a few seconds. This allows quick and efficient non-invasive inspection without causing delays in the movement of the cargo containers. The X-ray source may be any suitable high-energy radiation device capable of emitting radiation. Embodiments of the present invention may use an electron accelerator that produces a radiation of maximum X-ray energy about 6-20 MeV having a mean energy X-ray energy about half the maximum, i.e. 3-10 MeV. In one embodiment, the high energy X-ray source may emit a beam of 10 MeV electrons. The converter slab used in the X-ray source may be a tungsten converter slab that is approximately 7 mm thick. The slab may also act as a high-pass spectral filter for the emitted radiation. The X-ray source may emit pulses of radiation. The X-ray source may be placed a distance d1 that is above the container under inspection. Depending on the number of collimators used to create the fan beam and size of the container, the distance may vary. The d1 should be sufficient to allow a single pass of the container. In one embodiment the d1 is approximately 5.2 m to allow the fan beam to be as wide as an intermodal container. Extensive collimation as shown in FIGS. 3A-3B may be necessary to reduce the scattering of radiation into the deep absorption minimum produced by the high-z material. Although two collimators are shown above the container in FIGS. 3A and 3B, any number of collimators may be used. The slots in each collimator used may be substantially aligned with along the incident angle θ. In one embodiment, there may be an approximately 10 mm wide slot collimator of approximately 0.1 m thick tungsten below the X-ray source. A similar slot collimator may be placed above the container that matches an approximately 10 mm wide detector array. The detectors are modeled as a transverse row of point sensors approximately 0.2 m below the container, spaced approximately 10 mm apart, which respond to the X-ray energy flux, a fair approximation to the behavior of several practical scintillators. A lower collimator, referred to a Bucky collimator, may be placed between the container and the detectors. An end view of an exemplary Bucky collimator is shown in FIG. 4. Bucky collimator 400 consists of an approximately 0.16 m thick slab of tungsten, lead, or similar X-ray absorbing material with holes or tubes 402 bored or otherwise formed (such as by casting or punching) the lines 404 from each detector 406 to the radiation source 408. Tubes 402 may be approximately 5 mm wide and are arranged in a radially manner in relation to the radiation source 408. Bucky collimator 400 may reduce the scatter to improve the quality of the radiographic image generated from detectors 406. One or more additional collimators may be placed between the container and Bucky collimator 400. Note a Bucky collimator may have more holes or tubes than shown in FIG. 4 depending on the application. For example, in one embodiment the numbers of holes or tubes corresponds to the number of detector elements in the detector array. Embodiments of present invention use a source of high energy X-rays (and necessarily high energy electrons). These high energy sources increase the overall transmission, and improve the discrimination between high-Z and low or medium-Z opacities. In addition the coherent and Compton scattering cross-sections are less and the bremsstrahlung radiation pattern and the Compton scattering cross-section are more forward-peaked. Scattered radiation tends to fill in the deep and spatially localized absorption minima of chunks of high-Z material, which are their characteristic signature. This may be minimized, as discussed above, by increasing the electron (and therefore X-ray) energy, and by use of collimators, including a Bucky collimator, that intercepts scattered radiation arriving on oblique paths. One problem with using high energy sources of more energetic X-rays (and electron accelerators) is photoneutron production. For most nuclei the photoneutron energy threshold is about 8 MeV, so electron beams of energy greater than 8 MeV will produce some X-rays energetic enough to make neutrons and lead to a low level of neutron activation in innocent cargo. The induced radioactivity in the cargo is negligible. For example, depositing 10 MeV of X-ray energy (typically about three X-rays) in a 10 mm×10 mm detector on a path through the center of a 5 kg plutonium sphere in a very cluttered container (FIG. 4) will show the depth of absorption to a factor of about two, sufficient for the radiographic image to show the dense high-Z object. From the calculated results, this would require 1.1×1011 10 MeV electrons per image slice, or about 0.18 Joule (small compared to the capability of industrial radiographic accelerators). The container would be irradiated with about 1.3×10−3 J/m2 of X-rays on its upper surface, or a total of about 40 mJ of energetic X-rays. Even at photon energies of 10-20 MeV the photoneutron cross-section is no more than 0.01 of the total cross-section, so that these 2.5×1010 X-rays produce, at most. 2.5×108 photoneutrons. This should be compared to the cosmic ray neutron production of 0.1/kg/sec, or 3×103/sec for a 30 MT cargo. Even the highest energy radiography produces a neutron fluence and activation less than that produced by a day of cosmic ray exposure. The neutron production in the collimators, which absorb nearly all the X-rays, is also small. The 1200 pulses required to scan a 40 foot (12 m) container in 10 mm slices contain 1.3×1014 electrons. Using MCNPX, the photoneutron production in the 7 mm tungsten converter followed by a 0.1 m lead collimator is calculated. The neutron to electron ratio is 7×10−6 at 10 MeV, 7×10−4 at 15 MeV and 2.5×10−3 at 20 MeV (where the bremsstrahlung spectrum overlaps the nuclear giant dipole resonance). For 10 MeV electrons the dose to an unshielded operator at 20 m range who examines one container per minute would be 500 nanoSv/hr (using the standard relation of flux to dose rate). This is a factor of 50 times less than the occupational limit of 0.05 Sv/year (25 microSv/hr), and only a small fraction of the typical 2 mSv/year natural background. The advantages of radiography at energies of 10 MeV may be obtained with negligible personnel exposure. Further reduction in doses to operators, bystanders and the environment may be obtained with use of shielding. The embodiments of the present invention will now be described by way of the following examples. FIG. 5 is a computer model radiographic image obtained by detecting a 5 kg sphere of 6-plutonium (r=0.0422 m) at the center of a container uniformly filled with iron to a density of 300 kg/m3. This model is based on using an X-ray source is a beam of 10 MeV electrons which radiate bremsstrahlung when stopped by a 7 mm thick tungsten converter slab at a height of 5.2 m above the top of the container using a layout as shown in FIGS. 3A and 3B. Below the converter there is a 10 mm wide slot collimator made of tungsten 0.1 m thick. A similar slot collimator above the container matches a 10 mm wide detector array. The detectors are modeled as a transverse row of point sensors 0.2 m below the container, spaced 10 mm apart, which respond to the X-ray energy flux, a fair approximation to the behavior of several practical scintillators. A final Bucky collimator between the container and the detectors consists of a 0.16 m thick slab of tungsten with holes of 5 mm diameter bored along the lines from each detector to the radiation source. The incident electron beam is taken to be 13° from vertical. The radiographic image may be obtained using 1200 exposures of 40-foot voluminous container that is moved through a pulsed X-ray beam. The radiographic image shown in FIG. 5 illustrates the power of high energy X-ray radiography. The plutonium sphere is clearly and unambiguously revealed by the large peak 502. Many containers will contain pockets of innocent dense medium-Z material (large castings such as engine blocks, ingots, rod stock, etc.), and a terrorist may fill the empty space in a voluminous container with such objects in order to disguise a dense piece of fissionable material. Radiography must identify, or exclude the presence of, a threat in such a cluttered environment. FIG. 6 therefore shows the radiograph of a 5 kg sphere of 6-plutonium (r=0.0422 m) at the center of a very cluttered container. In addition to the threat object, it contains 230 spheres of half-density iron that model an automotive engine block, with internal voids, each 0.20 m in radius, totaling 30 MT. The iron spheres arc in planar square arrays, 0.50 m apart, 0.55 m and 1.05 m below the container's midplane. If the direction of irradiation were vertical the plutonium sphere would not be detectable because the line of sight through it would pass through the centers of two of the iron spheres, for a total of 3140 kg/m2 of iron. It is for this reason that oblique illumination was chosen. The plutonium is detectable even though lines of sight through it pass through one of the iron spheres because it has a characteristic signature—a combination of high attenuation and small dimension transverse to the beam—which is found only for massive chunks of high-Z material and for paths along the long axes of long slender objects. In innocent cargo long slender dense objects are packed with their longest axes horizontal, and dense loose cargoes are spread on the floor of the container. Therefore, near-vertical irradiation will almost never show regions of intense absorption in innocent cargo. In contrast, horizontal irradiation would often find this “false positive” result, requiring manual unloading and inspection. Another advantage of downward near-vertical illumination is that the Earth is an effective beam-stop; combined with a thin lead ground plane, its albedo is negligible and additional shielding would not be required. All documents, patents, journal articles and other materials cited in the present application are hereby incorporated by reference. Although the present invention has been fully described in conjunction with several embodiments thereof with reference to the accompanying drawings, it is to be understood that various changes and modifications may be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom. |
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047131993 | description | The drawing shows a depository 2 for dry storage especially interim storage, of spontaneously-heating radioactive waste and spent fuel cells. In the actual storage area there are separate storage rooms or cells 3 containing storage blocks 4 of concrete, which are made up of individual concrete blocks 6, in which several channels 8 (in FIG. 1 four channels are shown) are formed. The concrete blocks are stackable so that the channels are aligned with one another and form vertical cooling and storage channels 10 for the accommodation of tubular storage containers 12 of metal for the storage of residual heat-producing radioactive material. Several stacked concrete blocks 6 form a block segment 14. Several block segments 14 form a storage block 4. Each storage block 4 stands on a concrete base plate 16 which has transverse running cooling air channels 18 which here are formed between ribs or low walls 20 formed on the base plate 16. The cooling air channels 18 are connected with the air supply channels 22 (FIG. 3). Between the storage containers 12 and the inner wall of the channels 10 there is an annular gap 26 which connects with the cooling air channels 18. At their tops, the cooling and storage channels 10 open into an intermediate space 44 which connects to an exhaust air channel 28 through which the cooling air warmed in the depository is led off. The cooling air is supplied via shafts 30 whose inlet opening 32 is provided with filters 34 to pick up dust, micro-organisms, etc. The warmed air is exhausted via shafts or chimneys 36, the outlet openings 38 likewise being equipped with filters 40. The individual block segments 14 can, as shown schematically in FIG. 3, be braced by mean of bracing elements 42 on the base plate 16 to enhance the seismic security. The outer surface of the tubular storage containers 12 can also be provided with longitudinal ribs 43 (FIGS. 4 and 5) as cooling ribs to improve the heat dissipation. These cooling ribs 43 are preferably so designed that they at the same time serve as spacers for establishing the annular gap 26. With this design, additional spaces can be dispensed with. Cooling takes place through the air current produced by natural convection. In the annular gap 26 the air is heated and rises as in a chimney. The colder outside air flows in through the shafts 30 as cooling air. The actual storage area of the depository 2 is closed at the top by a concrete ceiling 48. Between the upper side 46 of the storage blocks 4 and the lower side of the concrete ceiling 48, an intermediate space 44 is left which at the same time constitutes a first more or less horizontally-running section of the exhaust air channels 28. As shown in FIG. 4, the concrete ceiling 48 has openings 50 that are in line with the storage and cooling channels 10 of the storage blocks 4. Through these openings the tubular storage containers 12 can be inserted into and withdrawn from the channels. The space between the underside of the concrete blocks 4 and the baseplate, that is to say, the size of the cooling air channels 18, is such that this space or the cooling air channels constitute an air feed distribution space through which the incoming air is stabilized and uniformly distributed to the annular gaps. Likewise, the space between the top side of the storage blocks 4 and the underside of the concrete ceiling is of such a size that it serves as an exhaust air space for the more uniform carrying off of the heated cooling air. The tubular storage containers 12 are provided on their outer side with several supports 52 in the form of radial arms that are distributed around the circumference (see FIG. 4, which shows a storage container with four evenly distributed supports). With these supports the storage containers are supported on the tops 54 of the top concrete blocks 56. Preferably they rest on recesses in the top 54 that in the represented embodiment have the form of annular enlargements of the top end of the channel 8. The recesses can, of course, be made individually, for example, as steps distributed around the channel end, depending on the arrangement of the supports. The upper part 60 of the storage container is enlarged in the area of the concrete ceiling 48, so that an annular shoulder or an annular transition surface 64 is formed between tube enlargement 62 and the part of the storage container under it. Into the upper part 60 of the storage container 12 there is inserted a concrete plug 66 that extends down almost to the material being stored which, in FIG. 4 for example, consists of several stacked blass ingots 67. The cross-sectional shape of the plug 66 matches that of the top of the storage container, so that the plug rests on the annular shoulder 64. The upper end of the storage container 12, extending a little above the plug 66, extends into a cylindrical enlargement 68 of the opening 50 and is closed by means of a cover 70. The enlargement 68 of the opening 50 provided with a top cover 72 that is spaced above the cover 70. In the cylindrical enlargement 68 there is also a sealing sleeve or ring 74 for sealing off the opening or the annular gap 26,80 of channel 10 against the environment. The sealing sleeve 74 is, on the one hand, inserted between storage container cover 70 and storage container 12 and, on the other hand, between top cover 72 and the wall of the enlargement 68. The sealing sleeve permits vertical movement of the part of the storage container above the support 52 due to thermal expansion without any sealing problems. The storage cells 3 are lined on the inside with an insulation 76. The size of the spaces 78 under the sealing sleeves 74 change with the thermal expansion of the storage container and thus with the change in position of the sealing sleeve. The depository 2 has a double-shell external wall 84. The space 86 between the two walls, which are made of concrete, is monitored for the penetration of water, especially of ground water. Any water that gets in is removed by pumps actuated by the monitoring means. |
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062164457 | description | DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The present invention provides a pulsed plasma thruster (PPT) that can be used as a rocket engine for small spacecraft. The PPT operates on a pulse basis where a spark is created at low voltage via the use of small separations of electrodes using micro-electromechanical systems (MEMS) technology, independent introduction of vapor from solids, and electrodes which are slightly radioactive and specially shaped. The spark is transferred to an arc via use of a power supply with three output sections. The arc creates a plasma consisting of constituents of PTFE, which is ablated by the arc, and the vapors from the solids. Referring to FIG. 2a, a pulsed plasma thruster (PPT) according to one embodiment of the invention is shown and denoted generally as 50. The PPT 50 includes a heater 52 or other means of generating heat that is small enough to accommodate the framework of a small spacecraft. In one embodiment, the heater 52 is a micro-sized heater based on micro-electromechanical systems or MEMS technology. The heater 52 is placed adjacent a subliming solid 54. The purpose of the subliming solid 54 is to provide a vapor source so that, in combination with the heater 52, the solid 54 generates a gas flow that assists ignition of an initial plasma arc in the spark region of the thruster 50. Thus, the heater 52 increases the temperature of the subliming solid 54 which, in turn, generates vapor. The vapor flows through a screen 56 and into an ignition section 58 of the thrust discharge chamber 70 where a spark partially ignites the solid fuel propellant 60 as well as some of the subliming solid 54 that has been vaporized. The action of the subliming solid 54 and resulting vapor, coupled with the screen 56 and configuration of the ignition section 58 assist in igniting a spark that creates a useful plasma arc. In general, the subliming solid 54 has the characteristic of being able to produce a vapor when heated. A low sublimation temperature of the solid 54 is desired so a large quantity of vapor gas is generated for relatively small incremental changes in temperature. This reduces the heat generating requirements of the heater 52. While some gases provide better ignition sources than others, the requirement that the solid 54 produce easily ionized vapor restricts selection of the material to certain compounds. Candidates include carbonates (X(HCO.sub.3) and carbamates (S(CO.sub.2 NH.sub.2)) which sublime into NH.sub.3, CO.sub.2, and H.sub.2 O. The use of subliming solids enables independent addition of vapor into the PPT, eliminates the requirements for valves and seals, and assures long term compatibility with space environments. FIG. 3 is a cross section of the PPT 50 taken along line 3--3 of FIG. 2a and illustrating the arrangement of the ignition section of the thrust discharge chamber 70 in greater detail. As shown, the screen 56 contains a plurality of holes 80 which are spaced and sized to provide optimum feeding of vapor from the subliming solid 54 into the thrust discharge chamber 70. The number of holes 80 depends on the size of the ignition section 58 and the requirement that plasma in the ignition chamber must be allowed to enter the chamber that holds the solid 54 Thus, the sizing, diameter and quantity of the holes 80 is influenced by the specific configuration of the PPT 50. Preferably, the velocity of the vapor into the ignition section 58 is kept relatively low. In general, many small holes are more effective than a few big holes. Also, the screen 56 is designed to separate the solid from the thrust discharge chamber 70 so that sparks and/or plasma does not interact with solid 54. As shown, the thrust discharge chamber 70 is comprised of the two oppositely disposed electrode plates 72 and 74 and two fuel propellants 60 and 62. The fuel propellants 60 and 62 are preferably PTFE based, although other fuel sources may be utilized. In one embodiment, MEMS based micro-heaters (not shown) are embedded in the fuel propellents 60 and 62 and their temperature varied to control the amount of PTFE ablated and to provide more control of the impulse generated by the PPT 50. In another embodiment, solids 54 are placed along the thrust discharge chamber 70 and nozzle 90. The solids 54 contain micro-heaters which are independently controlled to allow the introduction of vapor into the thrust discharge chamber at optimum locations and times during the firing cycle. This vapor provides additional control of the efficiency and the impulse bits generated by the PPT 50. Referring again to FIG. 2a, the PPT 50 also includes a set of electrode plates 72 and 74. The electrode plates 72 and 74 correspond to the anode and cathodes of the PPT 50, respectively. As shown, the distance "d" corresponds to the spacing between the electrode plates 72 and 74. In one embodiment, the distance "d" between the electrode plates 72 and 74 is 50 micrometers or less. Additionally, the electrode plates 72 and 74 are positioned so that they are evenly displaced about the central axis "x" running through the thrust discharge chamber 70 of the PPT 50. An advantage of the PPT 50 is the ability to create a reliable breakdown within the thrust discharge chamber 70 using low levels of power. This is achieved, in part, by keeping the spacing "d" between the electrode plates 72 and 74 small so that a spark is more efficiently generated and ignition is achieved using less spark energy. Recent advances in MEMS technology enables the manufacture of small clearances between the electrode plates 72 and 74. Thus, the fact that the PPT 50 incorporates MEMS technology provides a PPT 50 suitable for space missions where power is limited. According to various embodiments, the electrode plates 72 and 74 are spaced anywhere from 1 micrometer to 50 micrometers apart. In general, the closer the electrode plates 72 and 74 are spaced, the lower voltage is required to a ignite a breakdown. Coupled to the electrode plates 72 and 74 are corresponding electrode terminals 82 and 84 that extend through an insulating layer 86 and the housing 88. The electrode terminals 82 and 84 are used to deliver the ignition voltage to the thrust discharge chamber 70. The insulating layer 86 extends substantially over the thrust discharge chamber 70 and the thrust nozzle 90. As is known to those of ordinary skill in the art, the insulating layer 86 can be configured to increase the local field strengths existing between electrode plates 72 and 74. A disadvantage of prior art thrusters is that they require very high ignition voltages to operate. For example, the thruster 10 requires a DC supply anywhere from 2000 volts to 8000 volts. Such high voltages have been used in PPTs for a long time since they result in greater thrust. The present invention contemplates the use of voltages less than 300 volts. In one embodiment, the spacing of the electrode plates 72 and 74 is such that 50 volts is sufficient to create suitable thrust levels. This permits the PPT 50 to be utilized in typical satellite applications where 50 volts is commonly available. FIG. 2b illustrates another configuration of the PPT 50 according to the invention. Specifically, the PPT 50 is shown equipped with a means of adjusting the angle of the thrust nozzle 90 with respect to central axis "x". The hinges 92 and 94 are provided for this purpose although other means of achieving the same function can be employed. In this way, the PPT 50 becomes a fuel dynamic device since the angle of the thrust nozzle 90 has some effect on the amount of fuel utilized for certain levels of thrust. Referring to FIG. 4a, therein is shown the PPT 50 driven by a power source 100 with terminals 102 and 104 coupled to electrode terminals 82 and 84, respectively. In general, the power source 100 is capable of producing multiple volt-ampere signal forms that effect the shape and magnitude of the ignition signal used to spark the vapors in the ignition section 58. In one embodiment, the power source 100 comprises a flexible power processing unit that operates in the three segments: an open circuit to constant voltage segment, a constant voltage segment, and a constant current segment. The three segments are illustrated in the graph of FIG. 4b. The open circuit voltage, Vo, from the power source 100 is applied to the electrodes. The vapor from solid 54 is also introduced into the ignition section 58 of the thrust discharge chamber. A spark occurs in the ignition section 58. During the next segment, the voltage decreases to the constant voltage section of the power source 100 at current Ic. The current then increases at a constant voltage, Vc, to a constant current section where the current is held constant at Io. The values of Vo, Vc, Ic, and Io are preset to desired values dependent on the specific design and operating condition of the PPT. Designs of power supplies capable of such outputs are known to those of ordinary skill in the art. With reference to FIG. 5, the PPT 50 is equipped with micro-positioning devices 110 and 112 operably coupled to the electrode terminals 82 and 84, respectively. The purpose of the micro-positioning devices 110 and 112 is to adjust the positioning and spacing of the electrode plates 72 and 74 with respect to the central axis "x". Preferably, the micro-positioning devices 110 and 112 are MEMS based so that they fit the framework of a small spacecraft and require only small amounts of power to operate. In this way, the spacing between each electrode plates 72 and 74 can be varied as a function of axial distance from the upstream end of the thrust discharge chamber 70. While the invention has been described in conjunction with preferred embodiments, it should be understood that modifications will become apparent to those of ordinary skill in the art and that such modifications are therein to be included within the scope of the invention and the following claims. |
description | The present invention relates to a radiation protection arrangement, in particular an arrangement for screening the X-rays emitted by an X-ray source, which is provided for example for use at an angiographic workstation. To keep the radiation exposure caused by X-ray examinations as low as possible for those persons involved, it has long been known to use clothing for protection against radiation. A two-part garment for protection against radiation which is known for example from U.S. Pat. No. 4,196,355 comprises a vest for protecting the upper body and a skirt for protecting the lower body, the vest and skirt including or comprising a material which screens X-rays. The persons responsible for taking X-rays, for example the doctor or an assistant, wear the vest and skirt during the examinations so that they are protected from the X-rays. Although the known clothing for protection against radiation offers a very effective protection against excessive exposure to radiation in some cases, at angiographic workstations, as they are called, the protection which can be achieved with them is not adequate. The radiation exposure to personnel carrying out the procedure is particularly high at a workstation of this kind as a result of the multidirectional nature of the radiation, so merely wearing clothing for protection against X-rays cannot ensure the best possible radiation protection. Accordingly, appropriate additional devices for minimizing the exposure to radiation are required. The duty of minimization laid down by the German Radiological Protection Ordinance in this context provides that the dose limit values should not only be observed but as far as possible should not even be reached. It is therefore known to use what are called lower body protection arrangements which are arranged to the side of the table on which the patient lies. In a simple construction, a lower body protection system of this kind comprises a screening blanket in the form of a lead rubber blanket or lead sheet which is encased in PVC and has a lead equivalence value of 0.5 mm which reaches from the level of the table to the floor and protects the lower extremities of the personnel carrying out the procedure, which are not covered by the clothing for protection against X-rays, from scattered radiation. In this case, the lead equivalence value describes the absorption behavior of a body, in particular a laminate, which provides the same screening from X-rays as a lead panel of that thickness. A material having a lead equivalence value of 0.5 mm therefore corresponds to screening with lead which is 0.5 mm thick. In a particular construction, the lower body protection arrangement described above comprises a plurality of PVC lead rubber slats which are arranged laterally next to one another and at least partly overlapping. Moreover, to optimize the radiation protection, what are called radiation protection panels are used, which are arranged in the upper region of the treatment station and protect the head and upper body of the personnel carrying out the procedure, in particular their eyes, thyroid gland and acromioclavicular joint. On the underside of radiation protection panels of this kind, additional PVC lead rubber blankets may also be arranged to further improve the screening. When the lower body protection arrangements described above are used, it must be taken into account that these systems are frequently contaminated during use with bodily fluids, contrast media or other non-sterile liquids. However, cleaning the lead rubber blankets or lead rubber slats is complex and expensive, since it is imperative not to damage the lead sheets during the work. In particular the conventional processes for sterilization by boiling or using an autoclave or by steam-cleaning in a protective atmosphere with an appropriate gas mixture are not suitable, since the screening material could be damaged by high temperatures and hence the protective function could no longer be reliably guaranteed. A further problem area lies in the fact that the screening blankets used for lower body protection are of a fixed length, whereas the treatment table on which they are arranged and secured is adjustable in height within a range of approximately 70 cm to approximately 120 cm. This means that the best possible protection over the entire height is only guaranteed by the lead rubber blankets at a particular position of the treatment table. However, if the table is at a higher position, the lower regions of the legs of the personnel carrying out the procedure are no longer protected. By contrast, if the table is in a lower position, the lead rubber blankets cover the entire height of the table but the lower ends of the blankets lie on the floor, and in this position they are at particular risk from soiling, since the floor in the vicinity of the treatment or operating table is often covered with liquids. Furthermore, there is a risk of damage through stepping on them. Accordingly, the present invention has the object of providing a way of keeping radiation protection arrangements of the type described above clean and sterile in the simplest possible manner. This object is achieved by a radiation protection arrangement in accordance with claim 1 and by a cover in accordance with claim 19. The arrangement according to the invention substantially comprises two elements, on the one hand a screening element which comprises or contains the radiation protection material, and on the other a cover which completely surrounds the screening element and may be pulled over the screening element and completely separated from the screening element. Using a cover which is matched in its shape to the screening element and yet completely separate therefrom ensures that the screening element, which can itself only be cleaned and sterilized in a complex and expensive procedure, can be used in a sterile environment—such as an operating theatre—without itself having to be cleaned intensively after every use. Instead, it is sufficient to take away the removable cover and replace it with a clean cover, which may even be done while the procedure is under way. In this case, the cover comprises a material which, like conventional theatre gowns, can be sterilized in a suitable device quickly and in a standard procedure. For the screening element, by contrast, it is sufficient to clean only the surface thereof and to rub it down with a disinfectant. Moreover, the cover also provides a certain protection which protects the screening element from unintentional damage—for example from a scalpel. In accordance with a particularly advantageous further development of the present invention, the cover has means with the aid of which the arrangement comprising the cover and the screening element received therein is adjustable in length, which is done by turning up or tying up the cover. As a result of this, the length of the radiation protection arrangement can be adjusted individually and can for example be matched to the respective height position of the treatment table. The problem area described above, that the arrangement is too short to guarantee adequate protection or is too long and so lies on the floor, is thus obviated. The arrangement can be fixed in the turned-up form for example by press studs arranged on the cover, a hook-and-burr closure or a tie closure. The important point here is that the elements required to fix the arrangement are arranged exclusively on the cover and not on the screening element. This is because it is disadvantageous to attach press studs or other closures to the screening element, because this could damage the lead sheet required to screen the X-rays. FIG. 1 shows an angiographic workstation which is generally designated by the reference numeral 1 and whereof the essential components are a height-adjustable table 2 for the patient to lie on and an X-ray arrangement 3. The X-ray arrangement 3 is mounted to pivot in order to ensure as flexible as possible an alignment of the X-ray generator towards the patient 4. As a consequence of this, X-rays and the corresponding scattered radiation can be emitted in a wide variety of directions. In order, therefore, to make it possible to protect a person 5 working at the workstation 1 from this radiation as comprehensively as possible, in addition to the clothing for protection against radiation worn by the person 5, additional measures to protect against radiation are provided. In the present case, these comprise a radiation protection panel 6 which is intended to enable the upper body and head of the doctor 5 carrying out treatment to be screened. Moreover, a lower body protection arrangement 10 is provided which is secured to the lateral region of the treatment table 2. This lower body protection arrangement 10 comprises an upper part 12, which is arranged on a carrier rail 11 secured to the table 2, and a plurality of slats 13 which are secured to the underside of the carrier rail 11 and are arranged to overlap laterally next to one another. The overlapping arrangement of the slats 13 results in a particularly high level of flexibility of the arrangement, which makes very effective radiation protection possible. So that the radiation protection slats 13, which comprise lead sheets embedded in PVC, do not have to be cleaned or sterilized themselves, in accordance with the invention a cover is provided which can be pulled over the slats 13 to protect them. This will be explained below with reference to a first example embodiment in FIG. 2a. The lower body protection arrangement 20 illustrated in its individual parts in FIG. 2a comprises, first of all, the carrier rail 21 already mentioned above, to the upper side whereof an upper part 22 is to be secured. Towards the underside there extends a lead rubber blanket 23. The upper part 22 and the lead rubber blanker 23 have the lead sheets encased in PVC which have been mentioned above and each represent a screening element for screening the X-rays. The lead sheets themselves in this case have a lead equivalence value of at least 0.5 mm to make adequate screening possible. The upper part 22 and the lead rubber blanket 23 should, as already mentioned, not or only infrequently be cleaned or sterilized, since this can only be carried out in a highly complex operation if the lead sheets are not to be damaged. For this reason, in each case covers 24 and 25 are provided which can be pulled onto the two screening elements 22 and 23 in a simple manner and which, for cleaning and sterilization, can be taken off again and taken away. The cover 24 for the upper part 22 comprises a simple sheath which is pulled over the upper part 22. The cover 25 for the lower lead rubber blanket 23 also comprises a sheath which is approximately matched in its dimensions to the size of the lead rubber blanket 23 and is open to one side, and which is pulled onto the blanket 23 and secured to the carrier rail 21 by means of securing elements 26. In the example illustrated, the securing elements are formed by a plurality of cords 26, by means of which the cover 25 is bound firmly to the carrier rail 21. As an alternative to this, the cover 25 could, however, also be secured to the carrier rail 21 by means of a hook-and-burr closure or by press studs. A particular feature of the cover 25 for the lower lead rubber blanket 23 consists in the provision of a plurality of rows of press studs 27. These can be used to turn up the cover 25 with the lead rubber blanket 23 received therein and to fix it in this turned-up position. The press studs 27 thus represent a fixing device which makes it possible to adjust the length of the radiation protection arrangement comprising the lead rubber blanket 23 and the cover 25. As a result, the overall length can be matched to the height of the treatment table, so that on the one hand radiation screening is achieved over the entire height, and on the other the possibility of the radiation protection arrangement lying on the floor and possibly being contaminated there by liquids is prevented. The important point is that the press studs 27 are arranged exclusively on the cover 25 and not on the lead rubber blanket 23 itself, since this—and in particular the lead sheet—would be damaged if buttons or similar elements were attached thereto. FIG. 2a shows the radiation protection arrangement 20 in the assembled condition. As can be seen from the illustration, the screening elements 22 and 23 are completely surrounded by the covers 24 and 25, with the result that the screening elements 22 and 23 cannot themselves be soiled or contaminated. By contrast, the covers 24 and 25, which are preferably made from a material which is easy to clean and sterilize, for example the green cotton generally used in operating theaters, may be removed quickly and cleaned in a standard procedure. In this context, it is possible to change the covers 24 and 25 in the minimum of time, in particular even while treatment is still going on. FIG. 3 shows a further example embodiment of a radiation protection arrangement 30 according to the invention. In the present case, this comprises three individual elements each having a carrier rail 31a to 31c, on the undersides whereof lead rubber blankets 33a to 33c are arranged. On the upper side of the first carrier rail 31a, a radiation protection upper part 32a having a corresponding cover 34a is furthermore provided. Here again, each individual lead rubber blanket 33a to 33c is provided with its own cover 35a to 35c which corresponds approximately to the size of the corresponding lead rubber blanket 33a to 33c in its width and length. Provided on the upper sides of the covers 35a to 35c are, once again, tapes 36 for securing them to the carrier rails 31a to 31c. All three covers 35a to 35c have the fixing devices mentioned above, with the aid of which the length of the radiation protection arrangement can be varied. The first cover 35a has—like the cover illustrated earlier in FIGS. 2a and 2b—press studs 37. As an alternative to this, however, it is also possible to use a hook-and-burr closure, as illustrated in the middle arrangement. In this case, the cover 35b has two hook-type strips 38 which extend over the entire height so that when the lower end is flapped up the cover 35b can be fixed in the desired position, with the lead rubber blanket 33b, in a simple manner. A third possibility for adjusting the length consists in the use of ties 39, as provided in the case of the third cover 35c. A particularly preferred example embodiment of a lower body protection arrangement is illustrated in FIG. 4. The radiation protection arrangement 40 illustrated here is characterized in that there are arranged on the underside of the carrier rail 41 not a single lead rubber blanket but, rather, a plurality of individual lead rubber slats 43 arranged laterally next to one another but overlapping. This overlapping arrangement of the slats 43 on the one hand makes effective protection from radiation possible, but on the other this arrangement is particularly flexible, with the result that optimum radiation protection is ensured even in the greatest variety of situations. Furthermore, an upper part 42 for radiation protection is once again provided, having a single cover 44. In the present case, the cover for the individual slats 43 is formed by an arrangement which comprises a plurality of sheaths 45 arranged laterally next to one another and matched in their dimensions to the slats 43. The sheaths 45 are only connected to one another on their upper sides, by way of a common cuff 45a. Provided on this cuff 45a are, once again, the securing tapes 46 for securing the entire cover to the mounting strip 41. In this preferred example embodiment too, the intention is to make it possible to adjust the height of the radiation protection arrangement, which is once again done by using press studs 47. Because each sheath 45 has its own press studs 47, the individual slats can even be adjusted in length individually. It goes without saying that hook-and-burr closures or ties could, however, also be used for height adjustability, as described above. Finally, FIG. 5 is intended to illustrate a further example application of the radiation protection arrangement according to the invention. In this case, a screening element which is arranged on the underside of a radiation protection panel 6, as also illustrated in FIG. 1, is to be covered. The overall arrangement resulting from this is illustrated in FIG. 5. Just as in the case of the lower body protection systems, a screening element 52 is secured to the lower edge of the radiation protection panel 6 and has the effect of an additional screening of the X-rays. This screening element once again comprises a PVC blanket including a lead sheet and enclosed within a cover 54. The cover 54 substantially corresponds in its construction to the covers provided for the lower body protection devices. One difference, however, consists in the fact that in this application there is no need for the radiation protection arrangement 50 to be height-adjustable, and accordingly fixing devices in the form of press studs, hook-and-burr closures or ties are not required. In this case too, however, there is the advantage that the cover 54 can be cleaned and sterilized in a simple manner without putting any stress on the sensitive screening element 52. It should furthermore be noted that, on the underside of the radiation protection panel 6, a radiation protection arrangement in accordance with the example embodiment of FIG. 4, that is to say with a plurality of overlapping slats, could also be provided, which is particularly advantageous if the lower edge of the panel 6 is not a straight line but is, for example, curved. As a result of the present invention, it thus becomes possible to keep radiation protection arrangements clean and sterile in a simple manner. In particular in the case of lower body protection devices, it moreover opens up the possibility of making them adjustable in length and hence of adapting them to different situations. |
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claims | 1. A multi-leaf collimator for selectively blocking an incident beam of radiation, said collimator comprising:a plurality of independently adjustable leaves comprising a first leaf and a second leaf that is adjacent said first leaf, said first leaf having at least a first portion that extends from a substantially block-shaped second portion of said first leaf between said first leaf and said second leaf; wherein said first portion comprises a first material and said second portion comprises a second material that is different from said first material. 2. The collimator of claim 1 wherein said first portion is substantially block-shaped. 3. The collimator of claim 1 wherein said first portion has a cross-section that is substantially triangular in shape. 4. The collimator of claim 1 wherein said first material has a density that is greater than a density of said second material. 5. The collimator of claim 1 wherein an atomic number for said first material is greater than an atomic number for said second material. 6. The collimator of claim 1 wherein said first material is selected from the group consisting of: tungsten, tungsten alloys, tantalum, tantalum alloys, lead, and lead alloys; and wherein said second material is selected from the group consisting of: steel, brass, zinc, and copper. 7. The collimator of claim 1 wherein said first and second leaves are arranged side-by-side and are moveable in parallel. 8. The collimator of claim 1 wherein said first and second leaves are substantially aligned with each other and are moveable in opposite directions. 9. An apparatus comprising:a source operable for generating a beam of radiation onto a target area; anda multi-leaf collimator disposed between said source and said target area and operable for shielding said target area from said beam, wherein said collimator comprises at least a first pair of independently adjustable leaves that are moveable along a common line; said first pair of leaves including a first leaf having at least a first portion comprising a first thickness of a first material and a second portion comprising a second thickness of a second material that is different from said first material. 10. The apparatus of claim 9 wherein said second portion has a quadrilateral cross-section, wherein said cross-section is orthogonal to said common axis. 11. The apparatus of claim 9 wherein said first portion has a substantially quadrilateral cross-section, wherein said cross-section is orthogonal to said common axis. 12. The apparatus of claim 9 wherein said first portion has a substantially triangular cross-section, wherein said cross-section is orthogonal to said common axis. 13. The apparatus of claim 9 wherein said first thickness is less than said second thickness. 14. The apparatus of claim 9 wherein said first material is a higher density material and said second material is a lower density material. 15. The apparatus of claim 9 wherein said first material is a higher-Z material and said second material is a lower-Z material. 16. The apparatus of claim 9 wherein said first material is selected from the group consisting of: tungsten, tungsten alloys, tantalum, tantalum alloys, lead, and lead alloys; and wherein said second material is selected from the group consisting of: steel, brass, zinc, and copper. 17. The apparatus of claim 9 wherein said first pair of leaves comprises a second leaf separated from said first leaf by a gap, wherein said first material is disposed between said second material and said second leaf and wherein said first portion overlaps a corresponding portion of said second leaf. 18. The apparatus of claim 17 further comprising a second pair of independently adjustable leaves that are moveable along a common line, wherein said first and second pairs are arranged side-by-side and are moveable in parallel to each other. 19. A method of shaping an incident beam of radiation, said method comprising:blocking a first part of said beam using a first thickness of a first material comprising at least a first portion of a first leaf in a multi-leaf collimator; andblocking a second part of said beam using a second thickness of a second material comprising a second portion of said first leaf, said second portion having a substantially block shape, said second material different from said first material and said first thickness less than said second thickness, wherein said first portion extends from said second portion to prevent said first part of said beam from passing through a gap between said first leaf and a second leaf in said multi-leaf collimator. 20. The method of claim 19 wherein said first material has a density that is greater than a density of said second material. 21. The method of claim 19 wherein an atomic number for said first material is greater than an atomic number for said second material. 22. The method of claim 19 wherein said first material is selected from the group consisting of: tungsten, tungsten alloys, tantalum, tantalum alloys, lead, and lead alloys; and wherein said second material is selected from the group consisting of: steel, brass, zinc, and copper. 23. The method of claim 19 wherein said first and second leaves are arranged side-by-side and are moveable in parallel. 24. The method of claim 19 wherein said first and second leaves are substantially aligned with each other and are moveable in opposite directions. 25. The method of claim 19 wherein said first portion has a substantially rectilinear cross-section, wherein said cross-section is orthogonal to the longitudinal axis of said first portion. |
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052316556 | abstract | A collimator for use in an imaging system with a radiation point source is formed from a plurality of collimator plates stacked together. Passages in each collimator plate in conjunction with the respective passages in adjoining plates form a plurality of channels through the collimator. The channel longitudinal axes are aligned with selected orientation angles that correspond to the direct beam path from the radiation source to the radiation detectors. The collimator plates are made up of patterned sheets of radiation absorbent material or alternatively comprise patterned photosensitive material substrates coated with a radiation absorbent material. The cross-sectional shape of each channel corresponds to the cross-sectional shape of the radiation detecting area of the detector element adjoining the channel. A method of forming a collimator includes the steps of selectively removing material from the collimator plates to form the passages therein, and stacking the patterned collimator plates together to align them so that the respective adjacent passages form a channel aligned with respective selected orientation angles corresponding to direct paths of radiation from the radiation source to the detector elements in the assembled array. |
048088315 | claims | 1. A container for low energy radioactive samples comprising: a substantially planar carrier member having first and second opposed sides and an aperture formed therethrough; means for retaining a radioactive sample in said container and simultaneously for permitting low energy radiation from radioactive decay of the sample to exit therethrough, said means being connected to one side of said carrier member defining a cavity therewith, said cavity only being accessible via said aperture in said carrier member; and means removably attached to another side of said carrier member, opposite said one side, for sealing said aperture. means for spacing said means for retaining from said one side of said carrier. a blotter in said cavity. a mesh member in said cavity. a window spacer having an opening formed therethrough. a window spacer having an opening formed therethrough, said means for retaining being attached to said volume spacer. a blotter in said cavity. a window spacer having an opening formed therethrough. a second aperture formed through said carrier. a carrier member having an aperture formed therethrough; a spacer member having an opening formed therethrough and having one side attached to said carrier member; a window member attached to another side of said spacer member opposite said one side, said window member permitting low energy radiation from radioactive decays of the sample to exit therethrough, said opening in said spacer member defining a cavity between said carrier member and said window member, said cavity being accessible via said aperture in said carrier member; spacer means for recessing and exposing said window member, said spacer means mounted on said carrier; and means removably attached to said carrier member for sealing said aperture. a blotter member mounted between said carrier member and said window member. a carrier member having an aperture formed therethrough; a spacer member having an opening formed therethrough and an adhesive on opposite surfaces thereof, one of said surfaces adhered to said carrier; a window member covering said spacer opening and being adhered to the other of said spacer surfaces said window member permitting low energy radiation from radioactive decays of the sample to exit therethrough; a window spacer attached to said window, said window spacer having an opening formed therethrough; and means removably attached to said carrier member for sealing said aperture. a blotter member mounted between said carrier member and said window member, said blotter member including an aperture formed therein. a carrier layer having an aperture formed therethrough; a first spacer layer having one surface mounted on said carrier layer, said spacer layer having an opening formed therethrough; a transparent window layer attached to another surface of said first spacer layer opposite said one surface, said window member permitting low energy radiation from radioactive decays of the sample to exit therethrough, said opening in said spacer layer defining a cavity between said carrier layer and said window layer, said cavity being accessible via said aperture in said carrier layer; a second spacer layer connected to said first spacer layer and having a window exposing opening formed therein; and a tab layer removably adhered to a surface of said carrier layer opposite said first spacer layer. a layer of wicking material between said carrier layer and said window layer. a generally flat member having an upper surface and a lower surface and a sample-receiving cavity extending through said member from one of said surfaces to a generally flat window at the other of said surfaces of said member, said window forming one end of said sample-receiving cavity, said window having a thickness sufficient to contain said radioactive samples and yet to permit the passage therethrough of low energy beta radiation from a sample in said cavity; and means cooperating with the said one of said surfaces of said member for selectively enclosing the other end of said sample-receiving cavity to thereby completely contain a radioactive sample in said cavity between the upper and lower surfaces of said member. 2. The container of claim 1, wherein said means for retaining includes a transparent window member. 3. The container of claim 1, wherein said carrier member is a substantially disk-shaped member. 4. The container of claim 1, including: 5. The container of claim 4, wherein said means for spacing comprises projections extending from said one side. 6. The container of claim 5, wherein said projections are formed with said carrier member. 7. The container of claim 5, wherein said projections are attached to said carrier member. 8. The container of claim 4, wherein said means for spacing comprises a ring-shaped volume spacer extending from said one side. 9. The container of claim 8, wherein said spacer is attached to said carrier member. 10. The container of claim 8, wherein said spacer is formed with said carrier member. 11. The container of claim 4, wherein said means for spacing comprises a blotter in said cavity. 12. The container of claim 11, wherein said blotter has an aperture formed therethrough. 13. The container of claim 8, including: 14. The container of claim 13, wherein said blotter includes an aperture formed therethrough. 15. The container of claim 4, wherein said means for spacing comprises a mesh member. 16. The container of claim 8, including: 17. The container of claim 4, including: 18. The container of claim 8, including: 19. The container of claim 18, including: 20. The container of claim 19, wherein said blotter has an aperture formed therethrough. 21. The container of claim 1, wherein said aperture in said carrier includes a first diameter which gradually expands to a second diameter between said opposed sides. 22. The container of claim 21, including: 23. The container of claim 1, including: 24. A container for radioactive samples comprising: 25. The container of claim 24, wherein said carrier member is substantially planar. 26. The container of claim 24, wherein said spacer member includes adhesive on said one side and said opposite side. 27. The container of claim 24, including: 28. The container of claim 24, wherein said carrier member has another aperture formed therein. 29. The container of claim 28, wherein said removably attached means seals both apertures formed in said carrier member. 30. The container of claim 24, wherein said carrier member aperture includes a first diameter which gradually expands to a second diameter between a first and a second surface of said carrier, said second diameter being greater than said first diameter. 31. The container of claim 30, wherein said second diameter is adjacent said window member. 32. The container of claim 27, wherein said blotter member includes an aperture formed therein. 33. The container of claim 32, wherein said aperture in said blotter is coaxially aligned with said aperture in said carrier member. 34. The container of claim 24, wherein said carrier member, said spacer member, said window member and said spacer means are interconnected so as to have a common centroidal axis. 35. A container for radioactive samples comprising: 36. The container of claim 35, wherein said carrier member aperture, said spacer member opening and said window spacer opening have a common centroidal axis. 37. The container of claim 35, including: 38. The container of claim 37, wherein said carrier member aperture, said spacer member opening, said window spacer opening and said blotter member aperture have a common centroidal axis. 39. The container of claim 35, wherein said carrier member aperture includes a first diameter which gradually expands to a second diameter between a first and a second surface of said carrier, said second diameter being greater than said first diameter. 40. The container of claim 39, wherein said carrier member aperture and said window spacer opening have a common centroidal axis. 41. A laminated container for radioactive samples comprising: 42. The laminated container of claim 41, including: 43. The laminated container of claim 41, wherein said layers are interconnected so as to have a common centroidal axis. 44. The laminated container of claim 41, wherein said carrier layer aperture, said first spacer layer opening and said second spacer layer opening have a common centroidal axis. 45. The laminated container of claim 41 wherein said cavity is a disk-shaped cavity. 46. A container for holding a low energy radioactive sample during evaluation of the sample by radioactivity measuring equipment, the container comprising: 47. The container of claim 46 wherein said selective enclosing means comprises a layer of material removably applied to said one of said surfaces of said member to permit access to said sample-receiving cavity for the introduction of a radioactive sample into said cavity. 48. The container of claim 46 wherein said member comprises a first generally flat, disk-shaped member with an aperture therethrough, and a second generally flat, disk-shaped member attached to one surface of said first member and covering one end of said aperture, said second member having an aperture therethrough leading to the aperture in said first member, said window comprising a third generally flat, disk-shaped member attached to the other surface of said first member, whereby said sample-receiving cavity is formed in said first member between the second and third member, access to said cavity being through said aperture in said second member. 49. The container of claim 48 wherein said window comprises a plastic film adhesively attached to said first member. 50. The container of claim 47 wherein said window comprises a plastic film adhesively attached to said other of said surfaces of said flat member. |
051005859 | abstract | The invention is a process for selectively extracting strontium and technetium values from aqueous nitric acid waste solutions containing these and other fission product values. The extractant is a macrocyclic polyether in a diluent which is insoluble in water, but which will itself dissolve a small amount of water. The process will extract strontium and technetium values from nitric acid solutions which are up to 6 molar in nitric acid. |
047073276 | abstract | Container system for a high-temperature nuclear reactor, including an outer metallic pressure vessel having an inwardly-protruding flange, an inner metallic core barrel resting tightly on the flange, and means disposed below the flange at a lower end of the core barrel for feeding and discharging cooling fluid, the core barrel being gas-tight above the flange. |
claims | 1. A scanning probe microscopy (SPM) system for making a modification to an object, the SPM system comprising:a sample stage adapted to hold an object to be modified;a cantilever disposed above the sample stage;an SPM probe mounted on the cantilever and configured to perform nanolapping on the object, thereby modifying the object;a positioning system configured to position the SPM probe with respect to the object held on the sample stage, wherein the sample stage and the positioning system are each thermally insulated, wherein respective temperatures of the sample stage and the positioning system are separately controllable, and wherein the object is held at a temperature greater than 30° C. or less than 10° C. during the nanolapping; andan enclosure substantially surrounding the stage, the SPM probe, the cantilever and the positioning system, wherein the enclosure provides thermal isolation for the SPM system. 2. The SPM system as claimed in claim 1, wherein the SPM probe comprises a tip, the tip being comprised of a material having a carbon chemical or solubility affinity. 3. The SPM system as claimed in claim 2, wherein the material having a carbon chemical or solubility affinity is selected from a group consisting of manganese, titanium, and iron. 4. The SPM system as claimed in claim 1, wherein the SPM probe comprises a tip, the tip being comprised of a material having an affinity for hydrogen. 5. The SPM system as claimed in claim 4, wherein the material having an affinity for hydrogen is selected from a group consisting of diamond, titanium, and platinum. 6. The SPM system as claimed in claim 1 wherein the object is held at a temperature near absolute zero during the nanolapping. 7. The SPM system as claimed in claim 1 wherein the object to be nanolapped is made at least in part of diamond. |
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abstract | In one embodiment, an irradiation target encapsulation assembly, includes a container, at least one first irradiation target disposed in the container, at least one second irradiation target disposed in the container, and a positioning structure configured to position the first irradiation target closer to an axial center of the container than the second irradiation target. |
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claims | 1. An apparatus for controlling movement of a first component integrated with a second component, the apparatus comprising:a first clamp configured to directly engage an outer surface of the first component;a second clamp configured to directly engage an outer surface of the second component; anda plurality of connectors configured to connect the first and second clamps;wherein when the first clamp directly engages the outer surface of the first component, the second clamp directly engages the outer surface of the second component, and the plurality of connectors connects the first and second clamps, the connectors are further configured to allow movement of the first clamp relative to the second clamp in a first direction between the first and second clamps by sliding in the first direction relative to the first clamp, the second clamp, or the first and second clamps, andwherein when the first clamp directly engages the outer surface of the first component, the second clamp directly engages the outer surface of the second component, and the plurality of connectors connects the first and second clamps, the connectors are further configured to limit movement of the first clamp relative to the second clamp in a second direction perpendicular to the first direction. 2. The apparatus of claim 1, wherein the connectors are further configured to allow linear movement of the first clamp relative to the second clamp in the first direction. 3. The apparatus of claim 1, wherein the connectors are further configured to limit linear movement of the first clamp relative to the second clamp in the second direction. 4. The apparatus of claim 1, wherein the connectors are further configured to limit rotational movement of the first clamp relative to the second clamp about an axis defined in the first direction. 5. The apparatus of claim 1, wherein the connectors are further configured to prevent linear movement of the first clamp relative to the second clamp in the second direction. 6. The apparatus of claim 1, wherein the connectors are further configured to prevent rotational movement of the first clamp relative to the second clamp about an axis defined in the first direction. 7. The apparatus of claim 1, wherein the first clamp includes two or more first clamp sections. 8. The apparatus of claim 7, wherein the two or more first clamp sections are connected together using a plurality of first clamp bolts. 9. The apparatus of claim 1, wherein the first clamp includes two or more first clamp sections, andwherein the second clamp includes two or more second clamp sections. 10. The apparatus of claim 9, wherein the two or more first clamp sections are connected together using a plurality of first clamp bolts, andwherein the two or more second clamp sections are connected together using a plurality of second clamp bolts. 11. An apparatus for controlling movement of components in a nuclear power plant, the nuclear power plant including a reactor pressure vessel and a jet pump assembly within the reactor pressure vessel, the apparatus comprising:a first clamp configured to engage an outer surface of an inlet mixer of the jet pump assembly;a second clamp configured to engage an outer surface of a diffuser of the jet pump assembly; anda plurality of connectors configured to connect the first and second clamps;wherein when the first clamp engages the outer surface of the inlet mixer, the second clamp engages the outer surface of the diffuser, and the plurality of connectors connects the first and second clamps, the connectors are further configured to allow movement, due to thermal expansion, of the first clamp relative to the second clamp in an axial direction of the jet pump assembly by sliding in the axial direction relative to the first clamp, the second clamp, or the first and second clamps, andwherein when the first clamp engages the outer surface of the inlet mixer, the second clamp engages the outer surface of the diffuser, and the plurality of connectors connects the first and second clamps, the connectors are further configured to limit movement of the first clamp relative to the second clamp in a direction perpendicular to the axial direction of the jet pump assembly. 12. The apparatus of claim 11, wherein the connectors are further configured to allow linear movement of the first clamp relative to the second clamp in the axial direction of the jet pump assembly. 13. The apparatus of claim 11, wherein the connectors are further configured to limit linear movement of the first clamp relative to the second clamp in the direction perpendicular to the axial direction of the jet pump assembly. 14. The apparatus of claim 11, wherein the connectors are further configured to limit rotational movement of the first clamp relative to the second clamp about the axial direction of the jet pump assembly. 15. An apparatus for controlling movement of components in a nuclear power plant, the nuclear power plant including a reactor pressure vessel and a jet pump assembly within the reactor pressure vessel, the apparatus comprising:a first clamp configured to directly engage an outer surface of an inlet mixer of the jet pump assembly;a second clamp configured to directly engage an outer surface of a diffuser of the jet pump assembly; anda plurality of connectors configured to connect the first and second clamps;wherein when the first clamp directly engages the outer surface of the inlet mixer, the second clamp directly engages the outer surface of the diffuser, and the plurality of connectors connects the first and second clamps, the first clamp, second clamp, and connectors are further configured to allow movement, due to thermal expansion, of the inlet mixer relative to the diffuser in an axial direction of the jet pump assembly by sliding in the axial direction relative to the first clamp, the second clamp, or the first and second clamps, andwherein when the first clamp directly engages the outer surface of the inlet mixer, the second clamp directly engages the outer surface of the diffuser, and the plurality of connectors connects the first and second clamps, the first clamp, second clamp, and connectors are further configured to limit movement of the inlet mixer relative to the diffuser in a direction perpendicular to the axial direction of the jet pump assembly. 16. The apparatus of claim 15, wherein the first clamp, second clamp, and connectors are further configured to allow linear movement of the inlet mixer relative to the diffuser in the axial direction of the jet pump assembly. 17. The apparatus of claim 15, wherein the first clamp, second clamp, and connectors are further configured to limit linear movement of the inlet mixer relative to the diffuser in the direction perpendicular to the axial direction of the jet pump assembly. 18. The apparatus of claim 15, wherein the first clamp, second clamp, and connectors are further configured to limit rotational movement of the inlet mixer relative to the diffuser about the axial direction of the jet pump assembly. 19. A method for controlling movement of a first component integrated with a second component, the method comprising:engaging an outer surface of the first component with a first clamp;engaging an outer surface of the second component with a second clamp; andconnecting the first and second clamps using a plurality of connectors;wherein when the first clamp engages the outer surface of the first component, the second clamp engages the outer surface of the second component, and the plurality of connectors connects the first and second clamps, the connectors are configured to allow movement of the first clamp relative to the second clamp in a first direction between the first and second clamps by sliding in the first direction relative to the first clamp, the second clamp, or the first and second clamps, andwherein when the first clamp engages the outer surface of the first component, the second clamp engages the outer surface of the second component, and the plurality of connectors connects the first and second clamps, the connectors are further configured to limit movement of the first clamp relative to the second clamp in a second direction perpendicular to the first direction. 20. The apparatus of claim 11, wherein the first clamp is further configured to directly engage the outer surface of the inlet mixer of the jet pump assembly. 21. The apparatus of claim 11, wherein the second clamp is further configured to directly engage the outer surface of the diffuser of the jet pump assembly. |
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summary | ||
claims | 1. An apparatus for inspecting patterns, comprising:an electron source for generating an electron beam;focusing means for focusing the electron beam and irradiating the electron beam onto a specimen with one of the patterns formed thereon;a detector for detecting electrons generated from a surface of the specimen with the electron beam irradiated thereon;imaging means for forming an electron beam image of said one of the patterns based on a signal detected by the detector;determining means for determining a charge state of the specimen which allows the specimen to be inspected stably;potential adjusting means for changing at least one of a potential of the specimen and a potential of an electrode provided on a side of the electron source with respect to the specimen, to maintain the determined charge state of the specimen; andimage evaluation value computation means for obtaining the electron beam image formed by the imaging means at each of a plurality of potentials adjusted by the potential adjusting means and determining an image evaluation value of the electron beam image. 2. The apparatus for inspecting patterns according to claim 1, further comprising: display means for displaying the image evaluation value and said each of the potentials corresponding to the image evaluation value. 3. The apparatus for inspecting patterns according to claim 1, wherein the image evaluation value indicates at least one of contrast of the electron image and brightness of the electron beam image. 4. An apparatus for inspecting patterns, comprising:an electron source for generating an electron beam;focusing means for focusing the electron beam and irradiating the electron beam onto a specimen with one of the patterns formed thereon;a detector for detecting electrons generated from a surface of the specimen with the electron beam irradiated thereon;imaging means for forming an electron beam image of said one of the patterns based on a signal detected by the detector;determining means for determining a charge state of the specimen which allows the specimen to be inspected stably; andpotential adjusting means for changing at least one of a potential of the specimen or a potential of an electrode provided on a side of the electron source with respect to the specimen; to maintain the determined charge state of the specimen;the electron beam image formed by the imaging means at each of a plurality of potentials adjusted by the potential adjusting means being obtained, and one of the potentials with brightness of the electron beam image corresponding to said one of the potentials starting to decrease being set as an inspecting condition potential for the potential adjusting means. 5. The apparatus for inspecting patterns according to claim 1, wherein when the potential of the specimen or the potential of the electrode above the specimen is changed by the potential adjusting means, a setting condition range is set so that the potential is changed from positive to negative. 6. A method for inspecting patterns using an inspection apparatus, the inspection apparatus comprising means for irradiating an electron beam onto a surface of a specimen with one of the patterns formed thereon and scanning the specimen, means for detecting a signal secondarily generated from the specimen by the electron beam, and means for imaging the detected signal, for display, the method comprising the steps of:determining a charge state of the specimen which allows the specimen to be inspected stably,changing a potential of the specimen or a potential of an electrode set above the specimen with respect to the specimen, to maintain the determined charge state of the specimen,obtaining an electron beam image at each potential, andperforming numeric conversion on information indicating at least one of contrast of the obtained electron beam and brightness of the obtained electron beam image, for display. 7. A method for inspecting patterns using an inspection apparatus, the inspection apparatus comprising means for irradiating an electron beam onto a surface of a specimen with one of the patterns formed thereon and scanning the specimen, means for detecting a signal secondarily generated from the specimen by the electron beam, and means for imaging the detected signal, for display, the method comprising the steps of:determining a charge state of the specimen which allows the specimen to be inspected stably,changing a potential of the specimen or a potential of an electrode set above the specimen of the electron source with respect to the specimen, to maintain the determined charge state of the specimen,obtaining an electron beam image at each potential, andsetting a point of change with brightness of the electron beam image starting to decrease when the potential of the specimen or the potential of the electrode is changed. 8. The method for inspecting patterns according to claim 7, wherein the step of changing the potential of the specimen or the potential of the electrode comprises the steps of:extensively changing the potential in several stages, thereby obtaining the electron beam image in each of the stages;obtaining the point of change with the brightness of the obtained electron beam image starting to decrease;changing the potential in finer stages in the vicinity of the point of change, thereby obtaining the electron beam image in each of the finer stages again; andobtaining a point of change again from information on the electron beam image obtained again. 9. The method for inspecting patterns according to claim 6, wherein when the potential of the specimen or the potential of the electrode is changed, the potential is changed so that a charged condition of the specimen is changed from positive to negative. 10. The apparatus for inspecting patterns according to claim 2, wherein the image evaluation value indicates at least one of contrast of the electron beam image and brightness of the electron beam image. 11. The apparatus for inspecting patterns according to claim 2, wherein when the potential of the specimen or the potential of the electrode above the specimen is changed by the potential adjusting means, a setting condition range is set so that the potential is changed from positive to negative. 12. The apparatus for inspecting patterns according to claim 3, wherein when the potential of the specimen or the potential of the electrode above the specimen is changed by the potential adjusting means, a setting condition range is set so that the potential is changed from positive from negative. 13. The apparatus for inspecting patterns according to claim 4, wherein when the potential of the specimen or the potential of the electrode above the specimen is changed by the potential adjusting means, a setting condition range is set so that the potential is changed from positive to negative. 14. The method for inspecting patterns according to claim 7, wherein when the potential of the specimen or the potential of the electrode above the specimen is changed by the potential adjusting means, potential is changed so that a charged condition of the specimen is changed from positive to negative. |
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053486897 | claims | 1. A process for destroying alkali metal and alkaline earth metal hazardous waste and converting it into non-hazardous salt which comprises feeding said alkali metal or alkaline earth metal containing hazardous waste into a molten salt bath containing a molten salt selected from the group consisting of an alkali metal carbonate, an alkali metal halide, an alkaline earth halide, and mixtures thereof, feeding a mixture of carbon dioxide and oxygen into said molten salt bath, the proportions of carbon dioxide and oxygen being at least sufficient to react stoichiometrically with the alkali metal or alkaline earth metal in said waste, and reacting said alkali metal or said alkaline earth metal with said carbon dioxide and oxygen in said molten salt bath at a temperature above the melting point of the salt in said molten salt bath, and converting said alkali metal or said alkaline earth metal into a non-hazardous carbonate salt in said bath. introducing said sodium-containing hazardous waste into a molten sodium carbonate bath, introducing a mixture of carbon dioxide and oxygen into said molten sodium carbonate bath, the proportions of carbon dioxide and oxygen being at least 10% in excess of the stoichiometric amount required for reaction with said sodium in said waste, reacting said sodium in said waste with said carbon dioxide and oxygen in said molten sodium carbonate bath at temperature of between about 800.degree. C. and about 900.degree. C,. and converting said sodium into sodium carbonate in said bath. introducing said sodium-containing hazardous waste into a molten salt bath, said salt bath consisting of a mixture of sodium carbonate and a member selected from the group consisting of alkali metal chloride and alkaline earth metal chloride, introducing a mixture of carbon dioxide and oxygen into said molten salt bath, the proportions of carbon dioxide and oxygen being at least 10% in excess of the stoichiometric amount required for reaction with said sodium in said waste, reacting said sodium in said waste with said carbon dioxide and oxygen in said molten salt bath at a temperature between about 600.degree. C. and about 800.degree. C., and converting said sodium into sodium carbonate in said bath. feeding said alkali metal or alkaline earth metal containing hazardous waste into a molten salt bath containing a molten salt consisting of a mixture of sodium carbonate and a lower melting point salt consisting of a mixture of alkali metal chlorides and alkaline earth metal chlorides, said molten salt bath temperature ranging from about 600.degree. C. to about 800.degree. C., feeding a mixture of carbon dioxide and oxygen into said molten salt bath, the proportions of carbon dioxide and oxygen being at least sufficient to react stoichiometrically with the alkali metal or alkaline earth metal in said waste, and reacting said alkali metal or said alkaline earth metal with said carbon dioxide and oxygen in said molten salt bath at a temperature above the melting point of the salt in said molten salt bath, and converting said alkali metal or said alkaline earth metal into a non-hazardous carbonate salt in said bath. feeding said alkali metal or alkaline earth metal containing hazardous waste into a molten salt bath consisting of a mixture of sodium carbonate and a lower melting point salt selected from the group consisting of alkali metal halides, alkaline earth metal halides, and mixtures thereof, said molten salt bath temperature ranging from about 600.degree. C. to about 800.degree. C., feeding a mixture of carbon dioxide and oxygen into said molten salt bath, the proportions of carbon dioxide and oxygen being at least sufficient to react stoichiometrically with the alkali metal or alkaline earth metal in said waste, and reacting said alkali metal or said alkaline earth metal with said carbon dioxide and oxygen in said molten salt bath at a temperature above the melting point of the salt in said molten salt bath, and converting said alkali metal or said alkaline earth metal into a non-hazardous carbonate salt in said bath, said lower melting point salt being maintained by sparging chlorine or chlorinated hydrocarbon into said molten salt bath to convert carbonate therein to chlorides. feeding said sodium containing hazardous waste into a molten salt bath consisting of a mixture of two or more salts selected from the group consisting of NaCl, KCl and CaCl.sub.2, feeding a mixture of carbon dioxide and oxygen into said molten salt bath, the proportions of carbon dioxide and oxygen being at least sufficient to react stoichiometrically with the sodium in said waste, and reacting said sodium with said carbon dioxide and oxygen in said molten salt bath at a temperature above the melting point of the salt in said molten salt bath, and converting said sodium into non-hazardous sodium carbonate in said bath. feeding said alkali metal or alkaline earth metal containing hazardous waste into a molten salt bath containing a molten salt consisting of a eutectic of about 50% Na.sub.2 CO.sub.3 and about 50% NaCl, by weight, feeding a mixture of carbon dioxide and oxygen into said molten salt bath, the proportions of carbon dioxide and oxygen being at least sufficient to react stoichiometrically with the alkali metal or alkaline earth metal in said waste, and reacting said alkali metal or said alkaline earth metal with said carbon dioxide and oxygen in said molten salt bath at a temperature above the melting point of the salt in said molten salt bath, and converting said alkali metal or said alkaline earth metal into a non-hazardous carbonate salt in said bath. 2. The process of claim 1, and including adding a member selected from the group consisting of sulfate, phosphate and nitrate to said molten salt to lower the melting point of the salt. 3. The process of claim 1, wherein the temperature of said molten bath ranges from about 200.degree. C. to about 900.degree. C. 4. The process of claim 1, wherein said molten salt bath consists essentially of sodium carbonate and molten salt bath temperature ranges from about 600.degree. C. to about 900.degree. C. 5. The process of claim 3, wherein said waste contains alkali metal, and said alkali metal is sodium, and said sodium is converted to sodium carbonate in said molten salt bath. 6. The process of claim 1, wherein said molten salt bath consists of a mixture of sodium carbonate and a lower melting point salt selected from the group consisting of alkali metal halides, alkaline earth metal halides, and mixtures thereof, and said molten salt bath temperature ranges from about 600.degree. C. to about 800.degree. C. 7. The process of claim 1, wherein the proportions of carbon dioxide and oxygen are at least 10% in excess of the stoichiometric amount required for reaction with the alkali metal or alkaline earth metal in said bath. 8. A process for destroying sodium in hazardous waste and converting it into non-hazardous sodium carbonate which comprises 9. A process for destroying sodium in hazardous waste and converting it into non-hazardous sodium carbonate which comprises 10. The process of claim 9, wherein said member is a mixture of two or more salts selected from the group consisting of NaCl, and KCl and CaCl.sub.2. 11. The process of claim 9, wherein said salt bath consists of a eutectic alkali carbonate mixture consisting of 50% Na.sub.2 CO.sub.3 and 50% K.sub.2 CO.sub.3, by weight and a mixture of two or more salts selected from the group consisting of NaCl, KCl and CaCl.sub.2. 12. A process for destroying alkali metal and alkaline earth metal hazardous waste and converting it into non-hazardous salt which comprises 13. The process of claim 12, wherein said waste contains alkali metal, and said alkali metal is sodium, and said lower melting point salt consists of a mixture of two or more salts selected from the group consisting of NaCl, KCl and CaCl.sub.2. 14. A process for destroying alkali metal and alkaline earth metal hazardous waste and converting it into non-hazardous salt which comprises 15. The process of claim 1, wherein said molten salt bath consists of a member selected from the group consisting of an alkali metal halide, an alkaline earth halide, and mixtures thereof. 16. The process of claim 1, wherein said molten salt is a eutectic alkali carbonate mixture consisting of 50% Na.sub.2 CO.sub.3 and 50% K.sub.2 CO.sub.3, by weight. 17. A process for destroying sodium in sodium-containing hazardous waste and converting it into non-hazardous salt which comprises 18. A process for destroying alkali metal and alkaline earth metal hazardous waste and converting it into non-hazardous salt which comprises |
abstract | A radiation detector with an integrated collimator. The collimator may be deposited on an anode or cathode face of the radiation detector. An insulating material may be deposited between the collimator and the radiation detector if the collimator is deposited on the anode side. The collimator may be comprised of a single layer or of multiple layers. Patterning and etching may be used to create an aperture in the collimator to allow x-rays to impinge on a full charge collection region of the radiation detector intrinsic region. |
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051006090 | description | DETAILED DESCRIPTION OF THE INVENTION Since a natural-circulation BWR contains no recirculating devices nor external loops, regulating the speed of the prime drive motor so as to produce a controlled recirculation flow rate or throttling flow control valves located in external recirculation loops to obtain flow rate regulation are unavailable. Accordingly, the problem to be solved is to devise an improved means of obtaining effective load-following capability and/or enhancing spectral shift capability in sparger-type BWRs and for which the drawbacks in the form of added components are minimal and are acceptable considering the benefits obtained. With reference to the drawing, it will be appreciated that much of the reactor internals are conventional and have been omitted from the drawings as such components are unnecessary to the modifications which need to be made to the BWRs in accordance with the precepts of the present invention. The reactor internals, their construction, and operation are well known in the art, such as illustrated by reference to the following publications: Glasstone and Sesonke, Nuclear Reactor Engineering, pp 748-753, 3d Edition, VanNostrand. Reinholt (New York, NY, 1981); Wolfe and Wilkens, "Improvements in Boiling Water Reactor Designs and Safety", presented at American Nuclear Society Topical Meeting, Seattle, Wash., May 1-5, 1988; Duncan and McCandless, "An Advanced Simplified Boiling Water Reactor", presented at the American Nuclear Society Topical Meeting, Seattle, Wash., May 1-5, 1988; and Lahey and Moody, The Thermal Hydraulics of a Boiling Water Reactor, especially Chapter 2, pp 15-44, American Nuclear Society (LeGrange Park, Ill., 1977). Conventional BWRs, the ABWR, and the SBWR, all are described and discussed in the foregoing references, all of which are expressly incorporated herein by reference. While the description refers primarily to natural circulation BWRs, forced circulation reactors can be modified in accordance with the present invention also. Referring to FIG. 1 more particularly, reactor pressure vessel (RPV) 10 is seen to admit feedwater via inlet 12 and exhaust steam via outlet 14. Connected to inlet 12 is sparger 16. Sparger 16 is a ringshaped pipe having suitable apertures through which the feedwater is passed to within RPV 10. The design of spargers and their apertures is conventional and well-known to those skilled in the art. As described generally above and in particular in the references cited, with respect to the flow path of water within RPV 10, sub-cooled water located in the downcomer region identified at 24 flows downwardly between RPV 10 and shroud 26 in the annulus region identified at 28. The water flowing through annulus 28 then flows to the core lower plenum region identified at 30. Again, for simplicity many of the reactor internal components have not been illustrated in the drawing as these items are conventional and will be readily apparent to those skilled in the art. The water then flows through a guide tube region located within shroud 26 and below core 32, thence through the fuel orifices and past the fuel support casting and nosepiece lower tie plates. The water then enters the fuel assemblies disposed within core 32 wherein a boiling boundary layer is established, thus causing a lower non-boiling region and an upper boiling region within the fuel assemblies. Flow by-passing is to be provided as is necessary, desirable, or convenient in conventional fashion. Next, a mixture of water and steam enters core upper plenum 34 which is formed within shroud head 36 and disposed atop core 32. Core upper plenum 34 provides stand-off between the mixture exiting core 32 and entering standpipes 38 that are disposed atop shroud head 36 and in fluid communication with core upper plenum 34. It will be observed that downcomer region 24 is formed between the walls of RPF 10 and standpipes 38 which form the chimney. It will be appreciated that a variety of additional confining or direction means/members could be used as the chimney in place of standpipes 38. The liquid water elevation or level established within RPV 10 during normal operation of the BWR is identified at 44. Normal operation is defined to be a reactor output at expected or normal grid electrical demand with all components of the reactor operating nominally. Note that sparger 16 is located at about water elevation or level 44. Sparger 16 is located above the skirt bottom of the separator. The mixture flowing through standpipes 38 then enters steam separator/dryer assembly 40 that is to be provided in conventional or unconventinoal fashion. Separator 40 provides outlet communication for separated water to enter downcomer 24 and for steam to enter steam dome 42 and thence to be withdrawn from RPV 10 via outlet 14. The separated water in downcomer 24 and recycled feedwater from the turbine island portion of the power generating station entering inlet 12, then combine and the flow circulation commences again. From the foregoing description, it will be readily apparent that steam will condense if water level 44 is lower than the elevation of sparger 16 and there will be little or no sub-cooling. If water level 44 is raised to an elevation above sparger 16, there is less time for condensation and the sub-cooling will increase. The upward flow at the indicated sparger elevational level reduces with higher water levels and becomes is virtually zero at a suitably high water level so there will be no entrainment of feedwater towards steam separator dryer 40. Load following, then, is performed simply by reducing or increasing the feedwater flow and, thus, the elevation of water level 44. Consequently, the amount of steam that is condensed will be increased or decreased and so will the amount of sub-cooling and, consequently, the reactor power. Thus, it will be observed that the power level generated by the reactor can be increased or decreased by suitable operation of the sparger BWR disclosed herein. For spectral shift operation, it will be appreciated that the sparger BWR will be operated so as to reduce the sub-cooling and/or recirculation rate so as to increase the void fraction in the core and, thus, reduce the power level of the reactor. Withdrawal of the conventional control rods, not shown in the drawings, re-establishes the power level and enhances spectral shift operation of the reactor. As noted above, when operating the sparger BWR of the present invention in a spectral shift mode, load following still is possible responsive to grid electrical demand and/or other demands made of the reactor. Spectral shift may be compromised and/or control rod movement may be required, yet load following is believed to be achievable primarily through judicious operation of feedwater admitted into the reactor via the sparger disposed therewithin. As to the materials of construction, preferably all components are manufactured from materials appropriate for their use within a nuclear BWR. Further, it will be appreciated that various of the components shown described herein may be altered or varied in accordance with the conventional wisdom in the field and certainly are included within the present invention, provided that such variations do not materially vary within the spirit and precepts of the present invention as described herein. |
summary | ||
abstract | Carbon contamination of optical elements in an exposure tool is minimized by incorporating a hydrocarbon getter. Embodiments include EUV lithography tools provided with at least one hydrocarbon getter comprising a substrate and a high energy source, such as an electron gun or separate EUV source, positioned to direct an energy beam, having sufficient energy to crack heavy hydrocarbons and form carbon, on the substrate. Embodiments also include exposure tools equipped with a hydrocarbon getter comprising an energy source positioned to impinge a beam of energy on a quartz crystal thickness monitor, a residual gas analyzer, and a controller to control the electron-current and maintain the amount of hydrocarbons in the system at a predetermined low level. |
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claims | 1. A method of extracting strontium-89 from a uranyl sulfate water solution fueled nuclear reactor, the method comprising: operating said solution nuclear reactor whereby inert gaseous fission fragments are produced and migrate to the free volume above the solution surface, said gaseous fission fragments comprised of isotopes of beryllium, krypton and rubidium; pumping said inert gaseous fission fragments through a first delaying device to achieve an approximate ten minute delay whereby krypton-90 is substantially depleted; passing gas through a first filter to remove rubidium and strontium isotopes that were not precipitated in said first delaying device; pumping remaining gas through a second delaying device to achieve an approximate thirty minute delay; passing gas through a second filter to remove any remaining rubidium and strontium isotopes that were not precipitated out in said second delay device; pumping remaining gas back to the reactor; and extracting precipitated strontium-89 from said second delay device and from said second filter. 2. The method of claim 1 wherein the extraction of strontium-89 from said second delay device and said second filter is by an acid wash. claim 1 |
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claims | 1. Storage and dispatch container for radioactive miniature radiation sources arranged successively in a main body, comprising a main body with a capillary tube ( 8 ) arranged therein to accommodate the sources of radiation ( 15 ), the main body having a lower end-piece ( 2 ) with a fluid-medium connection ( 4 ) and an upper end-piece ( 3 ) with an input/output opening ( 3 a ) for the radiation sources which is lockable by a self-actuated locking mechanism ( 10 ); and a locking and opening device for loading and unloading the radiation sources from the container, wherein the self-actuated locking mechanism ( 10 ) is a plunger which is structured to interact with an adapter to allow free access to the upper opening of the capillary tube. 2. The container according to claim 1 wherein claim 1 the capillary tube ( 8 ) consists of quartz glass and the main body ( 1 ) of acrylic glass. 3. The container according to claim 1 wherein claim 1 the lower end-piece ( 2 ) and the upper end-piece ( 3 ) consist of aluminum. 4. The container according to claim 1 wherein claim 1 the radiation sources ( 15 ) in the capillary tube ( 8 ) are successively arranged end-to-end. 5. The container according to claim 1 wherein claim 1 the cross-sections of the capillary tube ( 8 ) and the main body ( 1 ) are circular. 6. The container according to claim 1 wherein claim 1 the internal diameter of the capillary tube ( 8 ) is continued in the lower end-piece ( 2 ) with a smaller diameter eccentric to the medium connection ( 4 ) and in the upper end-piece ( 3 ) with the same diameter to the input/output opening ( 3 a ). 7. The container according to claim 1 wherein claim 1 the upper end-piece ( 3 ) can be sealed with a closure cap ( 13 ). 8. The container according to claim 1 wherein claim 1 the main body ( 1 ) has level markings. 9. The container of claim 1 , wherein the Locking and opening device comprises claim 1 a slide valve ( 18 ) arranged between a headpiece ( 16 ) and a cover ( 22 ), and a cut-off needle ( 26 ) which alternatively opens or blocks an input/output channel ( 23 ) in a neck ( 17 ) upon actuation of the slide valve ( 18 ). 10. The container according to claim 9 wherein claim 9 the slide valve ( 18 ) has wings ( 18 a , 18 b ) projecting from opposite sides of the headpiece ( 16 ) and cover ( 22 ) and which serve to actuate the slide valve ( 18 ). 11. The container according to claim 9 wherein claim 9 the cut-off needle ( 26 ) is a cylindrical pin. 12. The container according to claim 9 wherein claim 9 the headpiece ( 16 ), the cover ( 22 ) and the slide valve ( 18 ) possess a centralized opening into which the opening of a correspondingly designed container fits. 13. The container according to claim 12 wherein claim 12 the opening in the slide valve ( 18 ) is oblong and of tapered form. 14. The container according to claim 13 wherein claim 13 the taper is chamfered in the direction of the headpiece ( 16 ). 15. The container according to claim 9 wherein claim 9 The neck ( 17 ) exhibits flutes in the main axis direction as well as a transverse drilling to accommodate the cut-off needle ( 26 ). 16. The container according to claim 9 wherein claim 9 The headpiece ( 16 ) has an insertion opening ( 24 ) for a catheter adapter ( 20 ). |
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summary | ||
claims | 1. A method of removing an upper internals package from a nuclear reactor having a reactor vessel with an upper flange surrounding an opening in the reactor vessel that is sealed by a mating flange on a closure head, the reactor vessel enclosing the upper internals package that seats above a plurality of fuel assemblies within a core of the reactor, the upper internals package including a plurality of rod travel housings in which control rod assembly drive rods are housed and through which the drive rods travel along a vertical path, the method comprising the steps of:removing the closure head from the reactor vessel;lowering a shield plate over the opening in the reactor vessel after removing the closure head from the reactor vessel, the shield plate being sized to cover the opening when supported on the reactor vessel upper flange and being formed from a material that lessens the radiation exposure of workers working above the shield plate covering the reactor vessel opening, with openings through the shield plate in-line with the rod travel housings through which the control rod assembly drive rods can be accessed, the shield plate including an integral lifting rig extending above an upper surface thereof;attaching the shield plate to the upper internals package;accessing the control rod assembly drive rods through the openings; andraising the shield plate to withdraw the upper internals package out of the reactor. 2. The method of claim 1 wherein the access openings include a drive rod latching tool that is reciprocally moveable along a substantially vertical travel path through the opening and into the rod travel housings to connect to the drive rods and decouple the drive rods from the corresponding control rod assemblies, including the steps of:attaching the drive rod latching tool to at least one of the drive rods;decoupling the drive rod from the corresponding control rod assembly; andraising the drive rod latching tool to raise the drive rod within the rod travel housing. 3. The method of claim 2 including the step of latching the drive rod in a raised position within the rod travel housing after the raising step. 4. The method of claim 2 wherein before the step of raising the shield plate the method comprises the step of lowering a shield cylinder over the shield plate and around the upper internals package. 5. The method of claim 4 including the step of supporting the shield cylinder from the shield plate when the shield cylinder is fully lowered around the upper internals package. 6. The method of claim 4 including the step of maintaining a negative atmosphere within the shield cylinder. 7. The method of claim 6 wherein the step of maintaining a negative atmosphere within the shield cylinder comprises venting air within the shield cylinder and filtering the vented air before being exhausted outside the shield cylinder. |
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description | The present application is a continuation of, and claims benefit under 35 USC 120 to, international application PCT/EP2014/053927, filed Feb. 28, 2014, which claims benefit under 35 USC 119 of German Application No. 10 2013 204 444.5, filed Mar. 14, 2013. International application PCT/EP2014/053927 also claims priority under 35 USC 119(e) to U.S. Provisional Application No. 61/781,874, filed Mar. 14, 2013. The contents of International application PCT/EP2014/053927 and German patent application DE 10 2013 204 444.5 are incorporated herein by reference. The invention relates to an illumination optical unit for a mask inspection system for use with EUV illumination light. The invention furthermore relates to a mask inspection system with such an illumination optical unit and an EUV light source. Mask inspection systems are known from DE 102 20 815 A1 and WO 2012/101269 A1. It is an object of the present invention to develop an illumination optical unit for such an inspection system in such a way that the throughput thereof is optimized for the EUV illumination light, which can be used for illuminating the illumination field. According to the invention, this object is achieved by an illumination optical unit for a mask inspection system for use with EUV illumination light, comprising: a hollow waveguide for guiding the illumination light, comprising an entry opening for the illumination light and an exit opening for the illumination light; and an imaging mirror optical unit, arranged down-stream of the hollow waveguide, for imaging the exit opening into an illumination field. The result of using a hollow waveguide and an imaging optical unit with at least one mirror for grazing incidence is an illumination optical unit, by which the illumination field can be illuminated, even while maintaining demanding requirements in respect of illumination homogeneity with, at the same time, a high throughput, i.e. a high transmission by the components of the illumination optical unit. The hollow waveguide produces good mixing of the illumination light. This results in a high efficiency of the illumination optical unit, while at the same time having a high homogeneity of the illumination of the illumination field with the illumination light. Illuminating the illumination field with a low dose variation is possible. To the extent that the mask to be inspected is scanned through the illumination field, it is possible for a variation of the illumination dose integrated in the scanning direction to achieve a value perpendicular to the scanning axis in the illumination field, which is less than 5%, and in particular, it can achieve a value which is less than 1%. An image-side numerical aperture of the imaging optical unit can be less than 0.2 and can be 0.1. The illumination field can have a typical dimension in an illumination field plane, which is less than 0.5 mm; i.e., for example, it can have an area in the region of at most 1 mm×1 mm, or else of at most 0.6 mm×0.6 mm. The illumination field can be rectangular and have dimensions of 0.6 mm×0.4 mm, or else of 0.1 mm×0.1 mm. An aspect ratio, in particular of the exit opening of the hollow waveguide, can be between 0.5 and 2, and can be e.g. 1. An inner cavity of the hollow waveguide used for reflecting the illumination light can be cuboid. The entry and exit openings can accordingly be rectangular and have the same dimensions. Typical dimensions of the entry and exit openings can lie in the range from 1 mm×1 mm to 5 mm×5 mm, e.g. at 1.0 mm×2.0 mm or at 1.5 mm×2.0 mm. The hollow waveguide can be longer than 300 mm, can be longer than 400 mm and can also be longer than 500 mm. A number n of the reflections of the illumination light in the hollow waveguide can be 10 at most. All surfaces of the illumination optical unit reflecting the illumination light can carry a highly reflective coating, in particular a ruthenium coating. The imaging mirror optical unit can have at least one mirror for grazing incidence of the illumination light, with a mean angle of incidence (α1, α2) which is greater than 60°. Such a mean angle of incidence of the mirror for grazing is an angle of incidence of a central ray of an illumination light beam incident on the respective mirror. The mean angle of incidence on the at least one mirror for grazing incidence can be greater than 65°, can be greater than 70°, can be greater than 75°, can be greater than 80° and can also be greater than 85°. The imaging mirror optical unit can have exactly two mirrors for grazing incidence of the illumination light, each with a mean angle of incidence (α1, α2) which is greater than 60°. Such an imaging mirror optical unit with exactly two mirrors was found to be particularly suitable. A sum of the mean angles of incidence of the illumination light on these two mirrors can be greater than 130°, can be greater than 135°, can be greater than 140°, can be greater than 145°, and can be 149°. A minimum distance between the optically used faces which is less than 300 mm leads to a compact configuration of the illumination optical unit. This minimum distance can be 50 mm or else 25 mm. Alternatively, or in addition thereto, the distance between the optically used faces of two neighboring mirrors can be greater than 3 mm. This ensures that the neighboring mirrors can each be mounted with the aid of a stable mirror mount. The imaging mirror optical unit can be embodied in the style of a Wolter telescope. Such an embodiment results in an illumination optical unit with a particularly high throughput. In particular, the imaging optical unit of the illumination optical unit can be embodied as a type I Wolter optical unit. The imaging mirror optical unit can have an ellipsoid mirror for grazing incidence of the illumination light, with a mean angle of incidence (α1) which is greater than 60°. The imaging mirror optical unit can have a hyperboloid mirror for grazing incidence of the illumination light, with a mean angle of incidence (α2) which is greater than 60°. Such embodiments of the mirrors as ellipsoid mirrors or as hyperboloid mirrors were found to be particularly suitable. At least two of the mirrors of the illumination optical unit or, if the illumination optical unit has more than two mirrors, all mirrors of the illumination optical unit can have a common axis of rotational symmetry. The ellipsoid mirror can be the first mirror of the imaging optical unit in the beam path of the illumination light downstream of the hollow waveguide. An entry back focus of the ellipsoid mirror can be greater than 150 mm, can be greater than 250 mm and can be greater than 300 mm. An exit back focus of the hyperboloid mirror can lie in the region between 50 mm and 100 mm and can be 60 mm. Greater back focuses of the illumination optical unit, in particular of a Wolter telescope, are possible, e.g. an exit back focus at infinity. Then, this can result in an illumination optical unit with a telecentric illumination of the illumination field. A minimum angle of incidence of the illumination light in the hollow waveguide can be greater than 80°. Such a minimum angle of incidence leads to a hollow waveguide with, firstly, a good mixing effect for an intensity of the illumination light in the exit opening and, secondly, high throughput. An overall reflectivity for the illumination light can be greater than 40%. Such an overall reflectivity results in a very advantageous throughput for the use of EUV illumination light. The overall reflectivity emerges as a product of the reflectivities of all mirror components of the illumination optical unit on which the illumination light is incident. A mask inspection system for inspecting a lithography mask can comprise: an illumination optical unit as discussed above; an EUV light source for producing the illumination light; a projection optical unit for imaging the illumination field in an image field; and a detection device for detecting illumination light incident on the image field. The advantages of such a mask inspection system correspond to those that were already explained above with reference to the illumination optical unit according to the invention. A wafer inspection system also can have a corresponding configuration. The inspection system can have an object mount for mounting the object to be inspected, which mount is mechanically coupled to an object displacement drive such that a scanning displacement of the object during this illumination is possible. The inspection system can be a system for an actinic mask inspection. An illumination optical unit 1 is a component of a mask inspection system for use with EUV illumination light 2. A beam path of the illumination light 2 is respectively depicted very schematically in the drawing and merely depicted for a chief ray 3 of a central field point of an illumination field 4 of the mask inspection system 5. The illumination light 2 is produced by an EUV light source 6. The light source 6 can produce EUV used radiation in a wavelength range between 2 nm and 30 nm, for example in the range between 2.3 nm and 4.4 nm or in the range between 5 nm and 30 nm, for example at 13.5 nm. The light sources conventional for EUV lithography systems or projection exposure apparatuses, that is to say e.g. laser produced plasma (LPP) sources or discharge produced plasma (DPP) sources, can also be used for the light source 6. After emission by the light source 6, the illumination light 2 is initially focused by a collector (not depicted here) and focused in an entry opening 7 in an entry plane 8 of a hollow waveguide 9. A largest part of the illumination light 2 experiences multiple reflections in the hollow waveguide 9. The number n of reflections in the hollow waveguide 9 is at most 10. An aspect ratio of the entry opening 7 and of an exit opening 10, with the same dimensions, for the illumination light 2 lies between 0.5 and 2. The entry opening 7 and the exit opening 10 are each rectangular with typical dimensions in the range between 1 mm and 5 mm. Typical dimensions of the entry opening 7 and of the exit opening 10 of the hollow waveguide 9 are 1.0 mm×2.0 mm or 1.5 mm×2.0 mm. An inner wall of a waveguide cavity of the hollow waveguide 9 is provided with a coating, e.g. a ruthenium coating, that is highly reflective for the illumination light 2. In accordance with the rectangular entry and exit openings 7, 10, the waveguide cavity is cuboid. In the beam direction of the illumination light 2, the hollow waveguide 9 has a typical length of 500 mm. An imaging optical unit 11 arranged downstream of the hollow waveguide 9 images the exit opening 10 of the hollow waveguide 9, lying in an exit plane 12, into the illumination field 4 in an object plane 13. An image-side numerical aperture of this image is 0.1. In order to simplify positional relations, a Cartesian xyz-coordinate system is used in the following text. The x-axis is perpendicular to the plane of the drawing in FIGS. 1 and 2. The z-axis in each case extends in the beam direction of the chief ray 3 of the illumination light 2. A reticle 13a to be inspected is arranged in the object plane 13. The reticle 13a has a mechanical functional connection to a reticle displacement drive 13b, by which the reticle 13a is displaced along an object displacement direction y during a mask inspection. By this approach, a scanning displacement of the reticle 13a in the object plane 13 is possible. The illumination field 4 has a typical dimension in the object plane 13 which is less than 0.5 mm, and which is 0.6 mm in the x-direction and 0.45 mm in the y-direction in the depicted embodiment. The x/y aspect ratio of the illumination field 4 corresponds to the x/y aspect ratio of the exit opening 10. The imaging optical unit 11 has two mirrors 14, 15 for grazing incidence of the illumination light 2. A mean angle of incidence α1 for the mirror 14 or α2 for the mirror 15 is greater than 60° in each case. A sum α=α1+α2 of these two mean angles of incidence is 149° in the illumination optical unit 1. In the depicted embodiment, the imaging optical unit 11 has exactly two mirrors for grazing incidence, namely the mirrors 14 and 15. A minimum distance d between the optically used faces of the two mirrors 14, 15 is 25 mm. The imaging optical unit 11 is embodied in the style of a Wolter telescope, namely in the style of a type I Wolter optical unit. Such Wolter optical units are described in J. D. Mangus, J. H. Underwood “Optical Design of a Glancing Incidence X-ray Telescope”, Applied Optics, Vol. 8, 1969, page 95 and the references cited therein. Instead of a paraboloid, use can also be made of a hyperboloid in such Wolter optical units. Such a combination of an ellipsoid mirror with a hyperboloid mirror also constitutes a type I Wolter optical unit. The first mirror 14 in the beam path of the illumination light 2 after the hollow waveguide 9 is embodied as an ellipsoid mirror. The subsequent mirror 15 in the beam path of the illumination light 2 is embodied as a hyperboloid mirror. The mirror faces of the two mirrors 14, 15 have a common axis of symmetry 16, which is plotted in the meridional section of the imaging optical unit 11 of FIG. 2. The optically used faces of the two mirrors 14, 15 cover an azimuth angle in the circumferential direction around the axis of symmetry 16, which is significantly less than 180°. An entry back focus e1 of the ellipsoid mirror 14 is approximately 330 mm. An exit back focus h2 of the hyperboloid mirror 15 is approximately 60 mm. In a variant (not depicted here) of the imaging optical unit 11, an exit pupil of the imaging optical unit 11 lies at infinity. This then results in a telecentric illumination optical unit on the illumination field side. A minimum angle of incidence for the illumination light 2 in the hollow waveguide 9 is 88°. A reflectivity of the hollow waveguide 9 for the illumination light 2 is approximately 90%. 73% of the illumination light 2 entering the hollow waveguide 9 are reflected by the first mirror 14 of the imaging optical unit 11. 57% of the illumination light 2 originally entering the entry opening 7 are reflected by the second mirror 15 of the imaging optical unit 11 into the illumination field 4. An overall reflectivity of the illumination optical unit 1 is therefore 57%. FIG. 2 moreover plots: an exit back focus e2 of the ellipsoid mirror 14, an entry back focus h1 of the hyperboloid mirror 15, the two focal points F1e and F2e of the ellipsoid mirror 14, the two focal points F1h and F2h of the hyperboloid mirror 15, a beam angle αe=2 α1 on the ellipsoid mirror 14, and a beam angle αh=2 α2 on the hyperboloid mirror 15. The illumination field 4 is imaged in an image field 18 in an image plane 19 via a projection optical unit 17 only indicated schematically in FIG. 2. A beam path of the chief ray 3 between the object field 4 and the image field 18 coincides with the axis of symmetry 16 in the schematic illustration of FIG. 2. This is not mandatory. The image field 18 is detected by a detection device 20, e.g. by a CCD camera or a plurality of CCD cameras. Using the mask inspection system 5, an inspection of e.g. a structure on the reticle 13a is possible. |
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045270686 | summary | FIELD OF THE INVENTION The invention relates to a concrete shielding housing for receiving and storing a fuel element container filled with spent nuclear reactor fuel elements. The container is suitable for transport and storage. The clear interior dimensions of the concrete shielding housing are somewhat larger than the outer dimensions of the fuel element container. The concrete shielding housing has a pallet-like base and at least one air inlet opening in the lower region of the housing and at least one air outlet opening in the upper region of the housing. BACKGROUND OF THE INVENTION In efforts to provide a temporary storage for fuel element containers in the open, it has been suggested to accommodate the containers in silo-like housings made of concrete or steel-reinforced concrete. In one type of concrete shielding housing, lateral air inlet passages are provided at the lower edge of the housing wall and lateral air outlet passages are provided at the upper edge of the wall underneath the cover. The base of the concrete shielding housng is configured as a separate pallet which can be moved about from one location to another with aid, for example, of a fork-lift truck. The fuel element container and the concrete shielding wall of the concrete shielding housing can be set down on this base. By means of the arrangement of the air inlet and air outlet passages in the concrete shielding housing, a natural ventilation within the housing is obtained for directing away heat produced by the radioactive decay of the materials stored in the container. In the above-mentioned concrete shielding housing, the base plate of the pallet-like base of the concrete shielding housing is provided with axial bores which extend clear through the base plate and serve as additional air inlet openings. Should moisture form in the interior of the concrete shielding housing, this can be conducted downwardly away from the interior of the housing through these bores. SUMMARY OF THE INVENTION It is an object of the invention to provide a concrete shielding housing of the type referred to above wherein an uncontrolled conduction of moisture from the interior of the housing to the ground or to the floor of the storage facility is prevented. The concrete shielding housing according to the invention includes a pallet-like base having a base plate. The housing has clear interior dimensions somewhat larger than the outer dimensions of the container. Air inlet means are formed in the lower portion of the housing for admitting air into the interior thereof and air outlet means are formed in the upper portion of the housing body for conducting the air away from the housing interior to the ambient. According to a feature of the invention, bore means are formed in the base plate and collection means are arranged beneath the base plate. This collection means communicates with the bore means for receiving and collecting the moisture formed in the interior of the housing. The bore means can include at least one axial bore which extends clear through the base plate. The collection means can be in the form of a collection pan which is mounted beneath the base plate of the pallet-like base. The axial bores in the base plate serve on the one hand for ventilating the interior of the housing and, on the other hand, to conduct moisture to the collection pan which has formed in or penetrated the interior of the housing. By means of the arrangement of the collecting pan, contaminated moisture can be collected and its seepage into the ground prevented. According to another feature of the invention, the collection pan is configured so as to have a location of lowest elevation and a drain plug threadably engages the pan at this location. The collected moisture can in this way be drained from the pan into a transportable container. |
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044977689 | description | DETAILED DESCRIPTION OF THE INVENTION Reference will now be made to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. FIG. 1 is a schematic representation of the apparatus of the instant invention. Gamma radiation photons are produced in a bremsstrahlung target 2 affixed to the LINAC beam tube terminus. The photons then pass through a polyethylene slab 3 which hardens the photon spectrum by preferentially filtering out photons of energy less than about 2 MeV. Some portion of the higher energy photons which pass through the filter (those above various reaction threshold energies) will produce photoneutrons in the neutron source 4. As will be discussed below, it is often unnecessary to provide a separate target to produce neutrons as photoneutrons in sufficient quantities may be produced in the walls of the chamber. Most of the photons will pass into the volume of the chamber 22 which contains the waste sample 5 where some will cause photofissions. Prompt photofission neutrons, emitted from the interaction of the gamma ray photons with matter in their path, will not be distinguishable from photoneutrons that are formed in the materials comprising the sample chamber. They therefore contribute to the overall flux of thermal neutrons. However, delayed neutrons from photofission processes are emitted continuously during the entire period between LINAC pulses, and therefore their measurement provides important information as to the contents of the sample. Photoneutrons and prompt photofission neutrons will thermalize in a few tens of microseconds and will persist as thermal neutrons for hundreds of microseconds, during which time they will generate thermal-neutron-fissions among fissile nuclides present in the sample. Prompt fission neutrons emitted from thermal fission are thus separable from the photoneutrons by use of time and energy discrimination and can serve along with the delayed neutrons from the photofission as an important quantitative analytical measurement. Means are provided for detection of both the thermalized neutron flux and the fast prompt and delayed neutron flux. Prompt and delayed fast neutron emission can be measured during the thermal die-away time using a fast neutron sensitive moderated .sup.3 He-proportional counter 23, which is shielded from the thermal neutron flux by cadmium 11, in the preferred embodiment of the instant invention. This detector also provides discrimination against any gamma radiation emissions during the counting period since such gammas generate much lower pulse heights in the detector and can be removed electronically from the signal of interest. Means are provided for generating an intense electron beam with maximum electron energies in excess of 10 MeV, since the photons to be generated therefrom must have at least this energy in order to produce significant photofissions and photoneutrons in their interaction with the materials upon which they impinge. Preferably, electron energies of about 12 MeV are provided with a pulse width of about 4 .mu.s. It is also preferred that the repetition rate lie between 1 and 60 Hz and the peak current between approximately 1 and 200 ma. Bremsstrahlung radiation can be generated in heavy metal targets 2 attached to the terminus of the electron accelerator beam tube 1. In a preferred embodiment of the apparatus of the instant invention an EG&G LINAC was employed. A 10 cm thick polyethylene slab 3 was placed in front of the target to harden the photon spectrum as mentioned above. The samples under investigation 5 and the neutron detectors 12, 23, were contained within a polyethylene enclosure 8 with internal dimensions 35.times.38.times.61 cm and 10 cm wall thickness. The outside of the enclosure was covered with 0.6 mm cadmium sheet 7 and a 10 cm thick layer of borated polyethylene 6 to reduce the effects of neutrons generated elsewhere in the concrete irradiation zone 20. In a preferred embodiment of the apparatus of the instant invention, a single 5 cm diameter.times.34 cm long proportional counter 9 filled to three atmospheres of .sup.3 He served as the primary fast neutron detector. The tube was encased in 1.25 cm of polyethylene 10 which was in turn wrapped with 1.7 mm of cadmium 11. This thickness of cadmium provides an attenuation factor for thermal neutrons of approximately 10.sup.8. A 2.5 cm diameter.times.51 cm long bare tube 12 containing 1% .sup.3 He (99% .sup.4 He) at low pressure was used as a neutron flux monitor. The LINAC beam current was monitored at the target 2 to provide normalization for the photofission yields. The proportional counter outputs were fed to singly-differentiating preamplifiers 15, which were in turn fed to linear amplifiers 16 and then to single-channel analyzers 17. The detected pulses were then directed to scalers 18, 19 outside of the irradiation cell. The scalers were gated on 21 after each LINAC burst by a pulse from the LINAC injector. Signals from both the primary detector and the flux monitor were summed during the irradiation, as was the LINAC beam current. FIG. 2 depicts the time sequence of emitted neutrons after an interrogation pulse of gamma radiation and photoneutrons. The first few hundred microseconds following the LINAC pulse are dominated by photoneutrons and prompt neutrons from photofission. Detection of these neutrons is complicated by residual effects of the intense gamma flux and electromagnetic noise on the counting system. The remainder of the first half millisecond is typically a period during which the initially fast neutrons are thermalized. The next two milliseconds (0.5-2.5 ms) is the period in which fast prompt neutrons from thermal-neutron-induced fissions are measured with the cadmium-wrapped detector 23. A second period, after the thermal interrogating flux has subsided, includes most of the remaining time before the next LINAC pulse (5.5-25.5 ms). During this period there is an approximately constant level of fast-neutron signal arising from delayed neutron emission. The first counting segment then, is generally dominated by counts from fissile nuclides present, and the second segment by counts from both fertile and fissile nuclides which have undergone photofission. It is arranged such that this later signal is comprised principally of neutrons from photofission by reducing the number of thermally-induced-fissions occuring while still maintaining a sufficiently strong prompt neutron signal to enable good signal statistics in a practical accumulating time period. This is achieved by controlling the number of thermal neutrons in the chamber. FIG. 3, curves a and b, display the time history of the observed neutron count rate arising from the simultaneous photon and neutron interrogation of 1 g of .sup.233 U which is a fissile nuclide. Curve a shows the .sup.233 U thermal-neutron-fission reaction neutrons, while Curve b shows the delayed neutron emission, 97% of which is from .sup.233 U photofission reactions. A LINAC beam energy of 12 MeV, a pulse width of 4 .mu.s, and a repetition rate of 30 Hz were used to obtain the data in FIG. 3. The peak beam current was about 200 ma and about 20,000 interrogating pulses were accumulated. Samples 5 were positioned at the center of the chamber 22 along the beam line at a point approximately 1 m from the bremsstrahlung target 2. Background count rates were obtained by irradiating with the samples removed. Net prompt neutron counts were normalized to the neutron flux monitor counts, and the delayed neutrons to the electron beam current monitor counts. FIG. 4, Curves a and b, display the time history of the neutron count rate arising from the simultaneous photon and neutron interrogation of 1 g of .sup.239 Pu. Here the contribution of each of the interrogating fluxes to the prompt and delayed neutron counts was investigated by comparing the detector response to a plutonium sample covered with an about 1.8 mm thick cadmium cover (Curve b), and to one without such a cover (Curve a). It is seen that the delayed neutrons are only weakly affected by the cadmium whereas the thermally-induced-fission, prompt neutrons are essentially absent with the cadmium present. This means that the photofission process (where the cadmium cladding should have a negligible effect) is the primary source of the delayed neutrons. In other words, by wrapping the plutonium sample, in the form of PuO.sub.2, thermal fission neutrons are prevented from reaching the fissile nuclides thereby preventing any thermal-neutron-fission neutron emision from contributing to the delayed neutron flux. Gamma radiation, on the other hand, easily passes through such a thin sheet of cadmium, and since they are of substantially greater energy than that required to cause photofission in plutonium, a substantial number of photofission neutrons are produced. The LINAC conditions were identical to those used in FIG. 3. To illustrate the method of this invention, the following examples are presented. The results of irradiating .sup.239 PuO.sub.2 with masses of 1, 0.2, and 0.05 g appear in lines 1-3 of Table 1. The background during both the thermal-fission prompt neutron region (0.5-2.5 ms) and the delayed neutron region (5.5-25.5 ms) was about 1% of the signal for the 1 g sample (line 8). This implies a similar sensitivity for the two counting periods. The net delayed neutron counts are approximately proportional to the quantities of the three masses investigated. However, the net prompt neutron counts were found to be reduced because of the self-masking effect most notably in samples of plutonium. That is, for compact samples (each sample was oxide powder in a doubly-encased, stainless steel cylinder about 3 cm long, 1 cm in diameter, with a total wall thickness of about 1.8 mm), the larger masses absorbed a sufficient number of thermal neutrons in their outer layers to lower the apparent effective mass of the entire sample. This is not a problem for delayed neutrons arising from photofission events. A useful feature of the simultaneous interrogation method of the instant invention is that the presence of photofission neutrons can, in certain cases, provide an internal measure of the masking effect. Self-masking is not a serious problem for waste samples since the fissile material density is generally low. TABLE 1 __________________________________________________________________________ Prompt neutron region Delayed neutron region (0.5-2.5 ms) (5.5-25.5 ms) Net Net Line Gross normalized Gross normalized Delayed Linac number Sample counts counts counts counts Prompt pulses __________________________________________________________________________ 1 .sup.239 Pu (1 g) 11081 1.418 1850 0.114 0.080 20,006 2 .sup.239 Pu (0.2 g) 2140 0.554 190 0.020 0.036 10,008 3 .sup.239 Pu (0.05 g) 1904 0.188 153 0.007 0.037 20,001 4 .sup.233 U (1 g) 19570 2.218 2987 0.150 0.068 20,010 5 .sup.235 U (0.19 g) 4999 0.501 946 0.047 0.094 20,004 6 .sup.238 U (1.5 g) 412 0.036 3939 0.196 5.44 20,003 7 .sup.238 U (1.5 g) 11855 1.40 6739 0.356 0.254 20,007 plus .sup.239 Pu (1 g) 8 background 100 0.012 13 0.0006 -- 20,001 __________________________________________________________________________ Yields from 1 g of .sup.233 U, 0.20 g of .sup.235 U and 1.5 g of .sup.238 U are given in Table 1, lines 4, 5, 6, respectively. The potential of the apparatus and method of the instant invention for distinguishing between fertile and fissile components of transuranic waste is illustrated by the results for .sup.238 U (line 6). That is, the lack of a significant thermal fission cross-section in .sup.238 U relative to the fissile nuclides is clearly shown by the high delayed-to-prompt-neutron ratio for .sup.238 U. Although the depleted uranium used did contain a small amount of .sup.235 U which contributed a small thermal fission yield, the presence of a more significant fissile nuclide concentration is easily handled by reducing the number of thermal neutrons available for capture by such fissile nuclides such that the fissile nuclide contribution to the delayed neutron flux is minimized while sufficient prompt neutrons exist for their determination. Even when this is not done, as for the results of a mixture of .sup.238 U and .sup.239 Pu, illustrated in line 7 of Table 1, it is very easy to tell that there are both fissile and fertile nuclides present. The net normalized prompt neutron flux is clearly the result of about 1 g of .sup.239 Pu as can be derived from line 1 of the table, while the net normalized delayed neutron flux can be seen to be the result of about 1 g of .sup.239 Pu and about 1.5 g of .sup.238 U (lines 1 and 6). Moreover, the delayed-to-prompt ratio has a value of 0.25, so that even where a substantial fissile nuclide concentration exists in the sample, it is easily observed that there must be a substantial fertile nuclide concentration by simply observing this ratio. The sensitivity of a preferred embodiment of our invention was estimated using a 3.sigma. criterion wherein the minimum detectable signal is taken to be three times the square root of the background. Background counts were typically 100 and 13 in the prompt- and delayed-neutron measurement intervals, respectively, as is seen in line 8 of Table 1. In the case of 1 g .sup.239 Pu, the net delayed neutrons are measured to be about 170 times the 3.sigma. value of 11, which gives a lower limit of detectability of about 6 mg. A similar treatment of the prompt-neutron yield of 1 g .sup.239 Pu gives a lower limit of about 3 mg. No corrections were made for matrix effects, and the detection system had only one .sup.3 He detection tube. Further, counting times were limited to about 11 min. By adding detectors to the system, increasing the counting time, or increasing the beam current, which in turn would increase the number of interrogation photons, the system sensitivity can be markedly improved. The quoted sensitivities can be converted to units which the United States Department of Energy uses, which translates to the fact that our invention can be used to assay plutonium contents of less than 10 nCi/g in 208 l (55 gal.) barrels. In summary, the apparatus and method of the instant invention can be used to determine the total fissile nuclide concentration and the total fertile nuclide concentration in a sample of transuranic waste by the use of simultaneous neutron and gamma radiation interrogation of the sample. An electron linear accelerator through the bremsstrahlung effect produces sufficient photons and photoneutrons in each electron pulse to perform sample analyses with high sensitivity. In so doing, the advantages of simultaneous photon interrogation and neutron interrogation can be realized along with the simplicity of a single source- and sample-handling system. Moreover, the prompt and delayed neutrons produced in the induced fissions can be counted using the same detection system and the same geometry, and since they are clearly separable temporally, the thermal neutron and photofission contributions to this emitted fission neutron flux are easily and quantitatively discernible. The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. For example, any electron accelerator providing greater than about 1 ma of beam current at electron energies in excess of about 10 MeV, and capable of operation at pulse rates between about 1 and 50 Hz can be used to provide an appropriate source of photons and photoneutrons for the sample interrogation. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto. |
abstract | A lithographic apparatus is provided. The apparatus includes an illumination system that conditions a beam of radiation, an article support member that supports an article to be placed in a beam path of the beam of radiation on the article support, and a movable carriage for moving the article support member. The carriage includes a compartmented composite structure provided with a non-composite mounting interface and/or cooling interface With such an arrangement, conventional interfacing using, for example metal or ceramic materials, can be applied in combination with the advantages of composite structures, such as a low specific weight, a high Young's modulus at places and directions where required, high strength, high stability, and high electrical resistivity. |
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055770819 | abstract | A method of forming a nuclear fuel assembly grid, as well as the resulting grid itself, are disclosed. In the formation of the grid, formed straps having slits are prepared, arranged into a grid form by intersecting the straps with each other through the slits, and the intersections of the associated straps are brazed. Prior to the step of arranging the straps, those portions to be brazed are subjected to a pretreatment, in which an paste, prepared of a mixture of a filler metal and a vehicle, is applied to the portions to be brazed to form a thin film thereon. |
040081710 | claims | 1. A process for reducing the volume of spent radioactively contaminated ion exchange material comprising the steps of: generating a slurry of water and ion exchange material and supplying the slurry to a fluid bed chamber; removing the free water from said slurry thus leaving wet ion exchange material; externally heating said chamber and the ion exchange material therein to a temperature between 40.degree. to 150.degree. C; evacuating said chamber to a pressure between 15 and 29" mercury and then while maintaining said pressure and external heat, introducing superheated steam thereinto at a temperature between about 200.degree.-500.degree. F to remove at least a portion of the intrinsic water in said material to thereby reduce the volume of the material; conducting the steam and said removed intrinsic water, from said chamber to a condenser; and discharging the dehydrated ion exchange material to a disposal drum. introducing superheated steam into said chamber to transport the partially dried material to said drum; and removing said steam from said drum. discharging steam from said drum to said condenser. 2. The process according to claim 1 including the step of continuing to impart heat to said material at substantially constant temperature to dry the material and as the drying rate decreases, increasing the temperature of the fluidized bed of material until the moisture content in said material is further reduced to a desired value. 3. The process according to claim 2 including isolating said chamber after said desired value is reached; and 4. The process according to claim 3 including utilizing the superheated steam in said chamber to transport said partially dried material to said drum through a nozzle wherein the material is caused to lose an additional amount of intrinsic water; and 5. The process according to claim 4 including introducing a supply of superheated steam into a mixing chamber for the nozzle so that the superheat content in the transporting steam and the superheat content in the nozzle injected steam is transferred to said material to further dry it to a desired value. |
056549920 | claims | 1. A method of repairing a neutron-irradiated structural material having a defect in a nuclear reactor internals, which comprises the steps of: covering said structural material to be repaired with a plate to cover over a portion thereof having the defect; welding said plate and said structural material by locally applying pressure on the surface of said plate and adding energy to the portion to which the pressure is applied thereby to generate thermal energy in the contact surfaces between said plate and said structural material. covering said structural material to be repaired with a plate to cover over a portion thereof having the defect; seam welding said plate and said structural material by locally applying pressure on the surface of said plate and adding electrical energy to the portion to which the pressure is applied using a roller electrode thereby to generate thermal energy in the contact surface between said plate and said structural material. said structural member and said plate are welded at a plurality of positions at a time by allowing current to flow in a plurality of electrodes having pressure applying means while applying pressure on the electrodes. in said welding step, mechanical energy is added as said energy to the portion to which the pressure is applied thereby to generate thermal energy caused by frictional resistance in the contact surface between said plate and said structural material. covering said structural material to be repaired with a plate to cover over a portion thereof having the defect; welding said plate and said structural material by giving mechanical vibration while locally applying pressure on the surface of said plate and adding mechanical energy to the portion to which the pressure is applied thereby to generate thermal energy caused by mechanically rubbing the contact surfaces of said plate and said structural material. said mechanical vibration is obtained by converting high frequency energy into mechanical vibration through magnetostriction. convex projections are provided on the surface of said cover plate to be welded to said structural material. concave notches are provided on the positions of said structural material contacting said convex projections on said cover plate, said cover plate being placed and welded to said structural material by engaging said convex projections on the welding surface of said cover plate with said concave notches. a reactor internal structure or component is used as a supporting portion for means for offsetting the reaction force produced when said pressure is applied. a supporting pillar is introduced between an upper grid plate and a core support plate of a light water reactor internals, said pillar supported with said upper grid plate and said core support plate being used as said supporting portion for means for offsetting the reaction force produced when said pressure is applied. a supporting pillar is introduced between a pressure vessel and a core shroud, said supporting pillar supported with the inner surface of the pressure vessel being used as said supporting portion for means for offsetting the reaction force produced when said pressure is applied. performing the work for clearing the oxide film existing on a region including the welding surface of said position of the structural material to be repaired with the cover plate; performing surface finishing of the region including the welding surface of said position of the structural material to an average roughness of 0.2 to 10 .mu.m; after performing said surface finishing, placing the cover plate and welding the plate to said position of the structural material. the outer periphery of the cover plate is continuously welded to said structural material so as to isolate the defect in said structural material from the outer environment. 2. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claim 1, wherein in said welding step, said energy is electrical energy, which is added to said portion to which the pressure is applied thereby to generate thermal energy in the contact surface between said plate and said repaired structural material. 3. A method of repairing a neutron-irradiated structural material having a defect in a nuclear reactor internals, which comprises the steps of: 4. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claim 2, wherein in said welding step, said plate and the structural material is welded by resistance spot welding. 5. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claims 2, wherein 6. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claim 1, wherein 7. A method of repairing a neutron-irradiated structural material having a defect in a nuclear reactor internals, which comprises the steps of: 8. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claim 7, wherein 9. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claim 1, wherein 10. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claim 9, wherein 11. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claim 1, wherein 12. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claim 11, wherein 13. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claim 11, wherein 14. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claim 1, wherein work for clearing the oxide film existing on a region including the welding surface of said position of the structural material to be repaired with the cover plate is performed before placing the cover plate on a position of the structural material to be repaired. 15. A method of repairing a neutron-irradiated structural material with a defect in a nuclear reactor internals according to claim 14, the method comprises the steps of: 16. A method of repairing a neutron-irradiated structural material with defect in a nuclear reactor internals according to claim 1, wherein |
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description | This application claims the benefit of Chinese Patent Application No. 201310356530.5 filed on Aug. 15, 2013 in the State Intellectual Property Office of China, the whole disclosure of which is incorporated herein by reference. 1. Field of the Invention The disclosure of the present invention relates to a radiation protection device and in particular to a radiation protection device for a system which is configured to perform safety inspection of a cargo or a vehicle by a ray. 2. Description of the Related Art In a conventional cargo or vehicle inspection system, generally a ray such as an x-ray, a gamma ray and a neutron ray is adopted to inspect the cargo or vehicle under inspection. Radiation protective shielding facility often needs to be built to ensure that the system satisfies related laws and regulations. Radiation protective shielding facility has various forms and includes a cast-in-situ concrete wall, a precast concrete wall, a steel-lead protection wall or facility in other structural forms. These structures generally need to be constructed or assembled in situ. The construction period is long and the construction cost is high. An object of an embodiment of the present invention is to provide a radiation protection device which can be built in situ quickly. Another object of an embodiment of the present invention is to provide a radiation protection device so that the amount of on-site work, construction time, and construction cost can be reduced. In accordance with an embodiment of the present invention, there is provided a radiation protection device for a system which is configured to perform safety inspection of a cargo or a vehicle by a ray, the radiation protection device comprising: at least one container, and a radiation protection part disposed within the container. In accordance with an embodiment of the present invention, the radiation protection part comprises a case and a radiation protection material accommodated in the case. In accordance with an embodiment of the present invention, the radiation protection material is filled into the case on site or at a site where the system is mounted. In accordance with an embodiment of the present invention, the radiation protection material comprises at least one of concrete, sandstone, and water. In accordance with an embodiment of the present invention, the radiation protection part comprises a protection wall such as a steel-lead protection wall or a concrete protection wall. In accordance with an embodiment of the present invention, the radiation protection part comprises a protection wall, and the protection wall has a protection wall body and a flange portion extending from at least a portion of an edge of the protection wall body. In accordance with an embodiment of the present invention, the radiation protection part comprises a protection wall, and the protection wall has a protection wall body and a flange portion extending from at least a portion of an edge of the protection wall body and forming a predetermined angle with the protection wall body. In accordance with an embodiment of the present invention, the predetermined angle ranges from about 45 degrees to about 90 degrees. In accordance with an embodiment of the present invention, the predetermined angle comprises about 90 degrees. In accordance with an embodiment of the present invention, the flange portion protrudes towards a side of the protection wall body from at least one of an upper edge and a lower edge of the protection wall body. In accordance with an embodiment of the present invention, the flange portion protrudes towards both sides of the protection wall body from at least one of a left edge and a right edge of the protection wall body. In accordance with an embodiment of the present invention, the protection wall body has a substantially rectangular shape, and the flange portion protrudes towards at least one of both sides of the protection wall body from at least one of four side edges of the protection wall body. In accordance with an embodiment of the present invention, the flange portion has a substantially flat shape. In accordance with an embodiment of the present invention, the flange portion has a substantially plate shape. In accordance with an embodiment of the present invention, the protection wall body has a substantially flat shape. In accordance with an embodiment of the present invention, the protection wall body has a substantially plate shape. In accordance with an embodiment of the present invention, the protection wall is integral, or composed of a plurality of separate elements. In accordance with an embodiment of the present invention, the case comprises a single case which is placed in the container or a plurality of cases which are arranged together in the container. With the radiation protection device according to the embodiment of the present invention, after the container is transported to the site, it can be directly put in place to be capable of shielding rays without needing operation or with only simple operation. The amount of on-site work, the construction time, and the construction cost are low. Referring to FIGS. 1 and 2, a system 10 configured to perform safety inspection of a cargo or a vehicle by a ray comprises a ray source 11 for emitting a ray 111 such as an x-ray, a gamma ray or a neutron ray and a detector 12 for receiving the ray 111 which has passed through an object under inspection. In FIGS. 1 and 2, the detector 12 is configured to detect the transmitted ray 111. However, a scattering detector such as a back scattering detector or a forward scattering detector may be also disposed to perform scattering inspection such as back scattering inspection and forward scattering inspection. Accordingly, the ray source 11 is disposed as a scattering ray source 11 such as a flying spot device. Referring to FIGS. 1 and 2, the system 10 further comprises a radiation protection device 15 for preventing the ray 111 of more than a predetermined dose from being leaked into an environment surrounding the system 10. The radiation protection device 15 is put according to radiation protection requirements of the system 10. The system 10 may further comprise a passage 16. The ray 111 is used to perform safety inspection of the cargo or vehicle passing through the passage 16. For example, the radiation protection device 15 is put on at least one side of the passage 16, for example, on one side or both sides of the passage 16. Referring to FIGS. 1 and 2, the radiation protection device 15 comprises: at least one container 151, and a radiation protection part 152 disposed within the container 151. The container 151 may be put on at least one side of the passage 16. A longitudinal direction of the container 151 may be substantially parallel to the passage 16. For example, one or more containers 151 may be disposed. The containers 151 may be overlapped in an up-down direction, juxtaposed in a left-right direction, or overlapped in the up-down direction and juxtaposed in the left-right direction. The radiation protection part 152 may comprise a case and a radiation protection material accommodated in the case. The radiation protection material may comprise at least one of concrete, sandstone, and water. The radiation protection material may be filled into the case on site or at a site where the system is mounted. In addition, the case may have any appropriate shape, such as a shape of a protection wall described later, thereby forming a protection wall after the radiation protection material is filled in the case. Referring to FIGS. 1 and 2, the radiation protection part 15 may comprise a protection wall 152 such as a steel-lead protection wall or a concrete protection wall. The protection wall 152 has a predetermined thickness, and may have a substantially flat shape or a substantially plate shape. Referring to FIGS. 1 and 2, according to an embodiment of the present invention, the protection wall 152 may have a protection wall body 1521, and a flange portion 1522 and 1523 extending from at least a portion of an edge or the entire edge, or some or all of edges (such as an edge or edges close to an inner wall of the container) of the protection wall body 1521. The flange portion 1522 and 1523 forms a predetermined angle with the protection wall body 1521. The predetermined angle may range from about 45 degrees to about 90 degrees. For example, the predetermined angle may comprise about 90 degrees. Referring to FIG. 1, in order to ensure that the ray is not leaked from an abutting portion where the containers abut against each other in the vertical direction when two or more layers of containers are put in the vertical direction, a bottom of the radiation protection wall within the container may be designed in a structure as shown in FIG. 1. Specifically, at a bottom or a top within the container, an additional radiation protection wall, i.e., the flange portion 1523, may be disposed in order to ensure that all of the rays passing through the abutting portion of the containers are attenuated through the additional radiation protection wall. Specifically, the flange portion 1523 protrudes towards one side or both sides of the protection wall body 1521 from at least one of an upper edge and a lower edge of the protection wall body 1521. For example, the ray is propagated from the ray source 11 towards the inspection passage 16 in a ray propagation direction D. The flange portion 1523 protrudes towards a downstream side, in the ray propagation direction D, of the protection wall body 1521 from at least one of the upper edge and the lower edge of the protection wall body 1521. Alternatively, the flange portion 1523 may protrude towards an upstream side or both the upstream and downstream sides, in the ray propagation direction D, of the protection wall body 1521 from at least one of the upper edge and the lower edge of the protection wall body 1521. Referring to FIG. 2, in order to ensure that the ray is not leaked from an abutting portion where the containers abut against each other in a left-right direction when the containers are put in a horizontal direction, the radiation protection wall within the container may be designed in a structure as shown in FIG. 2. Specifically, at one end or both ends within the container, an additional radiation protection wall, i.e., the flange portion 1522, may be disposed in order to ensure that all of the rays passing through the abutting portion of the containers are attenuated through the additional radiation protection wall. Specifically, the flange portion 1522 protrudes towards both sides of the protection wall body 1521 from at least one of a left edge and a right edge of the protection wall body 1521. For example, the flange portion 1522 protrudes towards both the upstream side and the downstream side, in the ray propagation direction D, of the protection wail body 1521 from at least one of the left edge and the right edge, in the longitudinal direction of the container 151, of the protection wall body 1521. Alternatively, the flange portion 1522 may protrude towards the upstream side or the downstream side, in the ray propagation direction D, of the protection wall body 1521 from at least one of the left edge and the right edge of the protection wall body 1521. In some embodiments, referring to FIGS. 1 and 2, the protection wall body 1521 may have a substantially rectangular shape, and the flange portion 1522 and 1523 may protrude towards at least one (such as one side or two sides) of both sides of the protection wall body 1521 from at least one (such as one, two, three, or all) of four side edges of the protection wall body 1521. In some embodiments, referring to FIGS. 1 and 2, the flange portion 1522 and 1523 may have a substantially flat shape or a substantially plate shape, or any other appropriate shape. The protection wall body 1521 may have a substantially flat shape or a substantially plate shape, or any other appropriate shape. Referring to FIGS. 1 and 2, the protection wall 152 may he integral or a one-piece wall. Alternatively, the protection wall 152 is composed of a plurality of separate elements arranged together. For example, adjacent portions of the elements adjacent to each other may have a recess and a protrusion, respectively. The adjacent portions are overlapped by engaging the protrusion with the recess. Alternatively, the adjacent portions of the elements adjacent to each other may be directly put to overlap each other, or may directly abut against each other. For example, a normal of an abutting surface of the adjacent portions may be substantially parallel to the ray 111 irradiated to the abutting surface, or forman angle of less than about 45 degrees with the ray 111 irradiated to the abutting surface. In some embodiments, all or some of the elements may have the structure of the protection wall 152. The elements may be placed on a support by disposing the support, directly arranged together, or fixed together. In some embodiments, the flange portions 1522 and 1523 and the protection wall body 1521 are separate elements, respectively. The protection wall body 1521 may be integral or a one-piece wall, or composed of a plurality of separate elements. For example, adjacent portions of the elements adjacent to each other may have a recess and a protrusion, respectively. The adjacent portions are overlapped by engaging the protrusion with the recess. Alternatively, the adjacent portions of the elements adjacent to each other may be directly put to overlap each other, or may directly abut against each other. For example, a normal of an abutting surface of the adjacent portions may be substantially parallel to the ray 111 irradiated to the abutting surface, or forman angle of less than about 45 degrees with the ray 111 irradiated to the abutting surface. Similarly, within the container 151, a single case may be placed, or a plurality of cases may be arranged together. The plurality of cases may be placed on a support by disposing the support, directly arranged together, or fixed together. As described above, the case may has the structure of the protection wall 152. In other words, the protection wall 152 is made as one or more cases into which the radiation protection material is filled. In some embodiments, normals of surfaces, irradiated by the ray 111, of the flange portions 1522 and 1523 and the protection wall body 1521 are substantially parallel to the ray 111 irradiated to the surfaces, or forman angle of less than about 45 degrees with the ray 111 irradiated to the surfaces. The flange portions 1522 and 1523 and the protection wall body 1521 may be disposed according to distribution of the sectorial ray beam or cone-shaped ray beam. Thereby, the normals of the surfaces, irradiated by the ray 111, of the flange portions 1522 and 1523 and the protection wall body 1521 are substantially parallel to the ray 111 irradiated to the surfaces, or forman angle of less than about 45 degrees with the ray 111 irradiated to the surfaces. In the longitudinal direction of the container 151, a section, in the vertical direction, of the protection wall 152 or the case within one container 151 is substantially equal to or slightly less than a section, in the vertical direction, of a chamber within the one container 151. It should be noted that while the embodiments of the present invention have been described in conjunction with the accompanying drawings, the present invention is not limited to the embodiments. For example, some of the abovementioned features may be combined into other embodiments unless they are in conflict with each other. The various possible combinations will not be listed for the sake of brevity. |
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048797359 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to baggage inspection devices for the non-intrusive inspection of baggage, and specifically to airport X-ray carry-on baggage inspection devices. 2. Description of the Prior Art Baggage inspection devices are used to inspect the contents of baggage in a non-intrusive fashion. The principle use of such non-intrusive devices is in airport security. The most common baggage inspection device is an X-ray carry-on baggage inspection device used at airport terminals. Existing X-ray baggage inspection devices are generally adapted to inspect baggage horizontally disposed upon a conveyor. Baggage that is vertically disposed upon the conveyor cannot be properly inspected. Most X-ray baggage inspection devices have an input port that is defined in part by a housing and in part by a conveyor. Ordinarily, the conveyor forms the lower boundary of the input port. Most input ports of X-ray baggage inspection devices are covered by a curtain comprising a plurality of strips of flexible material. The input port curtains have one serious drawback in that they do not encourage the proper placement of baggage on the conveyor, since it is readily apparent that the input port curtain will yield to allow the passage of baggage that is either horizontally or vertically disposed upon the conveyor. Since baggage that is vertically disposed upon the conveyor cannot be properly inspected, the conveyor must be halted, and the baggage must be moved from the vertical position to the horizontal position to allow proper inspection. Alternately, an attendant must be present at the entry to assure that the baggage is properly placed on the conveyor. Such interruptions in the operation of the inspection operation cause small time delays, which in the aggregate amount to substantial delays at airport terminals, where time if often of the essence. Additional personnel is costly, the action of changing the position of the baggage is an annoyance to the X-ray baggage inspection device operator. SUMMARY OF THE INVENTION The present invention encourages proper placement of baggage on a conveyor, but does not impede the conveyance of properly placed but over-sized carry-on baggage. As an apparatus, the invention consists of an improvement in an X-ray baggage inspection device of the type disposed above a conveyor, and having an input port with an upper boundary and a lower boundary, with the lower boundary being defined by the conveyor. A substantially rigid baffle having an upper edge and a lower edge is pivotally suspended from the upper boundary of the housing by the upper edge. The baffle substantially occludes an upper selected region of the input port, with the lower edge spaced a preselected distance above the conveyor, leaving an open space adjacent to the conveyor having a configuration suited for the passage of briefcase type baggage horizontally disposed upon the conveyor. Baggage having a height less than the preselected distance between the lower edge of the baffle and the conveyor will pass through the open space into the baggage inspection device. Baggage that has a height exceeding the preselected distance will cause the baffle to pivot inward. The present invention encourages the proper placement of baggage on the conveyor. Specifically, the baffle gives the appearance of a plate that is fixedly mounted to the upper region of the input port, preventing the passage of baggage vertically disposed upon the conveyor. The open space at the lower region of the input port is adapted in size and shape to suggest that the baggage be horizontally disposed upon the conveyor in order to pass into the baggage inspection device. If horizontally disposed baggage has a height exceeding the height of the opening, the baffle will pivot inward allowing such baggage to enter the baggage inspection device. |
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description | 1. Field of the Invention The present invention relates to an X-ray optical apparatus that radiates an X-ray onto an object, and particularly to an X-ray optical apparatus in which a relative position of an X-ray source and an optical element is optimized and an adjusting method thereof. 2. Related Background Art A technology that one-dimensionally parallelizes an X-ray using an optical element has been known. Japanese Patent Application Laid-Open No. 2000-137098 discloses a solar slit including metal foils which are disposed in an X-ray passage and laminated with an interval. Further, it is disclosed that a surface of a metal foil is formed to have a surface roughness to restrict the reflection of X-rays in order to form a parallel X-ray beam. Japanese Patent Application Laid-Open No. 2004-89445 discloses an X-ray generating device in which a collimator in which a plurality of minute capillaries is two-dimensionally arranged is combined with multiple X-ray sources which are arranged in a two-dimensional matrix to parallelize an X-ray. Japanese Patent Application Publication (Translation of PCT Application) No. H10-508947 discloses an optical system in which a divergence X-ray which is emitted from an X-ray source having a small spot size is efficiently captured in a monolithic optical element that includes a plurality of hollow glass capillaries to form a quasi-parallel beam. In the optical element disclosed in Japanese Patent Application Laid-Open No. 2000-137098, since only a parallel component of the X-ray is taken, only a very small part of generated X-ray is used, so that the usage efficiency is low. In the optical element disclosed in Japanese Patent Application Laid-Open No. 2004-89445, it is difficult to form uniform capillaries. Further, it is difficult to two-dimensionally arrange X-ray sources with a high density. In the optical element disclosed in Japanese Patent Application Publication (Translation of PCT Application) No. H10-508947, the hollow glass capillaries fused together and plastically shaped. Therefore, it is difficult to form uniform capillaries. Therefore, an optical element with a simple structure that efficiently parallelizes the generated X-ray to be emitted is required. Further, a relative position of the X-ray source and the optical element is important in order to obtain an X-ray with a high intensity and a high resolution. In the technology disclosed in Japanese Patent Application Laid-Open No. 2000-137098, the alignment of the relative position of the X-ray source and the optical element is performed so as to maximize the intensity of the X-ray which passes the solar slit. For example, in FIG. 16, if the X-ray source is moved in a y direction, when the X-ray source 1 is disposed in a range indicated by a dotted line, the intensity of the X-ray which passes the solar slit 31 is maximized and the intensity is not changed. An angular width α is hardly changed, so that the resolution of the image is less affected. In the meantime, if the X-ray source 1 deviates from the range of the dotted line, the intensity of the X-ray is lowered. Accordingly, an alignment method that maximizes the intensity of the X-ray as described above is applied. However, in the above-mentioned alignment method, if the relative position of the X-ray source and the optical element is deviated from the design, even though the deviation is negligible and does not lower the intensity of the X-ray, the resolution of the image is lowered in some cases. Further, even if other optical element of the related art is used, the resolution of the image is lowered in some cases when using the alignment method. The invention provides an X-ray optical apparatus which is capable of efficiently parallelizing the generated X-ray to be emitted with a simple structure and improving the resolution of the image and an adjusting method thereof. According to the present invention there is a method of adjusting an X-ray optical apparatus, the X-ray optical apparatus including an X-ray source and a reflective structure in which at least three reflective substrates are arranged with an interval and X-rays which are incident into a plurality of passages, both sides of each passage being put between the reflective substrates, are reflected and parallelized by the reflective substrate at both sides of the passage to be emitted from the passage. When one edge of the reflective structure is an inlet of the X-ray and the other edge is an outlet of the X-ray, a pitch of the reflective substrates at the outlet side is larger than a pitch at the inlet side. The method includes adjusting the relative positions of the X-ray source and the reflective structure so as to reduce a penumbra amount formed by the X-rays emitted from the passages. The present invention can efficiently parallelize the generate X-ray with a simple structure. Further, since the X-ray source and the reflective structure are disposed so as to reduce the penumbra amount of an image, so that a resolution of the image is improved. Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. Hereinafter, a slit lens is used as an X-ray reflective structure (hereinafter, referred to as a reflective structure). (1) Slit Lens As illustrated in FIG. 1, a slit lens 3 is arranged such that at least three reflective substrates 11 are arranged with an interval therebetween. An interval between adjacent reflective substrates is formed by a spacer. An X-ray 2 which is incident into a plurality of passages whose both sides are put between the reflective substrates 11 is reflected from the reflective substrate 11 at both sides of each of the passages and parallelized to be emitted from each of the passages. When one edge of the slit lens 3 is an inlet of the X-ray and the other edge is an outlet of the X-ray, a pitch of the reflective substrates 11 at the outlet side is larger than a pitch at the inlet side. Here, the pitch refers to a distance between top surfaces or bottom surfaces of the adjacent reflective substrates. The “parallelization” in the present invention means that an X-ray component in a laminated direction (y direction) of the reflective substrate 11 is reduced so that the emission direction of the X-ray becomes parallel (collimates) to a plane (xz plane) perpendicular to the y direction. (2) Resolving Power First, in an X-ray imaging apparatus according to the present invention, a penumbra amount (resolution) will be described with reference to FIGS. 1 and 2A, which is generated when an X-ray that is incident into the passage of the slit lens 3 from the X-ray source 1 and emitted from the passage is radiated onto a sample to project a transmission image onto an X-ray detector (hereinafter, referred to as a detector) 4. FIG. 1 is a conceptual diagram of a principle of parallelizing an X-ray in the present invention and FIG. 2A is a cross-sectional view of a YZ plane that passes through the X-ray source 1 of the X-ray optical apparatus illustrated in FIG. 1. As illustrated in FIG. 2A, if there is an infinitely small object A at the outlet of the slit lens 3 and a defocused state of an image of the object A is defined as a penumbra amount Δp of the image, the penumbra amount Δp is represented by Equation 1 using a divergence angle θout of the X-ray at the outlet of the slit lens 3 and a distance L3 between the outlet of the slit lens 3 and the detector 4 in an opposite direction.Δp=L3×θout (Equation 1) Equation 1 is established with respect to the X-ray which is emitted from each of the passages. The resolving power of an X-ray imaging apparatus is lowered as the penumbra amount Δp is increased. Therefore, in order to increase the resolving power, if the distance L3 is constant, it is important to lower the divergence angle θout. In other words, it is important to increase the degree of parallelization of the X-ray which is emitted from each of the passages in the slit lens 3. The resolving power of the X-ray imaging apparatus is determined by not only the penumbra amount Δp but also by larger one of the penumbra amount Δp and a pixel size Δd of the detector 4 (for example, a flat panel detector (FPD)). If the pixel size Δd is small, the detector 4 becomes expensive and it takes time to perform data transfer processing. In the meantime, if the penumbra amount Δp is lowered, for example, a size of the X-ray source 1 is required to be reduced, so that a load which may be applied to an optical system is increased as described below. Therefore, it is important to keep a balance between the pixel size Δd and the penumbra amount Δp. If an acceptable range of a ratio of the pixel size Δd and the penumbra amount Δp is 2, the following Equation 2 is established.0.5<Δp/Δd<2 (Equation 2) (3) Parallelization Principle A principle (parallelization principle) of parallelizing the X-ray, which is emitted from the passages in the slit lens 3, will be described with reference to FIGS. 2A and 2B. FIG. 2B is an enlarged view of a region enclosed by a two-dot chain line of FIG. 2A. Even though a glass plate is used as the reflective substrate 11, the reflective substrate 11 may be metal. As illustrated in FIG. 2A, the X-ray 2 which is emitted from the X-ray source 1 is divergence light and is radiated in all directions. The slit lens 3 is disposed so as to be separated by a distance L1 from the X-ray source in the opposite direction of the X-ray source 1. The slit lens 3 is arranged such that the glass plates having a gentle curvature are disposed in parallel with predetermined intervals and a pitch of the glass plates at the outlet of the X-ray is larger than a pitch at the inlet of the X-ray. 10 to 1,000 sheets of glass plates each having a thickness of 1 μm to 100 μm are laminated and the X-ray is reflected from both sides of the glass plate. An X-ray 2, which is incident into the passage between the glass plates 11a and 11b, travels while being reflected from both the glass plates 11a and 11b and then is emitted from the passage. Similarly in the passage between the glass plates 11b and 11c, the incident X-ray travels while being reflected from both the glass plates 11b and 11c and then is emitted from the passage, which is similar in the passage between other adjacent glass plates. Most of the X-rays 2 which are incident into the passages are parallelized as described above. However, among the X-rays 2 which are incident into the passages, an X-ray which travels in a horizontal direction is not reflected from the glass plate but is directly emitted from each of the passages. As described above, as the X-ray travels in the passage of the slit lens 3, an X-ray whose traveling direction is not a horizontal direction is reflected multiple times from the glass plate so that the traveling direction is gradually close to the horizontal direction. Then, the X-ray is parallelized and emitted from each of the passages. Further, an X-ray which travels in the horizontal direction is directly emitted from each of the passages. Accordingly, it is possible to efficiently parallelize the X-ray to be emitted with a simple structure. By doing this, the penumbra amount Δp, which is formed on the detector 4, becomes smaller. Here, a virtual plane 5 is set in a position which is separated from the glass plates at both sides of the passage with the same distance and a tangential plane 6 of the virtual plane 5 at the inlet of the slit lens 3 is considered. If the X-ray source 1 is disposed on tangential planes of a plurality of virtual planes 5 at the inlet side, more X-rays may be incident into the passages. If all tangential planes 6 of the plurality of virtual planes 5 which are set between the adjacent glass plates at the inlet side intersect on a common straight line and the X-ray source 1 is disposed on the straight line, a size of the X-ray source 1 may be reduced. Further, if the glass plates are parallel to each other at the outlet of the slit lens 3, that is, if the tangential planes 6 of the plurality of virtual planes 5 at the outlet side are approximately parallel to each other, the degree of parallelization of the X-rays emitted from the passages may be increased. FIG. 3 illustrates an X-ray reflectance of a quartz substrate with respect to an X-ray having a wavelength of 0.071 nm. A horizontal axis is a glancing angle θg at which the X-ray is incident onto each of the passages and a vertical axis is a reflectance of the X-ray. When the glancing angle θg is 0.5 mrad, the reflectance of the X-ray is 99.8% or higher. Therefore, it is understood that 90% or more of the X-rays pass the slit lens even if the X-rays are reflected 50 times. Further, when the glancing angle θg is 1.8 mrad, the reflectance of the X-ray is rapidly attenuated. In this case, the glancing angle θg is referred to as a critical angle and denoted by θc. When the X-ray source 1 is disposed on the tangential planes 6 of the plurality of virtual planes 5 at the inlet side, if the angular deviation of the tangential planes 6 is increased, a deviation in an angle at which each of the glass plates brings the X-ray source 1 into view is generated. Then, the X-ray 2 which is emitted from the X-ray source 1 is not reflected on a position where the glancing angle θg is larger than the critical angle θc in the glass plate. Accordingly, when a distance between the X-ray source 1 and the inlet of the slit lens 3 in the opposite direction is L1 and a critical angle of the glancing angle θg at which the X-ray is incident onto the passage is θc, the distance Δs between the X-ray source 1 and the passage in a direction perpendicular to the opposite direction needs to satisfy the following Equation 3.Δs<L1×θc (Equation 3) Therefore, it is required to determine a relative position of the slit lens 3 and the X-ray source 1, that is, a relative position of the glass plate and the X-ray source 1 so as to satisfy Equation 3. Here, the slit lens 3 will be described, in which the interval between adjacent glass plates is constant and all glass plates are formed such that a thickness at the outlet side is larger than a thickness at the inlet side as illustrated in FIG. 2A. Such a slit lens 3 may be manufactured by laminating glass plates having a wedge shaped thickness. In this case, a maximum glancing angle θgmax at which the X-ray is incident onto the passage and is reflected from the glass plate is represented by Equation 4.θgmax=(s+g)/2L1 (Equation 4) Here, s indicates a size of the X-ray source 1 (diameter of the light source) and is 2σ when an intensity distribution of the light source is approximated by a Gaussian distribution. g is an interval (gap) between adjacent glass plates. However, θgmax needs to be smaller than the critical angle θc. If the glass plates are parallel to each other at the outlet of the slit lens 3, the divergence angle θout of the X-ray which is emitted from each of the passages in the slit lens 3 is represented by Equation 5.θout=2×θgmax (Equation 5) In this case, the penumbra amount Δp is represented by Equation 6 based on Equations 1, 4, and 5.Δp=L3×(s+g)/L1 (Equation 6)Further, Equation 7 is established based on Equations 2 and 6.0.5×Δd<L3×(s+g)/L1<2×Δd (Equation 7) If the degree of parallelization of the glass plate is lowered, the X-ray does not reach a pixel of the detector 4 that detects an intensity of the X-ray or a pixel having an extremely weak X-ray intensity is generated. In order to remove such troubles, the parallelism A., of all the glass plates needs to satisfy larger one of an acceptable value Δout-a in the following Equation 8a and an acceptable value Δout-b in the following Equation 8b. Here, Δd indicates a pixel size of the detector 4.Δout-a<(s+g)/L1 (Equation 8a)Δout-b<Δd/L3 (Equation 8b) Here, a size of the penumbra amount Δp which is formed on the detector 4 when the position of the light source is deviated by δ in a y direction will be described with reference to FIGS. 4A and 4B. In FIG. 4A, when a distance between the light source center position Sc and the tangential plane 6 is deviated by δ in the y direction, a maximum glancing angle θgmax is represented by Equation 9 in accordance with the same manner as the manner by which Equation 4 is derived.θgmax=(s/2+g/2+δ)/L1 (Equation 9) Further, a divergence angle θout in this case will be described with reference to FIG. 4B. In order to simplify the description, two sheets of parallel plates are considered as the slit lens 3. The X-ray which is incident into the slit lens 3 is repeatedly reflected from the upper and lower glass surfaces while maintaining the glancing angle θg and emitted from the outlet in a +y direction or −y direction with respect to the virtual plane 5. An emission direction is determined based on the number of reflection in the slit lens 3 and the number of reflection is determined based on the glancing angle θg and a length L2 of the slit lens 3 in a z-direction. Further, as illustrated in FIG. 4B, if a final reflection point P matches with an emitting edge of the slit lens 3, the X-ray is reflected from the point P to be emitted in the −y direction. In this case, an X-ray which is incident at an angle which is slightly smaller than the glancing angle θg is emitted in the +y direction without being reflected from the emitting edge of the slit lens 3. Since the glancing angle θg of the X-ray which is incident into the slit lens 3 is continuous in the range of “0≦θg≦θgmax”, a maximum divergence angle θout may be considered to be represented by Equation 5. The penumbra amount Δp when the light source position is deviated by δ in the y direction is represented by Equation 10 based on Equations 1, 5, and 9.Δp=L3×(s+g+2δ)/L1 (Equation 10) It is understood that if the positional deviation δ of the light source is changed, the penumbra amount Δp is also changed. Next, a slit lens 3 will be described in which thicknesses of all glass plates are constant and an interval between adjacent glass plates at the outlet side is larger than an interval at the inlet side. Here, in order to simplify the description, as illustrated in FIG. 5, a straight guide in which the glass plates 11a and 11b form an angle θa is considered. If an angle formed by the virtual plane 5 and the X-ray 2 is referred to as a half divergence angle, an X-ray which is incident into the passage between the glass plates 11a and 11b with the half divergence angle θ0 (0.5×θa<θ0<θc) is reflected at a point P0 of the glass plate 11b and then reflected at a point P1 of the glass plate 11a. A half divergence angle θ1 after the first reflection is represented by Equation 11.θ1=θ0−θa (Equation 11) Therefore, the angle θn after n-th reflection is represented by Equation 12 in a range of “θ0−n×θa>0”.θn=θ0−n×θa (Equation 12) If θn<0.5×θa, the X-ray 2 does not reach the glass plate, so that the half divergence angle is not varied. Further, if an interval (gap) between the adjacent glass plates at the outlet side is gout, an interval (gap) between the adjacent glass plates at the inlet side is gin and a length of the glass plate is L2, Equation 13 is established.θa=(gout−gin)/L2 (Equation 13) In this case, since θa<θout, the penumbra amount Δp is represented by Equation 14 based on Equations 1 and 13.(gout−gin)×L3/L2<Δp (Equation 14)Further, Equation 15 is established based on Equations 2 and 14.0.5×Δd<L3×(gout−gin)/L2<2×Δd (Equation 15) For the same reason as the above reason with respect to the slit lens 3 having the structure illustrated in FIG. 2A, even in a slit lens 3 in which thicknesses of all glass plates are constant and an interval between adjacent glass plates at the outlet side is larger than an interval at the inlet side, the glass plates at the outlet of the slit lens 3 may be parallel to each other. Therefore, the parallelism Δout of all the glass plates needs to satisfy larger one of an acceptable value Δout-a in the following Equation 16a and an acceptable value Δout-b in the following Equation 16b. Here, Δd indicates a pixel size of the detector 4.Δout-a=(gout−gin)/L2 (Equation 16a)Δout-b<Δd/L3 (Equation 16b) In the meantime, a penumbra amount Δx in a dimension where the glass plate does not have a curvature, in other words, a direction (x-direction) perpendicular to both an opposite direction between the X-ray source 1 and the inlet of the slit lens 3 and a direction perpendicular to the opposite direction between the X-ray source 1 and the passage is represented by Equation 17 and determined by the relative positions of the slit lens 3, the X-ray source 1, and the detector 4.Δx=s×L3/(L2+L1) (Equation 17) Further, a slit lens 3, where the X-ray source 1 is disposed on the tangential planes of the plurality of virtual planes 5 at the inlet side and the tangential planes of the plurality of virtual planes at the outlet side intersect on a common straight line, may also be applied to the X-ray optical apparatus according to the present invention. The parallelization may be embodied with this structure. If all tangential planes 6 of the plurality of virtual planes 5 at the inlet side intersect on a common straight line and the X-ray source 1 is disposed on the straight line, a size of the X-ray source 1 can be reduced. In this case, the common straight line intersecting at the inlet side is a different line from the common straight line intersecting at the outlet side. A first exemplary embodiment of the present invention will be described in detail with reference to FIGS. 6, 7A, and 7B. FIG. 6 is a flow chart illustrating an adjusting method of an X-ray optical apparatus according to this exemplary embodiment. FIG. 7A illustrates an X-ray optical apparatus according to this exemplary embodiment. FIG. 7B is an enlarged view of a region B around an outlet of a slit lens 3 in FIG. 7A. In the exemplary embodiment, in order to measure a resolution when an image is projected by an X-ray 2 which passes through the slit lens 3, an object 31 (object for forming penumbra) is disposed between the slit lens 3 and a detector 4 and a penumbra amount formed on the detector 4 by the object 31 is measured. Since the object 31 is used to shield the X-ray, a material of the object 31 may absorb the incident X-ray like gold, platinum, or lead. In a state where the slit lens 3 is fixed, the position of the X-ray source 1 is moved in the y direction (step 1) and a change in the penumbra amount formed on the detector 4 is measured (step 2). A position where the penumbra amount is minimum, that is, a position of the light source (a position of the X-ray source 1) where the resolution becomes highest is derived (step 3) and the light source position is adjusted to the derived position (step 4). As described above, the light source position is adjusted to reduce the penumbra amount to increase the resolution. In FIG. 7A, the X-ray 2 which is radiated from the X-ray source 1 travels while being reflected from the passage of the slit lens 3, is emitted from the passage, and detected by the detector 4. The object 31 is disposed between the slit lens 3 and the detector 4. The object 31 is arranged to be moved to an arbitrary position at least in the y-axis direction by a moving mechanism 32. The object 31 is moved to the arbitrary position in an optical path when the positions of the X-ray source 1 and the slit lens 3 are adjusted and then removed out of the optical path after completing the position adjustment. Here, a distance L1 between the X-ray source 1 and the inlet of the slit lens 3 in the opposite direction is 100 mm, a length L2 of the slit lens 3 is 100 mm, and a distance L3 between the outlet of the slit lens 3 and the detector 4 in the opposite direction is 200 mm. A pixel size Δd of the detector 4 is 100 μm and a size s of the X-ray source 1 is 100 μm. An interval (gap) g between adjacent glass plates is constantly 10 μm and a thickness of all glass plates is 40 μm at the outlet side and 10 μm at the inlet side. A scanning method of the X-ray source 1 in the y direction will be described. The X-ray source 1 may be moved by using a mechanical moving mechanism or by electrical manipulation described below. A light source position moving mechanism 21 used in the exemplary embodiment, as illustrated in FIG. 8, includes an electron beam source 22, an electron lens 24 (lens electrode) that converges an electron beam 23, a deflector 26 that deflects the electron beam 23, and a transmissive target (hereinafter, referred to as a target) 25 for generating an X-ray, which are disposed in a vacuum container 27. An electron which is extracted from the electron beam source 22 is converged by the electron lens 24 and incident into the target 25. When the electron beam 23 is incident into the target 25, an X-ray is radiated from a surface opposite to a surface of the target into which the electron beam 23 is incident. Therefore, a position where the electron beam 23 is incident into the target 25 becomes a light source position 28. In this case, the electron beam 23 is deflected in the y direction by the deflector 26 so that the position of the electron beam 23 which is incident into the target 25 is moved in the y direction and the light source position 28 is moved in the y direction. By using such an X-ray source 1 described above, the light source position 28 may be moved by performing an electrical manipulation on the deflector 26. Here, a principle for measuring the penumbra amount in the exemplary embodiment will be described. As illustrated in FIG. 7B, the object 31 is disposed such that an edge thereof is located on the optical path in the slit. An X-ray which is radiated from an X-ray source 1 (not illustrated) passes through the slit lens 3 and a part of the X-ray passing the slit lens 3 is shielded by the object 31, so that a penumbra of the object 31 appears on a plane C which is disposed at a downstream of the slit lens 3. A solid line 33 indicates a state of the X-ray when the relative positions of the X-ray source 1 and the slit lens 3 are fitted to each other and a broken line 34 indicates a state of the X-ray when the relative positions of the X-ray source 1 and the slit lens 3 are deviate. A distribution of X-ray intensity in the y-direction on the plane C when the intensity of the X-ray source 1 does not have deviation or is uniform will be described with reference to FIG. 9. A y-direction position on the plane C is represented at a horizontal axis and the intensity of the X-ray is represented at a vertical axis. When the relative positions of the X-ray source 1 and the slit lens 3 are fitted to each other, in a region below a position y12, all X-rays that pass through the slit lens 3 are shielded by the object 31, so that the intensity is 0. In a region above a position y11, the X-ray reaches the detector 4 without being shielded by the object 31. A region between y11 and y12 indicates a defocused state caused when the X-ray source 1 has a size, that is, a penumbra amount and a size of the region is represented by “y11-y12”. If a penumbra amount when the light source position is deviated in the y direction is considered, the positional deviation of the X-ray source 1 increases the divergence angle θout in accordance with Equations 4 and 5. Therefore, in the intensity distribution on the detector, as indicated by the broken line, the intensity becomes 0 below the position y22 and the X-ray reaches the detector 4 without being shielded above the position y21. At this time, the penumbra amount is y21-y22. Further, in the X-ray optical apparatus according to the exemplary embodiment illustrated in FIG. 7A, a penumbra amount Δp on the detector when the light source position is deviated by δ in the y direction is represented by Equation 10 above. Based on the structure of the apparatus and the principle for the measurement of the penumbra amount described above, when the light source position is moved in the y direction while fixing the slit lens 3, the penumbra amount Δp is changed as illustrated in a graph in FIG. 10. In FIG. 10, the light source center position is a light source position (a position of the X-ray source 1) and the penumbra amount is a function of the light source center position when the position of the slit lens 3 is fixed. The y direction position of the X-ray source 1 is represented at the horizontal axis and the penumbra amount is represented at the vertical axis. From the graph of the change in the penumbra amount obtained by scanning measurement of the light source position, a light source position where the penumbra amount is minimum is derived (determined) as the light source center position where the light source is to be disposed. Thereafter, the X-ray source 1 is moved to the derived light source center position. With the structure according to the exemplary embodiment, the penumbra amount of the X-ray on an X-ray detector is measured while changing the relative positions of the X-ray source 1 and the slit lens 3. Further, the X-ray source is adjusted to the position where the penumbra amount is minimum, so that the X-ray source can be adjusted in a positional relationship where the highest resolution is obtained. In FIG. 7B, even though the penumbra amount is measured at an outside passage, the penumbra amount may be measured at other passage than the outside passage. In the exemplary embodiment, even though the light source position 28 is changed by deflecting the electron beam 23 in the X-ray source, the X-ray source (a main body of the light source) or the slit lens 3 may be moved. As the number of reflection on the glass plate is increased, an influence by an angle at the inlet side of the slit lens 3 is increased. Therefore, rather than the slit lens 3 in which the thicknesses of all the glass plates are constant and an interval between adjacent glass plates at the outlet side is larger than the interval at the inlet side, a slit lens 3 in which intervals between adjacent glass plates are constant and a thickness of all glass plates at the outlet side is larger than the thickness at the inlet side is preferable. A second exemplary embodiment of the present invention will be described with reference to FIGS. 11A and 11B. Here, only difference from the first exemplary embodiment will be described. In the exemplary embodiment, as illustrated in FIG. 11A, a one-dimensional grating 41 (hereinafter, referred to as a “slit array 41”) for forming a penumbra is provided. The slit array 41 is arranged to be moved to an arbitrary position at least in the y-axis direction by a moving mechanism 42. In the exemplary embodiment, the slit array 41 is disposed between a slit lens 3 and a detector 4 and a penumbra amount which is formed on the detector 4 by the slit array 41 is measured. The slit array 41 in the exemplary embodiment is illustrated in FIG. 11B. The slit array 41 is an element in which 30 slits each having an aperture width t1 of 20 μm and a length b1 of 300 mm are arranged in a plate shaped member which can shield the X-ray such as gold, platinum, or lead in the y direction with a pitch P1 of 650 μm. A length a1 of the y direction thereof is 19.5 mm. As illustrated in FIG. 11A, the slit array 41 is disposed at the downstream of the slit lens 3 so that the penumbra amount of each passage in the slit lens 3 may be measured. Actually, since the passages in the slit lens have different parallelism caused by a manufacturing error, the penumbra amount thereof may be slightly varied. By considering an average of the penumbra amount for every passage, the light source position is adjusted to minimize the penumbra amount of entire slit lenses. A size of the pitch P1 in the slit array 41 will be described with reference to FIG. 12. The pitch P1 is set to be 650 μm in order to avoid the X-rays which pass through the another passage in the slit lens from being superimposed each other on the detector when the deviation of the relative positions of the X-ray source 1 and the slit lens 3 is in a predetermined range. If the deviation of the relative positions of the X-ray source 1 and the slit lens 3 in the y direction is 0, the penumbra amount Δp is 220 μm in accordance with Equation 10 and the state of the X-ray at that time is represented by the solid line 43. Further, if the deviation of the relative positions of the X-ray source 1 and the slit lens 3 in the y direction is 100 μm (δ=100 μm), the penumbra amount Δp is 620 μm in accordance with Equation 10 and the state of the X-ray at that time is represented by the broken line 44. Here, since the pitch P1 of the slit array 41 is 650 μm, if the deviation of the relative positions of the X-ray source 1 and the slit lens 3 is within 100 μm, as illustrated in FIG. 12, the superimposition on the detector of the X-rays which pass through the another passage in the slit lens may be avoided. With the structure according to the exemplary embodiment, the penumbra amount of the X-ray on an X-ray detector is measured while changing the relative positions of the X-ray source 1 and the slit lens 3. Further, the X-ray source is adjusted to the position where the penumbra amount is minimum, so that the X-ray source is adjusted in a positional relationship where the highest resolution is obtained. Further, in the exemplary embodiment, the penumbra amounts of 30 passages may be independently and collectively measured. By calculating an average value of the penumbra amounts of the 30 passages, the influence by an error of each of the passages is smaller than that of the measurement at a single passage. Therefore, the relative positions of the X-ray source 1 and the slit lens 3 can be adjusted with a higher precision. A third exemplary embodiment of the present invention will be described with reference to FIGS. 13A and 13B. Here, only difference from the first and second exemplary embodiments will be described. In the exemplary embodiment, a first one-dimensional grating 51 (hereinafter, referred to as a “slit array 51”) for forming a penumbra is provided. Further, as illustrated in FIG. 13A, a second one-dimensional grating 52 (hereinafter, referred to as a “slit array 52”) for generating a moiré stripe is provided between the slit array 51 and a detector 4. The slit arrays 51 and 52 are arranged to be moved to an arbitrary position at least in the y-axis direction by a moving mechanism which is not illustrated. In the exemplary embodiment, the slit array 51 and the slit array 52 are disposed between a slit lens 3 and the detector 4 in order from an outlet side of the slit lens 3 and an interval of the moiré stripes of the X-ray formed by the two slit arrays is measured to estimate a penumbra amount from a measurement value. The slit array 52 in the exemplary embodiment is illustrated in FIG. 13B. The penumbra amount is detected by using an interval of the moiré stripes (stripe cycle) of the X-ray formed by the slit array 52 having an arbitrary pitch. The slit array 52 is an element in which 50 slits each having an aperture width t2 of 200 μm and a length b2 of 600 mm are arranged in a plate shaped member which can shield the X-ray such as gold, platinum, or lead in the y direction with a pitch P2 of 400 μm. A length a2 of the y direction thereof is 20 mm. The X-ray which passes the slit lens 3 and is taken out in a cycle by the slit array 51 has an intensity distribution having the same cycle as the cycle of the slit array 51 in the y direction. The X-ray is incident onto the slit array 52 for generating the moiré stripe, so that the moiré stripe is measured on the detector 4. The stripe cycle P of the generated moiré stripes is represented by the following relational expression (Equation 18) using a cycle Pa of the intensity distribution of the X-ray which is taken out by the slit array 51 and a period Pb of the slit array 52 for generating the moiré stripe.1/P=|1/Pa−1/Pb| (Equation 18) In other words, the stripe cycle P of the generated moiré stripe is extended by “Pb/|1/Pa−1/Pb|” times of the period Pa. The cycle of the intensity distribution in the y direction of the X-ray which is taken out by the slit array 51 is enlarged and the X-ray is incident onto the detector 4, so that the cycle of the intensity distribution of the X-ray may be increased with respect to the pixel size Δd of the detector 4 and the detection resolution of the intensity distribution in the y direction may be improved. Therefore, the penumbra amount can be measured with a higher precision and the light source position can be adjust with a higher precision. A method of determining the pitch Pb of the slit array 52 for generating a moiré stripe will be described. In the exemplary embodiment, the cycle of the slit array 51 is 650 μm, so that the Pa is 650 μm. If the period P of the intensity distribution to be measured on the detector, for example, is set to 1,300 μm which is twice of Pa, Pb is 433 μm from Equation 18. With the structure according to the exemplary embodiment, the penumbra amount of the X-ray with an extended cycle on an X-ray detector is measured while changing the relative positions of the X-ray source 1 and the slit lens 3. Further, the X-ray source is adjusted to the position where the penumbra amount is minimum, so that the X-ray source can be adjusted in a positional relationship where the highest resolution is obtained. A fourth exemplary embodiment of the present invention will be described with reference to FIGS. 14A and 14B. Here, only difference from the first to third exemplary embodiments will be described. In the exemplary embodiment, as illustrated in FIG. 14A, a solar slit 61 is disposed between a sit lens 3 and a detector 4, an intensity of an X-ray which passes through the solar slit is measured, and a penumbra amount is estimated from a measurement value. The solar slit 61 is an element in which a plurality of flat shielding plates is disposed with a regular interval so as to be parallel to each other. An X-ray which has a divergence angle having a predetermined angle or larger is shielded by a side wall of the shielding plate and an X-ray which has a divergence angle having a predetermined angle or less passes through the solar slit 61 without being shielded. In other words, an intensity of the X-ray that passes through the solar slit 61 is measured to calculate a divergence angle of the X-ray which is incident into the solar slit 61, so that the penumbra amount may be estimated by using the divergence angle. A range of the divergence angle of the X-ray which is shielded by the solar slit 61 is determined by an aperture angle of the solar slit 61. Here, the aperture angle φ is represented by the following Equation 19 using a length Ls of the solar slit shielding plate in an X-ray traveling direction and an interval ts between the shielding plates.φ=2×arctan(ts/Ls) (Equation 19) If the aperture angle φ is larger than the divergence angle θ, the X-ray which is incident into the solar slit 61 with the divergence angle θ may pass through the solar slit without being shielded by the solar slit shielding plate. In other words, the aperture angle φ may be set to be equal to or lower than a divergence angle θ to be detected. Here, if a divergence angle when there is no positional deviation of the X-ray source 1 and the slit lens 3, that is, when the divergence angle of the X-ray which is radiated from the slit lens 3 is minimum is θmin, an aperture angle φ of the solar slit may be represented by Equation 20.φ≦θmin (Equation 20) In this case, in accordance with Equation 19, when the length Ls of the solar slit shielding plate is constant, the interval ts of the shielding plates is reduced as φ is reduced, so that the intensity of detected X-ray is also reduced. In order to remove such a trouble, in the exemplary embodiment, the interval ts of the shielding plates is determined based on a condition where “φ=θmin”. A solar slit 61 used in the exemplary embodiment is illustrated in FIG. 14B. A length Ls of the solar slit is 100 mm, a width W is 300 mm, and a height H is 100 mm. Further, θmin is 1.1 mrad. In this case, the interval ts of the shielding plates is 55 μm based on the condition where “φ=θmin”. With the structure according to the exemplary embodiment, the intensity of the X-ray that passes through the solar slit 61 is measured while relatively changing the positions of the X-ray source 1 and the solar slit 3. Since a divergence angle with which the X-ray is incident into the solar slit 61 is calculated from the measured X-ray intensity, the X-ray source is adjusted to a position where the penumbra amount estimated from the divergence angle is minimum, so that the X-ray source may be adjusted in a positional relationship where the highest resolution is obtained. A fifth exemplary embodiment of the present invention will be described with reference to FIGS. 15A and 15B. Here, only difference from the first to fourth exemplary embodiments will be described. In the exemplary embodiment, in order to measure a penumbra amount of an optical system including an X-ray source 1 and a slit lens 3, as illustrated in FIG. 15A, a one-dimensional grating 71 (hereinafter, referred to as a “slit array 71”) for selecting a passage is disposed between the X-ray source 1 and the slit lens 3. The slit array 71 is an element for introducing an X-ray from the X-ray source 1 into only a specific passage at an inlet of the slit lens 3 so that an X-ray from the X-ray source is not incident into other passage than the selected passage. The X-ray which passes through the selected passage is emitted from the slit lens 3 with the divergence angle represented by Equation 5 and a range in a y direction where the X-ray is irradiated on the detector is as represented by Equation 10. In the second exemplary embodiment, a method that disposes the slit array for forming the penumbra at the downstream of the slit lens 3 to measure a penumbra amount formed by shielding the X-ray by the slit array is described. In the present exemplary embodiment, the slit array 71 is disposed at an upstream of the slit lens 3 so as to restrict the passage of the slit lens 3 into which the X-ray is incident from the X-ray source 1, measure the size of the X-ray emitted from a specific passage, and estimate a penumbra amount from a measurement value. The slit array 71 used in the exemplary embodiment is illustrated in FIG. 15B. The slit array 71 is an element in which 30 slits each having an aperture width t3 of 20 μm and a length b3 of 300 mm are arranged in a plate shaped member which can shield the X-ray such as gold, platinum, or lead in the y direction with a pitch P3 of 260 μm. A length a3 of the y direction thereof is 7.8 mm. The above-mentioned element is provided near the inlet of the slit lens 3. In this case, the slit array 71 is disposed so as not to block an opening of a selected specific passage. As described above, the slit array 71 and the slit lens 3 are disposed so as to fit the positions thoseof, so that the passages of the slit lens 3 may be restricted to be total 30 for every thirteen. If there is no deviation in the relative position of the X-ray source 1 and the slit lens 3, an X-ray which passes through one of the passages is detected with a size of 220 μm on the detector (irradiation range in the y direction) in accordance with Equation 10. Further, the relational position of the X-ray source 1 and the slit lens is deviated by 100 μm, the X-ray is detected on the detector to have a size of 620 μm. With this structure according to the exemplary embodiment, the size of X-ray on the detector is measured while relatively changing the position of the X-ray source 1 and the slit lens 3. Since the penumbra amount is minimized when the measured size of the X-ray is minimum, the X-ray source is adjusted to a position where the size of the X-ray is minimized, so that the X-ray source may be adjusted in a positional relationship where the highest resolution is obtained. While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. This application claims the benefit of Japanese Patent Application No. 2012-056843, filed on Mar. 14, 2012, which is hereby incorporated by reference herein in its entirety. |
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041397789 | abstract | A nuclear fuel assembly storage rack having a swivel base consisting of a plurality of plates with a hard ball centered and captured between the plates. The bottom base plate is fixed to the bottom of the storage rack and the top base plate has pins for locating the bottom nozzle of the fuel assembly. Since the top of the fuel assembly is clamped in the storage rack, the swivel base allows the fuel assembly to seek a position that minimizes torsional and bending stresses in the fuel assembly. |
048287881 | summary | FIELD OF THE INVENTION The invention relates to a support device for a discharge tank of a suspended pump for circulating the coolant fluid of a nuclear reactor, and in particular a primary pump of a fast neutron nuclear reactor of the integrated type. BACKGROUND OF THE INVENTION Primary pumps of fast neutron nuclear reactors which are generally cooled by a liquid metal such as sodium are disposed, in the case where the reactor is of the integrated type, inside the vessel of the reactor which also encloses the core immersed in the primary liquid sodium filling the vessel. These primary pumps comprise a generally cylindrical body disposed vertically and supported in its upper part by the slab of the reactor closing the vessel. The pump body communicates, in its lower part, with a discharge tank which generally has a spherical shape. This spherical tank is connected to two discharge pipes which open, at their end opposed to the end connected to the spherical tank, onto the bed supporting the core of the reactor. The liquid sodium which is drawn in by the pump in the region of ports extending through the case of its vertical body is discharged into the spherical tank and distributed in the discharge pipes and then re-injected under the assemblies of the core of the reactor. The discharge sphere is rigidly fixed to the plating which is a fixed structure of the reactor resting on the bottom of the vessel and carrying the bed which acts as a support for the assemblies of the core. Upon rapid variations in the operating conditions of the reactor, accompanied by rapid and large-amplitude variations in the temperature of the coolant fluid, and in the case of an abnormal operation of the reactor owing to an incident, which is also accompanied by large temperature variations, the discharge sphere, which is rigidly connected to the plating, is subject to considerable stresses of thermal origin. Indeed, the sphere has a tendency to move under the effect of variations in expansions accompanying the temperature variations, but it is practically immobilized by its rigid connection to the plating. High stresses result in the materials constituting the discharge sphere and the elements connected thereto. SUMMARY OF THE INVENTION An object of the invention is therefore to propose a support device for a discharge tank associated with a pump for circulating the coolant fluid of a nuclear reactor comprising a vertical body supported in its upper part and communicating in its lower part with the discharge tank carried by a fixed structure of the reactor and connected to discharge means opening out under the core of the reactor and symmetrically disposed relative to a vertical plane containing the axis Z-Z' of the pump, this support having a structure whereby it is possible to limit to a low value the stresses of thermal origin which are exerted on its discharge tank and elements connected thereto, in the event of rapid variations in the temperature of the coolant fluid of the reactor. For this purpose, the support device comprises at least one substantially planar metal strip disposed vertically on the axis Z-Z' of the pump and perpendicular to the plane of symmetry of the discharge means, the tank being fixed to the strip in a region located below the region of this strip ensuring its connection with the fixed structure so as to be suspended from the fixed structure by the strip. |
abstract | An imaging optical unit for EUV projection lithography serves to image an object field into an image field. Mirrors guide imaging light from the object field to the image field. An aperture stop is tilted by at least 1° in relation to a normal plane which is perpendicular to an optical axis. The aperture stop has a circular stop contour. In mutually perpendicular planes, a deviation of a numerical aperture NAx measured in one plane from a numerical aperture NAy measured in the other plane is less than 0.003, averaged over the field points of the image field. What emerges is an imaging optical unit, in which homogenization of an image-side numerical aperture is ensured so that an unchanging high structure resolution in the image plane is made possible, independently of an orientation of a plane of incidence of the imaging light in the image field. |
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056419678 | summary | FIELD OF THE INVENTION The invention relates to radiographic phosphor panels. The invention more particularly relates to radiographic phosphor panels containing oxosulfur functionalized polymer reducing agents. BACKGROUND OF THE INVENTION A radiographic phosphor panel contains a layer of phosphor, a crystalline material which responds to X-radiation on an image-wise basis. Like many other crystalline materials, radiographic phosphors have a crystal matrix which allows for the replacement of some atoms by other similar atoms, but does not readily accept other atoms or moieties. Radiographic phosphor panels can be classified, based upon their phosphors, as prompt emission panels and image storage panels. Intensifying screens are the most common prompt emission panels. Intensifying panels are used to generate visible light upon exposure of the intensifying panel to X-radiation. A sheet of photographic film is positioned to intercept the visible light generated and commonly is pressed against the intensifying panel within a light-tight cassette. Other prompt emission panels operate similarly, but in place of the photographic film have some other means for visualizing the X-radiation. Storage panels have storage phosphors, that have the capability of storing latent X-ray images for later release, apparently by locally trapping electron-hole pairs created by incident X-rays. Storage phosphors are distinguishable from the phosphors used in X-ray intensifying or conversion screens. In the latter, a latent image is not stored and X-radiation causes the immediate release of visible light from irradiated phosphor crystals. Radiation image storage panels are used in computed radiography. The panel is first exposed to X-radiation to create a latent image. The panel is then stimulated with longer wavelength radiation, resulting in the emission of radiation at a third wavelength. Typically a laser having a red or infrared beam is scanned over the panel, resulting in the emission of green or blue radiation. The emitted light is collected and the resulting signal is processed electronically to produce a final image. Degradation of final images due to panel discoloration has long been recognized for intensifying screens. There has not, however, been agreement as to the source of that discoloration. What has been noticed is that screens subject to prolonged exposure to photographic film have tended to become discolored. U.S. Pat. Nos. 4,374,905 and 4,360,571 state that the discoloration is due to "volatile organic constituents escaping from the associated photographic film" (U.S. Pat. No. 4,374,905, colunm 1, lines 40-59 and U.S. Pat. No. 4,360,571, column 1, lines 46-64). Great Britain Patent Application No. GB 2 017 140 A states: "[I]t has been discovered that screens containing lanthanum-oxy-halide phosphors tend to discolor rapidly when in use and in particular when held in contact with an X-ray film, . . . "Gadolinium-oxy-halides are similar . . . "In spite of intensive research into this discoloration defect the cause of it is not yet clearly known but it appears to be a complex reaction caused, in part at least, by the hydroscopic nature of the lanthanum-oxy-halide phosphors or gadolinium-oxy-halide phosphors, the nature of the binder and the presence of the X-ray film held in contact with the screen for a period of time. "Furthermore, under somewhat different conditions of use X-ray screens and in particular X-ray screens which contain lanthanum-oxyhalide or gadolinium-oxyhalide phosphors can lose speed due to a different defect which appears to involve only the phosphor. This is hydrolysis of the phosphor which is caused by water present in the phosphor layer due either to atmospheric moisture or aqueous cleaning fluid penetrating the protective layer of the screen. It is thought that quantities of halide or more surprisingly, the free halogen, released by hydrolysis may actually catalyze the discoloration of the binder or of compounds having migrated from the film." (page 1, lines 14-33) U.S. Pat. No. 4,374,905, to Rabatin, teaches a solution to both discoloration by "volatile organic constituents" and attack by water. The phosphor for an intensifying screen was milled with anhydrous MgSO.sub.4 or ZnSO.sub.4 (0.5 to 4 weight percent) during preparation of the screen. It was proposed that the protective action was based upon the reaction: EQU MgSO.sub.4 +2HOH.fwdarw.Mg(OH).sub.2 +2H.sup.+ +SO.sub.4.sup.2-. U.S. Pat. No. 3,836,784, to Bates et al, teaches that small amounts of "stabilizers", such as sodium thiosulfate or potassium thiosulfate can be included in the fluorocarbon binder of an intensifying screen. Bates et al, which used an iodide containing phosphor, noted: "[A]ctivated iodide phosphors are extremely hygroscopic. Absorption of small amounts of water rapidly reduces the conversion efficiency to a vanishingly small value. In order to employ activated iodide phosphors it is therefore necessary to provide the activated iodide phosphor in the screen in a form in which it remains stable for long periods of time. "Various ways have been taught for using thallium activated potassium iodide and protecting the iodide from moisture." (Bates et al, column 1, lines 20-30) U.S. Pat. No. 3,023,313 to De La Mater et al teaches the use of small amounts of sodium thiosulfate or potassium thiosulfate in the binder of an intensifying screen. Examples list 2 grams and 6 grams of sodium thiosulfate per 200 grams of potassium iodide phosphor. In U.S. Pat. No. 4,360,571, to Rabatin, phosphors were treated with fatty acids or metal salts of fatty acids to prevent discoloration by "volatile organic constituents" and attack by water. In GB 2 017 140 A, intensifying screens were stabilized against discoloration and hydrolysis by incorporation of a compound containing a free epoxy group and, optionally, a dialkyl tin compound such as dibutyl tin diocytl as an additional stabilizer. Radiation image storage panels, unlike intensifying screens, are subject to degradative losses of both emitted light and stimulating radiation. Since these effects are cumulative, discoloration can be an even more serious issue in storage panels than in intensifying screens. Yellowing of a phosphor layer of a radiation image storage phosphor panel, in which the phosphor contains iodine, is described in European Patent Specification No. EP 0 234 385 B1. The yellowing is ascribed to liberation of free iodine. The solution taught for the yellowing problem, is incorporation in the phosphor layer of a compound containing a free epoxy group and/or a compound selected from: phosphites, organotin compounds, and metal salts of organic acids, specifically: octylic acid, lauric acid, stearic acid, oleic acid, ricinoleic acid naphthenic acid, 2-ethylhexanoic acid, resin acid, synthetic carboxylic acid, benzoic acid, salicylic acid, organic phosphinous acid, phenol, and alkylphenol. U.S. patent application Ser. Nos. 157,797 (now abandoned) and Ser. No. 157,796 (now U.S. Pat. No. 5,427,868) both filed on 24 Nov. 1993 and entitled "Pigment Stabilized Radiation Image Storage Panel and Method for Preparing Radiation Image Storage Panel" and "Radiographic Phosphor Panel Having Binder Compatible Oxosulfur Stabilizer and Method for Preparing Phosphor Panel" disclose oxosulfur reducing pigment and binder-compatible oxosulfur compounds and complexes useful for preventing yellowing of phosphor panels. It would be desirable to provide improved radiation image storage panels with stability against yellowing and/or hydrolysis. SUMMARY OF THE INVENTION The invention, in its broader aspects, provides a radiation phosphor panel containing an oxosulfur functionalized polymer. The oxosulfur functionalized polymer acts as a reducing agent. The phosphor panel has a support and a luminescent layer overlaying the support. The luminescent layer includes phosphor crystals capable of absorbing X-radiation. The oxosulfur functionalized polymer reducing agents are present in a concentration sufficient to substantially increase the photostimulated luminescence of the panel. It is an advantageous effect of at least some of the embodiments of the invention that radiation image storage panels and prompt emission panels are provided which exhibit improved performance and enhanced stabilization against yellowing. DESCRIPTION OF PARTICULAR EMBODIMENTS The radiographic phosphor panel of the invention comprises an oxosulfur functionalized polymer reducing agent. The panel consists of a support, a luminescent layer and an optional overcoat layer. The luminescent layer includes phosphor crystals and a binder. The oxosulfur functionalized polymer reducing agent is preferably located in the luminescent layer. The luminescent layer can consist of one or more layers, for example one layer can contain the phosphor crystals and binder and a separate and adjacent layer can contain the oxosulfur functionalized polymer reducing agent. One or more oxosulfur functionalized polymer reducing agents with or without one or more other reducing agents may be present in the radiographic phosphor panel of this invention. The phosphor crystals in the luminescent layer can be any phosphor crystals that are capable of absorbing X-radiation and emitting electromagnetic radiation of a second wavelength. The phosphor crystals can be those that emit the second wavelength promptly after the absorption of the X-radiation and are used to construct prompt emission panels, or the phosphor crystals can be those that are able to store the absorbed energy and release it after exposure to electromagnetic radiation and are used to construct storage phosphors. The following description is primarily directed to radiographic image storage panels; however, the invention is not limited to storage panels. The term "radiographic phosphor panel" refers to both an image storage panel and a prompt emission panel. The phosphor in the storage panel can be chosen from radiographic phosphors generally. Halide containing phosphors are preferred, and most preferred are iodine containing phosphors, because the oxosulfur functionalized polymer reducing agents stabilize against discoloration associated with halide containing phosphors, particularly iodine containing phosphors. The following description is primarily directed to iodine containing phosphors; however, the invention is not limited to them. Examples of phosphors which include iodine are divalent alkaline earth metal fluorohalide storage phosphors containing iodine and alkali metal halide storage phosphors containing iodine. A mixture of phosphors, at least one of which contains iodine, could also be used, if desired, to form a panel having optimal properties for a particular application. Panel constructions containing more than one phosphor-containing layer are also possible, with iodine containing phosphors being present in one or more of the phosphor-containing layers. The term "oxosulfur functionalized polymer reducing agent" or "oxosulfur functionalized polymer reducing agent for iodine" is used to designate a chemical species capable of reducing free (molecular) iodine according to the half-reaction: EQU I.sub.2 +2e.sup.- .fwdarw.2I.sup.- or capable of reducing another halide according to the half-reaction: EQU X.sub.2 +2e.sup.- .fwdarw.2X.sup.-, where X is a halide. The oxosulfur functionalized polymer reducing agents are polymers functionalized with oxosulfur reducing agents. Specific examples of the polymer reducing agents include compounds of the general formula: ##STR1## where: Q is N or P; R.sup.1 is H or CH.sub.3 ; PA0 M' is a carbon chain and may be straight, branched or cyclic, for example, ##STR2## where n is 1 to 12; preferably is M' is C.sub.n H.sub.2n where n is 1 to 6; L is ##STR3## preferably ##STR4## G' represents units of an addition polymerizable monomer containing at least two ethylenically unsaturated groups; PA0 J' represents units of a copolymerizable ethylenically unsaturated monomer; PA0 R.sup.2, R.sup.3 and R.sup.4 are independently selected from the group consisting of carbocyclic groups and alkyl groups; PA0 D' is a counter ion and may be simple inorganic cation such as an alkali metal or a complex organic or inorganic cation; PA0 Z is S.sub.j O.sub.k D"-- or 1/2S.sub.j O.sub.k.sup.-, where j and k are positive integers such that the ratio, j/k is defined by 0.25<j/k<1.0; PA0 g is 0 to 20 mole percent; PA0 p is 0 to 90 mole percent; PA0 q is 10 to 100 mole percent, preferably 50 to 100 mole percent; PA0 where the addition of g, p and q equals 100 mole percent; PA0 f plus h is 1. f is 0 or 1; PA1 h is 0 or 1; and S.sub.j O.sub.k is inclusive of species in which S.sub.j O.sub.k is a free ion and species in which S.sub.j O.sub.k is a charge bearing moiety covalently linked to another group. Therefore, the oxosulfur functionalized polymer reducing agents can consist of monomers having uncharged species or charged anions. Preferably j is 2 and k is 3, that is, S.sub.2 O.sub.3.sup.2-, or j is 4 and k is 6, that is, S.sub.4 O.sub.6.sup.2-. Most preferably j is 2 and k is 3. D' can be selected on the basis of convenience and non-interference with the properties of the polymer. Examples of suitable counterions include Li.sup.+, Na.sup.+, K.sup.+, NH.sub.4.sup.+ and (ethyl).sub.4 N.sup.+. G' is a repeating unit of an addition polymerizable monomer containing at least two ethylenically unsaturated groups, such as vinyl groups generally having the structure: ##STR5## wherein r is an integer greater than 1 and preferably 2 or 3, each R.sup.6 is independently selected from hydrogen and methyl and R.sup.5 is a linking group comprising 1 or more condensation linkages such as amide, sulfonamide, esters such as sulfonic acid ester, arylene and the like, or a condensation linkage and an organic nucleus such as alkylene, such as methylene, ethylene, trimethylene, arylene, such as phenylene, phenylenedi(oxycarbonyl), 4,4'-isopropylidene bis(phenyleneoxycarbonyl), methylene(oxycarbonyl), ethylene di(oxycarbonyl), 1,2,3-propantriyltris(oxycarbonyl), cyclohexylene bis(methyleneoxycarbonyl), methyleneoxycarbonyl), ethylidyne trioxycarbonyl, and the like. The monomer used must be stable in the presence of strong alkali and must not be highly reactive so that hydrolysis does not occur during copolymerization. Suitable examples of monomers from which the repeating units (G') are formed are divinylbenzene, allyl acrylate, allyl methacrylate, N-allylmethacrylamide, 4,4'-isopropylidenediphenyl diacrylate, 1,3-butylene diacrylate, 1,3-butylene dimethacrylate, 1,4-cyclohexylenedimethylene dimethacrylate, diethylene glycol dimethacrylate, diisopropylene glycol dimethacrylate, divinyloxymethane, ethylene diacrylate, ethylene dimethacrylate, ethylidene diacrylate, ethylidene dimethacrylate, 1,6-diacrylamidohexane, 1,6-hexamethylene diacrylate, 1,6-hexamethylene dimethacrylate, N,N'-methylenebisacrylamide, neopentyl glycol dimethacrylate, phenylethylene dimethacrylate, tetraethylene glycol dimethacrylate, tetramethylene diacrylate, tetramethylene dimethacrylate, 2,2,2-tricholoethylidene dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, ethylidyne trimethacrylate, propylidene triacrylate, viny allyloxyacetate, vinyl methacrylate, 1-vinyloxy-2-allyloxyethane, and the like. Preferably the monomers from which the repeating units G' are formed are divinylbenzene, allyl acrylate, alyll methacrylate, 1,3-butylene dimethacrylate, 1,4-cyclohexylenedimethylene dimethacrylate, diethylene glycol dimethacrylate, methylene bisacrylamide and ethylene glycol dimethacrylate. More preferably G' is made from divinylbenzene, or ethylene glycol dimethacrylate. Ethylene glycol dimethacrylate is the most preferred monomer. J' is a repeating unit of an addition polymerizable monomer such as ethylene, propylene, 1-butene, isobutene, 2-methylpentene, 2-methylbutene, 1,1,4,4-tetramethylbutadiene, tyrene, alpha-methylstyrene, monoethylenically unsaturated esters of aliphatic acids such as vinyl acetate, isopropenyl acetate, allyl acetate, etc.; esters of ethylenically unsaturated mono- or dicarboxylic acids such as methyl methacrylate, ethyl acrylate, diethyl methylenemalonate, etc.; monoethylenically unsaturated compounds such as acrylonitrile, allyl cynanide, and dienes such as butadiene and isoprene. A preferred class of ethylenically unsaturated monomers which may be used to form the ethenic polymers of this invention includes the lower 1-alkenes having from 1 to 6 carbon atoms; styrene, and tetramethylbutadiene and methyl methacrylate. Preferably J' is a styrene, acrylic or methacrylic esters, acrylonitrile, acrylic or methacrylic acid. More preferably J' is styrene. Examples of R.sup.2, R.sup.3, and R.sup.4 groups include: carbocyclic groups such as aryl, aralkyl, and cycloalkyl such as benzyl, phenyl, p-methyl-benzyl, cyclohexyl, cyclopentyl and the like and alkyl preferably containing from 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, such as methyl, ethyl, propyl, isobutyl, pentyl, hexyl, heptyl, decyl and the like. Preferably R.sup.2, R.sup.3, or R.sup.4 are methyl, ethyl or phenyl. The weight average molecular weight of the polymer preferably ranges from 1.times.10.sup.5 to 1.times.10.sup.6 grams/mole. The preferred compounds according to formula I are those when f=0 and h=1. Examples of suitable oxosulfur functionalized polymeric reducing agents include: ##STR6## The polymers functionalized with oxosulfur reducing agents can be prepared by solution or emulsion polymerization. The polymeric materials according to this invention can be prepared by emulsion polymerizing a vinylbenzyl halide with a poly unsaturated monomer G' as described above and an .alpha.,.beta.-ethylenically unsaturated monomer J' as described above, generally in the presence of an anionic surfactant such as sodium lauryl sulfate. The above polymeric vinylbenzyl halide latex can be reacted with a tertiary amine or tertiary phosphine having the structure: ##STR7## wherein R.sup.2, R.sup.3, R.sup.4 and Q are described above, generally at temperatures of from about -20.degree. C. to about 150.degree. C. This produces a polymeric microgel latex which has a particulate character. An alternate method of preparing the polymer is to emulsion polymerize an N-vinylbenzyl-N,N-dialkylamine monomer with monomers G' and J' as described above in the presence of an anionic surfactant and a redox free-radical initiator. The resulting polymer tertiary amine latex is reacted with an alkylating agent having the structure R.sup.3 -Z' wherein R.sup.3 is as described above and Z' is a group which can be displaced to yield the anion Z'.sup.-, preferably Z".sup.- is a halide such as chloride or an alkyl or aryl sulfonate group. This reaction can take place at temperatures from about -20.degree. C. to about 150.degree. C. The resulting polymeric latex can then be ion-exchanged using a diafiltration apparatus to replace Z' with Z as defined above. The formation of the latex is described in more detail in U.S. Pat. No. 3,958,995 incorporated herein by reference. The monomers of the polymer reducing agent can be selected on the basis of convenience, non-toxicity, non-hygroscopicity, solubility in the solvent for a particular binder and non-interference with the desired characteristics of the panel produced. It is generally preferred that the oxosulfur functionalized polymer reducing agent and the product of its reaction with iodine of other halide be colorless, however, some coloration within a suitable wavelength range could be accommodated. It is generally preferred that the oxosulfur functionalized polymer reducing agents be soluble in a suitable solvent such that it can be dispersed in the binder on a substantially molecular basis. The oxosulfur functionalized polymer reducing agent should be further chosen such that it does not impart undesirable characteristics to the radiographic panel such as odor, and poor mechanical strength. It is generally taught in the art that the degradation of image storage panels results from both oxidation and hydrolysis of the phosphor as a result of its exposure to air, heat and moisture. This process is thought to liberate intensely colored and highly light absorbing iodine molecules from the panel, which in turn, stain the panel and dramatically degrade its speed. The oxosulfur functionalized polymer reducing agents of the present invention are effective reducing agents for molecular iodine. For example when S.sub.j O.sub.k is S.sub.2 O.sub.3.sup.2-, it rapidly reacts with iodine according to the following chemical equation: EQU S.sub.2 O.sub.3.sup.2- +I.sub.2 .fwdarw.2I.sup.- +S.sub.4 O.sub.6.sup.2- The concentration of the oxosulfur functionalized polymer reducing agent, preferably located in the luminescent layer of the phosphor panel, should be an amount sufficient to increase the photostimulated luminescence of the phosphor panel as compared to a control panel which does not contain a reducing agent and/or stabilizing compound. There is theoretically no upper limit of the concentration of stabilizing compounds in the layers of the panel, however, deterioration of panel characteristics at very high concentrations of stabilizing compound is expected, if, by no other means than displacement of phosphor or binder. Convenient concentrations of the oxosulfur functionalized polymer reducing agent are a fraction or few weight percent relative to the weight of the phosphor, or a range of about 0.1 to about 10.0, preferably 0.1 to 4 weight percent relative to the weight of the phosphor (also referred herein as (wt/wt)%). One or more oxsulfur functionalized polymer reducing agents can be used in combination with other reducing agents and/or stabilizing compounds, such as, oxosulfur reducing pigments, binder compatible oxosulfur reducing agents, epoxides, organotin compounds, phosphites, and metal salts of organic acids. The total concentration of the reducing agents and stabilizing compounds should not exceed 10 (wt/wt)%. The oxosulfur functionalized polymer reducing agents can optionally serve as the binder for the luminescent layer; thereby eliminating the need for additional binders. In a preferred embodiment, the luminescent layer of the phosphor panel of the invention contains phosphor, the oxosulfur functionalized polymer reducing agent, a conventional polymeric binder to give it structural coherence and other addenda, if desired. In general the conventional binders useful in the practice of the invention are those traditionally employed in the art. Conventional binders are generally chosen from a wide variety of known organic polymers which are transparent to x-rays, stimulating, and emitted light. Conventional binders commonly employed in the art include sodium o-sulfobenzaldehyde acetal of poly(vinyl alcohol); chlorosulfonated poly(ethylene); a mixture of macromolecular bisphenol poly(carbonates) and copolymers comprising bisphenol carbonates and poly(alkylene oxides); aqueous ethanol soluble nylons; poly(alkyl acrylates and methacrylates) and copolymers of poly(alkyl acrylates and methacrylates with acrylic and methacrylic acid); poly(vinyl butyral); and poly(urethane) elastomers. These and other useful conventional binders are disclosed in U.S. Pat. Nos. 2,502,529; 2,887,379; 3,617,285; 3,300,310; 3,300,311; and 3,743,833; and in Research Disclosure, Vol. 154, February 1977, Item 15444, and Vol. 182, June 1979. Research Disclosure is published by Kenneth Mason Publications, Ltd., Emsworth, Hampshire P010 7DD, England. Particularly preferred conventional binders are poly(urethanes), such as those commercially available under the trademark Estane from Goodrich Chemical Co., the trademark Permuthane from the Permuthane Division of ICI, and the trademark Cargill from Cargill, Inc. When used in combination with conventional binders, the oxosulfur functionalized polymer reducing agent is preferably binder compatible. The term "binder compatible" is used herein to indicate that the oxosulfur functionalized polymer reducing agent is not dispersed in particulate form in the binder, but rather is dispersed on a molecular basis or on a substantially molecular basis. Binder compatible is, for example, inclusive of what is sometimes referred to as a "solid solution". Binder compatible is also inclusive of a solid solution within one phase of a two binder system. When the oxosulfur functionalized polymer reducing agent and binder have solubility properties in common, the oxosulfur functionalized polymer reducing agent is usually binder compatible and the oxosulfur functionalized polymer reducing agent and binder can be dissolved in the same solvent and then solvent cast to form a single substantially uniform layer. In the phosphor panel, the oxosulfur functionalized polymer reducing agent and binder provide a solvent cast matrix for the phosphor and any other particulate addenda. Any suitable ratio of phosphor to conventional binder can be employed. Generally thinner phosphor layers and sharper images are realized when a high weight ratio of phosphor to binder is employed. Preferred phosphor to conventional binder weight ratios are in the range of from about 7:1 to 25:1 for panel constructions intended to withstand commercial exposure repetitions without loss of structural integrity. In the case in which oxosulfur functionalized polymer reducing agents are combined with conventional binders the total weight of binders and polymers with respect to the phosphor should be in the range from 5:1 to 25:1 (phosphor:binders). For limited or single exposure applications it is, of course, appreciated that any minimal amount of binder consistent with structural integrity is satisfactory. In particular embodiments of the invention, it may be desirable to add white pigment. Suitable pigments, are well known to those skilled in the art and include materials such as titania and barium sulfate. White pigments have been utilized in the art to increase resolution at the expense of speed. In particular embodiments of the invention, the phosphor is a storage phosphor which is the product of firing starting materials comprising a combination of species characterized by the relationship: EQU MFX.sub.1-z I.sub.z.uM.sup.a X.sup.a :yA:eQ:tD, where M is selected from Mg, Ca, Sr, and Ba; X is selected from Cl and Br; M.sup.a is selected from Na, K, Rb, and Cs; X.sup.a is selected from Cl, Br, and I; A is selected from Eu, Ce, Sm, and Tb; Q is an oxide selected from BeO, MgO, CaO, SrO, BaO, ZnO, Al.sub.2 O.sub.3, La.sub.2 O.sub.3, In.sub.2 O.sub.3, SiO.sub.2, TiO.sub.2, ZrO.sub.2, GeO.sub.2, SnO.sub.2, Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, and ThO.sub.2 ; and D is selected from V, Cr, Fin, Fe, Co, and Ni. Numbers are represented by the following: z is from 1.times.10.sup.-4 to 1, u is from 0 to 1, y is from 1.times.10.sup.-4 to 0.1, e is from 0 to 1, or more preferrably from 1.times.10.sup.-5 to 0.1, and t is from 0 to 1.times.10.sup.-2. The same designations appearing elsewhere herein have the same meanings unless specifically stated to the contrary. Groups of materials, for example the materials defined by M, are to be understood as inclusive of combinations of materials in that group. In some of those embodiments of the invention, the panel includes a divalent alkaline earth metal fluorohalide storage phosphor containing iodine which is the product of firing an intermediate, a combination of species characterized by the relationship: EQU (Ba.sub.1-a-b-c Mg.sub.a Ca.sub.b Sr.sub.c)FX.sub.1-z I.sub.z.rM.sup.a X.sup.a :yA:eQ where X, M.sup.a, X.sup.a, A, Q, z, y, and e have the same meanings as in formula (1) and the sum of a, b, and c is from 0 to 0.4, and r is from 1.times.10.sup.-6 to 0.1. In a particular embodiment of the invention, M.sup.a is potassium and the storage phosphor is further characterized as disclosed in U.S. patent application Ser. No. 300,116, filed Sep. 2, 1994 (now U.S. Pat. No. 5,464,568) by Joseph F. Bringley, Philip S. Bryan and Andrea M. Hyde, entitled: ALKALINE EARTH METAL FLUOROBROMOIODIDE STORAGE PHOSPHOR AND RADIATION IMAGE STORAGE PANEL, the disclosure of which is hereby incorporated herein by reference. In a particular embodiment of the invention, the phosphor is produced utilizing an oxosulfur reducing agent containing storage phosphor intermediate, disclosed in U.S. application Ser. No. 300,113, filed Sep. 2, 1994, (now U.S. Pat. No. 5,507,967) by Joseph F. Bringley, Philip S. Bryan and Andrea M. Hyde, entitled: STABILIZED PHOSPHOR INTERMEDIATES, STORAGE PHOSPHORS, RADIATION IMAGE STORAGE PANELS, AND PREPARATION METHODS; (hereafter referred to as "Stabilized Phosphor Intermediates Application), the disclosure of which is hereby incorporated herein by reference. The stabilized phosphor intermediate disclosed therein and its resulting phosphor have increased photostimulated luminescence in comparison to unstabilized controls. It is expected that increased photostimulated luminescent provided thereby is cumulative with the increased photostimulated luminescent provided in the claimed invention. Care is taken in the selection of inorganic cations so as to not cause deleterious effects on the phosphor produced. In the inventive phosphor of the Stabilized Phosphor Intermediates Application, the oxosulfur reducing agent is present in the unfired intermediate for the phosphor in an amount sufficient to increase relative photostimulated luminescence in the fired phosphor relative to the same phosphor absent said reducing agent for iodine. In a particular embodiment of the Stabilized Phosphor Intermediates Application, the phosphor has the general structure EQU MFX.sub.1-z I.sub.z.uM.sup.a X.sup.a :yA:eQ:tD EQU or EQU (Ba.sub.1-a-b-c Mg.sub.a Ca.sub.b Sr.sub.c)FX.sub.1-z I.sub.z.rM.sup.a X.sup.a :yA:eQ in which these formulas have the same meanings as discussed above and the oxosulfur reducing agent is present in the intermediates in a molar ratio of sulfur to alkaline earth metal of greater than 1.times.10.sup.-4 and less than 0.020. For the highest attainable speeds a white support, such as a titania or barium sulfate loaded or coated support is employed. Particular reflective supports which offer a balance of speed and sharpness are those containing reflective microlenslets, such as are disclosed in U.S. Pat. No. 4,912,333 to Roberts, et al. In those instances in which it is desired to reduce the effective thickness of a phosphor layer below its actual thickness the phosphor layer is modified to impart a small, but significant degree of light absorption. If the conventional binder and/or the polymers of the present invention are chosen to exhibit the desired degree of light absorption, then no other ingredient of the phosphor layer is required to perform the light attenuation function. It is specifically noted that the less structurally complex chromophores for ultraviolet absorption particularly lend themselves to incorporation in polymers. A separate absorber can be incorporated in the phosphor layer to reduce its effective thickness. The absorber can be a dye or pigment capable of absorbing light within a desired spectrum. Black dyes and pigments such as carbon black are, of course, generally useful with phosphors, because of their broad absorption spectra. With storage panels, it is preferable to include a dye or pigment which absorbs some of the stimulating radiation, generally provided by a laser; but mostly reflects emitted light. U.S. Pat. No. 4,491,736 to Teraoka teaches the use of such materials in storage panels. Apart from the phosphor layers and the assembly features described above, the panel can be of any conventional construction. Panels typically have one or more flexible or rigid support layers. Flexible layers are most commonly polymeric. The most common polymeric supports are films of high dimensional integrity, such as poly(ethylene terephthalate) film supports. In a preferred embodiment of the invention, support is provided by one or more polymeric layers and by a rigid plate of aluminum or the like. Metal layers, such as aluminum, enhance reflection. Paper supports, though less common than film supports, are known and can be used for specific applications. Dyes and pigments are commonly loaded into supports to enhance absorption or reflection of light. Air can be trapped in supports to reflect ultraviolet and visible light. Supports and the subbing layers used to improve coating adhesion can be chosen from among those employed for silver halide photographic and radiographic elements, as illustrated by Research Disclosure, Vol. 176, December 1978, Item 17643, Section XVII, and Research Disclosure, Vol. 184, August 1979, Item 18431, Section I. An overcoat layer, although not required, is commonly located over the luminescent layer for humidity and wear protection. If the panel includes an overcoat layer, the oxosulfur funtionalized polymer reducing agents may be located in the overcoat layer or the luminescent layer or both. The oxosulfur functionalized polymer reducing agents may be admixed with conventional overcoat binders and used for the overcoat layer. Suitable concentrations of oxosulfur functionalized polymer reducing agents when mixed with an conventional overcoat binder are in the range from about 0.05 to 50% by weight binder. The overcoat layer comprises a binder chosen using the criteria described above for the conventional binder in the luminescent layer. It is understood that the oxosulfur functionalized polymer reducing agents, the conventional binder if used in the overcoat layer, and the conventional binder forming the matrix in which the phosphor particles are held, are preferably formed of transparent resins that do not interfere with the passage of x-rays or stimulating radiation or the emitted light from the phosphors. The overcoat binder can be the same binder as in the luminescent layer or different and can also be chosen from polymers useful for supports. Since it is generally required that the overcoat layer exhibits toughness and scratch resistance, polymers conventionally employed for film supports are favored. For example, cellulose acetate is an overcoat commonly used with the poly(urethane) binders. Overcoat polymers are often used also to seal the edges of the phosphor layer. In a preferred embodiment of the invention, the overcoat is produced in accordance with a U.S. Pat. No. 5,401,971 by Luther C. Roberts, entitled: OVERCOATED RADIATION IMAGE STORAGE PANEL AND METHOD FOR PREPARING RADIATION IMAGE STORAGE PANEL, the disclosure of which is incorporated herein by reference. While anticurl layers are not required for the panels, they are generally preferred for inclusion. The function of the anticurl layer is to balance the forces exerted by the layers coated on the opposite major surface of a support which, if left unchecked, cause the support to assume a non-planar configuration, that is, to curl or roll up on itself. Materials forming the anticurl layers can be chosen from among those identified above for use as binders and overcoats. Generally an anticurl layer is formed of the same polymer as the overcoat on the opposite side of the support. For example, cellulose acetate is preferred for both overcoat and anticurl layers. Any one or combination of conventional panel features compatible with the features described herein can, of course, be employed. Conventional storage panel constructions are disclosed in U.S. Pat. No. 4,380,702 to Takahashi et al, the disclosure of which is hereby incorporated by reference. Conventional intensifying panel constructions are disclosed in Research Disclosure, Vol. 184, August 1979, Item 18431, hereby incorporated herein by reference. The radiographic panels of the invention are formed by conventional coating techniques. Phosphor powder, oxosulfur functionalized polymer reducing agents and other addenda are mixed with a solution of a resin binder material and coated by means such as blade coating onto a substrate. U.S. Pat. No. 4,505,989 to Umemoto et al, the disclosure of which is hereby incorporated herein by reference, describes suitable techniques known in the art for preparing an X-ray image storage panel. The following Examples and Comparative Example are presented to further illustrate and elucidate some preferred modes of practice of the invention. Unless otherwise indicated, all starting materials were commercially obtained. The X-ray storage phosphor BaFBr.sub..85 I.sub..15 :0.001Eu.sup.2+ was prepared by the following general procedure: In a 2000 ml beaker containing a Teflon coated magnetic stir bar, 269.54 grams of BaBr.sub.2.2H.sub.2 O and 62.22 grams of BaI.sub.2.2H.sub.2 O were dissolved in a 2 to 3 fold excess of distilled water and the solution filtered. To the filtered solution was then added 2.88 grams of fumed silica and 0.500 grams of BaS.sub.2 O.sub.3.H.sub.2 O followed by 0.088 grams KBr. 167.5 g of BaF.sub.2 containing 0.002 moles of EuF.sub.2 and 0.01 mol CaF.sub.2 were then added to the solution slowly with vigorous stirring. Stirring was maintained for about 1 hour and the resulting slurry was then spray-dried through an air driven rotary atomizer at an inlet temperature of 350.degree. C. and an outlet temperature of 110.degree. C. The resulting white powder was then placed into alumina crucibles and fired at a temperature of 840.degree. to 860.degree. C. for 3.5 hours under flowing nitrogen. The phosphor powders, after being allowed to cool under nitrogen, were then ground and sieved through a 38 micron screen yielding the finished phosphor. Preparation of Latex A To a two liter three-necked flask equipped with a stirrer and condenser was added 588 ml of degassed distilled water and 2.3 grams of sodium lauryl sulfate. The flask was placed in a 60.degree. C. bath. 0.09 grams of sodium metabisulfite and 1.44 grams of potassium persulfate were added followed by the contents of an addition flask containing a mixture of 161 ml of degassed distilled water, 171 grams of vinylbenzyl chloride, 16.5 grams of ethyleneglycol dimethacrylate, 7 grams of sodium lauryl sulfate, and 0.33 grams of sodium metabisulfite over a period of 45 minutes. After the addition was complete 0.04 grams of sodium metabisulfite and 0.14 grams of potassium persulfate were added. The resulting latex was stirred at 60.degree. C. under nitrogen for 2 hours and then cooled to give a translucent latex. Preparation of Polymer .chi. To latex A was added 3 ml of 50% sodium hydroxide in 283 ml of distilled water followed by the addition of 290 grams of trimethylamine in 261 grams of isopropyl alcohol over a period of 90 minutes. The contents was stirred at 60.degree. C. for 6 hours and then cooled to give a white dispersion. 500 grams of the above dispersion was added into the delivery system of a diafiltration apparatus. The diafiltration apparatus contained a 10,000 molecular weight cut off polysulfone diafiltration membrane. 1500 ml of a 10% solution of Na.sub.2 S.sub.2 O.sub.3 were added dropwise. The polymer dispersion was circulated through the apparatus until the permeate contained no chloride ion. The polymer was then isolated by freeze drying under vacuum. Preparation of Polymer .alpha. To a 2 liter 3-necked flask equipped with a stirrer and condenser was added 40 ml of n-butanol, 20 grams of N-vinylbenzyl-N,N-dimethyl-N-octadecylammonium chloride, and 0.4 grams of 2,2'-azobis(2-methylpropionitrile). The solution was stirred under nitrogen at 80.degree. C. for 16 hours to give a viscous solution. The solution was diluted with 100 ml of n-butanol and cooled to room temperature. The polymer was precipitated in 4 liters of acetone and dried in a vacuum oven. 1 gram of the above polymer was dissolved in 500 ml of ethanol and evaporated to dryness on a rotary evaporator. 10 grams of Na.sub.2 S.sub.2 O.sub.3 in 400 ml of water was added to the flask and stirred for 16 hours. The resulting solid was filtered and added to 5 grams of Na.sub.2 S.sub.2 O.sub.3 in 200 ml of water. The slurry was stirred for 16 hours and the solid collected by filtration. The solid was dried in a vacuum oven. Preparation of Polymer .beta. 20.0 grams of Latex A was introduced into a dialysis bag and followed by the addition of 10.0 grams of Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O. The dialysis bag was then closed at the top and placed into a 500 ml Erlenmeyer flask and the flask filled with distilled water. After 12 hours, 5 additional grams of Na.sub.2 S.sub.2 O.sub.3.5H.sub.2 O were introduced into the dialysis bag and the water in the Erlenmeyer flask was replaced. After an additional 24 hours, the dialysis bag was removed and placed into a 400 ml beaker. The bag was then flushed with distilled water for 48 hours. The resultant thiosulfate functionalized polymer was isolated by freeze drying. |
claims | 1. A component support comprising a plate and a cover, wherein:said plate further comprises a substantially planar plate body defining a spike aperture therethrough, said plate body further comprising first and second opposed deflectable latches extending to either side of said spike aperture, said plate body further defining first and second bracing apertures adjacent to said first and second latches, respectively;said cover further comprises a planar cover body comprising first and second bracing members insertable through said first and second bracing apertures of said plate body so as to prevent deflection of said first and second latches, respectively, said cover body further defining a spike passageway therethough so as to extend in overlying registry with said spike aperture of said plate body when said bracing members extend through said bracing apertures. 2. A component support of claim 1, wherein said cover body further defines a cylindrical bore in fluid communication with said spike passageway, said cylindrical bore being further across in dimension than said spike passageway so as to accommodate a vial therein. 3. A component support of claim 2, wherein said plate body further defines a second spike aperture therethrough, said plate body further comprising third and fourth opposed deflectable latches extending to either side of said second spike aperture, said plate body further defining third and fourth bracing apertures adjacent to said third and fourth latches, respectively; andwherein said cover further third and fourth bracing members insertable through said third and fourth bracing apertures of said plate body so as to prevent deflection of said third and fourth latches, respectively, said cover body further defining a second spike passageway therethough so as to extend in overlying registry with said second spike aperture of said plate body when said third and fourth bracing members extend through said third and fourth bracing apertures, respectively. 4. A component support of claim 3, wherein said cover body further defines a second cylindrical bore in fluid communication with said second spike passageway, said second cylindrical bore being further across in dimension than said second spike passageway so as to accommodate a vial therein. 5. A component support as claimed in claim 1 wherein said first and second bracing apertures are of non-circular cross-section and said first and second bracing members have a corresponding non-circular cross-section. 6. A component support as claimed in claim 1 wherein said first and second latches each further comprise a camming surface engageable by said first and second bracing member, respectively, for urging said first and second latches towards each other. 7. A radioisotope generator including one or more component supports as claimed in claim 1. 8. A radioisotope generator as claimed in claim 7, wherein said plate body is a closure plate of the generator and is said cover body is a cover plate of said generator such that insertion of said bracing members into said bracing apertures mounts said cover plate over said closure plate. 9. A radioisotope generator as claimed in 8, further including a spike comprising a hollow generally cylindrical body and a retaining plate, said hollow body being received in said spike apertures in said closure plate and said spike passageway of said cover plate and wheein said retaining plate is engaged by said opposed first and second latches for securely holding said spike in position. |
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abstract | A method and an arrangement for producing spherical fuel cores and/or breeder material cores by dripping a pouring solution containing uranyl nitrate and a solution containing at least one auxiliary agent into an ammoniacal precipitation bath to form microspheres, aging, washing, drying, and thermally treating the microspheres. In order to provide a continuous production method along with a constantly high core quality, it is proposed that 1) the microspheres from the precipitation bath be separated through a first separator and fed to the ammoniacal aging water for aging, 2) the contact duration of the microspheres with the liquid of the precipitation bath before being introduced into the aging water be set equally or substantially equally, 3) the microspheres be transferred from the aging water to a multi-stage cascade scrubber using a transfer device, wherein the microspheres are washed in the multi-stage cascade scrubber so as to be free or substantially free from ammonium nitrate and at least one auxiliary agent contained in the microspheres, and 4) after drying, the microspheres be calcinated while distributed in a monolayer during a thermal treatment. |
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claims | 1. A fast reactor comprising:a plurality of fuel assemblies forming a reactor core;a reactivity control assembly including a reactor shutdown rod of a backup reactor shutdown system and sectional neutron absorbers disposed around the reactor shutdown rod to suppress initial surplus reactivity, the reactor shutdown rod and the neutron absorbers being arranged in a hexagonal barrel-shaped wrapper tube at the center of the reactor core;a core barrel surrounding outer periphery of the reactor core;a reflector surrounding the outer periphery of the core barrel and adapted to move up and down;a bulkhead surrounding outer periphery of the reflector and forming an inner wall of a coolant flow channel of primary coolant;an upper support plate supporting the core barrel and the bulkhead;an intermediate heat exchanger arranged in an annular space above the upper support plate;an electromagnetic pump arranged below the intermediate heat exchanger;a reactor vessel containing the fuel assemblies, the reactivity control assembly, the reflector, the bulkhead, the intermediate heat exchanger and the electromagnetic pump and including an upper opening;an upper plug plugging the upper opening of the reactor vessel;a reactor shutdown rod drive mechanism for causing an inner extension tube to fall and to release the reactor shutdown rod by a gripper section that includes latch fingers, at a lowermost end of an outer extension tube by turning off power supply to a holding magnet at a time of scram; anda plurality of units of neutron absorber drive mechanism, each including a dual tube drive shaft including an outer extension shaft and an inner extension shaft, the outer extension shaft being adapted to be pulled up to allow both of the inner and outer extension shafts to be inserted and pushed down after getting to a handling head section of the neutron absorber so as to grasp the neutron absorber externally by the latch fingers of the gripper section and hang up entirely with the drive shaft to individually move the neutron absorber up and down, wherein the reactor shutdown rod drive mechanism and the neutron absorber drive mechanism are integrally formed and arranged at a center of the upper plug,wherein:the reactor shutdown rod has a cylindrical profile and a head is formed at the top of the reactor shutdown rod;the reactivity control assembly includes a cylindrical guide tube arranged in the wrapper tube to surround the reactor shutdown rod and the plurality of sectional neutron absorbers arranged peripherally between the guide tube and the wrapper tube, anda cylindrical neutron absorber handling rod is arranged so as to project from a top of the reactivity control assembly when the neutron absorber moves to a lowest position, a neutron absorber handling head being formed at a top of the neutron absorber handling rod. 2. A fast reactor comprising:a plurality of fuel assemblies forming a reactor core;a reactivity control assembly including a reactor shutdown rod of a backup reactor shutdown system and sectional neutron absorbers disposed around the reactor shutdown rod to suppress initial surplus reactivity, the reactor shutdown rod and the neutron absorbers being arranged in a hexagonal barrel-shaped wrapper tube at the center of the reactor core;a core barrel surrounding outer periphery of the reactor core;a reflector surrounding the outer periphery of the core barrel and adapted to move up and down;a bulkhead surrounding outer periphery of the reflector and forming an inner wall of a coolant flow channel of primary coolant;an upper support plate supporting the core barrel and the bulkhead;an intermediate heat exchanger arranged in an annular space above the upper support plate;an electromagnetic pump arranged below the intermediate heat exchanger;a reactor vessel containing the fuel assemblies, the reactivity control assembly, the reflector, the bulkhead, the intermediate heat exchanger and the electromagnetic pump and including an upper opening;an upper plug plugging the upper opening of the reactor vessel;a reactor shutdown rod drive mechanism for causing an inner extension tube to fall and to release the reactor shutdown rod by a gripper section that includes latch fingers, at a lowermost end of an outer extension tube by turning off power supply to a holding magnet at a time of scram; anda plurality of units of neutron absorber drive mechanism, each including a dual tube drive shaft including an outer extension shaft and an inner extension shaft, the outer extension shaft being adapted to be pulled up to allow both of the inner and outer extension shafts to be inserted and pushed down after getting to a handling head section of the neutron absorber so as to grasp the neutron absorber externally by the latch fingers of the gripper section and hang up entirely with the drive shaft to individually move the neutron absorber up and down, wherein the reactor shutdown rod drive mechanism and the neutron absorber drive mechanism are integrally formed and arranged at a center of the upper plug,wherein:the reactor shutdown rod drive mechanism includes:a latch link for opening the holding magnet when the holding magnet is de-excited to release the inner extension tube,a rod vertically running through the holding magnet;an armature arranged under the holding magnet in contact with the holding magnet, anda backup de-latch drive motor for forcibly releasing the armature from the holding magnet by pushing down the rod and by turn pushing down the armature by means of the rod. 3. A fast reactor comprising:a plurality of fuel assemblies forming a reactor core;a reactivity control assembly including a reactor shutdown rod of a backup reactor shutdown system and sectional neutron absorbers disposed around the reactor shutdown rod to suppress initial surplus reactivity, the reactor shutdown rod and the neutron absorbers being arranged in a hexagonal barrel-shaped wrapper tube at the center of the reactor core;a core barrel surrounding outer periphery of the reactor core;a reflector surrounding the outer periphery of the core barrel and adapted to move up and down;a bulkhead surrounding outer periphery of the reflector and forming an inner wall of a coolant flow channel of primary coolant;an upper support plate supporting the core barrel and the bulkhead;an intermediate heat exchanger arranged in an annular space above the upper support plate;an electromagnetic pump arranged below the intermediate heat exchanger;a reactor vessel containing the fuel assemblies, the reactivity control assembly, the reflector, the bulkhead, the intermediate heat exchanger and the electromagnetic pump and including an upper opening;an upper plug plugging the upper opening of the reactor vessel;a reactor shutdown rod drive mechanism for causing an inner extension tube to fall and to release the reactor shutdown rod by a gripper section that includes latch fingers, at a lowermost end of an outer extension tube by turning off power supply to a holding magnet at a time of scram; anda plurality of units of neutron absorber drive mechanism, each including a dual tube drive shaft including an outer extension shaft and an inner extension shaft, the outer extension shaft being adapted to be pulled up to allow both of the inner and outer extension shafts to be inserted and pushed down after getting to a handling head section of the neutron absorber so as to grasp the neutron absorber externally by the latch fingers of the gripper section and hang up entirely with the drive shaft to individually move the neutron absorber up and down, wherein the reactor shutdown rod drive mechanism and the neutron absorber drive mechanism are integrally formed and arranged at a center of the upper plug,wherein:the units of the neutron absorber drive mechanism are arranged around the reactor shutdown rod drive mechanism at regular intervals;the drive shaft of each of the units of the neutron absorber drive mechanism has a dual tube structure having the outer extension shaft and the inner extension shaft offset midway relative to each other, the gripper section being arranged at a bottom end of the inner extension shaft to externally grasp the handling head of the neutron absorber, a drive shaft supporting stopper being arranged at a top end of the inner extension shaft; andan entire outer housing has a sealed structure in addition to the cover gas seal section arranged on the upper surface of the upper plug. 4. The fast reactor according to claim 1, whereinthe reactor shutdown rod drive mechanism includes: an extension tube latch mechanism for hanging up an upper part of the outer extension tube; anda power cylinder arranged in the extension tube latch mechanism for pushing up only the outer extension tube; whereinthe latch finger grasping the reactor shutdown rod handling head is closed to allow the reactor shutdown rod to make a freefall when the outer extension tube is pushed up by the power cylinder. 5. The fast reactor according to claim 1, whereina large rectifier plate is arranged at a lower end of a protection barrel to allow entire reactor core to be projected on it. 6. The fast reactor according to claim 1, further comprising:a fuel loading/unloading machine inserted into an opening of the upper plug produced when the reactivity control assembly drive mechanism is removed; whereinthe fuel loading/unloading machine includes:a winching mechanism supported on a base arranged above the opening of the upper plug so as to be capable of horizontally moving in mutually orthogonal two directions; anda support mechanism for temporarily storing the fuel assembly hung up by the winching mechanism. 7. The fast reactor according to claim 1, further comprising:fuel loading/unloading rails of at least two routes arranged on a ceiling of a reactor building containing the reactor vessel to support the fuel loading/unloading machine, allowing the fuel loading/unloading machine to move in horizontal directions;a reactor pit plug arranged above the upper plug at the height of the ceiling of the reactor building; anda floor door valve capable of rotating around a vertical axis relative to the reactor pit plug and capable of opening, whereinthe winching mechanism being arranged above an opening of the floor door valve so as to be able to move to right above all of the plurality of fuel assemblies in the reactor core. 8. The fast reactor according to claim 2, whereinthe reactor shutdown rod drive mechanism includes: an extension tube latch mechanism for hanging up an upper part of the outer extension tube; anda power cylinder arranged in the extension tube latch mechanism for pushing up only the outer extension tube; whereinthe latch finger grasping the reactor shutdown rod handling head is closed to allow the reactor shutdown rod to make a freefall when the outer extension tube is pushed up by the power cylinder. 9. The fast reactor according to claim 2, whereina large rectifier plate is arranged at a lower end of a protection barrel to allow entire reactor core to be projected on it. 10. The fast reactor according to claim 2, further comprising:a fuel loading/unloading machine inserted into an opening of the upper plug produced when the reactivity control assembly drive mechanism is removed; whereinthe fuel loading/unloading machine includes:a winching mechanism supported on a base arranged above the opening of the upper plug so as to be capable of horizontally moving in mutually orthogonal two directions; anda support mechanism for temporarily storing the fuel assembly hung up by the winching mechanism. 11. The fast reactor according to claim 2, further comprising:fuel loading/unloading rails of at least two routes arranged on a ceiling of a reactor building containing the reactor vessel to support the fuel loading/unloading machine, allowing the fuel loading/unloading machine to move in horizontal directions;a reactor pit plug arranged above the upper plug at the height of the ceiling of the reactor building; anda floor door valve capable of rotating around a vertical axis relative to the reactor pit plug and capable of opening, whereinthe winching mechanism being arranged above an opening of the floor door valve so as to be able to move to right above all of the plurality of fuel assemblies in the reactor core. 12. The fast reactor according to claim 3, whereinthe reactor shutdown rod drive mechanism includes: an extension tube latch mechanism for hanging up an upper part of the outer extension tube; anda power cylinder arranged in the extension tube latch mechanism for pushing up only the outer extension tube; whereinthe latch finger grasping the reactor shutdown rod handling head is closed to allow the reactor shutdown rod to make a freefall when the outer extension tube is pushed up by the power cylinder. 13. The fast reactor according to claim 3, whereina large rectifier plate is arranged at a lower end of a protection barrel to allow entire reactor core to be projected on it. 14. The fast reactor according to claim 3, further comprising:a fuel loading/unloading machine inserted into an opening of the upper plug produced when the reactivity control assembly drive mechanism is removed; whereinthe fuel loading/unloading machine includes:a winching mechanism supported on a base arranged above the opening of the upper plug so as to be capable of horizontally moving in mutually orthogonal two directions; anda support mechanism for temporarily storing the fuel assembly hung up by the winching mechanism. 15. The fast reactor according to claim 3, further comprising:fuel loading/unloading rails of at least two routes arranged on a ceiling of a reactor building containing the reactor vessel to support the fuel loading/unloading machine, allowing the fuel loading/unloading machine to move in horizontal directions;a reactor pit plug arranged above the upper plug at the height of the ceiling of the reactor building; anda floor door valve capable of rotating around a vertical axis relative to the reactor pit plug and capable of opening, whereinthe winching mechanism being arranged above an opening of the floor door valve so as to be able to move to right above all of the plurality of fuel assemblies in the reactor core. |
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summary | ||
052157075 | abstract | An instrument thimble tube shroud is disclosed which has a central cup surrounding an instrument thimble tube to prevent fluid flow about the thimble tube from causing excessive vibration and wear. A plurality of arms extend radially from the cup and have locking pads disposed at the end of each arm, springs extending from the pads engaging recesses in an adjacent fuel assembly nozzle to lock the shroud in position and prevent movement of the shroud or rotation due to aggressive fluid flow. Utilizing the inventive shroud prevents vibration and damage to the instrument thimble tube passing therethrough, enhancing life of the instrumentation and allowing continued observation of dynamics within a nuclear reactor. |
059862750 | claims | 1. An apparatus permitting radioactive marking of nuclear images, said apparatus comprising: a body comprising an elongated spring, said elongated spring having a first end and a second end; a chamber mounted to said first end of said elongated spring, said chamber having an opening; and a radiation-shielding shutter, said shutter being mounted to said second end of said elongated spring and having an aperture therein, said aperture having a first position out of alignment with said opening in said chamber and a second position in alignment with said opening in said chamber; said elongated spring normally biasing said aperture of said shutter into said first position out of alignment with said opening in said chamber; wherein a hand force may be applied against the bias of said elongated spring to move said aperture of said shutter into said second position in alignment with said opening in said chamber and wherein releasing said elongated spring returns said aperture to said first position out of alignment with said opening in said chamber such that said radiation-shielding shutter occludes said opening in said chamber. 2. The apparatus of claim 1, wherein said chamber is provided with a radionuclide retaining means, said retaining means being configured to permit replacement of said radionuclide once said radionuclide has decayed. 3. The apparatus of claim 2, wherein said radionuclide retaining means is an absorbent textile. 4. The apparatus of claim 2, wherein said radionuclide is technetium 99 pertechnetate. 5. The apparatus of claim 1, wherein said sprung is provided with pads to permit the application of a force against said bias by an operators hand. 6. The apparatus of claim 1, wherein said radiation-shielding materials are comprised of lead. 7. A method for marking a location on a nuclear age, comprising applying a bias against the spring of the apparatus of claim 1 such that said shutter aperture is brought into alignment with said chamber which contains a source of radiation, maintaining said shutter aperture in alignment with said chamber for a period of time sufficient to emit radiation sufficient to mark said image, and releasing said force so that said shutter is biased from said chamber so that said chamber is occluded by said shutter and said shutter aperture is not in alignment with said shutter. 8. The method of claim 7, wherein said period of time is approximately 1-3 seconds. |
056174578 | summary | CROSS-REFERENCE TO RELATED APPLICATION This application is a Continuation of International Application PCT/DE94/00256, filed Mar. 4, 1994. BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a pressurized-water reactor having a multiplicity of fuel assemblies being mutually adjacently disposed in the interior of a pressure vessel on a core support at the bottom of the pressure vessel, each of the fuel assemblies containing a bundle of fuel rods disposed around control-rod guide tubes and being supported at apertures in a grid plate by a top carrying a top plate covering the bundle, a plenum being formed above the grid plate inside the pressure vessel, attachments protruding into the plenum at the upper surface of the grid plate, the plenum having a lateral outlet, and the pressure vessel having a device for deflecting a coolant flow from an inlet into the pressure vessel through the core support, for distributing it over the individual fuel assemblies and for guiding it along the fuel rods, through passage openings in the top plates of the fuel assemblies and through apertures in the grid plate into the plenum. Fuel assemblies of pressurized-water reactors contain a bundle of fuel rods which are disposed around control-rod guide tubes, with the bundle of fuel rods being covered by a top plate in the top of the fuel assembly. Inside a pressure vessel, a multiplicity of such fuel assemblies are disposed adjacently on a core support at the bottom of the pressure vessel and are supported with their top parts on the apertures of a grid plate. Formed above the grid plate inside the pressure vessel is a plenum into which attachments on the upper surface of the grid plate protrude. The plenum contains a lateral outlet, such as one or more outlet nozzles for a coolant flow. The coolant flow is guided by appropriate devices from an inlet in the pressure vessel to the core support at the bottom of the pressure vessel, is distributed there over the individual fuel assemblies, then flows along the fuel rods and emerges through passage openings in the top plates of the fuel assemblies in order to enter the plenum through the apertures in the grid plate. In this case, the core support at the bottom of the pressure vessel can already carry throttle plates or inserts in order to distribute the coolant flow uniformly over the entire cross section of the pressure vessel. The interstices between the fuel rods and the guide tubes of a fuel assembly are connected to one another and to the interstices between adjacent fuel assemblies so that coolant flows directed transversely to the fuel assemblies can occur in the pressure vessel. This may be desirable in order to achieve thorough mixing between hotter and cooler regions of the coolant, for which purpose spacers with appropriate deflection devices may be provided on different axial planes of the fuel assembly. Such spacers are required in any case in order to fix the lateral spacing of the fuel rods. However, apart from such spacers supporting the fuel rods, their own grid structures may also be provided additionally to hold further mixing devices on the fuel assemblies. The attachments which protrude from the upper surface of the grid plate into the dome of the pressure vessel (that is to say the plenum for the coolant heated on the fuel rods) are necessary, for example, to support the grid plate mechanically and to receive the control rods which can be introduced into the control-rod guide tubes. The partial flows of the coolant, into which the coolant is divided at the lower core support and which emerge after flowing through the individual fuel assemblies through the individual apertures in the grid plate, therefore have to overcome an individual flow resistance on their path to the outlet, which flow resistance is determined by the length of the respective flow path and the obstacles disposed in that path. A pressure thus occurs in the coolant when passing through the passage openings in the plates, which pressure is distributed inhomogeneously over the cross section of the pressure vessel. When passing through the top plates, the coolant thus suffers damming-up which, due to the geometrical configuration of the attachments on the top plate and of the lateral outlet, may be different for each fuel assembly and already leads to pressure differences and resultant transverse flows in the axial zone of the pressure vessel in which the fuel rods are seated. The pressure differences are already one of the causes of bending of the fuel rods and fuel assemblies. Additionally, the transverse flows cause the fuel rods and the structural elements of the fuel assemblies to vibrate and to be subjected to mechanical loading. In total, other physical loads on the fuel assemblies are thus intensified, in such a way that damage may occur on the fuel assemblies. In order to avoid horizontal pressure differences and transverse flows, the coolant can be guided vertically through the plenum in the dome of the pressure vessel and conducted away through corresponding vertical outlet nozzles which take into account the geometry of the attachments on the grid plate. However, that leads to a complicated construction or an impermissible structural height of the pressure vessel. SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a pressurized-water reactor with individually adapted pressure distribution in the coolant, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which avoids an inhomogeneous flow speed inside a reactor pressure vessel in such reactors with undesirable transverse flows in an axial region in which the fuel rods are seated, through the use of an individual adaptation of flow conditions in a region of the tops of the fuel assemblies and of a grid plate supporting the tops. This object is achieved by an individual throttling of the coolant flow when it passes through the individual tops of the fuel assemblies or, at the latest, when it passes through the grid plate. With the foregoing and other objects in view there is provided, in accordance with the invention, a pressurized-water reactor, comprising a pressure vessel having a bottom, an inlet, a lateral outlet, and an interior; a core support disposed at the bottom of the pressure vessel; a grid plate having apertures formed therein and having an upper surface, the grid plate defining a plenum above the grid plate in the interior of the pressure vessel, the plenum leading to the lateral outlet; plenum attachments protruding into the plenum at the upper surface of the grid plate; a multiplicity of mutually adjacent fuel assemblies disposed in the interior of the pressure vessel on the core support, each of the fuel assemblies containing a bundle of fuel rods and a top carrying a top plate covering the bundle and having passage openings formed therein, and each of the fuel assemblies being disposed around control-rod guide tubes and being supported at the apertures in the grid plate by the top; a device disposed in the pressure vessel for deflecting a coolant flow from the inlet, into the pressure vessel and through the core support, for distributing the coolant flow over the individual fuel assemblies and for guiding the coolant flow along the fuel rods, through the passage openings in the top plates of the fuel assemblies, through the apertures in the grid plate and into the plenum; and throttle plates each being attached in the top of a respective one of a plurality of the fuel assemblies, the throttle plates having throttle openings formed therein for an individual adaptation of pressure in the coolant flowing through the top of the respective fuel assembly. These features provide such an individual throttling when the flow passes through the top of the fuel assembly. In accordance with another feature of the invention, the throttle openings in the throttle plate have a smaller cross section than the passage openings in the top plate, the throttle openings have a cross-sectional area, and the greatest part of the cross-sectional area of the throttle openings is disposed above the passage openings in the top plate. In accordance with a further feature of the invention, the throttle plate is attached releasably in the top of the fuel assembly. In accordance with an added feature of the invention, the throttle plate and the top plate are bolted together to an upper end of the control-rod guide tubes. In accordance with an additional feature of the invention, there are provided common holding-down devices holding the top plate and the throttle plate in the top of the fuel assembly. In accordance with yet another feature of the invention, each of the throttle plates is disposed above a respective one of the top plates. With the objects of the invention in view, there is also provided a pressurized-water reactor, comprising a pressure vessel having a bottom, an inlet, a lateral outlet, and an interior; a core support disposed at the bottom of the pressure vessel; a grid plate having apertures formed therein and having an upper surface, the grid plate defining a plenum above the grid plate in the interior of the pressure vessel, the plenum leading to the lateral outlet; plenum attachments protruding into the plenum at the upper surface of the grid plate; a multiplicity of mutually adjacent fuel assemblies disposed in the interior of the pressure vessel on the core support, each of the fuel assemblies containing a bundle of fuel rods and a top and being supported by the top at the apertures in the grid plate; a device disposed in the pressure vessel for deflecting a coolant flow from the inlet into the pressure vessel, for distributing the coolant flow through the core support over the individual fuel assemblies and for guiding the coolant flow along the fuel rods, through the tops of the fuel assemblies and the apertures in the grid plate and into the plenum; and throttle elements associated with a plurality of the apertures in the grid plate, the throttle elements each having at least one passage opening formed therein for an individual adaptation of pressure in the coolant emerging from the tops of the fuel assemblies supported at the apertures in the grid plate. These features provide a corresponding individual throttling when the flow passes through the apertures in the grid plate. In accordance with a concomitant feature of the invention, the throttle inserts are inserted in the apertures in the grid plate. Correspondingly, a throttle plate may thus be attached in the top of a plurality of fuel assemblies (in particular in each case above the top plate). The throttle plate contains one or more throttle openings for the individual adaptation of the pressure in the coolant which flows through the top of the respective fuel assembly. However, a plurality of grid apertures, on which the respective fuel assemblies are supported, may also have throttle elements in each case with one or more passage openings which bring about the individual adaptation of the pressure in the coolant that flows through the top of the fuel assemblies. 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 pressurized-water reactor with individually adapted pressure distribution in the coolant, 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. |
claims | 1. A method of generating extremely short-wave radiation, in which a medium is transported through a vacuum space and each time a part of the medium in the vacuum space is irradiated with a pulsed and focused energy-rich laser beam, said part of the medium being converted into a plasma emitting extremely short-wave radiation, characterized in that the medium is embedded in at least a viscous flow of rare gas which is transported through the vacuum space parallel to the direction of movement of the medium. 2. A method as claimed in claim 1 , characterized in that at least two viscous flows of rare gas are passed through a part of the vacuum space in which a part of the medium, which is not yet irradiated, propagates. claim 1 3. A method as claimed in claim 1 , characterized in that helium gas is used as a rare gas. claim 1 4. A method as claimed in claim 1 , characterized in that a metal is used as a medium which, upon irradiation with a laser beam, forms a plasma emitting extremely short-wave radiation. claim 1 5. A method as claimed in claim 1 , characterized in that a continuous flow of individual liquid droplets is used as a medium which, upon irradiation with a laser beam, forms a plasma emitting extremely short-wave radiation. claim 1 6. A method as claimed in claim 5 , characterized in that water droplets are used as liquid droplets. claim 5 7. A method as claimed in claim 1 , characterized in that a clustered gas is used as a medium which, upon radiation with a laser beam, forms a plasma emitting extremely short-wave radiation. claim 1 8. A method as claimed in claim 7 , characterized in that the gas is xenon. claim 7 9. A method of manufacturing a device, in which the dimensions of the smallest details are smaller than 0.25 xcexcm, on a substrate, in which method different layers of the device are formed in successive steps by imaging by means of EUV radiation, for each layer, first a specific mask pattern on the substrate coated with a radiation-sensitive layer and by subsequently removing material from, or adding material to, areas marked by the mask image, characterized in that the EUV radiation is generated by means of the method as claimed in any one of claim 1 . claim 1 10. An extremely short-wave radiation source unit comprising: a source space connected on a first side to a vacuum pump; an inlet device provided on a second side of the source space for introducing the medium into the source space; a pulsed high-power laser, and an optical system for focusing the laser beam supplied by the laser on a fixed position within the source space where the mobile medium passes, characterized in that the source space on the second side is connected to a rare gas inlet for establishing a viscous flow of rare gas in the source space enveloping the medium, which flow is parallel to the direction of movement of the medium. 11. An extremely short-wave radiation source unit as claimed in claim 10 , in which the source space is enclosed by a wall having apertures for causing the laser beam to enter into and exit from the source space and for causing the generated extremely short-wave radiation to exit from the source space, characterized in that a tube is arranged in the source space on the second side of the source space and parallel to the direction of movement of the medium, which tube is connected to said inlet for establishing the viscous flow of rare gas. claim 10 12. An extremely short-wave radiation source unit as claimed in claim 11 , characterized in that a second tube is arranged parallel to the first tube in the source space, which second tube is connected to said inlet for establishing a second viscous flow of rare gas parallel to the direction of movement of the medium. claim 11 13. An extremely short-wave radiation source unit as claimed in claim 10 , characterized in that the source space is formed by a first closed part on the first side, a second closed part on the second side and a central part which communicates with the ambience, in that the wall of the second source space part is formed by a tube which is connected to said rare gas inlet, and in that the wall of the tube and the wall of the first source space part have such a shape at the area of the central part of the source space that they constitute an ejector geometry. claim 10 14. An extremely short-wave radiation source unit as claimed in claim 10 , characterized in that the source space is formed by a first closed part on the first side, a second closed part on the second side and a central part which communicates with the ambience, in that the wall of the second source space part is formed by an annular tube which is connected to said rare gas inlet, and in that the wall of the tube and the wall of the first source space part have such a shape at the area of the central part of the source space that they constitute an annular ejector geometry. claim 10 15. An extremely short-wave radiation source unit as claimed in claim 10 , characterized in that the inlet device is a device for transporting a metal tape or wire through the source space. claim 10 16. An extremely short-wave radiation source unit as claimed in claim 10 , characterized in that the inlet device has a tube for introducing a mobile medium into the source space. claim 10 17. An extremely short-wave radiation source unit as claimed in claim 16 , characterized in that the mobile medium is formed by liquid droplets. claim 16 18. An extremely short-wave radiation source unit as claimed in claim 17 , characterized in that the liquid droplets are water droplets. claim 17 19. An extremely short-wave radiation source unit as claimed in claim 16 , characterized in that the mobile medium is formed by a clustered gas. claim 16 20. An extremely short-wave radiation source unit as claimed in claim 19 , characterized in that the gas is xenon. claim 19 21. An extremely short-wave radiation source unit as claimed in claim 16 , characterized in that the inlet device comprises means for causing the tube for the mobile medium to vibrate. claim 16 22. A lithographic projection apparatus for imaging a mask pattern on a substrate provided with a radiation-sensitive layer, which apparatus comprises an illumination system for illuminating the mask pattern and a projection system for imaging the illuminated mask pattern on the substrate, the illumination system comprising an EUV radiation source, while the optical components of the illumination system and those of the projection system are present in a vacuum space, characterized in that the EUV radiation source is a radiation source unit as claimed in claim 10 . claim 10 |
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description | The present invention relates to a fixed cluster for a pressurized water nuclear reactor core of the type comprising: rods which are intended to be inserted into guide tubes of a nuclear fuel assembly, a support for the rods from which the rods extend in a longitudinal direction in a direction which is intended to be orientated vertically downwards when the fixed cluster is arranged on a nuclear fuel assembly, and at least one element for longitudinal abutment against the upper plate of the core of the nuclear reactor. In conventional manner, a nuclear fuel assembly comprises a bundle of nuclear fuel rods and a support skeleton for these rods. The skeleton comprises a lower nozzle, an upper nozzle and guide tubes which connect these two nozzles and which are intended to receive the rods of movable clusters for controlling the operation of the core of the nuclear reactor. Each movable cluster comprises a bundle of neutron-absorbing rods which are retained by a support. This support is generally referred to as a “spider” and is constituted by an upper head around which fins are distributed and are provided with members for mounting the neutron-absorbing rods. During an operating cycle of the core, the movable clusters will be displaced in order to introduce to a greater or lesser extent their rods into the corresponding guide tubes and thus to control the reactivity in the core of the nuclear reactor. In a nuclear reactor core, some nuclear fuel assemblies are not provided with movable clusters but instead are provided with clusters which are referred to as fixed clusters since they are not subjected to controlled movement during an operating cycle of the core. This is particularly the case for burnable poison clusters. At least some of the rods thereof comprise a burnable neutron poison which will allow the concentration of boron dissolved in the water of the cooling system to be reduced, primarily at the beginning of a cycle. This is also the case for end plug clusters with which some assemblies are provided. The rods of these end plug clusters occupy the guide tubes of the relevant assemblies in order to limit the hydraulic flow around the adjacent fuel assemblies which are themselves provided with movable clusters. This is also the case for neutron source clusters. These clusters which may be primary source clusters or secondary source clusters are involved in the start-up phases in order to initiate the reaction and/or calibrate the counting chains of the nuclear reactor. Document JP-7/218 672 discloses a fixed cluster of the above-mentioned type which is, more specifically, a burnable poison cluster. The rod support is constituted by a perforated plate which is provided at the center thereof with a cylindrical guide which extends upwards. This cylindrical guide can slide vertically relative to a bar which is in abutment below the upper plate of the core. The yoke arm extends through the water passage hole which is provided in the upper plate of the core above the relevant nuclear fuel assembly. A spring extends around the cylindrical guide between the rod support and the yoke arm. The spring acts counter to the upward movement of the support under the action of the hydraulic force of the water of the cooling system. Generally, movable clusters bring about lower pressure drops in the water of the cooling system than fixed clusters. In this manner, the ascending flow rate of the water of the cooling system will be greater through the assemblies which are provided with movable clusters than in assemblies which are provided with fixed clusters. This excess flow will become evident as an increased application force of the rods of the movable clusters in the cluster guides arranged above the upper core plate and with significant vibrations of the rods. These vibrations are caused by the flows of water which tend to develop, downstream of the assemblies which have an excessive supply of water from the cooling system and the assemblies which have an inadequate supply, in order to rebalance the distribution of water. In order to reduce the pressure drops caused by the fixed clusters, and therefore to reduce the above-mentioned difficulties, JP-7/218 672 has modified the shape of the rods of a fixed cluster in order to increase the flow rate inside the guide tubes of the nuclear fuel assembly. Although this solution allows the pressure drop to be reduced, it is also accompanied by a degradation of the cooling of the nuclear fuel rods of the associated assembly, since water flows in preference in the guide tubes rather than around the nuclear fuel rods. An object of the invention is therefore to solve this problem by providing a fixed cluster of the above-mentioned type which brings about smaller pressure drops in the water of the cooling system without impairing the performance of the core. The invention provides a fixed cluster of the above-mentioned type, characterised in that the support comprises: an upper head which has a longitudinal center axis, fins which extend radially outwards from the upper head, systems for mounting the rods so as to be distributed on the fins, and at least two elements for abutment against the upper plate of the core, which abutment elements each protrude longitudinally from a respective fin, beyond the mounting systems, in a direction which is intended to be orientated vertically upwards when the fixed cluster is arranged on a nuclear fuel assembly. According to specific embodiments, the fixed cluster may comprise one or more of the following features, taken in isolation or according to any technically possible combination: the abutment elements are arranged angularly about the longitudinal center axis in a substantially regular manner; the support comprises two abutment elements which are arranged in a substantially diametrically opposed manner relative to the longitudinal center axis; at least one portion of the upper head and the fins are integral; the mounting systems comprise members for receiving the upper ends of the rods and the nuts which are screwed to the upper ends in order to fix rods in the receiving members; the nuts protrude longitudinally from the members in a direction which is intended to be orientated vertically upwards when the fixed cluster is arranged on a nuclear fuel assembly, and nuts are arranged at various levels along the longitudinal center axis; the upper ends of the rods comprise shanks which extend through the nuts and which are welded to the nuts; and at least one fin comprises a passage for receiving an instrument. The invention also provides a core of a pressurized water nuclear reactor comprising an upper plate, a lower plate and nuclear fuel assemblies which are arranged between the upper plate and lower plate, the core further comprising fixed clusters and movable clusters which are arranged on respective nuclear fuel assemblies, the fixed clusters each comprising: rods which are intended to be inserted into guide tubes of the respective nuclear fuel assembly, a support for the rods from which the rods extend in a longitudinal direction in a direction which is intended to be orientated vertically downwards when the fixed cluster is arranged on the respective nuclear fuel assembly, at least one element for longitudinal abutment against the upper plate of the core of the nuclear reactor,characterised in that at least one of the fixed clusters is a fixed cluster as defined above, the abutment elements of the fixed cluster being in vertical abutment against the upper plate around a water passage hole which is provided in the upper plate above the nuclear fuel assembly on which the fixed cluster is arranged. According to one variant, at least one movable cluster comprises: rods which are intended to be inserted into guide tubes of the respective nuclear fuel assembly, a support for the rods from which the rods extend in a longitudinal direction in a direction which is intended to be orientated vertically downwards when the movable cluster is arranged on the respective nuclear fuel assembly; the shapes of the supports for the fixed cluster and the movable cluster are similar. According to another variant, the fixed cluster and the movable cluster are adjacent. The invention also provides an assembly comprising a nuclear fuel assembly and a fixed cluster which is capable of being arranged on the nuclear fuel assembly, characterised in that the fixed cluster is a fixed cluster as defined above. FIG. 1 illustrates a fixed cluster 1 for a pressurized water nuclear reactor (PWR). It is, for example, an end plug assembly. The cluster 1 principally comprises rods 3 and a support 5. The support 5 has a shape which is generally similar to that used in the prior art for movable clusters, with the exception of the main differences which are highlighted in the remainder of the description. This support 5, which can therefore be referred to as a “spider”, principally comprises: an upper head 7 whose longitudinal center axis C is intended to be orientated vertically when the cluster 1 is arranged on a nuclear fuel assembly in a nuclear reactor core, fins 9 which extend radially outwards from the upper head 7 and which are distributed angularly in a substantially regular manner about the axis C, and systems 10 for mounting the rods 3 on the support 5. The support 5 is produced from metal which withstands radiation, for example, steel such as the steel AISI 304. The upper head 7 has a hollow cylindrical shape with a circular base. It comprises a lower portion 11 from which the fins 9 extend. This lower portion 11 is, for example, integral with the fins 9, as described in document FR-2 742 912 and the corresponding document U.S. Pat. No. 5,889,832. The lower portion 11 of the upper head 7 and the fins 9 can be produced by means of moulding, machining or electro-erosion. The support 5 further comprises a back up ring 12 on the upper nozzle of the nuclear fuel assembly with which the cluster 1 is intended to be associated. This ring 12 comprises a collar 13 (FIG. 3) which may press downwards against a lower edge 15 of the upper head 7. The collar 13 is thus retained inside the central hole 17 provided in the upper head 7. The upper portion 19 of the upper head 7 is attached to the lower portion 11 and is fixed thereto, for example, by means of screwing, welding, soldering or adhesive-bonding. In the upper portion 19, the hole 17 terminates in an upper portion 20 which forms a cavity for coupling the upper head 7 to a tool for handling the fixed cluster 1. A thrust spring 21 is arranged in the hole 17 and is supported with the lower end thereof on the collar 13 and with the upper end thereof on an internal partition 23 which is provided inside the upper portion 19 of the upper head 7. The ring 12 can be moved by means of translation between a lowered position (FIGS. 1 and 3) and a raised position which is not illustrated. The spring 21 is compressed when the ring 12 moves into the raised position and returns the ring 12 towards the lowered position thereof. The fins 9 each comprise a radially inner portion 25 and a radially outer portion 27. The inner portions 25 have heights, taken along the center axis C, greater than those of the outer portions 27. The mounting systems 10 comprise members 29 for receiving the rods 3 and nuts 31 for fixing the rods 3 in the members 29. The members 29 are distributed on the fins 9 in a pattern which is similar to that of the distribution of the guide tubes in the nuclear fuel assembly for which the cluster 1 must be provided. This distribution can be seen in particular in FIG. 2. The majority of the fins 9 are provided with two members 29. Some of the members 29 are provided on inner portions 25 and others on outer portions 27. The members 29 have substantially the same height, taken along the axis C, as the portion 25 or 27 on which they are provided. However, a fin 9 may comprise, at a location corresponding to a guide tube, a passage 30 for receiving an instrument in place of a member 29. Each member 29 is provided for receiving an extension 33 of the end plug of a rod 3. In the example illustrated, each extension 33 comprises a portion 35 having a reduced cross-section, then extends through a hole 37 provided in the corresponding member 29. A nut 31 is screwed onto the upper end of the extension 33, this upper end protruding upwards beyond the relevant member 29. An end shank 39 protrudes upwards from the upper end of the extension 33 and extends through the nut 31. This end shank 39 has been molten and welded to the nut 31, thus blocking the nut 31 in terms of rotation relative to the rod 3 in question. The rods 3 are thus fixed to the support 5 and extend downwards from the support, parallel with the axis C. The rods 3 form a bundle with a distribution which corresponds to that of the members 29 and therefore that of the guide tubes of the nuclear fuel assembly for which the cluster 1 is intended. The members 29 are, in the example illustrated, integral with the fins 9 and have been produced at the same time as the fins and the lower portion 11 of the upper head 7. In contrast to what has been provided in the prior art for movable clusters, the fixed cluster 1 according to the invention comprises two fins 9 which have a greater radial length and whose radial ends are extended longitudinally upwards, each by an element 41 for support on the upper core plate of a nuclear reactor. In the example illustrated, the cluster 1 comprises two elements 41 which are provided on fins 9 which are diametrically opposed relative to the center axis C. Since the abutment elements 41 have a similar structure, only one will be described below. The abutment element 41 is in the form of a bar and it is integral with the fin 9. The abutment element 41 is therefore a rigid and solid element with significant radial spacing relative to the upper head 7. The abutment element 41 is arranged radially outwards relative to the adjacent nut 31 and protrudes upwards from the outer portion 27 of the associated fin 9 beyond the nut 31 in question. This can be seen in particular in FIG. 3. The radially inner surface 43 (FIG. 1) of the support element 41 is concave in the example illustrated in order to allow a tool to manoeuvre the nut 31. FIG. 4 illustrates the cluster 1 of FIGS. 1 to 3 which is provided in a nuclear fuel assembly 45 in a core 47 of a pressurized water nuclear reactor. In FIG. 4, only the support 5 of the cluster 1 has been illustrated and the rods 3 have not been illustrated. For the assembly 45, only the upper nozzle 49 is visible. It is also possible to see in this FIG. 4 a portion of the upper plate 51 of the core 47 and a pin 53 for positioning the assembly 45. In conventional manner, a hole 55 for the passage of water is provided in the upper plate 51 opposite the upper nozzle 49 of the assembly 45. In contrast to what has been provided in the prior art, the hole 55 is not partially blocked by a yoke arm of the fixed cluster 1 but instead the abutment of the fixed cluster 1 on the upper plate 51 is provided by the elements 41. More specifically, the elements 41 are in longitudinal abutment against the upper plate 51 around the hole 55. The cluster 1 is further in abutment against the upper nozzle 49 of the assembly 45 via the ring 12, thus compressing the spring 21. For reasons of simplification, this compression of the spring 21 has not been illustrated in FIG. 4. As indicated above, owing to the presence of the support elements 41, it is not necessary to provide a yoke arm which extends through the hole 55. The pressure drop brought about by the fixed cluster 1 is therefore reduced. This pressure drop is further reduced owing to the use of a support 5 which is in the form of a spider, that is to say, with a central upper head 7 and fins 9 which are distributed around it. This is illustrated by FIGS. 5 and 6 where the cross-hatched zones correspond to the flow cross-sections of the water of the cooling system downstream of the upper nozzle of a nuclear fuel assembly. The surface of the water flow cross-section Z2 with a fixed cluster 1 according to the invention (FIG. 6) is approximately 50% greater than the flow cross-section Z1 of a fixed cluster according to the prior art (FIG. 5). The pressure drop is further reduced owing to the streamlined shape of the support 5 and the fact that the spring 21 is arranged inside the upper head 7 and not at the outer side of the support 5 as in the prior art for fixed clusters. Furthermore, this reduction of the pressure drop is not accompanied by a deterioration of the cooling of the nuclear fuel rods and does not therefore impair the performance of the core. The use of a support 5 which has a spider-like structure also allows the structure of fixed clusters to be made more similar to that of movable clusters and therefore allows the differences between the pressure losses brought about by the different clusters within the same core 47 to be reduced. In this manner, in a preferred embodiment, in a nuclear reactor core 47, fixed and movable clusters 1 are used with supports 5 which have spider-like shapes. The distribution of water is more homogeneous in the nuclear fuel assemblies which prevents the associated problems, and in particular the transverse balancing flows. Furthermore, such a core 47 also allows a single type of handling tool to be used in order to manipulate the fixed clusters and the movable clusters. It can be seen that, in such a core, the shapes of the movable cluster supports may be slightly different from those of the fixed clusters, in particular in that they do not comprise an abutment element 41 which would prevent their free passage through the water passage hole 55 of the upper plate 51 of the core 47. In the same manner, only some movable and fixed clusters 1 may have supports 5 with similar shapes. Preferably, such movable and fixed clusters 1 with similar supports will be adjacent in the core 47. It can also be seen that, in the fixed cluster 1 of FIGS. 1 to 4, the position of the nuts 31 at different levels along the center axis C also allows the engagement of a handling tool to be facilitated. The engagement of such a tool, which comprises a housing for receiving the upper head 7 and the nuts 31, is carried out first of all via the upper portion 19 of the upper head 7, then via the nuts 31 which are located at the highest level and finally by the nuts 31 which are located at the lowest level. The stepped engagement of the nuts 31 allows it to be ensured that the relative position of the tool and the support 5 is correct and therefore allows this engagement to be carried out more rapidly. Furthermore, it can be seen that the retention force applied by the fixed cluster 1 to the fuel assembly 45 is greatly reduced compared with that of the prior art, since the spring 21 does not have to absorb all the hydraulic forces applied to the cluster 1 by the water of the cooling system. In the fixed cluster 1 of FIGS. 1 to 4, this absorption is provided directly by the abutment elements 41. In the prior art, the service-life of end plug clusters is often limited by the ageing of the spring. Since the spring 21 of the fixed cluster 1 is subject to fewer stresses, the service-life of the fixed cluster 1 is increased which allows the quantity of radioactive waste produced by the use of a nuclear reactor to be reduced. In the fixed cluster of FIGS. 1 to 4, the spring 21 therefore has the sole function of retaining the fixed cluster 1 in contact with the upper nozzle 49 and the force applied to the assembly 45 can therefore be reduced by at least 50% at the beginning of the service-life. This reduction of the force allows the deformation of the assembly 45 to be limited during operation. Furthermore, it can be seen that the support 5 comprises a smaller number of components owing, on the one hand, to the integral construction of the lower portion 11 of the upper head 7, the fins 9 and the members 29 and, on the other hand, to the blocking in terms of rotation of the nuts 31 by means of welding the shanks 39, which allows conventional pin-type stopping systems to be dispensed with. However, it will be seen that the support 5 may have a structure which is different from that described above, and, for example, be produced from a greater number of components. In this manner, by way of example, the fins 9 may have branches from which a plurality of fin portions extend, as described in EP-158 812. In the same manner, the number of passages 30 for receiving instruments and their positions may vary. Furthermore, the systems 10 for mounting rods may be different from those described above. In the example described above, two abutment elements 41 have been provided but this number may also vary in accordance with the requirements and limitations specific to the geometries of the reactors to be equipped, and in particular the position, the size and the shape of the water passage holes 55 of the upper plate 51 of the core 47. Preferably, the abutment elements are angularly distributed in a substantially regular manner about the axis C. Finally, since the abutment elements 41 are located radially at the outer side relative to the adjacent mounting systems 10, and therefore the adjacent rods 3, the fixed cluster 1 can be used at all locations of the core, and not only at those corresponding to the smaller holes 55. The cluster 1 therefore allows standardisation to be increased and costs to be limited. |
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claims | 1. A method for control of oxygen concentration in a coolant of a reactor plant including a reactor, the coolant located in the reactor, a gas system with an outlet to a space near the coolant of the reactor, a mass-exchange apparatus installed in the coolant, which contains solid-phase oxides of coolant and is adapted to flowing of the coolant through it, a disperser installed partially in the coolant and partially in the space near the coolant and adapted to supply gas from the space near the coolant to the coolant, and an oxygen sensor in the coolant, the method comprising:estimating an oxygen concentration in the coolant based on data received from the oxygen sensor in the coolant;comparing the estimated oxygen concentration in the coolant with a predetermined permissible value;estimating a change in oxygen concentration in the coolant;if the estimated change in oxygen concentration in the coolant shows reduction in concentration, then comparing a reduction value and/or a reduction rate of the oxygen concentration with a corresponding predetermined threshold value;if the estimated oxygen concentration in the coolant is below the predetermined permissible value and the reduction value and/or the reduction rate of the oxygen concentration is below the corresponding predetermined threshold value, then activating the mass-exchange apparatus;if the estimated oxygen concentration in the coolant is below the predetermined permissible value and the estimated reduction value and/or the estimated reduction rate of the oxygen concentration is above the corresponding predetermined threshold value, then supplying oxygen-containing gas from the gas system to the space near the coolant and/or activating the disperser; andif after the activating of the mass-exchange apparatus or after the supplying of the oxygen-containing gas and/or the activating of the disperser, the estimated oxygen concentration in the coolant is greater than or equal to the predetermined permissible value, then deactivating the mass-exchange apparatus or the disperser and/or stopping the supplying of the oxygen-containing gas from the gas system to the space near the coolant, wherein oxygen-free gas is supplied from the gas system to the space near the coolant in addition to stopping the supply of oxygen-containing gas from the gas system to the space near the coolant. |
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052805050 | summary | FIELD OF THE INVENTION This invention relates to isotope generators and more particularly to a method and apparatus for generating radioisotopes from a frozen target material by bombarding the frozen target with high energy particles. BACKGROUND OF THE INVENTION A number of radioisotopes are currently being utilized as markers and for other purposes in various medical, scientific, industrial and other applications. Since such radioisotopes frequently have a relatively short half-life, from a few hours on down to a few minutes, it is generally desirable that such radioisotopes be either produced at the site where they are going to be utilized, or at a site relatively close thereto. However, the equipment for generating radioisotopes is currently relatively large and expensive, normally involving the use of a cyclotron, and the equipment for some radioisotopes, including .sup.18 F, also suffer from a lack of uniform results and an inability to achieve high yields. The lack of high yields, coupled with the short half life of the radioisotopes, limits the procedures in which such radioisotopes can be used to procedures requiring small radioisotope quantities, and also limits the number of procedures which can be performed. The cost and bulk of the equipment also makes it impractical to have such equipment at anything other than major hospital centers or research facilities, and thus limits the locations where procedures such as positron emission tomography (PET), or other procedures requiring such radioisotopes, can be performed to such facilities or ones situated in close proximity thereto. However, the usefulness of procedures utilizing radioisotopes in medical diagnosis and other applications render the wider availability of such radioisotopes desirable. In particular, Fluorine-18 (.sup.18 F), primarily because of its relatively long half-life (110 minutes), has emerged as the most widely used radioisotope in PET procedures, and a need exists for a procedure to permit on site generation of the radioisotope. Current radioisotope generators normally operate by bombarding a selected target material with a high energy particle beam from a cyclotron or other particle accelerator. This results in a nuclear reaction leaving the desired radioisotope at the target. One of the reasons for the relatively low yield obtained with such radioisotope generators for radioisotopes such as .sup.18 F which are generated from a water based target is that there is a lack of proportionality between increases in the current of the high energy beam and the radioisotope yield. This lack of proportionality is particularly true for high beam currents (i.e. currents in excess in 15 microamps). This loss of yield stems from a number of sources, including bubbles formed from vapor produced in the target by local boiling, and radiolysis which reduces the effective thickness of the target layer. Radiolysis is the breaking of the chemical bonds of the target substance. For example, with a water target, various forms of water often being used as targets, radiolysis would result in the water breaking into hydrogen and oxygen gas which would be dissipated. Thus, radiolysis can result in a reduction in the effective thickness of the target layer which in extreme cases can result in a substantial percentage of the target material being lost. Since factors such as vapor production and radiolysis appear not to occur uniformly for a given beam current, yields of certain radioisotopes may vary substantially from batch to batch. In some situations, a substantial percentage, approaching 30%, of batches produce as little as 50% of the average yield. Since the time required to generate a batch of radioisotopes may be as long or longer than the half life of the radioisotope, unreliability in yield is a substantial limitation in utilizing such radioisotopes in a clinical setting since the yield from a given batch may not be adequate to meet a scheduled patient need. The inability to increase yield by increasing currents for the reasons indicated above also limits the usefulness of such procedures because of limited isotope availability. Still another problem with existing technology is the high cost of target materials such as enriched .sup.18 O water (i.e., $100/ml). Targets have, therefore, been designed with small volumes to reduce the cost of producing the radioisotopes. This has also held down the yields available, and means that the loss of target material due to vapor, radiolysis and the like discussed above can substantially add to radioisotope production costs. Radiolysis also results in an increase in pressure at the target. Since the high energy beam must be generated in a vacuum, if vacuum cannot be maintained at the target, then a window transparent to the high energy particles must be provided between the high energy particle source and the chamber containing the target. Such windows, which are generally in the form of a thin foil, absorb energy from the beam passing therethrough and, particularly for high energy beams, must be cooled in order to avoid their burning out. The pressure differential across such windows, with vacuum on one side and target pressure on the other, which pressure differential can at times be substantial, particularly for fluid or gaseous targets (fluid or gaseous being sometimes collectively referred to hereinafter as "liquid") also results in stresses on the window which lead to window failure. Therefore, the existence of such windows in a radioisotope generating system presents a severe maintenance problem which reduces the time which the equipment can be used for generating radioisotopes, and thus reduces the yield of radioisotope available from a given machine. The overhead required for cooling the window also adds to the complexity in the design and use of the equipment. The ability to either eliminate the need for a window, or as a minimum to reduce the stresses on the window is, therefore, another important factor in reducing cost for generating radioisotopes and in increasing the yield available from a given radioisotope generating device. While the problems discussed above are more common for radioisotopes, some of the problems, such as those caused by the need for a window to isolate target pressure, may also be present where stable isotopes, such as .sup.15 N or .sup.5 Li, are being generated. It is, therefore, desirable to provide an improved method and apparatus for generating isotopes in general, and radioisotopes in particular, which can be smaller and less expensive than prior art generators so as to be usable at a greater number of facilities. It is also desirable to reduce the losses of target material due to radiolysis and the like and to thus increase the yields available from a given quantity of target material. The improved method and apparatus should also permit vacuum or near vacuum pressure to be maintained in the chamber containing the target so that windowless operation may be achieved, or as a minimum, that pressure differentials across the window be minimized. The above would permit higher yields of radioisotopes to be obtained at lower cost. SUMMARY OF THE INVENTION In accordance with the above, this invention provides a cryogenic target for use in the generation of isotopes and an improved method and apparatus for the generation of isotopes by use of such a cryogenic target. More particularly, this invention provides a method and apparatus for producing a selected radioisotope (or other isotope) from a target material which is not normally a solid and which, when bombarded by selected high energy particles, produces the selected radioisotope. A surface is provided of a thermally and electrically conductive material such as copper which is cooled to a temperature below the freezing temperature of the target material. A thin layer of target material is then frozen on the surface and the target material is bombarded with high energy particles. The high energy beam is preferably at an angle to the surface such that the particles pass through a thickness of the target material greater than the thickness of the layer before reaching the surface. The bombarding continues for a selected time period great enough to permit production of a desired quantity of the radioisotope from the target material. When the bombardment is completed, the target material, which now has been altered nuclearly to contain the selected radioisotope, is removed from the surface. For the preferred embodiment, this is accomplished by melting and then extracting the radioisotope-containing target material. To form or deposit the thin layer of target material on the surface, a quantity of the target material is introduced in vapor form into the environment containing the target, preferably by directing the target material as a jet spray from a nozzle at the surface. The nozzle is preferably retractible when not in use. For the preferred embodiment, the surface on which the target material is deposited is the interior surface of a cone, the interior surface extending at an angle .theta./2 to the central axis of the cone. The bombarding beam of high energy particles is preferably directed at the interior surface of the cone in the direction of the cone's central axis, and thus at an angle .theta./2 to the surface of the target material. When the surface is a cone, the cone is preferably tilted so that its axis is oriented substantially vertical before the target material is melted. This permits the melted radioisotope containing target material to collect at the bottom or tip of the cone, with suitable means being provided for forcing the collected material from the cone tip. The surface is preferably located in an evacuated environment. Since energy from the high energy particles is dissipated in the cone, a means is provided for facilitating the cooling of the cone to dissipate such heat. For a preferred embodiment, this is accomplished by providing at least one fin extending from an exterior surface of the cone. For the preferred embodiment, there are a plurality of such fins which are integral and preferably coaxial with the cone. For the layer of frozen target material on the interior surface of the cone, there is a minimum depth t.sub.b that the high energy particles must pass through such layer to fully produce the radioisotope therefrom. For the preferred embodiment, the cone angle .theta. and the thickness t.sub.i of the target material layer are selected such that: EQU t.sub.i .ident.t.sub.b sine .theta./2 The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings: |
06236698& | claims | 1. A nuclear reactor instrumentation system, comprising: a plurality of in core nuclear instrumentation assemblies arranged in a gap between a number of fuel assemblies charged in a reactor core, said in core nuclear instrumentation assemblies each including a fixed type neutron detector assembly and a fixed type gamma thermometer assembly, wherein said fixed type neutron detector assembly comprises N fixed neutron detectors dispersively arranged in a core axial direction with a predetermined interval L, where N is an integer greater than and equal to four, and said fixed type gamma thermometer assembly comprises at least 2N-1 fixed type gamma ray heat detectors arranged in the core axial direction such that N of the at least 2N-1 fixed type gamma ray heat detectors are arranged at the same core axial position as the fixed type neutron detectors and a reminder N-1 of the fixed type gamnma ray heat detectors are arranged at an intermediate position in the core axial direction between said fixed type neutron detectors; a power range detector signal processing device operatively connected to said fixed type neutron detector assemblies through signal cables; and a gamma thermometer signal processing device operatively connected to said fixed type gamma thermometer assembly of the in core nuclear instrumentation assembly through a signal cable. 2. The system according to claim 1, wherein one of said fixed type gamma ray heat detectors of the fixed type gamma thermometer assembly is arranged at a position L/4 above the lowest fixed type neutron detector. 3. The system according to claim 1, wherein in a case where the effective fuel portion of the reactor core is divided into several nodes in the core axial direction, each of core axial positions of said fixed type neutron detector and the fixed type gamma ray heat detector are coincident with a center of each of the nodes. 4. The system according to claim 1, wherein said fixed type neutron detectors constituting the fixed type neutron detector assembly is arranged so as to be calibrated respectively by said fixed type gamma ray heat detectors located on the same core axial position and each of said fixed type neutron detectors is calibrated so as to be coincident with a converted gamma ray heating value obtained from the gamma ray heat detector located on the same core axial position. |
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041487451 | claims | 1. A method for preparing phosphoric acid ester used in reprocessing spent nuclear fuels and/or blanket materials for non-polluting storage, which phosphoric acid ester has been separated from hydrocarbons, which comprises contacting the separated phosphoric acid ester containing radionuclides and decomposition products with a solidification matrix which consists of crushed polyvinyl chloride (PVC), in a weight ratio of phosphoric acid ester to PVC of 5 to 1 or less. 2. The method according to claim 1 which comprises mixing tributyl phosphate dominant phosphoric acid ester with PVC chips at a temperature below the softening point of PVC and maintaining the resulting admixture at room temperature to form a solid, homogeneous mass. 3. The method according to claim 1 which comprises homogeneously mixing tributyl phosphate dominant phosphoric acid ester with PVC chips at a temperature above the PVC softening point and permitting the resulting admixture to cool and form a solid mass. 4. The method according to claim 1 wherein the weight ratio of phosphoric acid ester to polyvinyl chloride is at least 1:1. 5. The method according to claim 1 wherein the weight ratio of phosphoric acid ester to polyvinyl chloride is in the range of from 7:1.5 to 1:1. 6. The method according to claim 1 wherein the weight ratio of phosphoric acid ester to polyvinyl chloride is at least 1.47:1. 7. The method according to claim 1 wherein the weight ratio of phosphoric acid ester to polyvinyl chloride is at least 2.13:1. 8. The method according to claim 1 wherein the weight ratio of phosphoric acid ester to polyvinyl chloride is at least 2.67:1. 9. The method according to claim 1 wherein the weight ratio of phosphoric acid ester to polyvinyl chloride is at least 3.00:1. 10. The method according to claim 1 wherein the weight ratio of phosphoric acid ester to polyvinyl chloride is at least 4.00:1. 11. The method according to claim 1 wherein the weight ratio of phosphoric acid ester to polyvinyl chloride is at least 4.67:1. 12. The method according to claim 1 wherein the weight ratio of phosphoric acid ester to polyvinyl chloride is from 1.47:1 to 3:1. 13. A method for preparing phosphoric acid ester used in reprocessing spent nuclear fuels and/or blanket materials for non-polluting storage, which phosphoric acid esters have been separated from hydrocarbons, which comprises contacting the separated phosphoric acid ester containing radionuclides and decomposition products with crushed polyvinyl chloride (PVC) to form a liquid mixture having a weight ratio of phosphoric acid ester to PVC of 5 to 1 or less, adding spent ion exchanger contaminated with radio nuclides to the liquid mixture of phosphoric acid ester and PVC by stirring to form a resulting liquid having a minimum PVC content of about 14 weight percent and then permitting the resulting liquid mixture to cool until a solid mass is formed which consists of the phosphoric acid ester, the PVC, and the spent ion exchanger. 14. The method according to claim 13 wherein the spent ion exchanger is added in an amount of 20 weight percent, based on the total weight of the resulting liquid mixture. 15. An essentially nonvolatile mass which does not flow at room temperature and consists of an admixture of (a) at least one phosphoric acid ester contaminated with radioactive material and which has been separated from hydrocarbon and (b) polyvinyl chloride, in the weight ratio of phosphoric acid ester to polyvinyl chloride being at most 5 to 1. (a) at least one phosphoric acid ester contaminated with radioactive material and which has been separated from hydrocarbon, (b) polyvinyl chloride, and (c) radioactively contaminated spent ion exchanger, the weight ratio of phosphoric acid ester to polyvinyl chloride is at most 5 to 1, and in the mass contains at least about 14 weight percent of polyvinyl chloride. 16. A mass according to claim 15 wherein the phosphoric acid ester comprises tributyl phosphate. 17. An essentially nonvolatile mass which does not flow at room temperature and consists of an admixture of 18. A mass according to claim 17 wherein the phosphoric acid ester comprises tributyl phosphate. |
abstract | A target supply device 4 may include a tank 51, formed of a metal, that holds a target material, an insulating member 62 that makes contact with at least part of the periphery of the tank 51, and a heater 58 that is separated from the tank 51 and heats the tank 51 via the insulating member 62. |
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050842285 | abstract | The bearing unit of the sealing device of the thermocouple column (40) has an end part (23) in which is provided the bearing area (48) for the thermocouple column (40). This end part has two successive sections in the axial direction, a first section (25) being fastened to the outer end of the follower and a second section (26) being superposed on the first. The first section (25) has a peripheral annular throat (28) and at least three openings (29) traversing the sections (25) in an axial direction so as to open into the peripheral throat (28). The second section has openings (32) in the extension of the openings (29) of the first section. A mounting piece (30) consisting of two half-rings is introduced into the peripheral throat (28) and has tapped openings (35) in the extension of the openings (29, 32) of the first and of the second sections into which screws (36) are introduced and screws into the tapped openings ( 35). A sealing strip (31) is placed between the two sections (25, 26). A device (37, 45, 41) for pulling on the end of the thermocouple column (40) bears against the upper surface of the second section (26). |
claims | 1. A cask buffer body comprising:a shock absorber including a wood material, the shock absorber configured to be attached to a cask that stores a recycle fuel and configured having line-shaped sides and circular arc-shaped corners surrounding a periphery of the cask, the shock absorber absorbing a shock against the cask by being deformed, the shock absorber including a plurality of empty holes for adjusting a shock absorbing capability, the shock absorber comprising:a first shock absorber group including:a first shock absorber configured to absorb a shock generated by the horizontal falling or collision of the cask;a second a shock absorber group configured to absorb the shock when the cask vertically falls or collides or obliquely falls or collides, the second shock absorber group including:a second shock absorber;a third shock absorber; anda fourth shock absorber; anda third shock absorber group configured to absorb the shock when the cask vertically falls or collides, the third shock absorber group configured to sufficiently relax a shock force transmitted to a primary lid and a secondary lid of the cask, the third shock absorber group including:a fifth shock absorber;a sixth shock absorber;a seventh shock absorber; andan eighth shock absorber, whereinthe first shock absorber is made of a first material having a highest compressive strength among all of the first to the eighth shock absorbers, whereinthe second to the fourth shock absorbers are made of a second material lower in compressive strength than the first shock absorber, whereinthe fifth to the eighth shock absorbers are made of a third material lower in compressive strength than the second to the fourth shock absorbers, whereinthe first to the eighth shock absorbers are arranged by changing directions of fibers of the wood materials, whereinthe compressive strength is a Young's modulus or a compression strength when the shock absorber is compressed. 2. The cask buffer body according to claim 1, whereinthe first material is oak;the second material is red cedar; andthe third material is balsa. |
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claims | 1. A power source, comprising:a substrate comprising a structured surface;radioactive material disposed on the structured surface, wherein the radioactive material emits radiation particles;particle converting material disposed on at least a portion of the radioactive material, wherein the particle converting material converts one or more radiation particles emitted by the radioactive material into light;a sealing layer disposed on the structured surface such that the particle converting material and the radioactive material are hermetically sealed between the sealing layer and the structured surface; anda photovoltaic device disposed directly adjacent the structured surface of the substrate, wherein the photovoltaic device converts at least a portion of the light emitted by the particle converting material that is incident upon an input surface of the photovoltaic device into electrical energy. 2. The power source of claim 1, wherein the radioactive material comprises tritium. 3. The power source of claim 1, wherein the particle converting material comprises phosphor. 4. The power source of claim 1, wherein the particle converting material comprises quantum dots. 5. The power source of claim 1, wherein the substrate comprises glass. 6. The power source of claim 1, wherein the photovoltaic device comprises a photodiode. 7. The power source of claim 1, wherein the substrate further comprises a reflective layer disposed between the substrate and the particle converting material. 8. The power source of claim 1, wherein the substrate further comprises an anti-diffusion layer disposed between the radioactive material and the substrate. 9. The power source of claim 1, further comprising an antireflective layer disposed between the sealing layer and the input surface of the photovoltaic device. 10. The power source of claim 1, wherein the input surface of the photovoltaic device is disposed on the sealing layer. 11. The power source of claim 1, wherein the substrate comprises a first major surface and a second major surface, wherein the first major surface comprises the structured surface, the power source further comprising a reflector disposed adjacent the second major surface of the substrate such that the reflector faces the photovoltaic device. 12. The power source of claim 1, wherein the sealing layer includes one or more structures that are registered with the structured surface. 13. The power source of claim 1, wherein the structured surface has a cross-sectional shape in a plane parallel to the structured surface. 14. The power source of claim 1, wherein the structured surface has a cross-sectional shape in a plane orthogonal to the structured surface. 15. The power source of claim 1, wherein the structured surface comprises structures arranged in one or more of a periodic array on or in the structured surface, a random arrangement on or in the structured surface, or a pseudo-random arrangement on or in the structured surface. 16. The power source of claim 1, wherein the particle converting material is disposed on the at least a portion of the radioactive material in at least one pattern. 17. The power source of claim 1, wherein the sealing layer is disposed on and in contact with the particle converting material layer. 18. The power source of claim 17, wherein the sealing layer conforms to the shape of the particle converting material layer. 19. An implantable medical device comprising the power source of claim 1. |
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abstract | Marking of the cuts which have to be made, cutting of the section at two ends, removal of the section which has to be replaced, bevelling of the joint ends of the parts remaining after the section has been cut out from the pipe, adjustment of a new or replacement section for length and bevelling of its joining ends and positioning and narrow bevel welding of the ends joining the replacement section to the ends of the remaining parts of the pipe are performed outside the pipe. Within the pipe operations of machining and inspecting an internal part of the joining ends welded together are performed by remote control in a programmed way by introducing and positioning means for working within the pipe from a component of the primary circuit. The procedure is in particular used to effect the replacement of a section of a cold leg of the primary circuit using means for carrying out work comprising a robot arm secured to a supporting chassis borne by a carriage which moves the means for carrying out work within the cold leg inserted into the cold leg through the volute of the primary pump of the nuclear reactor. |
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abstract | A detection system combining an excitation radiation source providing excitation radiation to an analysis region of a sample within a substrate having a detection surface, a detector for detecting radiation collected from the analysis region comprising the detection surface of the sample resulting from the excitation, and a magnet arrangement beneath the analysis region of the sample, and stationary with respect to the excitation radiation source and light coupling arrangement, for attracting magnetic beads within the sample to the substrate surface. The detection radiation is collected from the detection surface of the substrate to give an enhanced surface specificity. |
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abstract | A process for encapsulating a radioactive object to render the object suitable for shipment and/or storage, and including the steps of preparing a plastic material, causing the plastic material to react with a foaming agent, generating a foaming plastic, encapsulating the radioactive object in the foaming plastic, and allowing the foaming plastic to solidify around the radioactive object to form an impervious coating. |
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047449411 | description | DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a building 1 of a fast neutron nuclear reactor, whose pile block 2 comprises a main vessel 3 and a safety vessel 4 in a well 5 of building 1. Pile block 2 and vessel 3 of the reactor are sealed in conventional manner by a concrete slab 6. In the lower part of building 1 are provided two floors, namely an upper floor 7 and a lower floor 8, separated from one another by elastic supports 9 made from fretted elastomer. These supports 9 permit an oscillatory horizontal displacement, with return to the initial position, of the upper part of building 1 with respect to the lower floor 8, which can be very useful for absorbing seismic shocks having horizontal components of a certain magnitude. Pile block 2 rests on building 1 in the following way. A lateral cylindrical concrete structure 19 integral with and peripherally and terminally extending the slab of reactor 6, serves as a support for pile block 2, via the series of elastic supports 10 placed between the bottom of cylindrical structure 19 and upper floor 7. In this embodiment, the vertical guidance means 12 are laterally distributed between supports 12a in the upper part and supports 12b in the lower part of block 2. The guidance means 12 are rigid in the horizontal plane and flexible in the vertical plane. The distribution of the vertical guidance means of the reactor block in well 5 between the top and bottom thereof makes it possible to completely prevent any rocking or oscillation of the reactor block assembly in the case of seismic shocks. The structure operates in the following way: the horizontal movement of the assembly is imposed by paraseismic supports 9 positioned beneath building 1; PA1 the vertical movement of reactor block 2 is regulated by the characteristics of the elastic supports and absorbers 10; PA1 the overall vertical movement of the remainder of buidling 1 is a function of its natural frequencies, which are dependent on the characteristics of the ground. The building of reactor 1 and the reactor block 2 are connected by pipes, cables, etc., which must have sufficient flexibility to accept the vertical differential movements occurring, in the case of an earthquake, between these two parts. FIG. 2 shows the second embodiment of the support structure according to the invention and has, with the same reference numerals, most of the components of the embodiment of FIG. 1. However, in this embodiment, the elastic supports 10 and guidance means 12 are positioned at the coupling slab 6 in the following way. According to the invention the absorbing elastic supports 10 are positioned between the upper ends of slab 6 and the vertical concrete caisson 11 directly surrounding the pile block 2. These absorber means make it possible to absorb the vertical components of a possible seismic wave, by preventing the rocking of the reactor vessel 3 with respect to building 1. The vertical elastic guidance means 12, positioned vertically between the peripheral ends of reactor slab 6 and the structures of building 1, enable pile block 2 to be guided in well 5 in a vertical direction, while preventing any horizontal displacement of block 2, as well as any rocking thereof under the effect of the horizontal components of a possible seismic wave, because it is then substantially integral with building 1. FIG. 3 is a plan view of reactor slab 6, which is peripherally provided with a certain number of support tenons, such as 13, which cooperate with mortises 14, cut from the concrete of the building of reactor 1, so as to laterally enclose the vertical elastic guidance means 12, preventing any horizontal rotation of slab 6 with respect to the building 1, under the effect of the horizontal component of a seismic wave. The constructional detail of the sector surrounded by a circle and designated A in FIG. 2 is shown in FIGS. 4 and 5, where it is possible to see the main components referred to hereinbefore and, in addition, the circular gallery 15 positioned beneath slab 6 and more particularly giving access to the first elastic support 10 and to the flexible tight joints 16, which obviate any leaks of radioactive material coming from the main vessel 3 and towards the outside thereof. Manholes 17, distributed over the periphery of the installation, permit the introduction of the individuals necessary for the different manipulations and the like in said gallery 15. FIG. 4 shows at 10, the elastic supports for absorbing the vertical components and the elastic guidance means 12, positioned vertically between tenons 13 and mortises 14, belonging respectively to slab 6 and to the concrete of reactor building 1. The guidance means 12 are rigid in the horizontal direction (in order to permit the displacement of slab 6 by building 1) and flexible in their vertical parallel planes (to permit the freedom of vertical movement of vessel 3). Between tenon 13 and mortise 14, there is a space forming an expansion joint 18 permitting, when the reactor temperature rises, the radial expansion of the slab. This arrangement, which is a consequence of the existence of tenons 13 and mortises 14 is very interesting, because it very simply solves the hitherto difficultly solvable problem of the radial expansion of the vessel and the slab supporting the same. Thus, by associating the three means constituted by supports 9, 10 and 12, it is possible to obtain a maximum, effective protection against the seismic wave of a certain magnitude, no matter whether their components are mainly horizontal or vertical. The antiseismic support structure according to the invention thus provides a double horizontal and vertical filtering of the seismic stresses, which considerably reduce the acceleration to which the slab and the components of the pile block are exposed in the case of an earthquake. Thus, it permits a simplified and much less costly construction than those available hitherto. Moreover, this structure very simply permits the construction of the system oscillating with three degrees of freedom (2 horizontal and one vertical), whose rigidity and absorbing or damping characteristics are accurately known. Thus, there is a very good knowledge of the dynamic response in the case of a shock, which is also very satisfactory from the reactor safety standpoint. FIG. 6 shows in greater detail the absorber 10 of FIG. 1. This viscoelastic absorber 10 has between its ends 20, 21, a series of springs 22 and a viscous absorber 23. This association makes it possible to increase the filtering qualities of the vertical component of a seismic shock, above a frequency of approximately 1 to 1.7 Hz. FIG. 7 diagrammatically shows the application of the invention to the seismic protection of a solid block 24, such as exists in buildings. As a result of the means according to the invention and which carry the same references as in FIG. 1, this block is stabilized and is protected against rocking or oscillating movements through the double filtering of the horizontal and vertical components above approximately 1 Hz. |
06212255& | abstract | A blood irradiator for providing a uniform dose of X-ray beam irradiation for blood contained within a transfusion bag. A first X-ray tube is positioned to irradiate said bag from one side of the bag, and a second X-ray tube is positioned to irradiate said bag from the opposite side of said bag concurrently with said first bag whereby a uniform dose of X-rays is provided to the blood. |
042382890 | description | DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings, particularly to FIG. 1, a reactor containment structure 10 shown therein comprises an inner vertical generally cylindrical wall 12 defining a reactor compartment 14, an outer vertical generally cylindrical wall 16 spaced from the inner wall 12 to define a generally annular condenser compartment 18 between the walls 12 and 16, a generally hemispherical head 20 supported by the outer wall 16, and a horizontal floor 22. The containment structure is preferably formed from concrete. As shown, the reactor compartment 14 is divided into upper and lower portions separated by an operating deck 24. The lower compartment completely encloses the fluid handling apparatus, i.e., reactor coolant system equipment, including a reactor vessel 26, steam generators 28, reactor coolant pumps 30, a pressurizer 32 shown in FIG. 2, and connecting piping 34. The upper compartment or portion contains a refueling canal 36 shown in FIG. 2, a crane 38 which is supported by the inner or crane wall 12, and additional refueling equipment (not shown). The steam generators 28 and the pressurizer 32 are enclosed by an extension 40 of the operating deck 24. The reactor vessel 26 is disposed in a well or sump 42 in the floor 22. The reactor vessel head 44 is enclosed by a primary shield 46 which is vented at 48. The vessel head enclosure is enclosed at the top by a removable concrete slab 50 which functions as a missile shield. The operation of the reactor power equipment is well known in the art and will not be described in this application. As shown more clearly in FIG. 2, the condenser compartment 18 is in the form of a completely enclosed, generally annular compartment which is located radially between the inner wall 12 and the outer wall 16, and in elevation, is generally above the operating deck 24. The condenser compartment 18 does not extend entirely around the containment structure, but does extend through an arc of approximately 300.degree. as shown in FIG. 2. Thus, the condenser compartment substantially encircles the reactor compartment 14. The ends of the condenser compartment are enclosed by vertical end walls 52. As shown more clearly in FIG. 4, the top of the condenser compartment 18 is enclosed by horizontally hinged doors 54, and the bottom of the compartment is enclosed by an insulated floor 56. Vertically hinged inlet doors 58 are disposed in door ports 60 located in the inner wall 12 below the operating deck 24 and communicating between the reactor compartment 14 and the condenser compartment 18. The condenser compartment 18 contains a quantity of fusible material 62, such as ice, in a solid state. The material 62 has the property of melting at a temperature lower than the condensation temperature of the condensable portions of the reactor coolant fluid which may escape from the reactor coolant system. The fusible material 62 is supported in the condenser compartment 18 in the manner fully described in a U.S. Pat. No. 3,726,759 issued to W. G. Taft, R. Schift and A. J. Iredale and assigned to the Westinghouse Electric Corporation. Briefly, the material is contained in cylindrical porous containers 64 which are retained in horizontally spaced relation by means of vertically spaced frames 66 as shown in FIG. 4. Approximately 2/3 of the containers 64 rest on radial beams 65 supported above the floor 56 by circumferential beams 67 and vertical columns 69 to provide space for the doors 58 to open. The remaining containers rest directly on the floor 56. As described in the Weems et al U.S. Pat. No. 3,432,286, in the event of a loss-of-coolant accident, the inlet doors 58 would open almost immediately due to the pressure rise in the lower compartment caused by the release of reactor coolant. This would allow the steam to flow from the lower compartment into the ice condenser. In turn, the door panels 54 at the top of the ice condenser would open and allow some of the air which was initially in the lower compartment and in the ice condenser compartment to flow into a plenum chamber 68 and thence into the upper reactor compartment through doors 70 located at the top of the plenum 68, as shown in FIG. 1. The ice condenser would very quickly begin to condense the steam, thereby limiting the peak pressure in the containment structure 10. As explained in U.S. Pat. No. 3,844,855 issued to S. J. Weems, H. W. McCurdy and J. W. Johnson and assigned to the Westinghouse Electric Corporation, the storage of a large quantity of a low temperature fusible solid, such as ice, for long periods of time cannot be economically accomplished by conventional refrigeration and insulation systems. Prior systems give rise to unacceptable temperature gradients and convection of the atmosphere in which the solid is stored. Such temperature gradients and convection currents cause mass transfer of the solid by sublimation and frosting. Established conventional methods of thermally insulating and cooling a cold storage compartment incorporate essentially separate insulation and cooling systems. The outermost boundaries of the compartment are lined with suitable low conductivity material and cooling is provided by a refrigerant circulating in pipes within the compartment or by circulating the compartment air over refrigerated coils. Such systems cause mass transfer of the solid material by sublimation and frosting since the refrigerated air is in direct contact with the solid material. As described in the aforesaid copending application, in order to minimize mass transfer of the solid material, such as ice, due to sublimation and frosting, air or other suitable fluid is circulated in a circuit which is closed and effectively sealed relative to the compartment to be cooled. The air, or other fluid, is cooled by passing over coils (not shown) located in the plenum 68 and forming part of a conventional refrigeration system. As shown more clearly in FIG. 4, all of the vertical walls of the condenser compartment 18 are lined with vertically extending insulated duct panels 72. Each panel 72 is a prefabricated integral air duct unit divided into downflow and upflow channels with a cross flow header at the bottom. Air is drawn from the plenum 68 through the refrigerator coils by fan units 74 and forced into the downflow channels through manifolds 76 which extend around the upper ends of the panels 72. The air flows down through the downflow channels of each panel and returns through adjacent upflow channels of the panel. The returning air exhausts directly into the plenum 68 through exhaust openings 78. In this manner the heat gain from the walls is absorbed directly by the refrigerated cooling air and none of the heat is required to flow through the ice containing portion of the condenser compartment. Sublimation of ice is thus minimized by minimizing heat flow through the ice containing portion of the condenser compartment because no sublimation can occur without heat flow. Furthermore, since the refrigerated cooling air is not in direct contact with the ice, it does not absorb moisture from the ice, thereby reducing loss of ice by frosting of the refrigerated cooling coils. As shown more clearly in FIGS. 5, 6 and 7, the inlet doors 58 at the bottom of the ice condenser 18 are thermally insulated panels mounted as vertically hinged pairs on an angle section frame 80 between concrete pillars 82 which support the crane wall 12 as shown in FIG. 4. As shown in FIGS. 5 and 6, each door panel comprises a foam plastic core 84, such as PVC (polyvinylchloride) with a bonded facing 86, which may be either sheet metal or plastic, and a relatively thick layer 88 of soft low density insulation, such as Fiberglas, retained by the facing 86. The doors are provided with spring arrangements 90, different types of which are described hereinafter, which produce a small force to resist door opening. The magnitude of the force produced by the springs when the doors are fully open is equivalent to a differential pressure of approximately one pound per square foot. The doors are normally held shut against a lip seal 92, mounted on the frame 80, by the static differential pressure due to the high density cold air in the ice condenser compartment compared with the warm air in the reactor compartment. In the fully closed position, the doors are required to compress a light spring arrangement, hereinafter described as the booster spring. This obviates the condition where with a number of doors in parallel between the compartments which are caused to open by a rising differential pressure across them, one door with the least resistance to opening will open first. When one door opens, flow is immediately initiated between the compartments, and the differential pressure across the remaining doors is that due to flow through the open door. This condition applies to the opening of the second door, and so on for all of the doors. Under the foregoing circumstances, it is possible to have a flow of steam due to a small leak from the reactor coolant system such that all the doors will not open and which would produce a maldistribution of energy into the condenser. For small breaks this is not significant for short periods of time, but the continuation of this condition would melt out local areas of fusible material from the ice bed, allowing increased bypass of steam into the upper compartment and giving rise to higher final peak pressure in the containment resulting from blowdown. In the fully closed position, the booster spring assembly is compressed approximately 1/4 inch. Under normal operating conditions, the cold head in the ice condenser is sufficient to maintain the door closed against the spring. Furthermore, the spring rate is such that, should the door open under normal operating conditions, the main proportioning spring assembly will return the door to the point where it begins to compress the booster spring assembly and thereafter the cold head forcing a flow of air from the ice condenser into the lower compartment of the containment develops sufficient differential pressure across the door to compress the booster spring approximately 1/4 inch allowing the doors to close fully. The opening mode is such that, on an increase in pressure in the lower compartment, the first door will open when the pressure in the lower compartment and the force of the booster spring combined overcome the cold head in the ice condenser. Thus, when the door opens, the cold head in the ice condenser relieves into the lower compartment, reducing the pressure holding the remaining doors closed. Before there can develop a positive differential pressure from the lower compartment to the ice condenser, and, therefore, before the flow can be induced into the bed, the pressure across all the doors will have balanced and the booster springs will have opened all the doors by 1/4 inch. Thereafter, the main proportioning spring assemblies are able to maintain the required distribution of steam into the ice bed for small break sizes. As shown more clearly in FIG. 8, the two doors 58 of each pair close against seals 94 supported by a vertical I-beam 96 mounted in the frame 80. The seals 94 are attached to a channel member 98 by bolts 100 which extend through metal members 102 bonded to the resilient seals 94. The channel member 98 is secured to the I-beam 96, as by welding. As also shown in FIG. 8, the doors 58 close against a compression spring 104 which may be of a leaf type and is the booster spring previously discussed. The spring 104 is mounted between a bar 105 and a block 106 secured in the channel member 98 by means of bolts 107. With zero differential pressure across the doors, the doors are slightly opened by the compression springs 104. Thus, all doors will open at any differential pressure which will cause steam to flow into the ice condenser and, within the limits of spring tolerances, the doors will all open equal amounts. The doors 70 enclosing the top of the condenser compartment 18 and forming the roof of the upper plenum 68 are similar to, but lighter than the lower doors 58. These top doors 70 are supported by a bridge crane support structure (not shown). The crane support structure comprises radial I-beams spanning the ice condenser annulus at the top of the crane wall 12. The doors 54 enclosing the ice compartment and forming the floor of the plenum 68 are similar to the doors described above. These doors 54 are supported by the upper ice basket positioning frame 66. A walkway 108 is provided between the two rows of doors 54. The upper door panels are hinged horizontally and are normally closed. Upon an increase in pressure in the ice condenser compartment, these doors will open as required allowing air to flow into the upper reactor compartment. In order to properly distribute the energy released from a loss-of-coolant accident to all sections of the condenser compartment, the ice condenser bottom doors and their port flow areas are so constructed that flow maldistribution is limited by one of two different mechanisms depending on the size of pipe break. Flow maldistribution is limited for accidents involving large pipe break sizes, which cause the doors to be blown fully open, by flow resistance due to differences in port flow areas in accordance with their location relative to the fluid-handling apparatus in the reactor compartment. For small pipe breaks, the inlet doors are only partly opened and maldistribution is limited due to differences in spring constants of the spring arrangements provided for the doors. Since the ice condenser inlet doors 58 are located all around the lower compartment and the different reactor coolant loops are located in certain regions of the lower compartment, the flow of steam from a pipe break would not be evenly distributed to the different sections of the ice condenser unless special means were provided to prevent such maldistribution. As shown in FIG. 2, the ice condenser compartment 18 may be divided into five areas with respect to the location of the fluid-handling apparatus in the reactor compartment 14. For a break at one end of the lower compartment as indicated at 110, the steam would tend to flow preferentially to nearby sections of the ice condenser. However, the steam flow into any section of the ice condenser is limited by the constructed flow resistance of the ice condenser inlet doors and the flow areas of the ports containing the doors. The resistances of the doors and the port flow areas are large relative to the resistance to flow around the reactor coolant system compartment, thereby tending to provide uniform flow to all sections of the ice condenser as shown by the arrows in FIG. 2. To provide a more uniform distribution of steam than would be possible with uniform orificing, fixed preferential orificing of the inlet doors and door ports can be provided. This can be done by making the doors 58 and their ports 60 of one size in areas 1 and 5, of a larger size in areas 2 and 4, and of a still larger size in area 3. Thus, the flow resistance is determined by the port flow areas since the flow resistance is inversely proportional to the port flow area squared. However, for manufacturing reasons it is desirable to make all doors and their port openings of the same size. When this is done, the net port flow area in any port opening can be determined by providing baffles 112 of one size for the ports 60 in areas 5 and 1 as shown in FIG. 3. Likewise, baffles 112a of a smaller size are provided for the port opening in areas 4 and 2. No baffles are provided for the port openings in area 3. As shown more clearly in FIG. 8, the baffles 112 may be secured to the I-beams 96 in a suitable manner, as by welding. In this manner the port flow areas of the port openings are determined in accordance with the location of the openings relative to the fluid-handling apparatus therefore, those ports having a large flow area or least resistance to flow, are located at the greatest distance from the fluid handling apparatus while those ports having small flow areas are located closer to the fluid handling apparatus. Thus, the end sections 1 and 5 of the ice condenser are provided with smaller than average door port flow areas, and the center section 3 is provided with a larger than average door port flow area. Such fixed preferential orificing is utilized to provide a more uniform distribution of energy into the ice condenser than would otherwise be the case with uniform orificing. The preferential orificing required for substantially uniform energy distribution around the condenser can be calculated mathematically based on straightforward thermodynamic principles. As explained hereinbefore, maldistribution for accidents involving small pipe breaks is limited by the spring tolerances of spring arrangements 90 provided for each door. FIG. 10 shows door opening characteristics as a function of door differential pressure based on different spring constants. Thus, curve "a" shows the opening characteristics for doors having an assumed spring constant of one value, curve "b" shows the characteristics for a spring constant of a higher value and curve "c" shows the characteristics for a spring constant of a lower value. The ratio of maximum steam flow which can enter the weakest sprung door as compared to the average steam flow going through the other doors of the ice condenser is such that a peak value of maximum to average flow into the different sections of the ice condenser is easily limited to a small value. Further, such maldistribution can be reduced additionally by preferential location of weaker and stronger springs in much the same manner as the door ports may be preferentially orificed for large pipe breaks. Thus, for the case of small pipe breaks wherein the bottom doors of the ice condenser are partly open, these doors limit the ratio of maximum to average flow of steam into any section of the ice condenser to a reasonably low value. As previously explained, the ratio of maximum to average flow of steam into the ice condenser for pipe break sizes large enough to fully open the doors is limited by the door port flow areas. This ratio is also kept to a reasonably low value. One spring arrangement 90 suitable for use with the doors 58 is shown in FIG. 9. A tension spring 114 is mounted in a housing 116 attached to an extension 118 on the door frame 80. One end of the spring 114 is adjustably attached to the housing 116 by means of a self-aligning connecting member 120. The other end of the spring 114 is attached to a plate 122 by means of a self-aligning connecting member 124. The plate 122 is bolted to an angle member 126, which, in turn, is bolted to an angle member 128 bolted to a door hinge 130. The tension of the spring 114 may be adjusted by means of the member 120. Another spring arrangement 90a suitable for biasing the door 58 toward the closed position is shown in FIG. 11. A compression spring 132 is mounted in a housing 134 attached to the door frame 80. The spring 132 actuates a spring seat 136 which is attached to a pivoted crank arm 138 by means of a link 140. The arm 138 pivots on a pin 142 supported by a bracket 144 attached to the door frame 80. The arm 138 is attached to a plate 146 which, in turn, is attached to the core 84 of the door 58. As previously stated, the spring 132 biases the door 58 toward its closed position. Another spring arrangement 90b is shown in FIG. 12. This arrangement can be used to limit maldistribution for small pipe breaks by causing all lower doors 58 to open fully if any one door 58 is opened. With this arrangement the doors 58 are biased toward the open position by spring members. All of the doors are held closed during normal operation by a single wire rope 148 which overcomes the individual door spring forces. As shown in FIG. 3, the wire rope 148 may be attached to the end walls 52 of the condenser compartment. The wire rope 148 is set to break and release the doors at the desired door pressure loading or for any case whereby any individual door opens. As shown in FIG. 12 a compression spring 132a is mounted in a housing 134a attached to the door frame 80. The spring 132a actuates a spring seat 136a connected to the crank arm 138 by a link 140a. The spring 132a is so disposed between the seat 136a and the housing 134a that the spring biases the door 58 toward the open position. An over-center gravity-opened door arrangement is shown in FIGS. 13 and 14. In this arrangement each door 58a rotates about a horizontal, bottom-mounted hinge 130a and is normally inclined at a slight offset, about 10.degree. from the vertical position. This 10.degree. offset is provided to permit the door panels to open to allow temporary venting of air into the ice condensor if needed during normal operation and to assure that the panels will reshut after this type of venting. The doors are normally held closed by the static differential pressure of the cold high density air in the condenser compartment. As shown in FIGS. 13 and 14, the doors 58a are mechanically connected together by link chains 150. The chains 150 are so connected that opening of any one door causes all doors to open. Sufficient slack is provided in the chains to permit any one door to swing past its dead center position after which it will cause the adjacent doors to open. This action is continued to cause all the doors to open as a result of any one door being opened by differential pressure. If desired, the hinge 130a for each door 58a may be so located that the door is in a vertical position when closed. As previously explained the doors are normally held closed by the differential air head due to the cold high density air in the condenser. If the steam pressure difference across the doors nullifies the cold air differential head, all doors will fully open due to gravity and admit steam flow to the condenser. From the foregoing description it is apparent that the invention provides a relatively simple spring-biased door arrangement to reliably seal the ice condenser compartment for normal plant operation, thereby preventing excessive moisture and heat gain. All doors will open automatically as necessary during a loss-of-coolant accident. No active system is required to open the doors, since the natural forces resulting from the accident itself will force the doors open. The inlet doors and door ports will properly distribute the energy to all sections of the ice condenser, thereby providing efficient operation of the condenser. In the event of large pipe break accidents, the inlet doors are fully opened. In the case of small pipe break accidents, the inlet doors are only partly opened. The door ports are sized to provide the necessary resistance to steam flow into any section of the ice condenser to limit the maximum flow of steam and energy to an acceptably low value. Furthermore, the door port flow areas are nonuniformly sized to preferentially orifice the flow of steam into certain sections of the condenser so as to reduce maldistribution to a low value. The doors evenly proportion the flow of steam into each section of the condenser for small pipe break accidents by providing suitable resistance to flow due to spring action which resists opening of any door. For small pipe breaks, the differential pressure which causes steam flow into the ice condenser is essentially the same value across each door, thereby causing each door to be open the same amount and steam to flow evenly into the condenser. However, if desired, different spring constants can be used to preferentially distribute steam flow into certain sections of the ice condenser. The doors are normally held closed against relatively light compression springs by the static differential pressure due to the cold high density air in the condenser compartment. These springs function to open all doors a small amount in case of a loss of this differential pressure by the opening of any one door. Since numerous changes may be made in the above-described construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all subject matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. |
abstract | The present invention relates to a method for controlling a pressurized water reactor (100) comprising the steps that involve measuring the effective power (Pe) of the nuclear reactor; acquiring a reference value for the desired power (Pc); acquiring an estimated duration (DURATION) for the increase in power in order to achieve said reference value of the target power (Pc) desired, said estimated duration (DURATION) corresponding to the time taken for the power to increase from said effective power (Pe) to said reference value for the target power (Pc); determining the reference position (Z) of at least one control rod cluster among said plurality of control rod clusters (40) in order to achieve said reference value for said target power (Pc) desired as a function of said estimated duration (DURATION), of said measured effective power (Pe) and of said reference value for said target power (Pc); monitoring the position of said at least one control rod cluster so as to position it in its reference position (Z). |
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abstract | A radiation-shielding container for storing a syringe includes a base assembly, a sleeve and a cap assembly securable to the base assembly. The base assembly includes a body portion defining a chamber portion for receiving the syringe and including a base portion coupled to the body portion. The base portion includes a radiation shield and a shell positioned proximate an outer surface of the radiation shield. The sleeve configured for receiving a portion of the syringe is housed within the chamber portion and releasably secured to the base assembly. The cap assembly defines a second chamber portion for receiving the syringe and includes a radiation shield and a shell positioned proximate an outer surface of the radiation shield. |
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abstract | A gas discharge source, in particular, for generating extreme ultraviolet and/or soft X-radiation, has a gas-filled intermediate electrode space located between two electrodes, devices for the admission and evacuation of gas, and one electrode that has an opening that defines an axis of symmetry and is provided for the discharge of radiation. A diaphragm exhibits at least one opening on the axis of symmetry and operates as a differential pump stage, between the two electrodes. |
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abstract | The present invention is a nuclear waste storage apparatus and a method of filling the storage apparatus while the storage apparatus remains substantially sealed. The innermost layer of the apparatus comprises a self-sealing bladder. An injection device pierces the bladder and fills it with radioactive waste in a liquid, slurry or paste form in a substantially sealed process. When the injector is removed, the self-sealing material of the inner bladder substantially closes the pierced portion of the bladder. The bladder is then coated with a protective coating, a radioactive barrier coating, and an outer impact resistant coating to complete the apparatus. |
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description | Aspects of the disclosure relate to combinatorial analysis and knowledge engineering. Businesses or other entities engaged in software product deployment are faced with the risk of Deployment Failures (DFs). DFs may include Post-Production Defects (PPDs) and Failed End-User Interactions at various levels, including the project and release levels. Failed End-User Interactions may also be called Failed Customer Interactions (FCIs). The likelihood of a DF is affected by a number of factors, including other DFs earlier in the production chain. For instance, a high level of design complexity in a project as conceived might lead to the late submission of a requirements document (an early-stage DF). The late requirements document would then increase the likelihood of a later-stage DF such as a failure to adequately test. The failure to adequately test might then increase the likelihood of an even later stage DF, such as an FCI. For the purposes of this application, a lower level failure state is a Root Cause (RC). An Intermediate point of failure resulting from one or more Root Causes is a Minor Effect (ME). An end-state failure mode resulting from one or more Root Causes and/or Minor Effects is a Top Event. A Top Event may also be referred to as a Primary Effect. In the example given immediately above, for instance, the high level of design complexity is a Root Cause, the failure to adequately test is a Minor Effect, and the FCI is a Primary Effect. Similarly, a physical environment defect may be a Root Cause which might increase the likelihood of a failed change error (Minor Effect), which could in turn increase the likelihood of the FCI (Primary Effect). A Minor Effect may simply be a conceptual label for two or more Root Causes and the relationship between those Root Causes. A Minor Effect that can be independently measured may be treated as Root Causes. Entities benefit from anticipating the risk of Deployment Failures at every stage by allowing the prediction of such issues early enough in the development lifecycle such that mitigating actions can be taken and any negative end-user impact can be limited. Conventionally, DF risk assessment is established by subjective opinion, usually by an individual with some experience in the field. Such subjective analyses are, however, unreliable and the mechanism for making such analyses is difficult to teach or share. Further, the subjective analyses are not readily scalable. That is, undertaking such subjective analyses in connection with more than one development project may often require the expertise of different individuals having particularized expertise Also, conventional DF risk assessment is generally at least partially retrospective, undertaken at the earliest only after Root Causes have aggregated to the level of Minor Effects. The conventional method generally allows for accurate DF risk assessment only at later stages in the deployment process, such as late-stage testing, which may be after the most efficient opportunities to mitigate have passed. Businesses or other entities often attempt to model or analyze failure processes of various systems. One mechanism for engaging in such modeling is the process of Fault Tree Analysis (FTA). FTA may be composed of logic diagrams that display the state of the system and it may be constructed using graphical design techniques. In an FTA, an undesired effect may be taken as the “Top Event” of a tree of logic. Then, each situation that could cause that effect is added to the tree as a series of logic expressions. Events for which no cause is recognized in the fault tree may be termed Base Events, and events within the fault tree that are neither Base Events or the Top Event may be termed Intermediate Events. Conventionally, fault tree analysis comprehends the combination of Base Events and Intermediate Events as Boolean or probabilistic structures. That is to say, as a descriptive matter, a fault tree may conceptualize the occurrence or failure of some event as related to the occurrence or failure of some set of other events in Boolean terms: Event A will occur if Event B AND Event C occur OR if Event D occurs. As a predictive matter, a fault tree may conceptualize the probability of the occurrence or failure of some event as related to the probability of the occurrence or failure of some set of other events in probabilistic terms: The probability of Event A occurring is determined by the mathematical evaluation of probability of Events B and C occurring OR the probability of Event D occurring. The Boolean, descriptive analysis can be understood as a special case of the probabilistic analysis, where the probabilities are either 100% (True) or 0% (False). Such Boolean/probabilistic combinations can be readily understood under mechanisms of algorithmic conversion well known to practitioners. For instance, in the example given, where the probability of Event X is designated P(x), then P(a)=(P(b)*P(c))+P(d). Conventionally fault trees may further include the assignment of weights to particular events, such that certain events are given more significance in the algorithm by the addition of a weight multiplier. In some circumstances, however, the application of conventional Boolean relationship algorithms and weighting to the fault tree structure is insufficient to adequately describe or predict the relationships between Base Events, Intermediate Events, and the Top Event. Moreover, in some circumstances the application of conventional relationship algorithms and weighting requires unwieldy and very complex fault tree structures to maintain the integrity of the representational aspect of the fault tree. It would be desirable, therefore, to provide a method or system for making less subjective DF risk assessments. It would also be desirable, therefore, to provide a method or system for describing the relationships between Base Events, Intermediate Events, and the Top Event of a fault tree more adequate to a comprehensive representation and allowing for a less complex fault tree which nonetheless maintains the integrity of the representation. Provided are methods and systems for objective DF risk assessments. Also provided are methods and systems for the analysis of fault trees using a novel system of valuation and evaluation. The methods and systems may encompass one or both of two general steps. First, an analytical model for predicting DF at various levels is created. Second, values are assigned to the analytical model and those assigned values are refined. The analytical model may be a fault tree analytical model (FTAM). The FTAM describes the various ways in which Root Causes may combine to cause Minor Effects and/or Primary Effects. Other type of analytical models may be used. For example multivariate models, neural networks or any other suitable type of analytical model. The model may be trainable based on any suitable training approach. For example, the model may be iteratively trained by comparison of a model output with a reference value. The FTAM may then be populated with initial, provisional ranks and weights, and data may be collected to support that version. The provisional model may then be applied to the data collected, thus resulting in further iterations of the model, which may then be deployed and fine-tuned. Fine-tuning may be done by comparison of the model to historical data and to ongoing project data. The methods and systems may encompass primarily the combination of assigned values in concordance with evaluation tables. The method may further involve refining such evaluation tables in light of empirical or historical information. Methods and systems for objective DF risk assessments are provided. Methods and systems for the analysis of fault trees using a novel system of valuation and evaluation are also provided. As a first step, the methods and systems may proceed by creating an FTAM. The FTAM may model the causal relationships between Root Causes, Minor Effects, and Primary Effects. The FTAM may include relationship algorithms reflecting the relationships between one or more Root Causes, one or more Minor Effects, and the Primary Effect. Where the FTAM demonstrates or reflects a relationship between any two events, those events can be said to be related to each other. Root causes may be assigned probability values and the relationship algorithms are then evaluated to further assign probability values to the Minor Effects and Primary Effects included in the FTAM. Where information about the probability value for one or more Root Causes is unavailable or incomplete, any given Minor Effect may be assigned a probability value independent of the missing information. The FTAM itself may similarly be cast at an intermediate level, such that individual Root Causes are not represented but the Minor Effects which subsume those Root Causes are represented. An FTAM may be comprehensive, or the FTAM may exclude certain types of ME or RC, such as human error, change coordination, and/or project execution failures. The RCs and MEs chosen for the FTAM may be measurable events. For example the RCs or MEs may be susceptible to the determination of historical frequency of occurrence or probability of occurrence given evidence of other events. In some embodiments, the FTAM may be built by beginning with one or more Primary Effects and methodically identifying the various pathways to the Primary Effects. In some embodiments, the FTAM may be take the form demonstrated in the attached Appendix A, wherein the Root Causes are depicted in circles, the various MEs and Primary Effects are depicted in rectangles, and the mechanisms of probability aggregation are depicted by AND-gates, OR-gates, and INHIBIT-gates consistent with the other figures in this application and the conventions of fault tree analysis. Once the analytical model has been established, values may be assigned to the analytical model and those assigned values may be refined. Initially, values may be assigned to the events of the model. In some embodiments, the initial values may not be available with respect to Root Causes, but only with respect to higher level failure modes such as Minor Effects. Such assignment may be accomplished, for instance, by the examination of historical data or by interviewing individuals with subject-matter expertise or by reference to known methods for such assignment. To the extent possible given the model and the available initial values, MEs may be derived by the application of the relationship algorithms reflected in the FTAM. Relative initial ranks and weights may be assigned through Analytical Hierarchy Processes (AHPs) of the sort generally known to persons skilled in the art. In one embodiment, the AHPs may involve first collecting initial data by setting measurement metrics and associated significance, applying weight to the metrics, assigning the weighted metrics to a prioritization matrix, systematically assigning individual project data to the appropriate metric level and then compositing the risk score by multiplying the metric weight by the assigned level for each metric. Having assigned the initial values, refining the initial values may require collecting data to support the model and then refining the assigned values by formalizing and quantifying the values assigned. In some embodiments, the data elements required may be identified and defined. Data collection may be prioritized by identifying the minimal cut-set of the FTAM and calculating the Fussell-Vesely importance ratings. Data collection may be used then to test the initial model established against historical data. Data collection may use a stratified, random sampling strategy or any other suitable approach. Further, the FTAM may be further refined by resetting the weights established earlier to a neutral value and proceeding with AHPs that utilize the data sets acquired during data collection. The model so developed may be tested against historical data and result sets. For instance, the event probabilities may be replaced with Boolean (0,1) values based on whether or not the actual events occurred, and unknown occurrences can maintain the baseline probabilities established. Running the model with those values will result in a probability of the Primary Effect. Probabilities from multiple historical runs may be compared to the actual occurrences of the Primary Effect helping to validate or refine the models. In some embodiments, the initial or revised weight assigned to an element may be zero, effectively removing that element from the analysis. In some embodiments, Bayesian logic may be employed to identify or validate already identified relationships between RCs or MEs within the model. Rather than events within a fault tree being assigned traditional Boolean or probability values, some events within the fault tree may instead be assigned values corresponding to members of one or more assignment sets. An assignment set may be well-ordered. For the purposes of this application, a well-ordered set is a set in which any non-empty subset includes a least member, and in which no two members are equal. The comparisons “least” and “equal” are made along a spectrum that may be chosen to comport with the analytical purposes of the FTAM. The members of an assignment set may be qualitative with respect to the events to which they are assigned. Qualitative, for the purposes of this application, means descriptive of some quality of the events that contributes to or detracts from the Top Event. When an assignment set is defined to include only three members, the assignment of members to fault tree events may be called a psi-valuation or T-valuation. An assignment set may be defined to include (HIGH, MEDIUM, LOW); or (H, M, L). For purposes of this application, HIGH and H are used interchangeably, similarly MEDIUM and M are used interchangeably as are LOW and L. Where an assignment set is defined to include (HIGH, MEDIUM, LOW), the assignment of members to fault tree events may be called an HML assignment or HML valuation. An HML valuation is a type of Ψ-valuation. In some embodiments, the Top Event of a fault tree is considered a negative or undesirable outcome. In such a case, the HIGH value is generally assigned where the event in question is, in isolation, relatively highly likely to lead to the Top Event, while the LOW value is assigned where the event in question is, in isolation, relatively unlikely to lead to the Top Event. This may be termed a HIGH-is-Bad assignment. For instance, if a fault tree Base Event is defined as “release size,” then the in a situation where a larger release size would be more likely to lead to the Top Event of that fault tree—such as failure in the on-time and fully operational deployment of the release—then a large release would be associated with a HIGH value for that Base Event. Further, an assignment set may be defined to include only two members. Where an assignment set is defined to include only two members, the assignment of members to fault tree events may be called a YN-valuation. Possible YN-valuations may be where the assignment set is defined to include (Yes, No) or (Y, N). Under the HIGH-is-Bad assignment scheme, the Y value may be assigned where the event in question, in isolation, contributes to the Top Event, which is to say makes the Top Event more likely to occur. Conventional fault trees are constructed using known logic gates such as AND-gates and OR-gates to combine the Boolean or probability values of the various Base and Intermediate Events. In some embodiments of the invention a fault tree may instead combine some of the various Base Events and Intermediate Events through a series of defined gates. The definition of the gates may include an expected number of Ψ-valued inputs, an expected number of YN-valued inputs, and a table indicating what outcome or result should proceed from the presentation to the gate of various combinations of possible input values. The definition of the results for any gate will intrinsically describe the type of valuation to which those results will be susceptible. In some embodiments each element in an FTAM may be assigned either a Ψ-valuation or a YN-valuation. The set that is the union of those two sets contains five members and is not well-ordered. In some embodiments, the union of those two sets may be closed under the operation of the various defined gates. Analysis of an FTAM in circumstances where each element of the FTAM may be assigned either a Ψ-valuation or a YN-valuation and where the five-member union of those sets is not well ordered and is closed under the operation of the gates in the FTAM may be termed “5-value logic.” Some gates by which Base Event and Intermediate Event values may be combined may include the gates described in FIG. 5, discussed below. In some embodiments, analysis of historical or observed data as applied to the fault tree may allow for data mining. Such data mining may result in refinements to the result tables of particular gates. Said refinements may include adding a weight element to the gates, or may include simply modifying the result table of particular gates to reflect the results of the data mining. Such modified gates may be termed “source-specific,” in that the result tables applicable to those gates are specific to the sources of the input data. For simplicity, modifying any of the predefined gates in order to create source-specific gates may be termed adjusting the “weight” of the gate or of the FTAM elements combined within that gate. Embodiments of the invention will now be described with reference to the drawings and the Appendix. In the following description of the various embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope and spirit of the present invention. As will be appreciated by one of skill in the art upon reading the following disclosure, various aspects described herein may be embodied as a method, a data processing system, or a computer program product. Accordingly, those aspects may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, such aspects may take the form of a computer program product stored by one or more computer-readable storage media having computer-readable program code, or instructions, embodied in or on the storage media. Any suitable computer readable storage media may be utilized, including hard disks, CD-ROMs, optical storage devices, magnetic storage devices, and/or any combination thereof. In addition, various signals representing data or events as described herein may be transferred between a source and a destination in the form of electromagnetic waves traveling through signal-conducting media such as metal wires, optical fibers, and/or wireless transmission media (e.g., air and/or space). FIG. 1 is a block diagram that illustrates a generic computing device 101 (alternatively referred to herein as a “server”) that may be used according to an illustrative embodiment of the invention. The computer server 101 may have a processor 103 for controlling overall operation of the server and its associated components, including RAM 105, ROM 107, input/output module 109, and memory 115. Input/output (“I/O”) module 109 may include a microphone, keypad, touch screen, and/or stylus through which a user of device 101 may provide input, and may also include one or more of a speaker for providing audio output and a video display device for providing textual, audiovisual and/or graphical output. Software may be stored within memory 115 and/or storage to provide instructions to processor 103 for enabling server 101 to perform various functions. For example, memory 115 may store software used by device 101, such as an operating system 117, applications 119, and an associated database 121. Alternatively, some or all of device 101 computer executable instructions may be embodied in hardware or firmware (not shown). As described in detail below, database 111 may provide storage for FTAMs, relationship algorithms, values of elements of FTAMs, weights and ranks of elements of FTAMs, and any other suitable information. Server 101 may operate in a networked environment supporting connections to one or more remote computers, such as terminals 141 and 151. Terminals 141 and 151 may be personal computers or servers that include many or all of the elements described above relative to server 101. The network connections depicted in FIG. 1 include a local area network (LAN) 125 and a wide area network (WAN) 129, but may also include other networks. When used in a LAN networking environment, computer 101 is connected to LAN 125 through a network interface or adapter 113. When used in a WAN networking environment, server 101 may include a modem 127 or other means for establishing communications over WAN 129, such as Internet 131. It will be appreciated that the network connections shown are illustrative and other means of establishing a communications link between the computers may be used. The existence of any of various well-known protocols such as TCP/IP, Ethernet, FTP, HTTP and the like is presumed, and the system can be operated in a client-server configuration to permit a user to retrieve web pages from a web-based server. Any of various conventional web browsers can be used to display and manipulate data on web pages. Additionally, applications 119, which may be used by server 101, may include computer executable instructions for invoking user functionality related to communication, such as email, short message service (SMS), and voice input and speech recognition applications. Computing device 101 and/or terminals 141 or 151 may also be mobile terminals including various other components, such as a battery, speaker, and antennas (not shown). Terminal 151 and/or terminal 141 may be portable devices such as a laptop, cell phone, blackberry, or any other suitable device for storing, transmitting and/or transporting relevant information. Relationship algorithms, values of elements of FTAMs, weights and ranks of elements of FTAMs, intermediate values necessary in the evaluation of relationship algorithms, and any other suitable information may be stored in memory 115. One or more of applications 119 may include one or more algorithms that may be used to perform the creation of FTAMs, the evaluation of relationship algorithms, the assignment or determination of values of elements of FTAMs, the determination or revision of weights and ranks of elements of FTAMs, and any other suitable tasks related to the creation, analysis, or processing of FTAMs. The invention may be operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well known computing systems, environments, and/or configurations that may be suitable for use with the invention include, but are not limited to, personal computers, server computers, hand-held or laptop devices, mobile phones and/or other personal digital assistants (“PDAs”), multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like. The invention may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices. FIG. 2 is a diagram of illustrative logic of an Intermediate Level FTAM 200. The Intermediate Level FTAM 200 describes a set of failure paths to the Top Event FCI 244. The FTAM 200 demonstrates the relationships between Minor Effects and the Primary Effect. Intermediate Level FTAM 200 is designated as “intermediate” because it does not demonstrate or describe the failure paths to the finest granularity that would be the case if Root Causes were included. Instead the Intermediate Level FTAM describes those paths in terms only or mostly of Minor Effects. The occurrence or likelihood of the Primary Effect (or Top Event) “Failed Customer Interaction” 244 of the FTAM is represented in a rectangle. All other rectangles (202-242) represent the occurrence or probability of the Minor Effect there named. Probabilities may be expressed as decimal values between 0 and 1. The Minor Effects are combined mathematically by combinations of AND-gates such as 250, OR-gates such as 252, and INHIBIT-gates such as 254. An AND-gate such as 250 combines the probabilities involved by multiplying them. That is, if P(a) is the probability of a and P(b) is the probability of b, then the probability of the two events combined through an AND-gate is the probability of a AND b and is given by: P(a AND b)=P(a)*P(b). An OR-gate such as 252 combines the probabilities by adding them. That is, if P(a) is the probability of a and P(b) is the probability of b, then the probability of the two events combined through an OR-gate is the probability of a OR b and is given by F(a OR b)=(P(a)+P(b)). An INHIBIT-gate such as 254 is a special case of the AND-gate and combines probabilities in the same fashion as an AND-gate. The INHIBIT-gate differs from the AND-gate only in that the input so combined is conditionally necessary, though not directly causal. The conditional input is often depicted in an oval, attaching to the INHIBIT-gate from the side. Describing the Intermediate Level FTAM 200 from the Top Event down, FCI 244 can occur if a Customer's expectation is not met in a manner unrelated to a technical failure 242 or if there occurs a Confirmed Technology Incident 240. A Confirmed Technology Incident 240 can occur if there is a confluence of all four of the following Minor Effects: a Safeguard Failure 232, an Initiated Transaction 234, Awareness of the Failure 236, and a Technology Problem 238. A Technology Problem 238 can occur if any of the following Minor Effects occurs: a Software Failure 224, a Failed Change 226, a Hardware Failure 228, or a Capacity Failure 230. The description of the Minor Effects which lead to a Failed Change 226 is slightly more convoluted. It requires that both a Safeguard Failure 216 occurs and any of the following Minor Effects: a Development Error Placed in Production 218, a Deployment Issue 220, and Inadequate Design 222. The Intermediate Level FTAM 200 further describes the Minor Effects which underlie the occurrence of a Development Error Placed in Production 218. The occurrence of a Development Error Placed in Production 218 requires the confluence of, on the one hand, a Defect (having been) Created in the Application 212 or a Defect Created in the Physical Environment 214 and, on the other hand, a Defect Deferred 208 or a Defect Missed in Testing 210. Finally, a Defect Created in the Application 212 can occur if deployment affects a High Risk System 202 and there is an inadequacy in Design Quality 204 and there is a high level of Design Complexity 206. As such, the Intermediate Level FTAM 200 relates the likelihood or occurrence of any or all of the various Minor Effects noted to each other and to the Primary Effect FCI 244. FIG. 3 is a diagram of Minor Effect “Deployment Issue” with some Root Causes shown 300. Within the context of the FTAM depicted in FIG. 3, the existence of a Deployment Issue 302 is the Top Event. Deployment Issue 302 is congruent to Deployment Issue 220, designated a Minor Effect in FIG. 2. The FTAM of FIG. 3 demonstrates the relationship between some Root Causes and a Deployment Issue 302. Parsing the FTAM of FIG. 3 from the “bottom” up, The combination through an OR-gate such as 352 of three Root Causes results in a Packaging/Build Error 306. Those three Root Causes are: the provision of Poor Packaging/Build Requirements 310, the Failure of Packaging/Build Tool 312, and Human Error 314. The combination through an OR-gate 352 of the Minor Effects of a Migration Issue 304, a Packaging/Build Error 306, and an Exceeded Planned Deployment Duration 308 results in the occurrence of the Top Event, a Deployment Issue 302. As depicted in the FTAM of FIG. 2, the Top Event there, a Failed Customer Interaction 244 is related to the Deployment Issue 220. Thus the Failed Customer Interaction 244 is shown to be related to, for instance, the Root Cause Packaging/Build Tool Failure 312. In one embodiment, the illustrative logic for a customer impact predictive FTAM is shown in Appendix A, where the Primary Effect is a Failed Customer Interaction (FCI). Describing the various relationships described therein in narrative form would be impractical and unnecessary. In a manner similar to that described in FIGS. 2 and 3, Appendix A demonstrates the relationship between the Top Event therein—a Failed Customer Interaction—and approximately 228 Root Causes and a number of Minor Effects. FIG. 4 is a diagram showing graphical representations of some of the gates consistent with principles of the invention. Gates are generally described by the type of input values they anticipate and a term describing in a general sense the mechanism of that gate's combination of the inputs. For instance, the 1Ψ-1Y-AND gate 401 shows one Ψ-valued input 402 and one YN valuation input 403 and, by combining them in a manner somewhat comparable to a traditional Boolean AND-gate, produces a Ψ-valued result 404. Similarly, the 1Ψ-1Y-OR gate 405 shows one Ψ-valued input 406 and one YN valuation input 407, and by combining them in a manner somewhat comparable to a traditional Boolean OR-gate, produces a Ψ-valued result 408 The 3Y-OR gate 409 shows three YN-valued inputs 410 and by combining them in a manner comparable to a traditional Boolean OR-gate, produces a YN-valued result 412. The 1Ψ-2Y-OR gate 413 shows one Ψ-valued input 414 and two YN-valued inputs 415, and produces a Ψ-valued result 416. The 2Ψ-OR gate 417 shows two Ψ-valued input 418 and produces a Ψ-valued result 419. The 2Ψ-AND gate 420 shows two Ψ-valued input 421 and produces a Ψ-valued result 422. The 2Ψ-1Y-OR gate 423 shows two Ψ-valued inputs 424 and one YN-valued input 425, and produces a Ψ-valued result 426. The 3Ψ-OR gate 427 shows three Ψ-valued inputs 428 and produces a Ψ-valued result 429. The 3Ψ-AND gate 430 shows three Ψ-valued inputs 431 and produces a Ψ-valued result 432. The 3Y-AND gate 433 shows three YN-valued inputs 434 and produces a Ψ-valued result 435. The 4Ψ-OR gate 436 shows four Ψ-valued inputs 437 and produces a Ψ-valued result 438. Similarly, the 2Ψ-1Y-OR gate 405 shows two Ψ-valued inputs 406 and 407, and one YN valuation input 408 combined in a manner similar to a traditional Boolean OR-gate 409. The 3Y-OR gate 410 shows three YN valuation inputs 411, 412, 413, all three combined in a manner similar to a traditional Boolean OR-gate 414. FIG. 5 is a diagram showing the input and result table for a 1Ψ-1Y-AND gate 501. Where the Ψ-valued input is High and the YN-valued input is Y 502, the gate result will be High 503. Where the Ψ-valued input is Medium and the YN-valued input is N 504, the gate result will be Medium 505. Where the Ψ-valued input is Low and the YN-valued input is N 506, the gate result will be Low 507. FIG. 6 is a diagram showing the input and result table for a 1Ψ-1Y-OR gate 601. Wherever the YN-valued input is Y 602, the gate result will be High 603. Wherever the Ψ-valued input is High 604, the gate result will similarly be High 605. Where the Ψ-valued input is Medium and the YN-valued input is N 606, the gate result will be Medium 607. Where the Ψ-valued input is Low and the YN-valued input is N 608, the gate result will be Medium 609. FIG. 7 is a diagram showing the input and result table for a 3Y-OR gate 701. Where all of the YN-valued inputs is N 702, the gate result is N 703. Where any of the YN-valued inputs is Y 704 the gate result is Y 705. FIG. 8 is a diagram showing the input and result table for a 1Ψ-2Y-OR gate 801. Wherever both of the YN-valued inputs are Y 802, the gate result is High 803. FIG. 9 is a diagram showing the input and result table for a 2Ψ-OR gate 901. Where either of the two Ψ-valued inputs is Medium and the other is Low 902, the gate result is Medium 903. FIG. 10 is a diagram showing the input and result table for a 2Ψ-AND gate 1001. Where either of the two Ψ-valued inputs is Medium and the other is Low 1002, the gate result is Low 1003. FIG. 11 is a diagram showing the input and result table for a 2Ψ-1Y-OR gate 1101. Where both of the Ψ-valued inputs is High and the YN-valued input is Yes 1102, the gate result will be High 1103. Where one of the Ψ-valued inputs is High, the other is Low, and the Y-valued input is No 1104, the gate result will be High 1105. Where one of the Ψ-valued inputs is Medium, the other is Low, and the Y-valued input is No 1106, the gate result will be Medium 1107. FIG. 12 is a diagram showing the input and result table for a 3Ψ-OR gate 1201. Where any of the Ψ-valued inputs is High 1202, the gate result will be High 1203. Where any of the Ψ-valued inputs is Medium and none are High 1204, the gate result will be Medium 1205. Where none of the Ψ-valued inputs is High or Medium 1206, the gate result will be Low 1207. FIG. 13 is a diagram showing the input and result table for a 3Ψ-AND gate 1301. Where all three Ψ-valued inputs are High 1302, the gate result will be High 1303. Where any two of the Ψ-valued inputs are High and the third is Low 1304, the gate result will be Medium 1305. Where any one of the Ψ-valued inputs is High, any other one is Medium, and any third one is Low 1306, the gate result will be Medium 1307. FIG. 14 is a diagram showing the input and result table for a 3Y-AND gate 1401. Where all three of the YN-valued inputs is Yes 1402, the gate result will be High 1403. Where any two (and only two) of the YN-valued inputs is Yes 1404, the gate result will be Medium 1405. Where only one of the YN-valued inputs is Yes 1406, or where none of the YN-valued inputs is Yes 1407, the gate result will be Low 1408. FIG. 15 is a diagram showing the input and result table for a 4Ψ-OR gate 1501. Where, for instance, of the four Ψ-valued inputs, two are High, one is Medium and one is Low 1502, the gate result will be High 1503. FIG. 16 is a diagram showing an input and result table of a modified (source-specific) 3Ψ-AND gate 1601. The three different Ψ-valued inputs to a 3Ψ-AND gate may, after data mining and analysis, be specific to certain sources within a fault tree. For instance, the three Ψ-valued inputs may be “Design Risk,” “Build & Test Risk,” and “Deployment Risk.” Those three factors may, in some embodiments, be elements in a fault tree where Project Risk is the Top Event, as demonstrated in FIG. 17. As represented in FIG. 16, the first column of Ψ-valued inputs 1602 may correspond to the “Design Risk” element, while the second column 1603 may correspond to the “Build & Test Risk” element and the third column 1604 may correspond to the “Deployment Risk” element. In some combinations, where one of the Ψ-valued inputs is High, one is Medium, and one is Low 1605, the gate result may be Medium 1606. However, in other combinations, with the same distribution of Ψ-valued inputs 1607, the gate result may be Low 1608. The source-specific 3Ψ-AND gate results are different from the standard 3Ψ-AND gate results in a number of instances 1609. FIG. 17 is a diagram showing an FTAM in which Project Risk 1701 is the Top Event. Project Risk may be correlative to a Deployment Failure. Each element of the FTAM of FIG. 17 may be susceptible to either a Ψ-valuation or a YN-valuation, and the gates are defined to combine those elements. The FTAM of FIG. 17 describes the relationship between some Root Causes, some Intermediate Causes, and Project Risk 1701 in terms of 5-value logic. Project Risk 1701 is the result of the combination of Design Risk 1702, Build & Test Risk 1703, and Deployment Risk 1704, as combined through a 3Ψ-AND gate 1705. The 3Ψ-AND gate 1705 may be identical in some respects to the 3Ψ-AND gate 430 in FIG. 4. Design Risk 1702 is the result of the combination of Design Complexity 1706 and (Lack of) Design Quality 1707, through a 2Ψ-AND gate 1708, which may be identical in some respects to the 2Ψ-AND gate 420. (Lack of) Design Quality 1707 is so named in order to maintain adherence to the HIGH-is-Bad assignment scheme, such that a HIGH value will, in isolation, contribute to the Top Event. Technical Complexity 1709, Project Size 1710, and Project Scope 1711 combine through a 3Ψ-AND gate 1712 to establish Design Complexity 1706. Technical Complexity 1709 is established by the combination through a 1Ψ-2Y-OR gate 1713 (which may be similar to 1Ψ-2Y-OR gate 413) of Root Cause High Risk System 1714, Unnamed Intermediate Event (“UIE”) 1715 and UIE 1716. UIE 1715 is established by the combination through a 3Y-OR gate 1717 (compare 3Y-OR gate 409) of three Root Causes: Vendor Development 1718, Build New Hardware 1727, and New Application 1719. UIE 1716 is established by the combination through a 2Ψ-OR gate 1720 of Root Cause Number of Applications 1721 and Root Cause Build and Test Hours 1722. Root Causes High Impact Project 1723 and Design Hours 1724 combine through a 1Ψ-1Y-OR gate 1725 to establish Project Size 1710. 1Ψ-1Y-OR gate 1725 may be identical in some respects to 1Ψ-1Y-OR gate 405. Root Causes Number of Organizations Impacted 1726 and (Existence of) Dependent Projects 1728 combine through a 1Ψ-1Y-OR gate 1729 to establish Project Scope 1711. 1Ψ-1Y-OR gate 1729 may be identical in some respects to 1Ψ-1Y-OR gate 405. Similarly, (Lack of) Design Quality 1707 is established by the combination through a 4Ψ-OR gate 1730 of three Intermediate Events, namely (Risk to) Resource Proficiency 1731, (Risk to) Deliverable Quality 1732, (Risk to) Deliverable Execution 1733, and the Root Cause (Lack of) Change Controls 1734. Root Cause Lack of Change Manager Proficiency 1735 is shown as establishing Risk to Resource Proficiency 1731. Risk to Deliverable Quality 1732 is established through the combination of Lack of Quality in Business Requirements 1736 and Requirement Related Defects 1737 through a 2Ψ-OR gate 1738, which may be identical in some respects to the 2Ψ-OR gate 417 of FIG. 4. Risk to Deliverable Execution 1733 is established by the combination through a 3Y-AND gate 1742 of Late Business Requirements 1739, Late High-Level Design 1740, and Late Low-Level Design 1741. Turning to Deployment Risk 1704, that element is established by the combination of an UIE 1743 and the Lack of a Deployment Safeguard 1766 through a 1Ψ-1Y-AND gate 1744. The UIE 1743 is itself established by the combination through a 1Ψ-1Y-OR gate 1747 or Release Size 1745 and Large Number of Dependent Projects 1746. Describing some aspects of the FTAM of FIG. 17 from the “bottom” up, Root Causes Number of Emergency Code Migrations 1748, Lack of Test Environment Availability 1749, and Testing Started Late 1749 combine through a 2Ψ-1Y-OR gate 1755 (which may be identical in some respects to 2Ψ-1Y-OR gate 423) to establish UIE 1752. UIE 1752 combines with Deferred Testing Defects 1753 and Number of Test Scripts Planned and Executed 1754 through 3Ψ-OR gate 1755, which may be identical in some respects to 3Ψ-OR gate 427, to establish Intermediate Event Testing Ineffectiveness 1756. Similarly, Resource Constraint 1757 and Historical Defect Rate 1758, both Root Causes, combine through a 2Ψ-OR gate 1759, which may be identical in some respects to the 2Ψ-OR gate 417 in FIG. 4, to establish UIE 1760. In turn, UIE 1760 combines with Code Related Defects 1762 and Code Delivered Late 1761, both Root Causes, through a 2Ψ-1Y-OR gate 1763 to establish Intermediate Event (Lack of) Build Quality 1764. Lack of Build Quality 1764 is so termed so as to accommodate the HIGH-is-Bad assignment scheme. Testing Ineffectiveness 1756 and Lack of Build Quality 1764. Combine through a 2Ψ-AND gate 1765 to establish Build and Test Risk 1703. 2Ψ-AND gate 1765 may be identical in some respects to 2Ψ-AND gate 420 in FIG. 4. Systems or methods for objective DF risk assessments are therefore provided. Also, methods and systems for the analysis of fault trees using a novel system of valuation and evaluation are provided. Persons skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which are presented for purposes of illustration rather than of limitation, and that the present invention is limited only by the claims that follow. |
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063234998 | description | DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Mode of Carrying Out the Invention [Description of Principle] FIGS. 4A and 4B are views for explaining the principle of the present invention. Reference symbol PL denotes a reduction electron optical system; and AX, an optical axis of the reduction electron optical system PL. Reference numerals 01, 02, and 03 denote point sources for emitting electrons; and I1, I2, and I3, point source images corresponding to the point sources. Referring to FIG. 4A, electrons emitted from the point sources 01, 02, and 03 which are located on a plane perpendicular to the optical axis AX on the object side of the reduction electron optical system PL form the point source images I1, I2, and I3 corresponding to the point sources on the image side of the reduction electron optical system PL. The point source images I1, I2, and I3 are not formed on the same plane perpendicular to the optical axis AX because of the aberrations (curvature of field) of the reduction electron optical system. In the present invention, to form the point source images I1, I2, and I3 on the same plane perpendicular to the optical axis AX, as shown in FIG. 4B, the point sources 01, 02, and 03 are located at different positions along the optical axis in accordance with the aberrations (curvature of field) of the reduction electron optical system. In addition, since the aberrations (astigmatism, coma, or distortion) of the reduction electron optical system change depending on the positions of the sources on the object side, desired source images are formed on the same plane by distorting the sources in advance. In the present invention, a correction electron optical system is arranged to form a plurality of intermediate images of a source on the object side of the reduction electron optical system and to correct in advance the aberrations generated when the intermediate images are reduced and projected on a target exposure surface by the reduction electron optical system. With this arrangement, a lot of source images each having a desired shape can be simultaneously formed in a wide exposure area. The plurality of intermediate images need not always be formed from one source, and may be formed from a plurality of sources, as a matter of course. Embodiments of the present invention will be described below in detail. First Embodiment [Description of Constituent Elements of Exposure System] FIG. 1 is a view showing an electron beam exposure apparatus according to the first embodiment of the present invention. Referring to FIG. 1, reference numeral 1 denotes an electron gun consisting of a cathode 1a, a grid 1b, and an anode 1c. Electrons emitted from the electron gun 1 form crossover image between the grid 1b and the anode 1c. The electron gun 1 has a function of changing the grid voltage so as to change the size of the crossover image. Since an electron optical system (not shown) for enlarging/reducing or shaping the crossover image is used, an enlarged/reduced or shaped crossover image can be obtained. With this arrangement, the size and shape of the crossover image can be changed (the crossover image will be referred to as a source hereinafter). Electrons emitted from the source are formed into an almost collimated electron beam through a condenser lens 2 whose front focal position is set at the position of the source. The almost collimated electron beam is incident on a correction electron optical system 3 in which a plurality of element electron optical systems (31, 32) (the number of element electron optical systems is preferably as large as possible, though two element electron optical systems are illustrated for the descriptive convenience) are aligned in a direction perpendicular to the optical axis. The plurality of element electron optical systems (31, 32) constituting the correction electron optical system 3 will be described later in detail. The correction electron optical system 3 forms a plurality of immediate images (MI1, MI2) of the source. The intermediate images form source images (I1, I2) on a wafer 5 through a reduction electron optical system 4. The elements of the correction electron optical system 3 are set to make the interval between the source images on the wafer 5 an integer multiple of the size of the source image. The correction electron optical system 3 changes the positions of the intermediate images along the optical axis in accordance with the curvature of field of the reduction electron optical system 4, and at the same time, corrects in advance any aberrations generated when the intermediate images are reduced and projected on the wafer 5 by the reduction electron optical system 4. The reduction electron optical system 4 is a symmetrical magnetic tablet consisting of a first projecting lens 41 and a second projecting lens 42. When the focal length of the first projecting lens 41 is represented by f1, and that of the second projecting lens 42 is represented by f2, the distance between the two lenses is f1+f2. The intermediate image on the optical axis AX is formed at the focal position of the first projecting lens 41, and the image of the intermediate image is formed at the focal point of the second projecting lens 42. This image is reduced to -f2/f1. Since the two lens magnetic fields are determined to act in opposite directions, Seidel's aberrations except five aberrations, i.e., spherical aberration, isotropic astigmatism, isotropic coma, curvature of field, and on-axis chromatic aberration, and chromatic aberrations associated with rotation and magnification are canceled in theory. A deflector 6 deflects the electron beams from the plurality of intermediate images to move the images of the plurality of intermediate images in the X and Y directions on the wafer. The deflector 6 is constituted by an MOL (Moving Object Lens) type electromagnetic deflector 61 which deflects a beam by a converging magnetic field and a deflection magnetic field satisfying the MOL condition, and an electrostatic deflector 62 which deflects a beam by an electric field. The electromagnetic deflector 61 and the electrostatic deflector 62 are selectively used in accordance with the moving distance of the source image. A dynamic focus coil 7 corrects any shift in focal position caused by deflection errors generated when the deflector is actuated. A dynamic stigmatic coil 8 corrects astigmatism generated by deflection. Each of deflectors 91 and 92 is constituted by a plurality of electrostatic deflectors for translating (in the X and Y directions) or deflecting (tilt with respect to the Z-axis) the electron beam from the plurality of intermediate images formed by the correction electron optical system. A Faraday cup 10 has two single knife-edges extending along the X and Y directions. An X-Y-Z stage 11 is movable in the X, Y, and Z directions while mounting the wafer 5 thereon, and is controlled by a stage drive control unit 23. The Faraday cup 10 fixed on the wafer stage detects the charge amount of the source image formed with the electron beam from the element electron optical system while moving through the knife-edges in cooperation with a laser interferometer 20 for detecting the position of the X-Y-Z stage. With this arrangement, the size and position (X,Y,Z) of the source image, and the current irradiated from the element electron optical system can be detected. The element electron optical system constituting the correction electron optical system 3 will be described below with reference to FIGS. 5A and 5B. Referring to FIG. 5A, reference numeral 301 denotes a blanking electrode consisting of a pair of electrodes and having a deflection function; 302, an aperture stop having an aperture (AP) for defining the shape of the electron beam passing through the aperture, on which a wiring layer (W) for turning on/off the blanking electrode 301 is formed; 303, a unipotential lens consisting of three aperture electrodes and having a converging function of setting the upper and lower electrodes at an acceleration potential V0 and keeping the intermediate electrode at another potential V1; and 304, a blanking aperture positioned on the focal plane of the aperture stop 302. The electron beam which is nearly collimated by the condenser lens 2 is formed into an intermediate image (MI) of the source on the blanking aperture 304 by the unipotential lens 303 through the blanking electrode 301 and the aperture (AP). If, at this time, no electric field is applied between the electrodes of the blanking electrode 301, an electron beam 305 is transmitted through the aperture of the blanking aperture 304. On the other hand, when an electric field is applied between the electrodes of the blanking electrode 301, an electron beam 306 is shielded by the blanking aperture 304. Since the electron beams 305 and 306 have different angular distributions on the blanking aperture 304 (the object plane of the reduction electron optical system), the electron beams 305 and 306 are incident on different areas at the pupil position (on a plane P in FIG. 1) of the reduction electron optical system, as shown in FIG. 5B. Therefore, in place of the blanking aperture 304, a blanking aperture 304' for passing only the electron beam 305 may be formed at the pupil position (on the plane P in FIG. 1) of the reduction electron optical system. The blanking aperture can be commonly used by other element electron optical systems constituting the correction electron optical system 3. In this embodiment, a unipotential lens having a converging function is used. However, a bipotential lens having a diverging function may be used to form a virtual intermediate image. Referring back to FIG. 1, the correction electron optical system 3 changes the positions of intermediate images formed by the element electron optical systems along the optical axis in accordance with the curvature of field of the reduction electron optical system 4. As a specific means therefor, identical element electron optical systems are used and set at different positions along the optical axis. As another technique, the element electron optical systems are set on the same plane, and the electron optical characteristics (focal length and major surface position) of the element electron optical systems, and more particularly, the unipotential lenses are changed to change the positions of the intermediate images along the optical axis. The latter means employed in this embodiment will be described in detail with reference to FIGS. 6A and 6B. Referring to FIG. 6A, blanking electrodes are formed for each aperture of the aperture stop 302 having two apertures (AP1, AP2) with the same shape, thereby constituting a blanking array. The blanking electrodes are independently wired to independently turn on/off the electric fields (FIG. 7). Unipotential lenses 303-1 and 303-2 constitute a lens array by bonding three insulators 307 to 309 each having an electrode formed thereon. The electrodes are wired such that upper and lower electrodes (303U, 303D) can be set at a common potential (FIG. 8), and intermediate electrodes (303M) can be independently set at different potentials (FIG. 9). The blanking array and ends array form an integral structure while interposing an insulator 310. The electrodes of the unipotential lenses 303-1 and 303-2 have the same shape. The focal lengths are different because the potentials of the intermediate electrodes are different. Therefore, the intermediate images (MI1, MI2) formed with electron beams 311 and 312 are located at different positions along the optical axis, respectively. FIG. 6B shows another example of the element electron optical system which uses two lens arrays shown in FIG. 6A. Each element electron optical system is constituted by two unipotential lenses arranged at a predetermined interval. With this arrangement, the focal length and principal plane position of each element electron optical system can be independently controlled. When the focal length of the unipotential lens 303-1 is represented by f1, that of a unipotential lens 303-1' is represented by f2, the distance between the unipotential lenses is represented by e, the synthesized focal length is represented by f, and the principal plane position on the image plane side (the distance from the unipotential lens 303-1' toward the source side) is represented by s, the following equations hold paraxially: EQU 1/f=1/f1+1/f2-e(f1.times.f2) EQU s=e.times.f/f1 By adjusting the focal length of each unipotential lens (the potential of the intermediate electrode of each unipotential lens), the synthesized focal length and principal plane position of each element electron optical system can be independently set within limited ranges. The focal position (intermediate image formation position) changes by a distance corresponding to the moving amount of the major principal plane, as a matter of course. The focal lengths of the element electron optical systems can be made almost equal, and just the focal positions can be changed. In other words, the intermediate images of the source can be formed by the element electron optical systems at the same magnification (finally, the source images I1 and I2 on the wafer 5 are formed at the same magnification) while changing just the positions of the intermediate images along the optical axis. Therefore, the intermediate images (MI1, MI2) of the electron beams 311 and 312 can be formed at different positions along the optical axis. In this embodiment, the element electron optical system is constituted by two unipotential lenses. However, the element electron optical system may be constituted by three or more unipotential lenses. To correct astigmatism generated when each intermediate image is reduced and projected on the target exposure surface by the reduction electron optical system 4, each element electron optical system generates astigmatism of opposite sign. To generate the astigmatism of opposite sign, the shape of the aperture electrode constituting the unipotential lens is distorted. As shown in FIG. 10A, when the unipotential lens 303-1 has a circular aperture electrode 350, electrons distributed in a direction M and electrons distributed in a direction S form intermediate images at almost the same position 313. However, when a unipotential lens 303-3 has an elliptical aperture electrode 351, electrons distributed in the direction M (along the short diameter) form an intermediate image at a position 314, and electrons distributed in the direction S (along the long diameter) form an intermediate image at a position 315. With this arrangement, astigmatism of opposite sign can be generated. As shown in FIG. 10B, the intermediate electrode 303M of the unipotential lens 303-1 is divided into four portions. The potentials of opposing electrodes are set to be V1, and the potentials of the other opposing electrodes are set to be V2. The potentials V1 and V2 may be changed by a focus control circuit, and the function of the unipotential lens 303-1 can also be obtained in this case. As described above, when the shape of the aperture electrode of the unipotential lens of each element electron optical system is changed in accordance with the astigmatism of the reduction electron optical system 4, astigmatism generated when each intermediate image is reduced and projected on the target exposure surface by the reduction electron optical system 4 can be corrected. One element electron optical system may be constituted by the unipotential lens 303-1 for correcting curvature of field and the unipotential lens 303-3 for correcting astigmatism such that the curvature of field and the astigmatism can be independently corrected or adjusted, as a matter of course. To correct coma generated when each intermediate image is reduced and projected on the target exposure surface by the reduction electron optical system 4, each element electron optical system generates coma of opposite sign. As a technique of generating the coma of opposite sign, the aperture on the aperture stop 302 is decentered with respect to the optical axis of the unipotential lens 303 in each element electron optical system. As another technique, the electron beams from the plurality of intermediate images are independently deflected by the deflectors (91, 92) in each element electron optical system. To correct distortion generated when each intermediate image is reduced and projected on the target exposure surface by the reduction electron optical system 4, the distortion characteristic of the reduction electron optical system 4 is determined in advance, and the position of each element electron optical system along the direction perpendicular to the optical axis of the reduction electron optical system 4 is set on the basis of the distortion characteristic. [Description of Operation] The source images (I1, I2) formed on the wafer 5 by the element electron optical systems (31, 32) are deflected by the deflector 6 starting from reference positions (A, B) by the same predetermined amount as indicated by arrows in FIG. 11A, respectively, in their respective scan fields to expose the corresponding scan fields of the wafer 5. In FIG. 11A, each cell indicates an area to be exposed to one source image. Each hatched cell indicates an area to be exposed, and each unhatched cell indicates an area not to be exposed. The procedures of preparing an exposure control data file for controlling the above exposure operation will be described below with reference to FIG. 41. Upon receiving the pattern data of an exposure pattern as shown in FIG. 11A, a CPU 12 divides the exposure area into scan fields in units of element electron optical systems in step S001. As shown in FIG. 11B, exposure control data consists of the position data (dx,dy) of the exposure position based on the start position (A, B) in each scan field and exposure data representing whether exposure is to be performed at the exposure position in each scan field ("1" is set for a hatched cell, and "0" is set for an unhatched cell). The exposure control data are arranged in the order of exposure, thereby preparing an exposure control data file. The scan field of each element electron optical system is deflected by the deflector 6 and moved from the reference position (A, B) in the same predetermined amount. Therefore, exposure data of a plurality of scan fields is combined with one position data. In step S002, when exposure is not performed in any scan field, i.e., when all exposure data are set at "0", the exposure control data are deleted (exposure data represented by DEL in FIG. 11B) to prepare a new exposure control data file as shown in FIG. 11C. The exposure control data file is stored in a memory 19 through an interface 13. By using the exposure control data prepared the above manner, a deflection control circuit 21 can be operated such that scanning is performed while skipping portions where all exposure data are set at "0". When the input pattern has a lot of repeated patterns at a specific period (pitch) (e.g., a DRAM circuit pattern consisting of a lot of patterns repeated at a period corresponding to the cell pitch), the CPU 12 sets the start position of each scan field in step S003 such that the interval of the start positions of the scan fields (the interval between the positions of sources formed on the wafer through the element electron optical systems) becomes an integer multiple of the specific period (pitch). With this processing, the number of exposure control data for which all exposure data are set at "0" increases, and the data can be further compressed. For this purpose, the magnification of the reduction electron optical system 4 is adjusted (the focal lengths of the first and second projecting lenses 41 and 42 are changed by a magnification adjustment circuit 22). Alternatively, the positions of intermediate images formed by the element electron optical systems are adjusted by the deflectors 91 and 92. Assume that a pattern has already been formed on the wafer 5, and that pattern is to be double-exposed to a pattern input to the apparatus. In some cases, the wafer may have expanded/contracted in processes before the double-exposure, and the previously formed pattern may also have expanded/contracted. In this apparatus, an alignment unit (wafer mark position detection unit) (not shown) is used to detect the positions of at least two wafer alignment marks on the wafer 5, thereby detecting the expansion/contraction ratio of the already formed pattern. The magnification of the reduction electron optical system 4 is adjusted by the magnification adjustment circuit 22 on the basis of the detected expansion/contraction ratio to increase/decrease the interval between the source images. At the same time, the gain of the deflector 6 is adjusted by the deflection control circuit 21 to increase/decrease the moving amount of the source image. With this arrangement, double-exposure can be satisfactorily performed even for an expanded/contracted pattern. Referring back to FIG. 1, the operation of this embodiment will be described. When a calibration instruction for the exposure system is output from the CPU 12, a sequence controller 14 sets, through a focus control circuit 15, the potentials of the intermediate electrodes of the element electron optical systems to form intermediate images by the element electron optical systems of the correction electron optical system 3 at predetermined positions along the optical axis. The sequence controller 14 controls a blanking control circuit 16 to turn on the blanking electrodes except that of the element electron optical system 31 (blanking on) such that only the electron beam from the element electron optical system 31 is irradiated on the X-Y-Z stage 11 side. Simultaneously, the X-Y-Z stage 11 is driven by the stage drive control unit 23 to move the Faraday cup 10 close to the source image formed by the electron beam from the element electron optical system 31. The position of the X-Y-Z stage 11 at this time is detected by the laser interferometer 20. While detecting the position of the X-Y-Z stage 11 and moving the X-Y-Z stage, the source image formed by the electron beam from the element electron optical system 31 is detected by the Faraday cup 10, thereby detecting the position and size of the source image and the irradiated current. A position (X1,Y1,Z1) where the source image assumes a predetermined size and a current I1 irradiated at that time are detected. The sequence controller 14 controls the blanking control circuit 16 to turn on the blanking electrodes except that of the element electron optical system 32 such that only the electron beam from the element electron optical system 32 is irradiated on the X-Y-Z stage 11 side. Simultaneously, the X-Y-Z stage 11 is driven by the stage drive control unit 23 to move the Faraday cup 10 close to the source image formed by the electron beam from the element electron optical system 32. The position of the X-Y-Z stage 11 at this time is detected by the laser interferometer 20. While detecting the position of the X-Y-Z stage 11 and moving the X-Y-Z stage, the source image formed by the electron beam from the element electron optical system 32 is detected by the Faraday cup 10, thereby detecting the position and size of the source image and the irradiated current. In this way, the sequence controller 14 detects a position (X2,Y2,Z2) where the source image has a predetermined size and a current I2 irradiated at that time. On the basis of the detection results, the sequence controller 14 translates the intermediate images in the X and Y directions by the deflectors 91 and 92 through an optical axis alignment control circuit 18 to locate the source images formed by the electron beams from the element electron optical systems 31 and 32 to hold a predetermined relative positional relationship along the X and Y directions. The sequence controller 14 also sets the potentials of the intermediate electrodes of the element electron optical systems again through the focus control circuit 15 to locate the source images formed by the electron beams from the element electron optical systems 31 and 32 within a predetermined range along the Z direction. In addition, the detected currents of the element electron optical systems, which are irradiated on the wafer, are stored in the memory 19. When pattern exposure is started in accordance with an instruction from the CPU 12, the sequence controller 14 calculates, on the basis of the sensitivity of a resist applied to the wafer 5 which has been input in the memory 19 in advance, and the current irradiated on the wafer by each element electron optical system which has been stored in the memory 19 as described above, the exposure time at the exposure position of the source image (the time of stay of the source image at the exposure position) formed by each element electron optical system, and transmits the calculated exposure time to the blanking control circuit 16. The sequence controller 14 also transmits the exposure control data file stored in the memory 19 as described above to the blanking control circuit 16. The blanking control circuit 16 sets the blanking OFF time (exposure time) for each element electron optical system. The blanking control circuit 16 also transmits a blanking signal as shown in FIG. 12 to each element electron optical system, on the basis of the exposure data for each element electron optical system and the blanking off time for each element electron optical system, which are stored in the transmitted exposure control file, in synchronism with the deflection control circuit 21, thereby controlling the exposure timing and exposure amount for each element electron optical system (the exposure time at each exposure position of field 1 is longer than that of field 2). The sequence controller 14 also transmits the exposure control data file stored in the memory 19 as described above to the deflection control circuit 21. On the basis of the position data in the received exposure control file, the deflection control circuit 21 transmits a deflection control signal, a focus control signal, and an astigmatism correction signal to the deflector 6, the dynamic focus coil 7, and the dynamic stigmatism coil 8, respectively, through a D/A converter in synchronism with the blanking control circuit 16. With this operation, the positions of the plurality of source images on the wafer are controlled. When the shift of the focus position caused by deflection errors generated when the deflector is actuated cannot be completely corrected by the dynamic focus coil, the potentials of the intermediate electrodes of the element electron optical systems may be adjusted through the focus control circuit 15 to set the source image within a predetermined range along the Z-axis, thereby changing the positions of the intermediate images along the optical axis. [Other Arrangement 1 of Element Electron Optical System] Other arrangement 1 of the element electron optical system will be described with reference to FIG. 13A. The same reference numerals as in FIG. 5A denote the same constituent elements in FIG. 13A, and a detailed description thereof will be omitted. This arrangement is largely different from the element electron optical system shown in FIG. 5A in the aperture shape on the aperture stop and the blanking electrode. The aperture (AP) shields an electron beam which enters near the optical axis of the unipotential lens 303 to form a hollow beam (hollow cylindrical beam). A blanking electrode 321 is constituted by a pair of cylindrical electrodes in correspondence with the aperture shape. The electron beam which is formed into an almost collimated beam by the condenser lens 2 passes through the blanking electrode 321 and an aperture stop 320 and forms an intermediate image of the source on the blanking aperture 304 through the unipotential lens 303. If, at this time, no electric field is applied between the electrodes of the blanking electrode 321, an electron beam 323 is transmitted through the aperture of the blanking aperture 304. On the other hand, when an electric field is applied between the electrodes of the blanking electrode 321, an electron beam 324 is deflected and shielded by the blanking aperture 304. Since the electron beams 323 and 324 have different angular distributions on the blanking aperture 304 (the object plane of the reduction electron optical system), the electron beams 323 and 324 are incident on different areas at the pupil position (P in FIG. 1) of the reduction electron optical system, as shown in FIG. 13B. Therefore, in place of the blanking aperture 304, the blanking aperture 304' for passing only the electron beam 323 may be formed at the pupil position of the reduction electron optical system. The blanking aperture can be commonly used by other element electron optical systems constituting the correction electron optical system 3. Since the space charge effect of a hollow electron beam (hollow cylindrical beam) is smaller than that of a nonhollow electron beam (e.g., a Gaussian beam), the electron beam can be brought to a focus on the wafer to form a source image free from any blur on the wafer. More specifically, when the electron beam from each element electron optical system passes through the pupil plane P of the reduction electron optical system 4, the electron beam on the pupil plane obtains an electron density distribution in which the electron density at the peripheral portion becomes higher than that at the central portion. With this arrangement, the above effect can be obtained. The electron density distribution on the pupil plane P can be obtained by the aperture (aperture for shielding light at the central portion) on the aperture stop 320 arranged at a position almost conjugate to the pupil plane P of the reduction electron optical system 4, as in this embodiment. [Other Arrangement 2 of Element Electron Optical System] Other arrangement 2 of the element electron optical system will be described below with reference to FIG. 14A. The same reference numerals as in FIG. 5A or 13A denote the same constituent elements in FIG. 14A, and a detailed description thereof will be omitted. This arrangement is largely different from the element electron optical system shown in FIG. 5A in the aperture shape on the aperture stop (the same shape as that of the aperture stop in FIG. 13A) and omission of the blanking electrode. The electron beam formed into an almost collimated beam by the condenser lens 2 passes through an aperture stop 322 and forms an intermediate image of the source on the blanking aperture 304 through the unipotential lens 303. When the intermediate electrode of the unipotential lens 303 is set at a predetermined potential, the electron beam is converged, and an electron beam 330 is transmitted through the aperture of the blanking aperture 304. On the other hand, when the intermediate electrode is set at the same potential as that of other electrodes, the electron beam is not converged, and an electron beam 331 is shielded by the blanking aperture 304. By changing the potential of the intermediate electrode of the unipotential lens 303, blanking can be controlled. Since the electron beams 330 and 331 have different angular distributions on the blanking aperture 304 (the object plane of the reduction electron optical system), the electron beams 330 and 331 are incident on different areas at the pupil position (P in FIG. 1) of the reduction electron optical system, as shown in FIG. 14B. Therefore, in place of the blanking aperture 304, the blanking aperture 304' for passing only the electron beam 330 may be formed at the pupil position of the reduction electron optical system. The blanking aperture can be commonly used by other element electron optical systems constituting the correction electron optical system 3. Second Embodiment [Description of Constituent Elements of Exposure System] FIGS. 15A-15C are views showing an electron beam exposure apparatus according to the second embodiment of the present invention. Reference numerals as in FIG. 1 denote the same constituent elements in FIGS. 15A-15C, and a detailed description thereof will be omitted. Referring to FIG. 15A-15C, electrons emitted from the source of an electron gun 1 are formed into an almost collimated electron beam by a condenser lens 2 whose front focal position is set at the position of the source. The almost collimated electron beam is incident on an element electron optical system array 130 (corresponding to the correction electron optical system 3 of the first embodiment) formed by arraying a plurality of element electron optical systems described with reference to FIG. 13A in a direction perpendicular to the optical axis, thereby forming a plurality of intermediate images of the source. The element electron optical system array 130 has a plurality of subarrays each of which is formed by arranging a plurality of element electron optical systems having the same electron optical characteristics. At least two subarrays have element electron optical systems with different electron optical characteristics. The element electron optical system array 130 will be described later in detail. A deflector 140 for deflecting (tilt with respect to the Z-axis) the electron beam incident on the subarray is arranged for each subarray. The deflector 140 has a function of correcting, in units of subarrays, the difference in incident angle between electron beams which are incident on subarrays at different positions because of the aberration of the condenser lens 2. A deflector 150 translates (in the X and Y directions) and deflects (tilt with respect to the Z-axis) electron beams from the plurality of intermediate images formed by the subarrays. The deflector 150 corresponds to the deflector 91 or 92 of the first embodiment. The deflector 150 is different from the deflector 91 or 92 in that the deflector 150 translates and deflects the plurality of electron beams from the subarrays at once. The plurality of intermediate images formed by the element electron optical system array 130 are reduced and projected on a wafer 5 through a reduction electron optical system 100 and a reduction electron optical system 4. In this embodiment, two-step reduction is employed to decrease the reduction ratio without making the exposure apparatus bulky. The reduction electron optical system 100 is constituted by a first projecting lens 101 and a second projecting lens 102, like the reduction electron optical system 4. That is, one reduction electron optical system is constituted by the reduction electron optical system 4 and the reduction electron optical system 100. When the number of electron beams from the element electron optical system array increases, the size of the beam incident on the reduction electron optical system increases, and blurs are generated in the source images due to the space charge effect. To correct these blurs, a refocus coil 110 controls the focus position on the basis of the number of source images (the number of blanking electrodes in the OFF state) irradiated on the wafer, which is obtained from a sequence controller 14. A blanking aperture 120 positioned on the pupil plane of the reduction electron optical system 100 is common to the element electron optical systems constituting the element electron optical system array and corresponds to the blanking aperture 304' shown in FIG. 13B. The element electron optical system array 130 will be described below with reference to FIG. 16. FIG. 16 shows the element electron optical system array 130 viewed from the electron gun 1 side. In the element electron optical system array 130, the element electron optical systems described in FIG. 13A are arrayed. The element electron optical system array 130 is constituted by a blanking array in which a plurality of apertures, blanking electrodes corresponding to the apertures, and a wiring layer are formed on one substrate, and a lens array constituted by stacking electrodes constituting a unipotential lens while interposing insulators. The blanking array and the lens array are positioned and coupled to make the apertures oppose the corresponding unipotential lenses. Reference numerals 130A to 130G denote subarrays each consisting of a plurality of element electron optical systems. In the subarray 130A, 16 element electron optical systems 130A-1 to 130A-16 are formed. Since the amounts of aberrations to be corrected in one subarray remain almost the same or fall within an allowance, the unipotential lenses of the element electron optical systems 130A-1 to 130A-16 have the same aperture electrode shape and are applied with the same potential. Therefore, wiring lines for applying different potentials to the electrodes can be omitted, though the blanking electrodes need independent wiring lines, as in the first embodiment. A subarray may be divided into a plurality of sub-subarrays, and the electron optical characteristics (focal length, astigmatism, coma, and the like) of the element electron optical systems of the sub-subarrays may be equalized, as a matter of course. At this time, wiring lines for intermediate electrodes are necessary in units of sub-subarrays. [Description of Operation] A difference from the first embodiment will be described. In the first embodiment, when calibration for the exposure system is to be performed, the position (X,Y,Z) where a source image assumes a predetermined size and the current I at that time are detected for all source images. In the second embodiment, at least one source image which represents the subarray is detected. On the basis of the detection result, the sequence controller 14 makes the deflector 15 translate the intermediate images in the subarray in a direction perpendicular to the optical axis of the reduction electron optical system by the same amount through an optical axis alignment control circuit 18 to locate the source image of the element electron optical system representing the subarray with a predetermined relative positional relationship along the X and Y directions. In addition, the potential of the intermediate electrode of each subarray is set again through a focus control circuit 15 to locate the source image of the element electron optical system representing the subarray within a predetermined range along the Z direction. Furthermore, the detected irradiation current of the element electron optical system representing the subarray is stored in a memory 19 as the irradiation current of each element electron optical system in the same subarray. The source images formed on the wafer 5 through the element electron optical systems in the subarray are deflected by the same moving amount by a deflector 6 starting from reference positions (full circles) in their respective scan fields to expose the wafer with the scan fields of the respective element electron optical systems adjacent to each other, as shown in FIG. 17. In this fashion, the wafer is exposed by all subarrays, as shown in FIG. 18. The scan fields are stepped by an amount Ly in the Y direction by a deflector 7. Again, the source images are deflected by the same amount by the deflector 6 starting from the reference positions (full circles) in the scan fields of the respective element electron optical systems to expose the wafer. When the above operation is repeated four times, e.g., in the order of 1+L , 2+L , 3+L and 4+L , an exposure field in which the exposure fields of the subarrays are adjacent is formed, as shown in FIG. 19. Third Embodiment [Description of Constituent Elements of Exposure System] FIGS. 20A to 20C are views showing an electron beam exposure apparatus according to the third embodiment of the present invention. The same reference numerals as in FIGS. 1 and 15 denote the same constituent elements in FIGS. 20A to 20C, and a detailed description thereof will be omitted. In this embodiment, at least one electrode for decelerating or accelerating the electron beam is added, and a means for changing the source shape is arranged in the second embodiment. A unipotential lens serving as an electrostatic lens constituting an element electron optical system array 130 can realize a smaller electron lens as the electrons have a lower energy. However, to extract a lot of electron beams from an electron gun 1, the anode voltage must be raised. As a result, electrons from the electron gun 1 may obtain a high energy. In this embodiment, a decelerating electrode DCE shown in FIG. 20A is arranged between the electron gun 1 and the element electron optical system array 130. The decelerating electrode is an electrode at a lower potential than the anode potential and adjusts the energy of electrons incident on the element electron optical system array 130. The decelerating electrode can have apertures corresponding to the element electron optical systems, as shown in FIG. 20A, or apertures corresponding to subarrays, as shown in FIG. 20B. In a reduction electron optical system (4, 100), when the energy of an electron beam is low, the convergence of the electron beam on the wafer is degraded by the space charge effect. Therefore, the energy of the electron beam from the unipotential lens must be raised (accelerated). In this embodiment, an accelerating electrode ACE as shown in FIGS. 20A to 20C is arranged between the element electron optical system array 130 and the reduction electron optical system (4, 100). The accelerating electrode is an electrode at a higher potential than that of the element electron optical system array and adjusts the energy of electrons incident on the reduction electron optical system (4, 100). Like the decelerating electrode, the accelerating electrode may have apertures corresponding to the element electron optical systems, as shown in FIG. 20A, or apertures corresponding to the subarrays, as shown in FIG. 20B. In the first, second, and third embodiments, the source image is transferred on the wafer and scanned to form a desired exposure pattern. The size of the source image is set to be 1/5 to 1/10 the minimum line width of the exposure pattern. When the size of the source image is changed in accordance with the minimum line width of the exposure pattern, the number of source image moving steps for exposure can be minimized. In this embodiment, an electron optical system 160 as shown in FIG. 20C is arranged to shape the source. The electron optical system 160 forms an image S1 of a source S0 of the electron gun 1 through a first electron lens 161 and further forms an image S2 of the source image S1 through a second electron lens 162. With this arrangement, when the focal lengths of the first electron lens 161 and the second electron lens 162 are changed, only the size of the source image S2 can be changed while fixing the position of the source image S2. The focal lengths of the first and second electron lenses 161 and 162 are controlled by a source shaping circuit 163. When an aperture having a desired shape is formed at the position of the source image S2, not only the size but also the shape of the source can be changed. Fourth Embodiment [Description of Constituent Elements of Exposure System] FIGS. 21A and 21B are views showing an electron beam exposure apparatus according to the fourth embodiment of the present invention. The same reference numerals as in FIGS. 1, 15A-15C, and 20C denote the same constituent elements in FIGS. 21A and 21B, and a detailed description thereof will be omitted. The electron beam exposure apparatus of this embodiment is a stencil mask type exposure apparatus. An electron beam from an electron gun 1 is shaped by a first shaping aperture 200 having an aperture for defining the illumination area. A stencil mask 230 having pattern through holes are illuminated using a first shaping electron lens 210 (constituted by electron lenses 211 and 212) and a shaping deflector 220. The drawing pattern elements of the stencil mask 230 are reduced and projected on a wafer 5 through a reduction electron optical system (4, 100). This embodiment is different from the conventional stencil mask type exposure apparatus in that a stop 241 is arranged near the pupil of the reduction electron optical system 100 to obtain an electron density distribution of the electron beam on the pupil plane in which the electron density at the peripheral portion becomes higher than that at the central portion. More specifically, a hollow beam forming stop 240 whose central portion is shielded as shown in FIG. 21A is arranged. As shown in FIG. 22, the electron beam from the stencil mask has the electron density distribution of a hollow beam. For reference, the electron density distribution of a conventional Gaussian beam is also shown in FIG. 22. As described in [Other Arrangement 1 of Element Electron Optical System], the space charge effect of the hollow beam is smaller than that of the conventional Gaussian beam. For this reason, the electron beam can be brought to a focus on the wafer to form a source image free from any blur on the wafer. The electron beam passing through the stencil mask can be regarded as a source positioned on the stencil mask. When an image of a source having the shape of the pattern of the stencil mask is to be formed on the wafer, a source image having an exact shape can be formed because of the small space charge effect. That is, an exposure pattern having the exact shape of the pattern of the stencil mask can be formed on the wafer. In this embodiment, the hollow beam forming stop 240 is arranged near the pupil plane of the reduction electron optical system 100. However, even when a stop having the same shape as that of the hollow beam forming stop 240 is arranged at a position conjugate to the pupil of the reduction electron optical system 100, e.g., the pupil position of the first shaping electron lens 210, or the position of the source S2, the same effect as described above can be obtained. The shape or potential of each electrode of the electron gun may be adjusted to form the source itself into a hollow beam shape. In this embodiment, even when the first shaping aperture 200 has a rectangular shape, and a second shaping aperture having a rectangular shape is arranged in place of the stencil mask to constitute a variable rectangular beam type exposure apparatus, the same effect as described above can be obtained with the same arrangement. According to the first to third embodiments, first, no stencil mask is required; PA1 second, a lot of source images having a desired shape can be formed in a wide exposure area; and PA1 third, since the source images are discretely arranged, the source images are not affected by the space charge effect. Therefore, a desired exposure pattern can be formed at a high throughput. By forming a hollow electron beam, the influence of the space charge effect is minimized. Particularly, as in the fourth embodiment, the limitation in patterns usable for a stencil mask can be minimized in a stencil mask type electron beam exposure apparatus, so that the throughout can be further increased. Second Mode of Carrying Out the Invention First Embodiment [Description of Constituent Elements of Electron Beam Exposure Apparatus] FIGS. 23A-23C are views showing the main part of an electron beam exposure apparatus according to the present invention. Referring to FIGS. 23A-23C, reference numeral 601 denotes an electron gun consisting of a cathode 601a, a grid 601b, and an anode 601c. Electrons emitted from the cathode 601a form a crossover image between the grid 601b and the anode 601c (the crossover image will be referred to as source hereinafter). The electrons emitted from the sources are formed into an almost collimated electron beam by a condenser lens 602 whose front focal position is set at the position of the source. The almost collimated electron beam is incident on an element electron optical system array 603. The element electron optical system array 603 is formed by arraying a plurality of element electron optical systems each consisting of a blanking electrode, an aperture, and an electron lens, in a direction perpendicular to an optical axis AX. The element electron optical system array 603 will be described later in detail. The element electron optical system array 603 forms a plurality of intermediate images of the source. Each intermediate image is reduced and projected by a reduction electron optical system 604 to form a source image on a wafer 605. The elements of the element electron optical system array 603 are set such that the interval between the sources on the wafer 605 becomes an integer multiple of the size of source image. The element electron optical system array 603 changes the positions of the intermediate images along the optical axis in accordance with the curvature of field of the reduction electron optical system 604, and at the same time, corrects in advance any aberration generated when each intermediate image is reduced and projected on the wafer 605 by the reduction electron optical system 604, as in the first mode of carrying out the invention. The reduction electron optical system 604 is a symmetrical magnetic tablet consisting of a first projecting lens 641 (643) and a second projecting lens 642 (644). When the focal length of the first projecting lens 641 (643) is represented by f1, and that of the second projecting lens 642 (644) is represented by f2, the distance between the two lenses is f1+f2. The object point on the optical axis AX is located at the focal position of the first projecting lens 641 (643), and the image point is set at the focal point of the second projecting lens 642 (644). This image is reduced to -f2/f1. Since the two lens magnetic fields are determined to act in opposite directions, the Seidel's aberrations except five aberrations, i.e., spherical aberration, isotropic astigmatism, isotropic coma, curvature of field, and on-axis chromatic aberration, and chromatic aberrations associated with rotation and magnification are canceled in theory. A deflector 606 deflects the plurality of electron beams from the element electron optical system array 603 to displace the plurality of source images in the X and Y directions on the wafer 605 by roughly the same amounts. The deflector 606 is constituted by a main deflector used when the deflection width is large, and a subdeflector used when the deflection width is small (neither are shown). The main deflector is an electromagnetic deflector, and the subdeflector is an electrostatic deflector. A dynamic focus coil 607 corrects any shift of the focus position of the source image caused by deflection errors generated when the deflector 606 is actuated. A dynamic stigmatic coil 608 corrects astigmatism caused by deflection errors generated by deflection, like the dynamic focus coil 607. A reflected electron detector 609 detects reflected electrons or secondary electrons generated when the electron beam from the element electron optical system array 603 irradiates an alignment mark formed on the wafer 605 or a mark formed on a stage reference plate 613. A Faraday cup 610 having two single knife-edges extending in the X and Y directions detects the charge amount of the source image formed by the electron beam from the element electron optical system. A .theta.-Z stage 611 with a wafer mounted is movable along the optical axis AX (Z-axis) and in a rotational direction about the Z-axis. A stage reference plate 613 and the Faraday cup 610 are fixed on the .theta.-Z stage 611. An X-Y stage 612 with the .theta.-Z stage mounted is movable in the X and Y directions perpendicular to the optical axis AX (Z-axis). The element electron optical system array 603 will be described below with reference to FIGS. 24A and 24B. In the element electron optical system array 603, a plurality of element electron optical systems are formed into a group (subarray), and a plurality of subarrays are formed. In this embodiment, seven subarrays A to G are formed. In each subarray, a plurality of element electron optical systems are two-dimensionally arrayed. In each subarray of this embodiment, 25 element electron optical systems D(1,1) to D(5,5) are formed. The element electron optical systems form source images which are arrayed on the wafer at a pitch Pb (.mu.m) in the X and Y directions through the reduction electron optical system 604. FIG. 25 is a sectional view of each element electron optical system. Referring to FIG. 25, reference numeral 701 denotes a blanking electrode consisting of a pair of electrodes and having a deflection function; and 702, a substrate common to the remaining element electron optical systems and having an aperture (AP) for defining the shape of the transmitted electron beam. A wiring layer (W) for turning on/off the blanking electrode 701 is formed on the substrate 702. Reference numeral 703 denotes an electron lens using two unipotential lenses 703a and 703b each consisting of three aperture electrodes and having a converging function for setting the upper and lower electrodes at an acceleration potential V0 and the intermediate electrode at another potential V1 or V2. Upper, intermediate, and lower electrodes 750 to 752 of the unipotential lens 703a and upper and lower electrodes 753 and 755 of the unipotential lens 703b have a shape shown in FIG. 26A. In all the element electron optical systems, the upper and lower electrodes of the unipotential lenses 703a and 703b are set at a common potential by a first focus/astigmatism control circuit 615. The potential of the intermediate electrode 751 of the unipotential lens 703a can be set for each element electron optical system by the first focus/astigmatism control circuit 615. For this reason, the focal length of the unipotential lens 703a can be set for each element electron optical system. An intermediate electrode 754 of the unipotential lens 703b is constituted by four electrodes as shown in FIG. 26B. The potentials of electrodes 703M can be independently set by the first focus/astigmatism control circuit 615. The potentials of the electrodes 703M are also independently set for each element electron optical system. Therefore, the focal length of the unipotential lens 703b can be changed along sections perpendicular to each other. The focal length of the unipotential lens 703b can be independently set for each element electron optical system. With this arrangement, the astigmatisms of the element electron optical systems can be independently controlled. As a result, when the potentials of the intermediate electrodes of the element electron optical systems are independently controlled, the electron optical characteristics (intermediate image formation positions and astigmatisms) of the element electron optical systems can be controlled. The electron beam formed into an almost collimated beam by the condenser lens 602 passes through the blanking electrode 701 and the aperture (AP) and forms an intermediate image of the source through the electron lens 703. If, at this time, no electric field is applied between the electrodes of the blanking electrode 701, an electron beam 705 is not deflected. On the other hand, when an electric field is applied between the electrodes of the blanking electrode 701, an electron beam 706 is deflected. Since the electron beams 705 and 706 have different angular distributions on the object plane of the reduction electron optical system 604, the electron beams 705 and 706 are incident on different areas at the pupil position (on a plane P in FIG. 23) of the reduction electron optical system 604. Therefore, a blanking aperture BA for passing only the electron beam 705 is formed at the pupil position (on the plane P in FIG. 23) of the reduction electron optical system. To correct curvature of field/astigmatism generated when the intermediate image is reduced and projected on the target exposure surface by the reduction electron optical system 604, the potentials of the two intermediate electrodes of each element electron optical system are independently set to change the electron optical characteristics (intermediate image formation position and astigmatism) of the element electron optical system. In this embodiment, however, to minimize the wiring lines between the intermediate electrodes and the first focus/astigmatism control circuit 615, element electron optical systems in the same subarray are set to have the same electron optical characteristics so that the electron optical characteristics (intermediate image formation positions and astigmatisms) of the element electron optical systems are controlled in units of subarrays. To correct distortion generated when the plurality of intermediate images are reduced and projected on the target exposure surface by the reduction electron optical system 604, the distortion characteristic of the reduction electron optical system 604 is determined in advance, and the position of each element electron optical system along the direction perpendicular to the optical axis of the reduction electron optical system 604 is set on the basis of the distortion characteristic. FIG. 27 is a block diagram showing the system configuration of this embodiment. A blanking control circuit 614 independently controls ON/OFF of the blanking electrode of each element electron optical system of the element electron optical system array 603. The first focus/astigmatism control circuit 615 independently controls the electron optical characteristics (intermediate image formation position and astigmatism) of each element electron optical system of the element electron optical system array 603. A second focus/astigmatism control circuit 616 controls the dynamic stigmatic coil 608 and the dynamic focus coil 607 to control the focal position and astigmatism of the reduction electron optical system 604. A deflection control circuit 617 controls the deflector 606. A magnification adjustment circuit 618 controls the magnification of the reduction electron optical system 604. An optical characteristic control circuit 619 changes the excitation current of the electromagnetic lens constituting the reduction electron optical system 604 to adjust the aberration of rotation and optical axis. A stage drive control circuit 620 drives and controls the .theta.-Z stage 611 and also drives and controls the X-Y stage 612 in cooperation with a laser interferometer 621 for detecting the position of the X-Y stage 612. A control system 622 controls the above-described plurality of control circuits, the reflected electron detector 609, and the Faraday cup 610 in synchronism with each other for exposure and alignment based on data from a memory 623 which stores information associated with a drawing pattern. The control system 622 is controlled by a CPU 625 which controls the overall operation of the electron beam exposure apparatus through an interface 624. [Description of Operation] The operation of the electron beam exposure apparatus of this embodiment will be described below with reference to FIG. 27. Upon receiving pattern data for exposing the wafer, the deflector 606 determines the minimum amount of deflection applied to the electron beam on the basis of the minimum line width and the type and shape of line width of the exposure pattern to be formed on the wafer. The pattern data is divided in units of exposure areas of each element electron optical system. A common array consisting of array elements FME is set at an array interval corresponding to the minimum deflection amount, and the pattern data is converted into data represented on the common array in units of element electron optical systems. For the descriptive convenience, processing associated pattern data in exposure using two element electron optical systems a and b will be described below. FIGS. 28A and 28B are views showing exposure patterns Pa and Pb to be formed by the element electron optical systems a and b, respectively, on a common array DM. More specifically, each element electron optical system irradiates an electron beam on the wafer at a hatched array position where the pattern is present by turning off the blanking electrode. Normally, the contour portion of the pattern must be precisely exposed. However, a portion except the contour portion of the pattern, i.e., inner portion of the pattern need not be precisely exposed, and a defined exposure amount need only be satisfied. This operation will be described with reference to FIG. 37. (S100) On the basis of data (pattern data) of array positions as shown in FIGS. 28A and 28B where exposure must be performed for each element electron optical system, the CPU 625 determines an area F (black portion) on an array consisting of array positions (array elements FME) at which the contour portion is exposed, an area R (hatched portion) on an array consisting of array positions (array elements FME) at which the inner portion of the pattern is exposed, and an area N (white portion) on an array consisting of array positions (array elements FME) at which exposure is not performed, as shown in FIGS. 29A and 29B. The contour portion may be regarded as an inner portion depending on the shape of the pattern. In this embodiment, the width of the contour portion corresponds to one array element FME. However, the width of the contour portion may be represented by two array elements FME. (S200) On the basis of the data associated with the areas F, R, and N shown in FIGS. 29A and 29B, the CPU 625 determines a first area FF (black portion) consisting of array positions at which the contour portion is exposed by at least one of the element electron optical systems a and b, a second area RR (hatched portion) different from the first area and consisting of array positions at which the inner portion of the pattern is exposed by at least one of the element electron optical systems a and b, and a third area NN (white portion) consisting of array positions at which neither of the element electron optical systems a and b perform exposure, as shown in FIG. 30A. The CPU 625 also divides the second area RR by an array element RME larger than the array interval of the array. At this time, an area which cannot be divided by the array element RME is added to the first area FF. The result is shown in FIG. 30B. When a plurality of electron beams are positioned in the first area FF on the array, the electron beams are deflected by the deflector 606 using the minimum deflection amount (array interval of the array) as a unit to perform exposure. With this operation, the contour portions of all exposure patterns to be formed on the wafer can be precisely reproduced. When the plurality of electron beams are positioned in the second area RR on the array, the electron beams are deflected by the deflector 606 using a deflection amount larger than the minimum deflection amount (array interval of the array) as a unit to perform exposure. With this operation, the inner portion of the pattern which does not need high precision can be formed with a smaller number of times of exposure operations. When the plurality of electron beams are positioned in the third area NN on the array, the positions of the electron beams are deflected without being set. With this operation, exposure can be performed while minimizing wasteful deflection of electron beams. (S300) On the basis of data associated with the areas FF, RR, and NN shown in FIG. 30B, the CPU 625 determines the array positions of the array elements FME and RME to be exposed, as shown in FIG. 31A, thereby preparing deflection control data for positioning the electron beams at the array elements FME and RME to be exposed, i.e., sequential data formed by sequentially arranging a plurality of data of array positions at which the electron beams must be set in the deflection path, as shown in FIG. 31B. In this embodiment, the second area RR is divided only by the array element RME larger than the array interval of the array elements FME on the array. However, an area constituted by the array elements RME may be divided by an array element XRME larger than the array element RME. At this time, an area which cannot be divided by the array element XRME may be constituted by the array elements RME. The result is shown in FIG. 31C. Deflection control data representing only the array elements FME, RME, and XRME to be exposed with the electron beams may be prepared. The area constituted by the array elements XRME can be exposed by deflecting the electron beam by the deflector 606 using, as a unit, a deflection amount larger than the unit deflection amount for an area constituted by the array elements RME. Therefore, the inner portion of the pattern which does not need high precision can be formed with a much smaller number of times of exposure operations. (S400) To perform pattern exposure, the blanking electrodes must be controlled on the basis of the array positions of the plurality of electron beams to irradiate the electron beams from the element electron optical systems. FIGS. 32A and 32B are views showing irradiation of electron beams from the element electron optical systems in correspondence with the array positions. More specifically, the electron beam is irradiated on a hatched array element. The CPU 625 prepares blanking control data corresponding to the array positions of each element electron optical system. (S500) From data of the exposure pattern to be formed on the wafer, as shown in FIG. 33, the CPU 625 prepares exposure control data including the array positions, the types of array elements, the blanking control data including the operation time of the blanking electrode of each element electron optical system. In this embodiment, the CPU 625 of the electron beam exposure apparatus performs the above processing. However, even when the processing is performed by an external processing unit, and the exposure control data is transferred to the CPU 625, the object and effect do not change. The CPU 625 directs the control system 622 through the interface 624 to "execute exposure". The control system 622 operates as follows on the basis of data on the memory 623 to which the exposure control data is transferred. The control system 622 directs the deflection control circuit 617, on the basis of the exposure control data from the memory 623, which is transferred in synchronism with the internal reference clock, to cause the subdeflector of the deflector 606 to deflect the plurality of electron beams from the element electron optical system a-ray 603, and also directs the blanking control circuit 614 to turn on/off the blanking electrodes of the element electron optical systems in accordance with the exposure pattern to be formed on the wafer 605. At this time, the X-Y stage 612 continuously moves in the X and Y directions. The deflection control circuit 617 controls the deflection position of the electron beam in consideration of the moving amount of the X-Y stage 612. The control system 622 changes the OFF time of the blanking electrode of each element electron optical system or changes the size of the source image on the wafer depending on the type of array element (FME, RME). Since the array element RME substantially has an exposure area larger than that of the array element FME, underexposure occurs if the same exposure time is set for the array elements FME and RME. The blanking electrode is controlled by the blanking control circuit 614 to prolong the exposure time for the array element RME. Alternatively, when the array element RME is to be exposed, the size of crossover image of the sources of the electron gun 601 may be increased by an electron gun control circuit 631. Furthermore, the focal length of the element electron optical system may be reduced by the first focus/astigmatism control circuit 615 to increase the size of the source image on the wafer (the magnification of the intermediate image formed by the element electron optical system is defined on the basis of the ratio of the focal length of the condenser lens 602 to that of the element electron optical system). However, when the focal length of the element electron optical system is to be decreased, the intermediate image formation position changes. In this case, the position variation of the source image on the wafer along the optical axis, which is caused by the variation of the intermediate image formation position, may be corrected by a refocus coil (not shown) arranged in the reduction electron optical system 604. When exposure of the array elements RME and exposure of the array element FME are alternately performed, the load on the control system increases. In view of this, the sequential control data may be changed to sequentially perform exposure first at deflection positions of the array elements RME, as shown in FIG. 34A, and next at deflection positions of the array elements FME, as shown in FIG. 34B. Consequently, the electron beams from the element electron optical systems scan to expose exposure fields (EF) on the wafer 605, as shown in FIGS. 32A and 32B. A plurality of electron beams from one subarray serve to expose a subarray exposure field (SEF) in which the exposure fields of the element electron optical systems in the subarray are adjacent to each other, as shown in FIG. 35. In this way, a subfield constituted by subarray exposure fields SEF(A) to SEF(G) on the wafer 605 formed by the subarrays A to G, respectively, is exposed, as shown in FIG. 36. After exposure of subfield 1+L shown in FIG. 19, the control system 622 directs the deflection control circuit 617 to make the main deflector of the deflector 606 deflect the plurality of electron beams from the element electron optical system array so as to expose subfield 2+L . At this time, the control system 622 commands the second focus/astigmatism control circuit 616 to control the dynamic focus coil 607 on the basis of dynamic focus correction data which has been obtained in advance, thereby correcting the focal position of the reduction electron optical system 604. At the same time, the control system 622 commands control of the dynamic stigmatic coil 608 on the basis of dynamic astigmatism correction data which has been obtained in advance, thereby correcting the astigmatism of the reduction electron optical system. The operation of step 1 is performed to expose subfield 2+L . The above steps 1 and 2 are repeated to sequentially expose subfields in the order of 3+L , 4+L , . . . , as shown in FIG. 19, thereby exposing the entire surface of the wafer. According to the first embodiment, even when the size of the exposure pattern to be formed becomes small, a decrease in throughput can be minimized. Second Embodiment This embodiment provides another operation of the electron beam exposure apparatus according to the first embodiment. Therefore, an electron beam exposure apparatus according to the second embodiment has the same arrangement as that of the electron beam exposure apparatus described in [Description of Constituent Elements of Electron Beam Exposure Apparatus] of the first embodiment. Prior to wafer exposure by this exposure apparatus, a CPU 625 directs a control system 622 through an interface 624 to perform "calibration". The control system 622 determines dynamic astigmatism correction data and dynamic correction data for each subarray in accordance with the flow chart in FIG. 44. (step S1100) As shown in FIG. 39C, cross marks are formed on a stage reference plate 613 at positions corresponding to elements which are set when the deflection area (MEF) of the main deflector of a deflector 606 is divided to form a matrix of nine elements. A position where an electron beam from an element electron optical system D(3,3) at the center of an element electron optical system array 603 shown in FIG. 24 is irradiated on the wafer without being deflected is set as a beam reference position. The control system 622 directs a stage drive control circuit 620 to move a X-Y stage 612 and set a mark (M(0,0) of the stage reference plate 613 at the beam reference position. The control system 622 directs a blanking control circuit 614 to turn off only the blanking electrode of the element electron optical system D(3,3) while keeping the remaining blanking electrodes ON so that only the electron beam from the element electron optical system D(3,3) becomes incident on the stage reference plate 613. Simultaneously, the control system 622 instructs a deflection control circuit 617 to make the main deflector of the deflector 606 deflect an electron beam BE from the element electron optical system D(3,3) to the position of a mark M(1,1). As shown in FIG. 39A, the mark M(1,1) is scanned with the electron beam BE in the X direction. Reflected electrons/secondary electrons from the mark are detected by a reflected electron detector 609 and input to the control system 622. The control system 622 obtains the blur of the beam in the X direction on the basis of the mark data. In addition, the mark M(1,1) is scanned with the electron beam BE in the Y direction, as shown in FIG. 39B. Reflected electrons/secondary electrons from the mark are detected by the reflected electron detector 609 and input to the control system 622. The control system 622 obtains the blur of the electron beam in the Y direction on the basis of the mark data. Next, the control system 622 directs a second focus/astigmatism control circuit 616 to change setting of a dynamic stigmatic coil 608 (change the dynamic astigmatism correction data), scans the mark M(1,1) with the electron beam BE again, and obtains the blurs of the beam in the X and Y directions in a similar manner. By repeating the above operation, the control system 622 obtains dynamic astigmatism correction data for substantially equalizing the blurs of the beam in the X and Y directions. With this operation, the optimum dynamic astigmatism correction data at the deflection position corresponding to the mark M(1,1) is determined. The above operation is performed for all marks, thereby determining optimum dynamic astigmatism correction data at deflection positions corresponding to the respective marks. (S1200) The control system 622 causes the main deflector of the deflector 606 to deflect the electron beam BE from the element electron optical system D(3,3) to the position of the mark M(1,1) and scans the mark M(1,1) in the X direction, as shown in FIG. 39A. Reflected electrons/secondary electrons from the mark are detected by the reflected electron detector 609 and input to the control system 622. The control system 622 obtains the blur of the beam on the basis of the mark data. At this time, the dynamic stigmatic coil 608 is controlled on the basis of the dynamic astigmatism correction data obtained previously. Next, the control system 622 directs the second focus/astigmatism control circuit 616 to change setting of a dynamic focus coil 607 (change the dynamic focus correction data), scans the mark M(1,1) with the electron beam BE again, and obtains the blur of the beam in a similar manner. By repeating the above operation, the control system 622 obtains dynamic focus correction data for minimizing the blurs of the beam. With this operation, the optimum dynamic focus correction data at the deflection position corresponding to the mark M(1,1) is determined. The above operation is performed for all marks, thereby determining optimum dynamic focus correction data at deflection positions corresponding to the respective marks. (S1300) A position where an electron beam from an element electron optical system A(3,3) of the element electron optical system array 603 shown in FIG. 24A is irradiated on the wafer without being deflected is set as a beam reference position. The control system 622 directs the stage drive control circuit 620 to move the X-Y stage 612 and set the mark (M(0,0) of the stage reference plate 613 at the beam reference position. The control system 622 directs the blanking control circuit 614 to turn off only the blanking electrode of the element electron optical system A(3,3) while keeping the remaining blanking electrodes ON so that only the electron beam from the element electron optical system A(3,3) becomes incident on the stage reference plate 613. Simultaneously, the control system 622 commands the deflection control circuit 617 to make the main deflector of the deflector 606 deflect the electron beam BE from the element electron optical system A(3,3) to the position of the mark M(1,1). As shown in FIG. 39A, the mark M(1,1) is scanned with the electron beam BE in the X direction. Reflected electrons/secondary electrons from the mark are detected by the reflected electron detector 609 and input to the control system 622. The control system 622 obtains the blur of the beam in the X direction on the basis of the mark data. In addition, the mark M(1,1) is scanned with the electron beam BE in the Y direction, as shown in FIG. 39B. Reflected electrons/secondary electrons from the mark are detected by the reflected electron detector 609 and input to the control system 622. The control system 622 obtains the blur of the electron beam in the Y direction on the basis of the mark data. At this time, the dynamic focus coil is controlled on the basis of the dynamic focus correction data obtained in step S1100, and the dynamic stigmatic coil 608 is controlled on the basis of the dynamic astigmatism correction data obtained in step S1100. Next, the control system 622 instructs a first focus/astigmatism control circuit 615 to change setting of the astigmatism of a subarray A (change the dynamic astigmatism correction data for each subarray), scans the mark M(1,1) with the electron beam BE again, and obtains the blurs of the beam in the X and Y directions in a similar manner. By repeating the above operation, the control system 622 obtains dynamic astigmatism correction data for the subarray A, which substantially equalizes and minimizes the blurs of the beam in the X and Y directions. With this operation, the optimum dynamic astigmatism correction data for the subarray A at the deflection position corresponding to the mark M(1,1) is determined. The above operation is performed for all marks, thereby determining optimum dynamic astigmatism correction data for the subarray A at deflection positions corresponding to the respective marks. (S1400) The control system 622 causes the main deflector of the deflector 606 to deflect the electron beam BE from the element electron optical system A(3,3) to the position of the mark M(1,1) and scans the mark M(1,1) in the X direction, as shown in FIG. 39A. Reflected electrons/secondary electrons from the mark are detected by the reflected electron detector 609 and input to the control system 622. The control system 622 obtains the blur of the electron beam on the basis of the mark data. At this time, the astigmatism of the element electron optical system of the subarray A is controlled on the basis of the dynamic astigmatism correction data for the subarray A obtained previously. Next, the control system 622 directs the first focus/astigmatism control circuit 615 to change setting of the intermediate image formation position of the element electron optical system of the subarray A (change the dynamic focus correction data for each subarray), scans the mark M(1,1) with the electron beam BE again, and obtains the blur of the beam in a similar manner. By repeating the above operation, the control system 622 obtains dynamic focus correction data for the subarray A, which minimizes the blurs of the beam. With this operation, the optimum dynamic focus correction data for the subarray A at the deflection position corresponding to the mark M(1,1) is determined. The above operation is performed for all marks, thereby determining optimum dynamic focus correction data for the subarray A at deflection positions corresponding to the respective marks. (S1500) The control system 622 performs the same operation as in step S1300 for electron beams from element electron optical systems B(3,3), C(3,3), E(3,3), F(3,3), and G(3,3) of the element electron optical system array 603 shown in FIGS. 24A and 24B. Consequently, the optimum dynamic focus correction data and optimum dynamic astigmatism correction data at deflection positions corresponding to the respective marks are determined for all the subarrays. The CPU 625 directs the control system 622 through the interface 624 to "execute exposure". The control system 622 operates in the following manner. The control system 622 directs the deflection control circuit 617 to make the subdeflector of the deflector 606 deflect the plurality of electron beams from the element electron optical system array, and at the same time, directs the blanking control circuit 614 to turn on/off the blanking electrodes of the element electron optical systems in accordance with the exposure pattern to be formed on a wafer 605. At this time, the X-Y stage 612 continuously moves in the X direction, and the deflection control circuit 617 controls the deflection position of the electron beam in consideration of the moving amount of the X-Y stage 612. As a result, an electron beam from one element electron optical system scans to expose an exposure field (EF) on the wafer 605 starting from the full square, as shown in FIG. 40. As shown in FIG. 35, the exposure fields (EF) of the plurality of element electron optical systems in the subarray are set to be adjacent to each other. Consequently, a subarray exposure field (SEF) consisting of the plurality of exposure fields (EF) on the wafer 605 is exposed. Simultaneously, a subfield constituted by subarray exposure fields SEF(A) to SEF(G) formed by the subarrays A to G, respectively, on the wafer 605 is exposed, as shown in FIG. 36. After exposure of subfield 1+L shown in FIG. 19, the control system 622 directs the deflection control circuit 617 to make the main deflector of the deflector 606 deflect the plurality of electron beams from the element electron optical system array so as to expose subfield 2+L . At this time, the control system 622 directs the second focus/astigmatism control circuit 616 to control the dynamic focus coil 607 on the basis of the above-described dynamic focus correction data, thereby correcting the focal position of the reduction electron optical system 604. At the same time, the control system 622 directs to control the dynamic stigmatic coil 608 on the basis of the above-described dynamic astigmatism correction data, thereby correcting the astigmatism of the reduction electron optical system. In addition, the control system 622 commands the first focus/astigmatism control circuit 615 to control the electron optical characteristics (intermediate image formation positions and astigmatisms) of the element electron optical systems on the basis of the dynamic focus correction data and dynamic astigmatism correction data for each subarray. The operation in step 1 is performed to expose subfield 2+L . The above steps 1 and 2 are repeated to sequentially expose subfields in the order of 3+L , 4+L , . . . , as shown in FIG. 19, thereby exposing the entire surface of the wafer. Third Embodiment FIG. 42 is a view showing the difference in constituent elements between the second embodiment and the third embodiment. The same reference numerals as in FIGS. 23A-23C denote the same constituent elements in FIG. 42, and a detailed description thereof will be omitted. In the third embodiment, a deflector 650 for deflecting an electron beam from a subarray is arranged on the reduction electron optical system 604 side of an element electron optical system array 603 in correspondence with each subarray of the element electron optical system array 603. The deflector 650 has a function of translating a plurality of intermediate images formed by the subarrays (in the X and Y directions) and is controlled by a control system 622 through a subarray deflection control circuit 651. The operation of this embodiment will be described next. Prior to wafer exposure by this exposure apparatus, a CPU 625 directs the control system 622 through an interface 624 to perform "calibration". The control system 622 operates in the following manner. A position where an electron beam from an element electron optical system A(3,3) of the element electron optical system array 603 shown in FIG. 24A is irradiated on the wafer without being deflected is set as a beam reference position. The control system 622 directs a stage drive control circuit 620 to move an X-Y stage 612 and set a mark M(0,0) of a stage reference plate 613 as in the second embodiment at the beam reference position. The control system 622 directs a blanking control circuit 614 to turn off only the blanking electrode of the element electron optical system A(3,3) while keeping the remaining blanking electrodes ON so that only the electron beam from the element electron optical system A(3,3) becomes incident on the wafer side. Simultaneously, the control system 622 directs a deflection control circuit 617 to make the main deflector of a deflector 606 deflect an electron beam BE from the element electron optical system A(3,3) to the position of a mark M(1,1). As shown in FIG. 39A, the mark M(1,1) is scanned in the X direction. Reflected electrons/secondary electrons from the mark are detected by a reflected electron detector 609 and input to the control system 622. The control system 622 obtains the deviation between the actual deflection position and the designed deflection position in the X direction on the basis of the mark data. The control system 622 directs the subarray deflection control circuit 651 to change setting of the X-direction translation of the intermediate image by the deflector 650 corresponding to a subarray A (change dynamic deflection correction data in the X direction) to cancel the deviation, scans the mark M(1,1) with the electron beam BE again, and obtains the deviation between the actual deflection position and the designed deflection position in a similar manner. By repeating the above operation, the control system 622 obtains dynamic deflection correction data for substantially canceling the deviation. Next, the control system 622 scans the mark M(1,1) in the Y direction, as shown in FIG. 39B. In the same way as described above, the control system 622 obtains dynamic deflection correction data in the Y direction for substantially canceling the deviation. With this operation, the optimum dynamic deflection correction data at the deflection position corresponding to the mark M(1,1) is determined. The above operation is performed for all marks, thereby determining the optimum dynamic deflection correction data at deflection positions corresponding to the respective marks. The control system 622 performs the same operation as for the electron beam from the element electron optical system A(3,3) for electron beams from element electron optical systems B(3,3), C(3,3), D(3,3), E(3,3), F(3,3), and G(3,3) of the element electron optical system array 603 shown in FIG. 24. Consequently, the optimum dynamic deflection correction data at deflection positions corresponding to the respective marks are determined for all the subarrays. In "execution of exposure", after exposure of subfield 1+L shown in FIG. 19, the control system 622 directs the deflection control circuit 617 to make the main deflector of the deflector 606 deflect the plurality of electron beams from the element electron optical system array so as to expose subfield 2+L . At this time, the control system 622 directs the subarray deflection control circuit 651 to control the deflector 650 corresponding to the subarray on the basis of the above-described dynamic deflection correction data for each subarray, thereby correcting the position of each intermediate image along the direction (X and Y directions) perpendicular to the optical axis. As described above, according to this embodiment, an electron beam exposure apparatus which can optimally correct deflection errors generated in the plurality of electron beams passing through the reduction electron optical system when the deflector is actuated in units of electron beams can be provided. Third Mode of Carrying Out the Invention An embodiment of a method of producing a device by using the above-described electron beam exposure apparatus and method will be described below. FIG. 45 is a flow chart showing the manufacture of a microdevice (a semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD, a thin-film magnetic head, a micromachine, or the like). In step 1 (circuit design), the circuit of a semiconductor device is designed. In step 2 (preparation of exposure control data), exposure control data for the exposure apparatus is prepared on the basis of the designed circuit pattern. In step 3 (manufacture of wafer), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a preprocess in which the exposure apparatus to which the prepared exposure control data is input and the wafer are used to form an actual circuit on the wafer by lithography. Step 5 (assembly) is called a postprocess in which semiconductor chips are formed from the wafer manufactured in step 4. The postprocess includes an assembly process (dicing and bonding) and packaging process (chip encapsulating). In step 6 (inspection), the operation confirmation test, durability test, and the like are performed for the semiconductor device manufactured in step 5. With these processes, a semiconductor device is completed and delivered (step 7). FIG. 46 is a flow chart showing the wafer process in detail. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by deposition. In step 14 (ion implantation), ions are implanted in the wafer. In step 15 (resist processing), a photosensitive agent is applied on the wafer. In step 16 (exposure), the circuit pattern is formed on the wafer by exposure using the above-described exposure apparatus. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are etched. In step 19 (resist removal), the unnecessary resist after etching is removed. By repeating these processes, multiple circuit patterns are formed on the wafer. When the manufacturing method of this embodiment is used, a high-integration semiconductor device which is conventionally difficult to manufacture can be manufactured at a low cost. The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to apprise the public of the scope of present invention the following claims are made. |
050826182 | abstract | The method consists in removing the cooling fluid of the primary circuit, and, as a function of the cooling fluid concentration, in passing either all of the cooling fluid into at least one electrodialysis module, or only a part of the cooling fluid into the electrodialysis modules and the other part towards at least one reverse osmosis apparatus, in adding to the cooling fluid, when it leaves the primary circuit, an additive to promote dissociation of the boric acid, and in then returning the cooling fluid into the primary circuit. |
summary | ||
051732521 | claims | 1. A spacer for use in combination with a fuel bundle, said fuel bundle having a plurality of fuel rods, a lower tie plate for supporting said plurality of fuel rods in side-by-side upstanding relation and defining a plurality of apertures for permitting water to be heated to enter said fuel bundle, an upper tie plate for maintaining the upper ends of said fuel rods in parallel side-by-side relation as supported on said lower tie plate and defining a plurality of apertures for permitting heated water and steam to escape from said fuel bundle, a channel for surrounding said fuel rods and extending from said lower tie plate toward said upper tie plate for confining said water flow around said fuel rods within said fuel bundle, and a plurality of spacers for placement within said channel between said tie plates around said fuel rods for maintaining said fuel rods in designed side-by-side spacing, the improvement to said spacer comprising: at least first and second side-by-side ferrules forming a ferrule pair for fitting around respective side-by-side fuel rods to maintain said fuel rods spaced apart one from another; each ferrule of said ferrule pair having at least one internal stop for permitting said fuel rod internal of said ferrule to be biased against said stop to a position of designed side-by-side alignment with respect to said fuel bundle at said spacer within said ferrule; each ferrule of said ferrule pair further defining an aperture for confrontation with a corresponding aperture of said adjacent ferrule of said ferrule pair to define a common aperture between said ferrule pair for receiving a spring between said ferrules, said common aperture of each ferrule defining at the sides thereof an opening sufficient to define respective first and second tab receiving slots to the exterior of said ferrule when confronted to a similar said ferrule at said tab receiving slot; a loop spring having first and second legs, said first spring leg for biasing a fuel rod interior of said common aperture of a first ferrule of said ferrule pair and a second spring leg for biasing a fuel rod interior of said common aperture of said second ferrule of said ferrule pair, said first and second legs of said spring moveable from a first position of compression for insertion of said spring through one of said first and second tab receiving slots to a second position of expansion with respect to said first and second tab receiving slots for trapping said spring in said common aperture; at least first and second tabs protruding from at least one of said spring legs, said first tab protruding from a first side of said spring and said second tab protruding from a second side of said spring, said tabs for maintaining said loop spring in said second position of expansion in said common aperture at said tab receiving slots; and said first and second ferrules confronted at said apertures and said main body of said loop spring being inserted in said common aperture, said tabs protruding into said tab receiving slots to maintain said loop spring in said common aperture and said rod biasing projection passing through said common aperture whereby said rod biasing projections on the respective spring legs of said loop spring can bias respective fuel rods in each said ferrule of said ferrule pair against said stops to maintain said fuel rods in designed side-by-side spacing. said common aperture further having a maximum width in the upper and lower portions of said aperture to allow insertion of the upper and lower tabs of said spring. a central fuel rod biasing projection slot at the middle of said common aperture allowing a rod biasing projection on the spring to be inserted; and, wherein said spring includes at least one rod biasing portion in at least one of said spring legs of said spring. said tabs form an integral portion of said loop of said loop spring. a plurality of fuel rods; a lower tie plate for supporting said plurality of fuel rods in side-by-side upstanding relation and defining a plurality of apertures for permitting water to be heated to enter said fuel bundle; an upper tie plate for maintaining the upper ends of said fuel rods in parallel side-by-side relation as supported on said lower tie plate and defining a plurality of apertures for permitting heated water to escape from said fuel bundle, a channel for surrounding said fuel rods and extending from said lower tie plate toward said upper tie plate for confining said water flow around said fuel rods within said fuel bundle; a plurality spacers for placement within said channel between said tie plates around said fuel rods for maintaining said fuel rods in designed side-by-side spacing; each spacer including at least first and second side-by-side ferrules forming a ferrule pair for fitting around respective side-by-side fuel rods to maintain said fuel rods spaced apart one from another; each ferrule of said ferrule pair having at least one internal stop for permitting said fuel rod internal of said ferrule to be biased against said stop to a position of designed side-by-side alignment with respect to said fuel bundle at said spacer within said ferrule; each ferrule of said ferrule pair further defining an aperture for confrontation with a corresponding aperture of said adjacent ferrule of said ferrule pair to define a common aperture between said ferrule pair for receiving a spring between said ferrules, said common aperture having sufficient dimension for defining at the sides thereof when confronted to another similar said ferrule respective first and second tab receiving slots to the exterior of said ferrules; a loop spring having first and second legs, said first spring leg for biasing a fuel rod interior of said first ferrule of said ferrule pair and a second spring leg for biasing a fuel rod interior of said second ferrule of said ferrule pair, said legs moveable from a first position of compression for insertion of said spring through one of said first and second tab receiving slots to a second position of expansion with respect to said first and second tab receiving slots for trapping said spring in said common aperture; at least first and second tabs protruding from at least one of said spring legs, said first tab protruding from a first side of said spring and said second tab protruding from a second side by said spring, said tabs for maintaining said loop spring in said second position of expansion in said common aperture at said tab receiving slots; and, said first and second ferrules confronted at said apertures and said main body of said loop spring being inserted in said common aperture, said tabs protruding into said tab receiving slots to maintain said loop spring in said aperture and said rod biasing projection passing through said common aperture slot whereby said rod biasing projections on the respective spring legs of said loop spring can bias respective fuel rods in each said ferrule of said ferrule pair against said stops to maintain said fuel rods in designed side-by-side spacing. said common aperture further having a maximum width in the upper and lower portions of said aperture to allow insertion of the upper and lower tabs of said spring. a central fuel rod biasing projection slot at the middle of said common aperture allowing a rod biasing projection on the spring to be inserted; and, wherein said spring includes at least one rod biasing portion in at least one of said spring legs of said spring. said tabs form an integral portion of said loop of said loop spring. a matrix of ferrules coextensive with the construction of said spacer for placement within the fuel bundle; said matrix including at least first and second side-by-side ferrules forming a ferrule pair for fitting around respective side-by-side fuel rods to maintain said fuel rods spaced apart one from another; each ferrule of said ferrule pair having at least one internal stop for permitting said fuel rod internal of said ferrule to be biased against said stop to a position of designed side-by-side alignment with respect to said fuel bundle at said spacer within said ferrule; each ferrule of said ferrule pair further defining an aperture for confrontation with a corresponding aperture of said adjacent ferrule of said ferrule pair to define a common aperture between said ferrule pair for receiving a spring between said ferrules, said common aperture of each ferrule defining at the sides thereof an opening sufficient to define respective first and second tab receiving slots to the exterior of said ferrule when confronted to a similar said ferrule at said tab receiving slot; a loop spring having first and second legs, said first spring leg for biasing a fuel rod interior of said common aperture of a first ferrule of said ferrule pair and a second spring leg for biasing a fuel rod interior of said common aperture of said second ferrule of said ferrule pair, said legs moveable from a first position of compression for insertion of said spring through one of said first and second tab receiving slots to a second position of expansion with respect to said first and second tab receiving slots for trapping said spring in said common aperture; at least first and second tabs protruding from at least one of said spring legs, said first tab protruding from a first side of said spring and said second tab protruding from a second side of said spring, said tabs for maintaining said loop spring in said second position of expansion in said common aperture at said tab receiving slots; and said first and second ferrules confronted at said apertures and said main body of said loop spring being inserted in said common aperture, said tabs protruding into said tab receiving slots to maintain said loop spring in said common aperture and said rod biasing projection passing through common aperture whereby said rod biasing projections on the respective spring legs of said loop spring can bias respective fuel rods in each said ferrule of said ferrule pair against said stops to maintain said fuel rods in designed side-by-side spacing. said common aperture further having a maximum width in the upper and lower portions of said aperture to allow insertion of the upper and lower tabs of said spring. a central fuel rod biasing projection slot at the middle of said common aperture allowing a rod biasing projection on the spring to be inserted; and, wherein said spring includes at least one rod biasing portion in at least one of said spring legs of said spring. said tabs form an integral portion of said loop of said loop spring. a spacer having a spacer matrix including at least first and second side-by-side ferrules forming a ferrule pair for fitting around respective side-by-side fuel rods to maintain said fuel rods spaced apart one from another; each ferrule of said ferrule pair having at least one internal stop for permitting said fuel rod internal of said ferrule to be biased against said stop to a position of designed side-by-side alignment with respect to said fuel bundle at said spacer within said ferrule; each ferrule of said ferrule pair further defining an aperture for confrontation with a corresponding aperture of said adjacent ferrule of said ferrule pair to define a common aperture between said ferrule pair for receiving a spring between said ferrules, said common aperture of each ferrule defining at the sides thereof respective first and second tab receiving slots to the exterior of said ferrules when confronted to a similar said ferrule at said common aperture; a loop spring having first and second legs, said first spring leg for biasing a fuel rod interior of said common aperture of said first ferrule of said ferrule pair and a second spring leg for biasing a fuel rod interior of said common aperture of said second ferrule of said ferrule pair, said first and second legs moveable from a first position of compression for insertion of said spring through one of said first and second tab receiving slots to a second position of expansion with respect to said first and second tab receiving slots for trapping said spring in said common aperture; at least first and second tabs protruding from at least one of said spring legs, said first tab protruding from a first side of said spring and said second tab protruding from a second side of said spring, said tabs for maintaining said loop spring in said second position of expansion in said common aperture at said tab receiving slots; and, said first and second ferrules confronted at said apertures and said main body of said loop spring being inserted in said common aperture, said tabs protruding into said tab receiving slots to maintain said loop spring in said aperture and said rod biasing projection passing through said common aperture slot whereby said rod biasing projections on the respective spring legs of said loop spring can bias respective fuel rods in each said ferrule of said ferrule pair against said stops to maintain said fuel rods in designed side-by-side spacing. said common aperture further having a maximum width in the upper and lower portions of said aperture to allow insertion of the upper and lower tabs of said spring. a central fuel rod biasing projection slot at the middle of said common aperture allowing a rod biasing projection on the spring to be inserted; and, wherein said spring includes at least one rod biasing portion in at least one of said spring legs of said spring. said tabs form an integral portion of said loop of said loop spring. 2. The invention of claim 1 and wherein said spring has upper and lower tabs on each side of said spring. 3. The invention of claim 2 and wherein said common aperture has a generally rectangular shape with a varying width; 4. The invention of claim 1 and including: 5. The invention of claim 1 and wherein said common aperture is generally I-shaped. 6. The invention of claim 1 and wherein: 7. A fuel bundle comprising: 8. The invention of claim 7 and wherein said spring has upper and lower tabs. 9. The invention of claim 8 and wherein said common aperture has a generally rectangular shape with a varying width; and 10. The invention of claim 7 and including; 11. The invention of claim 7 and wherein said common aperture is generally I-shaped. 12. The invention of claim 7 and wherein: 13. A fuel bundle spacer for placement within a fuel bundle channel between upper and lower tie plates around fuel rods for maintaining said fuel rods in designed side-by-side spacing, said spacer comprising: 14. The invention of claim 13 and wherein said spring has upper and lower tabs. 15. The invention of claim 14 and wherein said common aperture has a generally rectangular shape with a varying width; and 16. The invention of claim 13 and including: 17. The invention of claim 13 and wherein said common aperture is generally I-shaped. 18. The invention of claim 13 and wherein: 19. A spacer for use in combination with a fuel bundle, said fuel bundle having a plurality of fuel rods, a lower tie plate for supporting said plurality of fuel rods in side-by-side upstanding relation and defining a plurality of apertures for permitting water to be heated to enter said fuel bundle, an upper tie plate for maintaining the upper ends of said fuel rods in parallel side-by-side relation as supported on said lower tie plate and defining a plurality of apertures for permitting heated water and steam to escape from said fuel bundle, a channel for surrounding said fuel rods and extending from said lower tie plate toward said upper tie plate for confining said water flow around said fuel rods within said fuel bundle, and a plurality of spacers for placement within said channel between said tie plates around said fuel rods for maintaining said fuel rods in designed side-by-side spacing, the improvement to said spacers comprising: 20. The invention of claim 19 and wherein said spring has upper and lower tabs. 21. The invention of claim 20 and wherein said common aperture has a generally rectangular shape with a varying width; and, 22. The invention of claim 19 and including: 23. The invention of claim 19 and wherein said common aperture is generally I-shaped. 24. The invention of claim 19 and wherein: |
claims | 1. A technical installation, comprising: a plurality of system components, a plurality of girders supporting said system components, and a plurality of pressure-carrying lines, said girders having a defined target region at which impact is expected in an event of a pipe break of one of said pressure-carrying lines, and said girders having a segmented configuration in said target region, wherein said defined target region has a predetermined breaking point that is designed to break when subjected to a force that is lower than a force subjected to said defined target region by a broken one of said pressure-carrying lines. 2. The technical installation according to claim 1, wherein adjacent segments of said girder or of each of said girders having said segmented configuration are connected to one another with connection points thereof being rated for a load defined with a predetermined threshold shear force. 3. The technical installation according to claim 1, wherein adjacent segments of said girder or of each of said girders having said segmented configuration are connected to one another via screw connections. 4. The technical installation according to claim 3, wherein said segments are formed with a plurality of elongated holes, and connection bolts of said screw connections are guided in said elongated holes. 5. The technical installation according to claim 4, wherein said elongated holes are formed as open slots with openings in a direction of avoidance expected in the event of an impingement of a pressure-carrying line onto the respective said segment. 6. The technical installation according to claim 1 configured as a nuclear power plant. 7. The technical installation according to claim 6, wherein said nuclear power plant includes an access or operating platform forming a system component supported by said plurality of segmented girders. 8. A technical installation, comprising:a plurality of system components, a plurality girders supporting said system components, and a plurality of pressure-carrying lines;at least some of said girders including a plurality of segments in a target region at which an impact is expected in an event of a pipe break of one of said pressure-carrying lines;at least some of said girders including a plurality of connection regions releasably connecting an intermediate one of said plurality of segments to adjacent ones of said plurality of segments such that if the impact occurs, the impact displaces said intermediate one of said plurality of segments away from said adjacent ones of said plurality of segments in a manner such that said adjacent ones of said plurality of segments are not damaged;wherein said plurality of connection regions has a predetermined breaking point that is designed to break when subjected to a force that is lower than a force subjected to said target region by a broken one of said pressure-carrying lines. 9. The technical installation according to claim 8, wherein the plurality of connection regions withstand a maximum predetermined limiting shear force that is less than a force expected to be caused by the pipe break. 10. The technical installation according to claim 8, wherein the plurality of connection regions include cooperating holes and screws. 11. The technical installation according to claim 1, wherein said segmented configuration includes a middle segment that is designed with said predetermined breaking point. |
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abstract | A projection objective of a microlithographic projection exposure apparatus has a last optical element on the image side which is plane on the image side and which, together with an image plane of the projection objective, delimits an immersion space in the direction of an optical axis of the projection objective. This immersion space can be filled with an immersion liquid. At least one liquid or solid volume having plane-parallel interfaces can be introduced into the beam path of the projection objective, the optical thickness of the at least one volume being at least substantially equal to the optical thickness of the immersion space. By introducing and removing the volume, it is possible to convert the projection objective from dry operation to immersed operation in a straightforward way, without extensive adjustments to the projection objective or alignment work. |
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044302908 | description | DETAILED DESCRIPTION OF THE INVENTION As conducive to a full understanding of this invention, first a cusp magnetic field and its plasma confining function will be described. The term "particle" as used herein is intended to mean a charged particle, unless otherwise specified. FIG. 1 is a sectional view showing the fundamental shape of cusp magnetic field. As shown in FIG. 1, two equal circular coils 2 and 3 are disposed in parallel, with a central line 1 as their common axis, and these adjacent parallel coils carry equal currents as indicated by the current symbols in the figure. Magnetic flux is created as indicated by the thin arrows by the magnetomotive forces of the two circular coils 2 and 3. The magnetic flux thus created is of a so-called "absolute minimum B" type arrangement in which the magnetic field strength is zero at the center O thereof and is greater towards the outside. The magnetic flux is arranged radially from the central point O in the central plane 4 between the circular coils 2 and 3. It is assumed that plasma is generated in this magnetic field. In this case, the plasma is confined in a region 10 which is surrounded by curved surfaces 5 and 6 at which the internal pressure of the plasma is balanced with the magnetic pressure of the magnetic field. The curved surfaces 5 and 6 form circular line cusps 7 in the central plane 4 and point cusps 8 and 9 on the central line 1. Therefore, the magnetic field in this shape is called as "a cusp magnetic field." There are various configurations of cusp magnetic field. However, the description will be made with reference to a circular cusp magnetic field as shown in FIG. 1. The cusp magnetic field is of the "absolute minimum B" type. Therefore, it is advantageous in that it is essentially excellent in MHD stability and the plasma density can readily obtain a high .beta. value. On the other hand, the cusp magnetic field is of one open end system, and therefore a large amount of particle loss is caused through the line cusp and point cusp which are the open ends thereof. This particle loss is called as "cusp loss." In this connection, a mechanism causing the cusp loss will be described with reference to FIG. 2, which is an enlarged view of the vicinity of the line cusp 7. It is assumed that a particle, leaving the plasma region 10 along the line cusp 7, is at the position 11 in FIG. 2. Let's consider a first case where the particle is left from the plasma region by advancing perfectly in parallel with the magnetic flux. In this case, the electromagnetic action between the motion of the particle and the magnetic flux is not effected at all, and therefore the particle is moved along the orbit 12 thus leaving the plasma region 10. Furthermore, let's consider a second case where the motion of the particle is not completely in parallel with the magnetic flux, and its velocity component perpendicular to the magnetic flux is sufficiently smaller that the velocity component in parallel with the magnetic flux. In this case, the particle moves away from the plasma region 10 by going along a spiral orbit, as indicated by 13. In addition, let's consider a third case where the particle has the velocity component perpendicular to the magnetic flux which is sufficiently larger than the velocity component in parallel with the magnetic flux. In this case, the density of the magnetic flux encountered by the particle is increased as the particle is advanced, and therefore when the particle moves to a certain position, it is pushed back by the magnetic field and it is moved along an orbit 14, thus being returned inside of the plasma region 10. These cases will be described with reference to FIG. 3 which is a sectional view taken along the central plane 4 of the cusp magnetic field. The orbit 12 in the first case is coincident with a radius extended from the central point O, and the guiding center line of the spiral orbit 13 is also coincident with a radius extended from the central point O. The above-described cusp loss is caused in the first and second cases. In the cusp magnetic field, the magnetic field strength is zero at the central point O, and therefore the magnetic moment diabatic invariability of particles is not established. Accordingly, the particles can have an elimination condition with probability higher than that in a mirror magnetic field, and therefore the cusp loss in the cusp magnetic field is considerably great. The cusp loss can be somewhat reduced by increasing the magnetic field strength or enlarging the scale of the device; however, such treatment is still insufficient. Accordingly the present evaluation on the cusp magnetic field in the fundamental form is pessimistic that it could realize critical condition of thermonuclear reaction. In order to suppress the cusp loss, a cusp high frequency hybrid confinement system has been provided in which high frequency electric field close to the ion cyclotron frequency is applied to the vicinity of the line cusp and the point cusp. The experimental results of this system are hopeful one. In addition, the system is considerably effective to particles whose energy is relatively low. However, the system is not effective to a high energy particle which, having a large amount of motion, can pass through the high frequency electric field region in an extremely short period of time. The high energy particle is low in relative existence probability, but carries a relatively larger part of the entire plasma energy. Therefore, if a method of effectively stopping the escape of the high energy particle is not provided, the confined plasma loses the energy abruptly, as a result of which it becomes difficult to sustain the nuclear reaction. As the method of effectively stopping the escape of the high energy particle has not been provided yet, the problem must be solved by other methods. The invention is intended to offer a solution. The principle of the invention is as follows: That is, a plasma confining device according to the invention is so designed that a deflecting magnetic field is provided so as to intercept a particle escaped from the line cusp, and the particle is advanced in the opposite direction in the deflecting magnetic field so that the particle is returned from the line cusp to the plasma region. Because of this functional principle, the energy loss caused during the period of time of from the escape of the particle from the line cusp to the return to the plasma region is due to scattering and radiation, thus being limited, as a whole, to a small value. Accordingly, with the plasma confining device according to the invention, the cusp loss in the line cusp of the cusp magnetic field does not directly relate to the particle loss, and accordingly the particle loss and the energy loss can be markedly reduced. The principle of this invention can be applied to the linear open ends of a mirror magnetic field; however, it cannot be applied to the point cusps of a cusp magnetic field without modification. The concrete object and the applicaton limit of this invention are as roughly described above. Now, the embodiments of the invention and their operating principles will be described in detail. First, the most fundamental embodiment of the invention will be described. FIGS. 4 and 5 illustrate the plasma confining device according to the invention, which is applied to the biconical cusp magnetic field shown in FIGS. 1 and 3. The particles escaped from the line cusp 7 form a sheet-shaped plasma including the central plane 4. A magnet 40 is disposed in such a manner that the sheet-shaped plasma is between the magnetic poles 41 and 42 and that a magnetic field 43 is formed perpendicularly to the central plane 4 in the space between the magnetic poles. More specifically, the magnetic field is in the form of a ring having an edge 44 nearer to the plasma and an edge 45 farther from the plasma, and its magnetic flux density is equal at positions having the same distance (radius) from the central line 1 and has a constant or moderate magnetic potential gradient. It is assumed that one ion moves in a radial direction from the position 15 of the line cusp 7. This ion moves along a straight orbit 16 in the radial direction and reaches a position 17 on the magnetic edge 44. From this position 17, the ion moves along an orbit having a radius of curvature R=mv/qB (where B is the magnetic flux density of the magnetic field 43, q is the electric charge of the particle, m is the mass of the particle, and v is the velocity of the particle) and reaches a position 20 on the magnetic field edge 44. In this case, because of the uniformity of the magnetic flux density, the orbit 18 is symmetrical with a radius 19 passing through a position at which the tangential direction is perpendicular to the radial direction. Accordingly, the ion passes through the position 20 symmetrical with the position 17 and moves in the radial direction towards the center O. More specifically, the ion moves along an orbit 21 symmetrical with the orbit 16 and enters the line cusp 7 at a position 22 symmetrical with the position 15. Thus, finally the ion is returned into the plasma region 10. In the case where the particle is an electron, the deflection direction in the magnetic field 43 is opposite to that in the above-described case. In other words, the electron moves along a straight orbit 23 in a radial direction, and moves along an orbit having a radius of curvature R=mv/qB in the magnetic field 43. Thereafter, the electron moves along a straight orbit 25 in a radial direction towards the center O, and returns into the plasma region 10 through the line cusp 7. In this case, similarly as in the case of the ion, the orbits are also symmetrical with respect to a central line 26 of symmetry in a radial direction. In the two examples described above, the orbits are in the central plane 4 for convenience in description. However, in the case of a particle having a velocity component perpendicular to the magnetic flux, the orbit must be expressed in three-dimension, because it makes spiral motion. Therefore, the following example will be described by projecting the orbit onto the central plane 4. It is assumed that the particle is an ion, the ion escapes from the line cusp 7 at a position 27, advances along a spiral orbit 29 with a guiding center 28, and enters the magnetic field 43 at a position 30 on the magnetic field edge 44 with an angle .alpha..degree.. In this case, the ion moves along an orbit 31 having a radius of curvature R=mv/qB, and leaves, making an angle -.alpha..degree. with the radial direction, the magnetic field 43 at a position 33 symmetrical with the position 30 with respect to the central line 32 of symmetry in a radial direction which passes through the vertex of the orbit 31. Thereafter, the ion moves along a spiral orbit 35 having a guiding center 34, and enters the plasma region through the line cusp 7 at a position 36. In this case, the motion of the particle perpendicular to the central plane 4 in the magnetic field is not always symmetrical, and therefore the symmetry of the leaving and returning paths with respect to the central line 32 is not perfect. The embodiment of the invention which is applied to the most fundamental biconical cusp magnetic field, and its functional principle have been described. The object of this device resides in that the magnetic flux is allowed to perpendicularly interlink the sheet plasma formed by the group of particles escaped from the line cusp, and the uniform magnetic field is generated so that its edges are perpendicular to the advancement direction of the particles. As the device has been arranged in this manner, the particle (which may be an ion or an electron) which has escaped from the plasma region through the line cusp is deflected by the electromotive force caused by the relative motion between the magnetic field and the particle, as a result of which the advancement direction of the particle is reversed, so that it is returned into the plasma region through the line cusp. In this case, the motion of the particle is similar to reflection motion, and therefore the magnetic field will be referred to as "a reflector magnetic field" hereinafter. A variety of plasma confining devices can be formed in accordance with the above-described fundamental operating principle, and a variety of cusp magnetic fields and mirror magnetic fields with linear open ends are available. Therefore, it is, or course, difficult to describe all of the combinations of them, and so typical examples of them will be described hereinafter. First, some of the systems of generating the reflector magnetic field will be described. Similarly as in the device shown in FIGS. 4 and 5, one shown in FIG. 6 has a magnet with an iron core. However, the gap between the magnetic poles 41 and 42 of the magnet is getting wider towards the inside of the magnet 40 from its edge 44 nearer to the plasma. Accordingly, the magnetic flux density is larger at a position nearer to the plasma, that is, it decreases moderately as the position is moved inwardly of the magnet 40. In this case, the magnetic flux is in the form of arcs convex upwardly in the figure. This magnetic arrangement is used to improve the convergence of orbits in cyclotrons or synchrotrons. In the magnetic arrangement, only the electromagnetic deflection force 61 in the central plane 4 is applied to a particle 60 moving in the central plane; and a magnetic field component perpendicular to the central plane 4 applies an electromagnetic deflection force 63 in parallel with the central plane 4 to a particle 62 moving out of the central plane 4 and a magnetic field component in parallel with the central plane 4 applies a restoring force 64 perpendicular to the central plane 4 to the particle 62. The magnetic field component in parallel with the central plane 4 is zero on the central plane 4 but it is increased as it moves away from the central plane 4. That is, advantageously, the magnetic field component in parallel with the central plane 4 has the convergence action that the particle out of the central plane 4 is moved back to the central plane 4. FIG. 6 shows essential elements for forming the reflector magnet, such as a neutral particle catcher 65 and its exhaust pipe 66, and exciting coils 67 and 68. However, instead of the exciting coils 67 and 68, a permanent magnet may be employed. An example of the dimensions of such a reflector magnet is as follows: In the case of the average magnetic flux density B=1.0 Wb/m.sup.2, the radius of curvature R for a proton of 14.7 MeV is 0.54 m (R=0.54 m), and the radius of curvature R for an .alpha.-particle of 11.2 MeV is 0.47 m (R=0.47 m). Thus, the depth of the magnetic field 43 may be of this order. With respect to the distance between the reflector magnetic field and the cusp magnetic field circular coils 2 and 3, if the magnetic field strength is of the order of 10 Wb/m.sup.2 in the vicinity of the cusp the reflector magnetic field employing the iron core must be sufficiently remote from the coils so that the iron core is not magnetically saturated, and in practice it is necessary to select the radius of the reflector magnetic field to be five through seven times the radius of the cusp magnetic field coils. Reduction of the radius of the reflector magnetic field using the iron core can be accomplished by providing neutralizing coils 71 and 72 in the vicinity thereof as shown in FIG. 7. The coils 71 and 72 generate a neutralizing magnetic field 70 which will weaken the cusp magnetic field. In this case, the radius of the reflector magnetic field may be three or four times the radius of the cusp magnetic field coils. If this neutralizing magnetic field 70 is suitably set, then it may be employed as an element forming a diverter which catches and removes particles which are leaved away from the normal orbital plane, or it may serve to control the convergence of particles with respect to the central plane 4. In the above-described two examples, the reflector magnetic field is generated by using the magnet with the iron core. However, the reflector magnetic field can be generated by the use of a group of coils arranged as shown in FIG. 8 instead of the iron core. In this case (FIG. 8), electric currents are allowed to flow in the coils 81 and 82 in the same direction, while electric currents are allowed to flow in the coils 83 and 84 in a direction opposite to the aforementioned direction, so that the sum of the magnetomotive forces of these coils is substantially zero. If the coils are arranged in this manner, a reflector magnetic field 80 is generated in the space between the coils 81 and 82 and the coils 83 and 84, and the effect of the magnetic field is scarcely applied to the outside of the space. The space between the coils 81 and 82 is a path for particles, and the space between the coils 83 and 84 is a path for allowing neutral particles to escape. Several methods of creating the reflector magnetic field have been described as above. Now, how to apply this invention to a variety of cusp magnetic fields and mirror magnetic fields with linear open ends will be described with reference to a typical example thereof. In this example, a magnet with an iron core is applied to generate a reflector magnetic field. FIG. 9 is a sectional view showing a linear cusp magnetic field which is formed continuously and perpendicularly to the suface of the drawing. The cusp magnetic field is formed by four cusp magnetic field coils 91, 92, 93 and 94, and in the cusp magnetic field thus formed a plasma region 99 with line cusps 95, 96, 97 and 98 is formed. Reflector magnets 100 and 101 are provided for reducing the cusp loss of the line cusps 95 and 96, and similar reflector magnets (not shown) are provided for the line cusps 97 and 98. FIG. 10 is a sectional view taken along a central plane 102 passing through the line cusp 95 and a central line 90. However, it should be noted that the following description can be applied to the central planes of the remaining three line cusps. A reflector magnetic field 105 is generated between an edge 103, nearer to the plasma, of the reflector magnet 100 and an edge 104 remote from the plasma. A particle which has escaped in parallel with the magnetic flux from a plasma region 99 through the line cusp 95 is returned to the plasma region 99 through a straight orbit 106, a circular orbit 107 and a straight orbit 108 and through the line cusp 95 A particle having a velocity component perpendicular to the magnetic flux, which has escaped from the plasma region, is returned to the plasma region through a spiral orbit 109, a circular orbit 110 and a spiral orbit 111 and through the line cusp 92. As is apparent from the comparison of FIG. 5 with FIG. 10, with respect to a particle advancing in parallel with the magnetic field, in the case of circular cusp the inversion angle of the velocity vector of the particle in the reflector magnetic field is more than 180.degree., but in the case of a linear cusp it is just 180.degree., and the latter is the case where the advancement direction of particles is inverted. FIG. 11 shows another embodiment of the invention provided for a cusp magnetic field different in shape. In this case, the cusp magnetic field is similar in section to that shown in FIG. 9; however, it is moderately curved thus forming a ring as shown in FIG. 11. If the curvature radius of the cusp is sufficiently larger than that of a particle in the reflector magnetic field, the cusp magnetic field may be considered approximately equivalent to the linear cusp shown in FIG. 9. FIG. 12 shows a further embodiment of the invention provided for a cusp magnetic field whose shape is different from those of the above-described cusp magnetic fields. This cusp magnetic field corresponds to the linear cusp shown in FIG. 9, the length of which is limited. In the embodiment shown in FIG. 12, coils 120 and 121 generate the cusp magnetic field, which in turn forms a plasma region 122 and its line cusps 123, 124 and 125. The relation between the line cusp 123 and a reflector magnet 126 will not be described, because it can be estimated from the above-described biconical cusp magnetic field and linear cusp magnetic field. However, the relation between the line cusp 124 and a reflector magnet 127 and the relation between the line cusp 125 and a reflector magnet 128 will be briefly described. FIG. 13 is a sectional view taken along a central plane 129 passing through the line cusp 124. Because of the configuration of the coil 120, with respect to the magnetic flux on the central plane 129, it is extended perpendicularly to the line cusp 124 but it is curved at both ends. To the end, the reflector magnetic field should be curved at both ends. A particle, or an ion, which has escaped through the left end 131 of the line cusp 124 moves along an orbit 132 and along a circular orbit 133 in the reflector magnetic field 130. Thereafter, the ion moves along an orbit 134 and enters the plasma region 122 through the line cusp 124. On the other hand, an ion which has escaped through the right end of the line cusp 124 moves along an orbit 136 and along a circular orbit 137 in the reflector magnetic field 130, and further moves along an orbit 138. However, as this orbit 138 is shifted right from the right end 135 of the line cusp 124, the particle cannot return to the plasma region 122, as a result of which particle loss is caused. The particle loss may be somewhat reduced by modifying the configuration of the reflector magnetic field; however, with the finite linear cusp, it is difficult to completely eliminate the particle loss at the two ends. However, it should be noted that this particle loss is much less than the particle loss in the case where no reflector magnetic field is applied, and the use of the reflector field should be appreciated. A typical one of embodiments of the invention which is applied to a mirror magnetic field having linear open ends will be described with respect to FIG. 14. In this case, the mirror magnetic field is generated by YEN-YAN coils 140 and 141. The cusp magnetic field is different in many respects from the mirror magnetic field; however, in the case of the mirror magnetic field shown in FIG. 14, the open ends 143 and 144 of a confined plasma region 142 is similar in shape to the finite line cusp. In the case of the line cusp, it is a line whose width is very small, while in the case of the mirror magnetic field it is a line having some width. The sheet plasma which flows out of the line is thicker than the sheet plasma which flows out of the line cusp; however, the former is similar in characteristic to the latter, and therefore it is possible to reduce the particle loss by the reflector magnetic field. Reflector magnets 145 and 146 are shaped as shown in FIG. 16, so that the magnetic field edges are perpendicular to the advancement direction of particles. In this case, similarly as in the case of the finite linear cusp, the particle loss is more or less caused at the two ends. In each of the examples in FIGS. 4, 9, 12 and 14, the sheet plasma is flat, and in the example in FIG. 11 the sheet plasma is cylindrical. Finally, the case where the sheet plasma is conical. Shown in FIG. 15 is a kind of biconical cusp magnetic field which is generated by circular coils 150 and 151 arranged with the central line as the axis. A sheet plasma 154 flows out of a confined plasma region 152 through a line cusp 153. The sheet plasma 154 forms as its central surface a conical surface 156 including the line cusp 153 and having a point 155 on the central line 1 as its vertex. A reflector magnet 157 is disposed in such a manner that the sheet plasma is inserted therein. This arrangement is intended to prevent it from being repeated endlessly that a particle returned by being reflected by the reflector magnetic field passes through the plasma again to enter the opposite reflector magnetic field. In the case where an angle formed between the conical surface 155 and the radial direction is small, and in the case where the radius of the reflector magnetic field is so large that the curvature radius of a particle can be disregarded, the function of this device is similar to that of the device provided for the biconical cusp magnetic field. In this arrangement, it is necessary that the magnetic flux extended from the cusp magnetic field is as parallel with the conical surface 155 as possible. As is apparent from the above-described several examples, the reflector magnetic field generated by the device according to the invention acts effectively on the loss of particles from the line cusp of the cusp magnetic field and from the linear open ends of the mirror magnetic field, thereby to reduce the particle loss. However, since these examples are typical ones, the invention is not limited thereto or thereby. In practice, in application of the reflector magnetic field, reduction of the particle loss is naturally limited. In the case where the line cusp is in endless form, it is possible to completely eliminate the particle loss in single particle trajectory analysis. However, in practice, the orbit becomes irregular at a certain probability due to the interaction of particles because a number of particles pass across each other. This probability is in proportion to the square of the particle density and is in inverse proportion to the square of the particle energy. Accordingly, in order to improve the effect of the reflector magnetic field, it is preferable to minimize the number of low energy particles which flows out of the line cusp and to keep empty the orbital space extended from the line cusp and affected by the external reflector magnetic field, and furthermore it is desirable that these methods are used in combination with other systems such as for instance a cusp-HF hybrid confinement system. Thus, if, in the case where the particle loss at the open ends is of the sheet plasma in the plasma confining magnetic field of the open end system, the invention is applied to form the plasma confining device, the particle loss can be considerably reduced, whereby it is possible to approach the conditions necessary for generating and sustaining the thermonuclear reaction. |
abstract | A reactor in-core instrument handling system in which the signal leads are routed from the instrument sensors through an outer sheath through the upper reactor internals and out of and around the sheath in a substantially tightly wound spiral before exiting the reactor vessel. |
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claims | 1. A nuclear reactor comprising:a vessel divided into two discrete parts that are separate from one another;a reactor core located in the vessel and containing fuel rod assemblies;at least one internal structure being located within the vessel and having a flange portion extending between the two discrete parts of the vessel such that one of the two discrete parts is entirely separated from the other of the two discrete parts by the flange portion;insertion means for inserting a neutron-absorbing liquid in said fuel rod assemblies, located in the vessel;external control devices located outside the vessel and connected to said insertion means through a plurality of conduits located inside said flange portion of the internal structure; andsaid insertion means comprises a transmission means partly located in said conduits. 2. The nuclear reactor according to claim 1, wherein the neutron-absorbing liquid selected from the group consisting of a metal, a metal alloy, a metal with neutron-absorbing solid particles of a same density as the metal, and a metal alloy with neutron-absorbing solid particles of a same density as the metal alloy. 3. The nuclear reactor according to claim 1, wherein said internal structure is located above the core and the flange portion emerges on the outside of the vessel, laterally. 4. The nuclear reactor according to claim 1, further comprising at least one connection arm having a first end connected to said internal structure, said connection arm carrying conduits extending from said conduits located inside the flange portion of the internal structure, the connection arm being configured to assume:a stretched-out connection position, in which a second end of the connection arm is connected to said external control devices outside a pool containing the vessel, anda folded position, in which the connection arm is folded inside said internal structure, transmission components being inside the connection arm. 5. The nuclear reactor according to claim 1, wherein the transmission means comprises a helium tank located in said internal structure. 6. The nuclear reactor according to claim 1, wherein said internal structure includes an upper internal part comprising said flange portion and a lower internal part located below the upper internal part, inside the vessel. 7. The nuclear reactor according to claim 1, wherein said internal structure comprises a single internal part comprising said flange portion. 8. The nuclear reactor according to claim 1, wherein the means for injecting said liquid neutron absorber comprises, for each fuel rod assembly, at least one tank of liquid neutron absorber located in said internal structure. 9. The nuclear reactor according to claim 8, further comprising an assembly head providing connection between said internal structure and said injection channels located in the fuel rod assemblies, said assembly head being located below the internal structure. 10. The nuclear reactor according to claim 9, wherein liquid neutron absorber conduits located in the assembly head connect said at least one tank of liquid neutron absorber with the injection channels, each liquid neutron absorber conduit being extended by a swan-neck. 11. The nuclear reactor according to claim 10, further comprising, for each fuel rod assembly, a removable connection part located above said internal structure to provide connections between the conduits located in the internal structure and said means for injecting said liquid neutron absorber, the removable connection part including a space, the conduits of the internal structure opening in said space, said removable connection part further comprising conduits connecting the conduits of the internal structure with liquid neutron absorber tanks of the injection means controlled by said external control devices, via said space. 12. The nuclear reactor according to claim 11, wherein for each fuel rod assembly, a removable bell and seals are located in the space of the removable connection part, above an end of the conduit of the internal structure. 13. The nuclear reactor according to claim 12, further comprising, for each fuel rod assembly, a pneumatic distribution circuit, the removable connection part including lids, at a base of the removable bell, these lids providing a sealed connection between the conduits of the internal structure, the conduits of the removable connection part and conduits of the assembly head. 14. The nuclear reactor according to claim 11, further comprising, for each fuel rod assembly, an electrical distribution circuit, the removable connection part including lids at a base of the removable bell, the removable connection part being sealably mounted by a joint in said removable bell and configured to receive a ball valve carried at an end of a cable mounted in said internal structure, said ball valve being received in the space of the removable connection part. 15. The nuclear reactor according to claim 10, wherein, for each fuel rod assembly, at least two neutron absorber conduits connecting tanks of the liquid neutron absorber and the injection channels are located in the assembly head, the tanks being arranged on at least two different levels. 16. The nuclear reactor according to claim 1, wherein injection channels are located inside the fuel rod assemblies, each injection channel including an external tube and at least one capillary tube located in said external tube. 17. The nuclear reactor according to claim 16, wherein the external tube has a portion of variable section over its height. 18. The nuclear reactor according to claim 17, wherein the variable section is located in the upper portion of the external tube. 19. The nuclear reactor according to claim 16, wherein at least one of the injection channels comprises a bell inside which the external tube is located. 20. The nuclear reactor according to claim 16, wherein the injection channels are parallel to each other. 21. The nuclear reactor according to claim 1, further comprising pistons actuating control rods located between the fuel rod assemblies, said pistons being controlled via conduits extending through said internal structure. 22. The nuclear reactor according to claim 1, further comprising electrical or electromagnetic devices actuating control rods located between the fuel rod assemblies, said electrical or electromagnetic devices being controlled via conduits extending through said internal structure. 23. The nuclear reactor according to claim 11, wherein at least two removable connection parts have complementary self-locking shapes. 24. The nuclear reactor according to claim 11, wherein said removable connection part has water holes with a partly helical profile. 25. The nuclear reactor according to claim 1 further comprising:injection channels located inside the fuel rod assemblies; andconnection means between said internal structure and said injection channels located inside the fuel rod assemblies,wherein the insertion means further comprises means for injecting said liquid neutron absorber into said injection channels, andwherein the means for injecting a neutron-absorbing liquid comprises at least one tank of neutron-absorbing liquid under said internal structure. 26. The nuclear reactor according to claim 25, wherein the connection means comprises an assembly head providing connection between said internal structure and said injection channels located in the fuel rod assemblies, said assembly head being located below the internal structure. 27. A nuclear reactor comprising:a vessel;a reactor core located in the vessel and containing fuel rod assemblies;at least one internal structure located within the vessel and extending on a complete section of the reactor core;means for controlling an instantaneous power of said reactor; andmeans for ensuring emergency stopping of the reactor,wherein said internal structure comprises a single portion emerging outside the vessel, the single portion entirely separating two discrete parts of the vessel from one another,wherein said means for controlling instantaneous power of said reactor and said means for ensuring emergency stopping of said reactor include external control devices located outside the vessel, means for inserting a neutron-absorber in said fuel rod assemblies, and a plurality of conduits connecting said control devices to said inserting means through said single portion of the internal structure. |
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