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	description	The present application is a divisional of U.S. patent application Ser. No. 13/899,978, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-135348, filed Jun. 15, 2012, the entire content of which are incorporated herein by reference. Embodiments described herein relate to a method of recovering a nuclear fuel material. From the viewpoint of resources and reduction of environmental loads, the use of a thorium fuel has been studied. Almost all of natural thorium exists as thorium-232. Thorium-232 absorbs neutrons, and is transformed into uranium-233 through nuclear transmutation. Uranium-233 is a fissionable nuclide, and therefore can be used as a nuclear fuel. Reserves of thorium are larger than uranium. Therefore, the use of the thorium fuel can reduce the risk of resource depletion. Furthermore, the thorium fuel generates smaller amounts of high-radiotoxicity transuranic nuclides (TRU) than the uranium fuel. As a result, it is considered that the thorium fuel is able to reduce environmental loads. There are reports that a cycle with the use of the thorium fuel is effective in breeding of uranium-233 in light-water reactors and fast reactors, as well as in transmuting of TRU generated by a conventional uranium fuel cycle. What is required to make effective use of the thorium fuel cycle is a reprocessing technology to refine a nuclear fuel material from a thorium fuel. Therefore, what is required is processing a metal or metal oxide and recovering separately. Moreover, as for plutonium, the use of the technology of separately recovering plutonium comes with the issue of preventing nuclear proliferation. Therefore, the process requires a high degree of nuclear proliferation resistance so as not to allow plutonium to be recovered separately. As for the method of processing a uranium oxide fuel that has been used as a nuclear fuel of a conventional light water reactor, the following methods have been developed: a reduction method of uranium oxide, and a method of recovering uranium, plutonium and minor actinoids. As for the method of reprocessing the light water reactor fuel, as a method of reducing uranium oxide to metal, the following methods have been developed: a chemical reduction method, which uses a reducing agent, and an electrolytic reduction method. As for the chemical reduction method, as disclosed in Japanese Patent No. 3,763,980, the following method is available: the method of using metallic lithium as a reducing agent, and making it react with uranium, plutonium, and minor actinoids in a molten salt to reduce to metals, and recovering the metals of uranium, plutonium, and minor actinoids that are produced by the reduction. As for the electrolytic reduction method, as disclosed in Japanese Patent No. 4,089,944, the following method is available: the method of using lithium chloride, potassium chloride, and the eutectic salt of lithium chloride and potassium chloride for an electrolytic bath to carry out electrolytic reduction of a spent oxide fuel. Moreover, as disclosed in Japanese Patent No. 3,199,937 and Japanese Patent No. 3,486,044, the following method is available: the method of carrying out electrolytic separation of a metal fuel that is obtained by reduction, or a spent metal fuel, in an electrolysis tank that stores a molten salt phase and a metallic phase to recover the metals of uranium, plutonium, and minor actinoids. As for the method of recovering a nuclear fuel material pertaining to uranium oxide, for uranium, plutonium, and minor actinoids, the following methods are available: a method of reduction in a molten salt, and a method of recovering by electrolysis in a molten salt. For thorium oxide, no method has been established to recover a nuclear fuel material. If a nuclear fuel material is recovered in a similar way to that for uranium oxide, reduction cannot take place in the case of a chemical reduction method that uses metallic lithium because the thorium oxide is stable. Accordingly, it is difficult to carry out electrolytic reduction of thorium oxide with the use of lithium chloride, potassium chloride, and the eutectic salt of lithium chloride and potassium chloride. Thus, the problem is that the thorium metal cannot be recovered from the thorium oxide. The object of the present embodiment, therefore, is to provide a method of carrying out reduction of a thorium oxide to recover thorium metal. According to an embodiment, there is provided a nuclear fuel material recovery method of recovering a nuclear fuel material containing thorium metal by reprocessing an oxide of a nuclear fuel material containing thorium oxide in a spent fuel, the method comprising: a first electrolytic reduction step of electrolytically reducing the thorium oxide in a first molten salt of alkaline-earth metal halide; a first reduction product washing step of washing, after the first electrolytic reduction step, a reduction product obtained by the first electrolytic reduction step; and a main separation step of separating the reduction product, after the first reduction product washing step. According to another embodiment, there is provided a nuclear fuel material recovery method of recovering a nuclear fuel material containing thorium metal by reprocessing an oxide of a nuclear fuel material containing thorium oxide in a spent fuel, the method comprising: a first chemical reduction step of carrying out chemical reduction by letting the thorium oxide react with a first chemical reducing agent to produce thorium metal; and a separation step of carrying out separation and refining of the thorium metal after the first chemical reduction step. The following describes a method of recovering a nuclear fuel material according to embodiments of the present invention, with reference to the accompanying drawings. The same, or similar, portions are represented by the same reference symbols, and duplicate descriptions will be omitted. [First Embodiment] FIG. 1 is a flowchart showing a flow of a process of a method of recovering a nuclear fuel material according to a first embodiment of the invention. A spent Th oxide fuel for a light water reactor (referred to as “spent thorium fuel, ” hereinafter) contains uranium dioxide (also referred to as “UO2,” hereinafter), thorium dioxide (also referred to as “ThO2,” hereinafter), plutonium dioxide (also referred to as “PuO2,” hereinafter), minor actinoid oxide (also referred to as “MA2O3,” hereinafter), and fission product oxide (also referred to as “FPOX,” hereinafter). That is, the above substances are present in the form of oxide. Incidentally, the minor actinoids contain many trivalent elements, and are therefore written MA2O3, represented by trivalent elements. At a first electrolytic reduction step, the following substance is referred to as a first molten salt: calcium chloride (also referred to as “CaCl2,” hereinafter), or calcium oxide (also referred to as “CaO, ” hereinafter), or a mixture of calcium chloride and calcium oxide. Calcium oxide is an oxide, not a salt; it cannot be said that a mixture of calcium oxide that has melted with a molten salt of calcium chloride is exactly a molten salt. However, for descriptive convenience, the above substances are collectively referred to as molten salt (The same is true for the embodiments described later). In the first molten salt, a spent thorium fuel is put into a cathode basket 3a shown in FIG. 3, and electrolysis is carried out to perform electrolytic reduction of each component in the spent thorium fuel (First electrolytic reduction step S01). As a result, in the molten salt, oxides in the spent thorium fuel are respectively turned into the following substances: metal-state uranium (also referred to as “U, ” hereinafter); thorium (also referred to as “Th,” hereinafter); plutonium (also referred to as “Pu,” hereinafter); minor actinoids (also referred to as “MA,” hereinafter); and fission product oxide that is obtained by reduction (also referred to as “FP,” hereinafter). In this case, the first molten salt is not limited only to calcium chloride, calcium oxide, or a mixed salt of calcium chloride and calcium oxide. Instead, the first molten salt may contain at least one of the following substances: calcium chloride, magnesium chloride, calcium fluoride, and magnesium fluoride. The first molten salt may also contain other alkaline-earth metal halides. Furthermore, the first molten salt may contain an alkali metal halide. It is desirable that the temperature of the molten salt be about 850 degrees Celsius to about 900 degrees Celsius. At a first reduction product washing step, after step S01, each metal that is obtained by reduction at step S01 is washed to remove oxygen (S02). After step S02, a main separation step is started to carry out refining and separation of each metal. First, a first electrolytic separation is carried out. That is, electrolysis is carried out in a molten salt of lithium chloride (also referred to as “LiCl,” hereinafter), potassium chloride (also referred to as “KCl, ” hereinafter), or a mixture of lithium chloride and potassium chloride. As a result of the electrolysis, uranium and thorium are deposited on the anode side. That is, the above substances are separated in a metal state (S15). In this case, the molten salt used at the first electrolytic separation step may contain calcium chloride, magnesium chloride, calcium fluoride or magnesium fluoride; or a combination of the above substances. Furthermore, the molten salt may contain an alkali metal halide. After step S15, first, uranium and thorium, which are separated in a metal state, are transferred to another reactor vessel. After being transferred to another reactor vessel, uranium and thorium are distilled (S21), and an ingot of uranium and thorium is recovered (S22). After step S22, the weight of uranium and thorium recovered is measured (S23). After step S23, in order to produce a fuel, injection molding is carried out (S24). A process of mold removal and pin-end processing (S25) is carried out. In this manner, a metal fuel that is made of a mixture of uranium and thorium can be obtained. After step S15, for the plutonium and MA that have been separated from the uranium and thorium remaining in the cathode basket 3a, and transferred to another reactor vessel, a second electrolytic separation is carried out (S16). The second electrolytic separation is carried out after molten cadmium is injected into the molten salt, and the lower part of the reactor vessel 1 is filled with the molten cadmium. In an anode basket, plutonium and MA are stored; cadmium is placed on a cathode side as the process is carried out. Incidentally, in this case, the system is not limited to a method of directly putting the molten cadmium into the reactor vessel 1. At a cathode side, a cadmium basket may be provided; cadmium may be put into the cadmium basket. According to the above configuration, electrolysis is carried out, and an electrolytic separation enables plutonium and MA to be collected in the cathode-side cadmium (S16). After step S16, a molten salt and cadmium are distilled by a cathode processor (S26), and the ingot of the metals is recovered (S27). The weight thereof is measured (S28), and plutonium and MA are obtained. Incidentally, the molten salt that is used at each step is reclaimed and reused. That is, the first molten salt that is used during the first electrolytic reduction (S01) is reclaimed by a salt reclaim step (S50a). The molten salt that is used during the second electrolytic separation is separated by distillation from impurities such as FP (S32), and then is reclaimed by a salt reclaim step (S50c). Moreover, cadmium is distilled by a cathode processor and reclaimed (S26) and reused. The FP and waste salt that result from the cathode processor step S26 and the salt reclaim steps S50a and S50c are treated as wastes, and are subjected to disposal such as a glassification and other processes (S60). As described above, according to the present embodiment, in the same reactor vessel, oxides of a spent thorium fuel are reduced at once. Therefore, the steps are simplified, and a fewer types of molten salt are required. Moreover, a combination of uranium metal and thorium metal is separated from a combination of MA and plutonium metal when the two combinations are recovered. Therefore, the above substances can be mixed at a predetermined ratio, and a fuel whose concentration has been adjusted can be produced. As described above, each of the components, including thorium metal, can be recovered in the form of metal. [Second Embodiment] FIG. 2 is a flowchart showing a flow of a process of a method of recovering a nuclear fuel material according to a second embodiment of the present invention. The present embodiment is a variant of the first embodiment: Before the first electrolytic reduction step S01, a second electrolytic reduction step S03 and a second reduction product washing step S04 are added. That is, for a spent thorium fuel, the second electrolytic reduction step S03 and the second reduction product washing step S04 are carried out. After that, as in the case of the first embodiment, the first electrolytic reduction step S01 and the subsequent steps are carried out. First, the second electrolytic reduction is carried out (S03). That is, in a molten salt of lithium chloride, lithium oxide, or a mixture of lithium chloride and lithium oxide, electrolysis is carried out. As a result of the electrolysis, uranium dioxide, plutonium dioxide, and oxides of MA are mainly reduced, and uranium, plutonium, and MA are deposited on an anode side. That is, the above substances are reduced to metals. In this case, the second molten salt that is used at the second electrolytic reduction step S03 may contain any alkali metal halide other than lithium chloride. The second molten salt may further contain any alkaline-earth metal halide other than calcium chloride, magnesium chloride, calcium fluoride and magnesium fluoride. It is desirable that the temperature of the molten salt be around 650 degrees Celsius. Moreover, the molten salt that is used at the second electrolytic reduction step S03 is reclaimed for reuse. That is, the second molten salt that is used during the second electrolytic reduction (S03) is reclaimed by a salt reclaim step (S50b). FIG. 3 is a flowchart showing an electrolytic reduction process of the process of the method of recovering a nuclear fuel material according to the second embodiment of the invention, as well as a conceptual cross-sectional view of the inside of a reactor vessel 1. More specifically, FIG. 3 shows main steps, i.e. the second electrolytic reduction step S03 and the first electrolytic reduction step S01. As for oxides in a spent thorium fuel, only thorium oxide and uranium dioxide, which behave differently during the electrolysis, are shown. First, the second electrolytic reduction step S03 is carried out in a reactor vessel 1 that contains a molten salt of about 650 degrees Celsius of lithium chloride and lithium oxide. Into a cathode basket 3a that is on the side of a cathode electrode 3, a spent thorium fuel, which includes mainly ThO2 and UO2, is put. In this state, a potential difference is applied between an anode electrode 2 and the cathode electrode 3. First, UO2 is reduced to uranium metal. Meanwhile, ThO2 remains as oxide because ThO2 is not reduced with the current molten salt and in the current temperature condition. After the second electrolytic reduction step S03, the cathode basket 3a, along the substances inside the cathode basket 3a, is taken out, and is transferred to a reactor vessel 1 that contains another molten salt. In this case, the molten salt is a mixture of calcium chloride and calcium oxide; the temperature of the molten salt is about 850 degrees Celsius to about 900 degrees Celsius. In this state, a potential difference is applied between the anode electrode 2 and the cathode electrode 3. As a result, ThO2 is reduced (S01). Uranium remains in a metal state because the uranium has been reduced at the second electrolytic reduction step S03. In that manner, steps S03 and S01 are carried out. As the above steps of the present embodiment are carried out, first a uranium oxide and the like are reduced. Then, as the subsequent steps are carried out, a thorium oxide is reduced. Therefore, compared with the case where electrolytic reduction of oxides is performed at once by the first electrolytic reduction step, reduction of a uranium oxide, which is relatively easy to be reduced, and reduction of a thorium oxide, which is relatively difficult to be reduced, are carried out at different steps that provide conditions suitable for each. Therefore, the reduction steps can be efficiently performed. [Third Embodiment] FIG. 4 is a flowchart showing a flow of a process of a method of recovering a nuclear fuel material according to a third embodiment of the present invention. The present embodiment is a variant of the second embodiment: After the second reduction product washing step S04 and before the first electrolytic reduction step S01, electrolytic separation is carried out. More specifically, after the second reduction product washing step S04, in a molten salt of lithium chloride or potassium chloride, a first intermediate electrolytic separation is carried out (S115). At the second electrolytic reduction step S03, a uranium oxide, plutonium oxide, and MA oxide, which are relatively easy to be reduced, are reduced. At the first intermediate electrolytic separation step S115, uranium is separated among the reduced and refined uranium, plutonium, and MA. After the first intermediate electrolytic separation step S115, a distillation step S121 is perfomed to carry out distillation of salt, and uranium, which is produced by electrolytic separation at the first intermediate electrolytic separation step S115, is then recovered in the state of an ingot (S122). In order to produce a fuel, the weight of the recovered uranium metal is measured (S123), injection molding is carried out (S124), and a process of mold removal and pin-end processing (S125) is carried out. In this manner, a uranium metal fuel is produced. After the first intermediate electrolytic separation step S115, a second intermediate electrolytic separation is carried out (S116). In this case, as in the case of the second electrolytic separation of the first embodiment, a cathode electrode is used to carry out electrolytic separation (S26). As a result, plutonium and MA, which have been reduced to metals at the second electrolytic reduction step S03, are separated. The separated plutonium and MA are recovered in the state of an ingot (S122). The weight of the recovered plutonium and MA is measured (S123), injection molding is carried out (S124), and a process of mold removal and pin-end processing (S125) is carried out. Incidentally, cadmium used is reclaimed by a cathode processor for reuse. A molten salt of lithium chloride and potassium chloride that has been used during the electrolytic separation is reused after being reclaimed by a salt reclaim step (S50d). After the second intermediate electrolytic separation step S116, a thorium oxide, which has not been reduced, and part of FP oxides, are washed by a non-reduction product washing step (S117). After the non-reduction product washing step (S117), a thorium oxide, which has not been reduced, and part of FP oxides, are reduced by the first electrolytic reduction step S01, and thorium metal and FP are refined. The thorium metal that has been refined at the first electrolytic reduction step S01 is washed by the first reduction product washing step S02. After that, at a main electrolytic separation step S118, electrolytic separation of the thorium metal is carried out in a molten salt of lithium chloride and potassium chloride. The thorium metal that has been separated at the main electrolytic separation step S118 goes through a distillation step S131 before being recovered in the state of an ingot (S132). After the ingot recovery step S132, in order to produce a metal thorium fuel, the weight thereof is measured (S133), injection molding is carried out (S134), and a process of mold removal and pin-end processing (S135) is carried out. As a result, a metal thorium fuel is produced. Incidentally, the molten salt that has been used at the main electrolytic separation step S118 is distilled, and FP is removed therefrom (S131). After that, the salt is reclaimed (S50c) for reuse. As described above, according to the present embodiment, after the second electrolytic reduction step S03 at which electrolytic reduction of oxides of uranium, plutonium, and MA is carried out, electrolytic separation of uranium and electrolytic separation of plutonium and MA are sequentially carried out. After the substances are removed, the first electrolytic reduction step S01, which is a reduction step of thorium oxide, is carried out. According to the present embodiment, the uranium metal, the thorium metal, MA, and the plutonium metal are separated from each other when the above substances are recovered. Therefore, the above substances can be mixed at a predetermined ratio, and a fuel whose concentration has been adjusted can be produced. Moreover, the substances that have been turned into the state of metal are sequentially separated, and reduction of thorium oxide is then carried out. Therefore, the reaction in the processes is simplified, and there is an increase in reaction efficiency. Moreover, the processing of molten salt is reduced. [Fourth Embodiment] FIG. 5 is a flowchart showing a chemical reduction process of a process of a method of recovering a nuclear fuel material according to a fourth embodiment of the present invention, as well as a conceptual cross-sectional view of the inside of a reactor vessel 1. The present embodiment is a variant of the first, the second or the third embodiment. In this embodiment, instead of the first electrolytic reduction (Step S01) of each of these embodiments, chemical reduction is carried out. In the reactor vessel 1, a reducing agent (also referred to as a “first chemical reducing agent,” hereinafter), in which a mixture of calcium chloride and calcium metal is melted, is put, and is kept at about 850 degrees Celsius to about 900 degrees Celsius. Incidentally, the first chemical reducing agent may contain magnesium metal. A spent thorium fuel, which is represented by ThO2 and UO2 among other things, is put into a basket 4. A stirring unit 5 is rotated to stir a molten salt and promote a reaction. A molten salt of a mixture of calcium chloride and calcium oxide serves as a reducing agent, and ThO2 and UO2 are reduced. As a result, thorium metal and uranium metal remain in the basket 4 (First chemical reduction step S201). The other steps are the same as those of the first or third embodiment. According to the present embodiment described above, the use of the first reducing agent makes it possible to reduce a thorium oxide. [Fifth Embodiment] FIG. 6 is a flowchart showing a chemical reduction process of a process of a method of recovering a nuclear fuel material according to a fifth embodiment of the present invention, as well as a conceptual cross-sectional view of the inside of a reactor vessel 1. The present embodiment is a variant of the fourth embodiment: Before the first chemical reduction step S201, a second chemical reduction step S202 is added. Moreover, the present embodiment is also a variant of the second or third embodiment: Instead of the second electrolytic reduction (Step S03) of the second or third embodiment, chemical reduction is carried out. In the reactor vessel 1, a reducing agent (also referred to as a “second chemical reducing agent,” hereinafter), in which a mixture of lithium chloride and metallic lithium is melted, is put, and is kept at about 650 degrees Celsius. Incidentally, the second chemical reducing agent may contain at least metallic lithium or metallic potassium. A spent thorium fuel, which is represented by ThO2 and UO2 among other things, is put into a basket 4. A stirring unit 5 is rotated to stir a molten salt and promote a reaction. A molten salt of a mixture of lithium chloride and metallic lithium serves as a reducing agent, and UO2 is reduced. As a result, thorium dioxide and uranium metal remain in the basket 4 (Second chemical reduction step S202). After the second chemical reduction step S202, the first chemical reduction step S201 is carried out. However, the present embodiment is different from the fourth embodiment in that, at the first chemical reduction step S201, thorium dioxide and uranium metal are put into the basket 4. The molten salt in the reactor vessel 1, and the temperature of the molten salt are the same as in the fourth embodiment. According to the present embodiment described above, at the second chemical reduction step S202, first a uranium oxide is reduced. Then, at the first chemical reduction step S201 at which the first chemical reducing agent is used, a thorium oxide can be reduced. [Sixth Embodiment] FIG. 7 is a conceptual cross-sectional view of the inside of a reactor vessel 1, showing an electrolytic reduction process of a process of a method of recovering a nuclear fuel material according to a sixth embodiment of the present invention. The present embodiment is a variant of the fifth embodiment. As in the case of the fifth embodiment, in the reactor vessel 1, a first chemical reducing agent, in which a mixture of calcium chloride and calcium metal is melted, is placed. In the reactor vessel 1, the first chemical reduction step S201 is carried out. In the reactor vessel 1, part of an anode electrode 2 and part of a cathode electrode 3 are immersed. When the first chemical reduction step S201 is not carried out, voltage is applied to both electrodes from a direct-current power source 6. As a result, calcium chloride in the first chemical reducing agent is reduced, and is deposited on the cathode electrode 3. Chlorine gas is generated on the side of the anode electrode 2, and is discharged from an upper portion of the reactor vessel 1. In that manner, the metal calcium in the first chemical reducing agent can be obtained by electrolytic reduction of the first chemical reducing agent in the same reactor vessel 1 in which the first chemical reduction is carried out. [Seventh Embodiment] FIG. 8 is a conceptual cross-sectional view of the inside of a reactor vessel, showing an electrolytic reduction process of a process of a method of recovering a nuclear fuel material according to a seventh embodiment of the present invention. According to the sixth embodiment, a metallic component in the reducing agent is generated in the same reactor vessel in which the chemical reduction is carried out. However, according to the present embodiment, a reducing agent reduction reactor vessel 1a is used. That is, the first chemical reduction step is carried out in a reducing agent in which a mixture of calcium chloride and calcium metal is melted in the reactor vessel 1. Thorium dioxide is reduced, and thorium metal is obtained. The calcium metal in the reducing agent is generated in the following manner: a molten calcium chloride is put into the reducing agent reduction reactor vessel 1a, which is another reactor vessel having an anode electrode 2 and a cathode electrode 3; and voltage is applied from a direct-current power source 6 to reduce the calcium chloride. According to the present embodiment, the calcium metal, which is generated as described above, is introduced into the reactor vessel 1 for the first chemical reduction. Therefore, a required amount of the reducing agent can be supplied without causing radioactive contamination inside the reducing agent reduction reactor vessel 1a. [Eighth Embodiment] FIG. 9 is a flowchart showing a flow of a process of a method of recovering a nuclear fuel material according to an eighth embodiment of the present invention. The present embodiment is a variant of the first embodiment. According to the first embodiment, at the first electrolytic separation step S15, which comes after the first electrolytic reduction step S01 and the first reduction product washing step S02, electrolytic separation of thorium metal or the like, which has been reduced at the first electrolytic reduction, is carried out. According to the present embodiment, a spent fast-reactor metal thorium fuel, which is taken out from a fast reactor, is added, and is also processed. Accordingly, even from the spent fast-reactor metal thorium fuel, an electrolytically-refined thorium metal is recovered. Incidentally, the same operation can be carried out even at the first electrolytic separation step S15 of the second embodiment. The same operation can be carried out even at the main electrolytic separation step S118 of the third embodiment. In this manner, according to the present embodiment, even from a spent fast-reactor metal thorium fuel that is taken out from a fast reactor, an electrolytically-refined thorium metal is recovered. [Other Embodiments] The above has described several embodiments of the present invention. However, the embodiments are presented by way of example, and are not intended to limit the scope of the invention. Features of each of the embodiments may be used in combination. For example, the second chemical reduction step and the first electrolytic reduction step may be used in combination. Furthermore, the embodiments may be implemented in various other forms. Various omissions, substitutions, and changes maybe made without departing from the subject-matter of the invention. The above embodiments and variants thereof are within the scope and subject-matter of the invention, and are similarly within the scope of the invention defined in the appended claims and the range of equivalency thereof.
	summary
	abstract	A urethane based polymer composition is provided that exhibits superior shielding properties during and after exposure to high level radiation. The composite is formed by mixing a liquid isocyanate monomer, preferably 4,4′-diisocyanate monomer with a liquid phenolic resin, preferably phenol formaldehyde resin, and a phosphate ester flame retardant. An optional pyridine catalyst may be added to shorten the cure time. The resulting composition cures at room temperature and can be utilized in several manners, including spraying or pouring the composition prior to curing over radioactive material to prevent leakage of radiation. The uncured composite can be sprayed on the walls of a room or container to prevent leakage of radiation and can also be used to contain radiation prior to demolition. The uncured composite can also be molded into bricks or panels for use in construction. In a preferred embodiment, the polymer composition further incorporates radioactive waste, namely depleted uranium oxide, and can be used in conjunction with specially designed containers for storing radioactive material. The resulting polymer/waste composition cures at room temperature and does not deteriorate or suffer structural damage when exposed to higher levels of gamma radiation, nor do the mechanical or chemical properties undergo any detectable change. The composition is resistant to biodegradation and combustion, and does not creep or shrink during thermal cycling.
046801596	claims	1. A nuclear waste storage container assembly for storing radioactively-contaminated structural pieces and fuel rods of disassembled irradiated nuclear reactor fuel elements, the fuel rods giving off decay heat and the structural pieces giving off a decay heat less than the fuel rods, the storage container assembly comprising: a vessel defining a longitudinal axis and having a base wall and a cylindrical side wall extending upwardly from said base wall to conjointly define a storage space of circular cross section extending in the direction of said axis, said vessel further having an opening at one longitudinal end thereof communicating with said storage space; a plurality of elongated cans for storing said fuel rods therein, each of said cans having a circular-segmented cross section with one curved wall defining a curved wall surface having a radius of curvature corresponding to the radius of curvature of said cylindrical side wall; holding means for holding said plurality of cans and including structure defining a shaft-like enclosure extending in the direction of said axis for storing said structural pieces; said holding means being adapted for insertion into said storage space so as to cause said cans to be disposed radially of and in surrounding relationship to said axis; said holding means being configured to hold said cans in a circle-like arrangement one adjacent the other with the respective curved wall surfaces of all of said cans being in flush direct contact engagement with the cylindrical inner wall surface of said side wall so as to permit the direct transfer of said decay heat from all of said cans through said curved wall surfaces thereof directly to said vessel; each of said cans having respective mutually adjacent radial walls extending from said curved wall thereof which are limited in radial direction so as to permit said cans to be accommodated in said holding means in surrounding relationship to said enclosure; cover means for closing off said opening of said vessel; and, hold-down resilient means for holding said cans in position within said storage space and against the inner wall surface of said base wall so as to permit the transfer of further amounts of said decay heat from all of said cans directly to said vessel. a vessel defining a longitudinal axis and having a base wall and a cylindrical side wall extending upwardly from said base wall to conjointly define a storage space of circular cross section extending in the direction of said axis, said vessel further having an opening at one longitudinal end thereof communicating with said storage space; a plurality of elongated cans for storing said fuel rods therein, each of said cans having a circular-segmented cross section with one curved wall defining a curved wall surface having a radius of curvature corresponding to the radius of curvature of said cylindrical side wall; holding means for holding said plurality of cans and including structure defining a shaft-like enclosure extending in the direction of said axis for storing said structural pieces; said holding means being adapted for insertion into said storage space so as to cause said cans to be disposed radially of and in surrounding relationship to said axis; said holding means being configured to hold said cans in a circle-like arrangement one adjacent the other with the respective curved wall surfaces of all of said cans being in flush direct contact engagement with the cylindrical inner wall surface of said side wall so as to permit the direct transfer of said decay heat from all of said cans through said curved wall surfaces thereof directly to said vessel; and, each of said cans having respective mutually adjacent radial walls extending from said curved wall thereof which are limited in radial direction so as to cause said cans to conjointly define an elongated compartment within said vessel along said axis for storing said structural pieces therein. 2. The storage container assembly of claim 1, each of said cans having end faces at respective longitudinal ends thereof, said shaft-like enclosure being configured to have a square cross-section in a plane perpendicular to said axis; said hold-down resilient means being a plurality of spring means disposed between said cover and corresponding ones of one of the end faces of said cans. 3. The storage container assembly of claim 2, said holding means comprising a plurality of partition units extending between said enclosure and said inner wall surface of said vessel, each two mutually adjacent ones of said partition units conjointly defining a shaft-like compartment therebetween for receiving one of said cans therein. 4. The storage container assembly of claim 3, each of said partition units including two interconnected partition walls extending between said enclosure and said inner wall surface. 5. The storage container assembly of claim 3, said mutually adjacent radial walls of each of said elongated cans facing toward corresponding ones of said partition units when disposed in one of said shaft-like compartments; said storage container assembly further comprising guide means formed at the interface of each of said cans and the corresponding one of said shaft-like compartments for guiding said can into said shaft-like compartment. 6. The storage container assembly of claim 5, said guide means including inclined guide fins formed on said mutually adjacent sides of said cans and corresponding projections formed on said partition units for receiving said guide fins as the can is placed in the shaft-like compartment corresponding thereto. 7. The storage container assembly of claim 6, said guide means further including inclined surface means formed on said holding means for thrusting said cans outwardly and away from said axis into contact engagement with said inner surface wall of said vessel as said cans are placed into said corresponding ones of said compartments. 8. A nuclear waste storage container assembly for storing radioactively-contaminated structural pieces and fuel rods of disassembled irradiated nuclear reactor fuel elements, the fuel rods giving off decay heat and the structural pieces giving off a decay heat less than the fuel rods, the storage container assembly comprising:
	description	This application is a continuation of U.S. patent application Ser. No. 11/659,909, entitled “Method And Device For Removing Inflammable Gases In A Closed Chamber and Chamber Equipped With Such A Device,” which is the national phase of International Application No. PCT/FR2005/050647, filed on Aug. 4, 2005 (not published in English), which claims priority to the French Patent Application No. 04 51817 filed Aug. 9, 2004. The invention relates to a method and a device for removing inflammable gases, such as hydrogen, in a closed chamber containing radioactive matters, in the presence of solid or liquid organic compounds and possibly water capable of producing such gases, by radiolysis, or when the radioactive matters comprise compounds of this type and possibly water. The invention further relates to a closed chamber such as a receptacle, tank or container suitable for transporting or storing radioactive matters in the presence of organic compounds and possibly water, or comprising components of this type, said chamber being equipped with such a device for removing inflammable gases. The invention can be used in any closed chamber containing radioactive matters comprising organic compounds and possibly water, or radioactive matters in the presence of organic compounds and possibly water. As a non-limiting example, these radioactive matters may be technological waste from a facility for fabricating or reprocessing fuel elements for a nuclear reactor or issuing from such a reactor. Nuclear installations such as facilities for fabricating fuel elements for nuclear reactors generate a certain quantity of scrap, called “technological waste”. This technological waste may comprise a very wide variety of objects and materials such as motor parts, filters, scrap metal, rubble, glass, etc. This waste may also contain organic matter based on cellulose, such as paper, wood, cotton, or in the form of plastics such as packaging bags made of vinyl or polyurethane, boots, gloves, and miscellaneous objects made of polymer materials. All these wastes may also contain small quantities of liquids such as water and organic liquids (oils, hydrocarbons, etc.). All these wastes in themselves constitute radioactive materials, because they consist of metal parts activated during their residence in the installations, or organic or other materials contaminated by radioactive uranium or plutonium powder during their use in these installations. Technological waste is periodically removed to reprocessing and disposal centres. Their conveyance to these sites accordingly demands as many precautions as the transport of any other radioactive matter. In particular, the waste must be packaged and transported in containers or casks meeting the requirements of the regulations on the transport of radioactive matters on the public thoroughfare. In practice, transport is generally carried out by packing the technological waste in receptacles such as drums, bins or canisters, and by placing these receptacles in casks. The transport of technological waste raises a specific difficulty associated with the type of material transported. In fact, as explained above, this waste often contains organic matters, solid or in the form of residual liquids, or else a certain quantity of water, contaminated by uranium or plutonium, imparting a radioactive character to these materials. In fact, uranium and plutonium are emitters of a particles, which have the specific property of dissociating organic molecules to release gaseous compounds such as carbon monoxide, carbon dioxide, oxygen and nitrogen, as well as inflammable gases. This mechanism, called “radiolysis”, results in a dissociation of the molecules of the organic compounds containing carbon and hydrogen, like those comprised in plastics and hydrocarbons, or in a dissociation of the water molecules, with the production of hydrogen. The production of inflammable gases and particularly of hydrogen by radiolysis mainly raises problems when the technological waste is confined in a closed chamber of relatively limited volume. In fact, the radiolysis gases are then released in a confined volume, so that a high concentration of inflammable gases may be reached rapidly if the type of waste and the radiation intensity causes a significant production of these gases. The problem is particularly critical during transport, due to the fact that a large number of waste receptacles are generally placed in the same cask, in order to optimize transport capacity. In fact, this has the consequence of reducing the free space available in the cask for the inflammable gases which escape from the waste and the receptacles. It may also be observed that waste containment receptacles often themselves present a certain tightness, because they are closed by crimped lids that can be provided with seals. In this case, the inflammable gases preferably accumulate in the residual free space existing within each of the receptacles. Since these volumes are also very small, this can lead to high concentrations of inflammable gases in the containment receptacles themselves. In general, the inflammable gases produced by radiolysis form an explosive mixture when placed in the presence of other gases such as air, when their concentration exceeds a limit, called the “flammability limit”. The flammability limit varies according to the type of inflammable gas and according to the temperature and pressure conditions. In the case of hydrogen, the flammability limit in air is about 4%. This means that, if the hydrogen concentration in the air exceeds this level, a heat source or spark can suffice to ignite the mixture or to produce a violent explosion in a confined space. Various studies and observations have shown that the concentration of inflammable gases such as hydrogen, produced by radiolysis in a closed chamber containing radioactive matter comprising hydrogen-bearing components, can sometimes reach values of about 4% after a few days. This situation corresponds in particular to the case in which the technological waste emits intense a particles and contains numerous organic molecules. In fact, it is common for a cask to remain closed for a much longer time before being opened. This incurs the risk of accident, because a spark caused by impact or friction may be produced during transport in the chamber of the cask or in a receptacle filled with waste. In this eventuality, the ignition or explosion is liable to extend to the entire contents of the cask, implying the risk of a serious accident on the public thoroughfare. A comparable risk exists if the cask falls into an accidental situation of fire during its transport. Furthermore, the risk of accident subsists during the final operations of opening the cask and unloading the receptacles, and during their eventual opening. In fact, these operations demand numerous handling operations, which are potentially dangerous. It is therefore particularly important to take account of the risk of accumulation of inflammable gases in any closed chamber used to contain radioactive matter comprising hydrogen-bearing compounds. One technique for removing the inflammable gases such as hydrogen in a closed chamber such as a radioactive waste transport cask is essentially based on the introduction into the chamber of a catalyst for recombination of oxygen and hydrogen to water (or catalytic hydrogen recombiner), upon contact with which the hydrogen combines with the oxygen present in the air of the cavity to form water according to the catalytic hydrogen oxidation mechanism. Devices putting this technique into practice are described for example in documents EP-A-0 383 153 and EP-A-0 660 335. Document EP-A-0 383 153 describes a device for reducing the internal pressure in a radioactive waste storage receptacle. This device comprises a chamber placed in an opening of the wall or of the lid of the nuclear waste storage receptacle. The interior of this chamber receives a catalyst and comprises an opening communicating with the interior of the storage receptacle in which a sintered metal plug is placed. The catalyst is separated from the exterior by a metal fabric, a plate permeable to water vapour, or a lid of sintered metal. The hydrogen formed in the storage receptacle passes through the sintered metal plug and reaches the catalyst where the hydrogen is oxidized to water by the oxygen in the air. The catalyst used comprises a precious metal, for example palladium, on an inert support, for example alumina. In this document, use is made of an external oxygen source comprising ambient air, which is only feasible for hermetically closed chambers of perfectly sealed transport casks. Document EP-A-0 660 335 describes a device for reducing the overpressure in waste storage tanks, particularly radioactive waste producing hydrogen, in which a catalyst for recombination of hydrogen with oxygen and a desiccant are placed in a closed envelope placed inside the storage tank and communicating with its environment via a rupture disc. Inside the envelope are provided two separation sheets permeable to water vapour, below which two layers of desiccant are placed. In a first embodiment, two grids supporting the recombination catalyst are placed above the separation sheet. In a second embodiment, a layer of oxidant is placed above the separation sheet, kept in place by a separation sheet permeable to the gases. The desiccant is selected for example from silica gel, molecular sieves, dehydrated complexants such as for example copper sulphate or hygroscopic chemicals such as calcium chloride, magnesium sulphate, or phosphorus pentoxide, possibly on a support material. The recombination catalyst is selected in particular from catalysts coated with platinum or palladium. In this device, the recombiner becomes inoperative once all the oxygen in the chamber has been consumed. It has further been observed that these devices and methods, which use catalytic hydrogen recombiners, have the common feature of displaying lower efficiency particularly when the chamber contains carbon-bearing organic compounds. Hence a need exists for a method and a device for removing the inflammable gases, and particularly hydrogen, in a closed chamber containing radioactive matter comprising organic compounds, regardless of the types of organic compound and their carbon content, and possibly water. A need also exists for a method and a device for removing inflammable gases in a closed chamber, which serves to guarantee the removal of the inflammable gases, particularly of hydrogen over a long period, indeed a practically unlimited period. A further need exists for a method and a device for removing inflammable gases in a closed chamber, which is simple, reliable, safe, easy to use, does not demand lengthy and costly procedures, and which guarantees the effective removal of the inflammable gases such as hydrogen in a wide variety of conditions, that is, inter alia: in the presence of other radiolysis gases such as oxides like carbon monoxide and carbon dioxide, under irradiation and regardless of the type and intensity of this radiation, at various temperatures, these temperatures possibly being negative. It is an object of the invention to provide a method and a device which meet, inter alia, all the needs listed above. It is a further object of the invention to provide a method and a device which do not present the drawbacks, limitations, defects and disadvantages of the methods and devices of the prior art and which provide a solution to the problems raised by the methods and devices of the prior art, such as those described in documents EP-A-0 383 153 and EP-A-0 660 335. This object and others besides are achieved according to the invention, by a method for removing inflammable gases produced by radiolysis in a closed chamber containing radioactive matters comprising organic compounds and possibly water, or radioactive matters in the presence of organic compounds and possibly water, in which the following are placed inside the chamber: a) a catalyst of at least one reaction for oxidizing the inflammable gases by oxygen contained in the chamber atmosphere, supported by an inert solid support, b) a catalyst of at least the reaction for oxidizing CO to CO2. The reaction of oxidation of the inflammable gases by the oxygen present in the chamber atmosphere is generally, and essentially, a reaction for oxidizing hydrogen to water. Preferably, the catalyst a) is a catalyst of at least the reaction for oxidizing hydrogen to water. The catalyst a) supported by an inert solid support is a first active product that permits the continuous removal of the inflammable gases and in particular of the hydrogen, produced by radiolysis of the molecules, organic compounds and possibly water inside the chamber. This removal is achieved by the reaction for oxidizing the inflammable gases with the oxygen present in the chamber atmosphere, and particularly by the reaction of recombination of the hydrogen with the oxygen in the chamber atmosphere to produce water. The catalyst a) of this oxidation reaction, which is supported by an inert solid support, can be a precious metal that is advantageously selected from the group consisting of platinum, palladium and rhodium. The precious metal is present in a quantity that is generally lower than 0.1% by weight. The catalyst a) of this oxidation reaction may also be a rare earth, selected advantageously from the lanthanide group, such as lanthanum. The support of catalyst a) is an inert solid support. Inert support means a support that does not react chemically with the compounds present in the chamber, the chamber atmosphere, and the other active products. Preferably, the support of catalyst a) is a microporous inert solid support. This microporous support is generally selected from possibly activated molecular sieves. The term activated is a commonly used term in this technical field, which means that the compound forming the molecular sieve, such as alumina, has undergone treatment, particularly heat treatment, so as, in particular, to increase its specific surface area. This molecular sieve is preferably made of a material selected from aluminas and activated aluminas. The microporous inert solid support generally has a high specific surface area, that is a specific surface area generally of at least 200 m2/g, and preferably of at least 300 m2/g. The catalyst b) is a second active product, it catalyses the reaction for oxidizing CO to CO2. Preferably, the catalyst b) is a specific catalyst of the reaction of oxidizing CO to CO2. Specific means that the kinetics of oxidation of CO to CO2 catalysed by b) is much higher than that catalysed by a). Preferably, the catalyst b) comprises a mixture of manganese dioxide MnO2 and copper oxide CuO. The method according to the invention uses a combination of two active products, specific catalysts a) and b), which has never been described in the prior art as represented in particular by documents EP-A-0 383 153 and EP-A-0 660 335. The method according to the invention, essentially due to the use of such a specific combination of active products, catalysts a) and b), meets the needs and requirements listed above and provides a solution to the problems raised by the methods of the prior art. In particular, the inventors have succeeded in demonstrating that the efficiency of the methods of the prior art is substantially reduced in the presence of other radiolysis gases such as carbon monoxide CO; this drop in efficiency is explained by a poisoning of the H2 oxidation catalyst, a) such as palladium, by the carbon monoxide CO. Accordingly, by combining the oxidation catalyst of the inflammable gases with a catalyst b) of the reaction of CO to CO2, one surprisingly succeeds in preventing the poisoning of catalyst a) for oxidizing the inflammable gases by CO. The catalyst b) ensures the continuous removal of the carbon monoxide, by oxidation, to produce carbon dioxide, which causes no problem of poisoning of the catalyst a). Nothing in the prior art tended to imply that the drop in efficiency of the catalyst basically resulted from the presence of CO in the chamber. The prior art contained no indication that would have led a person skilled in the art to associate with the catalyst a), such as a recombiner, commonly used in this technical field, a specific catalyst b). The method according to the invention serves to remove effectively, over a very long period, indeed a virtually unlimited period, the inflammable gases such as hydrogen, present in the closed chamber. It preserves very high efficiency regardless of the waste present in the chamber and particularly if the waste contains organic compounds comprising carbon and hydrogen that are liable to liberate both CO and hydrogen. The method according to the invention operates perfectly in the presence of various radiolysis gases which, in addition to hydrogen, include for example CO, CO2, etc. The method according to the invention similarly operates perfectly in a broad range of temperatures and in particular at negative temperatures and under irradiation regardless of the nature thereof. Optionally, in addition to the two catalysts a) and b) which are always present, an oxygen source c) is placed in the chamber. This oxygen source is an optional third active product that serves to contend with the lack of oxygen, once all the oxygen initially present in the chamber has been consumed. This oxygen source may be in gaseous form or in solid form. If the oxygen source is in solid form, it is generally selected from solid peroxides. These compounds release oxygen in the presence of water which, for example, is the water formed during the oxidation of hydrogen by the catalyst a). These solid peroxides are generally selected from peroxides of alkali and alkaline earth metals and mixtures thereof, such as calcium peroxide, barium peroxide, sodium peroxide, potassium peroxide, magnesium peroxide and mixtures thereof. If the oxygen source is in gaseous form, it is generally formed by replacing all or part of the chamber atmosphere by pure oxygen. Optionally, a hygroscopic microporous inert solid support d) is also placed in the chamber. The hygroscopic microporous inert solid support is a fourth optional active product, which serves to ensure the continuous lowering of the moisture content of the chamber atmosphere, by adsorption of water. Depending on the temperature, the quantity of water removed generally represents 15% to 30% of the weight of the hygroscopic microporous support. The residual moisture in the chamber is thus maintained at a low value, for example less than 10% (moisture content) up to the saturation of said support. This serves in particular to collect the free water produced by the oxidation reaction, in particular the oxidation of hydrogen, catalysed by the catalyst a) and which would not have been absorbed in the micropores of the solid support, such as alumina, of the catalyst a), which can generally absorb up to 30% of its weight of water. The hygroscopic microporous support is preferably selected from molecular sieves. Advantageously, the molecular sieve of the microporous inert solid support d) is made of a material selected from materials of the aluminosilicate type (for example with the formula Na12—[(AlO2)12(SiO2)12] X H2O, where X is up to 27, or 28.5% by weight of anhydrous product). The hygroscopic microporous support generally has a high specific surface area, that is of at least 200 m2/g, and preferably at least 300 m2/g. It should be observed that this fourth active product is particularly present if the third active product consists of a source of oxygen gas. In fact, in this case, the presence of water that has not been absorbed by the support of catalyst a) such as alumina, is not necessary to generate oxygen, as opposed to the case in which the oxygen source consists of a solid peroxide which liberates oxygen only in the presence of water. Preferably, the microporous inert solid support supporting the catalyst a); the catalyst b); and possibly the oxygen source c) and the hygroscopic microporous support d) take the form of discrete elements, or particles, such as for example crystals, beads or granules, which may take the form of a powder. Thus in a preferred embodiment of the invention, the inert solid, preferably microporous, support supporting the catalyst a); the catalyst b); and the hygroscopic microporous support d), if any, are fractionated into discrete elements, such as for example crystals, beads or granules, having an envelope diameter generally of between about 2 mm and about 20 mm. The expression “envelope diameter” means the diameter of a fictitious sphere forming the envelope of said element. The active product c) is advantageously in a finely divided form such as a powder. In general, the active products a), b) and possibly c) and d) are placed, mixed or separately, in at least one receptacle that is at least partially permeable, such as a textile envelope, a strainer, a metal grid, or a perforated receptacle, such as a cartridge. Preferably, the active products a) and b) are mixed. On the other hand, the active products c) and d) must be separated. It is possible, for example, to disperse each of the active products between two grids in the form of superimposed layers, or to form a single layer with a mixture of the two compulsory active products a) and b), each of the optional active products c) and d) being packaged separately, for example in the form of separate layers. Several receptacles, such as cartridges, can be placed in the same closed chamber in order to increase the exchange area. The mass ratio of catalyst b) to catalyst a) is generally from 1/1 to 1/10, and preferably from 1/2 to 1/4, this mass ratio generally being given for a ratio of generally about 1:11 of the CO flow rate to the H2 flow rate. The invention further relates to a device for removing inflammable gases produced by radiolysis in a closed chamber containing radioactive matters comprising organic compounds and possibly water, or radioactive matters in the presence of organic compounds and possibly water, comprising: a) a catalyst of at least one reaction for oxidizing the inflammable gases by oxygen contained in the chamber atmosphere, supported by an inert solid support, b) a catalyst of at least the reaction for oxidizing CO to CO2, possibly an oxygen source c); possibly a hygroscopic microporous inert solid support d); a), b), c) and d) being such as defined above. Finally, the invention further relates to a closed chamber, suitable for containing radioactive matters comprising organic compounds and possibly water, or radioactive matter in the presence of organic compounds and possibly water, capable of producing inflammable gases, by radiolysis, said chamber further containing at least one device for removing inflammable gases as defined previously. The invention will be better understood from a reading of the detailed description that follows, provided for illustration and non-limiting, with reference to the drawings appended hereto in which: FIG. 1 is a graph that shows the hydrogen content (% by volume), in the chamber, measured by chromatography, as a function of time (t in hours) during the test performed in the example. The invention applies to any closed chamber, in which radioactive matters is placed comprising organic compounds and possibly water, or radioactive matters in the presence of organic compounds and possibly water. Organic compound in the sense of the invention means a compound comprising at least one carbon atom, at least one hydrogen atom and possibly at least one other atom selected for example from atoms of nitrogen, sulphur, phosphorus, oxygen and halogens. This chamber may have any shape and dimensions, as well as a more or less high level of tightness, without going beyond the scope of the invention. It may in particular be a receptacle such as a drum or a cylindrical or parallelepiped-shaped container. Furthermore, the chamber may be equally intended for transport, storage or the treatment of the radioactive matter concerned. Furthermore, the radioactive matter placed in the closed chamber may consist of all radioactive materials comprising organic compounds and possibly water, or of all radioactive materials in the presence of organic compounds and possibly water. In general, the invention applies more particularly to the case where said organic compounds are compounds which, in addition to hydrogen, emit or produce CO and CO2, such as certain plastics. In fact, it has been demonstrated according to the invention that CO poisons the catalyst a) and could be removed effectively by the catalyst b) to preserve the efficiency of the catalyst a). As a non-limiting example, the radioactive matter may consist of technological waste from a plant for the reprocessing or fabrication of nuclear fuel elements. As already stated, such waste is contaminated by radioactive plutonium or uranium and may contain a certain fraction of water or of solid or liquid organic compounds such as cellulose materials, plastics or hydrocarbons. According to the invention, at least two active products are placed in the closed chamber containing the radioactive matter. One of these active products, called below “active product A”, is designed to remove, by continuous catalytic oxidation by the oxygen present in the chamber, the inflammable gases, such as hydrogen, produced by radiolysis in the chamber atmosphere, under the effect of the radiation emitted by the radioactive isotopes present in said materials. The second active product, called below “active product B”, is an active product designed to remove the carbon monoxide by continuous oxidation and form CO2. These two active products A and B may optionally be combined with one or two other active products. These two other optional active products comprise a third product, called below “active product C”, designed to provide a source of O2, serving to contend with the lack of oxygen once all the oxygen initially present in the chamber has been consumed; and a fourth product, called below “active product D”, consisting of an active product absorbing water. The active product A comprises an inert solid support, preferably microporous, supporting a precious metal (impregnated with a precious metal), such as palladium, platinum or rhodium. As a variant, the inert solid support, preferably microporous, can also support a rare earth (be impregnated with a rare earth) advantageously selected from the lanthanide group, such as lanthanum. The active product D consists of a hygroscopic microporous support. The inert solid support of the active product A, if this support is microporous, and the hygroscopic microporous support of the optional active product D, generally both consist of a molecular sieve with a large developed surface area defined by a specific surface area, for example equal to or greater than 200, indeed 300 m2/g. Thus, if the microporous support of the active product A is impregnated with a precious metal or a rare earth, it has a very large reaction area for the oxidation of the inflammable gases produced by radiolysis in the chamber atmosphere and more particularly hydrogen. In the active product A, the precious metal or rare earth is a catalyst of the reaction for continuous oxidation of the hydrogen, by the oxygen present in the chamber. Generally, the presence of less than 0.1% by weight of precious metal in the microporous catalytic support serves to obtain the desired effect. The preferred microporous inert support of active product A and the hygroscopic microporous support of the optional active product D generally consist, as stated above, of a molecular sieve preferably selected for the microporous support of the active product D from the group of aluminosilicates, with the formula Na12[(AlO2)12(SiO2)12] X H2, where X can be up to 27, representing 28.5% of the anhydrous product, and for the microporous support of the active product A, from aluminas, preferably activated. In the active product A, the high specific surface area of the preferred microporous support serves to maximize the catalysing action of the precious metal or the rare earth. In fact, a large reaction surface area is provided on a support material, by using very little catalytic compound and in reduced volumes. Upon contacting the microporous inert support supporting the catalyst (impregnated with catalyst), the hydrogen combines with the oxygen in the chamber, to form water. The water thus formed is trapped and fixed deep in the micropores of the preferred support of product A, by molecular capillarity. By way of example, such a support can absorb up to 30% of its mass of water. The excess water, not absorbed by the microporous support of the active product A, is possibly trapped in the micropores of the hygroscopic microporous support forming the active product D. This makes it possible to prevent any formation of free water, which is liable to be decomposed again by radiolysis, by restoring a portion of the hydrogen removed. In fact, the water trapped deep in the microporous supports is less subject to the effects of the radiation emitted in the chamber atmosphere than if the water were free water. Alternatively, if the active product D is not present, the excess free water not absorbed by the support of the catalyst a) can then react with an active product C comprising a solid peroxide to cause a release of oxygen. Furthermore, it should be observed that the oxidation method thus put into practice operates perfectly because the chamber atmosphere cannot reach a high moisture content. More precisely, the efficiency of the active product D serves to guarantee a relative humidity of less than about 10% in the chamber atmosphere. This ensures a maximum yield of the oxidation reactions using active products A and B. The active product B, which must be placed inside the chamber, comprises a mixture of metal oxides, preferably in the form of granules, which allows the continuous removal of CO by oxidation to CO2. A preferred product comprises a mixture of manganese dioxide MnO2 and copper oxide CuO. The mixture of manganese dioxide MnO2 and copper oxide CuO generally represents about 80% of the weight of the product B (generally about 66% of MnO2 and 14% of CuO). This active product B plays a particularly important role when the gases present in the chamber contain CO. In fact, and without wishing to be bound by any theory, it has accordingly been demonstrated that the active sites of the active product A are blocked by CO because the CO molecule is larger than the H2 molecule. Hence it is the CO that is preferably converted by the catalyst a) and not the hydrogen. In other words, the hydrogen is not recombined because the CO blocks the active sites of the catalyst a). If, in addition to the catalyst a), a catalyst b) is placed in the chamber, this permits a much faster oxidation of CO to CO2 than the catalyst a). The active sites of the catalyst a) are then more available for the oxidation of the inflammable gases and particularly of hydrogen. A catalyst that can be used as the active product B is the product sold under the name Carulite® by Zander. This is a mixture comprising CuO and MnO2 which specifically catalyses the oxidation reaction of CO to CO2. For example, Carulite® catalyses this reaction at a rate that is ten times faster than the catalyst a), so that the catalyst a) remains available for the reaction for oxidizing the inflammable gases and in particular for the reaction for oxidizing hydrogen to water. The mass ratio of the active product B to the active product A is generally from 1/1 to 1/10, and preferably from 1/2 to 1/4. This ratio is generally determined for a ratio of the CO flow rate to the H2 flow rate that is generally about 1/11; this flow rate ratio is the one generally produced by technological waste. The active product C, which is optional, is defined as being an oxygen source. This oxygen source is generally in gaseous form or in solid form. In the latter case, it is generally a solid compound of the peroxide family which liberates oxygen in the presence of water. This water is generally the water formed during the oxidation of hydrogen by the catalyst a) and which has not been absorbed by the preferably microporous inert solid support of the catalyst a). Accordingly, if the active product C is such a solid peroxide, it is preferable not to use active product D, so that the water remains available to react with the peroxide and liberate the oxygen. The solid peroxide is generally selected from peroxides of alkali and alkaline earth metals such as peroxides of calcium, barium, sodium, potassium, magnesium and mixtures thereof. The oxygen source in solid form is initially introduced into the chamber when an oxygen deficit is anticipated. In order to be easily used and packed in the chamber, the active products A, B, C and D generally take the form of discrete elements or particles, such as granules, beads, crystals. Thus the microporous supports of the active products A, and possibly D, are advantageously fractionated into elements, particles, with small dimensions such as granules, beads or crystals. More precisely, each of the elements of the microporous supports preferably has an envelope diameter of between about 2 mm and about 20 mm. Each of said elements of microporous supports one (is impregnated with one) precious metal in the case of the active product A. The active product B is generally already in a fractionated form for example, that is to say generally in the form of granules of oxides MnO2 and CuO. When it is present, the active product C, if it is a solid product, generally takes the form of a powder. The fractionation of the microporous supports (active products A and D) and the already fractionated character of the active product B make it possible, optionally and as described more precisely below, to easily package at least one of the active products in various types of receptacle before placing them in the chamber. This fractionation also serves to maximize the efficiency of the properties of the microporous support, by further increasing the oxidation surface areas of the support of the active product A. In fact, when the hydrogen diffuses in the small elements forming the microporous catalytic supports, it is oxidized around the surfaces of all these elements. In other words, the total oxidation surface area corresponds to the sum of all the surface areas of the elements forming the support, which is much larger than the external surface area of the total volume occupied by said elements. The same argument applies to the fractionation of the supports of the active product D, which increases the water absorption surface areas. In consequence, the fractionation of the supports of the active product A and possibly D into small elements, the fractionated character of the active products B and C and the use of microporous materials with a high specific surface area combine to make the method according to the invention extremely efficient. The hydrogen is effectively oxidized on large surface areas, like the CO, and the water formed is trapped deep in the small elements, due to the capillarity properties of the microporous materials, particularly of the support material of the active product D. In a preferred embodiment of the invention, the microporous support of the active products A is activated alumina Al2O3, in the form of small granules. Activated alumina Al2O3 is a substance with a high specific surface area, more than 200 m2 per gram, indeed more than 300 m2/g. To obtain the best results, the alumina granules have an envelope diameter of a few millimetres, preferably of between about 2 mm and about 20 mm. In the case of the support of the active product A, the granules are slightly impregnated with precious metal (less than 0.1% by weight) or rare earth. Under these conditions, a quantity of granules impregnated with active product A corresponding to one liter by volume or about 800 g by weight, suffices to remove more than 400 liters of hydrogen in the free atmosphere of a closed chamber. In a particular application relative to the transport of radioactive matters, these matters are generally packed in receptacles such as drums lashed inside the container or cask. The active products are then advantageously placed inside these receptacles. This serves to remove the hydrogen directly where it is produced. Only a very small fraction of the hydrogen accordingly escapes from the receptacles to diffuse in the free volume of the container, where it is removed by the active products, also placed in small quantities in this free volume. If the receptacles are sealed, the active products can be placed in sufficient quantities exclusively inside these receptacles. In fact, the hydrogen concentration in the container atmosphere is then always insignificant because the hydrogen is removed in the receptacles and diffuses very little into the chamber of the container. It should be observed that the introduction of the active products into the receptacles serves to continue to prevent the accumulation of hydrogen after their final unloading. Moreover, if the receptacles are intended for storage on site for a long period, the active products can possibly be replenished to ensure the removal of hydrogen continuously on the storage site. In other words, the use of the method according to the invention is not limited to the removal of inflammable gases produced in a closed chamber during transport. In conclusion, the method according to the invention is particularly simple to use in combination with chambers of different types containing radioactive matter comprising organic components and possibly water. The handling operations necessary for placing the active products in the chamber are particularly simple and rapid to perform. The removal of the inflammable gases produced by radiolysis in the chamber is effectively guaranteed. Furthermore, the transport and storage times can be controlled very flexibly because it suffices to introduce appropriate quantities of active products into the chamber for the anticipated transport and/or storage period. The invention will now be described with reference to the following example, provided for illustration and non-limiting. This example illustrates the method of the invention using the following active products a) and b): active product a): alumina (microporous inert solid support) impregnated with palladium (catalyst) in the form of 3 mm beads and having a specific surface area of 300 m2/g; active product b): granules with the following chemical composition: 65% MnO2, 13% CuO, 9% Al2O3 and about 10% H2O. The granules are between 1 and 2 mm in size. The test was performed without active products c) and d). The test was performed as follows: A quantity of 25 grams of active product a) described above and a quantity of 12.5 g of active product b) described above (the products are packaged separately) were placed in a 20 liter chamber (Tedlar bag) containing 600 ml of hydrogen and 53 ml of carbon monoxide. The initial hydrogen concentration was about 5.6%. An H2/CO mixture was injected continuously with the following flow rates: 5.6 ml/h for carbon monoxide and 65 ml/h for hydrogen, representing an H2/CO flow rate ratio of 11.6. This ratio was representative of the ratio of flow rates of H2 and CO generated in a cask containing compacted waste produced by spent fuel reprocessing (of which the average composition was 90% of hulls and end-fittings and 10% of technological waste); the hydrogen and carbon monoxide flow rates were 2 liters/hour and 0.18 liters/hour, respectively. The test lasted 95 hours (up to the exhaustion of the oxygen present in the chamber). The hydrogen content in the chamber was measured throughout the test by chromatography. This content remained lower than 1% (by volume) throughout the test, as shown by the curve of the H2 content as a function of time (hours) shown in FIG. 1.
	description	The present invention relates to the fabrication of liquid crystal devices. It particularly relates to liquid crystal displays having a liquid crystal layer disposed on an alignment layer that affects substantially the alignment of molecules in the liquid crystal layer. However, the invention will also find application in conjunction with other liquid crystal applications. Liquid crystals are used in numerous display devices, such as notebook computers, desktop monitors, cellular telephone displays, high definition television, and the like, and in other photonic devices such as optical multiplexing coupler, switches, data storage, and so forth. The liquid crystal display typically includes a thin liquid crystal layer sandwiched between a pair of substrates of glass or another substantially light transmissive material. At least one of the substrates must be transparent. The display usually also includes one or two optical polarizer layers that cooperate with the liquid crystal layer and with biasing electronics to locally optically modulate optical path length of the LC film that in turn determines the opacity or reflectance of the liquid crystal display and changes pixel intensity. In an active matrix liquid crystal display, independently addressable thin film transistors are fabricated on the substrate to serve as the biasing electronics. In backlit displays, a backlight is disposed behind the liquid crystal display, and the biasing electronics locally modulate opacity of the liquid crystal display to darken or brighten pixels. In reflective displays, the reflectance of the display is modulated. Color filters matched with primary color sub-pixels are included in color displays. Moreover, some liquid crystal displays employ a flexible substrate material such as a polymer film or flexiglass to provide a flexible display. Regardless of the specific configuration and the type of liquid crystal display, a common element is one or more alignment surfaces that bias molecules of the liquid crystal toward a selected spatial alignment or orientation. A well known approach to forming the alignment surface is the rubbing method, in which a polyimide or other polymeric film is deposited on the substrate and physically rubbed using a velvet cloth to produce a directional or anisotropic template for molecules of the liquid crystal. The rubbing method is convenient and widely used in the industry; however, the method has substantial disadvantages, including a high potential for contamination, mechanical defects and damage, static charge generation which can damage the transistors in active matrix displays, and difficulty of obtaining uniformity in rubbing strength over large areas. As the liquid crystal display industry moves toward larger area and higher resolution displays, there has been an increasing desire to develop an improved method for forming the alignment surface which does not involve physically contacting the substrate. For example, U.S. Pat. No. 5,770,826 issued to Chaudhari et al. discloses a non-contact method that uses a low energy ion beam to define the alignment surface. Other methods include deposition of a Langmuir-Blodgett film, oblique angle deposition of silicon oxide or other inorganic materials, exposure of a polymer film to polarized ultraviolet radiation, and plasma irradiation. While these methods improve upon the rubbing method by eliminating physical contact, they have a number of disadvantages. Direct formation of an alignment surface that is uniform over large areas by direct deposition of an anisotropic alignment layer is difficult, especially for substrate areas on the order of several square meters which are preferred for large-area displays and for high manufacturing throughput. The ion beam and plasma irradiation methods are both performed in a vacuum environment, which is difficult to achieve over a large-area substrate and reduces manufacturing throughput. Moreover, as these methods are performed prior to sealing of the liquid crystal film, they can introduce contamination that degrades the liquid crystal display. The present invention contemplates an improved apparatus and method which overcomes the aforementioned limitations and others. In place of rubbing, deposition, UV or plasma exposure, this method uses exposure to electron beam, which can be performed at ambient conditions. The exposure modifies the surface properties that causes the liquid crystal molecules to anchor at specific orientations with respect to the substrate. According to one aspect, an apparatus is disclosed for producing an alignment surface on an associated substrate of a liquid crystal display. An electron source produces a collimated electron beam. A substrate support supports the associated substrate with a surface normal of the substrate arranged at a preselected angle relative to the collimated electron beam. A scanner relatively moves the collimated electron beam of predetermined energy (voltage) and flux (current) across the associated substrate at the preselected angle and at a predetermined frequency. According to another aspect, an apparatus is disclosed for producing an alignment surface on an associated substrate of a liquid crystal display. A particle source produces a collimated particle beam passing through air. A substrate support supports the associated substrate in air with a surface normal of the substrate arranged at a preselected angle relative to the collimated particle beam. A rastering mechanism relatively rasters the collimated particle beam across the associated substrate at the preselected angle and at a predetermined frequency. According to yet another aspect, a method is provided for producing an alignment surface on an associated substrate of a liquid crystal display. A processing area of the associated substrate is bombarded with a collimated electron beam at a preselected beam angle. The processing area is rastered over the associated substrate. Numerous advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment. With reference to FIG. 1, an apparatus 10 for forming an alignment surface on a substrate 12 of a liquid crystal display is described. The substrate 12 can be a rigid substrate such as a glass substrate, or a flexible substrate such as a polymer film substrate. The substrate 12 is arranged in a generally flat or planar fashion on a substrate support 20 that includes a generally planar surface 22 supported at a preselected angle α relative to the horizontal by a pivotally secured first edge 24 and a second edge 26 that is supported on at a selected height by support pins 28, 30 or other fasteners secured to vertical rods 32, 34. A lip 36 disposed on the first edge 24 prevents the substrate 12 from sliding off the tilted planar surface 22. The lip 36 is optionally omitted if friction between the substrate 12 and the planar surface 22 is sufficient to retain the substrate 12. The lip 36 can also be omitted if the substrate is fixed in its position by other means. An electron source 40 (shown diagrammatically) includes an electron-generating filament 42, a positively biased anode or assembly of electrodes 44 that draws electrons from the filament 42, and an acceleration grid 46 that accelerates and directs the electrons through a thin metal window 48 or other aperture to form a high energy electron beam 50. The acceleration grid 46 is electrically biased to impart a selected kinetic energy to the electron beam 50, and may include an array or other arrangement of variably electrically biased grid electrodes along the direction of the electron beam 50 to shape the acceleration field. The electron beam 50 is preferably substantially collimated by the acceleration grid 46 or other collimation component or components of the electron source 40. However, there may be some divergence of the electron beam 50, as is shown in FIG. 1. In FIG. 1 the electron beam 50 has a generally square cross-section; however, the electron beam can have a circular, elliptical, or otherwise-shaped cross-section. In a preferred embodiment, the imparted kinetic energy is at least one hundred kilo electron volts (100 keV). A suitable electron source is an electron linear accelerator (linac). Advantageously, for electron kinetic energies of around 1 MeV or higher the particle range in air is of order one meter or longer. Hence, the electron beam 50 passes through an ambient 52, which is preferably an air ambient, and bombards the substrate 12 in a processing area 54 that substantially corresponds to a footprint of the electron beam 50 on the substrate 12. Because of the high range in air of high energy electrons, an air ambient at about atmospheric pressure can be used, and so no vacuum chamber or other airtight enclosure is required. Instead of an air ambient, a controlled gas ambient can be employed. For example, a selected gas ambient at a pressure greater than or equal to about 1 millitorr can be arranged around the substrate 12 using a suitable airtight enclosure (not shown) and a vacuum pump, and related equipment. It will be appreciated that such a relatively high-pressure ambient is not compatible with low energy electron bombardment, ion beam bombardment, and plasma alignment surface formation methods, but is compatible with the apparatus 10 which applies high energy electron bombardment. Moreover, since the electron beam 50 readily passes through air, even in the case of a non-air ambient the airtight enclosure suitably is restricted to encompass the substrate 12 without extending over the electron source 40. Optionally, the selected ambient can be a vacuum ambient. Due to its simplicity, however, an air ambient with no enclosure, as shown in FIG. 1, is preferred unless the substrate 12 has a chemistry that adversely reacts with air during electron bombardment. For a substrate 12 having typical dimensions of a few meters on a side, the processing area 54 is typically substantially smaller than the area of the substrate 12. For example, the processing area 54 may be a few centimeters on a side. The processing area 54 is preferably rastered or scanned across the surface of the substrate 12 using a suitable scanner. In the embodiment illustrated in FIG. 1, the electron beam is rastered in a direction indicated by arrow 66 by a suitable beam deflector, such as by controlling a deflecting potential difference applied to the electron beam by electrodes of the assembly of electrodes 44. The frequency, rate, or speed of rastering can be controlled, and is typically around 100 Hz. The substrate support 20 is arranged on a linear track 70 that is movable in a linear direction (indicated by arrow 72) generally transverse to the direction of electron beam rastering. By rastering the electron beam in one direction and moving the substrate in the transverse direction at a predetermined speed, the processing area 54 is suitably scanned across the surface in a manner which controls the radiation dosage of the exposure. Substrates of substantially arbitrary size can be processed or scanned without placing the substrate in vacuum. Moreover, since the apparatus 10 preferably operates in air there is no substrate size restriction imposed by a finite-sized vacuum chamber. In some embodiments in which the processing area 54 is coextensive with the area of the substrate 12, the rastering component of the scanning is suitably omitted. With continuing reference to FIG. 1 and with further reference to FIG. 2, the geometry of electron bombardment achieved by the apparatus 10 is described. An x-y coordinate system shown in FIG. 1 lies in the plane of the substrate 12. FIG. 2 shows a cross-section of the substrate 12 taken parallel to the y-direction and perpendicular to the x-direction. In FIG. 2, the direction in which electrons 50 travel through the substrate is represented by parallel dotted arrows slanted at the preselected angle α relative to a surface normal 80 of the substrate 12. The angle α in FIGS. 1 and 2 are identical due to the geometric configuration of the substrate support 20. It will be appreciated that the electron bombardment landing angle α shown in FIG. 2 can be achieved in other ways besides the exemplary tilting of the planar surface 22 shown in FIG. 1. For example, the substrate can be arranged horizontally, and the electron source tilted at the electron bombardment landing angle α. The electron beam 50 at useful energies has a long range in air of typically a few meters; moreover, the electron beam 50 readily passes through the relatively thin substrate 12 for most substrate materials and material combinations. Without limiting the scope of the invention to any particular theory of operation, it is believed that electron bombardment by the electron beam 50 causes a rearrangement of atoms or molecules on or in an exposed alignment layer 82 of the substrate 12. This can occur via induction of a chemical reaction or by breaking certain chemical bonds in the substrate accompanied by rearrangement of constituent atoms or molecular groups. The atomic or molecular rearrangement introduces some degree of physical and chemical anisotropy to the surface 84 of the alignment layer 82, and also possibly to an interior of the alignment layer 82. The anisotropy relates to the direction and preselected angle α of the electron beam 50. In some types of substrates the alignment layer 82 is a polymeric material, for example, containing bi-phenyl side chain groups. Without limiting the scope of the invention to any particular theory of operation, it is believed that bi-phenyl rings having a direction generally perpendicular to the beam direction have a higher probability of interaction with the electron beam, and a higher probability of the corresponding chemical bonds being damaged by the electrons, as compared with bi-phenyl rings whose direction is generally parallel to the electron beam. It will be recognized that other physical mechanisms can account for the formation of an alignment surface by electron bombardment. The mechanism may differ depending upon the material or materials making up the alignment layer. In general, the bombardment is believed to result in physical and/or chemical anisotropy on the surface of the substrate 12 which biases molecules of a subsequently applied liquid crystal layer (not shown in FIG. 2) toward a selected alignment. Moreover, because most materials exhibit some response to high energy electron bombardment, a suitable alignment surface is expected to be produced on the alignment layer 82 for a large number of organic and inorganic alignment layer materials. Indeed, it is contemplated that a suitable alignment surface can be produced on a bare glass substrate or a glass substrate coated with indium tin oxide (ITO) using the apparatus 10. Since the apparatus 10 does not require evacuation, the substrate 12 resides in ambient 52 which is preferably an air ambient. The substrate 12 can be partially processed prior to the electron bombardment. For example, in FIG. 2 the substrate 12 includes a glass substrate 90 on which thin film transistors 92 and other circuitry defining an active matrix have been fabricated, after which the alignment layer 82 was deposited. The partially fabricated substrate 12 including the thin film transistors 92 and other active matrix circuitry and the alignment layer 82 are then exposed to high energy electron bombardment by the apparatus 10 as shown in FIG. 2. After the electron bombardment, the liquid crystal layer is applied on top of the alignment layer 82. Molecules of the applied liquid crystal layer tend to align with an anisotropy of the alignment surface introduced by the electron bombardment. With reference to FIG. 3, another advantage of the apparatus 10 is described. As shown in FIG. 3, processing by the apparatus 10 to form the alignment surface can be postponed until at or near the end of the liquid crystal display manufacturing process. A substantially completed liquid crystal display 12′ includes an alignment layer 82′, glass substrate 90′, and thin film transistors 92′ that generally correspond to the alignment layer 82, glass substrate 90, and thin film transistors 92 shown in FIG. 2. Further display manufacturing processes performed prior to the electron bombardment have additionally added a bottom polarizer layer 100, liquid crystal layer 102, spacer elements 104, top alignment layer 106, color filter layer 108 (if needed), and top polarizer layer 110. Other liquid crystal display components can also be added prior to processing by the apparatus 10. The substantially completed liquid crystal display 12′ including components 82′, 90′, 92′, 100, 102, 104, 106, 108, 110 is then processed by the apparatus 10 to form alignment surfaces at a first surface 84′ of the bottom alignment layer 82′ and at a second surface 112 of the top alignment layer 106. Because the high energy electrons of the electron beam 50 penetrate through the substantially completed liquid crystal display 12′, the surfaces 84′, 112 are processed and rendered anisotropic by the electron bombardment. Advantageously, this processing occurs after the liquid crystal layer 102 is applied and sealed, reducing the likelihood of contamination during alignment surface formation. Moreover, the processing occurs in the ambient 52 which is preferably an air ambient. Of course, if certain components of the liquid crystal display are sensitive to damage from electron bombardment, processing to add these components should be delayed until after the electron bombardment. In one actually performed alignment surface formation process, a thin polymer alignment layer with bi-phenyl side chain groups deposited on a 2.4 m×1.2 m substrate was processed using 0.7 MeV electron bombardment with an electron beam current of 1 milliampere at a preselected landing angle α of 80°. These results are only examples; in general, process parameters such as the electron kinetic energy, electron beam current, and landing angle α are optimized for a given alignment layer configuration. It will be appreciated that the apparatus 10 is exemplary only. Optionally, the electron source 40 can be replaced by another particle source that produces high energy particles having a long range in air and adequate interaction with the selected alignment layer material. For example, a proton beam can be employed; however, the range of high energy protons (for example, in the million electron volt range) is typically a few centimeters or less, which complicates adaptation of the apparatus 10 to proton sources. Substitution of a high energy photonic particle source such as an x-ray or gamma ray source is also contemplated. The electron source 40 is preferred, however, due to its long range in air coupled with strong high energy electron interaction with typical alignment layer materials. Moreover, the mechanical structure of the apparatus 10 is exemplary. Those skilled in the art can readily construct other mechanical arrangements for producing a relative rastering of the processing area 54 across the substrate 12. For example, the substrate could be immobile, and rastering in two transverse directions, such as x and y directions, provided by electromagnetic beam deflectors. With reference to FIG. 4, a modified apparatus 10″ is modified in that it includes a different substrate support 20″ that is suited for handling a rolled flexible substrate 12″ such as a flexiglass or polymer film substrate. The electron beam 50 produced by the electron source 40 passes through air 52 and is rastered in a direction 66″ across the substrate 12″. The substrate support 20″ includes cylinder 120 on which the flexible substrate 12″ is wrapped. A rotary motor 122 electrically driven by power leads 124 rotates a drive shaft 126 coupled to the cylinder 120 about a cylinder axis 128 at a rotation rate ω to effect an unwrapping of the flexible substrate 12″ off the cylinder 120 at a linear rate r×ω where r is a radius of the substrate 12″ on the cylinder 120 and the rotation rate ω is measured in radians per second. Rather than employing continuous rotation, the motor 122 can be a stepper motor that performs the unwrapping in discrete steps. By rastering the beam in the direction 66″ and wrapping or unwrapping the substrate 12″ by rotation of the cylinder 120, the substrate 12″ is scanned by the processing electron beam 50. The electron beam 50 irradiates the substrate 12″ over a processing area 54″ disposed on the wrapped substrate 12″ or around where the substrate 12″ unwraps from the cylinder 120 so that substrate still on the roll is not exposed to the electron beam. The preselected angle α correlates with an angular position of the processing area 54″ on the cylinder 120 or with an angle of the substrate 12″ in the unwrapping region. The angle α can be adjusted by adjusting the take-off angle at which the substrate 12″ is unwrapped, and/or by arranging the processing area 54″ at a selected angular position on the substrate. Typically, the unwrapped portion of the substrate 12″ is taken up on a take-up spool (not shown). Rather than applying the electron bombardment at the unwrapping cylinder 120, the electron bombardment can instead be applied during wrapping onto the take-up spool. The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
	summary
063273233	summary	FIELD OF THE INVENTION The present invention relates to a plurality of reactor vessels within a single containment building. BACKGROUND OF THE INVENTION Nuclear reactors use the thermal energy produced through fission to produce energy. Typically, a coolant such as water flows about nuclear fuel elements contained within a reactor vessel under such a high pressure that it remains in liquid form at a temperature far above the normal boiling point. The coolant goes to a heat exchanger including a feedwater header, where it gives up heat to a secondary stream of water that turns to steam while the primary stream of coolant returns to the reactor vessel. The steam is then used to run a steam generator turbine. Alternatively, the pressure is adjusted so that steam generation occurs as the water passes over the fuel elements. In the latter case, the steam passes directly from the reactor vessel to one or more steam generated turbines and is then condensed by a condenser before returning to the reactor vessel. Nuclear reactors are designed to operate safely without releasing radioactivity to the outside environment. Nevertheless, it is recognized that accidents can occur. As a result, the use of multiple barriers has been adopted to deal with such accidents. These barriers include the fuel cladding, the reactor coolant or steam supply system, and thick shielding. As a final barrier, the reactor is housed in a large steel containment building. Containment buildings vary considerably in design from plant to plant. Many are vertical cylindrical structures covered with a hemispherical or shallow domed roof and with a flat foundation slab. Other containment buildings may be spherical in shape. Containment buildings are often not visible since they are usually surrounded by a steel or concrete outer building that also include many non-essential plant support systems, structures and auxiliary buildings which need not be included within the containment building. Nevertheless, these other systems and auxiliary structures and buildings must be located in close proximity to the reactor containment building. A containment building houses the entire primary system of a nuclear reactor including the reactor vessel, reactor coolant or recirculation systems, pumps, and steam generators. The containment building includes a number of compartments for the housing of auxiliary equipment, safety systems, and various other systems. The containment building is designed and tested to prevent any radioactivity that escapes from the reactor from being released to the outside environment. As a consequence, the building must be airtight. In practice, it must be able to maintain its integrity under circumstances of a drastic nature, such as accidents in which most of the contents of the reactor are released to the building. It has to withstand pressure buildups and damage from debris propelled by an explosion within a reactor. It must past tests to show it will not leak even when its internal pressure is well above that of the surrounding air. Typically, a containment building is designed to sustain internal pressures in the range of 45 to 60 psig. However, much higher pressures, even exceeding 100 psig, may be sustained. The containment building is also designed and tested to protect a reactor against outside forces. Such outside forces include natural or man-made forces such as earthquakes, floods, tornadoes, explosions, fires and even airplane crashes. One of the major factors influencing containment building design and placement is economic, since a containment building is one of the most expensive structures of a nuclear power plant. Containment buildings are currently usually designed in accordance with site-specific requirements established for each nuclear power plant. Site-specific designs prevent the standardization of the containment building and further increase cost. As a result of such expenses, it is desirable to maximize the amount of energy generated by such a plant. There is a current limit of approximately 1800 MW of thermal power heat generation from a single reactor. However, core stability is less than ideal at such a reactor unless substantial expensive modifications are made. As a result, in modern practice, a single reactor has been placed in a single containment building having an energy output on the order of approximately 850 to 1450 MW. The greatest core stability occurs at approximately 1100 MW of thermal power generation. SUMMARY OF THE INVENTION A nuclear reactor plant includes at least two or more reactor vessels each having an independent ability to generate thermal energy which is transferred away from the reactor vessels by means of coolant contained within a coolant system. The thermal energy is received by at least one steam generator which converts the thermal energy to electricity. In one preferred embodiment, the reactors operate completely separately from one another. However, the containment building requires significantly less material than if two separate containment buildings were required. For example, if a spherical containment building is used, the revised diameter of the building is only approximately 1.2 to 1.3 times the original diameter. In a second preferred embodiment the reactor vessels are independently controlled and include their own coolant systems. However, they jointly provide heat to a common header having a plurality of steam generators connected to it. The second embodiment represents a partial integrated control philosophy. In a third preferred embodiment, the reactor vessels are completely integrated with one another by means of a single control and coolant or steam supply system.
	summary
053234286	claims	1. In a device a hub which is clamped to a flange formed on the upper end of a nozzle in manner to establish a hermetic seal between said hub and said flange, said hub being formed with a stepped bore therein through which a column member extends; seal means disposed in said bore about said column member; a retaining nut threadedly received in said stepped bore, said retaining nut being adapted to directly engage and press said seal means into sealing engagement with a wall portion of said stepped bore and a wall portion column member which is located within said stepped bore in a manner which establishes a hermetic seal between said hub and said column member; a resilient washer disposed on the upper side of said retaining nut; and an annular load ring which is threadedly received on a portion of said column, said load having a plurality through holes; and a plurality of bolts respectively threadedly received in said plurality of through holes, said bolts being arranged to adjust the pressure applied by said resilient washer to the top of said retaining nut. wherein said means for selectively applying a force to the top of said retainer nut comprises a plurality of bolts which are threadedly received in threaded bores formed in said annular load ring, said plurality of bolts being arranged to directly engage said belleville washer and to produce a reaction which tends to drawn said column member in a direction wherein a shoulder which is formed about said column member engages and compresses said seal means. a hub which is clamped to a flange formed on the upper end of said nozzle in manner to establish a hermetic seal between said hub and said flange, said hub being formed with a stepped bore through which said column member extends; seal means disposed in said bore about said column member, said seal being supported by a seal carrier; a retaining nut threadedly received in said stepped bore, said retaining nut being adapted to directly press said seal into sealing engagement with a wall portion of said stepped bore and a wall portion column member which is located within said stepped bore in a manner which establishes hermetic seal between said hub and said column member; and an annular load ring which is threadedly received on a portion of said column, said load ring including means for selectively applying a force to the top of said retainer nut. a flange formed about an upper portion of said nozzle; a hub releasably connected to said flange by a clamp; a stepped bore formed in said hub through which said column arrangement is disposed; a grafoil seal arrangement disposed in said stepped bore; a retaining nut which is threadedly received in said stepped bore and which can directly apply a pressure to said grafoil seal arrangement; and loading means threadedly received on said column arrangement for applying pressure on said retaining nut. an elastomeric spacer which can be inserted into said stepped bore when said retaining nut is removed, said elastomeric spacer protecting threads which are formed on the wall of said stepped bore and engaging the external wall of a bullet shaped cover which is placed over the top of said column arrangement when the nuclear reactor is conditioned for a predetermined operation. 2. A sealing arrangement as set forth in claim 1, further comprising a belleville washer which is interposed between said annular load ring and said retaining nut; and 3. A sealing arrangement for device having a nozzle portion and a column member disposed through said nozzle portion, comprising: 4. A sealing arrangement as set forth in claim 1 wherein said seal means includes a seal carrier which is received at the bottom of the stepped bore and at least one graphite containing seal member carried on said seal carrier. 5. A sealing arrangement as set forth in claim 3 wherein said seal means includes a seal carrier which is received at the bottom of the stepped bore and at least one graphite containing seal member carried on said seal carrier. 6. In a nuclear reactor including an in-core-instrument, a head which is lifted when the reactor is refuelled, and a nozzle arrangement which includes a column arrangement through which the in-core-instrument is disposed, said nozzle comprising: 7. A nuclear reactor as set forth in claim 6 further comprising: 8. A nuclear reactor as set forth in claim 6 wherein said loading means comprises a loading ring which is threadedly connected to said column arrangement and a resilient washer interposed between said loading ring and said retaining nut. 9. A nuclear reactor as set forth in claim 8 wherein said loading ring includes a plurality of bolts which can be screwed down on said resilient washer in a manner which adjustably varies the pressure applied by said resilient washer to said retaining nut. 10. A nuclear reactor as set forth in claim 8, wherein said loading means further includes a plurality of bolts which are respectively disposed in a plurality of threaded bores formed in said loading ring, said bolts engaging said resilient washer in a manner which distorts said resilient washer and produces a reaction which tends to move a shoulder which is formed on said column arrangement and on which said graphoil seal rests, toward said retaining ring and induces compression of said graphoil seal.
051223309	abstract	An apparatus and method for monitoring corrosion to members within the core of a nuclear reactor, particularly fuel rod cladding. A sensor means is submerged inside the core of a nuclear reactor near the member of fuel rods. The sensor means is comprised of a generally cylindrical section having an outer surface that is subject to corrosion and radiation, and has a cross-sectional area A.sub.1. The sensor means additionally has a reference section subjected to radiation but not to corrosion, and having a cross-sectional area A.sub.2. At least one pair of first probes, separated by a length L.sub.1, is placed in electrical contact with the cylindrical section. At least one pair of second probes separated by a length L.sub.2, is placed in electrical contact with the reference section. A current is passed throughout the sensor means to produce a potential gradient in the cylindrical section and reference section. The change in potential in the reference section, and the cylindrical section is measured and used to calculate the subsequent cross-sectional area in the cylindrical section between the first probes. Preferably, the cylindrical section and reference section are made from the same material as the member.
	description	This invention relates to a system and a method for producing a fibre-type multiphoton microscopic image of a sample, for use in endoscopy or fluorescence microscopy. The field of application targeted is more specifically that of in vivo and in situ imaging. In conventional confocal fluorescence imaging, a photon excites a molecule. The deexcitation of the latter causes the radiation of a fluorescent photon. The energy of the excitation photon corresponds exactly to the quantity of energy necessary for raising the molecule to a given excited state. The source used is a laser emitting excitation photons in the visible range (between approximately 400 nm and 650 nm). In multiphoton microscopy, in other words non-linear fluorescence microscopy, and more particularly in two-photon microscopy, the quantity of energy required for the transition is provided, not by an excitation photon, but by two photons (or more in multiphoton imaging), each having an energy two times (or more) less than that of the conventional excitation photon. In fact, excitation photons are used in the near infrared (700 nm to 1000 nm) which are less energetic than the excitation photons in the conventional case. However, the fluorescent photon emitted by the molecule is identical to that emitted in the conventional case. In two-photon (or multiphoton) microscopy the mechanisms involving two (or more) photons have an efficiency which is proportional to the square (or more) of the instantaneous intensity of the excitation source. A high excitation efficiency can only be obtained by means of significant spatial and time constraints. The spatial constraint involves an accurate focussing of the excitation beam in the tissue, or a high spatial density of the photons in the illumination focal volume. Two-photon microscopy therefore has a major advantage which is its natural confocality since all the fluorescence detected originates only from the elementary volume excited at depth. The fluorescence emitted is not an integral of the volume comprised between the surface of the sample and the elementary volume excited; this in particular makes it possible to limit any problem of photobleaching of the fluorophores situated between the surface and the focussing plane. The time constraint involves a laser source generating ultra short and very intense pulses, i.e. a high time density of the photons in the illumination focal volume. Moreover, as regards illumination standards, two-photon microscopy is appreciable since the near infrared produces less photons-matter interaction, and a pulsed excitation with ultra short pulses considerably reduces the problems associated with phototoxicity. A drawback in fibre-type linear fluorescence microscopy resides in the fact that the penetration distance of the excitation beam into the sample is low, less than about a hundred micrometers. An increase in the power of these beams with a view to improving the penetration distance would certainly cause physiological damage, in particular due to the fact that generally the operation is carried out virtually continuous. Thus, organs lying at greater depth in the sample are not accessible. Two-photon microscopy makes it possible to overcome this drawback since it allows a theoretical penetration distance greater than 400 micrometers. In fact, the excitation photons, situated in the near infrared, are individually less energetic, poorly absorbed by the tissue which is essentially composed of water and therefore not very destructive compared with those used in linear fluorescence. The two-photon microscopy systems commonly used are table microscopes such as for example an upright microscope constituted by a raised optical carriage holding scanning and detection devices for constituting images. Such an acquisition system cannot be applied in particular to in vivo and in situ endoscopy. In fact, a table microscope is often bulky, uses standard lenses for the illumination and collection of the signal, requires that the animal be held under the lens, and requires long integration times (which means great sensitivity). Document GB2338568, Optiscan, “Two-photon endoscope or microscope method and apparatus” proposing a two-photon microscopy device, is known. This device uses a single optical fibre for conveying the pulses from the laser to the sample. In order to limit the phenomenon of linear and non linear dispersion of the pulses in the optical fibre, compensation means, in particular by prisms, are disclosed. The document U.S. Pat. No. 6,369,928, Optical Biopsy Technologies, describes a two-photon fluorescence scanning microscope for the acquisition of a microscopic image. This microscope comprises at least two optical fibres: each used as a source and also as a receiver of the fluorescence beam obtained by illumination of the other optical fibre. In particular, two characteristics of this system constitute constraints for miniaturization: 1) the scanning takes place on the distal side of the fibres, i.e. between the fibres and the sample; 2) the two incident beams maintain an angle of incidence in the sample, therefore a distance between the fibres. The purpose of the present invention is a novel miniaturized multiphoton microscopy system for an application in endoscopy in particular. Another purpose of the invention is a novel multiphoton microscopy system allowing the acquisition of an image in the sample at depth. At least one of the above-mentioned aims is obtained with a system for fibre-type multiphoton imaging of a sample, in particular for use in endoscopy or in fluorescence microscopy, this system comprising a pulsed laser for generating a multiphoton excitation laser beam. According to the invention, this system also comprises: an image guide constituted by a plurality of optical fibres and allowing the sample to be illuminated by a point-by-point scanning, in particular in a subsurface plane, compensation means for compensating for the dispersion effects of the excitation pulse in the image guide, these means being arranged between the pulsed laser and the image guide, scanning means for directing in succession the excitation laser beam into a fibre of the image guide. Preferably, in order to obtain significant depths, the system comprises an optical head to focus the excitation laser beam leaving the image guide into the sample. Preferably, the dimensions of the optical head and the image guide are such that they can easily slide into an operating channel. The system according to the invention allows the production of an offset in vivo, in situ, fluorescence image with a microscopic resolution. The image guide or “fiber bundle”, has a flexibility and a size which allow an application in endoscopy in particular by insertion into an operating channel. According to an advantageous characteristic of the invention, different compensation means can be envisaged, such as for example: a dispersive line containing at least two prisms; a dispersive line containing at least two diffraction gratings; a dispersive line containing means for modulating the phase and the spectral amplitude of the pulse; another image guide, called a second image guide, which is associated with a dispersive line containing at least two prisms or two diffraction gratings, so that the phase shifts introduced by this second image guide and the principal image guide are compensated for by the phase shift introduced by the dispersive line; a single optical fibre making it possible to optimize the response of the image guide, this single optical fibre being associated with a dispersive line containing at least two prisms or two diffraction gratings, so that the phase shifts introduced by this single optical fibre and the image guide are compensated for by the phase shift introduced by the dispersive line; or an optical fibre with abnormal dispersion at the laser wavelength. These compensation devices can also serve to compensate for dispersions introduced by any other element (optical head, lenses, mirrors, etc.) of the system. According to the invention, injection means are provided which are arranged on the proximal side of the image guide and making it possible to focus in succession the excitation laser beam into a given fibre of the image guide. First detection means for detecting a fluorescence signal originating from the sample are also provided. According to an advantageous characteristic of the invention, second detection means are also provided for detecting a second harmonic generation (SHG) signal originating from the sample. The complementarity between the properties of two-photon fluorescence and second harmonic generation makes it possible to access in particular local information about the molecular orders (symmetry, organization) and their interaction with their close environment. In order for the signals originating from the sample to reach these detection means, the system also comprises a dichroic filter which is able to allow only the fluorescence and second harmonic signals to pass through to the detectors. In particular, this dichroic filter is arranged between the scanning means and the image guide. Thus, the signals originating from the sample do not pass through the scanning means again. In the same way, it is not necessary to arrange a filtering hole in front of each detector. In this case one takes advantage of the fact that multiphoton microscopy has a natural confocality. The system according to the invention can also comprise a tunable dichroic filter which is able to separate the fluorescence signal from the second harmonic generation signal originating from the sample. Generally, the system comprises a processing unit which manages all of the elements, in particular the synchronization between the excitation means and the detection means. This unit carries out an image processing which can for example be based on that described in the document WO 2004/008952, Mauna Kea Technologies. For example it is possible to control a slow scanning of the sample so as to produce high quality images integrating a large number of photons over a long time. However, according to an advantageous embodiment of the invention, the scanning means scan the sample at a speed corresponding to the acquisition of a number of images per second sufficient for a use in real time. In a complementary manner, the detection means detect the fluorescence signal at a detection frequency corresponding to a minimum sampling frequency of the fibres one-by-one. More precisely, respecting the sampling of the fibres (according to the Shannon criterion) makes it possible to obtain a point-by-point image which corresponds well to each fibre. This makes it possible to not lose information by sampling all of the fibres one-by-one while respecting a mean minimum number of images per second, namely in practice at least 12 images per second for a maximum mode of 896×640 pixels. The choice of the detection frequency (bandwidth of the detector) as a function of this minimum sampling then makes it possible for each fibre to detect the largest possible number of fluorescence photons. Thus, according to a possible embodiment, using an image guide with approximately 30,000 flexible optical fibres, the sampling frequency and the bandwidth of the detection system (an avalanche photodiode or equivalent) are set to approximately 1.5 MHz, corresponding approximately to 12 pixels per fibre, then making it possible to obtain at least the 12 images/s in maximum mode 896×640 pixels. In practice, the deflection of the beam is adjusted by determining a rapid scanning frequency of a “line” resonant mirror and a slow scanning frequency of a “frame” galvanometric mirror. This allows an appropriate rapid scanning of the fibres in order to obtain an image in real time. The galvanometric mirrors can also have scanning frequencies suitable for a slow acquisition; in this case, the photodetector has a bandwidth suited to the slow acquisition speed. According to the invention, the scanning means can also scan the sample on a line in a subsurface plane so as to produce a linescanning. It is thus possible to measure the intensities or speeds of certain elements observed. The pulsed laser can be a femtosecond laser or a picosecond laser. The choice of a type of laser depends on the type (in terms of sensitivity in particular) of fluorescence targeted. For example, a picosecond laser has longer pulses and is therefore a laser which is a priori useful for high yield fluorophores. In fact, it is possible to use for example pulse widths comprised between 10 picoseconds and 10 femtoseconds. Moreover, according to the invention, the pulsed laser and the compensation means are tunable as regards wavelength. Thus a laser can be used the wavelength of which can vary between 700 nm and 1000 nm, preferably between 800 nm and 870 nm, which already allows a large number of fluorophores to be detected. At each wavelength of the laser, the compensation is adjusted. According to another feature of the invention, a method of fibre-type multiphoton imaging of a sample is proposed, in particular for use in endoscopy or in fluorescence microscopy, in which a multiphoton excitation laser beam is generated. According to the invention: the excitation laser beam is passed through compensation means making it possible to compensate for dispersion effects, the sample is scanned by directing in succession the excitation laser beam into a fibre of an image guide constituted by a plurality of optical fibres, the sample is illuminated by a point-by-point scanning from the excitation laser beam originating from the image guide, and a fluorescence signal emitted by the sample is detected. Advantageously, the entire fluorescence signal leaving the image guide is detected. Thus there is no de-scanning and the fluorescence signal is not filtered before detection by a photodetector. In a variant of the invention without an optical head, the image guide is constituted by several thousands of optical fibres the distal ends of which are intended to be placed bare directly in contact with the surface of the sample, each fibre being able to produce a divergent beam capable of exciting a micro-volume from the sample situated from the surface to a maximum depth depending in particular on the core diameter of the optical fibres. Over the first ten micrometers for example, the beam also has a diameter which is more or less identical to the diameter of the core of the optical fibre. For an image guide called probe “S”, the diameter of the optical fibres used is sufficiently small, for example 1 micrometer, for the multiphoton phenomenon to appear. This variant therefore differs from the variant with an optical head in that it does not provide the scanning of a signal which is focussed at the output of each fibre but the scanning of a divergent signal at the output of each fibre. The non focussing of the signal at the fibre output makes it possible to obtain images of a volume situated just under the surface of the tissue which can be exploited and are interesting from a medical point of view in particular. These images are not “confocal” since they do not originate from a subsurface planigraphic plane scanned point-by-point, but are images that may however be qualified as “highly resolved” since they are produced by the scanning in succession micro-volumes situated directly under the surface. One of the advantages of such a variant resides in the fact that for an endoscopic application, the diameter of the endoscopic probe can be very small depending solely on the diameter of the image guide and therefore on the number of its optical fibres. This makes it possible to envisage fields of application, such as for example the field of neurology, where the size of the endoscopic probe is a critical factor in overcoming inherent problems in the miniaturization of the focussing optical head. According to another advantageous characteristic of the invention, the system comprises filtering and detection means for respectively separating and detecting several fluorescence signals emitted by several fluorophores which are present in the sample and which are excited by the excitation laser beam. In fact, ideally a pulsed laser beam is generated the wavelength of which has been determined in order to excite a given fluorophore. However, other fluorophores can be sensitive to this wavelength, and then also emit fluorescence signals. It is also possible to deliberately introduce fluorophores and to use a wavelength of the laser beam capable of exciting these fluorophores simultaneously. Preferably, the fluorescence signals have wavelengths which are sufficiently distanced from one another that they can be separated by filtering. The system comprises processing means for producing a final image comprising coloured zones as a function of the fluorescence signals of the fluorophores. The present invention is therefore able to carry out multimarking by detection path. The filtering means can comprise a tunable band-pass filter which allows the different fluorescence signals to pass sequentially towards a common detector. The filtering means can also comprise a separator which is able to send, as a function of the wavelength, each fluorescence signal towards a different detector. According to yet another advantageous characteristic of the invention, the system also comprises a spectrometer which is able to produce a spectrum using a part of the signal originating from the sample. This spectrometer can be combined with a shutter directing a part of the signal originating from the sample towards the spectrometer at predetermined times corresponding to the times when the excitation signal scans an area of interest. Alternatively, it is also possible to control the pulsed laser in such a way that only the areas of interest are illuminated. The spectrum produced is then processed within the processing means. The part of the signal deflected towards the spectrometer is preferably less than 10% of the useful signal. In FIG. 1 a sample 10 is seen which can be a biological tissue or a cell culture. Generally, the fluorescence observed can originate from an exogeneous compound (typically an administered marker) or an endogenous compound which is either produced by cells (transgenic type marker) of a biological tissue, or naturally present in the cells (autofluorescence). Non-linear two-photon absorption requires a very high energy density to be conveyed into a reduced volume. For this purpose, a pulsed laser 2 is used in femtosecond regime with pulse widths of 100 fs. It is a Titanium-Sapphire laser pumped by a 1 to 532 nm solid laser. The repetition frequency of the laser 2 is approximately 80 MHz with an average power of the order of 1 Watt. The wavelength of the excitation beam leaving the laser 2 can be adjusted between 700 and 1000 nm, near infrared, preferably between 800 nm and 870 nm. In fact, the performance of the system depends essentially on the characteristics of the source: peak power and pulse width desired in particular at the output of the image guide. At the output of the laser 2 a Faraday isolator 21 is provided in order to prevent the stray reflections from returning to the laser cavity 2. The isolator 21 is optionally followed, when necessary, by a device 3 for shaping and injection of the excitation laser beam. This device 3 is constituted by an afocal optical magnification system different from 1, comprising lenses which allow modification of the diameter of the laser beam. The magnification is calculated such that the diameter of the laser beam is suited to injection means provided for directing this laser beam into compensation means 4. These compensation means are adjusted as regards position and angle as a function of the wavelength of the excitation beam. Generally, the function of the compensation means 4 is to pre-compensate the broadening of the excitation pulses in the optical fibres of the image guide 8. This temporal broadening is due to the linear chromatic dispersion and to the non-linear effects of the optical fibres (self-phase modulation causing a spectral broadening). The system makes it possible to obtain a pulse width at the output of the image guide 8 of a few hundreds of femtoseconds with an average power of a few tens of milliwatts. Scanning means 5 then recover the thus pre-compensated excitation pulses. According to the example chosen and represented in FIG. 1, these means include a resonant mirror M1 at 4 KHz serving to deflect the beam horizontally and therefore to produce the lines of the image, a galvanometric mirror M2 at 15 Hz, generally between 10 and 40 Hz, serving to deflect the beam vertically and therefore to produce the frame of the image; and two afocal unit-magnification systems, AF1 situated between the two mirrors and AF2 situated after the mirror M2, these afocal systems being used in order to conjugate the planes of rotation of the two mirrors M1 and M2 with the plane of injection into one of the fibres. According to the invention, the scanning speed is determined in order to allow an observation of the tissues in vivo in situ. For this purpose the scanning must be sufficiently rapid so that there are at least 12 images/s displayed on the screen for a display mode of 896×640 pixels corresponding to the slowest mode. For display modes having less pixels, the number of images acquired per second is thus still greater than 12 images/s. In a variant, the scanning means can comprise in particular a rotary mirror, integrated components of the MEM type (X and Y scanning mirrors), or an acousto-optic system. The mirrors M1 and M2 can also be two galvanometric mirrors the scanning frequencies of which are such that less than ten images per second are used, for example 1 to 3 images per second. In this case, the bandwidth of the associated photodetector is adjusted to the speed of acquisition imposed by the galvanometric mirrors. The integration time can be long so as to increase the sensitivity of the system. The excitation beam deflected at the output of the scanning means 5 is directed towards the optical means 7 in order to be injected into one of the fibres of the image guide 8. The dichroic filter 6 arranged between the scanning means 5 and the injection means 7 remains transparent to the excitation beam. The injection means 7 are constituted here by two optical units E1 and E2. The first optical unit E1 allows partial correction of the optical aberrations at the edge of the field of the scanning means 5, the injection being thus optimized over the entire optical field, at the centre and at the edge. The second optical unit E2 is intended to carry out the injection itself. Its focal length and its numerical aperture have been chosen in order to optimize the rate of injection into the optical fibres of the guide 8. According to an embodiment which makes it possible to obtain the criterion of achromaticity, the first unit E1 is constituted by a doublet of lenses, and the second unit E2 by two doublets of lenses followed by a lens situated close to the image guide. In a variant, these injection optics could be constituted by any other type of standard optics, such as for example two triplets, or by lenses with a graded index (with a correction of the chromatism by diffractive optical elements) or by a microscope lens. The image guide 8 is constituted by a very large number of flexible optical fibres, for example 30,000 fibres made of germanium-doped silica, each single-mode, of 2 μm diameter, with a numerical aperture of 0.23 and spaced at intervals of 3.8 μm relative to its neighbour. The cross section of the guide is of the order of 0.8 mm. In practice, it is possible to use either all of the fibres of the image guide, or a sub-unit chosen from these fibres, for example centred. In a variant, the image guide can comprise multimode fibres of 1.9 μm diameter, with a numerical aperture of 0.42 and spaced at 3.3 μm for a cross section of the guide of the order of 0.65 mm. The distal end of the optical fibre is connected to an optical head 9 which focuses the excitation laser beam into the sample 10 in an elementary volume. This elementary volume or point is situated at a given depth located at a few hundreds of μm from the surface of the sample which the optical head 9 is intended to be placed in contact with. This depth can be for example 200 μm. The optical head 9 therefore makes it possible to focus the flux leaving the image guide into the sample, but also to collect the flux of fluorescence returning from the sample. The optical head 9 has a magnification of 2.4 and a numerical aperture on the sample of 0.5. Since two-photon microscopy naturally has a confocal character, it is not necessary to filter the fluorescence signal collected by the photodetector: all the different fluxes of this signal are sent towards the photodetector, which improves the sensitivity of the system. With these magnification and numerical aperture values, the axial resolution is of the order of 15 μm and the lateral resolution of the order of 2 μm. The numerical aperture is also chosen in such a way as to optimize the number of photons recovered which must be as large as possible. The optical head can be constituted by standard optics (doublet, triplet, aspheric) and/or by lenses with a graded index (GRIN). During operation, the optical head is in particular intended to be placed in contact with the sample 10. In an optimal manner, the optical head comprises refractive optics with a magnification of 4 and a numerical aperture of 1. This optical head is of the water-immersion and non-achromatic type. The fluorescence signal therefore passes through the image guide 8 and the injection means 7 then reflects off the dichroic filter 6 which directs this fluorescence signal towards a fluorescence detector 12 via a coloured rejection filter 11 and a focussing lens E3. The dichroic filter 6 has a transmission efficiency of 98 to 99% at the excitation wavelength and therefore reflects the other wavelengths. The fluorescence signal, originating from the sample via the optical head and the image guide, is thus sent towards the detection path. The rejection filter 11 makes it possible to totally eliminate the 1 to 2% of stray reflections at the excitation wavelength and which still pass towards the detection path. The detector 12 has a maximum sensitivity at the fluorescence wavelength studied. It is possible for example to use an avalanche photodiode (APD) or a photo multiplier. Moreover, according to the invention, the bandwidth is chosen in order to optimize the integration time of the fluorescence signal. It is 1.5 MHz in real time, which corresponds to the minimum sampling frequency of the image guide with an optimized integration time on each pixel. The system according to the present invention is in particular remarkable by the fact that it makes it possible to combine second harmonic generation microscopy with multiphoton microscopy. It involves detecting the second harmonic generation signal emitted at the same time as the fluorescence signal by the sample. For this purpose, a tunable dichroic filter 13 or any other device is provided placed between the dichroic filter 6 and the rejection filter 11, and making it possible to separate the second harmonic generation signal from the fluorescence signal. A detector SHG 14 receives this second harmonic generation signal. The electronic and computational means 16 (such as a micro-computer) for control, analysis and digital processing of the detected signal and for viewing include the following boards: a synchronization board 17, the functions of which are; to control in a synchronized manner the scanning, i.e. the movement of the line M1 and frame M2 mirrors; to control in a synchronized manner with the fluorescence images, the analysis of the data originating from the SHG detector 14; to know at all times the position of the laser spot thus scanned; to manage all the other boards by means of a microcontroller itself being able to be controlled; and to control the pre-compensation means so as to manage the wavelength tunability of the system; a detector board 15 which comprises for each detection path an analogue circuit which in particular produces an impedance match, an amplifier, an analogue-to-digital converter then a programmable logic component (for example an FPGA circuit) which shapes the signal. The micro-computer 16 also comprises a digital acquisition board (not represented) which makes it possible to process a digital data flow at variable frequency and to display it on a screen using a graphics board (not represented). By way of a non-limitative example the image processing used in the present invention can be a simple adaptation of the image processing as described in particular in the document WO 2004/008952 and/or the document WO 2004/010377. As regards the case of an image guide without an optical head, the operation of the apparatus is the same as that described previously with the exception of the following: at the output of the guide, the divergent light emerging from the injected fibre is diffused in the sample and the fluorescence signal is collected in a micro-volume situated between the surface and a depth of a few μm (according to the core diameter of the fibres and their NA). Thanks to the scanning, the sample is illuminated micro-volume by micro-volume. At each moment, the micro-volume excited in the tissue then emits a fluorescence signal which has the characteristic of being shifted towards smaller wavelengths. This fluorescence signal is captured by the image guide, then follows the reverse path of the excitation beam as far as the dichroic filter 6 which will transmit the fluorescence signal towards the detection path. The signals detected, one after the other, are in particular processed in real time thanks to the same image processing as that described above with reference to FIG. 1 in order to allow the reconstruction of an image in real time viewed on the screen. FIGS. 2 to 14 illustrate a few examples of pre-compensation devices. The pre-compensation consists in preparing the ultra-short laser pulse by providing it with the spectral width and the phase modulation which will lead to its optimum temporal compression at the output of the image guide 8. The technique used aims to compensate for the group velocity dispersion of the whole of the system and to also compensate for the inevitable non-linear effects which the light pulse undergoes during its propagation in the image guide 8. The pre-compensation principle envisaged conforms with that published by S. W. Clark, F. O. Ildlay, and F. W. Wise, “Fiber delivery of femtosecond pulses from a Ti:sapphire laser”, Optics Letters Vol. 26, NO. 17, Sep. 1, 2001. Typically the pre-compensation comprises two parts: a section of optical fibre followed by a dispersive line with diffraction gratings. the section of optical fibre constituted by a single optical fibre or an image guide: the single optical fibre used is single-mode for the laser wavelength. The length of the section is close to that of the multi-core image guide 8. This length is optimized as a function of the other parameters of the system such as for example the length of the image guide,the wavelength of the laser beam, the power and the width of the pulses at the input and at the output of the image guide, etc. The mode diameter of this fibre is greater than the mode diameter of the cores of the image guide in order to balance the non-linear effects encountered in the two parts of the pre-compensation. Thus an optical fibre with a large mode area (LMA) or belonging to the new generation of optical fibres with a structured air-silica cladding is used. This section of single-mode fibre is characterized by a certain rate of normal group velocity dispersion (principally of the order 2 and 3) and by the appearance of non-linear effects of spectral broadening (especially over the first millimeters of the section) which are controlled by the mode diameter. This section, constituted by a single optical fibre or a second image guide, provides the excitation laser pulses with a phase shift. This phase shift serves to pre-compensate the dispersion in the principal image guide 8, but it can also serve to compensate any other dispersion introduced by the rest of the system such as the optical head for example. the dispersive line with diffraction gratings: this part comprises two diffraction gratings, operating in reflection which are planar and have great efficiency, associated with a reflecting plane mirror which is totally reflective. The diffraction gratings face each other and are arranged parallel a few centimeters from one another. The laser beam successively strikes these two gratings with oblique incidence before reaching the plane mirror which reflects the light back approximately onto itself. The laser beam thus strikes the gratings four times before reemerging from the dispersive line. The aim of this dispersive line is to introduce a high rate of abnormal group velocity dispersion into the system. This equates to delaying the most red photons of the laser spectrum which corresponds to the reverse behaviour to that which occurs both in the section of single-mode fibre mentioned above but also in the image guide. This device known by the name “Treacy line” is widely used in amplification systems with frequency drift of femtosecond laser chains where it then plays the role of pulse compressor at the end of the chain. The dispersive line is characterized by a certain rate of abnormal group velocity dispersion (principally of the order 2 and 3) depending on the pitch of the gratings, the inter-grating distance and the angle of incidence on these gratings. FIGS. 2 to 14 are simplified diagrams of the system according to the invention in which the pre-compensation device 4 is shown in detail. For the sake of clarity, the device 3 does not appear. The same elements of FIG. 1 are shown again in FIGS. 2 to 14 with the same references. The laser 2, the scanning system 5, the dichroic filter 6 which transmits the excitation beam towards the sample and which returns the fluorescence signal to the detector 12 are seen. FIGS. 2 to 7 illustrate basic compensation devices not comprising a first section. The beam leaving the Faraday isolator 21 is directed directly towards a dispersive line with diffraction gratings or prisms. In FIG. 2, this line comprises two diffraction gratings 23, 24 and a mirror 25. The course of the laser beam in the dispersive line is as follows: reflection off the first diffraction grating 23 towards the second diffraction grating 24, reflection off the second diffraction grating 24 towards the mirror 25 where it is totally reflected towards the second grating 24 then the first grating 23. The pulse 19 leaving the dispersive line is longer than that 18 leaving the laser 2. The beam originating from the diffraction grating 23 then reflects off the mirror 22 in the direction of the scanning system 5 then towards the image guide 8. FIGS. 2 to 14 are top views; in particular in FIGS. 2, 3, 6-9, the laser beam leaving the laser 2 towards the grating 23 passes above the mirror 22 without passing through it. By contrast, the laser beam from the grating 23 towards the scanning system is reflected off the mirror 22. This mirror 22 can be replaced by a separator which allows the excitation beam of the laser to pass towards the dispersive line and reflects the excitation beam of the dispersive line towards the scanning system, the two beams then being aligned. But, in this last case, the losses caused by the separators are significant (only 25% of the incident signal is used). The linear dispersion and the non-linear effects in the image guide 8 modify the temporal and spectral profile of the excitation pulse which returns to being approximately identical to the profile 18 of the pulse leaving the laser 2. The dispersive line provides a phase shift of −Δφ so as to approximately compensate for the phase shift +Δφ provided by the image guide 8. In FIG. 3, the two diffraction gratings are replaced by two prisms 26 and 27, the course of the excitation laser beam is identical. In FIGS. 4 and 5, the dispersive line and the mirror 22 are replaced by respectively four diffraction gratings for FIG. 4 and four prisms for FIG. 5. The excitation laser beam is reflected successively off the four diffraction gratings 28, 29, 30 and 31 (prisms 32, 33, 34 and 35). FIGS. 6 and 7 correspond to FIGS. 2 and 3 in which a phase and amplitude mask 36 has been introduced upstream of the mirror 25. This mask makes it possible to improve the pre-compensation performance by precisely adjusting the shape of the pulse relative to the dispersion of the image guide. It can be constituted by the assembly of different glass slides acting on the spectral phase and by a filter which can be varied in a transverse manner and acting on the spectral amplitude. FIGS. 8 to 11 correspond respectively to FIGS. 2 to 5 but with in addition a section 37 arranged either upstream of the mirror 22 (FIGS. 2 and 3) or upstream of the four diffraction gratings (FIG. 4) or of the four prisms (FIG. 5). This section can be constituted by a single optical fibre or an image guide wherein the characteristics of each optical fibre constituting it are approximately identical to those of the principal image guide. This single optical fibre or second image guide provides a positive phase shift +Δφ1. The image guide 8 also provides a positive phase shift +Δφ2. Thus, the dispersive line (FIGS. 8 to 11) provides a negative phase shift of Δφ1+Δφ2). As seen in FIG. 12, the pre-compensation stage can also be obtained using a single section 38 of optical fibre with abnormal dispersion at the laser wavelength. This specific fibre has a nil dispersion at shorter wavelengths than that of the laser wavelength. This is obtained by using a section of new-generation fibre with an optimized length having one of the following structures:—concentric dual-core fibres, fibre with a structured air-silica cladding, photon fibre with a hollow core and with a structured air-silica cladding, photon fibre with a hollow core and with a Bragg cladding. This section of pre-compensating fibre is also characterized by a mode diameter which is optimized in order to take into account the non-linear effects associated with the propagation in this waveguide. In a variant of the above, the pre-compensation can be integrated into the scanning system as can be seen in FIGS. 13 and 14. In fact, any one of the compensation devices described in FIGS. 2 to 11 can be inserted on an optical path in the scanning system 5. This invention therefore relates to a microscope based on an image guide the advantages of which are the compactness and the flexibility, which allows a use in endoscopy by insertion of said image guide into the tissue. Finally, the combination of multiphoton microscopy with a fibre-type microscopy by means of an image guide allows the acquisition of a fluorescence image of an element situated at depth in the sample observed. In practice, the system can be adaptable, i.e. designed without the laser source and thus being able to interface with laser sources already existing in laboratories. This invention can have numerous applications, in particular where non-invasive or slightly invasive methods are required. These applications are for example urethral endoscopy when an optical probe with a diameter less than 1 mm is inserted into a bladder for example; colonoscopy in small animals; viewing of the cornea and the retina; viewing of the muscle fibres and the nerves; microcirculation of leukocytes and blood flow; vascular and renal architecture; the membranes of hepatic cells; and in situ neurobiology for viewing the deep cerebral structures of live small animals for example or potential clinical applications for humans. Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without exceeding the scope of the invention.
	summary
	claims	1. A nuclear reactor, comprising a nuclear fuel reactor core inside a pressure vessel; the pressure vessel having a shroud surrounding said reactor core and a downcomer of an outer region of said shroud; and a containment vessel surrounding said pressure vessel and having a pressure suppression pool, said nuclear reactor being one of a light water reactor and a heavy water reactor, wherein said pressure vessel contains the reactor core and a first heat exchanger for generating secondary steam, an inside of said containment vessel except a region installing said pressure vessel being vertically partitioned into three compartments, the pressure suppression pool having cooling water being formed in the upper compartment, a drywell for placing a feed water pipe of secondary cooling water, a main steam pipe of secondary steam being formed in the middle compartment, a wetwell of pressure suppression space being formed in the lower compartment, said drywell communicating with said pressure suppression pool through a plurality of vent pipes, an upper space of said pressure suppression pool communicating with said wetwell through a plurality of communicating pipes, a heat pipe containment vessel cooling system having a condensing heat exchanger arranged in a space above said pressure suppression pool and a first heat dissipater arranged outside said containment vessel in a position at a level higher than a level of said condensing heat exchanger, an interior of said condensing heat exchanger being filled with a heat medium, a gravitational water injection system being constructed as a plurality of gravitationally flow-down water injection pipes having an isolation valve between said pressure suppression pool and said pressure vessel, a pressure vessel bottom water flooding system being constructed as a plurality of pressure vessel bottom water flooding pipes between said pressure suppression pool and a lower portion of said drywell, an upper end of said gravitationally flow-down water injection pipe being arranged at a level higher than an upper end of said bottom, an upper end of said pressure vessel bottom water flooding pipe being arranged at a level higher than an upper end of said bottom, a lower portion of said pressure vessel bottom water flooding pipe being branched to a plurality of systems, at least one of said plurality of systems being connected to a fuse valve arranged in contact with an outer surface of a bottom portion of said pressure vessel, at least one other of said plurality of systems being opened to a lower space of said drywell through an isolation valve, a reactor core isolation cooling system being constructed as a cooling vessel and a second heat dissipater, said cooling vessel being filled with a coolant and containing a second heat exchanger in said coolant, said cooling vessel being arranged at a level higher than said reactor core inside said containment vessel, said second heat exchanger being connected to said pressure vessel using an inflow pipe and a water injection pipe, a lower end of said inflow pipe and a lower end of said water injection pipe being opened to said pressure vessel at a level lower than a water surface level in said pressure vessel during operation of said nuclear reactor, said second heat dissipater being arranged outside said containment vessel at a level higher than said cooling vessel, an upper end of said cooling vessel communicating with a cooler through a gas inflow pipe, said cooler communicating with said cooling vessel through a liquid returning pipe. 2. A nuclear reactor according to claim 1 , wherein claim 1 at least one heat exchanger system arranged inside said pressure vessel, said at least one heat exchanger system being heated by primary cooling water recirculating through said reactor core to generate steam to be supplied to a turbine or a heat supply system, a secondary steam passage of said at least one heat exchanger system being branched to communicate with a portion under water of a pressure suppression pool arranged inside said containment vessel through an isolation valve, a secondary cooling water passage of said at least one heat exchanger system being branched to communicate with a portion under the water of said pressure suppression pool inside said containment vessel through an isolation valve, decay heat generated by said reactor core during reactor core isolation being heat exchanged by said at least one heat exchanger system to condense steam generated by the decay heat under the water of said pressure suppression pool and at the same time to supply the water of said pressure suppression pool to said at least one heat exchanger system. 3. A nuclear reactor according to claim 1 , wherein claim 1 at least one heat exchanger system arranged inside said pressure vessel, said at least one heat exchanger system being heated by primary cooling water recirculating through said reactor core to generate steam to be supplied to a turbine or a heat supply system, a third heat exchanger being arranged under water of a pressure suppression pool inside said containment vessel, a secondary steam passage of said at least one heat exchanger system in said pressure vessel being branched to communicate with said third heat exchanger under the water of a pressure suppression pool through an isolation valve, a secondary cooling water passage of said at least one heat exchanger system in said pressure vessel being branched to communicate with said third heat exchanger under the water of the pressure suppression pool through an isolation valve, decay heat generated by said reactor core during reactor core isolation being heat exchanged by said at least one heat exchanger system in said pressure vessel to condense steam generated by the decay heat using said third heat exchanger under the water of said pressure suppression pool and at the same time to supply the condensed water to said at least one heat exchanger system in said pressure vessel. 4. A nuclear reactor, comprising: a pressure vessel having a shroud surrounding a nuclear fuel reactor core inside the pressure vessel and a downcomer of an outer region of said shroud; and a containment vessel surrounding said pressure vessel and having a pressure suppression pool, said nuclear reactor being a light water reactor or a heavy water reactor; a heat pipe containment vessel cooling system having a condensing heat exchanger arranged in a space above said pressure suppression pool, wherein an inside of said condensing heat exchanger is filled with a heat medium; and a heat dissipater arranged outside said containment vessel in a position at a level higher than a level of said condensing heat exchanger, said heat dissipater communicating with said condensing heat exchanger through a gas inflow pipe and a liquid returning pipe to form a closed loop for the heat medium. 5. A nuclear reactor, comprising: a nuclear fuel reactor core inside a pressure vessel, the pressure vessel having a shroud surrounding said reactor core and a downcomer of an outer region of said shroud; a containment vessel surrounding said pressure vessel and having a pressure suppression pool, said nuclear reactor being a light water reactor or a heavy water reactor, wherein an inside of said containment vessel except a region installing said pressure vessel is vertically partitioned into three compartments, a pressure suppression pool having cooling water being formed in the upper compartment, a drywell for placing a feed water pipe of secondary cooling water and a main steam pipe of secondary steam being formed in the middle compartment, a wetwell of a pressure suppression space being formed in the lower compartment, said drywell communicating with said pressure suppression pool through a plurality of vent pipes, an upper space of said pressure suppression pool communicating with said wetwell through a plurality of communicating pipes. 6. A nuclear reactor, comprising: a nuclear fuel reactor core inside a pressure vessel, the pressure vessel having a shroud surrounding said reactor core and a downcomer of an outer region of said shroud; a containment vessel surrounding said pressure vessel and having a pressure suppression pool, said nuclear reactor being one of a light water reactor and a heavy water reactor, wherein a pressure vessel bottom water flooding system is comprised of a pressure vessel bottom water flood pipe, a lower portion of the pressure vessel bottom water flooding pipe is branched to a plurality of systems, and at least one of said plurality of systems is connected to a fuse valve arranged in contact with an outer surface of a bottom portion of said pressure vessel, and at least the other one of said plurality of systems is opened to a lower space of said drywell through an isolation valve.
	summary
	summary
040617009	abstract	A process for fabricating a body of a nuclear fuel material has the steps of admixing the nuclear fuel material in powder form with a binder of a compound or its hydration products containing ammonium cations and anions selected from the group consisting of carbonate anions, bicarbonate anions, carbamate anions and mixtures of such anions, forming the resulting mixture into a green body such as by die pressing, heating the green body to decompose substantially all of the binder into gases, further heating the body to produce a sintered body, and cooling the sintered body in a controlled atmosphere. Preferred binders used in the practice of this invention include ammonium bicarbonate, ammonium carbonate, ammonium bicarbonate carbamate, ammonium sesquicarbonate, ammonium carbamate and mixtures thereof. This invention includes a composition of matter in the form of a compacted structure suitable for sintering comprising a mixture of a nuclear fuel material and a binder of a compound or its hydration products containing ammonium cations and anions selected from the group consisting of carbonate anions, bicarbonate anions, carbamate anions and mixtures of such anions.
044410255	claims	1. A protective apparel device comprising a main body portion having support straps in the shoulder region thereof, and means to selectively distribute the weight of said device by transfering its weight selectively between the lower body region and the shoulder region of the user, said means comprising flaps integral with said main body portion for securing said apparel to the body of the user, said flaps being characterized by a main body portion having shoulder support straps, securing flaps integral with said main body which cross in the region of the lower back of the user when in normal use with the outermost ends thereof removeably affixed to the front of said main body in a generally downward orientation, and means for so removeably affixing said flaps to said main body in selectively variable positions of extension about the body of the user to increase the degree of extension of said flaps about the body of the user to cause the weight of said apron to be increasingly transferred from the shoulders of the user to the lower body region. 2. The device described in claim 1 wherein said fastening means is a Velcro fastener. 3. The device described in either of claims 1 or 2 made from material which is protective against x-ray radiation. 4. The device described in either of claims 1 or 2 comprising an apron. 5. The device described in either of claims 1 or 2 comprising an apron made from material which is protective against x-ray radiation. 6. A protective apron comprising
041742931	description	DESCRIPTION OF THE PREFERRED EMBODIMENT To carry out the process disclosed in this invention a molded seamless container 2 as shown in FIG. 1 hereof or a commercial steel drum 16, having a leak-proof plastic liner 18 as shown in FIG. 2 having funnels 10 connected to tubes 8 having holes 12 suspended in the container, is free flow filled with dry portland cement having a particle size ranging from 120 to 400 mesh. The dry powdered cement is densified in the container by mechanical agitation of the powder in the container by means such as vibrating the container, tamping the powder down, and the like, until the powdered cement in the container has a bulk density ranging from about 1.3 to about 1.8 grams per cubic centimeter. Care should be taken to avoid getting significant amounts of cement in the tubes and/or funnel and the level of the dry cement should be mainained below the wide lip of the funnel. The aqueous solution containing the radioactive wastes therein is then dispersed in situ within the densified cement by pouring it into the funnels 10 and allowing it to be carried by tubes 8 thru porous openings 12 throughout the body of the cement 14. The amount of aqueous solution that can be dispersed in the densified powdered portland cement ranges from about 15 weight percent to about 30 weight percent, based upon the weight of the powdered portland cement in the container. Thereafter the container is sealed off from the atmosphere and the water-cement mixture is left in a quiescent state and allowed to set and cure to form a free standing monolith using the aqueous solution containing the radioactive waste to provide the water of hydration to form a solid cement body. To seal the container a screw-type cap 4 with threads 6 as shown in FIG. 1 or a compression-type lid 20 as shown in FIG. 2 can be employed. This step of sealing the water-cement mixture during the curing step provides several benefits, first it prevents the release of tritium containing water during the curing step, secondly it allows the container to be placed in relatively low-cost storage facilities during curing, and thirdly it permits accurate quality control during processing since it prevents atmospheric humidity from having an effect during this stage of the processing. When curing of the water-cement mixture is completed, the containers are unsealed and a solution of monomer with polymerization catalyst dissolved therein is introduced upon the upper surface of the cured cement in an amount sufficient to provide both for complete impregnation of the cement by the monomer-catalyst solution and for a layer of the monomer-catalyst solution to be formed fully covering the upper surface of the cured concrete in the container. The container is again resealed in the preferred embodiment of our invention to prevent evaporation of the monomer and the container is then stored in a quiescent place until the monomer has polymerized into a solid polymer. Thereafter the container can be shipped to a permanent disposal area such as an underground storage dump. The layer of solid polymer on top of the cement provides a safety seal in the event of container seal leakage or accidental opening of the lid. Throughout the entire processing, care must be taken to ensure that the cement containing the radioactive wastes entrained therein is maintained at a temperature below 99.degree. C. and preferentially maintained at a temperature below 90.degree. C. This temperature limit is required to prevent the vaporization and escape of low-boiling point radioactive wastes such as water molecules containing tritium isotopes. The term mesh sizes as used in this invention refers to U.S. Standard sieve sizes and is well known to those skilled in the art. Since the curing of the cement accomplished by the cement particles being hydrated by the water molecules contained in the aqueous solution containing the radioactive wastes is an exothermic reaction, care must be taken to provide sufficient means for cooling if large blocks of cement are to be formed in the practice of our invention. The cooling can be accomplished by mechanical cooling such as maintaining the blocks in a cool temperature. Preferentially, we recommend that geometric-sized and shaped containers be employed that will prevent the material in the container from overheating when the containers containing such materials are kept at room temperature. Precaution must be taken to ensure that the radiation inherent in the aqueous solutions containing radioactive wastes does not in itself raise the temperature of the product both during and after processing. In general we have found that aqueous solutions having a heat production rate of one watt per liter can be easily handled by our process provided that the mass of concrete has at least one dimension of about one foot when processing is carried out with the exterior container being in an atmosphere having a temperature ranging from 10.degree. C. to 40.degree. C. In general, any liquid monomer having a viscosity such that it can completely penetrate the cement concrete matrix without the need for vacuum and/or pressure and which can be polymerized in situ by heat, chemicals or radiation is preferred although not essential to this process. Impregnation of the cured concrete at atmospheric pressure and at ambient temperature has been demonstrated using addition type vinyl homomonomers and comonomers (mixture of homomonomers) in varying proportions containing a chemical initiator with or without a promoter for the purpose of initiating the polymerization reaction. Some of the monomer systems which have been used successfully to demonstrate this process are: ______________________________________ Monomer.sup.(a) Initiator.sup.(c) Promoter ______________________________________ Styrene benzoyl peroxide heat methyl " " methacrylate 90% styrene- 10% TMPTMA.sup.(b) benzoyl peroxide dimethyl aniline 60% styrene- 40% acrylonitrile " heat vinyl ester methyl ethyl cobalt DOW470 ketone peroxide napthenate (MEKP) ______________________________________ .sup.(a) Comonomers can be used in varying proportions although those indicated above gave excellent results .sup.(b) trimethylolpropanetrimethyacrylate .sup.(c) any initiator capable of initiating free radical polymerization can be used. The impregnation of cement castings with solutions of monomers and catalysts is well known to those skilled in the art. The choice of monomer and polymerization catalyst and the amount thereof to be used in the practice of our invention will of course be dependent upon the porosity of the cured cement to be impregnated and the rate at which polymerization is desired. In general we favor the use of slow acting polymerization catalysts in the practice of our invention. However any polymerization catalyst can be successfully employed provided that the quantity employed does not cause the monomer to polymerize too rapidly or prevents complete impregnation of the cured cement in the container. A novel and beneficial use of our process is in the formation of radiation devices. When our process is utilized to make such devices, the porous tubes used to disperse the aqueous solution in situ within the powdered portland cement can act as reinforcing rods and the container can be shaped to optimize the desired radiation effects for the radiation process which the device is intended. Thus a tubular shaped radiation device can easily be produced using the process disclosed in this invention, i.e., a pipe section for the irradiation of liquids being passed therethrough can be prepared using this invention. In general there are five main types of portland cement useable in our invention, the compositions of which are given in the following chart: ______________________________________ COMPOUND COMPOSITION OF PORTLAND CEMENT Compound composition, percentage Free Ignition Type of cement 1 2 3 4 CaSO.sub.4 CaO MgO loss ______________________________________ Type I 49 25 12 8 2.9 0.8 2.4 1.2 Type II 46 29 6 12 2.8 0.6 3.0 1.0 Type III 56 15 12 8 3.9 1.3 2.6 1.9 Type IV 30 46 5 13 2.9 0.3 2.7 1.0 Type V 43 34 4 12 2.7 0.4 1.6 1.0 ______________________________________ 1--3CaO . SiO.sub.3 2--2CaO . SiO.sub.2 3--3CaO . Al.sub.2 O.sub.3 4--4CaO . Al.sub.2 O.sub.3 Fe.sub.2 O.sub.3 In the preferred embodiment of our invention we use type II portland cement. FIG. 3 (Page 49 of handbook) shows the heat of hydration given in calories per gram of cement for each of the five types of portland cement. From this, one skilled in the art can readily calculate both amounts and dimensions of the shape of bodies formable in the practise of our invention which are compatible with the thermodynamic requirements of this invention. A very significant advantage gained when our invention is employed and the cement is densified prior to the addition of the aqueous solution containing the radioactive waste material is a substantial reduction in the bulk volume of the end product which must be stored. Further, it greatly lessens the chances of channeling in the product which can produce localized radioactive hot spots in the final product which are very undesirable from both a thermodynamic and lixiviation standpoint. These and other advantages will be readily recognized by those skilled in the art. Portland cement found useable in this invention is made by intimately intergrinding a properly proportioned mixture of argillaceous (containing alumina and silica) and calcareous (containing lime) materials, which mixture is burned until it approaches fusion. The resulting clinker, when pulverized with 21/2 to 5 percent of gypsum (CaSO.sub.4 2H.sub.2 O), forms a product which does not slake and which possesses the property of combining chemically with water and hardening in its presence. Some types of cement may require small quantities of iron ore or siliceous materials in their manufacture. For practical purposes, portland cement may be considered as being composed of four principal compounds, the approximate percentages of which can be calculated from the chemical analysis. In addition to these major compounds, small amounts of calcium sulfate, magnesium oxide, alkalies, and other materials are present. While from a purely technical standpoint the validity of assuming the quantitative distribution of the major compounds in cement is subject to question, their utility in correlating cement properties is of real value. The major compounds with their chemical formulas and accepted abbreviations are as follows: ______________________________________ Tricalcium silicate 3 CaO . SiO.sub.3 Dicalciium silicate 2 CaO . SiO.sub.2 Tricalcium silicate 3 CaO . Al.sub.2 O.sub.3 Tetracalcium alumino-ferrite 4 CaO . Al.sub.2 O.sub.3 Fe.sub.2 O.sub.3 ______________________________________ The following example is given to illustrate a practice of a preferred embodiment of our invention. A cylindrical glass battery jar with a diameter of 111/2 inches and a height of 24 inches was filled to a height of 20 inches with dry portland type III cement having a fineness (as measured by air-permeability testing) of 2,800 cm.sup.2 /g. with less than 3 weight percent greater than 170 mesh. This required 43.6 kilograms of cement. The cement was vibrated in its container with a Syntron Vibra-Flow Model V51 vibrator at a Controller setting of 5 for a period of five minutes to densify. The height of the concrete in the container after vibration was 17 inches, reflecting an increase in density of from 1.28 gram/cm.sup.3 to 1.51 gram/cm.sup.3. A glass injector tube was inserted along the centerline of the cement cylindrical axis to a depth of 10 inches. The injector was a 1/2 inch diameter.times.12 inch long glass tube containing twelve injector ports. The ports were located in groups of four at three levels along the injector length. In each group, ports were located 90.degree. from one another about the axis of the injector. Taking the bottom of the injector as x equals 0, the port groups were located at x equals 0.5 inches, 5 inches, and 9.5 inches. Injector hole size was increased towards the top of the injector such that the hydraulic head was equal for all ports. A chromelalumel thermocouple was inserted into the cement near the injector for thermal measurements of cement during curing and polymerization exotherms. Tritiated aqueous waste was added through the injector to produce a water to cement ratio of about 0.25 by weight. This required 10.9 kilograms of water and gave a loading of 10.7 liters of waste per cubic foot of concrete. The waste was added at a rate of 15 liters per hour. The cement casting was allowed to cure at 70.degree. F. for twenty-four hours. The peak temperature of the concrete casting was 70.degree. C. Styrene monomer to which 1/2 weight percent A1BN (2,2 Azobis-(2-methylpropionitrile)) was added as a polymerization catalyst was added to the top of the cement casting and allowed to soak in. Monomer was also added to fill the injector tube. The monomer was allowed to soak for approximately 4 hours, after which time, it was observed that no additional monomer was soaking in. The excess monomer was siphoned off the top of the casting. The casting was heated to 50.degree. C. for 16 hours in order to polymerize the monomer. The peak casting temperature as indicated by the thermocouple was 75.degree. C. The resultant increase in casting weight due to polymer was 7.2 kilograms, corresponding to a polymer loading of 13 weight percent in the cement casting. There was thin film of polymer on the top of the casting. A second experiment was carried out wherein high alumina cement was substituted for the portland cement in the above experiment. A thermocouple placed in the center of the sample indicated a peak temperature of 186.degree. C., approximately 8 hours after the water was dispersed in the cement. Substantial water was observed to be boiling off from the sample at that time. The working example describes the injector tube used for a 111/2 inch diameter.times.17 inch high casting. The following are considerations relative to injector design and placement for various casting sizes. For a cylindrical casting, the injector is placed along the cylinder axis such that the distance of the lower end of the injector from the casting bottom (x) is equal to or slightly greater than the casting radius (r). This assumes a hole is located at or near the lower end of the injector and the casting height is greater than or equal to 2 r. Water is translated radially by capillary action and cement absorption. In addition to these factors, downward motion is also aided by gravity. Since it is desirable for water to reach the casting sides and bottom at the same approximate time, the lowest injector hole should not be closer to the casting bottom than it is to the casting sides. Capillary action and absorption also give rise to an upward component of motion, but since this is opposed by gravity, the uppermost injector hole should be located closer to the surface of the casting than the sides. We suggest that the distance of the uppermost injector hole from the casting surface (y) be approximately 1/2 the casting radius assuming that the casting height h is greater than or equal to the casting diameter. These considerations also apply to a rectangular prism although the waste loading/ft.sup.3 will probably be somewhat lower due to difficulties in introducing waste into corners before surface break through occurs. Water must be introduced slowly into the cement to avoid channeling and oversaturation. Water passsage through an injector hole is proportioned to the hole size and hydrostatic head in the injector tube at the hole. We have tended to keep the hydrostatic head at the uppermost injector hole below two feet. The additional hydrostatic head at the lower injector hole is dependent upon the length of the injector. For a 55 gallon drum size, the injector length is approximately 2 feet and the maximum hole size recommended would be about 1/8" in diameter. For very long injectors or high hydrostatic head, a smaller hole size might be required. This would be determined by observation of channeling for waste injection under anticipated conditions. If the hydrostatic head due to the length of the injector is equal or greater than the imposed head above the injector, water flow rates should be equalized by decreasing the hole area towards the bottom of the injector in proportion with the increase in hydrostatic head. Porous metal frit materials might be quite useful for waste injection because of the small controllable hole size and large number and even distribution of holes. As yet we have not tried this. Thus the size of the injector holes should be done in accordance with the principles stated above. Porous metal frit injectors can be used in the practice of this invention. In other injectors, the holes should be located no further apart along the injector length than the radius of the casting. Closer placement is preferable. Also, injectors should be located at 90.degree. or less from one another about the axis of the injector. Each orientation about the injector axis should be spaced no further apart than the casting radius. A hole at the bottom of the injector is not recommended since insertion in the dry cement may possibly plug up the hole. All holes are preferentially located on the sides of the injector with the lowermost holes close to the end of the tube. The injector can be made of metal, plastic and/or glass. Material of preference may depend upon whether the injector is removed and reused or left in the casting during impregnation and disposal.
044329296	summary	BACKGROUND OF THE DISCLOSURE The invention described below is a control circuit cooperative with a pulsed neutron generator tube. Such a tube also requires certain power supplies. Well logging techniques utilizing pulsed neutron irradiation are commercially attractive techniques. Through the pulsed neutron technique, the thermal neutron lifetime or the thermal neutron decay time of the strata of the earth formations in the near vicinity of a well are tested and analyzed. This enables compilation of elemental constituents and a variety of information can be obtained. As an example, the porosity of particular strata can be determined in the near vicinity of a borehole. Typically, such devices comprise an evacuated tube enclosing a deuterium-tritium accelerator source. The neutron source is typically an evacuated and sealed glass, metal or ceramic housing comprising an outer envelope. Operative equipment within the envelope comprises a target which is electrically insulated and maintained at a relatively high potential. Another element is a source of ions to be accelerated toward the target by the high voltage maintained at the target. There is additionally a replenisher element to stablize the gas pressure within the evacuated envelope. Relatively low pressures are desirable for operation of the device. The apparatus has a replenisher which incorporates a heater element surrounded by a surface capable of absorbing or emitting gas molecules into the evacuated tube envelope dependent on the temperature of the heater element. This enables the pressure within the chamber to be controlled. When the surface is heated, thermal emission of absorbed gases occurs. On cooling, the surface absorbs the gases from the atmosphere. The pressure of gas within the housing controls the supply of positively charged ions for acceleration toward the target, and, therefore, adjusts the rate of production of neutrons. This gas is ordinarily deuterium or deuterium mixed with tritium. Typically, the target is impregnated with tritium. The electrostatic repulsive force between accelerated ions and the nuclei of tritium atoms at the target is overcome to enable nuclear fusion. This produces an unstable helium isotope (N=5) which decays by neutron emission of approximately 14 MEV energy level. Operation of the tube during a logging run must be stabilized in a certain pattern. High output is generally desirable to promote an adequate irradiation. On the other hand, consistency is also desirable, at least in the form of a desired average current level to avoid source induced drift in the data. Moreover, the tube is pulsed periodically. The manner and technique of pulsing is, in part, set forth in U.S. Pat. No. 4,264,823 incorporated herein by reference. Operation of a pulsed neutron generator tube thus requires cooperation of the supporting structure. One supporting structure is the power supply which forms the replenisher current. It is a fairly large current, typically ranging around two amperes. Accordingly, the oilwell logging tool must include a replenisher current supply capable of going as high as about five amperes maximum. The present invention includes an interlock system cooperative with the replenisher current supply to protect the pulsed neutron generator tube in the event of failure of the replenisher current power supply. In similar fashion, the ion source must be pulsed with a relatively large voltage pulse, a typical value being in the range of about 2,000 volts. There is, therefore, incorporated in this disclosure supporting structure which is a high voltage pulsed power supply for the ion source. This disclosure sets forth a control circuit which interlocks with that source. The target is impressed with a relatively high voltage. A high voltage power supply capable of perhaps 100,000 volts is normally required. In the event a malfunction deprives the target of its high voltage while replenisher current is applied to the neutron generator tube, the device may be damaged. The target current is of interest. There is a range of current levels that is desirable for proper operation. If the target current is outside that range, it is indicative of damage. Excessive current may well damage the device. A current which is too low is indicative of other malfunctions. A typical pulsed neutron generator tube is obtained from Kaman Sciences Corporation of Colorado Springs, Colo. The device is packaged within an evacuated chamber pressurized by SF6 (sulphur hexafluoride) gas. A loss of gas typically indicates an alarm condition. The system for driving the pulsed neutron generator tube is set forth in the previously referenced patent. This enables the tube to form neutron irradiation in a time dependent pattern to accomplish desired results. The system includes the tube enclosed within a fluid tight sonde suspended by a well logging cable in a borehole. The logging cable conducts signals of interest to the surface. Control and recording equipment are normally located at the surface. BRIEF DESCRIPTION OF THE INVENTION This disclosure sets forth an interlock system for a pulsed neutron generator tube. The present system enables the tube to be switched on and operated by bringing certain signals or voltage levels to the tube in a selected sequence. Moreover, it interlocks against the loss of a supply voltage or current to thereby protect the tube against malfunction. This interlock circuit thus monitors the described parameters for operation of the tube and switches the tube off should a malfunction occur. It also monitors envelope pressure, the loss of which may also signal a catastrophic malfunction. The circuit utilizes digital components to form a fail safe system whereby operation of the tube occurs in a controlled fashion to prevent damage resulting from operation without adequate gas.
	abstract	A high sensitivity transient grating ultrafast radiation to optical image converter is based on a fixed transmission grating adjacent to a semiconductor substrate. X-rays or optical radiation passing through the fixed transmission grating is thereby modulated and produces a small periodic variation of refractive index or transient grating in the semiconductor through carrier induced refractive index shifts. An optical or infrared probe beam tuned just below the semiconductor band gap is reflected off a high reflectivity mirror on the semiconductor so that it double passes therethrough and interacts with the radiation induced phase grating therein. A small portion of the optical beam is diffracted out of the probe beam by the radiation induced transient grating to become the converted signal that is imaged onto a detector.
	description	The present invention relates to a method of producing a probe suitable for stably mounting a nanotube at a base member with a sufficient bonding strength in a scanning probe microscope provided with a probe utilizing a carbon nanotube as a probe tip, such a probe, and such a scanning probe microscope. In recent years, scanning probe microscopes and electron microscopes using carbon nanotubes and other nanotubes as tips of probes have been proposed (Patent Document 1). Nanotubes are utilized in scanning probe microscopes as probe tips provided at the front ends of cantilevers and are utilized in electron microscopes as electron source probes. Patent Document 1 generally discloses a surface signal scan probe for electronic apparatuses and a method of producing the same. Electronic apparatuses include scanning probe microscopes. The probe disclosed in Patent Document 1 is produced utilizing carbon nanotubes and other various types of nanotubes. This is so as to try to realize a high resolution, high rigidity, and high bending modulus probe. In probe tips of scanning probe microscopes, research and studies have been conducted to increase the resolution from the viewpoint of how to make them sharper. In this sense, nanotubes may become important technology for the future. Patent Document 1 (Japanese Patent Publication (A) No. 2000-227435) discloses an example of a method of producing a probe utilizing a carbon nanotube. A carbon nanotube is easy to produce, is inexpensive, and is suitable for mass production. The Patent Document 1 explains as an optimal method of production the method of production using electrophoresis to arrange a carbon nanotube at a metal plate of a holder etc. The carbon nanotube arranged at the holder is mounted at a mounting base end in the state attached to the holder. The mounting base end is for example the probe tip of an atomic force microscope. This mounting work (assembly work) is performed while positioning under observation by a scanning electron microscope (SEM). After the mounting work, the region including the mounting base end is formed with a coating film so as to bond the carbon nanotube to the mounting base end. As the method for forming the coating film, the method of using electron beam irradiation based on an SEM to form a carbon film, the method of breaking down reactive coating gas by an electron beam to form a coating film, and also the examples of CVD or PVD have been proposed. The carbon film formed by electron beam irradiation based on an SEM is usually called a “carbon contamination film”. Further, technology for forming a coating film at an intermediate part between the carbon nanotube and mounting base end to form a coating film and increase the carbon nanotube in thickness and strength has already been proposed. According to the method of producing a probe utilizing a nanotube described in the above Patent Document 1, the problem arises that the produced probe is insufficient in strength. That is, when bonding the carbon nanotube to the mounting base end, the bonding coating film is formed via the carbon contamination film arising due to SEM observation, so the bonding strength becomes insufficient. Further, when strengthening a probe made using a carbon nanotube, since only one side is coated, sufficient strengthening is not possible. Further, since the bonding is via a carbon contamination film, the problem also arises that the conductivity is difficult to secure. [Patent Document 1] Japanese Patent Publication (A) No. 2000-227435 The subject of the present invention is to increase the bonding strength by a bonding means, increase the conductivity performance of a probe, and improve the bonding performance of the bonding means when producing a probe by mounting a carbon nanotube etc. to a mounting base end and bonding them by a bonding coating film or other bonding means. An object of the present invention, in view of the above subject, is to provide a method of producing a probe by mounting a carbon nanotube etc. to a mounting base end and using a carbon film for bonding which method of producing a probe can eliminate the effects of the carbon contamination film etc., improve the bonding strength, improve the conductivity of the probe, and further strengthen the bonding performance by coating the entire circumference rather than one-sided coating. Another object of the present invention is to provide a probe having a high bonding strength and high conductivity and a scanning probe microscope provided with such a probe. The method of producing a probe, probe, and scanning probe microscope according to the present invention is configured as follows to achieve the above objects. The method of producing a probe according to the present invention is a method of producing a probe comprised of a carbon nanotube or other nanotube, a base (mounting base end) holding this nanotube, and a bonding part (coating film etc.) bonding the nanotube to the base, which method comprises performing the work of attaching the nanotube and base under observation by an observation device and, at a stage before bonding by the bonding part, stripping a contamination film formed by the observation device. In the above method of producing a probe, the contamination film is removed at a stage before bonding using the bonding part of the contamination film. Due to this, the surface of the nanotube is exposed. Therefore, when bonding the nanotube and base after this, the coating film etc. is directly bonded to the nanotube, the problem of the insufficient strength due to the contamination film is eliminated, and the bonding strength can be improved. Further, by suitably eliminating the contamination film, the probe can also be enhanced in conductivity. The method of producing a probe according to the present invention provides the above method of production wherein preferably the observation device is an electron microscope and the contamination film is a carbon film. The method of producing a probe according to the present invention provides the above method of production wherein preferably the carbon film is removed by focused ion beam processing. The method of producing a probe according to the present invention provides the above method of production wherein preferably the carbon film is removed by heating. The method of producing a probe according to the present invention is a method of producing a probe comprised of a nanotube, a base holding this nanotube, and a bonding part bonding the nanotube to the base, characterized in that the bonding by the bonding part is performed after reattaching the nanotube from the holder to which it had been attached to the base. The method of producing a probe according to the present invention provides the above method of production wherein preferably the bonding by the bonding part is performed while rotating the nanotube and base about their axes. The method of producing a probe according to the present invention provides the above method of production wherein preferably a bonding region formed by the bonding part is formed near the end of the base. The method of producing a probe according to the present invention is for producing a probe comprised of a nanotube, a base holding this nanotube, and a bonding part bonding the nanotube to the base, characterized in that the bonding by the bonding part is performed while rotating the nanotube and base about their axes. Since the bonding part is formed at the entire circumference of the part where the nanotube and the base are bonded, the strength of the bond becomes higher than the case of just a single side. The method of producing a probe according to the present invention provides the above method of production wherein preferably the bonding by the bonding part is performed after reattaching the nanotube from the holder to which it is attached to the base. The method of producing a probe according to the present invention provides the above method of production wherein preferably the bonding part is a carbon film formed by electron beam irradiation. The method of producing a probe according to the present invention provides the above method of production wherein preferably the bonding part is a film of a substance formed by introducing a reactive gas and electron beam irradiation. The method of producing a probe according to the present invention provides the above method of production wherein preferably the bonding part is a film of a substance formed by focused ion beam irradiation. The scanning probe microscope according to the present invention is provided with a probe tip part provided so that a probe tip faces a sample and a measurement part for measuring a physical quantity occurring between the probe tip and sample when the probe tip scans the surface of the sample, wherein this measurement part holds the physical quantity constant while the probe tip scans the surface of the sample so as to measure the surface of the sample, the probe tip is comprised of a nanotube, a base holding this nanotube, and a bonding means for bonding the nanotube to the base, and a contamination film formed by an observing means is stripped off at a stage before bonding by the bonding means. The scanning probe microscope according to the present invention is provided with a probe tip part provided so that a probe tip faces a sample and a measurement part for measuring a physical quantity occurring between the probe tip and sample when the probe tip scans the surface of the sample, wherein this measurement part holds the physical quantity constant while the probe tip scans the surface of the sample so as to measure the surface of the sample, the probe tip is comprised of a nanotube, a base holding this nanotube, and a bonding means for bonding the nanotube to the base, and the bonding means is a coating film provided over the entire circumferences of the nanotube and base. In the scanning probe microscope, the probe tip part is a cantilever having the probe tip at its front end. The probe according to the present invention is used for a scanning probe microscope or electron microscope, is provided with a probe tip comprised of a nanotube, a base holding this nanotube, and a bonding means bonding the nanotube to the base, and is stripped of a contamination film formed by an observing means at a stage before bonding by the bonding means. Alternatively, the probe according to the present invention is used for a scanning probe microscope or electron microscope and is provided with a probe tip comprised of a nanotube, a base holding this nanotube, and a bonding means bonding the nanotube to the base, the bonding means being a coating film provided over the entire circumferences of the nanotube and base. According to the method of producing a probe of the present invention, there is provided a method of producing a probe by attaching a nanotube to a mounting base end under observation by an SEM etc. and bonding the them by a coating film etc. wherein a carbon contamination film formed due to the SEM etc. is stripped off at a stage before the bonding work to enable bonding without the effects of the carbon contamination film etc., so the nanotube and mounting base end may be directly bonded, the strength may be improved, and the conductivity may be improved. According to the present invention, when detaching the holder from the nanotube after the mounting work, the contamination film is broken and the surface of the nanotube is exposed. According to the probe of the present invention, it is possible to increase the bonding strength and increase the conductivity. Further, by using this probe as an AFM probe, it is possible to utilize this as AFM lithography based on its high conductivity. According to the scanning probe microscope of the present invention, by providing a probe having a high bonding strength and conductivity, it is possible to raise the durability of the device and possible to release the charge due to the high conductivity so eliminate the effects of static electricity and thereby improve the measurement accuracy. Below, preferred embodiments of the present invention will be explained based on the attached drawings. Referring to FIG. 1, the method of producing a probe according to a first embodiment of the present invention will be explained. In FIG. 1, 11 indicates a holder (metal sheet), 12 a carbon nanotube, and 13 a mounting base end. The carbon nanotube 12 is produced by for example the electrophoresis method and is obtained in the state attached to the holder 11. The carbon nanotube 12 is a cylindrical member with a cross-sectional diameter of 1 nm to several tens of nm. The mounting base end 13 is for example a probe tip formed at a cantilever used for an atomic force microscope. This probe tip, that is, the mounting base end 13, is usually produced utilizing semiconductor film forming technology etc. The carbon nanotube 12 is attached and bonded to the front end of the mounting base end 13, whereby a probe is assembled and produced. In FIG. 1, three partial views (A), (B), and (C) are used to show steps 1 to 3 of the method of production. At step 1, the holder 11 is used to attach a carbon nanotube 12 to the front end of the mounting base end 13. A carbon film is formed (carbon contamination film 14) and a bonding coating film 15 is used to bond the carbon nanotube 12 and the mounting base end 13. At step 1, as shown by the arrow 16, force is applied to separate the holder 11 from the carbon nanotube 12. The results are shown in step 2. At step 2 of (B) in FIG. 1, the holder 11 is separated from the carbon nanotube 12. At this time, the carbon contamination film 14 is also partially shredded and separated together with the holder 11. As a result, at the right part of the carbon nanotube 12 shown in (B) of FIG. 1, a part arises where there is no carbon contamination film and therefore a part of the carbon nanotube 12 forming the surface is exposed. At step 3 of (C) of FIG. 1, the carbon contamination film 14 is peeled off and the exposed part of the surface of the carbon nanotube 12 is utilized to again form a bonding coating film 17. The new bonding coating film 17 is formed to cover the exposed part of the carbon nanotube 12, the remaining carbon contamination film 14, and the first bonding coating film 15. In this way, the carbon nanotube 12 is bonded to the mounting base end 13 by the new bonding coating film 17 after the attachment work and after detachment of the holder 11. According to the first embodiment, the bonding coating film 17 is used to bond the carbon nanotube 12 and the mounting base end 13. The bonding is performed in the state after removing the carbon contamination film 14 to eliminate its effects. Further, the new bonding coating film 17 is used to bond the carbon nanotube 12 and the mounting base end 13 near the front end or at a projecting part of the mounting base end 13. Due to the above, direct bonding becomes possible and an improvement of the bonding strength and improvement conductivity can be achieved. Referring to FIG. 2, a method of producing a probe according to a second embodiment of the present invention will be explained. In FIG. 2, elements the same as elements explained in FIG. 1 are assigned the same reference notations and explanations are omitted. Steps 1 to 3 of (A) to (C) are basically the same as the case of the first embodiment. In FIG. 2, 11 indicates a holder, 12 a carbon nanotube, 13 a mounting base end, 14 a carbon contamination film, 15 a first bonding coating film, and 21 a new bonding coating film added after bonding. In the method of producing a probe according to the second embodiment, due to the relationship of the carbon contamination film 14 and bonding coating film 15, a wide region 22 with no coating film is secured. Therefore, when bonding again by the bonding coating film 21 at step 3, the area of the surface of the bonding coating film 21 is increased and the bonding portion is formed including a part in addition to near the end of the mounting base end 13. According to the method of producing a probe of the second embodiment, it is possible to increase the region of the exposed part of the carbon nanotube 12, possible to increase the region directly contacting the bonding coating film 21, and possible to improve the bonding strength. Referring to FIG. 3, a method of producing a probe according to a third embodiment of the present invention will be explained. In FIG. 3, elements the same as elements explained in FIG. 1 or FIG. 2 are assigned the same reference notations and explanations are omitted. (A) to (C) of FIG. 3 show steps 1 to 3 of the method of producing a probe according to the third embodiment. In FIG. 3, 11 indicates a holder, 12 a carbon nanotube, 13 a mounting base end, 14 a carbon contamination film, and 31 a bonding coating film. In the method of producing a probe according to the third embodiment, at step 1, the holder 11 provided with the carbon nanotube 12 is attached to the mounting base end 13. At this time, the holder 11 and carbon nanotube 12 and the mounting base end 13 are bonded by the carbon contamination film 14. In this state, at step 2, before the coating work, part of the carbon contamination film 14 is removed. The carbon contamination film 14 is removed using for example a method using a focused ion beam (FIB) or a method using heating. After this, as shown at step 3, the bonding coating film 31 is formed between the carbon nanotube 12 and the mounting base end 13. After this, at a suitable timing, the holder 11 is removed. According to the third embodiment, before the coating work for forming the bonding coating film 31, it is possible to remove part of the carbon contamination film 14 and bring the bonding coating film 31 into direct contact with the carbon nanotube 12, reliably eliminate the effect of the carbon contamination film 14, and enlarge the direct contact area to increase the strength of the bond. Referring to FIG. 4, a method of producing a probe according to a fourth embodiment of the present invention will be explained. In FIG. 4, elements the same as elements explained in FIG. 1, FIG. 2, etc. are assigned the same reference notations and explanations are omitted. (A) to (C) of FIG. 4 show steps 1 to 3 of the method of producing a probe according to the fourth embodiment. This fourth embodiment is a modification of the second embodiment. In FIG. 4, 11 indicates a holder, 12 a carbon nanotube, 13 a mounting base end, 14 a carbon contamination film, and 15 a bonding coating film. The state shown by step 1 of (A) in FIG. 4 is the same as the state shown by step 1 of (A) in FIG. 2. In the fourth embodiment, at the stage of transition from step 1 to step 2, the holder 11 is separated from the carbon nanotube 12, then, as shown by the arrow 41, the carbon nanotube 12 is arranged so as to match with the axis of rotation and the mounting base end 13 is rotated while performing coating work for imparting a bonding coating film. For this reason, as shown by (C) in FIG. 4, the entire circumference of the carbon nanotube 12 can be given the bonding coating film 42. More particularly, the bonding part between the carbon nanotube 12 and the mounting base end 13 and the surrounding part including that bonding part are given the bonding coating film 42 over the entire circumference in the circumferential direction. The rotation drive mechanism used may be one of any configuration. In the above, the coating film 42 is a carbon film formed by electron beam irradiation, a film of a desired substance formed by introducing a reactive gas and by electron beam irradiation, or a film of a desired substance deposited by FIB irradiation. According to the fourth embodiment, since a new bonding coating film can be provided over the entire circumference, the contact region between the carbon nanotube and the bonding coating film can be increased, the bonding strength can be improved, and the conductivity can be improved. In the above embodiments, as the bonding coating film, a carbon film formed by electron beam irradiation, a film of a desired substance formed by introducing a reactive gas and by electron beam irradiation, a film of a desired substance deposited by focused ion beam irradiation, etc. is used. Next, an example of a scanning probe microscope provided with a probe produced by the above-mentioned method of production will be explained with reference to FIG. 5. This scanning probe microscope envisions as a typical example an atomic force microscope (AFM). The bottom part of the scanning probe microscope is provided with a sample stage 111. The sample stage 111 carries a sample 112 on it. The sample stage 111 is a mechanism for changing the position of the sample 112 by a three-dimensional coordinate system 113 comprised of a perpendicular X-axis, Y-axis, and Z-axis. The sample stage 111 is comprised of an XY-stage 114, Z-stage 115, and sample holder 116. The sample stage 111 is usually comprised of a rough (or coarse) movement mechanism causing displacement (change of position) at the sample side. The sample stage 111 has a sample holder 116 on the top surface of which a relatively large area, sheet shaped sample 112 is placed and held. The sample 112, for example, is a substrate or wafer on the surface of which an integrated circuit pattern of a semiconductor device is fabricated. The sample 112 is fixed on the sample holder 116. The sample holder 116 is provided with a sample-fixing chuck mechanism. In FIG. 5, at a position above the sample 112, an optical microscope 118 provided with a drive mechanism 117 is arranged. The optical microscope 118 is supported by the drive mechanism 117. The drive mechanism 117 is comprised of a focus use Z-direction movement mechanism 117a for moving the optical microscope 118 in the Z-axis direction and an XY-direction movement mechanism 117b for moving it in the X-and Y-axis directions. Due to the way they are attached, the Z-direction movement mechanism 117a moves the optical microscope 118 in the Z-axis direction, while the XY-direction movement mechanism 117b moves the unit of the optical microscope 118 and the Z-direction movement mechanism 117a in the X-and Y-axis directions. The XY-direction movement mechanism 117b is fixed to a frame member, but in FIG. 5, illustration of the frame member is omitted. The optical microscope 118 is arranged so that its object lens 118a faces downward and is arranged at a position approaching the surface of the sample 112 from directly above it. The optical microscope 118 is provided at its top end with a camera 119. The camera 119 captures an image of a specific area of the sample surface covered by the object lens 118a and outputs the image data. Above the sample 112, a cantilever 121 provided with a probe tip 120 at its front end is arranged in a close state. The cantilever 121 is fixed to a mount 122. The mount 122, for example, is provided with an air suction part (not shown). This air suction part is connected to an air suction device (not shown). The cantilever 121 is affixed and mounted so that this large area base is held by suction on the suction part of the mount 122. As the probe tip 120, the above-mentioned probe is used. The probe tip 120 is formed with a mounting base end 13 and a carbon nanotube 12. The front end of the probe tip 120 is formed by the carbon nanotube 12 attached to the front end of the probe. The mount 122 is attached to a Z-fine movement mechanism 123 causing fine movement in the Z-direction. Further, the Z-fine movement mechanism 123 is attached to the bottom surface of a cantilever displacement detector 124. The cantilever displacement detector 124 has a mechanism attaching a laser light source 126 and a photodetector 127 to a support frame 125 in a predetermined relationship. The cantilever displacement detector 124 and the cantilever 121 are held in a constant positional relationship, whereby the laser light 128 emitted from the laser light source 126 is reflected at the back surface of the cantilever 121 and strikes the photodetector 127. This cantilever displacement detector is comprised of an optical lever type optical detection device. This optical lever type optical detection device can detect any torsion, flexing, or other deformation at the cantilever 121. The cantilever displacement detector 124 is attached to an XY-fine movement mechanism 129. The XY-fine movement mechanism 129 allows the cantilever 121 and probe tip 120 etc. to move by fine distances in the X- and Y-axis directions. At this time, the cantilever displacement detector 124 is moved simultaneously, so the cantilever 121 and the cantilever displacement detector 124 are unchanged in positional relation. In the above, the Z-fine movement mechanism 123 and the XY-fine movement mechanism 129 are usually comprised by piezoelectric devices. The Z-fine movement mechanism 123 and the XY-fine movement mechanism 129 make the probe tip 120 move by fine distances (for example several to 10 μm, maximum 100 μn) in the X-axis direction, Y-axis direction, and Z-axis direction. The above XY-fine movement mechanism 129 is attached to the above-mentioned not shown frame member to which the unit of the optical microscope 118 is attached. Due to the mounting relationship, the field of observation of the optical microscope 118 includes a specific area of the surface of the sample 112 and the front end (back surface) of the cantilever 121 including the probe tip 120. Next, the control system of the scanning probe microscope will be explained. The control system is comprised of a comparator 131, controller 132, first control device 133, and second control device 134. The controller 132 is for example a controller for realizing a measurement mechanism using an atomic force microscope (AFM). Further, the first control device 133 is a control device for controlling the drive operations of the plurality of drive mechanisms etc., while the second control device 134 is a higher control device. The comparator 131 compares a voltage signal Vd output from the photodetector 127 and a preset reference voltage (Vref) and outputs a difference signal s1. The controller 132 generates a control signal s2 so that this difference signal s1 becomes 0 and gives this control signal s2 to the Z-fine movement mechanism 123. Receiving the control signal s2, the Z-fine movement mechanism 123 adjusts the cantilever 121 in height position to maintain a constant distance between the probe tip 120 and the surface of the sample 112. A control loop from the photodetector 127 to the Z-fine movement mechanism 123 is a feedback servo control loop for detecting the state of deformation of the cantilever 121 by the optical lever type optical detection device when the probe tip 120 scans the sample surface and maintaining the distance between the probe tip 120 and the sample 112 to a predetermined constant distance based on the reference voltage (Vref). Due to this control loop, the probe tip 120 is kept a constant distance from the surface of the sample 112. When scanning the surface of the sample 112 in this state, it is possible to measure relief shapes on the sample surface. Next, the first control device 133 is a control device for driving the different parts of the scanning probe microscope and is provided with the following functional parts. The optical microscope 118 is changed in position by the drive mechanism 117 comprised of the focus use Z-direction movement mechanism 117a and the XY-direction movement mechanism 117b. The first control device 133 is provided with a first drive controller 141 and a second drive controller 142 for controlling the operations of the Z-direction movement mechanism 117a and XY-direction movement mechanism 117b. The image of the sample surface or cantilever 121 obtained in the optical microscope 118 is captured by the camera 119 and acquired as image data. The image data obtained by the camera 119 of the optical microscope 118 is input to the first control device 133 and processed by an internal image processor 143. In the feedback servo control loop including the controller 132 etc., the control signal s2 output from the controller 132 means the height signal of the probe tip 120 in a scanning probe microscope (atomic force microscope). The height signal of the probe tip 120, that is, the control signal s2, can give information relating to the height position of the probe tip 120. The control signal s2 including the height position information of the probe tip 120, as explained above, is given for controlling the drive operation of the Z-fine movement mechanism 123 and is acquired by the data processor 144 in the control device 133. The scan by the probe tip 120 of the sample surface for the measurement area of the surface of the sample 112 is performed by driving the XY-fine movement mechanism 129. The drive operation of the XY-fine movement mechanism 129 is controlled by an XY-scan controller 145 providing an XY-scan signal s3 to the XY-fine movement mechanism 129. The drive operations of the XY-stage 114 and the Z-stage 115 of the sample stage 111 are controlled by an X-drive controller 146 outputting an X-direction drive signal, a Y-drive controller 147 outputting a Y-direction drive signal, and a Z-drive controller 148 outputting a Z-direction drive signal. Note that the first control device 133, in accordance with need, is provided with a storage (not shown) storing and preserving the set control data, input optical microscope image data, data relating to the height position of the probe tip, etc. The second control device 134 is provided at a position above the first control device 133. The second control device 134 stores and runs a usual measurement program, sets and stores the usual measurement conditions, stores and runs an automatic measurement program, sets and stores measurement conditions, stores measurement data, processes the measurement results, displays information on the display device (monitor) 135, and performs other processing. For setting the measurement conditions, it has functions for setting basic matters such as the measurement range and measurement speed and the angle of inclination, setting measurement conditions for when measuring the different inclinations and postures and other conditions of automatic measurement, and files for setting these conditions. Further, it is configured with a communication function and can be given a function enabling communication with an external device. To give the second control device 134 these functions, it is comprised by a processing unit constituted by a CPU 151 and a storage 152. The storage 152 stores and preserves the program and condition data etc. Further, the second control device 134 is provided with an image display controller 153, a communicator, etc. In addition, the second control device 134 is connected through an interface 154 to an input device 136. The input device 136 enables setting and changes of the measurement program, measurement conditions, data, etc. stored in the storage 152. The CPU 151 of the second control device 134 provides higher control instructions etc. through the bus 155 to the different functional parts of the first control device 133 and is provided with image data and data relating to the height position of the probe tip from the image processor 143, the data processor 144, etc. Next, the basic operation of the scanning probe microscope (atomic force microscope) will be explained. The front end of the probe tip 120 of the cantilever 121 is made to approach a predetermined area of the surface of the semiconductor substrate or other sample 112 placed on the sample stage 111. Usually, a probe tip approach mechanism constituted by the Z-stage 115 brings the probe tip 120 close to the surface of the sample 112 and applies atomic force to make the cantilever 121 flex. The amount of flexing due to the flexing of the cantilever 121 is detected by the above-mentioned optical lever type optical detection device. In this state, the probe tip 120 is made to move over the sample surface to scan the sample surface (XY-scan). The XY-scan by the probe tip 120 of the surface of the sample 112 performed by moving the probe tip 120 side by the XY-fine movement mechanism 129 (fine movement) or by moving the sample 112 side by the XY-stage 114 (rough movement) so as to create relative movement in the XY-plane between the sample 112 and the probe tip 120. The probe tip 120 side is moved by giving an XY-scan signal s3 for XY-fine movement to the XY-fine movement mechanism 129 provided with the cantilever 121. The scan signal s3 for XY-fine movement is given from the XY-scan controller 145 in the first control device 133. On the other hand, the sample side is moved by giving drive signals from the X-drive controller 146 and Y-drive controller 147 to the XY-stage 114 of the sample stage 11. The XY-fine movement mechanism 129 is comprised utilizing a piezoelectric device and enables high precision and high resolution scanning movement. Further, the measurement range measured by the XY-scan by the XY-fine movement mechanism 129 is restricted by the stroke of the piezoelectric device, so even at the maximum becomes a range determined by a distance of about 100 μm or so. According to the XY-scan by the XY-fine movement mechanism 129, a narrow range is measured. On the other hand, the XY stage 114 is comprised utilizing an electromagnetic motor as the drive part, so this stroke can be increased up to several hundred mm. According to the XY-scan by the XY-stage, a wide range is measured. In the above way, a predetermined measurement area on the surface of the sample 112 is scanned by the probe tip 120 and the amount of flexing of the cantilever 121 (amount of deformation due to flexing etc.) is controlled to become constant based on a feedback servo control loop. The amount of flexing of the cantilever 121 is controlled so as to constantly match with a reference target amount of flexing (set by reference voltage Vref). As a result, the distance between the probe tip 120 and the surface of the sample 112 is held at a constant distance. Therefore, the probe tip 120, for example, moves along (scans) the surface of the sample 112 while following its profile. The height signal of the probe tip is obtained to enable measurement of the profile of the surface of the sample 112. The configurations, shapes, sizes (thicknesses), and layouts explained in the above embodiments are only shown schematically to an extent enabling the present invention to be understood and worked. Further, the numerical values and compositions (materials) are only shown for illustration. Therefore, the present invention is not limited to the explained embodiments and can be changed in various ways within the scope of the technical idea shown in the claims. The present invention utilizes a carbon nanotube or other nanotube as a probe of a scanning probe microscope etc. It eliminates the influence of the carbon contamination film by bonding the nanotube and thereby is utilized as a probe having a high bonding strength and conductivity. [FIG. 1] Step diagrams showing a method of production according to a first embodiment of the present invention. [FIG. 2] Step diagrams showing a method of production according to a second embodiment of the present invention. [FIG. 3] Step diagrams showing a method of production according to a third embodiment of the present invention. [FIG. 4] Step diagrams showing a method of production according to a fourth embodiment of the present invention. [FIG. 5] A view of the configuration of a scanning probe microscope according to the present invention. 11 holder 12 carbon nanotube 13 mounting base end 14 carbon contamination film 15 bonding coating film 16 bonding coating film 21 bonding coating film 31 bonding coating film 42 bonding coating film
	description	This application is a continuation application of U.S. application Ser. No. 10/544,668, filed May 3, 2006 now U.S. Pat. No. 1,365,306, the contents of which are incorporated herein by reference. This invention relates to an electron-beam length measuring technology including a standard component (or a reference sample) for length measurement used for electron-beam metrology. The standard component for length measurement used for the conventional electron-beam metrology has used a diffraction grating fabricated by laser interferometer lithography and anisotropic chemical etching on a semiconductor substrate having a surface of plane direction of the (110) plane. A calibration method of it is performed by diffraction angle measurement of the diffraction grating using laser light (for example, see Japanese Patent Application Laid-Open No. 7-71947). The minimum dimension that is achievable with above-mentioned conventional standard component depends on a resolution limit of the laser interferometer lithography method; one half of a wavelength of the laser light used is the limit of a pitch dimension. With the use of an Ar ion laser of a wavelength of 351.1 nm currently used in the laser interferometer lithography equipment, a pitch dimension of about 200 nm is the limit. On the other hand, exposure equipment in which the laser light source is changed to a short wavelength light source has many technical problems and its development is difficult. At the same time, diffraction angle measurement of a diffraction grating using laser light used for calibration has also a measurement limit; for the minimum pitch dimension of about 200 nm or less, measurement is difficult. However, since miniaturization of the semiconductor device has been accelerated, the minimum processing dimension is breaking 100 nm. In order to control dimensions of this fine processing, the electron-beam metrology system is being used, and in order to manage absolute precision of this system, a dimensional standard component is indispensable. However, the conventional dimensional standard component is becoming unable to support the minimum processing dimension of the latest semiconductor devices. In addition, diffraction grating patterning using the laser interferometer lithography method can basically produce only simple line-and-space patterns. For this reason, the same pattern is rendered over the whole surface of the sample, and consequently automatic defining of the position cannot be done for samples in which no alignment mark is used. Therefore, it is not possible to specify exactly which diffraction grating pattern was used at the time of calibration of the metrology system. In the case of the electron-beam metrology system, contamination adhesion associated with beam irradiation causes variation in dimensions of a sample. If the automatic alignment is impossible, it is necessary to perform calibration through the mediation of a human operator, and so automatic calibration cannot be performed. The object of this invention is to provide an electron-beam length measuring technology that contains a standard component (or a reference sample) for length measurement having a finer standard dimension, and a producing method for the standard component. In order to attain the above-mentioned objects, in this invention, the standard component has a structure of the conventional diffraction grating pattern having a finer pattern in it. The conventional diffraction grating pattern (an array of first diffraction gratings) is specified about 200 nm or more, and the pitch dimension is used as an absolute dimension by diffraction angle measurement of the diffraction grating using laser light. A grating pattern (array of second diffraction gratings) whose minimum dimension is equal to or less than 100 nm is mixed in this diffraction grating pattern. A dimension of this pattern cannot be determined by the conventional diffraction angle measurement of the diffraction grating using the laser light; therefore, the electron-beam metrology system or the scanning probe microscope is used and a pitch dimension of the conventional diffraction grating pattern found in the above procedure as an absolute dimension value is used as a standard. In this determination, by arranging both patterns in the same scanning range of an electron beam or a scanning probe, higher-precision calibration becomes possible. In this way, by mixing a pattern whose diffraction grating can be measured by the conventional diffraction angle measurement using laser light and a fine pattern that corresponds to the minimum processing dimension of the latest semiconductor devices, the standard component for length measurement and calibration in which fineness is compatible with high-precision becomes possible. In production of this dimension standard component, it is impossible to mix the conventional diffraction grating pattern and a fine pattern corresponding to a minimum processing size of the latest semiconductor device by the laser interferometer lithography method that is used in the conventional dimension standard component, in terms of resolution and freedom in pattern creation. In order to solve this problem, the electron-beam exposure method that is excellent in resolution and has no limitation in pattern shape is used. Especially, in order to produce a high-precision dimension standard component whose uniformity within a sample surface is improved, electron-beam cell projection method where a desired pattern is made on a stencil mask and reduction projection exposure is conducted with an electron beam is effective. That is, because a drawing pattern has all been made in the stencil mask, exposure is done repeatedly with this mask while the beam is deflected each time, whereby patterning with excellent reproducibility can be conducted without causing any variation in dimensions at each shot. By combining this patterning method and wet chemical etching that has etching dependency on a plane direction and is used for the conventional dimension standard component, it becomes possible to produce a dimension standard component suitable for the electron-beam metrology system and the scanning probe microscope. Since this producing method allows large freedom in production of a pattern within the stencil mask, it is possible to make not only a diffraction grating but various patterns. Then, a diffraction grating pattern is prepared in an area smaller than a maximum exposure area when cell projection is done. A stencil mask in which a diffraction grating pattern exists together with cross mark patterns in the surrounding of the diffraction grating and, at the same time, in an area of the maximum irradiation area is produced, and exposure is conducted by the electron-beam cell projection method. By this, the exposure is conducted in such a manner that: a pattern containing the diffraction gratings is exposed to be a fixed length and to be a fixed width, this pattern is arranged cyclically in longitudinal and horizontal directions at fixed intervals, respectively, and the cross mark patterns are arranged between the patterns. Moreover, position detection mark patterns, such as cross mark patterns, are formed by the same electron-beam cell projection method or the electron-beam variable shaping method in pair positions—up side and down side, or right side and left side—in the outside of a group of patterns arranged cyclically at the fixed intervals. In the sample produced by such exposure, when the electron-beam metrology system etc. is calibrated, it is possible to automatically specify positions of a pattern used for the calibration, because sample rotation correction and specification of calibration positions within the pattern can be specified by using the position detection marks, such as a cross mark pattern. Then, the following scheme is possible: a procedure from pattern alignment to system calibration is automated, the number of beam irradiation of the pattern used in the calibration is recorded, and if the number reaches a fixed number, the field of view is moved to a different pattern position automatically and the calibration is done. By virtue of this scheme, degradation in calibration precision due to adhesion of contamination to the sample caused by beam irradiation does not occur, and an excellent signal waveform can be obtained always at the time of measurement; therefore, high-precision calibration can be attained automatically. Moreover, since a direction of the diffraction grating can be set to an arbitrary direction by combining the patterning method based on the electron-beam cell projection method and dry etching, in a wafer-shaped standard component of a large area, a plurality of groups of patterns containing diffraction gratings and alignment marks can be arranged on the above-mentioned wafer. At this time when patterning is conducted by the electron-beam cell projection method, it is possible to prepare a group of patterns that is obtained by rotating a group of patterns by 90 degrees or 45 degrees. The use of this standard component makes it possible to calibrate dimensions in longitudinal, horizontal, and oblique directions for one sample. Hereafter, typical configuration examples of this invention will be described. (1) A standard component for length measurement, comprising a semiconductor member on which a pattern consisting of an array of first diffraction gratings whose pitch dimension is specified as an absolute dimension by an optical measurement method, characterized in that the pattern has a structure that contains an array of the second diffraction grating different from the first diffraction grating in a predetermined cycle in a portion within the array of the first diffraction gratings. (2) A standard component for length measurement, comprising a semiconductor member on which a pattern consisting of an array of first diffraction gratings whose pitch dimension is specified as an absolute dimension by an optical measurement method, characterized in that the pattern has a structure that contains an array of the second diffraction grating that is different from the first diffraction grating in terms of at least one of the length of a straight line part of the first diffraction grating, a pitch dimension of the array, and a direction in which the second diffraction grating is repeated cyclically in such a way that the array of the second diffraction grating is parallel to the array of the first diffraction grating. (3) A standard component for length measurement, comprising a semiconductor member on which plurality of patterns each consisting of an array of first diffraction gratings whose pitch dimension is specified as an absolute dimension by an optical measurement method, wherein each of the patterns has a structure that an array of second diffraction gratings different from the first diffraction gratings is arranged in a part within the array of the first diffraction gratings in a predetermined cycle. (4) The above-mentioned standard component for length measurement, characterized in that the pattern contains an array pattern whose minimum pitch dimension is equal to or less than 100 nm. (5) The above-mentioned standard component for length measurement, characterized in that the semiconductor member is made up of a Si substrate, and the pattern is a depression-and-projection-shaped pattern that has surfaces of plane directions of the (110) plane and the (111) plane of the Si substrate. (6) The above-mentioned standard component for length measurement, characterized in that the first diffraction grating and the second diffraction grating have predetermined lengths and widths, respectively, and are arranged cyclically at predetermined intervals, respectively, and marks for specifying positions of the patterns are arranged in peripheral portions of the pattern. (7) The above-mentioned standard component for length measurement, characterized in that the plurality of patterns are arranged two-dimensionally and cyclically at predetermined intervals within a predetermined area, and marks for position detection are arranged between the adjacent patterns of the plurality of patterns. (8) A method for producing a standard component for length measurement, comprising the step of forming a pattern consisting of an array of first diffraction gratings whose pitch dimension is specified as an absolute dimension by an optical measurement method on a surface of a semiconductor member, characterized by further comprising the step of forming an array of second diffraction gratings different from the first diffraction gratings in a predetermined cycle in a part within the array of the first diffraction gratings in the pattern by the electron-beam batch exposure method using a stencil mask. (9) An electron-beam metrology system comprising: electron beam length measuring means for measuring processing dimensions of a sample by irradiating and scanning an electron beam; and calibrating means for calibrating a dimension based on a secondary electron signal waveform obtained by scanning the electron beam on a standard component for length measurement; characterized in that the standard component for length measurement has an array of first diffraction gratings whose pitch dimension was specified by an optical measurement method as an absolute dimension on a semiconductor substrate, and has a pattern that contains an array of second diffraction gratings different from the first diffraction gratings in a predetermined cycle in a part within the array of the first diffraction gratings. (10) A method of calibrating a standard component for length measurement that consists of a plurality of patterns containing a diffraction grating pattern having a fixed pitch dimension, characterized in that for calibration of a pitch dimension of the diffraction grating pattern, diffraction angle measurement using laser light is used, and for calibration of dimensions of other patterns, an electron-beam metrology system or a scanning probe microscope that was calibrated by the pitch dimension of the diffraction grating pattern found by the above-mentioned diffraction angle measurement is used. (11) A method of calibrating a metrology system by using a semiconductor member having diffraction grating patterns and mark patterns for position detection, characterized in that: the mark is detected and its position is found; a portion that is in a diffraction grating pattern that has this mark position used for calibration as a standard and, at the same time, the part wherein its pitch dimension was found in advance by diffraction grating measurement using laser light is aligned; a pitch dimension of the diffraction grating pattern part is measured; this result is subjected to dimensional calibration using the pitch dimension found by the diffraction angle measurement as a standard; and the number of calibration in the pattern position is recorded, and if the number exceeds a fixed number, other pattern position is aligned with respect to the mark position and the calibration is performed. (12) The above-mentioned method of calibrating a metrology system, characterized in that a plurality of pitch dimensions that are found by a single scan of electron beam scanning are obtained when finding a pitch dimension of the diffraction grating pattern, the pitch dimensions are averaged, and the averaged pitch dimension is used for calibration. (13) The above-mentioned method of calibrating a metrology system, characterized in that in the semiconductor member, a part within the diffraction grating pattern contains a diffraction grating pattern that is different from the above-mentioned diffraction grating in terms of at least one of the length of its straight line part, its pitch dimension, and a periodical repeating direction; a part on which diffraction angle measurement using laser light was conducted in advance and whose pitch dimension was found is aligned; a pitch dimension of the diffraction grating pattern part is measured; after performing dimensional calibration on this result using a pitch dimension found by the diffraction angle measurement as a standard, the position just under the electron beam is shifted to a position of the different diffraction grating pattern using the mark position as a standard and the dimension of the different diffraction grating is measured; and this dimension value is used for dimensional calibration of length measurement of another pattern as a standard value. (14) The above-mentioned method of calibrating a metrology system, characterized in that a series of the calibration operations are memorized in a controller of the metrology system and calibration is performed automatically. Hereafter, embodiments of this invention will be described with reference to the drawings. An example of a dimension standard component for an electron-beam metrology system of this invention is shown in FIG. 1 and FIG. 2. FIG. 3 shows the conventional dimension standard component for the electron-beam metrology system. Conventionally, a depression-and-projection pattern 15 on a semiconductor substrate of the (110) plane (for example, a silicon (Si) substrate, a compound semiconductor substrate, such as of GaAs and InP) has been fabricated by laser interferometer lithography method and wet chemical etching as a diffraction grating pattern in a fixed direction as shown in FIG. 3. The pitch dimension of the diffraction grating 9 is about 200 nm; this value has been found by the diffraction angle measurement using a laser. The pattern is uniformly formed all over the sample surface 8 of 4-mm square. In the case where the electron-beam metrology system is calibrated using this standard component, there are two problems below. First, a first problem is fineness. As described above, the minimum processing dimensions go below 100 nm in the latest semiconductor patterns. However, in the conventional diffraction grating patterns by laser interferometer lithography, the minimum pitch dimension is 200 nm, and one pitch portion of the diffraction grating pattern could not be fitted in the field of view of an image at 200,000× magnification or more at which the length of the semiconductor patterns are measured; therefore, dimension calibration at this magnification is impossible. The second problem is that, since the whole sample is a uniform pattern and there is no alignment mark within the sample, calibration positions cannot be specified automatically. For this reason, in the electron-beam metrology system etc., the calibration is performed after an operator defined the position. In this invention, the electron-beam batch exposure method was used as the pattern exposure method. Although this method can achieve patterning with a pitch dimension of equal to or less than 100 nm, optical diffraction angle measurement was difficult in diffraction gratings of this pitch dimension because of wavelength limit. Consequently, in this invention, a diffraction grating pattern as shown in FIG. 1 was fabricated. This diffraction grating pattern is composed of a diffraction grating pattern (an array of first diffraction gratings) 1 each of whose diffraction gratings has a length of 3 μm and a pitch of 200 nm and a diffraction grating pattern (an array of second diffraction gratings) 2 each of whose diffraction gratings has a length of 0.5 μm and a pitch of 400 nm and is disposed in a central part of the diffraction grating pattern 1 as shown in FIG. 1. Moreover, cross marks 3 of a length of 0.5 μm for alignment are arranged in four corners surrounding the diffraction grating pattern 1. In the standard component shown in FIG. 2, the area of 5 μm squares consisting of these patterns, as a basic unit, is arranged repeatedly in both longitudinal and horizontal directions over 1-mm square to constitute a pattern array 4 as shown in an enlarged view of FIG. 2. Further, cross marks 7 for correcting sample rotation are arranged in four corners in the surrounding of this calibration pattern area 6. Next, a method for producing the standard component of this invention will be described. First, a thermal oxide film 100 nm thick or less is formed on a Si substrate having a surface whose plane direction is the (110) plane, and a resist is coated on the surface. Next, using electron-beam batch exposure equipment on which a stencil mask having apertures 10, 11 shown in FIG. 4 is loaded, the pattern aperture 10 for calibration is selected by beam deflection and exposure is conducted on the above-mentioned substrate with the use of beam deflection. Next, the marks 7 for sample rotation correction as shown in FIG. 2 are exposed by the electron-beam variable formation method on the right and left sides in the surrounding of an area on which the diffraction grating patterns were exposed using the rectangular aperture 11. After development, the oxide film is etched by using the resist as a mask, and subsequently subjected to anisotropic chemical etching with a potassium hydroxide aqueous solution. In the above-mentioned electron beam exposure, a direction of the diffraction grating pattern is set to the <112> direction on the (110) Si substrate, whereby from the above-mentioned pattern, anisotropic chemical etching will give a depression-and-projection shape whose vertical cross section consists of (110) and (111) crystallographic planes and has small edge roughness, like the diffraction grating pattern 15 of FIG. 8. Since the electron-beam batch exposure method is used as a diffraction grating pattern, exposure is done by using the same stencil mask for any position in the sample; therefore, uniform pattern formation with variation in dimension of 5 nm or less is possible. For absolute dimensional calibration of this standard component, diffraction angle measurement using a laser was employed. A pitch dimension of 200.00 nm with precision of 1 nm or less was able to be found by irradiating narrowly converged He—Cd laser light onto a diffraction grating pattern area 6 of 1-mm square in the above-mentioned standard component and measuring its diffraction angle. Next, a method of calibrating the electron-beam metrology system using the standard component according to this invention will be described. As shown in FIG. 5, a standard component 13 is mounted on the holder 16, and subsequently placed on a stage 14 of the electron-beam metrology system. First, in order that an electron beam 32 emitted from an electron-beam lens-barrel 34 is irradiated on the standard component 13 having a diffraction grating pattern as shown in FIG. 1, the stage 14 is moved. At 100,000× magnification, the electron beam 32 is scanned in the scan position B shown in FIG. 1, and a secondary electron signal waveform is obtained with a secondary electron detector 33. FIG. 9 shows a secondary electron signal waveform 17 obtained. A pitch dimension a of the diffraction grating is found from this secondary electron signal waveform 17. Similar measurements are conducted at ten or more points on the same standard component, and the average of the pitch dimension is calculated. This average value is converted to a value of a pitch dimension of 200.00 nm that was found from the optical diffraction angle, whereby the electron-beam metrology system can be calibrated at 100,000× magnification. Next, the pitch dimension b between two diffraction grating patterns that exist in the same field of view is found at the same 100,000× magnification. The pitch dimension b between the two diffraction grating patterns was found 100.05 nm from the secondary electron signal waveform 17 shown in FIG. 9. Next, calibration at 200,000× magnification was performed. At this magnification, since one pitch amount of the diffraction grating 1 shown in FIG. 1 does not fit in deflection of the measuring beam even when the secondary electron signal waveform is obtained by scanning an electron beam onto the diffraction grating pattern, the pitch dimension of the diffraction grating measured optically cannot be found. Then, by scanning an electron beam on the diffraction grating pattern in the scan position B, a secondary electron signal waveform 18 as shown in FIG. 10 was obtained. Since the pitch dimension b was found from this secondary signal waveform 18, calibration of the electron-beam metrology system at 200,000× magnification was able to be performed by converting this value to a value of 100.05 nm that was found at 100,000× magnification. After the calibration, the stage moved the semiconductor pattern formed on a wafer 12 to the measurement position, and the pattern dimension of 67 nm was able to be found by measuring it at 200,000× magnification that is most suitable to dimensional measurement of this pattern and thereby it was successfully checked that high-precision processing relative to a designed dimension 65 nm was achieved. Next, an automatic calibration method of the electron-beam metrology system using the standard component of this invention will be described. As shown in FIG. 5, the standard component 13 for calibration mounted on the stage of the electron-beam metrology system is moved just under the electron-beam lens-barrel 34, and the electron beam 32 is irradiated onto it. Then, the cross marks 7 for sample rotation correction, as shown in FIG. 2, on the right and left sides of the standard component 13 for calibration are detected, a rotation value of a sample pattern with respect to the stage is found, and it is memorized in memory of the metrology system. Next, a horizontal and longitudinal coordinate system is corrected for a sample pattern based on the above-mentioned memorized rotation value, and the stage is moved, the cross marks 3 for alignment arranged at four corners in the surrounding of the diffraction grating pattern 1 shown in FIG. 1 are detected by electron beam scanning of the electron-beam metrology system, and a precise position of each diffraction grating is registered in the electron-beam metrology system. The cross mark 3 for alignment was automatically detected based on the above-mentioned registered data by conducting these operations, a desired pattern within the standard component was detected by pattern recognition, whereby a diffraction grating pattern on any position on the sample was able to be automatically detected with excellent reproducibility and with precision of 50 nm or less. Next, a calibration procedure of movement to a diffraction grating pattern, beam scanning on the diffraction grating, grabbing the secondary electron signal waveform, measurement of the pitch dimension, and conversion thereof to the calibration value was programmed in a control computer of the electron-beam metrology system along with a procedure of the above-mentioned alignment. Thus, a series of steps of the electron-beam metrology system calibration was able to be performed automatically. In this occasion, the system was able to be programmed in such a manner that the number of irradiation of the diffraction grating pattern part onto which the beam was irradiated at the time of calibration was memorized in the above-mentioned program, and when it reached a fixed number, a position of the diffraction grating pattern was changed. In the case where measured values exhibit variation when the same location is used for calibration ten or more times in a preliminary experiment, measurement of the same location may be limited to, for example, about five times, being less than ten times. Since such calibration was performed cyclically and performance was maintained by system management, patterns in almost all areas have been used after one year. By changing it with a new standard component, calibration management was able to be further performed continuously. When the above-mentioned standard component was loaded on another electron-beam metrology system, there was a case where pattern recognition for alignment operated erroneously because the above-mentioned position detection pattern 3 was as fine as 0.5 nm in length. Consequently, large marks 20 each having a line width of 1 μm and a length of 3 μm were arranged so that position detection was able to be done at low magnification of the order of 10,000 times. Concretely, a standard component 5 was produced that has a pattern consisting of the large marks 20 each having a line width of 1 μm and a length of 3 μm are arranged between a diffraction grating pattern 23 and the next diffraction grating pattern, as shown in FIG. 11, in periodical positions by patterning using the electron-beam batch exposure method with an aperture 19 on the stencil mask selected, as shown in FIG. 4. By conducting an alignment operation at 10,000× magnification using this standard component 5, automatic calibration free from pattern recognition error was enabled. Note that in FIG. 11, only one diffraction grating pattern is shown between the mark 20 and the next mark 20, but the following pattern structure may be adopted: the above-mentioned mark 20 is arranged once cyclically after a plurality of diffraction grating patterns 20 continues. Although in this embodiment, the diffraction grating pattern as shown in FIG. 1 was used. However, patterns 21, 22 different from a diffraction grating used for optical diffraction angle measurement, as shown in FIGS. 6 and 7, in pitch dimension or repeating direction produced the similar result. Next, an embodiment of a standard component having a wafer shape will be described. After coating a resist on an 8-inch (100) Si wafer, the aperture 10 on the stencil mask shown in FIG. 4 is chosen. As shown in FIG. 12, a group of patterns 29 that contains longitudinal-direction diffraction grating patterns and marks for position detection are exposed on an area 27 of 1-mm square on a wafer 24 by the electron-beam batch exposure method. Further, an aperture 101 on the stencil mask shown in FIG. 4 is chosen, and a group of patterns 30 that contains a horizontal-direction diffraction grating patterns and marks for position detection are exposed on an area 26 of 1-mm square on the wafer by the electron-beam batch exposure method. Furthermore, an aperture 102 on the stencil mask shown in FIG. 4 is chosen, and a group of patterns 31 that contains in the 45-degree direction horizontal-direction diffraction grating patterns and marks for position detection are exposed on an area 28 of 1-mm square on the wafer 24 by the electron-beam batch exposure method. Next, a step 0.1 μm deep is formed on the Si wafer using these resist pattern by Si dry etching. In this etching, the step that has an angle of 80 degrees or more, close to a vertical plane, was formed in any of cross-sections of the diffraction gratings 29, 30, 31 in the longitudinal, horizontal, and oblique directions. Calibration was performed with the 8-inch wafer-shaped standard component 24 containing these patterns loaded in the electron-beam metrology system. First, the stage 14 is moved so that the diffraction grating pattern 27 in the longitudinal direction of the standard component existing in a position of the wafer 12 of FIG. 5 is just under the electron beam 32. The diffraction grating pattern 27 is scanned horizontally with an electron beam at 50,000× magnification in the scan position A shown in FIG. 1 to obtain a secondary electron signal waveform. FIG. 13 shows a secondary electron signal waveform 32 obtained. Pitch dimensions c1 to c5 are found from intervals of peaks of this secondary electron signal waveform 32, and an average value c of these values is found. This average value was converted to a value of a pitch dimension 200.00 nm found from optical diffraction angle, whereby calibration of the electron-beam metrology system at 50,000× magnification was able to be performed with a fewer number of beam scanning. Next, an electron beam is scanned on two diffraction grating patterns existing in the same field of view at the same 50,000× magnification in the scan position B shown FIG. 1 to obtain a secondary electron signal waveform 33 shown in FIG. 14. A pitch dimension d between the two diffraction grating patterns was found as 100.05 nm from this secondary electron signal waveform 33. Next, the stage is moved so that the diffraction grating pattern 26 existing in a horizontal direction of the standard component 24 is just under the electron beam. At 50,000× magnification, an electron beam is scanned longitudinally to obtain a secondary electron signal waveform. Similarly as in the longitudinal direction, pitch dimensions are found from respective intervals between peaks of this signal waveform and an average value c of these values is calculated. This average value was converted to a value of a pitch dimension 200.00 nm found from optical diffraction angle, whereby calibration of the electron-beam metrology system at 50,000× magnification was able to be performed with a fewer number of beam scanning. Next, from a secondary electron signal waveform obtained by scanning an electron beam on the two diffraction grating patterns existing within the same field of view at 50,000× magnification, the pitch dimension d between the two diffraction grating patterns was found 100.08 nm. Subsequently, the stage is moved in such a way that the diffraction grating 28 whose grating angle lies in a 45 degrees of the standard component 24 is just under the electron beam. At 50,000× magnification, an electron beam is scanned in a 45 degree direction to obtain a secondary electron signal waveform. Similarly, pitch dimensions are found from intervals of respective peaks of this signal waveform, and an average c of these values is found. This average value was converted to a value of a pitch dimension of 200.00 nm that was found from the optical diffraction angle, whereby the electron-beam metrology system was able to be calibrated at 50,000× magnification in a fewer number of scanning. Next, at the same 50,000× magnification, two diffraction grating patterns existing in the same field of view are scanned with an electron beam to obtain secondary electron signal waveforms. From these signal waveforms, a pitch dimension d between two diffraction grating patterns was calculated to be 100.02 nm. In this way, dimensional calibration for beam deflection in a plurality of directions was able to be performed using one standard component. The wafer-shaped standard component was taken out of the system and a wafer on which a semiconductor pattern on which the operator intends to conduct length measurement was inserted therein. A length measurement value in a longitudinal-direction pattern at 50,000× magnification was calibrated with a pitch dimension of 200.00 nm. In the case of higher magnification than the above, calibration was performed with a pitch dimension between diffraction grating patterns (d=100.05 nm). Similarly, for a pattern in the horizontal direction and a pattern in a 45 degree direction, precise length-measured values were obtained based on respective calibration. In this calibration method, the wafer-shaped standard component was kept outside the system, and when calibrating the system, the standard component was inserted into the electron-beam metrology system appropriately and the calibration was performed. In the above-mentioned case, the cross mark was used as a pattern for position detection. However, the similar effect can be obtained in this invention with any pattern as long as it allows a coordinate position of the mark to be specified. Although, in the above-mentioned embodiment, explanation was done by taking as an example the calibration of the electron-beam metrology system, this invention is also applicable to calibration of scanning type probe microscopes, such as an AFM (Atomic Force Microscope) and an STM (Scanning Tunnel Microscope). Moreover, although in the above-mentioned embodiment, length measurement in the horizontal direction was described for the sample mounted on the holder; if two samples produced similarly are arranged in the holder so as to be orthogonal to each other, calibration of length measurement can be performed for patterns in the longitudinal and horizontal directions. As described in the foregoing in detail, according to this invention, the standard component has a dimension less than optically measurable dimension, whereby dimensional calibration of an apparatus for measuring the next generation semiconductor patterns (such as critical dimension of the pattern or size of a pattern edge) that are equal to or less than 100 nm is possible. In addition, by using position detection patterns of the standard component, automatic system calibration is also possible. According to this invention, the electron-beam length measuring technology can be achieved that makes possible calibration of fine dimensions less than a pitch dimension measurable by the optical diffraction angle measurement and automatic calibration; therefore, high-precision length measurement calibration that matches the next generation semiconductor processing can be realized.
	description	The present invention relates to a lithographic apparatus and methods. A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. The lithographic apparatus includes a projection system to project a patterned radiation beam onto the substrate. The projection system may include optical elements, such as mirrors or lenses. The projection system provides for a projection of the patterned radiation beam onto a target portion of the substrate. As accuracy and resolution of the pattern to be projected onto the substrate increases year after year, requirements on accuracy of the projection system increase too. A difficulty associated with a conventional projection system is that a position of the output beam of the projection system and thus a position of an image with respect to the substrate shows a tolerance due to, e.g., vibrations in the lithographic apparatus, tolerances of optical components or other components in the projection system, temperature deviations causing thermal effects such as expansion, drift of one or more sensors involved, and other causes. Further factors influencing a position of the output beam of the projection system include positioning errors of a light source or positioning errors of the patterning device which also may result in a positioning error of the output beam of the projection system. One way to compensate for such errors could be by a displacement of the substrate, thus displacing the substrate to compensate for a position error of the output beam of the projection system irradiating (a part of) the substrate. However, such a solution may only be partly effective, as a positioning of the substrate to compensate for any position errors in the output beam of the projection system is slow as it requires a displacement of the substrate as well as the substrate table by which the substrate is held, and this solution being associated with a positioning (thus acceleration and deceleration) of a part having a considerable mass. It is desirable to enhance a performance of a positioning of the radiation beam as projected by the projection system. According to an embodiment of the invention, there is provided a lithographic apparatus including a projection system configured to project a radiation beam onto a target portion of a substrate; wherein the projection system includes a movable optical element to influence by a displacement thereof a position quantity of the radiation beam as projected by the projection system, the optical element being movable by an optical element actuator; and wherein the lithographic apparatus further includes a projection system control device or projection system controller, operationally connected to the optical element actuator to drive the optical element actuator to influence the position quantity of the radiation beam as projected by the projection system. According to an embodiment of the invention, there is provided a lithographic apparatus including: a projection system configured to project a radiation beam onto a target portion of a substrate, the projection system including two optical elements at least partly determining an optical path of the projection system, a position quantity of one of the optical elements being controllable by a control loop, wherein the lithographic apparatus includes a feed forward control device, the feed forward control device having a feed forward control device input operationally connected to a signal in the control loop of one of the two optical elements, and a feed forward control output operationally connected to an actuator to affect a position quantity of the other one of the optical elements based on the signal of the control loop of the one of the optical elements. According to an embodiment of the invention, there is provided a device manufacturing method including projecting a beam of radiation onto a target portion of a substrate via a projection system, the method including controlling a position quantity of a movable optical element of the projection system to influence a position quantity of the radiation beam as projected by the projection system. According to an embodiment of the invention, there is provided a device manufacturing method including projecting a beam of radiation onto a target portion of a substrate via a projection system, the projection system including two optical elements at least partly determining an optical path of the projection system, a position quantity of one of the optical elements being controlled by a control loop, including affecting a position quantity of the other one of the optical elements based on the signal of the control loop. In the figures, same references and symbols refer to same or similar items. FIG. 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus includes: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or EUV radiation) and a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters. The apparatus also includes a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. The support structure supports, i.e. bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example, if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix. The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”. As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask). Alternatively, the apparatus may be of a transmissive type (e.g. employing a transmissive mask). The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure. Referring to FIG. 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD (not shown in FIG. 1) including, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system. The illuminator IL may include an adjuster AD (not shown in FIG. 1) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO (not shown in FIG. 1). The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. The radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the support structure (e.g., mask table MT), and is patterned by the patterning device. After being reflected on the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the mask MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies. The depicted apparatus could be used in at least one of the following modes: Step mode: the mask table MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at once (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. Scan mode: the mask table MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the mask table MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. Another mode: the mask table MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed. FIG. 2 shows a detailed view of a projection system PS of the lithographic apparatus. In this embodiment, the projection system includes a plurality of mirrors, in this example 4 mirrors, indicated by M1 . . . M4. An incoming beam of the projection system enters the projection system after having been reflected by a suitable part of the patterning device held by the support structure MT is reflected successively by the mirrors M1, M2, M3 and M4 to leave the projection system and irradiate a part of the substrate W held by the substrate table WT. In a practical implementation, the radiation irradiating the substrate W may include a single beam (such as in beam lithography applications) or may include a patterned image (patterned by e.g. a patterning device MA such as a mask, reticle, etc.). In the example shown in FIG. 2, the support (such as the mask table) MT is positioned above the projection system PS, however also other configurations, such as the configuration shown in FIG. 1 where the mask table MT is positioned in a different position, are possible too. The skilled person will however understand the principles as outlined below. According to embodiments of the invention, one or more of the mirrors, and in this embodiment in particular the mirror M4 is movable by an actuator ACT. The actuator may include a position actuator such as an electric or pneumatic motor, a piezo electrical element, etc. The actuator is driven by a positioning system control device Con, or positioning system controller, being adapted to drive the actuator ACT. By changing a position of the mirror M4, a position of the patterned beam as projected by the projection system PS onto the substrate W will change. In the view shown in FIG. 2, a rotation of the mirror M4 in clockwise direction is likely to cause a displacement (in particular a rotation) of a patterned beam OB projected by the projection system PS to the left in a plane of drawing, while a rotation of the mirror M4 in anti-clockwise direction will cause a displacement of the output beam OB on the substrate W to the right in the plane of the drawing. In the example shown in FIG. 2, the mirror M4 forms a movable optical element, however it is also possible that any other element of the projection system PS forms such a movable optical element, such as e.g. any of the mirrors M1-M3. The mirrors M1-M4 together define an optical path along which a beam entering the projection system propagates. A benefit of making use of a movable optical element which is situated, along the optical path in this example defined by the mirrors M1-M4, near an output of the projection system PS, thus along the optical path near the substrate W, is that in general a sensitivity of this mirror is high: In general, this mirror has a large footprint, and therefore a small tilt of the mirror causes a comparably large translation of the output beam with respect to the substrate. Alternatively, any of the other mirrors M1-M3 (or in general terms: any of the optical elements) could be used also, however a smaller sensitivity of such mirror would require a larger tilting thereof which is related to its smaller footprint. In the below, the patterned beam as projected by the projection system will in short be indicated by output beam OB. Due to the high sensitivity of a displacement of the mirror M4, only small displacements thereof are required, thus making a fast correction possible and introducing little vibrations, shocks or other mechanical disturbances due to a displacement of the mirror M4, as its displacement is relatively small. The lithographic apparatus may further include an optical sensor, in this example the line of sight sensor LOS to determine a line of sight through the projection system. The optical sensor provides a position signal representative of the position of the patterned radiation beam as projected by the projection system. The optical sensor is operationally connected (as indicated by the dotted line) to the projection system control device Con or projection system controller. The projection system control device Con is arranged to drive the actuator ACT in dependency on the position signal as provided by the position sensor (in this example the line of sight sensor LOS). The optical sensor may provide a position signal representative of the position of the output beam OB with respect to the projection system PS itself, with respect to the substrate table WT, or with respect to any other reference, such as the metrology frame MF as schematically depicted in FIG. 2. Being provided with the position signal, the projection system control device Con, or projection system controller, is able to drive the actuator ACT to position the mirror M4 such that the output beam OB leaves the projection system PS at a desired position. The desired position may be a desired position with respect to the projection system, with respect to the substrate table WT or with respect to the metrology frame MF or with respect to any other reference. The lithographic apparatus may further include a projection system position measurement device to measure a position of the projection system with respect to a reference, such as the metrology frame MF. Further, the lithographic apparatus may include a substrate table position measurement system to measure a position of the substrate table WT with respect to the metrology frame MF or any other suitable reference. In a practical embodiment, the line of sight sensor provides a position signal representative of a position of the output beam OB with respect to the metrology frame, as the line of sight sensor LOS is mechanically connected to the metrology frame MF. As the position of the substrate table WT with respect to the metrology frame is known too, as it is measured by the substrate table positioning system (not shown), any deviations in the position of the output beam OB with respect to the position of the substrate table WT can be corrected accordingly, according to the invention by setting the position of the movable optical element, in this example the mirror M4. Thus, instead of displacing the substrate table WT to correct for a position error in the output beam OB, the position of the movable optical element is corrected, which can provide for a correction at a much higher bandwidth, as the mass of the mirror M4, or any other suitable optical element, is in most practical embodiments lower than a mass of the substrate table WT. In embodiments in which the displacement of the optical element (such as in this example the mirror M4) includes a rotation, a further benefit comes into existence, being that a rotation of the optical element may require a much lower force as compared to a translation: A translation involves application of a force to the optical element to be translated, the force being equal to its mass times an acceleration of the optical element (in accordance with Newton's Law ). A rotation however involves application of a force with respect to a centre of the optical element to be rotated, which is smaller. Furthermore, a rotation of the optical element alters an optical angle of incidence as well as an optical exit angle, thus having a dual effect on displacement of the output beam. As a result, a rotation of the optical element required a much lower force then a translation thereof to achieve a similar effect on a displacement of the output beam. A still further benefit is that in a practical implementation the optical element (such as the mirror M4) includes a higher dynamic internal stiffness than the substrate table. Thus, a positioning of the mirror to compensate for any displacement of the output beam could be performed with a higher speed (or e.g. a more aggressive control loop) than a positioning of the substrate table to compensate for the displacement. Connections between the control device Con, or controller, and the actuator ACT, and between the control device Con and the line of sight sensor LOS may include any type of suitable connection, such as an analogue connection (e.g. an electrical analogue line), or any type of digital connection (e.g. multiplexed, bus structure, etc). The line of sight sensor may include a sensor such as described in co-pending U.S. patent application 2004/0189966 which is incorporated herein by reference. The sensor (a line of sight sensor or any other sensor) may provide a position signal with respect to any reference. Examples of such a reference include the metrology frame, the projection system, the substrate table etc. In an embodiment where the control device, or controller, is arranged to drive the optical element actuator in dependency on the position signal provided by the sensor, this positioning of the radiation beam as projected by the projection system can therefore take place with respect to any such reference. A projection system including movable optical elements which are capable of influencing a position of an output beam of the projection system are described in EUV Alignment and Testing of a Four-Mirror Ring Field EUV Optical System, K. A. Goldberg et al, EIPBN 2000, EUV Lithography, #172, which is incorporated herein by reference. The movable optical element as referred to in this document may include any movable optical element as described in the literature referred to, instead of or in addition to the examples as described in this document. FIG. 3a-c show control loops, in accordance with embodiments of the invention, providing schematic examples of a control loop as established by the projection system control device Con, or projection system controller, the position actuator ACT, the movable optical element M4, and the line of sight sensor LOS. FIG. 3a shows a control loop including a controller C, a movable optical element, schematically indicated by Pm, and two feed back paths. The controller C includes the projection system control device Con, or projection system controller, as depicted and described with reference to FIG. 2, and Pm in FIG. 3a includes the actuator ACT and the movable optical element, in this example the mirror M4. The item Pm may further include the line of sight sensor LOS and a position sensor sensing a position of the movable optical element, in this example the mirror M4. This sensor is not shown in FIG. 2. The setpoint S in FIG. 3a is provided with a setpoint value representing a position quantity, such as in FIG. 3a a nominal position of the mirror M4. A first feed back path extends from an output signal Xmirror of a position sensor sensing a position of the mirror via a transfer function Hm to the controller C. A second feed back path extends from an output signal XLOS of the line of sight sensor via a transformation TLOS and a transfer function HLOS to the controller C. The transformation TLOS transforms one or more coordinates as provided by the output signal of the line of sight sensor into angular information. Due to the dual feed back paths, an over determined control system may have been created. Interference between the dual control loops is prevented by a suitable choice of transfer functions of the filters HLOS and Hm. The transfer function of Hm may include a low pass filter while the transfer function of HLOS may include a high pass filter, or vice versa. Such a filtering may be implemented in an analogue way or making use of digital filters having a stated frequency characteristic, however it is also possible that such a desired characteristic is obtained by having one of the feed back paths run at a significantly lower sample frequency than the other one of the feed back paths. This not only leads to a simple implementation but also reduces processing load in a numeric implementation including e.g. a microprocessor or other numeric device. Alternatively, it is possible that one of the feed back paths shown in FIG. 3a is implemented in software while the other one is implemented in hardware. Thus, the configuration shown in FIG. 3a offers a flexible way of implementation. FIG. 3a as well as FIGS. 3b and 3c which will be described below each provide an example of a combined control system. If a position of the mirror is altered, XLOS is changed, as a transfer characteristic of the projection system is changed. Thus, a change in a position of the mirror will reflect in a change of the output signal of the XLOS as well as a change of the output signal Xmirror. The control system as described in FIGS. 3a-c each provide a solution to be able to cope with this dependency in the control loop. FIG. 3b shows a control loop which has been modified with respect to FIG. 3a. The output signal XLOS is led to a transformation TLOS, which may be the same as the transformation TLOS in FIG. 3a. Then, the output signal of the transformation TLOS as well as the position of the mirror Xmirror are both provided to a transfer represented by a transfer function HS. The transfer function HS includes a dual input transfer function. The transfer function HS may include a hardware filter or may be implemented in software. With reference to FIG. 3a, it was described that the transfer function of HM and the transfer function of HLOS may differ, e.g. one including a low pass filter characteristic while the other one including a high pass filter characteristic. In the same manner, the transfer function of the HS in FIG. 3b may differ depending on the input: a transfer function from the input Xmirror to the output may, e.g., include a low pass filter characteristic while a transfer function from the transformed line of sight information may include a high pass filter characteristic or vice versa. An advantage of the configuration as shown in FIG. 3b as compared to the configuration shown in FIG. 3a is that the configuration in FIG. 3b is more simple to implement. FIG. 3c shows yet another alternative for the control loop as depicted in FIGS. 3a and 3b. In FIG. 3c, the signal XLOS as provided by the line of sight sensor is also provided to a transformation TLOS, which may be identical to the transformation TLOS shown in FIGS. 3a and 3b. To avoid any over-determination in the control loops, the signal Xmirror comprises a signal in 4 degrees of freedom at maximum. Thus, instead of providing a signal Xmirror in 6 degrees of freedom, supplemented by a signal XLOS including 2 degrees of freedom and thus resulting in an over-determined system, information regarding 2 degrees of freedom is left away in the signal Xmirror. In a practical implementation, the signal XLOS includes a rotation information with respect to two rotation axes of the mirror M4. To prevent over-determination, the signal Xmirror includes at maximum 4 degrees of freedom, e.g. not including the rotation information of the mirror around the two axes as is provided by the signal XLOS. An advantage of the configuration as depicted and described with reference to FIG. 3c is that it allows for a more simple implementation, as the dual input filter HS to filter out a part of the information provided by Xmirror, and XLOS is not required any more and fewer sensors are required. In the configuration depicted in FIG. 3c, a further filter may be included in the feed back path (not depicted). Summarizing, each of the examples of control loops as depicted in FIGS. 3a-3c will attempt to position the movable optical element such that the output beam of the projection system leaves the projection system at a predetermined position with regard to a reference. The predetermined position is influenced by a signal provided to the setpoint input S. As described with reference to FIG. 2, the line of sight sensor (or any other suitable sensor) may provide a position information with reference to the projection system, or e.g. the metrology frame MF. If in the control loops as depicted in FIGS. 3a-3c, the line of sight sensor provides a position information with reference to the projection system itself, the control loops will tend to control the output beam with respect to the projection system itself, and in case that the line of sight sensor provides a position information with respect to the metrology frame as a reference, then the control loops depicted in FIGS. 3a-3c will attempt to control the position of the output beam with respect to the metrology frame. The additional possibilities offered by a distance measurement between projection system and metrology frame and a distance measurement between substrate table and metrology frame are further explained with reference to FIG. 4. In the highly schematic view of a part of the lithographic apparatus, as depicted in FIG. 4, a first distance measuring system is shown, measuring a distance between the projection system PS and the metrology frame MF, the distance being indicated by A, the distance measuring system being indicated by DMA. Likewise, a second distance measuring system DMB is shown measuring a distance B between the substrate table WT and the metrology frame MF. The distance information as provided by the distance measurement system DMA and DMB, are provided to the projection system control device Con, or projection system controller. It is possible that the distances A and B as measured by the respective distance measurement systems are each provided to the control device Con separately, however it is also imaginable that the distance information are combined, e.g. by a subtraction, a difference between the distances A and B being provided to the control device Con. The projection system control device Con, or projection system controller, is thus provided with information concerning the detected position of the substrate, as represented by the measured distance B, possibly in combination with the measured distance A. As shown in FIG. 4, the control device Con further includes a position information setpoint input PSP, indicated as position setpoint in the below. The position setpoint PSP provides to the control device Con a position setpoint information of the substrate. The position setpoint information may include a desired position of the substrate table WT (a positioning of the substrate table WT with respect to the projection system PS will result in a positioning of the substrate W with respect to the patterned output beam of the projection system), but may also include another position information, such as a desired position of the patterned output beam. The position setpoint information thus provides a position information representing a desired position at which the output beam is to irradiate the substrate. For a description of the actuator ACT, the movable mirror M4, and the line of sight sensor LOS, reference is made to FIG. 2. With the aid of the position setpoint input PSP, a position information is provided to the control device Con. The position setpoint provides setpoint information related to a position of the output beam OB with respect to the substrate W, or provides any other position related information. Should, e.g., an actual position of the substrate (as measured by the measurement system DMB) not coincide with a position information as supplied to the position setpoint input PSP, then according to the invention the control device Con drives the actuator ACT to position the mirror M4 such that a position of the output beam OB is amended to correct for the position error of the substrate W. According to the state of the art, the substrate table WT is positioned by a coarse positioning system, commonly indicated as long stroke (i.e. a positioning system including a long stroke actuator) and a fine positioning system, commonly indicated as short stroke (i.e. comprising a short stroke actuator). A coarse positioning of the substrate table is thus provided by the long stroke actuator and associated positioning system while a fine positioning is provided by the short stroke actuator. The set up as described with reference to FIG. 4 now makes it possible to substitute a part of the positioning function of the short stroke actuator and long stroke actuator, or its positioning function in its entirety, by a positioning of the output beam OB as described with reference to FIG. 4. It is imaginable that the fine positioning as currently implemented by the short stroke actuator and related positioning system may be abandoned, thus only the coarse positioning of the substrate making use of the long stroke actuator and related positioning system being provided, a function of the fine positioning of the substrate table being accomplished by a positioning of the mirror M4 as described with reference to FIG. 4, thus effectively fine positioning the output beam OB with respect to the substrate W instead of fine positioning the substrate W with respect to the output beam OB. An advantage of a positioning of the mirror M4, thus a positioning of the output beam to replace a fine positioning of the substrate table WT, is that a mass of the mirror M4 (or of another suitable optical element) is in general smaller, than a mass of the substrate table WT holding the substrate W, thus enabling a significantly faster positioning and allowing to counteract any positioning disturbances within a significantly larger frequency band. Also, other advantages as described above and being related to rotation instead of translation, and being related to the dynamic stiffness of the to be displaced mirror, are applicable too. As a displacement of the mirror M4 effectively results in a change of an optical imaging of the projection system PS, i.e. a change of the optical transfer characteristic of the projection system PS, a situation may occur where the substrate W, at the location where it is irradiated by the output beam OB, is not in the focus plane of the projection system PS due to the amended transfer characteristic of the projection system by a change of the position of the mirror M4. Further, other optical effects might occur due to a change in the position of the mirror M4. Also, due to a displacement of the mirror M4 from is nominal position, a change of a length of the optical path from the mirror M4 to the substrate W might change. To compensate this, it is possible to provide for a displacement of the mask table MT (and possibly also other elements such as one or more other mirrors), thus effectively displacing the mask MA. To accomplish this, suitable position actuators for displacing the mask table MT might be included (not shown in FIG. 4), as well as a suitable position control system (also not shown in FIG. 4). Thus, a displacement of the mirror M4 changing an optical output parameter of the projection system PS may be compensated for by an appropriate displacement of the mask table MT to displace the mask MA. In a current, common implementation, the projection system comprises a 4:1 projection system, in which case a displacement of the mask table MT and a displacement of the substrate table WT (or instead thereof a displacement of the mirror M4 having a comparable effect) will be in a related 4:1 relationship to each other. FIG. 5 shows a symbolic control scheme of the control system as depicted and described with reference to FIG. 4. The control scheme comprises a first part consisting of the controller Cmirror, as well as the actuator and movable mirror M4, a transfer function of which being schematically indicated by Pm, and two feed back paths respectively including a transfer function Hm and a transfer function HLOS supplemented by a transformation TLOS. This first part substantially corresponds to the control scheme as depicted in FIG. 3a. This part might also be replaced by the control schemes as depicted in FIG. 3b resp. 3c. The control scheme as depicted in FIG. 5 further includes a second part including a wafer stage position controller Cws and a wafer stage actuator plus wafer stage, a transfer function of which being schematically indicated by Pws. The second part is provided with a wafer stage setpoint WTSP information at a wafer stage setpoint input. The first part of the control scheme depicted in FIG. 5 thus controls the movable mirror M4 in a manner similar to the one described with reference to FIGS. 3a-3c, while the second part includes a position control system for controlling a position of the substrate table as is known in the art. The control scheme depicted in FIG. 5 further includes a path from the second part to the first part. This path starts at an error signal of the substrate table control loop, i.e. an input of the controller Cws. The path includes an actuator feed forward path from the error signal of the substrate table position control loop (i.e. the second part) to the actuator of the movable mirror M4, this path being formed by Tws and Hwsff. This feed forward path provides for an immediate compensation, i.e. a position error of the substrate table, as present at the input of the controller Cws results in a feed forward correction of the position of the mirror M4 via the feed forward path, thus a position error of the substrate table being compensated by a suitable alteration of the position of the mirror M4. The feed forward path also includes a setpoint feed forward path including Tws and Hwspos. The position of this setpoint feed forward path prevents that a change of position of the mirror M4 effectuated via the actuator feed forward path is counter acted by the feed back loops of the first path of the control scheme of FIG. 5. The actuator feed forward path thus enables a fast feed forward correction while the setpoint feed forward path provides for an accurate, steady state feed forward correction. As has also been remarked with reference to FIG. 2 and FIGS. 3a-3c, the control systems as depicted in FIGS. 4 and 5 may also consist of a control system in up to 6 degrees of freedom, i.e. although only a single line, a single actuator, a single sensor, a single setpoint signal, a single controller, etc. has been depicted, all these elements might be present in up to 6 fold for a positioning, position correction, etc. in up to 6 degrees of freedom. FIG. 6 shows a schematic view of a projection system PS of a lithographic apparatus according to a further embodiment of the invention. Mirrors M1-M4 defining an optical path through the projection system PS may, but need not necessarily be identical or similar to the ones described with reference to FIGS. 2 and 4. In addition to the projection system as shown in FIGS. 2 and 4, FIG. 6 also shows a position control system for another mirror, in this example being mirror M2. The position C2 to control a position of the mirror M2 based on a position data as provided by the sensor S2, and an actuator ACT2 to position the mirror M2. The actuator (which may include a motor, piezo electric actuator or any other suitable positioning device) is driven by the controller C2. The position controller system may also include a setpoint input to provide a setpoint position, i.e. a desired position, to e.g. the controller C2 thus offering a setpoint to the position control loop. The position control loop of mirror M2 serves to stabilize the mirror M2, i.e. to counter act any disturbances, such as caused by mechanical vibrations of the lithographic apparatus or a part thereof, etc. The signal which is supplied by the controller C2 to the actuator ACT2 is substantially proportional to a force by the actuator ACT2 on the mirror M2. The force acting on the mirror M2 is substantially proportional to a disturbance within a frequency range within which the position control loop of the mirror M2 is active. The signal provided by the controller C2 to the actuator ACT2 can be applied within a frequency range of the position control loop of the mirror M2 as a measure for a magnitude of the disturbance. In a lithographic apparatus, at least a part of the disturbance accelerations on the projection system PS, and in particular on the mirrors thereof, is common to all mirrors, in other words: a mirror M2 is subjected to a certain disturbance, then most likely one or more of the other mirrors, such as the mirror M4 will likely be subjected to a same disturbance. In a projection system such as the one depicted in FIG. 6, the sensitivity of the mirror which is, along the optical path through the projection system, more near to an output of the projection system then to an input of the projection system, is higher (The remarks on sensitivity in the description to FIG. 2 are applicable to the embodiment described here also). A signal which provides an indication of a force to be exerted by an actuator on a mirror to compensate for any disturbances, may be applied as a feed forward correction to correct a position quantity of another one of the mirrors, as the other one of the mirrors is likely to be subject to a same or similar acceleration, disturbance, etc. Advantageously, the correction is applied to mirror M4, providing for an effective correction due to its high sensitivity. In the example shown in FIG. 6, a signal substantially proportional to an acceleration of mirror M2 may be used. However a signal related in any way to an acceleration of this mirror or of any other optical element in the projection system, such as any of the other mirrors, might be applied too. Similarly, instead of applying the feed forward to correct a position of the mirror M4, a position or other position quantity of any other optical element in the projection system might be corrected instead thereof or in addition thereto. As depicted in FIG. 6, a feed forward path is created from an input of the actuator ACT2 of the mirror M2 to an acceleration estimator AE. The acceleration estimator includes a transfer function which includes, in this implementation a factor equal to a quotient of a mass of mirror M2 and a mass of the mirror M4, as according to Newton's law force and acceleration are interrelated to each other dependent on the mass of the optical element in question. In addition thereto, the acceleration estimator AE may also include suitable filtering to filter e.g. undesired frequency components out of the signal provided to the acceleration estimator AE. The acceleration estimator might also include a further input (not shown) which is connected to a setpoint input of the position control loop of the second mirror, enabling the acceleration estimator to prevent to give an output signal (and hence to provide a feed forward signal to the mirror M4) when a setpoint of the second mirror changes or has changed, as such change of setpoint may also result in forces acting on the mirror in question and thus will also provide a signal to the acceleration estimator. To thus prevent that such forces would also lead to a feed forward to the other optical element, i.e. in this example the mirror M4, the transfer function of the acceleration estimator is chosen such that a change in the reference signal and hence a change on a reference signal input (not shown) of the acceleration estimator AE, will counter act, seen from a perspective of an output of the acceleration estimator AE, a signal provided to the acceleration estimator by the acceleration estimator input which is provided with a signal derived from a signal provided by the controller C2 to the actuator ACT2, the latter signal being in response to a change on the reference input of the position control loop of the second mirror M2. The acceleration estimator may be implemented in analogue electronics, may include a digital, numeric implementation or any other suitable implementation. As shown in FIG. 6, the output of the acceleration estimator may act directly on the actuator ACT4 of the mirror M4, however it is also imaginable that the output signal of the acceleration estimator is amplified, filtered or subjected to any other suitable transfer function before being supplied to the actuator ACT4 of the mirror M4. Mirror M4 may also be controlled by a position control loop including a sensor, controller and actuator similar to the one described with reference to mirror M2. In that case, the signal as provided by the acceleration estimator may be fed into the position control loop of mirror M4 by supplying a feed forward signal to an input of the actuator of the position control loop of mirror M4 (e.g. actuator ACT4) and supply a suitable signal derived from the output of the acceleration estimator AE to a setpoint input of the position control loop of the mirror M4. The signal provided to the actuator of the position control loop of mirror M4 will provide for an immediate response of the actuator driving the mirror M4 in reaction to a signal provided by the acceleration estimator AE, and the signal provided to the setpoint input of the position control loop of the mirror M4 will prevent that a feed forward has provided to the actuator input will be compensated by the position control loop of M4 itself. Thus, with the feed forward as described with reference to FIG. 6, no physical accelerometers are required to measure a vibration level of the projection system, as—at least within a certain frequency band—such accelerations are derived from a signal provided to an actuator of one of the optical elements, in this example the mirror M2. Furthermore, as commonly a noise level of a position control loop of the mirrors is low, and the mass of the mirrors may be high, a quality of the acceleration signal thus derived is to be considered good. Consequently, accelerometers which tend to increase a mass of the projection system and which require a certain building volume may be avoided, thus reducing a total mass and volume of the projection system. Also, in case that the lithographic apparatus would make use of a vacuum environment in which the projection system would be placed, further advantages become apparent as sensors and cables of such accelerometers tend to gas out contaminating such a vacuum environment. The acceleration estimation as described with reference to FIG. 6 may not only be provided for a single degree of freedom, that is applicable to up to 6 degrees of freedom, in which case a plurality of actuators, a plurality of acceleration estimators, etc. may be applied. The projection system as described with reference to FIG. 6 thus includes a feed forward control device, or feedforward controller, (i.e. in this example the acceleration estimator AE) an input of the feed forward being connected to a signal in a control loop of one of the optical elements (i.e. in this example the position control loop of M2), an output of the feed forward being connected to an actuator of another optical element (in this example the actuator of the mirror M4) to effect a position quantity thereof. Thus, with the projection system as described with reference to FIG. 6, an optical transfer characteristic thereof can be improved, as a correction signal to correct a disturbance, acceleration, etc. on one of the optical elements may be used to derive a feed forward signal to correct a position of another one of the optical elements of the projection system. For an optimum correction, an output beam sensitivity (i.e. a displacement of the output beam as a result of a displacement of the respective optical element) of the other one of the optical elements, i.e. the optical element corrected by the feed forward, should be larger than such output beam sensitivity of the one of the optical elements, i.e. the optical elements of which the acceleration signal is derived. A first device manufacturing method according to an embodiment of the invention will now be described with reference to FIG. 4: the method includes projecting a patterned beam of radiation (in this example the output beam OB) onto a target portion of the substrate W via the projection system PS. The method includes controlling a position of a movable optical element of the projection system (in this example the position of the mirror M4) to influence a position of the patterned radiation beam OB as projected by the projection system. The method may further include detecting a position of the substrate (in FIG. 4 by the measurement system DMB), providing a position information representing a desired position at which the patterned output beam is to irradiate the substrate (i.e. via the position setpoint PSP), and driving the optical element actuator (in this example actuator ACT of mirror M4), making use of the position information and the detected position of the substrate, to position the movable optical elements (in this example M4) to irradiate the substrate substantially at the desired position. The invention further includes a device manufacturing method which will be explained with reference to FIG. 6. The method includes projecting a patterned beam of radiation OB onto a target portion of the substrate W via the projection system PS. The projection system comprises two optical elements (in this example M2 and M4) at least partly determining the optical path of the projection system PS. The method further includes controlling a position quantity of one of the optical elements (in this example the mirror M2) by a control loop (in this example the position control loop of M2) and affecting a position quantity of the other one of the optical elements (in this example the mirror M4) based on a signal derived from the control loop (thus in this example the input signal of the actuator in the control loop of mirror M2). The position quantity may include a position, velocity, acceleration, etc. For both methods according to embodiments of the invention, the same or similar benefits hold and the same or similar preferred embodiments are possible as described with reference to the lithographic apparatuses according to the invention as described above. In the exemplary embodiments described above, a position of the output beam of the projection system is influenced. Within the scope of the invention, it is not only possible to influence the position of the output beam, however it is also possible to influence any position quantity in general. In this document, the term position quantity may include a position, a velocity, an acceleration, a jerk or any other position related quantity. Thus, the influencing of the position quantity of the radiation beam as projected by the projection system may include influencing of a position, velocity, acceleration, jerk etc. thereof. Hence, where in the above description the term position is used, this can also be interpreted as to comprise a velocity, acceleration, jerk etc. as well. Furthermore, where in this document the term position quantity, positioning, moving, displacing or any related or similar term is used, e.g. when referring to the movable optical element or when referring to the patterned radiation beam or output beam, this is to be interpreted as a position quantity, movement, etc. in respect to any one or more degrees of freedom. In particular, in an embodiment, the position quantity of the movable optical element will be set by the actuator ACT in 6 degrees of freedom, i.e. a position quantity in a three dimensional coordinate system as well as rotational position quantities with respect to all axes of the coordinate system. To achieve this, the actuator ACT may include a plurality of actuator devices, e.g. 6 independent actuators. Further, the wording change a position quantity of a beam, influence a position quantity of a beam or displace a beam are to be understood as a change of position quantity or direction of the beam in any degree of freedom, thus including any translation, any rotation as well as any combination of one or more translations and rotations. The terms displacement, movement, change of position etc. may thus include any type of displacement, movement, change of position etc. including a rotation around any axis, a translation in any direction and/or any combination of translations and/or rotations. The lithographic apparatus according to an embodiment of the invention may include a patterning device, the projection system projecting a patterned beam onto the substrate, however other implementations are possible too, including applications where a non patterned beam scans a target portion of the substrate, ‘writing’ a pattern on it by suitable movements of the beam. The idea according to the invention may be applied in any kind of these lithographic apparatuses. The movable optical element may include any type of optical element including a lens, a mirror or any other transmissive and/or reflective element to influence any parameter of a beam, such as its direction, convergence, divergence, spatial distribution or any other optical parameter. The movable optical element may be movable in any degree of freedom, comprising e.g. a translation in any direction, a rotation with respect to any axis or any combination of translation(s) and/or rotation(s). The influencing of the position quantity of the radiation beam as projected by the projection system may include an influencing of any position quantity parameter of the radiation beam including its position quantity and/or direction with respect to any coordinate system. Further, the influencing of the position quantity of the radiation beam may include any rotation of the beam with respect to any axis. The optical element actuator may include any type of actuator constructed to have effect on a position quantity of the optical element, including a pneumatic or electric motor, a piezo electric actuator, etc. The movable optical element may be movable with respect to the projection system in which it is comprised and/or with respect to any part thereof. The sensor to provide the position quantity signal representative of the position quantity of the radiation beam may include any type of sensor, including e.g. an optical sensor such as a line of sight sensor a camera and may derive the position quantity signal from a position quantity of the radiation beam and/or from a position quantity of any other optical beam, such as a measurement as applied in the line of sight sensor. Alternatively, any other sensor, sensing device or other data collection device to determine a signal representative of the position quantity of the radiation beam may be applied. The projection system control device, or projection system controller, may include suitable hardware, such as analogue and/or digital electronics, and/or may partly or fully be implemented in software comprising suitable software instructions to, when executed on a programmable device such as a microcomputer, microcontroller, digital signal processor etc., perform a function as specified in this document. The same remarks as made here with reference to the projection system control device are also applicable to any other control device mentioned in this document, such as the feed forward control device. The term projection system control device as used herein can also be considered or termed as a projection system controller. Similarly, the term feed forward control device can also be considered or termed as a feed forward controller. Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers. Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured. The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams. The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components. While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.
	abstract	A molded hunting blind includes a one piece molded body. The molded hunting blind also includes a molded door and a plurality of windows at least one archery door with a taper configured to limit movement or at least one gun door with a gun rest and an arm rest. A method to mold a one piece hunting blind body is also described.
047926929	summary	DESCRIPTION A dental irradiation apparatus comprising a lamp for producing a convergent beam of radiation and an optical waveguide having an entrance surface disposed wtthin the beam and an exit surface adapted to be oriented with respect to a location to be irradiated is known from German Offenlegungsschrift No. 2,507,601. The optical waveguide provided in that apparatus has a constant diameter over its substantial length which, in practice, is about 8 mm, and the waveguide is bent near its exit end by an angle of about 60.degree. and has at its tip a conical portion of decreasing diameter. A similar irradiation apparatus without such a tapering tip portion is disclosed in U.S Pat. No. 4,298,806. The known apparatus permit photopolymerizable tooth fillings to be cured in situ by occlusal irradiation. Radiation-settable materials are known to shrink during polymerization at a degree which increases with the polymerization temperature. Since the filling material always shrinks towards the source of radiation, there is a tendency for the material to lift off the bottom and/or the sides of the cavity in case of a purely occlusal irradiation. This tendency may be counteracted by irradiating the filling material disposed in the cavity from the bottom or sides of the cavity. To this end, it is necessary either to penetrate the tooth itself with radiation of a correspondingly high intensity or, in case of multi-facial fillings, to apply the radiation totthe filling material from an interdentalapical position Either way of irradiation is practically impossible with the conventional optical waveguides It is an object of the present invention to devise a dental irradiation apparatus with an optical waveguide which enaables irradiation of individual dental areas in situ from any desired direction at an intensity which is sufficient to cure photopolymerizable fillings starting from the cavity walls. To meet with this object, the dental irradiation apparatus according to the present invention includes an optical waveguide having an entrance surface disposed in a convergent beam of radiation produced by a lamp and an exit surface adapted to be oriented with respect to the location to be irradiated, the angle of convergence being smaller than approximately 30.degree. with respect to the optical axis defined by the lamp, and the waveguide being conically shaped over a substantial part of its length with a diameter decreasing from the entrance surface to the exit surfcce. On account of the angle at which the radiation enters the optical waveguide and also because of the taper of the waveguide and the increased radiation divergence resulting therefrom, a substantially semi-spherical lobe of approximately constant radiation intensity is achieved at the exit surface of the waveguide; as a consequence, the end of the waveguide may be placed in practically any desired orientation with respect to the location to be irradiated while the material is still reliably cured. This is of great significance in view of the limited space, particularly in interdental areas or in case of curing distal molar fillings. Because of the constant radiation density, there is no danger of the filling material being exposed to excessive radiation intensity and thus overheated, inspite of large irradiance. If transparent interdental wedges are used, a very large amount of radiation may be coupled into the small axial end face of the wedge which radiation is emitted by the lateral wedge surfaces to cure filling material starting from a proximal-apical region. While the entrance surface may have a sufficient cross-section to receive a corresponding amount of irradiance, the exit surface of the optical waveguide according to the present invention is comparatively small, thereby permitting direct irradiation of interdental areas which cnnnot be reached by conventional waveguides. Due to the decrease in diameter, high intensity radiation is obtained at the exit surface which penetrates even relatively thick dentin layers. In the interior of the tooth, starting from the cavity walls, an intensive curing of the filling material is achieved, which strongly adheres to the tooth wall. German utility model specification No. 8,504,351 discloses an optical waveguide for a dental irradiation apparatus which has a portion conically tapering from an entrance surface. This portion, however, is followed by a portion increasing in cross-section towards an exit surface which is larger than the entrance surface. This waveguide serves to irradiate larger surfaces with parallel light as uniformly as possible, and it is ipportant in the practical use of this waveguide that the exit surface be placed on the surface to be cured in a substantially flush manner. In a preferred embodiment of the invention, the material of the waveguide has a refractive index ratio with respect to the invironment of greater than about 1.3, preferably about .sqroot.2. The radiation emitted by the lamp may thus have a great angle of convergence without being totally reflected at the exit surface. A great angle of convergenee of the radiation beam emiteed by the lamp is advantageous in that, in case a substantially point-shaped source of radiation is used with an ellipsoidal reflector, the reflector may be comparatively short in the direction of the optical axis, while utilizing a given portion of the overall radiation produced. When the refractive index is about .sqroot.2, a substantially semi-spherical lobe of radiation is actually achieved at the exit surface. With a smaller refractive index the exit angle also decreases. In another preferred embodiment of the invention, the ratio of the diameter of the exit surface to that of the entrance surface ranges from about 0.5 to about 0.2 and is preferably about 0.3, with the diameter of the entrance surface being about 10 mm, that of the exit surface about 3 mm, and the length of the waveguide being about 100 mm. With these dimensions, a waveguide is achieved which is easy to handle in practice and which can be used in connection with available lamps and irradiation apparatus, while a reasonable portion of the overall amount of available radiation is utilized. Preferably, a portion of the waveguide close to its exit surface is bent about an angle of approximately 60 to 90.degree., preferably 75.degree.. With this shape, even such dental areas which are difficult to access can be sufficiently irradiated. In order to avoid radiation to exit from the peripheral surface of the bent waveguide portion, the diameter of that portion is essentially constant. In a furteer preferred embodiment of the invention, the exit surface of the waveguide is crowned, and the tapering of the waveguide in a portion immediately before the exit surface is more pronounced than over its remaining length to enable placing the radiation spill closer to fillings in interdental spaces. At the same time, a drop of radiation intensity in the vicinity of an angle of 90.degree. with respect to the optical axis is avoided near the exit surface, as far as possible.
	summary
	claims	1. A multi-beamlet multi-column particle-optical system comprising a plurality of particle-optical multi-beamlet columns,the plurality of particle-optical multi-beamlet columns being disposed in an array for simultaneously exposing a same substrate;with each particle optical column having an optical axis and comprising:a beamlet generating arrangement comprising at least one multi-aperture plate having a plurality of apertures for generating a pattern of multiple beamlets of charged particles, andan electrostatic lens arrangement downstream of the beamlet generating arrangement, the electrostatic lens arrangement comprising at least one electrode element,the at least one electrode element having an aperture allowing the generated multiple beamlets of charged particles to pass through, the aperture being defined by an inner peripheral edge facing the optical axis, the aperture having a centre and a predetermined shape in a plane orthogonal to the optical axis;wherein in at least one of the plurality of charged particle columns, the predetermined shape of the aperture of the at least one electrode element is a non-circular shape with at least one of a protrusion and an indentation from an ideal circle about the centre of the aperture, andwherein a first distance between a point on the inner peripheral edge of the aperture disposed closest to the centre of the aperture is at least about 5% smaller than a second distance between a point on the inner peripheral edge of the aperture disposed furthest away from the centre of the aperture. 2. The particle-optical system according to claim 1, wherein the electrode element comprises an annular inner electrode member having an inner peripheral edge and wherein the aperture is formed by the inner peripheral edge. 3. The particle-optical system according to claim 1, wherein the electrostatic lens arrangement of the at least one of the plurality of charged particle multi-beamlet columns comprises two or more electrode elements which are disposed coaxially and spaced apart in the direction of the optical axis. 4. The particle-optical system according to claim 3, wherein the apertures of the at least two electrode elements have substantially the same non-circular shape. 5. The particle-optical system according to claim 4, wherein the aperture of a first electrode element of the at least two electrode elements has an area that is by at least 5% larger than an area of the aperture of a second electrode element of the at least two electrode elements. 6. The particle-optical system according to claim 1, the plurality of columns comprising a first group of columns comprising at least one column, wherein the aperture of the at least one electrode element of the electrostatic arrangement of each column of the first group of columns has a first shape, and further comprising a second group of columns comprising at least one column, wherein the aperture of the at least one electrode element of the electrostatic arrangement of each column of the second group of columns has a second shape that is different from the first shape. 7. The particle-optical system according to claim 6, whereinthe first shape is different from the second shape with respect to at least one of a number of indentations, a number of protrusions, a shape of a protrusion, a shape of an indentation, a size of a protrusion, a size of an indentation, a symmetry of the shape and any combination thereof. 8. The particle-optical system according to claim 6, whereineach column of the first group of columns is surrounded by a first configuration of neighbouring columns and each column of the second group of columns is surrounded by a second configuration of neighbouring columns, and wherein the first configuration is different from the second configuration. 9. The particle-optical system according to claim 8, wherein the first configuration differs from the second configuration with respect to at least one of a number of neighbouring columns disposed closest to the respective column, a number of neighbouring columns disposed second closest to the respective column, a symmetry of the configuration of neighbouring columns and any combination thereof. 10. The particle-optical system according to claim 1, wherein the non-circular shape comprises a shape having one, two or four indentations extending from an ideal circle towards the centre of the aperture, the ideal circle having a radius equal to the second distance. 11. The particle-optical system according to claim 1, wherein each column has at least one closest neighbouring column and at least one second closest neighbouring column, and wherein a number of indentations in the shape of the aperture of the at least one electrode element of at least one column is equal to a number of second closest columns around the at least one column, with the indentations extending from the ideal circle towards the centre of the aperture, the ideal circle having a radius equal to the second distance. 12. The particle-optical system according to claim 1, wherein the particle-optical multi-beam columns are arranged in a rectangular array of N rows 1 to N and M lines 1 to M orthogonal to the rows,wherein a third group of columns is comprised of columns disposed in line 1, rows 2 to N−1, and line M rows 2 to N−1, and in row 1, lines 2 to M−1 and row N, lines 2 to N−1, and wherein the apertures of the at least one electrode element of the electrostatic arrangement of each column of the third group of columns have a same third shape. 13. The particle-optical system according to claim 1, wherein the particle-optical multi-beam columns are arranged in a rectangular array of N rows 1 to N and M lines 1 to M orthogonal to the rows,wherein a fourth group of columns is comprised of columns disposed in line 1, row 1, in line 1, row N, in line M, row 1 and in line M row N,and wherein the apertures of the at least one electrode element of the electrostatic arrangement of each column of the fourth group of columns have a same fourth shape. 14. The particle-optical system according to claim 1, wherein the particle-optical multi-beam columns are arranged in a rectangular array of N rows 1 to N and M lines 1 to M orthogonal to the rows,wherein a fifth group of columns is comprised of columns disposed in lines 2 to M−1 in respective rows 2 to N−1,and wherein the apertures of the at least one electrode element of the electrostatic arrangement of each column of the fifth group of columns have a same fifth shape. 15. The particle-optical system according to claim 1, wherein the at least one electrode elements of the electrostatic arrangements of neighbouring columns have a same distance from a substrate plane and are arranged on a mounting structure extending substantially in a plane orthogonal to the optical axes of the neighbouring columns. 16. The particle-optical system according to claim 1, further comprising a first and a second mounting structure,wherein the optical axes of columns disposed adjacent to one another are arranged in parallel,wherein each of the adjacent columns comprises two or more electrode elements with a first electrode element and at least a second electrode element being arranged coaxially and spaced apart in the direction of the optical axis of the column,wherein the first electrode elements of the adjacent columns have a same first distance from a substrate plane and are arranged on the first mounting structure,wherein the second electrode elements of the adjacent columns have a same second distance from the substrate plane and are arranged on the second mounting structure, the first and second mounting structures being arranged parallel to one another in a plane orthogonal to the optical axes of the columns. 17. The particle-optical system according to claim 16, wherein the first and second mounting structures are spaced apart by electrically insulating spacer elements. 18. The particle-optical system according to claim 3, wherein the electrode elements further comprise a substantially cylindrical shielding member, the substantially cylindrical shielding member having a radius equal to or greater than the second distance. 19. The particle-optical system according to claim 1, wherein the aperture is shaped and arranged such as to provide multi-pole correction for electrostatic fields generated within the electrode arrangement. 20. The particle-optical system according to claim 1, wherein each beamlet generating arrangement comprises a charged particle source for generating a beam of charged particles, and a beam patterning structure downstream of the charged particle source, the beam patterning structure comprising at least the multi-aperture plate and being configured to blank out at least a portion of the charged particle beam such that a pattern of multiple beamlets is formed downstream of the patterning structure. 21. The particle-optical system according to claim 1, wherein the centre of the at least one aperture of the electrode element of the electrostatic lens arrangement of a first column is disposed at least 50 mm from the centre of the at least one aperture of the electrode element of the electrostatic lens arrangement of a second column, with the second column being arranged closest to the first column in the array of multi-beam charged particle columns. 22. The particle-optical system according to claim 1, wherein the shape of the aperture is asymmetric with respect to the optical axis of the respective multi-beam particle-optical column. 23. The particle-optical system according to claim 1, wherein the centre of the aperture is disposed on the optical axis of the respective multi-beamlet particle-optical column. 24. A method of exposing a substrate by multi-beam multi-column exposure, comprising:generating a plurality of multiple beamlet patterns by a respective plurality of multi-beamlet particle-optical columns of the particle-optical system according to claim 1 and directing the plurality of multiple beam let patterns towards a substrate to be exposed;generating electrostatic fields by applying electric potentials to the at least one electrode elements of the electrostatic lens arrangements of the plurality of multi-beamlet particle-optical columns,transmitting the multiple beamlet patterns through respective apertures of the electrode elements of the electrostatic lens arrangements of the plurality of multi-beamlet particle-optical columns.
039487245	claims	1. A device for handling rod-shaped members of a nuclear reactor comprising a reaction vessel, a reactor core containing rod-shaped members in the reaction vessel, a rotary cover on the reaction vessel, means for rotating the rotary cover, a slot in said rotary cover, a hoisting unit arranged on said rotary cover, means for moving said hoisting unit along said slot, a grip for grasping a rod-shaped member, transmission means interconnected with said hoisting unit for movement of said grip in the slot, whereby through rotation of said rotary cover and movement of said hoisting unit along the slot, said grip may be moved into position for transfer of any desired rod-shaped member. 2. Device according to claim 1 wherein said slot is disposed radially in the rotary cover. 3. Device according to claim 1 including a shielding box enclosing said hoisting unit and grip. 4. Device according to claim 3 including a carriage on which said hoisting unit rests, motor means for moving the carriage along said slot, and an expandable barrier between said carriage and the wall of said shielding box to prevent passage of vapors from said reaction vessel into said shielding box containing said hoisting unit. 5. Device according to claim 1 including an insertable shielding block across said slot to seal the interior of said reaction vessel. 6. Device according to claim 1 including an annular ring surrounding said rotary cover. 7. Device according to claim 6 wherein said annular ring has ducts into which said rod-shaped members may be transferred.
	claims	1. A transmission electron microscope having:a target body position on the electron optical axis of the microscope,an electrically conductive body off the axis of the microscope,an electron source for producing an axial electron beam which, in use, impinges upon a target body located at the target body position, anda system for simultaneously producing a separate off-axis electron beam which, in use, impinges on the electrically conductive body causing secondary electrons to be emitted therefrom;wherein the electrically conductive body is located such that the emitted secondary electrons impinge on the target body to neutralise positive charge which may build up on the target body, andwherein the system for producing an off-axis electron beam comprises an aperture body positioned between the electron source and the target body position, the aperture body having an axial aperture for transmission of the axial electron beam and further having an off-axis aperture for production of the off-axis electron beam. 2. A transmission electron microscope according to claim 1, wherein the off-axis electron beam is a paraxial electron beam. 3. A transmission electron microscope according to claim 1, wherein the off-axis electrically conductive body is located adjacent the target body position. 4. A transmission electron microscope according to claim 1, wherein the aperture body has a plurality of off-axis apertures for production of respective off-axis electron beams, each off-axis electron beam, in use, impinging on the off-axis electrically conductive body or a respective off-axis electrically conductive body. 5. A transmission electron microscope according to claim 1, further having at least one condenser lens between the electron source and the target body position, the aperture body being positioned between the condenser lens and the target body position, the aperture body limiting the illuminating field of the condenser lens. 6. A transmission electron microscope according to claim 1, wherein the system for producing an off-axis electron beam comprises a further electron source. 7. A transmission electron microscope according to claim 1, wherein:the target body position is a specimen position,the axial electron beam, in use, impinges upon a specimen, andthe emitted secondary electrons impinge on the specimen to neutralise positive charge which may build up on the specimen. 8. A transmission electron microscope according to claim 7, wherein the off-axis electrically conductive body is provided by a specimen support which holds the specimen at the specimen position. 9. A transmission electron microscope according to claim 1, wherein:the target body position is a phase plate position,the axial electron beam, in use, impinges upon a phase plate, andthe emitted secondary electrons impinge on the phase plate to neutralise positive charge which may build up on the phase plate. 10. A transmission electron microscope according to claim 1, wherein:the target body position is an electron biprism position,the axial electron beam, in use, impinges upon an electron biprism, andthe emitted secondary electrons impinge on the electron biprism to neutralise positive charge which may build up on the electron biprism. 11. A transmission electron microscope according to claim 1, having a plurality of target body positions spaced on the electron optical axis of the microscope, a plurality of respective electrically conductive bodies off the axis of the microscope, and a system for simultaneously producing a plurality of separate off-axis electron beams which, in use, respectively impinge on the electrically conductive bodies.
056339046	description	DETAILED DESCRIPTION A dry fuel transfer system generally comprises three main elements: the loading stand assembly which is placed partially under water in the spent nuclear fuel (SNF) storage pool and into which SNF rods or fuel assemblies are transferred; the transfer container which is landed on the loading stand and into which fuel assemblies are transferred from the loading stand assembly; and the discharge stack-up which includes a discharge stand onto which the transfer container is landed, and a transportation cask into which fuel assemblies are transferred from the transfer container. The transfer container 10 is shown in FIG. 1. It includes an integral hoist 12 attached to closure head 14, a main container body 16 and a shielded gate 18. FIG. 2 shows the container body 16 and closure head 14 in greater cross-sectional detail. The transfer container body 16 is preferably a cylindrical shell that is rabbeted at each end to fit with and fasten to closure head 14 and shielded gate 18 (FIG. 3). The fastening means (not shown for clarity) may be any conventional means such as a bolted flange joint. The container body 16 includes neutron shielding 21 (FIG. 2), a steel, exterior strength shell 20, shielding material 22 and a light steel, interior shell 24 that contains the radiation shielding material 22. Selection of the type of material 22 and thickness as defined by interior shell 24 will depend on the amount of radiation expected to be emitted by the particular fuel assemblies that will be carried in the transfer container. The interior of body 16 is provided with guide rails 26 that are attached at their upper end to closure head 14 and supported along their length by body supports 28. Guide rails 26 provide a locating sliding fit for a sliding sleeve 32 (see FIG. 11--omitted from FIG. 2 for clarity) that translates vertically within body 16. The exterior of transfer container body 16 has mounted thereon at least two lifting structures 44, well known in the art, located 180 degrees apart for hoisting and erecting the transfer container. As illustrated in FIG. 3, transfer container body 16 can be adapted to extend its length with the addition of one or more container body extensions 17, that also include extensions 27 for guide rails 26. This feature allows the transfer container to be easily adapted to accommodate varying lengths of fuel assemblies in a variety of applications. Closure head 14 (FIG. 2) forms the top of transfer container 10, provides mounting support for integral hoist 12 (FIG. 4) and holes with tight clearance fittings for the hoist cable 34 and grapple control cable 36 (FIG. 7). The closure head 14 is constructed the same as body 16 with neutron shielding 37, a steel, exterior strength shell 38, radiation shielding material 22 and a light steel interior shell 40 that contains material 22. The lower surface 42 of closure head 14 is cup-shaped with a rabbeted surface for mating with and extending over the upper end of body 16. The rabbeted fit ensures that radiation must pass through a sufficient amount of shielding to protect personnel. Two holes, or vertical channels, 46 and 48 pass through closure head 14 to provide tight clearance passage of hoist cable 34 and grapple control cable 36, respectively. These holes receive cables 34 and 36 through a seal assembly 52. The integral hoist 12 is shown generally in FIG. 1, but a preferred embodiment is shown in the several views of FIGS. 4 through 6. Hoist 12 is an electrically driven cable and drum hoist that is mounted on the top of closure head 14 via mounting plates 54. Hoist 12 includes two drums 55 and 57 that store the hoist lift cable 34 and the grapple control cable 36, respectively. Preferably, hoist 12 utilizes current art single-failure proof technology to ensure that the load lifted by the hoist is not dropped due to hoist failure. Cables 34 and 36 are delivered from the stowage drums 55 and 57 via pulleys 50, 53, and 51 and pass through seal assembly 52 and tight clearance passages or holes 46 and 48 of closure head 14 (FIG. 2). Hoist 12 includes motor 56 which, through gear box 58, drives the cable drum 55 directly and drum 57 indirectly through hoist cable 34 wound thereupon. Each of the drums 55, 57 are supported by drum mounting blocks 60. Motor 56 includes an integral rotary position encoder 64, shown only generally in phantom in FIG. 6, to provide data indicating the length of hoist cable 34 and/or grapple control cable 36 paid out from the cable drums. Position encoder 64 is connected electrically by cable to remote controller 66 to provide the length data to the controller and enable remote monitoring. Remote controller 66 is preferably a conventional computer with standard programming and input/output (I/O) capabilities. Note that for purposes of illustration, individual cables are shown connected between hoist 12 and remote controller 66 but in actual practice all cables would be routed so that only a single, multi-wire cable 67 (FIG. 1) would connect between the remote controller 66 and transfer container 10. Motor 56 is also connected to controller 66 via the same cable 67 to enable remote actuation of hoist 12. As an additional monitoring feature, the connecting shaft 68 to the cable drum 55 includes a strain gauge bridge 70, shown generally in FIG. 6, for detecting the size of the load attached to the hoist cable. Bridge 70 is connected electrically by the same multi-wire cable 67 to remote controller 66, which is programmed by conventional techniques to determine from the load detected whether one or more fuel assemblies have been latched or released by grapple assemblies attached to the hoist cable. Remote controller 66 is preferably provided with a control panel and/or display 72 that indicates to an operator the length of the cables paid out from the drums, the load carried by the hoist cable (e.g. in pounds), and other indicators to be discussed further hereinafter. Control panel 72 will preferably also provide control switches or dials for activating the hoist motor 56 to raise and lower the hoist cable and attached grapple assembly. As shown in FIG. 7, the hoist cable 34 is attached, within container body 16, to common grapple bracket 74 of grapple assembly 75 via connector 76. FIGS. 28-31 give a perspective view of the grapple assembly within body 16. Common grapple bracket 74 has attached thereto a number of grapples 78 for latching and releasing spent nuclear fuel (SNF) assemblies or rods 80 (see, for example, FIG. 30). FIG. 8 shows an embodiment of the present invention with four grapples 78 connected to four arms 82 of the bracket 74. Grapple control cable 36 (FIG. 7) is routed along or through arms 82 to each of grapples 78. Central post 84 of bracket 74 is provided with a locking ring 86 that is received in an opening 88 in closure head 14 (FIG. 2). Ring 86 automatically trips grapple locking mechanism 89 (FIG. 2) within head 14 via a pin, lug, key or other suitable tripping device. Mechanism 89, which may be pneumatically, electrically, hydraulically or mechanically activated and released, latches ring 86 in position in opening 88. Ring 86 can be locked in position in opening 88 to lock the grapple assembly 75 in its fully retracted position with (FIG. 31) or without (FIG. 28) fuel assemblies attached. Thus, the grapple assembly can be held in its fully retracted position independent of the hoist 12. Again with reference to FIGS. 7 and 8, a number of grapples 78 are connected to a respective number of arms 82 of common grapple bracket 74. Each grapple 78 functions to securely latch a fuel assembly 80, while it is hoisted into transfer container 10 and retained therein, while container 10 is moved, or while the fuel assemblies are lowered out of the transfer container and into a cask for storage or transport. Preferably, grapples 78 are actuated by electrical solenoids that are powered through grapple control and data cable 36. Pneumatic or mechanical actuation may also be employed. The control and data cable 36 is connected electrically to remote controller 66. This connection is shown for illustration purposes only in FIG. 6 with the control and data cable connector shown at 90. Preferably, however, all electrical cables will be routed within a single multi-wire cable with only a single multi-pin or multi-wire external connector for connecting with a single multi-wire cable 67 to controller 66. Each grapple 78 is individually actuated by remote controller 66 through operator action using control dials or switches on control panel 72. Panel 72 will preferably display indications of which grapples are actuated. Individual actuation of the grapples allow selective latching and hoisting in one embodiment, of only one, two, three or four fuel assemblies. This feature is useful in situations where, for example, one or two fuel assemblies are already contained in a storage or transportation cask and others are to be added from/to the transfer container. Grapples 78 are attached to the arms 82 of the common grapple bracket 74 by current art, commercially available, quick release fittings 79 and to the grapple control cable 36 by quick release connectors 81 so that the grapples 78 can be interchanged with another type of grapple suitable for different fuel assemblies. Thus, transfer container 10 can be readily reconfigured to suit various applications. FIGS. 9 and 10 illustrate an alternative or auxiliary common grapple bracket embodiment 74A with eight grapples 78 for holding up to eight fuel assemblies. Selection of a particular maximum number of fuel assemblies to be simultaneously maneuvered and held by transfer container 10 will depend on the particular application to which the present invention is applied. The fuel assemblies are lifted into and out of container body 16 while positioned in a sliding sleeve 32, which is best shown in FIGS. 11 and 12. Sleeve 32 is a box shaped structure that translates (slides) on guide rails 26 vertically within body 16. In its uppermost position (FIG. 28), the top of sleeve 32 is raised up to closure head 14, and in its lowermost position (FIG. 30) the bottom of sleeve 32 is lowered outside of transfer container 10. Sleeve 32 contains a number of runners 92 that slide on guide rails 26 (FIG. 2) of body 16. As best shown in FIG. 12, sleeve 32 is internally divided along its length by walls 94 to provide a number of compartments 96 configured to receive a corresponding number of fuel assemblies. Sleeve 32 is preferably constructed in a geometrical configuration that effects a spatial relationship between fuel assemblies appropriate to ensure subcriticality of the fuel assemblies while in the transfer container. Such configuration must be determined for each application (i.e. type, shape, etc. of fuel assemblies to be handled) of the present invention using techniques well known in the art. Alternatively, or additionally, sleeve 32 (including walls 94) is constructed of a material which may contain boron (neutron poisons) as a component. Sliding sleeve 32 includes an opening 98 at the intersection of walls 94 that serves as passage for the common grapple bracket 74, hoist cable 34 and grapple control cable 36. FIG. 13 illustrates an alternate or auxiliary sliding sleeve embodiment 32A configured to accommodate up to eight fuel assemblies. In FIG. 13, lifting plates 100 are removed to better illustrate the relationship of walls 94 and configuration of the eight compartments 96. Sleeve 32 is moved up and down by and in conjunction with grapple assembly 75. Sleeve 32 includes lifting plates 100 that engage, with their lower surfaces, the upper surfaces of common grapple bracket arms 82. When grapple bracket 74 is raised by hoist 12, it engages lifting plates 100 thereby raising sleeve 32. When the grapple assembly 75 is locked in its uppermost raised position within body 16, sleeve 32 is securely retained by the locked bracket 74. When the common grapple bracket 74 is unlocked and lowered by integral hoist 12, sliding sleeve 32 descends by gravity as it is lowered by the common grapple bracket. When the lower end of sliding sleeve 32 mates with the upper end of the loading stand fuel basket 102 (see FIG. 30), it aligns with the fuel basket. As best seen in FIG. 14, sliding sleeve 32 aligns with fuel basket 102 through cooperation of flange 33 that seats inside of flanged lip 103 of fuel basket 102. When aligned with the fuel basket, the sliding sleeve 32 guides the common grapple bracket 74 as it is further lowered by the integral hoist 12 until the grapples 78 contact the standard latching features of the fuel assemblies contained in the loading stand fuel basket 104 and are actuated to latch the fuel assemblies. As the integral hoist 12 raises the common grapple bracket 74 and the latched fuel assemblies, the sliding sleeve 32 remains mated and aligned to the fuel basket 104 providing locational control of the fuel assemblies as they are lifted. The fuel assemblies are lifted fully into the sliding sleeve 32 whereupon the common grapple bracket 74 engages the top of the sliding sleeve 32 and causes the integral hoist 12 to retract the sliding sleeve 32 with the latched fuel assemblies into the transfer container 10. FIG. 15 illustrates the interchangeability of auxiliary sliding sleeve 32A with standard sliding sleeve 32, and the interchangeability of auxiliary common grapple bracket 74A of grapple assembly 75 with standard common grapple bracket 74. The arrows show the removal of the standard sliding sleeve 32 and the installation of the auxiliary sliding sleeve 32A. The sliding sleeve and grapple assembly are lowered through and out of the transfer container body 16. At that position the sliding sleeve is not held by the guide rails. The common grapple bracket 74 is disconnected from the lifting cable 34 and the grapple control cable 36 is disconnected from its end fitting. The auxiliary common grapple bracket 74A and grapple control cable are connected to the lifting cable and grapple control cable end fitting, respectively. The auxiliary sliding sleeve 32A and common grapple bracket 74A are then raised into the transfer container body by the integral lifting hoist 12 while aligning the auxiliary sliding sleeve 32A onto the guide rails 26. Sliding sleeve 32 passes into and out of container body 16 through shielded gate 18. Gate 18, as shown in detail in FIGS. 16, 17 and 18, mounts to the lower end of container body 16 via a rabbeted fit (see FIG. 3, for example) and is connected to body 16 by a bolted flange or and other suitable fasteners. As best shown in FIGS. 16 and 17, gate 18 is constructed with a steel shell 104 that encloses shielding material 22. Gate 18 includes an opening 106 in its center that may be circular (as shown) or rectangular, but appropriately sized and shaped to allow passage of sliding sleeve 32 vertically through it. Mounted within shell 104 of gate 18 are two doors 108, 110, preferably semicircular (as shown in phantom in FIG. 18). Doors 108, 110 translate horizontally within gate 18 toward and away from one another to close and open, respectively, gate opening 106. Doors 108 and 110 each include a double stepped mating interface 112 and 114, respectively for creating a double seal when the doors are closed together. Seals 116 and 117 are provided for the mating and sealing faces of the doors so that the interior of the transfer container can be sealed and pressurized or purged with inert gas. Doors 108, 110 are actuated by an external power source such as gear motor 118 that drives a linked pair of opposed thread Acme type screws 120, 122. Gear motor 118 is preferably electrically connected to and controlled by remote controller 66, and remote control panel 72, preferably, provides an indication of the status (i.e. closed, open) of doors 108, 110. Shell 104 has connected thereto lips 124 (FIG. 18) each with an alignment hole 126 that mates with a corresponding pin that extends up from an adapter plate 128 (FIG. 22) on a loading stand assembly 132 (FIG. 19), as will be discussed in detail hereinafter. Holes 126 and the pins of the adapter plate ensure that transfer container 10 is properly aligned with the fuel basket in the loading stand when the transfer container is landed on the loading stand. Fuel assemblies, e.g. spent nuclear fuel (SNF) rods, are transferred into transfer container 10 from a spent nuclear fuel (SNF) storage pool 134 utilizing the loading stand assembly 132, as best shown in FIG. 19. The SNF storage pool 134 is typically located near a nuclear reactor to store spent fuel assemblies under water. As shown in FIG. 19, water W is maintained at a level L within the walls 136 of the pool. In order to transfer the spent fuel assemblies out of pool 134, loading stand assembly 132 is placed in the pool so that it is underwater except at its uppermost region. The loading stand includes a number of support columns 138 that provide the primary structural support for the assembly. Columns 138 are preferably adjustable in length by adding sections, e.g. lower sections 140 in FIG. 19, so that the loading stand assembly 132 extends from the floor F of the pool to the top of the pool. Columns 138 are tied together by bracing 146 and 174. As best shown in FIGS. 20 and 21, each support column 138 includes a pin 144 for engaging a corresponding hole 148 in loading stand adapter plate 128. Shims 142 (FIG. 21) are placed over pins 144 on top of columns 138 as necessary to level the loading stand adapter plate 128 when it is placed on top of the columns 138. Shims 142, which are thin disks or washers, permit the level of each of the four corners of the adapter plate to be adjusted to compensate for any unevenness in the floor F of the storage pool 134. Loading stand adapter plate 128 (FIG. 22) is mounted on top of the loading stand support columns 138 (see FIG. 19, for example) and may be shimmed at the mounting interface to level the adapter plate, as described above with reference to FIG. 21. Plate 128 includes a slot 150 to allow the pool fuel handling crane (not shown) to move fuel from storage racks (not shown) in the pool to the fuel basket 102 in the loading stand assembly. The center of plate 128 includes opening 152 that is dimensioned to accept the transition shield 154 and includes a lip 156 that supports transition shield 154, which is also slotted to permit movement of the fuel handling tool. Loading stand adapter plate 128 includes alignment pins 158 that are received in holes 126 of shielded gate 18 (FIG. 18) to properly align the transfer container 10 when it is loaded onto the loading stand assembly. Loading stand assembly 132 can be secured to withstand earth vibrations, such as seismic events, by deck anchored hold-down supports 178 attached on one end to the loading stand adapter plate 128 and appropriately anchored on their opposite end to the ground or a deck (not shown). The transition shield 154 is a shielded structure as best seen in FIGS. 19 and 22) that is open on the top and bottom and mounted within the loading stand support columns 138. A serpentine slot 151 is provided in the front of the shield to provide access for a fuel handling tool (not shown) to pass when transferring fuel assemblies into the fuel basket 102. The inner dimensions are sized to allow passage of the sliding sleeve 32 of the transfer container and entry from below of the fuel basket 102 as it elevates the fuel assemblies above the surface of the water for removal from the pool. The transition shield 154 is located such that its top is even with the top of the loading stand adapter plate 128. Part of the shield is below the pool water and part of the shield is above the water. In cross section its construction is generally similar to that of the transfer container body 16 and functions to provide radiation shielding for fuel assemblies as they are removed from the pool and drawn up through the shielded gate 18 into the transfer container. The fuel basket 102 as best shown in FIGS. 23 and 24 provides a number of compartments 160 for receiving fuel assemblies from the fuel storage pool fuel movement crane (not shown) as the fuel is moved from the fuel storage racks (not shown) in the storage pool. When the basket is loaded, the loading stand elevator 162 lifts the SNF basket vertically into the transition shield 154 and partially out of the water. The upper limit of travel is defined by the outer flange 164 of the basket 102 which mates with the bottom surface of the transition shield 154. As shown in FIG. 26, flange 164 of basket 102 includes alignment pins or bars 165 that are received in corresponding holes or channels 167 of transition shield 154 as basket 102 is raised in the direction of the arrows by the loading stand elevator. The upper surface of the basket provides a locating feature (i.e. flanged lip 103) which mates with and aligns the sliding sleeve 32 as it is lowered from the transfer container, as previously described with reference to FIG. 14. This aligns the grapples of the transfer container with the standard grapple points on top of the fuel assemblies within the basket. Basket 102 is preferably constructed in a geometrical configuration that effects a spatial relationship between fuel assemblies to ensure subcriticality of the fuel assemblies while in the basket and matches that of the sliding sleeve 32. Such configuration must be determined for each application (i.e. type, shape, etc. of fuel assemblies to be handled) of the present invention using techniques well known in the art. Alternately, or additionally, basket 102, (including walls 166) is constructed of a neutron absorbing material (neutron poisons), e.g. boron or material containing boron as a component. FIG. 25 shows an alternate or auxiliary embodiment 102A of the fuel basket that is capable of accepting up to eight fuel assemblies and matches the sliding sleeve 32A. The loading stand elevator 162 (FIG. 27) raises and lowers fuel basket 102 from a point above the floor F of the SNF storage pool up to the basket unloading position which is partially above the pool water and partially within the transition shield 154. Elevator 162, as best seen in FIG. 27, is preferably a cable drive system powered by an electrical hoist motor 168 which drives stowage drums 170 and linking mechanical drives 169 which are mounted to the underside of adapter plate 128. Motor 168 drives four hoist drums 170 that provide a balanced lift of fuel basket 102 as it is raised and lowered. Lift cables are channeled within the elevator guide slotted tubes 176 (FIG. 19). Basket 102 rides on and is guided by elevator guide tubes 176 that are passed through holes 180 in basket flange 164 (FIG. 24). The operation of the present invention will now be described in the environment of a nuclear site. Standard equipment and procedures are mentioned but not described in detail herein as such equipment and procedures are well known in the art. Prior to the commencement of spent nuclear fuel (SNF) transfer operations, the appropriate equipment is assembled both in the wet cask loading area of the site's SNF storage pool and in an appropriate dry cask loading area. The loading stand 132 is assembled and lowered into the site's SNF storage pool. A discharge stack-up is assembled in the designated dry cask loading area. An exemplary discharge stack-up is disclosed in U.S. Pat. No. 5,319,686, having the same assignee as the present patent application, and incorporated in its entirety herein by reference. To commence SNF transfer operations, the fuel assemblies 80 will be transferred from locations in fuel storage racks to positions in the fuel basket 102 of the loading stand. This transfer is accomplished by the use of the storage pool's standard fuel handling crane. An appropriate number of pressurized water reactor (PWR) or boiling water reactor (BWR) fuel assemblies 80, or other fuels or high level waste may be transferred into the fuel basket 102 each transfer cycle. The appropriate access hatches or doors to the storage pool building are opened and the transfer container 10 is brought into the storage pool area. The transfer container 10 is landed on the loading stand 132 (FIG. 28) while being properly located by the alignment pins 158 on the loading stand adapter plate 128. The movement of the transfer container may be accomplished by the use of an approved on-site crane. Once the transfer container 10 is seated on the loading stand 132, power, the remote controller 66 and the remote control panel 72 are connected to the transfer container and the electronic equipment is allowed to warm up. The remote control panel 72 and remote controller 66 are located in a low radiation area away from the transfer container to minimize personnel radiation exposure. The shielded gate 18 is then opened, via the remote control panel 72, providing an opening for the grapple assembly 75 and the sliding sleeve 32 to pass through. Prior to lowering the grapple assembly and sliding sleeve, the loading stand elevator 162 is activated and the fuel basket 102, with the fuel assemblies to be transferred, is raised to a height which ensures that the top of the fuel basket is above the surface of the storage pool water and within the transition shield 154 (FIG. 29). This reduces contamination of the grapple assembly and sliding sleeve while grappling fuel assemblies. With the fuel basket in the raised position, the transfer container grapple assembly 75 and sliding sleeve 32 are lowered, via the remote control panel 72, to rest atop the fuel basket and over the fuel assemblies (FIG. 30). The grapples are actuated remotely and latched to the fuel assemblies. Latching is confirmed by a series of electric sensors and the measurement of the proper weight is confirmed as displayed on the remote control panel. The grapple is designed to prevent the latching mechanism from releasing while the grapple is holding the weight of the fuel assembly. This ensures that inadvertent operation of a release button on the remote control panel, while raising or lowering the fuel assembly does not cause the grapple to release. Once latched, the grapple assembly, sliding sleeve, and all the fuel assemblies are raised into the transfer container. The sliding sleeve, which travels with the grapple assembly, ensures by proper fuel spacing that the fuel assemblies remain in a subcritical arrangement. In addition, the sliding sleeve is designed to protect the integrity of each fuel assembly and minimize any possible interference by continuously guiding each fuel assembly as it is removed from the fuel basket. Once the grapple assembly, sliding sleeve, and fuel assemblies are completely raised into the transfer container, the grapple assembly, with the fuel assemblies attached, is automatically secured in the transfer container. The loading stand elevator is activated to lower the fuel basket. The transfer container shielded gate is activated, via the remote control panel, to close and seal the bottom of the transfer container (FIG. 31). Then, the power and remote control panel are disconnected from the transfer container. Once the SNF basket is in its lower position, the transfer container is lifted off of the loading stand and moved to an SNF cask loading area by the on-site crane. The above process is then reversed to unload the fuel assemblies from the transfer container and into an SNF cask. The emptied transfer container is then moved back again onto the loading stand in the storage pool and additional fuel assemblies are loaded therein.
048184748	abstract	The core of a pressurized water nuclear reactor is partly formed from dismantlable assemblies (10), whereof the rods contain mixed UO.sub.2 -PuO.sub.2 oxide pellets, said assemblies (10) being subdivided into concentric zones (12,14,16) with a plutonium concentration decreasing from the inside to the outside. At the end of each irradiation cycle, the rods (C.sub.3) located in peripheral zone (16) are discharged and the rods (C.sub.2,C.sub.1) located in the other zones (12,14) are transferred towards the outside of assembly (10) into zone (14,16) adjacent to that which they previously occupied. New rods (C.sub.4) with a single enrichment are then introduced into the thus freed central zone (12).
058754075	description	DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for immobilizing waste chloride salts containing radionuclides and hazardous nuclear material for permanent disposal, and, in particular, a method for immobilizing waste chloride salts containing cesium, in a synthetic form of pollucite. Zeolite is a tectosilicate mineral comprised of SiO.sub.4 and AlO.sub.4, with large vacant spaces within its crystalline structure for cations. Chabazite (NaAlSi.sub.2 O.sub.6), a mineral within the zeolite group, is ideal for pollucite formation because the silicon to aluminum ratio of chabazite is identical to that of pollucite (CsAlSi.sub.2 O.sub.6), that is, the ratio of silicon to aluminum in chabazite and pollucite is (Si:Al=2). Another advantage is the commercial availability of the chabazite. The method is a one-step, direct thermal conversion at low temperatures of cesium, in the form of dry, non-aqueous cesium chloride, to pollucite by mixing and heating the cesium chloride with chabazite. The cesium is ion-exchanged and a reaction occurs to form pollucite in a single heat treatment step. The combination of cesium chloride and chabazite is heated to above the melting point of CsCl, or above about 700 .degree. C., forming pollucite. For example, a mixture of CsCl and chabazite was combined at ambient temperature, in a ratio of about 0.6 g of CsCl to 1 g of chabazite, the mixture having a cesium to aluminum ratio of 0.5. The mixture was heated in an alumina crucible to a temperature above 700.degree. C. to form the pollucite product. Analysis of the pollucite revealed a complete conversion of the CsCl to pollucite, with no NaCl or CsCl evident as by-products of the conversion process. FIG. 1 shows an x-ray diffraction pattern of the pollucite produced. Surprisingly, pollucite forms in the presence of the chloride ion. In particular, chloride ion appears to remain in the structure of the pollucite, apparently occluded as sodium chloride. Importantly, the method does not involve an aqueous ion exchange step, elevated temperatures (about 1000.degree. C.) and pressures, or complex starting materials and processing steps, as required by prior art methods. An advantage of the invention, therefore, is the ability to convert dry, solid cesium chloride without dissolving the cesium chloride in an aqueous solution to perform an ion exchange step. The solid cesium chloride is substantially dry, meaning dry to a great extent or degree, or being largely but not necessarily wholly without moisture. In other words, the cesium chloride is to a great extent free or relatively free of liquid, especially water. Thus, the method can be used with processes that require very dry environments, such as pyrochemical processes. Table 1 provides composition data for chabazite prior to mixing with cesium chloride, and the final, synthesized pollucite. The values are presented as mole/mole of Al. In particular, the retention of cesium and sodium in the pollucite is 0.922 and 0.587, respectively. TABLE 1 ______________________________________ Sample Al Si Na Ca Cs ______________________________________ Pollucite 1.000 3.663 0.587 0.058 0.922 Chabazite 1.000 3.633 1.393* 0.019 0.002 ______________________________________ Chabazite was ion exchanged in 1 M NaCl at 90.degree. C. Importantly, mixtures of sodium chloride and chabazite do not result in conversion to analcime (NaAlSi.sub.2 O.sub.6), which has the same structure of pollucite (CsAlSi.sub.2 O.sub.6), indicating that the presence of cesium is required for the structural conversion to pollucite to occur. FIG. 2 shows that by mixing sodium chloride with chabazite and heating the mixture to a temperature above about 700.degree. C., without cesium present, albite or anorthite feldspars are produced. In the preferred embodiment, the pollucite is further cooled, and, next, heated with glass, including glass frit, and hot pressed at a temperature up to about 725.degree. C. to form a solid pollucite and glass product. Alternatively, glass frit may be added to the CsCl and chabazite prior to heating, which results in lowering the temperature required for conversion to pollucite to about 700.degree. C., by apparently speeding up the reaction time, with no apparent affect on the formation of the pollucite. The reduction in temperature reduces the risk of volatilizing the cesium. The radionuclide cesium is thus encapsulated and immobilized in the solid pollucite and glass product, which is leach resistant and suitable for long term storage. In an alternate embodiment, zeolite A is heated with cesium chloride to a temperature above 750.degree. C. Zeolite A shows a partial reaction to pollucite and has a silicon to aluminum ratio of 1. The reaction product is a mixed pollucite (CsAlSi.sub.2 O.sub.6)-sodalite (Na.sub.4 Al.sub.3 Si.sub.3 O.sub.12 Cl) phase. FIG. 3 shows an x-ray diffraction pattern for the sodalite/pollucite product. In another embodiment, the retention of cesium in ceramic forms comprised of zeolite A, or zeolite A converted to sodalite, is surprisingly improved by adding up to 10% chabazite by weight to the waste form compositions (either zeolite A containing the radionuclides or zeolite A converted to sodalite containing the radionuclides) prior to their conversion to the final product. This embodiment is particularly applicable to mixed chloride salts having a low concentration of cesium (<2 wt. %). For example, in a typical electrometallurgical treatment process, the primary component of the salt is an LiCl--KCl eutectic (melting point of 355.degree. C.), containing cesium, strontium, barium, rare earth fission products, and transuranics. One method of producing ceramic waste forms containing the radioactive wastes is to blend zeolite A powder with the waste salt and heat the mixture to trap the fission products within the zeolite A structure in an ion exchange step. The salt-loaded zeolite powder can serve as the waste product, or it can be further heated to a temperature sufficient to convert the salt-loaded zeolite powder to sodalite. Next, the salt-loaded zeolite powder or the resulting sodalite is mixed with glass frit and consolidated by hot isostatic pressing (HIP) at elevated temperatures and pressures to form a composite ceramic. By adding 10% chabazite by weight to the waste products prior to the HIP step, in accordance with this embodiment of the method, the cesium retention in the composite ceramic is significantly improved. To demonstrate the significant improvement in the cesium retention rates according to this embodiment of the method, a baseline composition was established for the zeolite A and the sodalite waste products, without the addition of chabazite. A 50:50 mixture of a borosilicate glass and zeolite A and a 50:50 mixture of borosilicate glass and sodalite powder were hot pressed under conditions appropriate to retain the crystalline structure of each material. Both the zeolite A and sodalite ceramic compositions showed good retention of fission products based on standard leach tests. However, for both the zeolite A and sodalite ceramic compositions, cesium was the fission product most readily released. Next, up to 10% chabazite by weight was added to both the zeolite A and the sodalite waste products prior to the HIP step. The chabazite tended to sorb the lower charged alkali and alkaline earth cations to a greater extent than zeolite A during blending, which is, in part, attributable to the higher ratio of silicon to aluminum in chabazite relative to zeolite A, which favors sorption of lower charge species. When the chabazite is added to the powder mixture prior to the HIP cycle but after blending, cesium chloride that is expelled by zeolite A or sodalite during the HIP step can react with chabazite to form pollucite. However, pollucite has not been detected in the diffraction patterns for either the zeolite A or the sodalite waste products. Thus, it is preferable to add the chabazite during the blending step. Table II below provides leach test data for the baseline ceramic waste forms and ceramic waste forms containing chabazite, for three day and twenty-eight day MCC-1 tests in deionized water at 90.degree. C. TABLE II ______________________________________ Leach Rate Test Results for Ceramic Waste Forms Containing Chabazite % Cesium Release % Chloride Release* 28 28 Sample 3 day day 3 day day ______________________________________ Zeolite Waste Form 10% Chabazite added 0.1 0.3 0.21 0.37 Baseline WF Average, without Chabazite 0.28 NM 0.54 NM Sodalite Waste Form Chabazite added to Zeolite A prior to in blend 0.025 0.16 0.16 0.39 10% Chabazite added after conversion to Sodalite 0.02 0.13 0.09 0.32 Baseline WF Average, without Chabazite 0.08 0.65 0.63 0.57 Other Compositions Chabazite blended with salt, then with Zeolite A 0.047 0.19 0.04 0.13 ______________________________________ % Release = 100Mass of Species Lost/total Mass of species in Waste Form The foregoing description of a 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. The embodiments described explain the principles of the invention and practical applications and should enable others skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. While the invention has been described with reference to details of the illustrated embodiment, these details are not intended to limit the scope of the invention, rather the scope of the invention is to be defined by the claims appended hereto.
	description	This application is a continuation of U.S. patent application Ser. No. 12/978,198, filed on Dec. 23, 2010, which claims priority to Japanese Patent Application No. 2009-298093, filed on Dec. 28, 2009, the contents of all of which are hereby incorporated by reference. Technical Field The present invention relates to a core of a light water reactor and a fuel assembly and more particularly to a core of a light water reactor and a fuel assembly preferably applied to a boiling water reactor. Background Art When actinide nuclide having many isotopes burns in a core in a state that it is enriched in a nuclear fuel material in fuel assemblies loaded in a core of a light water reactor, the actinide nuclide transfers successively among the isotopes by nuclear reaction such as neutron capture and nuclear fission. In the actinide nuclide, since odd-numbered nucleus that has a large nuclear fission cross section with respect to a resonance and thermal neutrons, and even-numbered nucleus that undergoes fission only for fast neutrons are present, in general, isotopic composition in the actinide nuclides included in the fuel assembly largely change as the actinide nuclides burn. It is known that this isotopic composition change depends on the neutron energy spectrum at the position at which the fuel assembly is loaded in the core. Current light water reactor uses slightly enriched uranium as nuclear fuel. However, since the natural uranium resource is finite, it is necessary to successively replace fuel assemblies used in the light water reactor with recycle fuel assemblies including a nuclear fuel material which is formed by enriching depleted uranium, which is a residual after uranium enrichment, natural uranium, thorium, or degraded uranium with the transuranic nuclide (hereinafter referred to as TRU) extracted from the spent fuel assemblies of the light water reactor. Further, depleted uranium, natural uranium, thorium, degraded uranium, and TRU are referred to as a nuclear fuel material. The fuel assembly having the nuclear fuel material is loaded in the core of the light water reactor. It is desirable that U-233 newly generated by absorbing neutrons by the TRU and thorium are recycled as a useful resource over a very long period during which a commercial reactor is predicted to be necessary and during the period, the quantities of TRU and U-233 always increase or be maintained almost constant. In the light water reactor occupying most of the current commercial reactors, the technology of realizing a breeder reactor for increasing or maintaining almost constant the quantity of fissionable Pu while the nuclear fuel material burns, is described in Japanese Patent 3428150 (U.S. Pat. No. 5,812,621) and R. TAKEDA et al., Proc. of International Conference on Evaluation of Emerging Nuclear Fuel Cycle Systems. GLOBAL '95 Versailles, France, September, 1995, P. 938. In the light water reactor realizing the breeder reactor described in Japanese Patent 3428150 and R. TAKEDA et al., Proc. of International Conference on Evaluation of Emerging Nuclear Fuel Cycle Systems. GLOBAL '95 Versailles, France, September, 1995, P. 938, a plurality of fuel assemblies, each of which has a hexagonal transverse cross section, are disposed in the core, each fuel assembly being formed by closely arranging a plurality of fuel rods in a triangular grid. In the core of this light water reactor, the amount of water around the fuel rods is lessened due to the close arrangement of the fuel rods, and thereby the proportion of resonant energy neutrons and fast energy neutrons are increased. In addition, the height of a mixed oxide fuel section of the TRU is reduced and blanket zones loaded with depleted uranium are disposed above and below the mixed oxide burning part so as to maintain a negative void coefficient, which is a safety criterion. The core is formed in two stacked stages by applying the concept of a parfait-type core described in G. A. Ducat et al., “Evaluation of the Parfait Blanket Concept for Fast Breeder Reactors”, MITNE-157, January, 1974, thereby a breeding ratio of 1 or more is ensure, keeping the economy. To recycle TRU, the reprocessing of spent fuel is indispensable. Due to a fear that consumer TRU is diverted to weapons of mass destruction, there has been an increasing demand for nuclear non-proliferation and thereby restrictions on TRU recycling have been severe. Further, it is certain that an electric power generating system superior to a fission reactor is put into practical use on some day in the future. At that time, the value of TRU is lowered from a very useful fuel equivalent to enriched uranium to a cumbersome long-life waste material. Therefore, in order to spread a light water reactor using uranium as nuclear fuel widely in the world, to prepare the disposal method of TRU remaining in the spent nuclear fuel, that is, a TRU burner reactor for fissioning the TRU to a fission product is a most important object in the nuclear power development. Japanese Patent Laid-Open No. 2008-215818 and R. TAKEDA et al., Proc. of International Conference on Advanced Nuclear Fuel Cycles and Systems. GLOBAL '07 Boise, USA, September, 2007, P. 1725, propose a light water breeder reactor for keeping the isotopic composition of the TRU almost constant and recycling the TRU and the TRU burner reactor for permitting the TRU to fission in order to realize multiple-recycling for repeatedly executing the recycling for reusing the TRU obtained by reprocessing the spent nuclear fuel as new nuclear fuel. The light water breeder reactor has a core for recycling nuclear fuel in a state that the TRU quantity is kept constant or is increased and loading the fuel assemblies increasing the burn-up and nuclear proliferation resistance. The TRU burner reactor is a nuclear reactor for successively gathering the TRU while decreasing the TRU recovered by reprocessing the nuclear fuel by nuclear fission and permitting all the TRU to fission excluding the last one core in order to prevent the TRU from becoming a long-life radioactive waste material, when the light water reactor reaches an ending time of the mission. The light water reactor described in R. TAKEDA et al., Proc. of International Conference on Evaluation of Emerging Nuclear Fuel Cycle Systems. GLOBAL '95 Versailles, France, September, 1995, P. 938 and R. TAKEDA et al., Proc. of International Conference on Advanced Nuclear Fuel Cycles and Systems. GLOBAL '07 Boise, USA, September, 2007, P. 1725 for recycling the TRUs recovered from the spent nuclear fuel, to meet the design criteria for abnormal transient and accidents, keeps the TRU quantity constant with a sufficient safety margin, effectively uses the TRUs as seeded fuel, and burns all depleted uranium, thereby realizes long-term stable energy supply. Furthermore, such a recycle reactor can be realized as permits all the TRUs to fission and preventing the TRUs from becoming a long-life waste material when the nuclear fission reactor ends the mission and thus the TRUs become unnecessary. Patent Literature 1: Japanese Patent 3428150 Patent Literature 2: Japanese Patent Laid-open No. 2008-215818 Non Patent Literature 1: R. TAKEDA et al., Proc. of International Conference on Evaluation of Emerging Nuclear Fuel Cycle Systems. GLOBAL '95 Versailles, France, September, 1995, P. 938 Non patent Literature 2: G. A. Ducat et al., “EVALUATION OF THE PARFAIT BLANKET CONCEPT FOR FAST BREEDER REACTORS”, MITNE-157, January, 1974 Non patent Literature 3: R. TAKEDA et al., Proc. of International Conference on Advanced Nuclear Fuel Cycles and Systems. GLOBAL '07 Boise, USA, September, 2007, P. 1725 Non patent Literature 4: W. S. Yang et al., A Metal Fuel Core Concept for 1000 MWt Advanced Burner Reactor GLOBAL '07 Boise, USA, September, 2007, P. 52 Further, in the spread of the light water reactor, an apprehension of a TRU newly produced by the light water reactor to become a long-life radioactive waste material and a fear of the TRU to be diverted to weapons of mass destruction are large faults. The movement is becoming stronger of intending to remove the faults for the spread of the light water reactor finally, by establishing a technology of reducing the number of spent fuel assemblies to a small number as far as possible by permitting the TRU from the light water reactor to fission anyway and repeating the recycling in a state of the isotopic composition of a high nuclear non-proliferation resistance, before the TRU covers a role as seeded fuel for permitting the depleted uranium for long-term stably energy supply to fission. And, if the technology can be executed only by changing the fuel assemblies in the light water reactor in operation at present, it is more desirable. In recent years, there is a movement of making the concept for the safety of the nuclear reactor severe. For example, a core of a higher safety potential having a safety margin capable of sufficiently responding to an accident (anticipated transient without scram (ATWS)) beyond the limits of the design criteria of a composite event such that all the control rods cannot be inserted when core flow rate is suddenly reduced from some cause is required. Therefore, the inventors supposed a state that the overall core is filled with steam (a state that the overall core becomes 100% void) which is an event considered to be severest and examined a further improvement of the margin for intrinsic safety of the light water reactor. Even though the overall core becomes 100% void, positive reactivity is applied to the core. The application of the positive reactivity must be avoided and the margin for the intrinsic safety of the light water reactor must be improved more. An object of the present invention is to provide a core of a light water reactor and a fuel assembly capable of more improving the safety margin without impairing the economical efficiency of fuel of the light water reactor. A feature of the present invention for attaining the above object is a core in which a nuclear fuel material zone having nuclear fuel material including transuranic nuclides is formed in the core and a neutron absorbing member is disposed above the nuclear fuel material zone having a height within the range from 20 cm to 250 cm. In the core in which the nuclear fuel material zone having a height within the range from 20 cm to 250 cm is formed, even though the overall core becomes a state of 100% void from some cause during the operation of the light water reactor, the neutron absorbing member disposed above the nuclear fuel material zone absorbs the neutrons leaking from the nuclear fuel material zone because quantity of neutrons leaking out from the nuclear fuel material zone is large. Therefore, even though the overall core becomes the state of 100% void, positive reactivity is not applied to the nuclear fuel material zone because the leaked neutrons which are returned to the nuclear fuel material zone by reflecting on a component member existing outside the nuclear fuel material zone is extremely reduced in quantity. Consequently, the margin for the intrinsic safety of the light water reactor can be improved, thus the safety margin can be improved more without impairing the economical efficiency of fuel of the light water reactor. The zone where the nuclear fuel material is arranged in the core is a nuclear fuel material zone. The height of the nuclear fuel material zone is the same as an active fuel length of a fuel assembly. It can also attain the above object that in each fuel rod included in the fuel assembly loaded in the core, an outside diameter of a plenum formed above the nuclear fuel material zone including the transuranic nuclide of the fuel rod is 3 mm or more and is smaller than an outside diameter of the fuel rod in the nuclear fuel material zone. Length of the plenum is within a range from 400 mm to 2500 mm. The outside diameter of the portion of the plenum of the fuel rod at the length within the range from 400 mm to 2500 mm is 3 mm or more and is smaller than the outside diameter of the fuel rod in the nuclear fuel material zone, so that even when a composite event beyond limits of the design criteria (a first accident beyond the design basis accident which will be described later) such that core flow rate is suddenly reduced from some cause during the operation of the BWR and all control rods cannot be inserted into the core occurs, the leaked neutrons which are returned to the nuclear fuel material zone by reflecting on a component member for demarcating the plenum is reduced in quantity. Therefore, even when the first accident beyond the design basis accident occurs, the void coefficient becomes negative due to the intrinsic safety of the BWR, so that by the operation of a high pressure core injection system, reactor power is spontaneously reduced to the power that the fuel rods are coolable, and the safety margin of the core is increased. Furthermore, the volume of the plenum is increased, so that the soundness of the fuel rod is increased. Therefore, the safety margin can be improved more without impairing the economical efficiency of fuel of the light water reactor. It can also attain the above object that in the nuclear fuel material zone in the core, an upper blanket zone, an upper fissile zone where nuclear fuel material including transuranic nuclides exists, an internal blanket zone, a lower fissile zone where the nuclear fuel material including the transuranic nuclides exists, and a lower blanket zone are formed in this order from above in the axial direction of the core and a rate of fissionable plutonium occupying in all the transuranic nuclides in the lower fissile zone is made larger than a rate of the fissionable plutonium occupying in all the transuranic nuclides in the upper fissile zone. The thermal margin in the lower fissile zone is decreased and the thermal margin in the upper fissile zone is increased because a rate of fissionable plutonium occupying in all the nuclear fuel materials in the lower fissile zone is larger than a rate of fissionable plutonium occupying in all the nuclear fuel materials in the upper fissile zone. Since void fraction in the upper fissile zone is higher than void fraction in the lower fissile zone, the increase degree of the thermal margin in the upper fissile zone becomes larger than the decrease degree of the thermal margin in the lower fissile zone, thus in the overall core, the thermal margin is increased. Thus, the safety margin of the light water reactor can be improved more without impairing the economical efficiency of fuel of the light water reactor by that the rate of fissionable plutonium occupying in all the nuclear fuel materials in the lower fissile zone is larger than the rate of fissionable plutonium occupying in all the nuclear fuel materials in the upper fissile zone, because the thermal margin is increased and the safety margin is increased as mentioned above. It is another characteristic that a plurality of fuel assemblies including transuranic nuclides which are different in the recycle frequency are loaded in the core, and among the fuel assemblies, a plurality of fuel assemblies including the transuranic nuclides having the smallest recycle frequency are disposed in a central region of the core, and between the central region and an outermost layer region of the core, the fuel assemblies including the transuranic nuclides having larger recycle frequencies are disposed on the side of the outermost layer region of the core. By forming the core disposing the fuel assemblies as mentioned above based on the recycle frequency of the transuranic nuclides included in the fuel assemblies, the number of spent fuel assemblies can be decreased. Namely, by disposing the fuel assemblies including the transuranic nuclides having larger recycle frequencies among the plurality of fuel assemblies loaded in the core on the side of the outermost layer zone of the core, even though the overall core becomes the state of 100% void, the shift of the power distribution in the radial direction toward the central region of the core can be moderated and the number of spent fuel assemblies can be decreased. The nuclear fuel reprocessing is performed for the spent nuclear fuel included in the spent fuel assemblies taken out from the nuclear reactor. The transuranic nuclides included in the spent nuclear fuel are retrieved by the nuclear fuel reprocessing for the spent nuclear fuel and using the retrieved transuranic nuclides, a fresh fuel assembly is manufactured. The fresh fuel assembly is loaded in the core of the nuclear reactor, during a predetermined operation cycle number, is used in the nuclear reactor, and then is taken out from the nuclear reactor as a spent fuel assembly. The nuclear fuel reprocessing is executed for the spent nuclear fuel included in this spent fuel assembly taken out and the transuranic nuclides are retrieved. As mentioned above, the transuranic nuclides are recycled and used. The recycle frequency of the transuranic nuclide is frequency that the transuranic nuclide is retrieved from the spent nuclear fuel by the nuclear fuel reprocessing, is included in a fresh fuel assembly, and is used in the nuclear reactor. (A1) In the core of the light water reactor loading a plurality of fuel assemblies having the nuclear fuel material including a plurality of isotopes of the transuranic nuclide, having the nuclear fuel material zone, the height of which is within the range from 20 cm to 250 cm, including a nuclear fuel material, and the height of the nuclear fuel material zone is within the range from 20 cm to 250 cm, and disposing the neutron absorbing member above the nuclear fuel material zone, more preferable constitutions will be explained below. (A2) Preferably, in A1 aforementioned, it is desirable that the fuel assembly has a lower fuel support member for supporting each lower end portion of a plurality of fuel rods internally forming the nuclear fuel material zone and an upper fuel support member for supporting each upper end portion of the plurality of fuel rods, wherein the plenum is formed above the nuclear fuel material zone in each of the fuel rods, and the neutron absorbing members are disposed below the upper fuel support member. (A3) Preferably, in A2 aforementioned, it is desirable that the neutron absorbing members are disposed between the mutual plenums of the neighboring fuel rods. (A4) Preferably, in any one of A1 to A3 aforementioned, it is desirable that a length of the neutron absorbing members in an axial direction of the core is within a range from 20 mm to 700 mm and the distance between an upper end of the nuclear fuel material zone and a lower end of the neutron absorbing members is within a range from 230 mm to 500 mm. (A5) Preferably, in any one of A1 to A4 aforementioned, it is desirable that a total of cross sectional areas of all the neutron absorbing members is within a range from 10 to 50% of the cross sectional area of a fuel assembly lattice. (A6) Preferably, in A1 aforementioned, it is desirable that another neutron absorbing member is disposed below the nuclear fuel material zone. (A7) Preferably, in A2 or A3 aforementioned, it is desirable that a neutron absorbing material filling zone is formed under the nuclear fuel material zone in the fuel rods. (A8) Preferably, in A7 aforementioned, it is desirable that a length of the neutron absorbing material filling zone in the axial direction of the core (or the fuel assembly) is within a range from 10 mm to 150 mm. (A9) Preferably, in A7 or A8 aforementioned, it is desirable that an outside diameter of a portion facing to the neutron absorbing material filling zone of the fuel rod is larger than an outside diameter of a portion of the nuclear fuel material zone of the fuel rod and an interval between mutual outside surfaces of the portions facing to the neutron absorbing material filling zone of the neighboring fuel rods is within a range of 1.3 mm or more. (A10) Preferably, in A2 or A3 aforementioned, it is desirable that an outside diameter of a portions of the plenum of the fuel rod is smaller than an outside diameter of the portion of the nuclear fuel material zone of the fuel rod and is within a range of 3 mm or more and a length of the plenum in the axial direction of the core (or the fuel assembly) is within a range from 400 mm to 2500 mm. (A11) Preferably, in A2 or A3 aforementioned, it is desirable that the plenums include a first region and a second region disposed above the first region, and an outside diameter of a portion of the first region of the fuel rod is smaller than an outside diameter of a portion of the nuclear fuel material zone of the fuel rod, and an outside diameter of a portion of the second region of the fuel rod is smaller than the outside diameter of the portion of the nuclear fuel material zone of the fuel rod and is larger than the outside diameter of the portion of the first zone, and the neutron absorbing member is disposed between a lower end of the second region and the upper end of the nuclear fuel material zone. (A12) Preferably, in A2 or A3 aforementioned, it is desirable that the plenums include the first zone and the second zone disposed above the first zone, and the outside diameter of the portions of the fuel rods in the first zone is larger than the outside diameter of the portions of the fuel rods in the second zone and is smaller than the outside diameter of the portions of the fuel rods in the nuclear fuel material zone, and the neutron absorbing members are arranged above the upper end of the first zone. (A13) Preferably, in any one of A1 to A12 aforementioned, it is desirable that the neutron absorbing member include either of boron and hafnium. (A14) Preferably, in any one of A7 to A9 aforementioned, it is desirable that the neutron absorbing material filling zone includes either of boron and hafnium. (A15) Preferably, in A1 aforementioned, it is desirable that the nuclear fuel material zone includes an upper blanket zone, an upper fissile zone, an internal blanket zone, and a lower fissile zone, and the upper blanket zone, upper fissile zone, internal blanket zone, and lower fissile zone are disposed in the axial direction of the core in this order, and the upper fissile zone and lower fissile zone include a plurality of isotopes, and, in a state that fuel assemblies of a burnup of 0 are included, a rate of fissionable plutonium occupying in all the transuranic nuclides in the lower fissile zone is larger than a rate of fissionable plutonium occupying in all the transuranic nuclides in the upper fissile zone. (A16) Preferably, in A15 aforementioned, it is desirable that in the state that fuel assemblies of a burnup of 0 are included, a total of a height of the lower fissile zone and a height of the upper fissile zone is within a range from 350 mm to 600 mm and the height of the upper fissile zone is within a range from 1.1 times to 2.1 times of the height of the lower fissile zone. (A17) Preferably, in A15 or A16 aforementioned, it is desirable that in the state that the fuel assemblies of a burnup of 0 are included, an average of an enrichment of fissionable plutonium of all the transuranic nuclides in the lower fissile zone and an enrichment of fissionable plutonium of all the transuranic nuclides in the upper fissile zone is within a range from 16% to 20% and the enrichment of fissionable plutonium of all the transuranic nuclides in the lower fissile zone is within a range from 1.05 times to 1.6 times of the enrichment of fissionable plutonium of all the transuranic nuclides in the upper fissile zone. (A18) Preferably, in any one of A15 to A11 aforementioned, it is desirable that the lower blanket zone is disposed below the lower fissile zone in the nuclear fuel material zone. (A19) Preferably, in any one of A1 to A18 aforementioned, it is desirable that a rate of plutonium-239 occupying in all the transuranic nuclides included in the nuclear fuel material zone is either within a range from 40% to 60% or within a range from 5% or more to less than 40%. (A20) Preferably, in any one of A1 to A19 aforementioned, it is desirable that a rate of a cross sectional area of fuel pellet occupying in a cross sectional area of a unit fuel rod lattice is within a range from 30% to 55%. Preferably, it is desirable that the fuel assemblies are provided with a plurality of fuel rods, a lower fuel support member for supporting a lower end portion of each of the fuel rods, an upper fuel support member for supporting an upper end portion of each of the fuel rods, and a plurality of neutron absorbing members, wherein the plurality of fuel rods internally have a nuclear fuel material zone, in which a nuclear fuel material including a plurality of isotopes of transuranic nuclides exists, at a height within the range from 20 cm to 250 cm and a plenum formed above the nuclear fuel material zone, and the neutron absorbing members are disposed above the nuclear fuel material zone, and each of the aforementioned elements of (A2) to (A20) for the core of the light water reactor of (A1) are added to the fuel assembly. In the fuel assemblies, the “state that the fuel assemblies of a burnup of 0 are included” of (A15) to (A17) is changed to the “state of a burnup of 0”. (B1) In the core of the light water reactor in which a plurality of fuel assemblies having a nuclear fuel material are loaded, and in a nuclear fuel material zone including the nuclear fuel material, an upper blanket zone, an upper fissile zone, an internal blanket zone, and a lower fissile zone are arranged in the axial direction of the core in this order, and a plurality of isotopes of transuranic nuclides are included in the upper fissile zone and lower fissile zone, and, in a state that fuel assemblies of a burnup of 0 are included, a rate of fissionable plutonium occupying in all the transuranic nuclides in the lower fissile zone is made larger than a rate of fissionable plutonium occupying in all the transuranic nuclides in the upper fissile zone, more preferable constitutions will be explained below. (B2) Preferably, in B1 aforementioned, it is desirable that, in the state that the fuel assemblies of a burnup of 0 are included, a total of a height of the lower fissile zone and a height of the upper fissile zone is within a range from 350 mm to 600 mm and the height of the upper fissile zone is within a range from 1.1 times to 2.1 times of the height of the lower fissile zone. (B3) Preferably, in B1 or B2 aforementioned, it is desirable that, in a state that fuel assemblies of a burnup of 0 are included, an average of an enrichment of fissionable plutonium of all the transuranic nuclides in the lower fissile zone and an enrichment of fissionable plutonium of all the transuranic nuclides in the upper fissile zone is within a range from 16% to 20% and the enrichment of fissionable plutonium of all the transuranic nuclides in the lower fissile zone is within a range from 1.05 times to 1.6 times of enrichment of fissionable plutonium of all the transuranic nuclides in the upper fissile zone. (B4) Preferably, in any one of B1 to B3 aforementioned, it is desirable that the lower blanket zone is disposed under the lower fissile zone in the nuclear fuel material zone. (B5) Preferably, in any one of B1 to B4 aforementioned, it is desirable that a rate of plutonium-239 occupying in all the transuranic nuclides included in the nuclear fuel material zone is within either of a range from 40% to 60% and a range from 5% or more to less than 40%. (B6) Preferably, in any one of B1 to B5 aforementioned, it is desirable that a rate of a cross sectional area of fuel pellet occupying in a cross sectional area of an unit fuel rod lattice is within a range from 30% to 55%. Preferably, it is desirable that the fuel assembly is provided with a plurality of fuel rods, a lower fuel support member for supporting each lower end portion of the plurality of fuel rods, an upper fuel support member for supporting each upper end portion of the plurality of fuel rods, and neutron absorbing members, wherein the plurality of fuel rods internally form a nuclear fuel material zone in which a nuclear fuel material including a plurality of isotopes of a transuranic nuclide exists, and the nuclear fuel material zone includes the upper blanket zone, upper fissile zone, internal blanket zone and lower fissile zone, and the upper blanket zone, upper fissile zone, internal blanket zone, and lower fissile zone are arranged in the axial direction of the core in this order, and the upper fissile zone and lower fissile zone include the plurality of isotopes, and in the state of a burnup of 0, a rate of fissionable plutonium occupying in all the transuranic nuclides in the lower fissile zone is larger than a rate of fissionable plutonium occupying in all the transuranic nuclides in the upper fissile zone, and each of the elements of (B2) to (B6) for the core of the light water reactor of (B1) are added to the fuel assembly. In the fuel assemblies, the “state that the fuel assemblies of a burnup of 0 are included” of (B2) and (B3) is changed to the “state of a burnup of 0”. According to the present invention, the safety margin can be improved more without impairing the economical efficiency of fuel of the light water reactor. The inventors made various studies in order to realize a light water reactor capable of further increasing safety margin without impairing the economical efficiency of fuel of the light water reactor. As a result, the inventors found that in a core having structure of any one of (1) neutron absorbing members are disposed above nuclear fuel material zone having nuclear fuel material existing in the core and including transuranic nuclides and the nuclear fuel material zone having a height within a range from 20 cm to 250 cm, (2) an outside diameter of a plenum which is formed above nuclear fuel material zone and has a length within a range from 400 mm to 2500 mm is 3 mm or more and smaller than an outside diameter of a fuel rod in the nuclear fuel material zone, and (3) a rate of fissionable plutonium (hereinafter referred to as fissionable Pu) occupying in all the nuclear fuel materials in a lower fissile zone is made larger than a rate of fissionable plutonium occupying in all the nuclear fuel materials in an upper fissile zone, the safety margin can be increased more without impairing the economical efficiency of fuel of the light water reactor. Furthermore, the inventors also studied multiple-recycling of nuclear fuel material including transuranic nuclides. As a result, the inventors newly found that (4) the number of spent fuel assemblies can be reduced by that among a plurality of fuel assemblies different in recycle frequency of the transuranic nuclides, a plurality of fuel assemblies including the transuranic nuclides having the smallest recycle frequency are disposed at a central part of the core, and between the central part and the outermost layer zone of the core, the fuel assemblies including the transuranic nuclides having larger recycle frequencies are disposed on the side of the outermost layer zone of the core. The nuclear fuel material includes fissionable materials (U-235. Pu-239, etc.) and fertile materials (Th-232, U-238, etc.). The safety margin is handled by classifying the safety level into the following three stages. The level 1 is a design basis accident, and the level 2 is a first accident beyond the design basis accident, and the level 3 is a second accident beyond the design basis accident. The design basis accident is an object event of safety examination (an abnormal transient and an accident). For the design basis accident, the intrinsic safety of the nuclear reactor and ordinary safety system operate, thus with respect to “abnormal transient”, it is required to design the reactor so as to be able to control the reduction of the MCPR (minimum critical power ratio) so long as the fuel rod is not burn out. The fuel rod is reusable. With respect to “accident”, it is required to design the reactor so as to maintain a highest temperature of 1200° C. or lower of a cladding of the fuel rod, and a shape of the fuel rod, and be able to continue the cooling of the fuel rod. The first accident beyond the design basis accident is currently not an object event of safety examination, though in the light water reactor, it is an event to be taken into account at the time of design. In the first accident beyond the design basis accident, an accident considered to be severest is a composite event that coolant supply pumps (recirculation pumps or internal pumps) for supplying coolant to the core are all stopped and at that time, an accident that all the control rods are not operated occurs simultaneously. For the composite event, it is required to design the reactor so that a high pressure core injection pump of the emergency core cooling system (the capacity is about 5% of the total capacity of the coolant supply pumps) operates, and the fuel rod is automatically lowered down to the coolable power at a negative reactivity coefficient due to the intrinsic safety of the BWR and at the flow rate of the high pressure core injection pump. The second accident beyond the design basis accident is an event on assumption that the overall core becomes a state of 100% void regardless of the accident scenario. For this second accident beyond the design basis accident, it is required to design so as to prevent insertion of positive reactivity. The core of (1) aforementioned is equivalent to the core of the light water reactor realizing the safety margin of the level 3 (the second accident beyond the design basis accident). The core of (2) aforementioned is equivalent to the core of the light water reactor realizing the safety margin of the level 2 (the first accident beyond the design basis accident). The core structure of (1) to (4) aforementioned will be explained below in detail. The core structures of (1) to (4) aforementioned are respectively applied to the light water reactor for filling and recycling the transuranic nuclides recovered from the spent nuclear fuel by the nuclear fuel recycling in the fuel rods of fresh fuel assemblies. In the light water reactor, the core of the light water reactor with the performance as a breeder reactor improved will be explained below. For example, a boiling water breeder reactor having a residual ratio of fissionable Pu of 1 or more was realized firstly by Japanese Patent 3428150. To realize a breeder reactor in the light water reactor, the neutron energy in the core must be kept high. However, the mass of hydrogen atoms forming water used as coolant in the light water reactor is generally small compared with the mass of Na used as coolant in a fast breeder reactor, so that in a light water breeder reactor, the rate of coolant per unit volume of the nuclear fuel material must be made smaller because the neutron energy lost by one collision is large. When the recycling is performed with a nuclear fuel material that a rate of Pu-239 occupying in all the TRUs is within a range of larger than 60%, faults may be caused that (a) the cooling capacity for the nuclear fuel material in the core is insufficient, (b) the burnup of the fuel assembly is reduced and the economical efficiency of fuel is impaired, and (c) the fuel rod gap composing the fuel assembly becomes too narrow and the manufacture of fuel assemblies becomes difficult. When the recycling is performed with a nuclear fuel material that the rate of Pu-239 occupying in all the TRUs is lower than 40%, faults may be caused that (d) a rate of odd-numbered nuclides having a large nuclear fission cross section becomes lower than a rate of even-numbered nuclides having a small nuclear fission cross section and it is difficult to realize a residual ratio of 1 or more of fissionable Pu and (e) the core becomes large in order to maintain the critical state, thus the void coefficient which is an index of safety gets worse. Therefore, in the light water breeder reactor, it is necessary to keep the rate of Pu-239 occupying in all the TRUs within a range from 40% to 60%. Further, when the recycling is performed with a nuclear fuel material in which a rate of Pu-240 occupying in all the TRUs is within a range of smaller than 35%, the aforementioned faults of (a), (b), and (c) are caused. When the recycling is performed with a nuclear fuel material that the rate of Pu-240 occupying in all the TRUs is larger than 45%, the faults of (d) and (e) are caused. Therefore, in the light water breeder reactor, it is necessary to keep the rate of Pu-240 occupying in all the TRUs within a range from 35% to 45%. Next, the core of the light water reactor (TRU burner reactor) for using TRUs examined to be disposed as a long-life radioactive waste material when they become unnecessary as a nuclear fuel material and finally realizing fission of all the TRUs except the TRUs for one core will be explained. The inventors considered, when the TRUs become unnecessary, to permit the TRUs (are permitted) to fission to reduce in quantity, gather the TRUs scattered in many cores according to the reduction quantity, and finally, maintain the TRUs only in one core. At this time, to prevent the TRUs from becoming a long-life radioactive waste material, when the nuclear fuel material is recycled in a state that the rate of Pu-239 occupying in all the TRUs is 40% or more, the speed for reducing the TRUs is slow and it takes a very long period of time to gather the TRUs in one core. Further, when the recycling is performed using a nuclear fuel material that a rate of Pu-239 occupying in all the TRUs is lower than 5%, the core becomes large and the void coefficient gets worse. Therefore, in the TRU burner reactor, the rate of Pu-239 occupying in all the TRUs must be set within the range from 5% or more to less than 40%. Further, when the nuclear fuel material is recycled in a state that a rate of Pu-240 occupying in all the TRUs is 35% or lower in order to prevent the TRUs from becoming a long-life waste material, the speed for reducing the TRUs is slow and it takes a very long period of time to gather the TRUs in one core. Further, when the recycling is performed using a nuclear fuel material that a rate of Pu-240 occupying in all the TRUs is 45% or more, the core becomes large and the void coefficient gets worse. Therefore, in the TRU burner reactor, the rate of Pu-240 occupying in all the TRUs must be set within the range from 35% to 45%. Here, an overview of a parfait core which is a kind of the core of the light water reactor will be explained. The parfait core has fuel assemblies, which are fresh fuel assemblies (the burnup is 0) to be loaded, including a lower blanket zone, a lower fissile zone, an internal blanket zone, an upper fissile zone and an upper blanket zone disposed in this order from an lower end to an upper end. Therefore, also in the parfait core, a lower blanket zone, a lower fissile zone, an internal blanket zone, an upper fissile zone and an upper blanket zone are formed from the lower end of the nuclear fuel material zone toward the upper end of the nuclear fuel material zone. The lower fissile zone and upper fissile zone include TRU oxide fuel (or mixed oxide fuel of a TRU oxide and an Uranium oxide) including a fissionable material. The lower blanket zone, internal blanket zone, and upper blanket zone have uranium oxide fuel including a small quantity of content of the fissionable material and a large quantity of content of the fertile material such as U-238. Each fuel rod included in the fuel assemblies loaded in the core of the light water reactor internally forms a plenum. The plenum stores a volatile fission product (FP gas) generated by fission of a fissionable material included in the nuclear fuel material filled in the fuel rod and suppresses the increase of inner pressure of the fuel rod. The aforementioned core structure of (1) will be explained below. Cooling water (coolant) for cooling the fuel assemblies loaded in the core of the BWR flows in the core from underneath as subcooling water at about 5° C. to 10° C. and becomes a two-phase flow including saturated water, steam, and water while cooling the fuel assemblies. This cooling water is a two-phase flow having a void volume rate of about 60% to 90% at the core exit. Therefore, the distribution of hydrogen atoms for greatly contributing to moderation of neutrons in the axial direction of the core decreases from the lower end of the core toward the upper end of the core. Such a BWR has a characteristic that even when the power of the core is increased and the core flow rate is lowered from some cause, and the temperature of the fuel rods rises, and there is fear that the fuel soundness may be impaired, the void fraction at the core outlet is increased, and the neutron quantity leaking upward from the core is increased, and negative reactivity is inserted to the core, and the power of the nuclear reactor is automatically reduced, thus the soundness of the fuel rods is maintained. The inventors studied a further improvement measure of the safety margin in the BWR having the aforementioned characteristic. In this study, the second accident beyond the design basis accident aforementioned is taken into account. The overview of this study will be explained below. The inventors, when studying the improvement measure of the safety margin, used a core of a BWR having a nuclear fuel material zone including TRUs obtained by the nuclear fuel reprocessing at a height within the range from 20 cm to 250 cm as the core of the light water reactor which is a study object. In the BWR forming the nuclear fuel material zone including the TRUs at a height within the range from 20 cm to 250 cm, even during the operation of the BWR, there are a large quantity of neutrons leaking upward and downward from the nuclear fuel material zone. If the height of the nuclear fuel material zone is lowered to less than 20 cm, even in the core with the fuel rods disposed closely, the loading quantity of the nuclear fuel material is reduced, and when continuing the rated power operation, the fuel assemblies must be exchanged frequently. Therefore, the operation rate of the nuclear power generation plant is lowered and the economical efficiency of fuel is impaired. When the height of the nuclear fuel material zone is increased higher than 250 cm, the neutrons leaking from the nuclear fuel material zone is reduced in quantity and even if the neutron absorbing member is disposed above the nuclear fuel material zone, when the overall core enters the state of 100% void, positive reactivity is inserted to the nuclear fuel material zone. Therefore, the height of the nuclear fuel material zone is set within the range from 20 cm to 250 cm. When the overall core becomes the state of 100% void from some cause, the self control function which is an intrinsic safety function of the BWR is impaired. The self control function is a function that automatically reduces the reactor power when the core flow rate is suddenly lowered from some cause, by that the void fraction in the nuclear fuel material zone is increased suddenly, and the void fraction of the two-phase flow in the reflector zone formed above the nuclear fuel material zone is increased, and the neutron leaking rate from the nuclear fuel material zone is increased, and the effective neutron multiplication factor in the nuclear fuel material zone is decreased. A part of the neutrons leaked upward from the nuclear fuel material zone is reflected from the component member (in the current fuel rods, a part of a cladding made of zirconium alloy) forming the plenum of each fuel rod and is returned to the nuclear fuel material zone. Even though the overall core becomes the state of 100% void, the quantity of neutrons leaking upward from the nuclear fuel material zone is increased because the rate of the two-phase flow existing between the plenums of the neighboring fuel rods to the component member is lowered. Therefore, the quantity of neutrons reflected from the component member for forming the plenums and returned to the nuclear fuel material zone is increased. However, since the increase quantity of the neutron leak quantity from the nuclear fuel material zone is small compared with the increase quantity of the infinite neutron multiplication factor when the void fraction in the nuclear fuel material zone becomes the 100% void state from the value at the time of the rated power operation, positive reactivity is inserted to the core, concretely, to the nuclear fuel material zone. As a result of various studies, the inventors confirmed newly that even when the overall core becomes the state of 100% void, positive reactivity is not inserted to the core because the neutrons leaking upward from the nuclear fuel material zone are absorbed by the neutron absorbing member (for example, B4C or Hf) disposed above the nuclear fuel material zone. Due to the aforementioned arrangement of the neutron absorbing member, the insertion of positive reactivity can be prevented, so that the margin for the intrinsic safety of the BWR is improved, and as a result, the safety margin of the BWR is improved. Therefore, the inventors found a new knowledge that by applying the core structure of (1) to the core of the light water reactor, the safety margin can be improved for a multiple accident while breeding ratio of the TRU is kept. The study results aforementioned will be explained below in detail. The results of the studies executed by the inventors for an object of the core of the light water breeder reactor will be explained below. The light water breeder reactor as a study object is the core of a BWR that for example, the electric power is 1350 MW, and 720 fuel assemblies having 271 fuel rods per each fuel assembly are loaded in the core, and the breeding ratio is 1.01. Each fuel assembly has a nuclear fuel material including TRUs obtained by the nuclear fuel reprocessing and the rate of Pu-239 occupying in all the TRUs included at the time of a burnup of 0 is a value within the range from 40% to 60%. The inventors disposed the neutron absorbing members (including B4C and Hf, for example) between the fuel rods at the position of each plenum in the fuel assemblies in the axial direction of the fuel assemblies based on the knowledge concerning the core structure of (1). In each fuel rod, the plenum is positioned above the upper end of the active fuel length (the nuclear fuel material zone). Therefore, the neutron absorbing members are disposed between the plenums downward from the lower end of the upper fuel support member (for example, the upper tie-plate) of each fuel assembly for holding the upper end portion of each fuel rod and upward from the nuclear fuel material zone. When B4C is used, for example, neutron absorbing members composed so as to fill B4C in a sealed container are disposed between the plenums. When Hf is used, Hf, which is a metal, is formed in a plate or bar shape for example, and is disposed between the plenums as a neutron absorbing member. During the operation of the BWR, in each fuel assembly, a vapor-liquid two-phase flow flows between the fuel rods at the plenum position. Even when the BWR is stopped, cooling water exists in the core. The two-phase flow or cooling water existing between the fuel rods upward from the nuclear fuel material zone functions as a reflector of neutrons. Therefore, it may be said that the neutron absorbing members are disposed in the reflector above the nuclear fuel material zone. The zone where the two-phase flow or cooling water exists upward from the nuclear fuel material zone is referred to as a reflector zone. The inventors studied the arrangement of the neutron absorbing members between the fuel rods at the plenum position. FIG. 1 shows changes of the inserted reactivity to the core and void coefficient in the state that the overall core becomes 100% void due to the distance between the upper end of the nuclear fuel material zone and the lower end of the neutron absorbing members disposed between the plenums (the distance between the nuclear fuel material zone and the neutron absorbing members). A characteristic A indicates a relation between a distance between the nuclear fuel material zone and the neutron absorbing members and the void coefficient and a characteristic B indicates a relation between the distance and the inserted reactivity. The distance between the nuclear fuel material zone and the neutron absorbing members is a distance in the axial direction of the core. The characteristics A and B are characteristics obtained from an object of the core of the light water breeder reactor in which the fuel assemblies including the neutron absorbing members with a length of 500 mm disposed in the neighborhood of each fuel rod as shown in FIG. 18 are loaded. If the lower end of each neutron absorbing member approaches excessively the upper end of the nuclear fuel material zone the effect that the neutrons are reflected on the nuclear fuel material zone is lowered due to the influence of the neutron absorbing member during the operation of the BWR. As a result, the effective neutron multiplication factor in the nuclear fuel material zone is lowered, and to compensate for the lowering, the height of the nuclear fuel material zone must be increased, and even though the overall core becomes the state of 100% void, the inserted reactivity to the core is increased. If the distance between the nuclear fuel material zone and the neutron absorbing members becomes shorter than 230 mm, even when the overall core becomes the state of 100% void, positive reactivity is inserted to the core. Therefore, when the overall core becomes the state of 100% void, the distance between the nuclear fuel material zone and the neutron absorbing members must be set to 230 mm or more in order to avoid the application of positive reactivity to the core. Further, according to the characteristic B, if the distance between the nuclear fuel material zone and the neutron absorbing members becomes shorter, the volume of the two-phase flow zone (the reflector zone) between the nuclear fuel material zone and the neutron absorbing members becomes smaller, and the change of the effective neutron multiplication factor due to the change of the void coefficient of the core becomes smaller, and thus the void coefficient gets worse. If the distance between the nuclear fuel material zone and the neutron absorbing members becomes extremely longer, the influence of the reflector zone on the nuclear fuel material zone becomes smaller. Therefore, probability that the neutrons leaking in the reflector zone return again to the nuclear fuel material zone is increased and the void coefficient gets worse. When the distance between the nuclear fuel material zone and the neutron absorbing members exceeds 500 mm, the void coefficient becomes −1×10−4% Δk/k/% void or less and there are possibilities that a fault (for example, an event that restrictive conditions of the MCPR cannot be satisfied) may be caused from viewpoint of a transient characteristic of the core. From the aforementioned, it is preferable that the distance between the nuclear fuel material zone and the neutron absorbing members in the axial direction of the core is within the range from 230 mm to 500 mm. Further, even during the rated operation of the BWR, the neutron absorbing members disposed in the reflector zone absorb neutrons leaking upward from the nuclear fuel material zone. If the neutron absorbing members approach excessively the upper end of the nuclear fuel material zone, the quantity of neutrons returned from the reflector zone to the nuclear fuel material zone is reduced by the neutron absorbing function of the neutron absorbing members during the rated operation of the nuclear reactor. Therefore, the reactor power at the upper end portion of the nuclear fuel material zone is reduced. When the distance between the nuclear fuel material zone and the neutron absorbing members is 230 mm or longer, such a problem will not arise. Next, the inventors studied the length of the neutron absorbing members in the axial direction of the fuel assemblies. A relation between the length of the neutron absorbing members and the inserted reactivity and a relation between the length and pressure loss between the upper end of the nuclear fuel material zone and the upper end of the neutron absorbing members are shown in FIG. 2. A characteristic C indicates change of the inserted reactivity due to the length of the neutron absorbing members. A characteristic D indicates change of the pressure loss between the upper end of the nuclear fuel material zone and the upper end of the neutron absorbing members due to the length of the neutron absorbing members. The characteristics C and D are characteristics when the distance between the upper end of the nuclear fuel material zone and the upper end of the neutron absorbing members is 300 mm. When the length of the neutron absorbing members becomes less than 20 mm, positive reactivity is inserted to the core (refer to the characteristic C shown in FIG. 2) in a state that even though the overall core becomes the state of 100% void. Thus, the length of the neutron absorbing members is set to 20 mm or more. When the length of the neutron absorbing members exceeds 700 mm, the increase quantity of the pressure loss between the nuclear fuel material zone and the neutron absorbing members becomes 20% or more of the pressure loss of the overall core. The influence of such an increase in the pressure loss between the nuclear fuel material zone and the neutron absorbing members on the characteristic of the core cannot be ignored. Therefore, the length of the neutron absorbing members is set to 700 mm or less. Thus, it is preferable that the length of the neutron absorbing members is within the range from 20 mm to 700 mm. The neutron absorbing members may be disposed under the nuclear fuel material zone. When the overall core becomes the state of 100% void in the state that the neutron absorbing members are disposed under the nuclear fuel material zone, the neutrons leaking downward from the nuclear fuel material zone can be absorbed by the neutron absorbing members. Therefore, even though the overall core becomes the state of 100% void, the quantity of neutrons which leak downward from the nuclear fuel material zone and are returned to the nuclear fuel material zone is reduced extremely by disposing the neutron absorbing members under the nuclear fuel material zone. Also in this case, even though the overall core becomes the state of 100% void, positive reactivity is not inserted to the core. To dispose the neutron absorbing members under the nuclear fuel material zone, the neutron absorbing members may be disposed at the lower end of each fuel rod included in the fuel assemblies. Concretely, a neutron absorbing material (for example, B4C or Hf) is filled (for example, refer to FIGS. 17 and 27) at the lower end in the cladding of each fuel rod. A plurality of fuel pellets including TRUs are filled in the cladding above the neutron absorbing member filling zone. An outside diameter of the lower end portion of the fuel rod where the neutron absorbing material filling zone exists is the same as the outside diameter of the fuel rod above the neutron absorbing material filling zone. The length of the neutron absorbing material filling zone is within a range from 10 mm to 150 mm. To minimize the quantity of neutrons which leak downward from the nuclear fuel material zone and are returned to the nuclear fuel material zone smallest, it is preferable to permit the upper end of the neutron absorbing material filling zone to make contact with the lower end of the nuclear fuel material zone. However, even if the upper end of the neutron absorbing material filling zone is separated away from the lower end of the nuclear fuel material zone by 5 mm at its maximum, even when the overall core becomes the state of 100% void, the insertion of positive reactivity to the core can be avoided. The upper end of the neutron absorbing material filling zone disposed under the nuclear fuel material zone is separated downward away from the lower end of the nuclear fuel material zone, thus the bad influence on the power in the lower end portion of the nuclear fuel material zone by the absorption of neutrons in the neutron absorbing material filling zone can be reduced. The neutron absorbing material filling zone is formed separately from the control rod inserted into the core from underneath. In the BWR, the control rods are inserted between the fuel assemblies loaded in the core from the underneath of the core. Therefore, a neutron absorbing material is disposed under the nuclear fuel material zone except the control rod. The arrangement of the neutron absorbing material under the nuclear fuel material zone can suppress remarkably the return of neutrons leaking under the nuclear fuel material zone to the nuclear fuel material zone. Next, the study results by the inventors of an object of the core of the TRU burner reactor described in R. TAKEDA et al., Proc. of International Conference on Advanced Nuclear Fuel Cycles and Systems. GLOBAL '07 Boise, USA, September, 2007, P. 1725 will be explained. The core of the TRU burner reactor as an object of study is the core of a BWR that for example, is loaded with 720 fuel assemblies having 397 fuel rods per each fuel assembly, having an electric power of 1350 MW. When repeating the recycling of the TRUs in order to reduce the TRUs in quantity, namely, when repeating, every operation recycle, the loading of the fuel assemblies having a nuclear fuel material including TRUs obtained by the nuclear fuel reprocessing wherein the rate of Pu-239 occupying in all the TRUs included at the point of time when the burnup is 0 is within the range from 5% to below 40% to the core, the reactivity rate by the fast neutron flux is high compared with a core of a breeding ratio of 1, so that there is a case that an diameter of the neutron absorbing member disposed above the nuclear fuel material zone must be large compared with the core in the neighborhood of the breeding ratio of 1. In this case, naturally, the outside diameter of the plenum portion of each fuel rod is narrower than the outside diameter of the lower portion of the fuel rod than the plenum. However, even in the core of the TRU burner reactor, preferably, it is desirable that the distance between the nuclear fuel material zone and the neutron absorbing members is within the range from 230 mm to 500 mm and the length of the neutron absorbing members is within the range from 20 mm to 700 mm. Even in the core of the TRU burner reactor, similarly to the light water breeder reactor, it is possible to dispose the neutron absorbing members (B4C or Hf) under the nuclear fuel material zone. Even in the TRU burner reactor, the control rods are inserted into the core from underneath. Similarly to the light water breeder reactor, when the neutron absorbing members are disposed at the lower end of the fuel rods under the nuclear fuel material zone, to obtain an essential effect by the neutron absorbing members, there is a case that it is desirable to make the outside diameter of the lower part of the fuel rod in which the neutron absorbing material filling zone is formed lager than the outside diameter of the fuel rods above the neutron absorbing material filling zone. However, the width of the gap formed between the fuel rods is controlled not to be 1.3 mm or less at the lower end of the fuel rods in which the neutron absorbing material filling zone is formed, in consideration of the pressure loss of the fuel assemblies. Similarly to the light water breeder reactor, it is preferable that the length of the neutron absorbing material filling zone is within the range from 10 mm to 150 mm. The upper end of the neutron absorbing material filling zone and the lower end of the nuclear fuel material zone can be separated from each other by 5 mm at its maximum. The inventors studies various characteristics of the core of the light water reactor when the overall core becomes the state of 100% void from some cause. Firstly, in the nuclear fuel material zone, a power distribution in the axial direction and a void fraction distribution in the axial direction will be explained by referring to FIG. 3. In FIG. 3, a characteristic E indicates an average power distribution in the axial direction of the core during the rated power operation of the nuclear reactor. A characteristic F indicates an average power distribution in the axial direction of the core when the overall core becomes the state of 100% void from some cause during the rated power operation which is one of the severest composite events as a beyond design basis accident. A characteristic G indicates an average void fraction distribution in the axial direction of the core in correspondence with the power distribution of the characteristic E. Each characteristic shown in FIG. 3 is obtained from an object of the TRU burner reactor, though even in the light water breeder reactor, characteristics showing the similar tendency to each characteristic shown in FIG. 3 can be obtained. According to FIG. 3, it is found that when the overall core becomes the state of 100% void, the power distribution in the axial direction of the core is shifted on the lower end side of the nuclear fuel material zone and the lower reflector zone existing under the nuclear fuel material zone plays a role of a dump tank of surplus neutrons generated at the time of the accident. The lower reflector zone is a zone existing under the nuclear fuel material zone in which there exists the gap formed between the fuel rods under the lower end of the nuclear fuel material zone and cooling water under the fuel holding portion of the lower tie-plate in the lower tie-plate. When all the control rods are withdrawn from the nuclear fuel material zone, that is, when the upper end of the neutron absorbing material filling zone of the control rods is disposed under the nuclear fuel material zone and in the neighborhood of the lower end of the nuclear fuel material zone, in the nuclear fuel material zone having no lower blanket zone, the thermal neutron flux distribution in the axial direction of the core when the overall core becomes the state of 100% void from some cause, is indicated by a characteristic H in FIG. 4. A characteristic J shown in FIG. 4 indicates a thermal neutron flux distribution in the axial direction of the core when in the fuel rods, the neutron absorbing material is disposed in the portion under the nuclear fuel material zone, and the outside diameter of the fuel rods in the portion with the neutron absorbing material filled is the same as the outside diameter of the fuel rods above the portion with the neutron absorbing material filled. A characteristic K shown in FIG. 4 indicates a thermal neutron flux distribution in the axial direction of the core when in the fuel rods, the neutron absorbing material is disposed in the portion under the nuclear fuel material zone, and the outside diameter of the fuel rods in the portion with the neutron absorbing material filled is larger than the outside diameter of the fuel rods above the portion with the neutron absorbing material filled. Both characteristics J and K indicate the thermal neutron flux distribution in the axial direction of the core in a state that the control rods are withdrawn when the characteristic H is obtained and in the state that the overall core becomes the state of 100% void from some cause in the nuclear fuel material zone. The thermal neutron flux distribution of the characteristics J and K is remarkably lowered from that of the characteristic H, so that the neutron absorbing material is disposed under the nuclear fuel material zone, thus even when the overall core becomes the state of 100% void from some cause, the lower reflector zone existing under the nuclear fuel material zone plays a role of the dump tank of neutrons. Therefore, an occurrence of excess reactivity can be prevented. A relation between a rate of the cross sectional area of the neutron absorbing material filling zone under the nuclear fuel material zone to the cross sectional area of the fuel assembly lattice and the inserted reactivity when the overall core becomes the state of 100% void is shown in FIG. 5. If the rate becomes 35% or more, even when the overall core becomes the state of 100% void, positive reactivity is not inserted to the core. Therefore, in the core of the light water reactor that is loaded with fuel assemblies having a nuclear fuel material including the TRUs obtained by the nuclear fuel reprocessing, wherein the rate of Pu-239 occupying in all the TRUs included at the time of a burnup of 0 is within the range from 5% or more to less than 40%, the safety margin can be improved. The neutron absorbing members are disposed above the nuclear fuel material zone having a nuclear fuel material existing in the core and including a transuranic nuclide and having a height within the range from 20 cm to 250 cm, thus the safety margin can be increased more without impairing the economical efficiency of fuel of the light water reactor. The multiple-recycling of the TRUs can be continued. Preferably, it is desirable that the distance between the nuclear fuel material zone and the neutron absorbing members in the axial direction of the core is within a range from 230 mm to 500 mm and the length of the neutron absorbing members is within a range from 20 mm to 700 mm. The neutron absorbing members are disposed above the nuclear fuel material zone, and furthermore, the neutron absorbing material filling zone is disposed under the nuclear fuel material zone, thus when the overall core becomes the state of 100% void, the reactivity inserted to the core can be made more negative. Also in the light water breeder reactor and TRU burner reactor, when the rate of the cross sectional area of the fuel pellets (filled in the fuel rods) occupying in the cross section area of the unit fuel rod lattice in the channel box exceeds 55%, the gap between the fuel rods becomes less than 1 mm, so that the assembling of the fuel assemblies is very difficult. Thus, the rate of the cross sectional area of the fuel pellets occupying in the cross section area of the unit fuel rod lattice must be set to 55% or less. When the area rate becomes less than 30%, the fuel rods become extremely narrow and the quantity of the nuclear fuel material in the cross section becomes smaller. Therefore, the length of the fuel rods must be increased, and the void coefficient becomes positive. Consequently, the area rate must be set to 30% or more. Furthermore, the inventors studied how much the neutron absorbing members should be disposed per each fuel assembly lattice above the nuclear fuel material zone. Each of the neutron absorbing members is disposed between the nuclear fuel material zone and the upper fuel support member (for example, the upper tie-plate) in the neighborhood of the plenum portion formed in the fuel rod. When the overall core becomes the state of 100% void from some cause, a total of the cross sectional areas of all the neutron absorbing members disposed above the nuclear fuel material zone must be set to 10% or more of the cross sectional area of the fuel assembly lattice in order to prevent positive reactivity from being inserted to the core. The fuel assembly lattice is a region including a surrounding zone enclosed by the width ½ of the gap (the water gap in the BWR) formed between the neighboring fuel assemblies, and the cross section of one fuel assembly among them. The cross sectional area of the fuel assembly lattice is a total value of the cross sectional area of the surrounding zone and the cross sectional area of the fuel assemblies. The total of the cross sectional areas of all the neutron absorbing members must be controlled to 50% or less of the cross sectional area of the fuel assembly lattice because a two-phase flow at a predetermined flow rate must flow between the respective plenum portions of the neighboring fuel rods and the neutron absorbing members arranged between the plenum portions during the operation of the light water reactor. Based on the study results aforementioned, the total of the cross sectional areas of all the neutron absorbing members is preferably set within the range from 10 to 50% of the cross sectional area of the fuel assembly lattice. Even under the nuclear fuel material zone, the total of the cross sectional areas of all the neutron absorbing material filling zones formed in the fuel assemblies is preferably set within the range from 10 to 50% of the cross sectional area of the fuel assembly lattice except the cross sectional area of the control rods. The core structure of (2) can be added to the core structure of (1). Namely, the neutron absorbing members are disposed above the nuclear fuel material zone existing in the core, having a nuclear fuel material including a transuranic nuclide and having a height within the range from 20 cm to 250 cm, and the outside diameter of the plenums formed above the nuclear fuel material zone and having a height within the range from 400 mm to 2500 mm is set to 3 mm or more and is smaller than the outside diameter of the fuel rods in the nuclear fuel material zone. By doing this, even though the overall core becomes the state of 100% void, the insertion of positive reactivity to the nuclear fuel material zone can be avoided. The soundness of the fuel rods is increased. The quantity of the neutron absorbing members (for example, the thickness of the neutron absorbing members) disposed between the plenums of the neighboring fuel rods can be increased because the outside diameter of the plenums is 3 mm or more and is smaller than the outside diameter of the fuel rods in the nuclear fuel material zone. By doing this, even though the overall core becomes the state of 100% void, the reactivity inserted to the nuclear fuel material zone can be made more negative. Even in a pressurized water nuclear reactor (PWR) that cluster control rods are inserted into a plurality of guide tubes installed in each fuel assembly loaded in the core from above the core and a fast breeder reactor (FBR) that the control rods are inserted into the core from above, it is possible to form a nuclear fuel material zone including TRUs in the core and dispose the neutron absorbing members above and below the nuclear fuel material zone. The aforementioned core structure of (2) will be explained below. Each of the fuel rods included in the fuel assemblies loaded in the core of the light water reactor, for example, the core of the BWR internally stores a plurality of fuel pellets including a TRU. Even when a discharge rate of a volatile fission product from the fuel pellets is larger than that of uranium oxide pellets, to continue the TRU recycling while ensuring the soundness of the fuel rods and sufficiently keeping the safety potential of the BWR, it is necessary to increase plenum volume formed in the fuel rods and keep the void coefficient within a predetermined range. Further, in a commercial reactor put into practical use, realization of high burnup of the fuel assemblies in which the generation quantity of the volatile fission product is increased is required from the viewpoint of the economical efficiency of fuel, so that the volume of the plenums in the fuel rods must be increased. When the volume of the plenums installed on the upper part of the fuel rods is made larger, the self control function which is an intrinsic safety function of the BWR is impeded. In the state that the plenum volume is increased, when a first accident beyond the design basis accident is caused from some cause, the self control function is impeded. Even when a first accident beyond the design basis accident is caused from some cause, that is, a composite accident that an accident that the coolant supply pumps (the recirculation pumps or internal pumps) for supplying coolant to the core are all stopped and at that time, all the control rods are not operated is simultaneously caused occurs, the safety margin of the core of the BWR must be improved. The inventors studied an improvement measure of the safety margin capable of improving the safety margin of the core of the light water reactor without using the core structure of (1) when the first accident beyond the design basis accident is caused. The core of the light water reactor used as an object of study is the core of a BWR having a nuclear fuel material zone including TRUs obtained by the nuclear fuel reprocessing at a height within the range from 20 cm to 250 cm. When the first accident beyond the design basis accident is caused, the high pressure core injection system of the emergency core cooling system is operated. The inventors, as a result of examination, found a new knowledge that even when the plenum volume in the fuel rods is increased, the outside diameter of the plenum portion of the fuel rods is made smaller than the outside diameter in the nuclear fuel material filling zone under the plenum portion of the fuel rods, thus the reactivity to be inserted to the core when the first accident beyond the design basis accident is caused is reduced. Based on this new knowledge, the inventors reached the conclusion that the outside diameter of the plenum at a length within the range from 400 mm to 2500 mm formed above the nuclear fuel material zone may be set to 3 mm or more and may be made smaller than the outside diameter of the fuel rods in the nuclear fuel material zone. As mentioned above, by use of the core structure of (2), even when first accident beyond the design basis accident is caused, the quantity of leaking neutrons which are reflected on the component members for forming the plenums and are returned to the nuclear fuel material filling zone is reduced, and the soundness of the fuel rods is increased by increase of the plenum volume. Accordingly, the safety margin can be increased more without impairing the economical efficiency of fuel of the light water reactor. The aforementioned study results will be explained in detail. The inventors studied an object of the core of the light water reactor having the nuclear fuel material zone including the TRUs obtained by nuclear fuel reprocessing. The multiplication factor of fissionable Pu of the core is 1.01. FIG. 6 shows the results obtained by the study and shows the change of the inserted reactivity to the plenum length. This inserted reactivity is inserted reactivity when the overall core becomes the void state. A scattering cross section area of hydrogen is comparatively large in the energy zone of 500 keV or less, though it is suddenly reduced as the energy zone approaches 1 MeV, so that fast neutrons of 1 MeV or more pierce from the nuclear fuel material zone into the reflector zone by deep penetration. On the other hand, the neutrons lose a large quantity of energy by one collision with hydrogen atoms because the mass of hydrogen atoms composing the two-phase flow passing through the fuel assemblies is almost the same as that of neutrons. Therefore, when the upper reflector existing above the nuclear fuel material zone is composed of only the two-phase flow including water and the steam, the probability in which fast neutrons leaking once from the nuclear fuel material zone to the upper reflector are returned again to the nuclear fuel material zone is low. However, when component member (for example, the cladding made of a zircaloy) for forming each of the plenums in the fuel rods exists in the upper reflector zone, the mass of zirconium atoms of the cladding made of the zircaloy is larger than the neutron mass and the energy of neutrons lost by one collision with zirconium atoms is very small. Therefore, neutrons returning again to the nuclear fuel material zone appear during repetitive collisions of neutrons with zirconium atoms. In FIG. 6, a characteristic L indicates change of the inserted reactivity to the plenum length when the outside diameter of the plenum portion formed in the fuel rod is the same as the outside diameter of the portion in the nuclear fuel material filling zone under the plenum portion of the fuel rod. A characteristic M indicates change of the inserted reactivity to the plenum length when the outside diameter of the plenum portion formed in the fuel rod is smaller than the outside diameter of the portion in the nuclear fuel material filling zone under the plenum portion of the fuel rod. Concretely, the cross sectional area of the plenum portion is half the cross sectional area of the portion of the fuel rod in the nuclear fuel material filling zone. If a composite event (a first accident beyond the design basis accident) occurs that the coolant supply pumps for supplying coolant to the core are all stopped from some cause and furthermore, all the control rods are not operated, the reactor power is increased, the temperature of the fuel pellets in the fuel rod rises, and the discharge rate of the volatile fission product from the fuel pellets is increased. In addition, the inner pressure of the cladding of the fuel rod rises, and the gap between the cladding and the fuel pellets is widened, and thus, the heat transfer rate from the fuel pellets to the cladding is lowered, and the temperature of the fuel pellets rises furthermore. The occurrence of the composite event causes such a positive feedback state. However, the plenum length is increased and the plenum capacity is increased, thus the occurrence of such a positive feedback state can be prevented and the soundness of the fuel rods can be improved. As shown by the characteristic M in FIG. 6, if the outside diameter of the plenum portion formed in the fuel rod is smaller than the outside diameter of the portion of the fuel rod in the nuclear fuel material filling zone under the plenum portion, when the overall core becomes the state of 100% void, the reactivity inserted to the nuclear fuel material zone becomes 1 dollar or less. Therefore, when the outside diameter of the portion of the plenum in the fuel rod is smaller than the outside diameter of the portion of the fuel rod in the nuclear fuel material filling zone, even though the composite event of the first accident beyond the design basis accident occurs, the fuel rod is automatically reduced in power down to the coolable power at the flow rate of the cooling water supplied to the core by the operation of the high pressure core injection system and the safety of the BWR is ensured. Thus, when the outside diameter of the portion of the plenum is smaller than the outside diameter of the portion in the nuclear fuel material filling zone, the safety margin of the core of the BWR can be improved. In the fuel rod, when the outside diameter of the plenum portion is the same as the outside diameter of the portion in the nuclear fuel material filling zone, the plenum length is set to about 200 mm and when the outside diameter of the plenum portion is made smaller than the outside diameter of the portion in the nuclear fuel material filling zone under the plenum portion, the plenum length is set to about 200 mm to 300 mm, thus even when the overall core becomes the state of 100% void, the insertion of positive reactivity can be avoided. The aforementioned core structure of (3) will be explained below. Multiple-recycling of TRUs obtained by the nuclear fuel reprocessing is proposed (refer to Japanese Patent Laid-Open No. 2008-215818 and R. TAKEDA et al., Proc. of International Conference on Advanced Nuclear Fuel Cycles and Systems. GLOBAL '07 Boise, USA, September, 2007, P. 1725). To realize the multiple-recycling of TRUs, nuclear fuel materials recovered from spent nuclear fuel generated from various light water reactors (BWR and PWR) must be used. Even in the light water reactor, the BWR and PWR are different from each other in the neutron energy spectrum when the fissionable material included in the nuclear fuel material existing in the core is burned. Further, the generated spent fuel assemblies include various ones such as spent fuel assemblies immediately after taken out from the core and spent fuel assemblies stored in the fuel storage pool over a long period of time. In the spent nuclear fuel included in the spent fuel assemblies stored in the fuel storage pool, the nuclear decay of the isotopes is different and the composition of included TRUs is different according to a difference in the storage period of the spent fuel assemblies. A plurality of fresh fuel assemblies manufactured using a nuclear fuel material including TRUs recovered from such various spent nuclear fuel by the nuclear fuel reprocessing must be loaded in the core of one light water reactor. The variations of the power of each fuel assembly which is manufactured depending on the difference in the TRU composition in the nuclear fuel material including recovered TRUs and is loaded in the core are increased and there is concern that the thermal margin of the core may be reduced. Therefore, it is desired to increase the thermal margin of the core of the light water reactor. The inventors made various studies in order to realize the core of a light water reactor for increasing the thermal margin. As a result of study, the inventors found that the rate of fissionable Pu occupying in all the nuclear fuel materials in the lower fissile zone formed in the nuclear fuel material zone is made larger than the rate of fissionable Pu occupying in all the nuclear fuel materials in the upper fissile zone formed in the nuclear fuel material zone, thus the thermal margin of the core of the light water reactor can be increased without impairing the economical efficiency of fuel of the light water reactor. Using the core structure of (3), a linear heat generating rate of the fuel rod, a central temperature of the fuel rod, and the thermal margin of the MCPR and the like can be increased. Furthermore, the multiple-recycling of TRUs can be realized. The core structure of (3) can be realized by the parfait core in which the lower blanket zone, lower fissile zone, internal blanket zone, upper fissile zone, and upper blanket zone are formed successively from the lower end of the nuclear fuel material zone toward the upper end of the nuclear fuel material zone. To increase the thermal margin like this, it is desirable to increase the height of the nuclear fuel material zone, namely, the total length of the fuel rod in the axial length. In the core of the BWR, from the lower end of the nuclear fuel material zone toward the upper end of the nuclear fuel material zone, the density of the cooling water which is a neutron moderator is lowered. Therefore, the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone is lowered, and the height of the upper fissile zone is increased, and the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone where the density of coolant is higher than that in the upper fissile zone, thus the utilization factor of neutrons is improved. The breeding ratio and void coefficient of the core do not get worse. The increase in the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone causes a reduction in the height of the lower fissile zone. However, the increase range of the height of the upper fissile zone is larger than the decrease range of the height of the lower fissile zone, so that as a result, the height of the nuclear fuel material zone is increased. In the core of the light water reactor with the thermal margin increased wherein the rate of fissionable Pu occupying in all the nuclear fuel materials in the lower fissile zone formed in the nuclear fuel material zone is made larger than the rate of fissionable Pu occupying in all the nuclear fuel materials in the upper fissile zone formed in the nuclear fuel material zone, even if a first accident beyond the design basis accident occurs, the reactor power can be lowered automatically down to the power capable of cooling the fuel assemblies in the core by the capacity of coolant which can be supplied from the high pressure core injection system of the emergency core cooling system. Furthermore, in such a light water reactor core, even when the overall core becomes the state of 100% void from some cause, no positive reactivity is inserted. The core of the light water reactor having the constitution of (3) can improve more the safety margin without impairing the economical efficiency of fuel of the light water reactor because the thermal margin is increased. The inventors, as a concrete structure for realizing the core structure of (3), thought out a core structure of (I) and a core structure of (II) which will be described below. In the core structure of (I), the total of the height of the lower fissile zone in the nuclear fuel material zone and the height of the upper fissile zone is within a range from 350 mm to 600 mm and the height of the upper fissile zone is within a range from 1.1 to 2.1 times the height of the lower fissile zone. In the core structure of (II), an average of the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone and the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone is within a range from 14% to 22% and the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone is within a range from 1.05 to 1.6 times of the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone. In either of the core structure of (I) and (II), the thermal margin can be increased more without impairing the economical efficiency of fuel of the light water reactor. The study results aforementioned will be explained in detail below. The aforementioned study was executed for the core of the light water breeder reactor, for example, an object of the core of the BWR that the electric power is 1350 MW, and 720 fuel assemblies having 271 fuel rods per each fuel assembly are loaded in the core, and the breeding ratio is 1.01. In the light water breeder reactor, it is important that the negative void coefficient which is one of the important indexes of the breeding ratio, thermal margin and safety is satisfied in the well-balanced state under the effective neutron multiplication factor 1 which is a critical restrictive condition. As a result of the study of the inventors executed for the core of the BWR as a study object, it is found that the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone is lowered, and the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone is increased, thus as mentioned above, the thermal margin of the core can be increased without deteriorating the breeding ratio and void coefficient. Generally, when the enrichment of fissionable Pu is increased, the neutron spectrum in the fissile zone in which a fissionable material exists is shifted on the high energy side, and the number of neutrons generated when the TRUs undergo fission is increased, and fast fission of the fertile material such as U-238 is increased. Therefore, the number of neutrons leaking in the blanket zone from the fissile zone is increased and it contributes to an increase in the breeding ratio. However, since the height of the fissile zone necessary to keep the core critical is reduced, the total length of the fuel rod is shortened, and the thermal margin is reduced. On the other hand, the absolute value of the negative void coefficient of the core is increased and the safety margin is increased. However, when the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone is lowered and the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone is increased, as mentioned previously, the height of the nuclear fuel material zone can be increased. Therefore, the thermal margin of the core is increased. The inventors studied the core that the rate of fissionable Pu occupying in all the nuclear fuel materials in the lower fissile zone is made larger than the rate of fissionable Pu occupying in all the nuclear fuel materials in the upper fissile zone formed in the nuclear fuel material zone. FIG. 7 shows one of the study results. The inventors studied the changes of the respective heights of the upper fissile zone, lower fissile zone, and nuclear fuel material zone in a fresh fuel assembly loaded in the equilibrium core of the light water breeder reactor when the ratio of the enrichment of fissionable Pu in the upper fissile zone to the enrichment of fissionable Pu in the lower fissile zone (hereinafter simply referred to as the ratio of the enrichment of fissionable Pu) is changed. FIG. 7 shows a relation between the ratio of the enrichment of fissionable Pu and the height of each zone. A characteristic P indicates change of the height of the upper fissile zone due to the ratio of the enrichment of fissionable Pu. A characteristic Q indicates change of the height of the lower fissile zone due to the ratio of the enrichment of fissionable Pu. A characteristic R indicates the change of the height of the nuclear fuel material zone due to the ratio of the enrichment of fissionable Pu. In consideration of the criticality of the core and the flatness of the power distribution in the axial direction of the core, when the enrichment of fissionable Pu in all the TRUs in the upper fissile zone is 17% and the enrichment of fissionable Pu in all the TRUs in the lower fissile zone is 19%, the height of the upper fissile zone becomes about 1.1 times of the height of the lower fissile zone. When the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone is 14% and the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone is 22%, the height of the upper fissile zone becomes about 2.1 times of the height of the lower fissile zone. Each characteristic shown in FIG. 7 indicates evaluation results when an average of the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone and the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone is 18%. Even if the average of the enrichment of the upper fissile zone and lower fissile zone is changed between 16% and 20%, the height of the upper fissile zone and the height of the lower fissile zone to the ratio of the enrichment of fissionable Pu are changed similarly to the above case when the average of enrichment is 18%. The inventors studied, in a fresh fuel assembly loaded in the equilibrium core of the light water breeder reactor, the change of the void coefficient in each state that the ratio of the enrichment of fissional Pu is changed, and the change of the reactivity inserted to the core when the overall core becomes the state of 100% void, in each state that the ratio of the enrichment of fissional Pu is changed. FIG. 8 obtained from the study results shows a relation between the ratio of the enrichment of fissional Pu and the void coefficient, and a relation between the ratio of the enrichment of fissional Pu and the inserted reactivity when the overall core becomes the state of 100% void. A characteristic S indicates the change of the void coefficient due to the ratio of the enrichment of fissional Pu. A characteristic T indicates the change of the inserted reactivity due to the ratio of the enrichment of fissional Pu. Since the BWR has a density distribution of hydrogen atoms for bearing the neutron moderation function in the axial direction of the core, it is desirable that the enrichment of fissional Pu in the lower fissile zone having a large hydrogen atom density is made higher than the enrichment in the upper fissile zone having a small hydrogen atom density. If the enrichment of fissional Pu is made excessively higher than 22%, the increase effect of the enrichment of fissional Pu becomes weak due to the self shielding effect of various TRUs in the resonance energy zone. Thus, the quantity of fissional Pu necessary to keep the core critical is increased unnecessarily and the economical efficiency of fuel of the BWR is impaired. Additionally, if the enrichment of fissional Pu is made excessively lower than 14%, the neutron energy spectrum is transferred to the low energy side, and the breeding ratio is lowered, and furthermore, the deterioration of the void coefficient exceeds 10%, and there are possibilities that the economical efficiency of fuel and safety of the BWR may be impaired. However, as indicated by the characteristic T in FIG. 8, if the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone becomes smaller than 1.05 (about 18.5/17.5) times of the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone, the inserted reactivity when the overall core is assumed to become the state of 100% void exceeds 1 dollar (about 0.34% ΔK) and the core becomes a prompt critical region. The core must be avoided from entering the prompt critical region. Therefore, in correspondence with the case that a first accident beyond the design basis accident occurs and the high pressure core injection system is operated, the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone must be set to a value not less than 1.05 times of the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone. When the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone exceeds 1.6 (22/14) times of the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone, the absolute value of the negative void coefficient is reduced, and depending on the kind of an abnormal transient or an accident, there are possibilities that a case that it is difficult to meet the safety basis may occur. Thus, the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone is set to a value not more than 1.6 times of the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone. According to the characteristic T shown in FIG. 8, the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone is set to a value not less than 1.25 (20/16) times of the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone, thus even if the overall core becomes the state of 100% void from some cause, the insertion of positive reactivity to the core can be avoided. Therefore, the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone is within the range from 1.05 to 1.6 of the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone, thus the thermal margin of the core can be increased. As a result, the safety margin of the core can be improved without impairing the economical efficiency of fuel of the core. Preferably, it is desirable that the enrichment of fissionable Pu in all the nuclear fuel materials in the lower fissile zone is within the range from 1.25 to 1.6 of the enrichment of fissionable Pu in all the nuclear fuel materials in the upper fissile zone. The aforementioned indicates the study results for the equilibrium core, though the same may be said with an initial core and a transition core toward the equilibrium core. The aforementioned core structure of (4) will be explained below. It is considered that the spent nuclear fuel included in the spent fuel assemblies generated in a large quantity from the light water reactor is responded by either of a method for executing the nuclear fuel reprocessing and recycling TRUs and a method for directly executing ground disposal of the spent fuel assemblies. However, a site of the ground disposal of the spent fuel assemblies is not determined easily, and thus a way of intermediate storage of the spent fuel assemblies may be considered. On the other hand, there is concern that the apprehension for a TRU newly generated by the operation of the light water reactor to become a long-life radioactive waste material may prevent additional establishment of a light water reactor. Therefore, as a present countermeasure for the spread of the light water reactor, the inventors studied that the TRU is permitted to fission using the BWR in operation at present and the number of spend fuel assemblies is greatly reduced. As an example that a TRU is recycled by the light water reactor in operation at present, only one recycling of only Pu among TRUs which is referred to as the so-called Pu thermal use is executed in Europe. However, when repeatedly continuing the TRU recycling, the restrictive conditions for safety cannot be met, so that it is necessary to repeat the multiple-recycling of TRUs while the restrictive conditions for safety are met and greatly reduce the number of spent fuel assemblies. The inventors studied a countermeasure capable of reducing the number of spent fuel assemblies. As a result, the inventors found that a plurality of fuel assemblies including transuranic nuclides the recycle frequencies of which are different are loaded, and among these fuel assemblies, a plurality of fuel assemblies including the transuranic nuclide having the smallest recycle frequency are disposed at the central part of the core, and between the central part and the outermost layer zone of the core, the fuel assemblies including the transuranic nuclides having larger recycle frequencies are disposed on the side of the outermost layer zone of the core (the core structure of (4)), thus the number of spend fuel assemblies can be reduced. The core structure of (4), for example, can be realized as described below. Namely, TRUs different in the recycle frequency are included in separate fuel assemblies and these fuel assemblies are loaded in the core of one light water reactor. Each fuel assembly that TRUs having the same recycle frequency are enriched when the burnup is 0 and an in-core fuel dwelling time is different is loaded in the core in the neighboring state. A plurality of fuel assemblies including the transuranic nuclide having the smallest recycle frequency are disposed at the central part of the core, and between the central part and the outermost layer zone of the core, the fuel assemblies including the transuranic nuclides having larger recycle frequencies are disposed on the side of the outermost layer zone of the core. The TRUs different in the recycle frequency must be loaded separately in different fuel assemblies without being mixed. When enriching and multiple-recycling TRUs obtained by reprocessing spent nuclear fuel generated in the light water reactor using slightly enriched uranium and TRUs as nuclear fuel in uranium, the TRU loading quantity of the fresh fuel assembly may be decided for every fuel assembly including TRUs of the same recycle frequency so that an average values of the infinite effective multiplication factors of all the fuel assemblies which include the TRUs of the same recycle frequency and are different in the in-core fuel dwelling times become almost the same value. As the recycle frequency of a TRU is increased, the rate of Pu-239 in the TRU is reduced. Therefore, the core structure of (4) is the same as that when the TRU is multiply recycled, a plurality of fuel assemblies having a nuclear fuel material including the highest rate of Pu-239 in the TRU are disposed at the central part of the core, and between the central part and the outermost layer zone of the core, the fuel assemblies having a nuclear fuel material including a lower rate of Pu-239 in the TRU is disposed on the side of the outermost layer zone of the core. In the recycle light water reactor using a nuclear fuel material including TRUs obtained by the nuclear fuel reprocessing, the improvement of safety, increase of the thermal margin, and reduction of the number of spent fuel assemblies can be aimed at by use of the core structure of (4). The aforementioned study will be explained in detail below. The study was executed for an object of the core of the ABWR in operation at present. The object core of the ABWR is a core, for example, using slightly enriched uranium having an average enrichment of 4.8% where the electric power is 1350 MW and 872 fuel assemblies having 74 fuel rods per each fuel assembly are loaded in the core. The fuel assemblies using slightly enriched uranium as a nuclear fuel material, for example, are loaded in the core of the ABWR. For example, the core of the BWR where fresh fuel assemblies manufactured using the nuclear fuel material obtained by enriching only Pu recovered by reprocessing the spent nuclear fuel in the spent fuel assemblies generated in the ABWR in depleted uranium, natural uranium, or degraded uranium are loaded is generally referred to as a Pu thermal core. Among the Pu thermal cores, a core in which no fuel assemblies including slightly enriched uranium are loaded and all the fuel assemblies loaded have the nuclear fuel material including Pu recovered by the nuclear fuel reprocessing is referred to as Full MOX core. In the core of the light water reactor loading fuel assemblies having a nuclear fuel material including not only Pu but also all the TRUs recovered by the nuclear fuel reprocessing, the core loading only fuel assemblies including TRUs of a recycle frequency of one is called a TRU first generation recycle core. The core loading fuel assemblies including TRUs of a recycle frequency of two obtained by reprocessing the spent nuclear fuel included in the spent fuel assemblies taken out from the TRU first generation recycle core is called a TRU second generation recycle core. The core loading fuel assemblies including TRUs of a recycle frequency of three obtained by reprocessing the spent nuclear fuel included in the spent fuel assemblies taken out from the TRU second generation recycle core is called a TRU third generation recycle core. As the recycle frequency of fuel assemblies including TRUs is increased like this, the generation number of the core is increased. If the TRU recycle frequency is increased like this, the rate of the nuclides of even-numbered nucleus in the TRU is increased and the absolute value of the negative void coefficient is reduced. Therefore, the safety margin of the core is reduced and the TRU multiple-recycling cannot be continued. According to W. S. Yang et al., A Metal Fuel Core Concept for 1000 MWt Advanced Burner Reactor GLOBAL '07 Boise, USA, September, 2007, P. 52, in the FBR, a system capable of prolonging the TRU recycle generation than the aforementioned recycle system is studied. The Advanced Burner Reactor (ABR), in the TRU first generation recycle, uses the depleted uranium including the TRUs obtained by reprocessing the spent fuel of the light water reactor as a nuclear fuel material. In the TRU second generation recycle, it is tried to fill and recycle all the TRUs obtained by reprocessing the spent nuclear fuel included in the spent fuel assemblies taken out from the TRU first generation recycle core and to compensate for the insufficient TRUs reduced due to burn in the TRU first generation recycle core with the TRUs obtained by reprocessing the spent nuclear fuel of the light water reactor. As long as the light water reactor and ABR are operated continuously in parallel like this, the TRUs from the spent nuclear fuel generated from the light water reactor are continuously stored in the core of the light water reactor and fuel recycle equipment. Therefore, for the present, the storage of TRUs in other than the nuclear reactor can be avoided. If the concept of the ABR is tried using the ABWR, the TRU multiple-recycling can be continued longer than the Full MOX multiple-recycle core. However, though the TRU multiple-recycling has its limit to the TRU fourth generation recycle core, the number of spent fuel assemblies generated is reduced to about 1/10 compared with the case of no execution of the TRU recycling. By use of the core structure of (4), when the TRU multiple-recycling is continued up to the TRU eighth generation recycle core, the number of spent fuel assemblies generated is reduced to less than 1% of the number generated when the TRU recycling is not executed. As a result of the study of the inventors for an object of the ordinary Full MOX TRU multiple-recycle core, as a cause of transfer of the void coefficient to the positive side when the TRU recycling is continued, it is found that there are two events such that (I) the rate of even-numbered nucleus in the TRU is increased and (II) as the void coefficient in the core rises, the power distribution in the radial direction is transferred in the direction that it is high in the central portion of the core and low in the peripheral portion. In FIG. 9, a characteristic V indicates power distribution in the radial direction of the core during the rated power operation of the BWR. A characteristic X indicates power distribution in the radial direction of the core when the overall core becomes the state of 100% void. As the recycle generation of the TRU recycle core advances, the rise rate of the infinite neutron multiplication factor of the fuel assemblies when the void fraction of coolant is increased is increased. Using the event, a plurality of fuel assemblies including transuranic nuclides the recycle frequencies of which are different are loaded, and among the fuel assemblies, a plurality of fuel assemblies including the transuranic nuclide having the smallest recycle frequency are disposed at the central part of the core, and between the central part and the outermost layer zone of the core, the fuel assemblies including the transuranic nuclides having larger recycle frequencies are disposed on the side of the outermost layer zone of the core, thus the shift of the power distribution to the central part of the core in the radial direction can be relaxed. By doing this, the TRU multiple-recycling becomes feasible while the safety basis is satisfied and the number of spent fuel assemblies generated can be reduced. The relaxation of the shift of the power distribution to the central part of the core will be explained concretely below. The inventors found that one of main causes of insertion of large positive reactivity to the nuclear fuel material zone when the overall core becomes the state of 100% void is that when the overall core transfers to the state of 100% void from the state of the void distribution in the rated power of the BWR, the power distribution in the radial direction is shifted to the central part of the core of a high neutron importance. When executing the TRU multiple-recycling, the rate of Pu-239 in all the TRUs is reduced successively as the TRU recycle frequency is increased and when the void fraction is increased, the increase quantity of the infinite neutron multiplication factor of the fuel assemblies including TRUs is increased. As a consequence, the fuel assemblies including TRUs having a small recycle frequency is loaded at the central part of the core, and the fuel assemblies including TRUs having a large recycle frequency is loaded in the peripheral part of the core, thus it can be relaxed that the power distribution which is generated when the overall core transfers to the state of 100% void from the state of the void distribution during the rated power operation, shifts to the central part of the core in the radial direction. Therefore, even though the overall core becomes the state of 100% void, a core free of insertion of positive reactivity can be realized. Further, the flattening of the power distribution in the radial direction of the core, between the fuel assemblies including TRUs different in the recycle frequency, is executed by adjusting the rate of the number of fuel assemblies to be loaded. In an example of the core of the light water reactor to which the core structure of (4) is applied, a state of the core when the operation of the reactor is started in one operation cycle is shown in FIG. 10. This core of the light water reactor has a plurality of fuel assemblies A to H, which are fuel assemblies from a plurality of fuel assemblies including TRUs of the recycle frequency of one to a plurality of fuel assemblies including TRUs of the recycle frequency of eight, separately including TRUs of each of the recycle frequencies of one to eight. In FIG. 10, the alphabets A, B, C, D, E, F, G, and H indicate the recycle frequencies of the TRUs. In FIG. 10, the numerals 1, 2, 3, 4, and 5 added after the alphabets indicate the stay period (the number of operation cycles) of each of the concerned fuel assemblies in the core. For example, the fuel assembly B3 is a fuel assembly which includes TRUs of the recycle frequency of two and is experiencing the operation in the third operation cycle after it is loaded in the core. The numeral “5” indicates a fuel assembly in experience in the fifth operation cycle. The fuel assemblies A to C and a part of the fuel assembly D are taken out from the nuclear reactor as a spent fuel assembly after finishing of the operation in the fourth operation cycle after loaded in the core. The remainder of the fuel assembly D and the fuel assemblies F to H stay in the core until finishing of the operation in the fifth operation cycle after loaded in the core. In the equilibrium core, the TRUs recovered after reprocessing the spent nuclear fuel included in the fuel assembly A4 taken out from the core as a spent fuel assembly are all scattered and filled in a plurality of fuel assemblies B1 freshly manufactured. The TRUs recovered after reprocessing the spent nuclear fuel included in the fuel assembly B4 taken out from the core as a spent fuel assembly are all scattered and filled in a plurality of fuel assemblies C1 freshly manufactured. Similarly, the TRUs recovered from the spent nuclear fuel included in the fuel assembly C4 taken out from the core are all scattered and filled in a plurality of fresh fuel assemblies D1 and the TRUs recovered from the spent nuclear fuel included in the fuel assembly E5 taken out from the core are all scattered and filled in a plurality of fresh fuel assemblies F1. The TRUs recovered from the spent nuclear fuel included in the fuel assembly G5 are all scattered and filled in a plurality of fresh fuel assemblies H1 and finally, only the fuel assembly H5 remains as a spent fuel assembly. A to H is determined so as to make the infinite effective multiplication factors of the respective fuel assemblies almost equal and so as to keep the power distribution in the radial direction of the core flat. In the core shown in FIG. 10, the respective numbers of the fuel assemblies A to H at the time of a burnup of 0 are respectively 100 each, 40 each, 24 each, 16 each, 12 each, 8 each, 4 each, and 4 each. A plurality of fuel assemblies including TRUs of the same recycle frequency are disposed so that the fuel assemblies different in the in-core fuel dwelling time are disposed side by side. The fuel assemblies including TRUs having larger recycle frequencies are disposed on the side of the outermost layer zone of the core, thus when the void fraction of the core is increased, the increase of the infinite neutron effective multiplication factor at the central part of the core is made relatively smaller than the increase of the infinite neutron effective multiplication factor in the peripheral part of the core, compared with the core in which only the fuel assemblies including TRUs of the same recycle frequency are loaded. Therefore, the shift of the power distribution in the radial direction to the central part of the core is reduced. As a result, although the nuclear fuel assemblies including separately each TRU of up to the recycle frequency of eight are loaded in the core, keeping the void coefficient at −4×10−4% Δk/% void, the light water reactor can be operated. In this core, it is found that the number of spent fuel assemblies can be reduced to 0.5% or less compared with the case that the TRU is not recycled. The example that each fuel assembly from the fuel assemblies including TRUs of the recycle frequency of one to the fuel assemblies including TRUs of the recycle frequency of eight coexist in one core is explained above, though the following core structure may be used. For example, the core loading only fuel assemblies including TRUs of the recycle frequency of one, the core loading fuel assemblies including TRUs of the recycle frequency of one and fuel assemblies including TRUs of the recycle frequency of two, and the core loading fuel assemblies including TRUs of the recycle frequency of one, fuel assemblies including TRUs of the recycle frequency of two, and fuel assemblies including TRUs of the recycle frequency of three may be considered. Further, the case that all the TRUs recovered from each spent fuel assembly taken out from the light water reactor are recycled is discussed above, though to the case that only Pu among the recovered TRUs is recycled and the case that several nuclides among the TRUs are identified and are recycled together with Pu, the concept when all the TRUs are recycled can be applied straight. By combining several core structures among the core structure of (1), (2), and (3), the safety margin can be improved more. For example, when the core structure of (1) is combined with the core structure of (2), the safety margin is increased more than that of the individual the core structure of (1) and when the combination of the core structures of (1) and (2) is furthermore combined with the core structure of (3), the safety margin is increased more than that of the combination of the core structures of (1) and (2). The aforementioned may be said with the combination of other two core structures including the core structure of (2) and the combination of other two core structures including the core structure of (3). The embodiments of the present invention with the aforementioned concept applied will be explained in detail below with reference to the accompanying drawings. A core of a light water reactor according of embodiment 1 which is a preferable embodiment of the present invention will be explained in detail below by referring to FIGS. 11 to 20 and Table 1. A core 20 of the light water reactor of the present embodiment includes the aforementioned core structures of (1), (2), and (3). TABLE 1NuclideComposition (wt %)Np-2370.5Pu-2382.9Pu-23944.0Pu-24036.0Pu-2415.2Pu-2424.9Am-2413.6Am-242M0.1Am-2431.3Cm-2441.1Cm-2450.3Cm-2460.1 The core 20 of the light water reactor is a core for electric power of 1350 MW, though the power scale is not limited to it. The number of fuel assemblies loaded in the core 20 is changed, thus a core of another power scale to which the present embodiment can be applied can be realized. The overview of the boiling water reactor (BWR) which is a light water reactor for electric power of 1350 MW to which the core 20 of the present embodiment is applied will be explained by referring to FIG. 11. A BWR 1 disposes the core 20, a steam separator 21 and a steam dryer 22 in a reactor pressure vessel 27. The core 20 is surrounded by a core shroud 25 in the reactor pressure vessel 27. A core support plate 17 disposed at a lower end portion of the core 20 is placed inside the core shroud 25 and mounted to the core shroud 25. An upper grid plate 18 disposed at an upper end portion of the core 20 is disposed in the core shroud 25 and mounted to it. A plurality of control rods 42 are arranged in an insertable position into the core 20. The control rods 42 are inserted into the core 20 from underneath. Steam separators 21 are disposed above the core 20 and the steam dryer 22 is disposed above the steam separator 21. A plurality of internal pumps 26 are installed at the bottom of the reactor pressure vessel 27 and the impellers of the internal pumps 26 are disposed in a downcomer 29 formed between the reactor pressure vessel 27 and the core shroud 25. A main steam pipe 23 and a water feed pipe 24 are connected to the reactor pressure vessel 27. The BWR 1, as an emergency core cooling system when coolant fed to the core is lost from some cause, is provided with a low pressure core injection system 31 and a high pressure core injection system 32. In the core 20, as shown in FIG. 12, 720 fuel assemblies 41 are loaded. A plurality of Y-shaped control rods 42 are installed at a rate of one each per three fuel assemblies 41 and 223 control rods 42 are disposed. The respective control rods 42 are connected to the respective control rod drive mechanisms installed at the bottom of the reactor pressure vessel 27. The control rod drive mechanisms are driven by a motor and can finely adjust the movement of the control rods 42 in the axial direction. The control rod drive mechanisms execute each operation of withdrawal of the control rods 42 from the core 20 and insertion of the control rods 42 into the core 20. The control rods 42 of about ⅕ of the 223 control rods 42 are control rods for adjusting the reactor power by inserting into and withdrawing from the core 20 of the BWR 1 in operation and the residual control rods of about ⅘ are in a state withdrawn completely from the core 20 of the BWR 1 in operation, are the control rods 42 to be inserted into the core 20 when stopping the nuclear reactor. The fuel assembly 41 has a nuclear fuel material zone 16 in which the nuclear fuel material is filled and in the nuclear fuel material zone 16, five zones of an upper blanket zone 5, an upper fissile zone 6, an internal blanket zone 7, a lower fissile zone 8, and a lower blanket zone 9 are formed successively from above. Additionally, the fuel assembly 41 has a zone for forming an upper reflector zone 10 above the upper blanket zone 5 in the state that it is loaded in the core 20 and furthermore, has another zone for forming a lower reflector zone 11 under the lower blanket zone 9 in the state that it is loaded in the core 20 (refer to FIG. 16). The core 20 has a nuclear fuel material zone 12 including the nuclear fuel material, an upper reflector zone 10A, and a lower reflector zone 11A. The upper reflector zone 10A is formed above the nuclear fuel material zone 12 and is formed by the upper reflector zone 10 of each of the fuel assemblies 41 loaded in the core 20. The lower reflector zone 11A is formed under the nuclear fuel material zone 12 and is formed by the lower reflector zone 11 of each of the fuel assemblies 41 loaded in the core. The nuclear fuel material zone 12 of the core 20 is formed by the nuclear fuel material zones 16 of all the fuel assemblies 41. The nuclear fuel material zone 12 has five zones of an upper blanket zone 5A formed by the upper blanket zones 5, an upper fissile zone 6A formed by the upper fissile zones 6, an internal blanket zone 7A formed by the internal blanket zones 7, a lower fissile zone 8A formed by the lower fissile zones 8, and a lower blanket zone 9A formed by the lower blanket zones 9. The upper blanket zone 5A, upper fissile zone 6A, internal blanket zone 7A, lower fissile zone 8A, and lower blanket zone 9A are disposed in this order from an upper end of the nuclear fuel material zone 12 toward a lower end of the nuclear fuel material zone 12. The core 2 is a parfait core. The zones 10A, 5A, 6A, 7A, 8A, 9A, and 11A are disposed in the same positions as those of the respective zones 10, 5, 6, 7, 8, 9, and 11 of the fuel assembly 41 in the height direction of the core 20. In the cross section of the zone where the nuclear fuel material of the fuel assembly 41 is loaded, 271 fuel rods 44 with an outside diameter of 10.1 mm are arranged in an equilateral triangle lattice in a channel box 13 which is a hexagonal cylinder as shown in FIG. 13. The shape of the cross section of the fuel assembly 41 is hexagonal and the gap between a plurality of fuel rods 44 included in the fuel assembly 41 is 1.3 mm. A fuel rod row in the outermost layer includes nine fuel rods 44. The control rods 42 having a Y-shaped cross section have three blades extending toward the outside from the tie-rod positioned at the center. Each blade has a plurality of neutron absorbing members 3 filled with B4C which is neutron absorbing material and is arranged at an interval of 120° around the tie-rod. The control rod 2 has a follower made of carbon, which has a smaller slowing down power than light water, in an insertion end that is first inserted into the core 20. The structure of the fuel assembly 41 will be explained below by referring to FIG. 17. The fuel assembly 41 is provided with an upper tie-plate (upper fuel support member) 14, a lower tie-plate (lower fuel support member) 15, a plurality of neutron absorbing members (for example, neutron absorbing rods) 3, a plurality of fuel rods 44, and a channel box 13. The lower end portion of each of the fuel rods 44 is supported by the lower tie-plate 15 and the upper end portion of each of the fuel rods 44 is supported by the upper tie-plate 14. Each of the fuel rods 44 has a sealed cladding made of a zirconium alloy and in the cladding of each of the fuel rods 44, in the axial direction, a plenum 2, the nuclear fuel material zone 16, and the neutron absorbing material filling zone 4 are arranged in this order from the upper end toward underneath. A plurality of fuel pellets including the nuclear fuel material are filled in the nuclear fuel material zone (the active fuel length) 16 positioned above the neutron absorbing material filling zone 4 filled with B4C which is a neutron absorbing material. In the neutron absorbing material filling zone 4, a hafnium rod may be disposed. The rate of the cross sectional area of the fuel pellet occupying a cross sectional area of unit fuel rod lattice in the channel box 13 is 53%. An outside diameter of the fuel rod 44 (an outside diameter of the cladding) at the respective positions of the neutron absorbing material filling zone and the nuclear fuel material zone 16 is equal to 10.1 mm. The outside diameter of the fuel rod 44 (the outside diameter of the cladding) at the position of the plenum 2 is 5.8 mm and is smaller than the outside diameter of the fuel rod 44 at the position of the nuclear fuel material zone 16. A length of the plenum 2 is 1100 mm. The plenum 2 is interconnected to the neutron absorbing material filling zone 4 and the nuclear fuel material zone 16 in the fuel rod 44 In the nuclear fuel material zone 16, each of the fuel rods 44 is held by a fuel spacer (not shown) at several locations in the axial direction. The fuel spacers hold the intervals between the mutual fuel rods 44 at a predetermined width. The portion of the plenum 2 of each of the fuel rods 44 is supported by three fuel spacers 33 at three locations. Each of the neutron absorbing members 3 is held on the upper tie-plate 14 by a support rod (support member) 45 made of a zirconium alloy. In the neutron absorbing member 3, B4C pellets are filled in the sealed tube with an outside diameter of 6 mm. This tube is attached to the support rod 45. The neutron absorbing member 3 may be structured so as to fill the hafnium rods in the tube. Each of the neutron absorbing members 3 is disclosed between the mutual plenums 2 of the neighboring fuel rods 44 and the neutron absorbing members 3 are installed in a ratio of one per one fuel rod (refer to FIG. 18). Each of the neutron absorbing members 3 is disposed between the upper end of the nuclear fuel material zone 12, that is, the upper end of the nuclear fuel material zone 16 and a lower end of the upper tie-plate 14. A length of the neutron absorbing members 3 is 500 mm and a distance between the upper end of the nuclear fuel material zone 16 and the lower end of the neutron absorbing members 3 is 300 mm. In the present embodiment, a rate of a total cross sectional area of all the neutron absorbing members 3 to a cross sectional area of the fuel assembly lattice is 16.8%. A rate of a total cross sectional area of all the neutron absorbing material filling zone 3 to the cross sectional area of the fuel assembly lattice is 49.3%. In the value of 49.3%, a cross sectional area of the control rod 42 is not included. When the BWR 1 is in operation, the cooling water in the downcomer 29 is pressurized by the rotation of the internal pump 26 and is supplied to the core 20. The cooling water supplied into the core 20 is introduced to each of the fuel assemblies 41 and is heated by the heat generated by fission of the fissional material and a part of it becomes steam. A vapor-liquid two-phase flow including cooling water and steam moves up in the upper reflector zone 10 in the fuel assembly 41. The vapor-liquid two-phase flow is introduced to the steam separator 21 from the core and the steam is separated by the steam separator 21. Moisture is removed more from the separated steam by the steam dryer 22. The steam in which the moisture was removed is supplied to a turbine (not shown) through the main steam pipe 23 and rotates the turbine. A generator (not shown) connected to the turbine is rotated and power is generated. Steam discharged from the turbine is condensed by a condenser (not shown) to condensed water. The condensed water, as feed water, is introduced into the reactor pressure vessel 27 through the water feed pipe 24. The cooling water separated by the steam separator 21 is mixed with the aforementioned feed water in the down corner 29 and is pressurized again by the internal pump 26. The arrangement of the fuel assemblies 41 in the equilibrium core will be explained by referring to FIGS. 14 and 15. Fuel assemblies 41E in the operation cycle of which is the fifth cycle and staying in the core for the longest time in the in-core fuel dwelling time, are disposed in a core outermost layer region 46 of the core 20 having low neutron impedance. Fuel assemblies 41A, which have the highest neutron infinite multiplication factor and stay in the core 20 in a first cycle in the in-core fuel dwelling time are loaded in a core outer region 48 internally adjacent to the core outermost layer region 46, flattening the power distribution in radial directions of the core 20. Fuel assemblies 41B, 41C, and 41D in the operation cycles of which are respectively second cycle, third cycle, and fourth cycle in the in-core fuel dwelling time, are dispersed in a core inner region 50. By such an arrangement, the power distribution in the core inner region 50 is intended to flatten. The fuel assemblies 41A, 41B, 41C, 41D, and 41E are respectively the fuel assembly 41 shown in FIG. 13 and FIGS. 19 and 20 which will be described later. The lower tie-plates 15 of these fuel assemblies are supported by a plurality of fuel supports (not shown) installed on the core support plate 17. Coolant paths through which the cooling water is fed to the fuel assemblies supported by the fuel support are formed in the fuel support and an orifice (not shown) attached in the fuel support is disposed at the inlet of each of the coolant paths. In the core 20, three regions of the core outermost layer region 46, the core outer region 48, and the core inner region 50 are formed in the radial direction (refer to FIG. 15). The orifice disposed in the core outermost layer region 46, where the power of the fuel assembly 41 is smallest, has a smallest bore and the bore is increased in the order of the orifice positioned in the core outer region 48 and the orifice positioned in the core inner region 50. The bore of the orifice positioned in the core inner region 50 is largest. The height of each of the zones in the nuclear fuel material zone 16 of the fuel assembly 41 is as shown below as shown in FIG. 16. The height of the upper blanket zone 5 (the upper blanket zone 5A) is 70 mm, and the height of the upper fissile zone 6 (the upper fissile zone 6A) is 283 mm, and the height of the internal blanket zone 7 (the internal blanket zone 7A) is 520 mm, and the height of the lower fissile zone 8 (the lower fissile zone 8A) is 194 mm, and the height of the lower blanket zone 9 (the lower blanket zone 9A) is 280 mm. Furthermore, the upper reflector zone 10 (upper reflector zone 10A) with a length of 1100 mm from the upper end of the nuclear fuel material zone 16 toward above is formed. The upper reflector zone 10 includes cooling water (when the BWR 1 is in operation, a vapor-liquid two-phase flow) existing between the mutual plenums 2 of the fuel rods 41. The lower reflector zone 11 (lower reflector zone 11A) with a length of 70 mm from the lower end of the nuclear fuel material zone 16 toward underneath is formed. The lower reflector zone 11 includes cooling water existing between the mutual neutron absorbing material filling zones 4 of the fuel rods 41. The numerical values of the length of the upper reflector zone 10 and the length of the lower reflector zone 11 indicate the length among the length of the fuel rods arranged in the fuel assemblies in the axial direction. The same may be said with the length of the upper reflector zone 10 and the length of the lower reflector zone 11 in each embodiment described later. The neutron absorbing members 3 and support rods 45 are disclosed in the upper reflector zone 10 (upper reflector zone 10A). When the burnup of the fuel assembly 41 is zero, in all the fuel rods 44 (the fuel rods 44A to 44E shown in FIG. 19) of the fuel assembly 41, depleted uranium is filled in the three blanket zones of the upper blanket zone 5, the internal blanket zone 7 and the lower blanket zone 9, and when the TRU weight is assumed as 100, mixed oxide fuel at an enrichment of 15.7 wt % of fissionable Pu with the depleted uranium mixed at a rate of weight 213 is filled in the upper fissile zone 6, and when the TRU weight is assumed as 100, mixed oxide fuel at an enrichment of 20.2 wt % of fissionable Pu with the depleted uranium mixed at a rate of weight 143 is filled in the lower fissile zone 8. The upper blanket zone 5, internal blanket zone 7, and lower blanket zone 9 include no TRUs. The average enrichment of fissionable Pu in the upper fissile zone 6 and the lower fissile zone 8 is 17.5 wt %. The TRU is a material recovered by the nuclear fuel reprocessing from the nuclear fuel material (spent nuclear fuel) included in the fuel assembly 41 taken out from the reactor pressure vessel 27 as a spent fuel assembly. In each blanket zone, the mixed oxide fuel is not filled. Further, in each blanket zone, instead of depleted uranium, natural uranium or degraded uranium recovered from the spent fuel assemblies may be used. The fuel assembly 41 has a plurality of fuel rods 44A to 44E as fuel rods 44 and these fuel rods are arranged as shown in FIGS. 19 and 20. FIG. 19 shows a cross section of the fuel assembly 41 in the upper fissile zone 6. FIG. 20 shows a cross section of the fuel assembly 41 in the lower fissile zone 8. The mixed oxide fuel filled in the respective upper fissile zones 6 of the fuel rods 44A to 44E has the enrichment of fissionable Pu indicated below in the state of a burnup of 0 (refer to FIG. 19). In the fuel rod 44A, the enrichment of fissionable Pu is 8.4 wt %, and in the fuel rod 44B, the enrichment of fissionable Pu is 11.2 wt %, and in the fuel rod 44C, the enrichment of fissionable Pu is 14.5 wt %, and in the fuel rod 44D, the enrichment of fissionable Pu is 15.9 wt %, and in the fuel rod 44E, the enrichment of fissionable Pu is 17.2 wt %. The mixed oxide fuel filled in the respective lower fissile zones 8 of the fuel rods 44A to 44E has the enrichment of fissionable Pu indicated below in the state of a burnup of 0 (refer to FIG. 20). In the fuel rod 44A, the enrichment of fissionable Pu is 13.1 wt %, and in the fuel rod 44B, the enrichment of fissionable Pu is 15.9 wt %, and in the fuel rod 44C, the enrichment of fissionable Pu is 19.2 wt %, and in the fuel rod 44D, the enrichment of fissionable Pu is 20.7 wt %, and in the fuel rod 44E, the enrichment of fissionable Pu is 21.4 wt %. In each blanket zone of the fuel rods 44A to 44E, there exists no TRU, though each mixed oxide fuel in the upper fissile zone 6 and lower fissile zone 8 of the fuel rods 44A to 44E includes the TRUs of the composition shown in Table 1. In the fuel assembly 41, the rate of fissionable Pu-239 in all the TRUs is 44 wt % in the state of a burnup of 0. Table 1 shows the composition of the TRUs existing in the nuclear fuel material included in the fresh fuel assemblies loaded in the core which is obtained by reprocessing the nuclear fuel material in the spent fuel assemblies. This spent fuel assemblies stayed outside the BWR 1 for two years in the fuel storage pool and fuel reprocessing equipment and for one year in the fuel manufacture equipment, that is, for three years in total after taken out from the core 20. During the operation of the BWR 1, the volatile fission product generated by fission of the fissionable material in each of the fuel rods 44 is stored in the plenum 2. Since the plenum 2 has the length of 1100 mm, it can store the sufficient quantity of the volatile fission product generated by fission of the fissionable material. Therefore, the soundness of the fuel rods 44 can be ensured. According to the present embodiment, even though it is assumed that the overall core becomes the state of 100% void, which is an impossible event as an initiating event in the ABWR, neutrons leaking upward or downward from the nuclear fuel material zone 12 can be absorbed by the neutron absorbing members 3 and neutron absorbing material filling zones 4 because a plurality of neutron absorbing members 3 with a length of 500 mm are disposed at the position 300 mm upward from the upper end of the nuclear fuel material zone 12 and a plurality of neutron absorbing material filling zones 4 are disposed downward from the lower end of the nuclear fuel material zone 12. Therefore, even though the overall core becomes the state of 100% void, the insertion of positive reactivity to the nuclear fuel material zone 12 can be avoided. When such a state occurs, negative reactivity is inserted to the nuclear fuel material zone 12. In addition, the core 20 has the upper fissile zone 6 with an enrichment of fissionable Pu of 15.7 wt % and a height of 283 mm and the lower fissile zone 8 with an enrichment of fissionable Pu of 20.2 wt % and a height of 194 mm. The average enrichment of fissionable Pu in the upper fissile zone 6 and the lower fissile zone 8 is 17.5 wt %. The total of the height of the lower fissile zone 8 and the height of the higher fissile zone 6 is 477 mm, and the height of the higher fissile zone 6 is 1.46 times of the height of the lower fissile zone 8. The enrichment of fissionable Pu in the lower fissile zone 8 is 1.29 times the enrichment of fissionable Pu in the higher fissile zone 6. In such core 20, the breeding ratio is 1 or more and the thermal margin can be increased more. As a result, the core 20 of the present embodiment can reduce a maximum linear heat generating rate by 2% in comparison with that when the enrichment of fissionable Pu in both upper and lower fissile zones are the same and the void coefficient is negative. The BWR 1 having such a core 20 can continue the TRU multiple-recycling. Since the present embodiment has the core structures of (1), (2), and (3), even though the overall core becomes the state of 100% void, the positive reactivity is not inserted to the nuclear fuel material zone 12, and the soundness of the fuel rods 44 is increased, and the thermal margin is increased. Consequently, the safety margin can be improved more without impairing the economical efficiency of fuel of the light water reactor. In the core 20 of the present embodiment, when the same electric power of 1350 MW as that of the ABWR is generated by using the reactor pressure vessel 27 of almost the same size as that of the current ABWR, a discharge burnup of the nuclear fuel material zone 12 including the upper fissile zone 6A, lower fissile zone 8A, and internal blanket zone 7A excluding the upper blanket zone 5A and lower blanket zone 9A becomes 53 GWd/t and the discharge burnup of the nuclear fuel material zone 12 including the upper blanket zone 5A and lower blanket zone 9A becomes 45 GWd/t. In the core 20, the void coefficient becomes −3×10−4Δk/k/% void and the MCPR becomes 1.3. Therefore, in the core 20, a breeding ratio of 1.01 can be realized in the state that the rate of each isotope of the TRU is kept substantially constant as mentioned above. In the present embodiment, a flow path area of the vapor-liquid two-phase flow formed between the mutual plenums 2 of the fuel rods 44 on a section II-II of FIG. 17 becomes narrower the neutron absorbing members 3 are disposed in the upper reflector zone 10 and the pressure loss in the upper reflector zone 10 is increased. Since the pressure loss in the upper reflector zone 10 is smaller than the pressure loss of the core 20, there is no problem particularly. In the upper blanket zone 5 and the upper reflector zone 10, the pressure loss in the upper reflector zone 10 can be reduced by forming a plurality of openings passing through the side wall of the channel box 13. Neutron absorbing members 3A shown in FIG. 21 and neutron absorbing members 3B shown in FIG. 22 may be used in place of the neutron absorbing members 3 shown in FIGS. 17 and 18. A fuel assembly 41F shown in FIG. 21 has a structure that in the fuel assembly 41 shown in FIG. 17, the neutron absorbing members 3 are exchanged with the neutron absorbing members 3A. Other structures of the fuel assembly 41F are the same as that of the fuel assembly 41. The neutron absorbing members 3A are circular bodies and are disposed so as to surround the plenum 2 of each of the fuel rods 44. The neutron absorbing members 3A are structured so as to attach a circular sealed vessel 38 with an outside diameter of 8.8 mm arranged so as to surround the outside surface of the fuel rod 44 to the outside surface of the fuel rod 44 and to fill B4C in the circular zone formed between the outside surface of the fuel rod 44 and the sealed vessel. An upper end and lower end of the sealed vessel are sealed. When applying the neutron absorbing members 3A, the support rods 45 are not necessary. The fuel assembly 41G shown in FIG. 22 has a structure that in the fuel assembly 41 shown in FIG. 17, the neutron absorbing members 3 are exchanged with the neutron absorbing members 3B. Other structures of the fuel assembly 41G are the same as that of the fuel assembly 41. The neutron absorbing members 3B are an Hf plate and are disposed between the arrangement of the fuel rods 44. Both ends of each Hf plate with a thickness of 1.5 mm are attached to a frame member 5 with a hexagonal cross section. The frame members 5 are arranged along the inner surface of the channel box 13 and are attached to the upper tie-plate 14 by a plurality of support rods 45 and are disposed so as to enclose the plenum 2. By use of the neutron absorbing members 3A and 3B, the similar effect to embodiment 1 can be obtained. A core of a light water reactor according to embodiment 2 which is another embodiment of the present invention will be explained in detail below by referring to FIGS. 23 to 27 and Table 2. A core 20A of the light water reactor of the present embodiment has the aforementioned core structures of (1) and (2). TABLE 2NuclideComposition (wt %)Np-2370.1Pu-2384.8Pu-2398.5Pu-24039.1Pu-2414.5Pu-24226.0Am-2414.5Am-242M0.2Am-2434.8Cm-2444.5Cm-2451.4Cm-2461.1Cm-2470.2Cm-2480.3 The core 20A of the light water reactor has a structure that the fuel assembly 41 is exchanged with a fuel assembly 41H in the core 20 of embodiment 1. Other structure of the core 20A is the same as that of the core 20. The portion of the core 20A different from the core 20A will be explained. The core 20A is a parfait core similarly to the core 20. The BWR which is a light water reactor to which the core 20A is applied has a structure that the core 20 is exchanged with the core 20A in the BWR. The BWR has a structure similar to the BWR 1 except the core 20 and is a TRU burner reactor having the core 20A. The fuel assembly 41H (refer to FIGS. 23 and 25) loaded in the core 20A has 397 fuel rods 44F with an outside diameter of 7.2 mm arranged in an equilateral triangle lattice in the channel box 13. The gap between the mutual fuel rods 44F is 2.2 mm and a fuel rod row in the outermost layer includes nine fuel rods 44. The rate of the cross sectional area of the fuel pellets occupying in the cross sectional area of the unit fuel rod lattice in the channel box 13 is 36%. In the core 20A, the fuel assemblies 41A to 41D different in the experienced operation cycle number are disposed as shown in FIG. 24 in the state of the equilibrium core. The fuel assemblies 41D, the operation cycle of which is the fourth cycle, are disposed in the core outermost layer region 46 (refer to FIG. 15). The fuel assemblies 41A, the operation cycle of which is the first cycle, are disposed in the core outer region 48 and the fuel assemblies 41B, 41C, and 41D, the operation cycles of which are respectively the second cycle, third cycle and fourth cycle, are respectively scattered and disposed in the core inner region 50. There exists an intermediate zone, in which a plurality of fuel assemblies 41B are disposed circularly, between the core inner region 50 and the core outer region 48. The power distribution of such a core in the radial direction is flattened more. The fuel assemblies 41A to 41E shown in FIG. 24 are respectively the fuel assembly 41H. The nuclear fuel material zone 16A wherein the nuclear fuel material of the fuel assembly 41H exists (refer to FIG. 26) has a structure that the lower blanket zone 9 is removed from the fuel assembly 41. In the nuclear fuel material zone 16A, as shown in FIG. 26, the height of the upper blanket zone 5 is 20 mm, and the height of the upper fissile zone 6 is 218 mm, and the height of the internal blanket zone 7 is 560 mm, and the height of the lower fissile zone 8 is 224 mm. Additionally, the height of the upper reflector zone 10 formed above the upper blanket zone 5 is 1100 mm and the height of the lower reflector zone 11 formed under the lower fissile zone 8 is 70 mm. The nuclear fuel material zone 12 of the core 20A does not have the lower blanket zone 9A. The nuclear fuel material zone 12 includes the upper blanket zone 5A, upper fissile zone 6A, internal blanket zone 7A, and lower fissile zone 8A having the same heights as the respective heights of the upper blanket zone 5, upper fissile zone 6, internal blanket zone 7, and lower fissile zone 8. The structure of each of the fuel assemblies 41H will be explained below by referring to FIG. 25. Each of the fuel assemblies 41H has the same structure as that of the fuel assembly 44 except that the fuel rods 44 of the fuel assembly 41 are exchanged with the fuel rods 44F. The fuel rods 44F has the nuclear fuel material zone 16A aforementioned and has the plenum 2 above the nuclear fuel material zone 16A and the neutron absorbing material filling zone 4A under the nuclear fuel material zone 16A. The outside diameter of the plenum 2 is 3.7 mm and the length of the plenum 2 is 1100 mm. In the nuclear fuel material zone 16A of the fuel rod 44F, the upper blanket zone 5, upper fissile zone 6, internal blanket zone 7, and lower fissile zone 8 exist. The outside diameter of the portion of the fuel rod 44F in the neutron absorbing material filling zone 4A is 8.1 mm and is larger than the outside diameter of the portion of the fuel rod 44F in the nuclear fuel material zone 16A (refer to FIGS. 25 and 27). The neutron absorbing members 3 with an outside diameter of 6.2 mm are disposed between the plenums 2. A rate of a total cross sectional area of all the neutron absorbing material filling zone 4A to the cross sectional area of the fuel assembly lattice is 44.0%. The value 44.0% does not include the cross sectional area of the control rods 42. When the burnup of the fuel assembly 41H is 0, all the fuel rods 44F (the fuel rods 44A to 44E shown in FIG. 19) of the fuel assembly 41H fill the upper blanket zone 5 and the internal blanket zone 7 with depleted uranium and fill the upper fissile zone 6 and the lower fissile zone 8 with TRU oxide fuel including TRUs of the composition shown in Table 2 in the state of a burnup of 0. The enrichment of fissionable Pu of the TRU oxide fuel is 13.0 wt % and the rate of Pu-239 in the TRU is 8.5 wt %. The TRUs used in the fuel assembly 41H are obtained by reprocessing the spent nuclear fuel included in the spent fuel assembly. Each blanket zone is not filled with the mixed oxide fuel and does not include TRUs. Further, in each blanket zone, natural uranium or degraded uranium recovered from the spent fuel assembly may be used instead of depleted uranium. During the operation of the BWR, a sufficient quantity of the volatile fission product generated by the fission of the fissionable material in each of the fuel rods 44F can be stored in the plenum 2 with a length of 1100 mm. Therefore, the soundness of the fuel rods 44F is increased. According to the present embodiment, even if it is assumed that the overall core becomes the state of 100% void, which is an impossible event as an initiating event in the ABWR, the insertion of positive reactivity to the nuclear fuel material zone 12 can be avoided because a plurality of neutron absorbing members 3 with a length of 500 mm are disposed at the position 300 mm upward from the upper end of the nuclear fuel material zone 12 and a plurality of neutron absorbing material filling zones 4A are disposed downward from the lower end of the nuclear fuel material zone 12. When the state results, negative reactivity is inserted to the nuclear fuel material zone 12. Furthermore, the present embodiment can obtain the effects occurred in embodiment 1. The present embodiment has the core structures of (1) and (2), so that even when the overall core becomes the state of 100% void, positive reactivity is not inserted to the nuclear fuel material zone 12 and the soundness of the fuel rods 44F is increased. Therefore, the present embodiment can improve more the safety margin without impairing the economical efficiency of fuel of the light water reactor. In the core 20A of the present embodiment, when the same electric power of 1350 MW as that of the ABWR is generated by using the reactor pressure vessel 27 of almost the same size as that of the current ABWR, the discharge burnup becomes 65 GWd/t, and the void coefficient becomes −3×10−4Δk/k/% void, and the MCPR becomes 1.3. In the core 20A, while the keeping of the rate of the TRU isotopes is realized, the weight of the TRUs obtained by reprocessing the spent nuclear fuel in the spent fuel assembly after 3 years from takeout of the fuel assembly 41H from the core 20A as a spent fuel assembly reduces a weight of 8.3% from the TRU weight of the fresh fuel assembly 41H loaded in the core. In addition, during the period from loading of the fuel assembly 41H in the core 20A to takeout, the TRU fission efficiency which is a rate of the TRU fission weight occupying in all the fission weights of the nuclear fuel material in the fuel assembly 41H is 55%. Further, the keeping of the rate of the TRU isotopes means that the rates of the TRU isotopes are the same in the n TRU recycle generation and (n+1) TRU recycle generation. Even in the present embodiment, either of the neutron absorbing members 3A and 3B may be used instead of the neutron absorbing members 3. A core of a light water reactor according to embodiment 3 which is another embodiment of the present invention will be explained below by referring to FIG. 28. The core of the light water reactor of the present embodiment has the aforementioned core structure of (1), (2), and (3) similarly to the core 20 of embodiment 1. The core of the present embodiment has a structure that in the core 20 of embodiment 1, the fuel assembly 41 is exchanged with a fuel assembly 41I. Other structure of the core of the present embodiment is the same as that of the core 20. The fuel assembly 41I has a structure that in the fuel assembly 41, the fuel rods 44 are exchanged with fuel rods 44G. Other structure of the fuel assembly 41I is the same as that of the fuel assembly 41. Each of the fuel rods 44G included in the fuel assembly 41I has a structure that the plenum 2 of the fuel rod 44 is exchanged with a plenum 2A. The fuel rod 44G has the plenum 2A, and the nuclear fuel material zone 16 and the neutron absorbing material filling zone 4 similar to that of the fuel rod 44. The plenum 2A is disposed above the nuclear fuel material zone 16 and the neutron absorbing material filling zone 4 is disposed under the nuclear fuel material zone 16. The outside diameters of the respective portions of the fuel rod 44G in the nuclear fuel material zone 16 and the neutron absorbing material filling zone 4 are 10.1 mm. The rate of the cross sectional area of the fuel pellets occupying in the cross section area of the unit fuel rod lattice in the channel box 13 is 53%. The plenum 2A has a first zone 35A and a second zone 35B. An outside diameter of the portion of the plenum 2A in the first zone 35A is 4.8 mm and an outside diameter of the portion of the plenum 2A in the second zone 35B is 4.4 mm. The outside diameter of the portion in the first zone 35A is larger than the outside diameter of the portion in the second zone 35B. The first zone 35A is a large diameter portion and the second zone 35B is a small diameter portion. The second zone 35B is positioned above the first zone 35A. A length of the first zone 35A is 300 mm and an upper end of the first zone 35A is positioned at a position (the lower end of the neutron absorbing member 3) 300 mm upward away from the upper end of the nuclear fuel material zone 16. A lower end of the second zone 35B is disposed at the same position as that of the upper end of the first zone 35A. Each of the neutron absorbing members 3 is disposed between the mutual second zones 35B which are the small diameter portion of the neighboring fuel rods 44G. The outside diameter of the neutron absorbing member 3 is larger than the outside diameter (6 mm) of the neutron absorbing members 3 used in embodiment 1 such as 7.4 mm. The rate of the total cross sectional area of all the neutron absorbing members 3 to the cross sectional area of the fuel assembly lattice is 26.7%. The core of the light water reactor of the present embodiment meets all the restrictive conditions and can maintain the breeding ratio 1.01. Furthermore, in the present embodiment, even if it is assumed that the overall core becomes the state of 100% void, which is impossible as an initiating event in the ABWR, the positive reactivity is not inserted to the nuclear fuel material zone 12. Particularly, in the present embodiment, even when the overall core enters the state of 100% void, the reactivity inserted to the core in the present embodiment becomes negative more than the reactivity inserted at that time in embodiment 1 because the outside diameter of the neutron absorbing member 3 is larger than the outside diameter of the neutron absorbing members 3 in embodiment 1. Furthermore, the present embodiment can obtain the effects occurred in embodiment 1. The present embodiment has the core structures of (2) and (3), so that the soundness of the fuel rods is increased and the thermal margin is increased. Accordingly, the present embodiment can improve more the safety margin without impairing the economical efficiency of fuel of the light water reactor. A core of the light water reactor according to embodiment 4 which is a further embodiment of the present invention will be explained below by referring to FIGS. 29 and 30. The core of the light water reactor of the present embodiment has the aforementioned core structures of (1) and (3) similarly to the core 20 of embodiment 1. The core of the present embodiment has a structure that in the core 20 of embodiment 1, the fuel assembly 41 is exchanged with a fuel assembly 41J. Other structure of the core of the present embodiment is the same as that of the core 20. The fuel assembly 41J has a structure that in the fuel assembly 41, the fuel rods 44 are exchanged with fuel rods 44H. Other structure of the fuel assembly 41J is the same as that of the fuel assembly 41. Each of the fuel rods 44H included in the fuel assembly 41J has a structure that the plenum 2 of the fuel rod 44 is exchanged with a plenum 2B. The fuel rod 44H has the plenum 2B, and the nuclear fuel material zone 16 and the neutron absorbing material filling zone 4 similar to that of the fuel rod 44. The plenum 2B is disposed above the nuclear fuel material zone 16 and the neutron absorbing material filling zone 4 is disposed under the nuclear fuel material zone 16. Outside diameters of the respective portions of the fuel rod 44H in the nuclear fuel material zone 16 and the neutron absorbing material filling zone 4 are 10.1 mm. The rate of the cross sectional area of the fuel pellet occupying in the cross section area of the unit fuel rod lattice in the channel box is 53%. The plenum 2B has a first zone 35C and a second zone 35D. An outside diameter of the portion of the plenum 2B in the first zone 35C is 5.8 mm and an outside diameter of the portion of the plenum 2B in the second zone 35D is 7.4 mm. The outside diameter of the portion in the second zone 35D is larger than the outside diameter of the portion in the first zone 35C. The first zone 35C is a small diameter portion and the second zone 35D is a large diameter portion. The second zone 35D is positioned above the first zone 35C. A length of the first zone 35C is 800 mm and a length of the second zone 35D is 300 mm. The lower end of the second zone 35D is positioned at a position (the upper end of the neutron absorbing member 3) 800 mm upward away from the upper end of the nuclear fuel material zone 16 and is positioned at the same position as that of the upper end of the first zone 35C. Each of the neutron absorbing members 3 with an outside diameter of 6 mm is disclosed between the mutual first zones 35C which are the small diameter portion of the neighboring fuel rods 44H. The core of the light water reactor of the present embodiment meets all the restrictive conditions and can maintain the breeding ratio 1.01. In the present embodiment, the volume of the plenum 2B is larger than that of the plenum 2 of embodiment 1 because the second zone 35D of the plenum 2B existing above the upper end of the neutron absorbing member 3 is a larger diameter portion. Thus, the pressure in the fuel rod 44H is lowered more and the soundness of the fuel rods 44H used in the present embodiment is increased more than that of the fuel rods 44H used in embodiment 1. The present embodiment can obtain the effects occurred in embodiment 1. The present embodiment has the core structures of (1) and (3), so that even if the overall core becomes the state of 100% void, the insertion of positive reactivity to the core can be avoided, and the thermal margin is increased. Accordingly, the present embodiment can improve more the safety margin without impairing the economical efficiency of fuel of the light water reactor. A core of a light water reactor according to embodiment 5 which is another embodiment of the present invention will be explained below by referring to FIG. 31 and Table 2. The core of the light water reactor of the present embodiment has the aforementioned core structures of (1) and (3). The light water reactor to which the core of the light water reactor of the present embodiment is applied is a TRU burner reactor. The core of the light water reactor of the present embodiment has a structure that in the core 20A of embodiment 2, the fuel assembly 41H is exchanged with a fuel assembly 41K. Other structure of the core of the present embodiment is the same as that of the core 20A. The fuel assembly 41K has a structure that in the fuel assembly 41H, the fuel rods 44F are exchanged with the fuel rods 44I. Other structure of the fuel assembly 41K is the same as that of the fuel assembly 41H. The rate of the cross sectional area of the fuel pellet occupying in the cross section area of the unit fuel rod lattice in the channel box is 36%. Each of the fuel rods 44I included in the fuel assembly 41K has a structure that the plenum 2 of the fuel rod 44F is exchanged with the plenum 2B. The fuel rod 44J has the plenum 2B, and the nuclear fuel material zone 16 and the neutron absorbing material filling zone 4A similar to that of the fuel rod 44. The plenum 2B having the first zone 35C and second zone 35D in embodiment 4 is disposed above the nuclear fuel material zone 16 and the neutron absorbing material filling zone 4A is disposed under the nuclear fuel material zone 16. The outside diameter of the portion of the plenum 2B in the first zone 35C is 3.7 mm and the outside diameter of the portion of the plenum 2B in the second zone 35D is 5.6 mm. The outside diameter of the portion in the second zone 35D is larger than the outside diameter of the portion in the first zone 35C. The second zone 35D is positioned above the first zone 35C. The lower end of the second zone 35D is positioned at a position (the upper end of the neutron absorbing member 3) 800 mm upward away from the upper end of the nuclear fuel material zone 16 and is positioned at the same position as that of the upper end of the first zone 35C. Each of the neutron absorbing members 3 with an outside diameter of 8.1 mm is disposed between the mutual first zones 35C which are the small diameter portion of the neighboring fuel rods 44I. The core of the light water reactor of the present embodiment meets all the restrictive conditions and can maintain the breeding ratio 1.01. In the present embodiment, the volume of the plenum 2B becomes larger than the volume of the plenum 2 used in embodiment 2 because the plenum 2B existing above the upper end of the neutron absorbing member 3 has the second zone 35D. Therefore, the pressure in the fuel rod 44I can be lowered and the soundness of the fuel rods 44I used in the present embodiment is increased more than that of the fuel rods 44F used in embodiment 2. The present embodiment can obtain the effects occurred in embodiment 2. The present embodiment has the core structures of (1) and (3), so that even if the overall core becomes the state of 100% void, the insertion of positive reactivity to the core can be avoided, and the thermal margin is increased. Accordingly, the present embodiment can improve more the safety margin without impairing the economical efficiency of fuel of the light water reactor. A core of a light water reactor according to embodiment 6 which is another embodiment of the present invention will be explained below by referring to FIGS. 32 to 34 and Table 3. The core 20B of the light water reactor of the present embodiment has the aforementioned core structures of (1) and (2). The light water reactor to which the core of the light water reactor of the present embodiment is applied is a TRU burner reactor. TABLE 3NuclideComposition (wt %)Np-2370.2Pu-2384.2Pu-2394.0Pu-24037.7Pu-2413.4Pu-24233.0Am-2414.3Am-242M0.2Am-2435.7Cm-2444.4Cm-2451.3Cm-2461.1Cm-2470.2Cm-2480.3 The core 20B of the present embodiment has a structure that in the core 20A of embodiment 2, the fuel assembly 41H is exchanged with a fuel assembly 41L. Other structure of the core 20B of the present embodiment is the same as that of the core 20A. The fuel assembly 41L has a structure that in the fuel assembly 41L, the fuel rods 44F are exchanged with the fuel rods 44J. Other structure of the fuel assembly 41L is the same as that of the fuel assembly 41H. The shape of the longitudinal section of the fuel assembly 41L is the same as the shape of the longitudinal section, shown in FIG. 25, of the fuel assembly 41H. The core 20B of the present embodiment is a one fissile zone core of electric power of 450 MW and is a core applied to the TRU burner reactor. The fuel assembly 41L loaded in the core 20B has 331 fuel rods 44J with an outside diameter of 8.7 mm arranged in an equilateral triangle lattice in the channel box 13. The gap between the mutual fuel rods 44J is 1.6 mm and a fuel rod row in the outermost layer includes ten fuel rods 44. The rate of the cross sectional area of the fuel pellet occupying in the cross section area of the unit fuel rod lattice in the channel box is 46%. In the core 20B the fuel assemblies 41A to 41D different in the experienced operation cycle number are disposed as shown in FIG. 33 in the state of the equilibrium core. The fuel assemblies 41D, the operation cycle of which is the fourth cycle, are disposed in the core outermost layer region 46. The fuel assemblies 41A, the operation cycle of which is the first cycle, are disposed in the core outer region 48 and the fuel assemblies 41B, 41C, and 41D, the operation cycles of which are respectively the second cycle, third cycle and fourth cycle, are respectively scattered and disposed in the core inner region 50. There exists an intermediate zone, in which a plurality of fuel assemblies 41B are disposed circularly, between the core inner region 50 and the core outer region 48. The power distribution of such a core 20B in the radial direction is flattened more. The fuel assemblies 41A to 41D shown in FIG. 33 are respectively the fuel assembly 41L. The nuclear fuel material zone 16B wherein the nuclear fuel material of the fuel assembly 41L exists (refer to FIG. 34) has the upper blanket zone 5, a fissile zone 34, and the lower blanket zone 9. The upper reflector zone 10 exists above the upper end of the upper blanket zone 5 and the lower reflector zone 11 exists below the lower end of the lower blanket zone 9. The height of the upper blanket zone 5 is 20 mm, and the height of the fissile zone 34 is 201 mm, and the height of the lower fissile zone 9 is 20 mm. Besides, the height of the upper reflector zone 10 is 1100 mm and the height of the lower reflector zone 11 is 70 mm. Although not shown, the nuclear fuel material zone 12 of the core 20B includes the upper blanket zone 5A, fissile zone 34A, and lower blanket zone 9A having the same heights as the respective heights of the upper blanket zone 5, fissile zone 34, and lower blanket zone 9. The upper blanket zone 5A, fissile zone 34A, and lower blanket zone 9A are disposed in this order in the axial direction of the core 20B. The outside diameter of the portion of the plenum 2 of the fuel rod 44J is 4.2 mm and the outside diameter of the neutron absorbing members 3 is 6.7 mm. The outside diameter of the portion of the neutron absorbing material filling zone 4A of the fuel rod 44J is 9.0 mm. The rate of the total cross sectional area of all the neutron absorbing members 3 to the cross sectional area of the fuel assembly lattice is 26.0%. The rate of the total cross sectional area of all the neutron absorbing material filling zone 4A to the cross sectional area of the fuel assembly lattice is 46.7%. When the burnup of the fuel assembly 41L is 0, all the fuel rods 44J (the fuel rods 44A to 44E shown in FIG. 19) of the fuel assembly 41L fill the upper blanket zone 5 and the lower blanket zone 9 with depleted uranium and fill the fissile zone 34 with TRU oxide fuel including TRUs of the composition shown in Table 3 in the state of a burnup of 0. The enrichment of fissionable Pu of the TRU oxide fuel is 7.4 wt % and the rate of Pu-239 in the TRU is 4.0 wt %. The TRUs included in the fuel assembly 41L are obtained by reprocessing the spent nuclear fuel included in the spent fuel assembly. Each blanket zone is not filled with the mixed oxide fuel and does not include TRUs. Further, in each blanket zone, natural uranium or degraded uranium recovered from the spent fuel assembly may be used instead of depleted uranium. During the operation of the light water reactor to which the core 20B of the present embodiment is applied, a sufficient quantity of the volatile fission product generated by the fission of the fissionable material in each of the fuel rods 44J can be stored in the plenum 2 with a length of 1100 mm. Therefore, the soundness of the fuel rods 44 is ensured. According to the present embodiment, even if it is assumed that the overall core becomes the state of 100% void, which is an impossible event as an initiating event in the ABWR, the insertion of positive reactivity to the nuclear fuel material zone 12 can be avoided because a plurality of neutron absorbing members 3 with a length of 500 mm are disposed at the position 300 mm upward from the upper end of the nuclear fuel material zone 12 and a plurality of neutron absorbing material filling zones 4A are disposed downward from the lower end of the nuclear fuel material zone 12. When the state results, negative reactivity is inserted to the nuclear fuel material zone 12. Furthermore, the present embodiment can obtain the effects occurred in embodiment 2. The present embodiment has the core structures of (1) and (2), so that it can improve more the safety margin without impairing the economical efficiency of fuel of the light water reactor. In the core 20B of the present embodiment, when the electric power of 450 MW is generated by using the reactor pressure vessel 27 of almost the same size as that of the current ABWR, the discharge burnup becomes 75 GWd/t, and the void coefficient becomes −3×10−5Δk/k/% void, and the MCPR becomes 1.3. In the core 20B, while the keeping of the rate of the TRU isotopes is realized, the weight of the TRUs obtained by reprocessing the spent nuclear fuel in the spent fuel assembly after 3 years from takeout of the fuel assembly 41L from the core 20B as a spent fuel assembly reduces a weight of 7.4% from the TRU weight of the fresh fuel assembly 41L loaded in the core. In addition, during the period from when the fuel assembly 41L is loaded in the core 20B to takeout, the TRU fission efficiency which is a rate of the TRU fission weight occupying in all the fission weights of the nuclear fuel material in the fuel assembly 41L is 80%. A core of a light water reactor according to embodiment 7 which is another embodiment of the present invention will be explained below by referring to FIGS. 10, 35, and 36 and Table 4. A core 20C of the light water reactor of the present embodiment has the core structure of (4). The core 20C of the light water reactor of the present embodiment is a core of the ABWR in which the electric power is 1350 MW and 872 fuel assemblies 41M are loaded. A plurality of control rods 47 with a cross-shaped cross section are inserted into the core 20C and withdrawn from the core 20C to control the reactor power. TABLE 4Taken-NuclideABCDEFGHout fuelTRU weight (t)1.511.201.040.930.860.790.700.700.67Np-2376.665.003.933.242.702.312.001.821.63Pu-2382.767.6510.0311.4412.3312.9813.3713.3913.45Pu-23948.8131.4724.8521.2118.4816.5314.9413.7012.47Pu-24023.0528.4129.9330.8531.4532.2233.1834.4135.47Pu-2416.959.508.667.606.685.905.124.183.66Pu-2425.058.4410.5612.0313.5014.5215.3816.0316.68Am-2414.674.765.756.547.127.568.018.668.97Am-242M0.020.060.090.110.130.140.160.180.20Am-2431.472.623.143.423.693.833.903.953.99Cm-2430.010.020.020.020.020.020.020.010.01Cm-2440.501.822.552.883.093.092.952.652.43Cm-2450.040.210.400.520.610.650.680.700.70Cm-2460.010.040.090.130.180.220.260.280.30Cm-2470.000.000.000.010.020.020.020.030.03Cm-2480.000.000.000.000.000.010.010.010.01 One fuel assembly 41M has 74 fuel rods and a cross section of the fuel assembly 41M is a square. In the fuel assembly 41M, as shown in FIG. 36, the 74 fuel rods with an outside diameter of 11.2 mm are arranged in the cylindrical channel box 13A with a square cross section. These fuel rods 44K are arranged in a square lattice shape. Two water rods 39 are arranged in the central portion of the cross section of the fuel assembly 41M. The height of the nuclear fuel material zone in which the nuclear fuel material of the core 20C is loaded is 3.71 mm. A plurality of fuel assemblies 41J loaded in the core 20C includes the fuel assemblies A, B, C, D, E, F, G, and H as shown in FIG. 10. These fuel assemblies fill TRUs different in the recycle frequency in the fuel rods 44K as a nuclear fuel material. Concretely, each of the fuel rods 44K of the fuel assemble A with a burnup of 0 is filled with the TRUs (TRUs of a recycle frequency of 1) obtained by reprocessing the spent nuclear fuel of the spent fuel assembly taken out from the equilibrium core. Each of the fuel rods 44K of the fuel assemble B with a burnup of 0 is filled with the TRUs (TRUs of a recycle frequency of 2) obtained by reprocessing the spent nuclear fuel of the fuel assembly A which is a spent fuel assembly taken out from the equilibrium core. Each of the fuel rods 44K of the fuel assemble C with a burnup of 0 is filled with the TRUs (TRUs of a recycle frequency of 3) obtained by reprocessing the spent nuclear fuel of the fuel assembly B which is a spent fuel assembly taken out from the equilibrium core. Similarly, each of the fuel rods 44K of the fuel assemble D with a burnup of 0 is filled with the TRUs (TRUs of a recycle frequency of 4) obtained from the spent nuclear fuel of the fuel assembly C and each of the fuel rods 44K of the fuel assemble E with a burnup of 0 is filled with the TRUs (TRUs of a recycle frequency of 5) obtained from the spent nuclear fuel of the fuel assembly D. Each of the fuel rods 44K of the fuel assemble F with a burnup of 0 is filled with the TRUs (TRUs of a recycle frequency of 6) obtained from the spent nuclear fuel of the fuel assembly E, and each of the fuel rods 44K of the fuel assemble G with a burnup of 0 is filled with the TRUs (TRUs of a recycle frequency of 7) obtained from the spent nuclear fuel of the fuel assembly F, and each of the fuel rods 44K of the fuel assemble H with a burnup of 0 is filled with the TRUs (TRUs of a recycle frequency of 8) obtained from the spent nuclear fuel of the fuel assembly G. The TRUs (TRUs of a recycle frequency of 1) filled in each of the fuel rods 44K of the fuel assembly A are recovered from the spent nuclear fuel of the fuel assembly with slightly enriched uranium filled in the fuel rods which does not include TRUs when the burnup is 0. TRUs different in the recycle frequency are not mixed and are separately filled in the fuel rods of different fuel assemblies (for example, the fuel assemblies A, B, C, etc.). In the core 20C, among the fuel assemblies A to H different in the recycle frequency of the TRUs, a plurality of fuel assemblies A including the TRUs having the least recycle frequency are disposed at the central part, and between the central part and the outermost layer zone of the core, the fuel assemblies including the TRUs having higher recycle frequencies are disposed on the side of the outermost layer zone of the core. Concretely, each fuel assembly of the fuel assemblies B, C, D, E, F, G, and H, in the alphabetic order, is disposed from the central part of the core where the fuel assemblies A are disposed toward the outermost layer zone. The core 20C includes 100 fuel assemblies A1, 40 fuel assemblies B1, 24 fuel assemblies C1, 16 fuel assemblies D1, 12 fuel assemblies E1, 8 fuel assemblies F1, 4 fuel assemblies G1, and 4 fuel assemblies H1. These numbers of fuel assemblies are the numbers when the fuel assemblies A1, B1, C1, D1, E1, F1, G1, and H1 are in the state of a burnup of 0. The fuel assemblies A to H loaded in the core 20C include fuel assemblies different in the in-core fuel dwelling time (the operation cycle number). The numerals 1, 2, 3, 4, and 5 attached after the alphabet (for example, A to H described next to the fuel assembly) for discriminating the fuel assembly including TRUs different in the recycle frequency indicate the in-core fuel dwelling time (the operation cycle number) of the concerned fuel assembly (for example, the fuel assembly A, the fuel assembly B, etc.). As the number increases, it means that the in-core fuel dwelling time is longer. The fuel assembly with “1” attached is a fuel assembly in the first cycle of the in-core fuel dwelling time and the fuel assembly with “5” attached is a fuel assembly in the fifth cycle of the in-core fuel dwelling time. For example, the fuel assembly A1 is a fuel assembly that includes TRUs of a recycle frequency of 1 and that is experiencing the operation in the first operation cycle after loaded in the core 20C. The fuel assembly E5 is a fuel assembly that includes TRUs of a recycle frequency of 5 and that is experiencing the operation in the fifth operation cycle after loaded in the core 20C. The fuel assemblies A to C and a part of the fuel assembly D are taken out from the nuclear reactor as a spent fuel assembly after finishing of the operation in the fourth operation cycle after loaded in the core 20C. The rest of the fuel assembly D and the fuel assemblies F to H are taken out from the nuclear reactor as a spent fuel assembly after finishing of the operation in the fifth operation cycle after loaded in the core 20C. In a plurality of fuel assemblies including TRUs of the same recycle frequency, the fuel assemblies different in the in-core fuel dwelling time are arranged in the neighborhood of each other. For example, in a certain fuel assembly A1, the fuel assemblies A4 are adjoined in right side and left side in FIG. 10 and the fuel assemblies A3 are adjoined up and down in FIG. 10. Table 4 shows the weight of each of the TRUs of the fuel assemblies A to H and the fuel assembly taken out as a spent fuel assembly and the composition of each of the TRUs. A to H shown in Table 4 are equivalent to the fuel assemblies A to H. The fuel assembly taken out as a spent fuel assembly is, for example, the fuel assembly H5. According to the core 20C of the present embodiment, when the void fraction of the core 20C is increased, the increase of the infinite neutron effective multiplication factor at the central part of the core 20C is made relatively smaller than the increase of the infinite neutron effective multiplication factor in the core outermost layer zone. Therefore, the shift of the power distribution to the central part of the core is reduced (refer to FIG. 9). Thus, although the nuclear fuel assemblies H1 to H5 including the TRUs of a recycle frequency of eight are loaded in the core 20C, the discharge burnup of the fuel assembly H5 taken out from the core 20C as a spent fuel assembly becomes 45 GWd/t and the void coefficient of the core 20C becomes −4×10−4% Δk/% void. In the core 20C, the number of generated spent fuel assemblies can be reduced to 0.5% or less compared with the case that the TRUs are not recycled. Though mixed oxide fuel of TRUs and depleted uranium is used as a nuclear fuel material in the fuel assemblies loaded in the core 20C of the present embodiment, natural uranium or degraded uranium recovered from spent fuel assemblies may be used instead of depleted uranium. Further, Pu extracted from the TRUs or several minor actinoid nuclides in the TRUs and Pu may be used instead of the TRUs. A core of a light water reactor according embodiment 8 which is another embodiment of the present invention will be explained below by referring to FIGS. 37 and 38. The core of the light water reactor of the present embodiment has the aforementioned core structures of (1), (2), and (3) similarly to the core 20 of embodiment 1. The core of the present embodiment has a structure that in the core 20 of embodiment 1, the fuel assembly 41 is exchanged with a fuel assembly 41N. Other structure of the core of the present embodiment is the same as that of the core 20. The fuel assembly 41N has a structure that in the fuel assembly 41, the fuel rods 44 are exchanged with the fuel rods 44L. Other structure of the fuel assembly 41N is the same as that of the fuel assembly 41. Each of the fuel rods 44L included in the fuel assembly 41N has the plenum 2, nuclear fuel material zone 16, and neutron absorbing material filling zone 4 similarly to the fuel rods 44 included in the fuel assembly 41. The outside diameters of the respective portions of the fuel rod 44L in the plenum 2, nuclear fuel material zone 16, and neutron absorbing material filling zone 4 are the same as the outside diameters of the portions of the fuel rods 44. The nuclear fuel material zone 16 in which the nuclear fuel material of the fuel assembly 41N exists has the upper blanket zone 5, upper fissile zone 6, internal blanket zone 7, lower fissile zone 8, and lower blanket zone 9 as shown in FIG. 37. The upper reflector zone 10 exists above the upper end of the upper blanket zone 5 and the lower reflector zone 11 exists under the lower end of the lower blanket zone 9. The height of the upper blanket zone 5 is 70 mm, and the height of the upper fissile zone 6 is 242 mm, and the height of the internal blanket zone 7 is 520 mm, and the height of the lower fissile zone 8 is 220 mm, and the height of the lower blanket zone 9 is 280 mm. The total of the height of the lower fissile zone 8 and the height of the higher fissile zone 6 is 462 mm and the height of the higher fissile zone 6 is 1.10 times the height of the lower fissile zone 8. The height of the upper reflector zone 10 is 1100 mm and the height of the lower reflector zone 11 is 70 mm. In the present embodiment, the fuel pellets filled in the higher fissile zone 6 of the fuel rod 44L, different from other embodiments, are all hollow pellets. In the fuel rod 44L, all the fuel pellets filled respectively in the upper blanket zone 5, internal blanket zone 7, lower fissile zone 8, and lower blanket zone 9 other than the higher fissile zone 6 are solid pellets used in other embodiments. When the burnup of the fuel assembly 41N is 0, all the fuel rods 44L of the fuel assembly 41N fill the three blanket zones with depleted uranium and fill the higher fissile zone 6 and lower fissile zone 8 with mixed oxide fuel. In the higher fissile zone 6 and lower fissile zone 8 of the fuel assembly 41N, assuming the TRU weight as 100, the enrichment of fissionable Pu with depleted uranium mixed at a rate of a weight of 173 are 18.0 wt % each. The TRUs are recovered from the spent nuclear fuel included in the fuel assembly 41N which is a spent fuel assembly by reprocessing. Each blanket zone is not filled with the mixed oxide fuel and does not include TRUs. Further, in each blanket zone, natural uranium or degraded uranium recovered from the spent fuel assembly may be used instead of depleted uranium. Fuel rods 44N to 44R are used as fuel rods 44L arranged in the fuel assembly 41N. The fuel rods 44N to 44R are arranged in the channel box 13 as shown in FIG. 38. In the fuel assembly 41N with a burnup of 0, the enrichment of fissionable Pu respectively in the higher fissile zone 6 and lower fissile zone 8 are 10.7 wt % in the fuel rods 44N, 13.5 wt % in the fuel rods 44Q, 16.8 wt % in the fuel rods 44P, 18.2 wt % in the fuel rods 44Q, and 19.5 wt % in the fuel rods 44R. The present embodiment can obtain each effect occurred in embodiment 1. The present embodiment has the core structures of (1), (2), and (3), so that even when the overall core becomes the state of 100% void, positive reactivity is not inserted to the nuclear fuel material zone 12, and the soundness of the fuel rods is increased, and the thermal margin is increased. Accordingly, the present embodiment can improve more the safety margin without impairing the economical efficiency of fuel of the light water reactor. The core of the present embodiment meets all the restrictive conditions and can maintain the breeding ratio 1.01. Furthermore, in the present embodiment, the enrichment of fissionable Pu are made equal to each other in the respective higher fissile zone 6 and lower fissile zone 8 of the fuel rods 44N to 44R of the fuel assembly 41N. Thus, in the present embodiment, the kind of the enrichment of fissionable Pu can be reduced from 9 kinds to 5 kinds compared with the fuel assembly 41N used in embodiment 1 different in the enrichment of fissionable Pu in the higher fissile zone 6 and lower fissile zone 8 and in correspondence to it, the kind of fuel pellets to be manufactured can be reduced. A core of a light water reactor according to embodiment 9 which is another embodiment of the present invention will be explained below by referring to FIG. 39. The core of the light water reactor of the present embodiment has the aforementioned structure of (2). The core of the present embodiment has a structure that in the core 20 of embodiment 1, the fuel assembly 41 is exchanged with a fuel assembly 41Q. Other structure of the core of the present embodiment is the same as that of the core 20. The fuel assembly 41Q has such a structure that the neutron absorbing members 3 and the neutron absorbing material zone 4 are removed in the fuel assembly 41. Other structure of the fuel assembly 41Q is the same as that of the fuel assembly 41. The fuel assembly 41Q has a plurality of fuel rods 44S. The fuel rods 44S have such a structure that the neutron absorbing material zone 4 is removed from the fuel rods 44. In the present embodiment, the outside diameter of the portion of the plenum 2 of the fuel rods 44S is 5.8 mm and the length of the plenum 2 is 1100 mm. The outside diameter of the portion of the nuclear fuel material zone 16 of the fuel rods 44A is 10.1 mm. The rate of the cross sectional area of the fuel pellet occupying in the cross section area of the unit fuel rod lattice in the channel box is 53%. Therefore, the soundness of the fuel rods can be increased because the volume of the plenum 2 is increased. Furthermore, even though the overall core becomes the state of 100% void, the reactivity inserted to the nuclear fuel material zone 12 becomes 1 dollar or less because the outside diameter of the portion of the plenum 2 formed in the fuel rods 44S is smaller than the outside diameter of the portion in the nuclear fuel material zone 16 under the plenum portion. Consequently, even though a composite event of a first accident beyond the design basis accident occurs, the fuel rods are automatically reduced in the power down to the coolable power at the flow rate of cooling water injected into the core by the operation of the high pressure core injection system, thus the safety margin of the BWR is kept. Accordingly the present embodiment can increase more the safety margin without impairing the economical efficiency of fuel of the light water reactor. The core of the present embodiment meets all the restrictive conditions and can maintain the breeding ratio 1.01. A core of a light water reactor according to embodiment 10 which is another embodiment of the present invention will be explained below by referring to FIG. 40 and Table 5. The core of the light water reactor of the present embodiment has the aforementioned core structures of (1), (2), and (3) similarly to the core 20A of embodiment 2. TABLE 5NuclideComposition (wt %)Np-2370.2Pu-2385.0Pu-23913.4Pu-24040.8Pu-2414.6Pu-24221.1Am-2414.7Am-242M0.2Am-2434.1Cm-2443.6Cm-2451.1Cm-2460.8Cm-2470.2Cm-2480.2 The core of the present embodiment has a structure that in embodiment 2, the fuel assembly 41H is exchanged with a fuel assembly 41R (refer to FIG. 41). Other structure of the core of the present embodiment is the same as that of the core 20A. The nuclear fuel material zone 16A in the fuel assembly 41R loaded in the core of the present embodiment has the upper blanket zone 5, upper fissile zone 6, internal blanket zone 7, and lower fissile zone 8 similarly to the fuel assembly 41H. The height of the upper blanket zone 5 is 50 mm, and the height of the upper fissile zone 6 is 183 mm, and the height of the internal blanket zone 7 is 560 mm, and the height of the lower fissile zone 8 is 173 mm. The upper reflector zone 10 with a height of 1100 mm exists and the lower reflector zone 11 with a height of 70 mm exists below the lower fissile zone 8 above the upper blanket zone 5. The height of the upper fissile zone 6 is 1.06 times the height of the lower fissile zone 8. In the fuel assembly 41R, 397 fuel rods with an outside diameter of 7.6 mm are arranged in an equilateral triangle lattice in the channel box 13. The gap between the mutual fuel rods is 1.8 mm and a fuel rod row in the outermost layer includes eleven fuel rods 44. When the burnup of the fuel assembly 41R is 0, all the fuel rods of the fuel assembly 41R fill the upper blanket zone 5 and the lower blanket zone 9 with depleted uranium and fill the upper fissile zone 6 and lower fissile zone 8 with TRU oxide fuel including TRUs of the composition shown in Table 5 in the state of a burnup of 0. The enrichment of fissionable Pu of the TRU oxide fuel is 18.0 wt % and the rate of Pu-239 in the TRU is 13.4 wt %. The present embodiment can obtain each effect occurred in embodiment 2. The core of the present embodiment can efficiently extinguish the TRUs even in the TRU composition different from the TRU composition of the fuel assembly 41H loaded in the core 20A of embodiment 2. A core of a light water reactor according to embodiment 11 which is another embodiment of the present invention will be explained below by referring to FIG. 41 and Table 6. The core of the light water reactor of the present embodiment has the core structures of (1) and (2) similarly to the core 20A of embodiment 2. TABLE 6NuclideComposition (wt %)Np-2375.49Pu-2382.51Pu-23944.25Pu-24025.79Pu-2418.45Pu-2427.44Am-2413.89Am-242M0.01Am-2431.59Cm-2440.54Cm-2450.03Cm-2460.01 The core of the present embodiment has a structure where in embodiment 2, the fuel assembly 41H is exchanged with a fuel assembly 41S (refer to FIG. 41). Other structure of the core of the present embodiment is the same as that of the core 20A. The nuclear fuel material zone 16A in the fuel assembly 41S loaded in the core of the present embodiment has the upper blanket zone 5, upper fissile zone 6, internal blanket zone 7, and lower fissile zone 8 similarly to the fuel assembly 41H. The height of the upper blanket zone 5 is 20 mm, and the height of the upper fissile zone 6 is 217 mm, and the height of the internal blanket zone 7 is 560 mm, and the height of the lower fissile zone 8 is 224 mm. Further, the height of the upper reflector zone 10 is 1100 mm and the height of the lower reflector zone 11 is 70 mm. The cross section of the fuel assembly 41S is the same as that shown in FIG. 23. When the burnup of the fuel assembly 41S is 0, all the fuel rods of the fuel assembly 41S fill the upper blanket zone 5 and internal blanket zone 7 with thorium oxide. When the burnup of the fuel assembly 41S is 0, the upper fissile zone 6 and lower fissile zone 8 of this fuel assembly 41S loaded in the core 20A of the present embodiment include the TRUs (hereinafter referred to as current core discharge TRUs) having the composition shown in Table 6 obtained by reprocessing the spent fuel assembly (including slightly enriched uranium) with a discharge burnup of 45 GWd/t taken out from the current ABWR core and mixed oxide fuel of thorium. The core loaded with the fuel assembly 41S of a burnup of 0 is a TRU first generation recycle core (hereinafter referred to as an RG1 core). In the current ABWR core, a fuel assembly including slightly enriched uranium is loaded. The current core discharge TRU having the composition shown in Table 6 is added to the TRU obtained by reprocessing the fuel assembly 41S taken out from the RG1 core as a spent fuel assembly, by the quantity that will make the core critical. The core loading the fuel assembly 41S of a burnup of 0 including mixed oxide fuel of the TRUs obtained by the addition and thorium in the upper fissile zone 6 and lower fissile zone 8 is a TRU second generation recycle core (hereinafter referred to as an RG2 core). Hereafter, every repetition of the TRU recycling, the current core discharge TRU is added to the TRU obtained by reprocessing the fuel assembly 41S which is a spent fuel assembly generated from the TRU recycle core of each generation, by the quantity that will make the core critical, and the fuel assembly 41S of a burnup of 0 including the TRU obtained by the addition and mixed oxide fuel of thorium in the upper fissile zone 6 and lower fissile zone 8 is loaded in the core 20A, and until the composition of the TRU obtained by reprocessing the fuel assembly 41S which is a spent fuel assembly taken out from the core 20A becomes almost constant, the TRU recycling is repeated. In FIG. 42, a characteristic 54 indicates weight of the current core discharge TRU added to fresh fuel assembly of a burnup of 0 loaded in the recycle core of each recycle generation and a characteristic 53 indicates weights of the TRUs in the spent fuel assemblies taken out from these recycle cores. In FIG. 43, a characteristic 55 indicates weight rate of Pu-239 included the TRUs in the fuel assembly of a burnup of 0 loaded in the recycle core of each recycle generation and a characteristic 56 indicates weight rate of Pu-239 included in the TRUs in the spent fuel assemblies taken out from these recycle cores. Each blanket zone is not filled with the mixed oxide fuel and does not include TRUs. The core of each recycle generation from the RG1 core to the RG10 core is loaded with fuel assemblies including the current core discharge TRU and having a discharge burnup of 65 GWd/t. In these recycle generation cores, the current core discharge TRU undergoes fission. In the present embodiment, in these recycle generation cores, when the void coefficient is negative like a characteristic 57 shown in FIG. 44, and like the characteristic 58, when the overall core becomes the state of 100% void, which cannot be caused as an initiating event in the BWR, and furthermore, even when it is assumed that all the control rods are not operated, no positive reactivity is inserted. The present embodiment can obtain each effect occurred in embodiment 2. The present embodiment can efficiently extinguish the TRUs, even in a nuclear fuel material of the TRU composition different from that of embodiment 2. In W. S. Yang et al., A Metal Fuel Core Concept for 1000 MWt Advanced Burner Reactor GLOBAL '07 Boise, USA, September, 2007, P. 52, the concept of a sodium cooling type ABR for permitting the TRU recovered by reprocessing the spent nuclear fuel of the light water reactor to fission and reduce in quantity is described. Furthermore, the literature describes that the TRUs generated from the light water reactor can be imprisoned in the light water reactor, ABR, and fuel cycle equipment by operating the light water reactor and ABR in operation at present in the coexistence thereof, and the TRUs need not be stored outside the nuclear reactor, and the quantity of a long-life radioactive waste material can be reduced greatly. However, the neutron energy in the core of the ABR is increased because the ABR uses a nuclear fuel material with TRUs enriched in depleted uranium and uses Na as a coolant. Therefore, simultaneously with that the enriched TRUs undergoes fission and are reduced in quantity, there are many TRUs newly created from U-238. To store all the quantity of TRUs from the light water reactor in operation at present in the ABR, the ABR needs to be built at a rate of one ABR per each light water reactor. It is expected that the power generation cost of the ABR becomes higher than that of the light water reactor, so that compared with the case of the operation of only the light water reactor, there is concern that the economical efficiency of fuel may be impaired. Therefore, instead of enriching the TRUs in depleted uranium, a fuel assembly including a nuclear fuel material with TRUs enriched in thorium for newly generating no TRUs is loaded in a TRU burner reactor described in Japanese Patent Laid-Open No. 2008-215818 including low neutron energy in the core and is operated, thus new generation of TRUs is prevented and the TRU fission efficiency can be promoted. Therefore, the TRUs of three light water reactors can be permitted to fission by one TRU burner reactor of the present embodiment, thus a Na cooling ABR of a high power generation cost is unnecessary and the economical efficiency of fuel is improved greatly. A core of a light water reactor according to embodiment 12 which is another embodiment of the present invention will be explained in detail below by referring to FIGS. 45 and 46 and Tables 7 and 8. The core of the present embodiment is the core 20C similar to that of embodiment 7 and is a core of the ABWR in which the electric power in operation at present is 1350 MW and 872 fuel assemblies having 74 fuel rods per each fuel assembly are loaded. This core is the core of the TRU burner reactor. With respect to the structure of the present embodiment, the portion different from that of embodiment 7 will be explained and the explanation of the same portion as that of embodiment 7 will be omitted. TABLE 7NuclideComposition (wt %)Np-2376.66Pu-2382.76Pu-23948.81Pu-24023.05Pu-2416.95Pu-2425.05Am-2414.67Am-242M0.02Am-2431.47Cm-2430.01Cm-2440.50Cm-2450.04Cm-2460.01 The cross section of the core 20C of the present embodiment is the same as that shown in FIG. 35 and the cross section of the fuel assembly 41M loaded in the core 20C is the same as that shown in FIG. 36. In the core 20C, the fuel assembly 41M in which the height of the nuclear fuel material zone is 3.71 m is loaded. Further, in the core of the PWR, fuel assemblies including slightly enriched uranium are loaded. The core loading a fuel assembly of a burnup of 0 having mixed oxide fuel of the TRUs (hereinafter referred to as current core discharge TRUs) having the composition shown in Table 7 obtained by reprocessing the spent fuel assembly with a discharge burnup of 50 GWd/t taken out from the core of the PWR, and depleted uranium is a TRU first generation recycle core (hereinafter referred to as an RG1 core). The current core discharge TRUs having the composition shown in Table 7 are added to the TRUs obtained by reprocessing the fuel assembly taken out from the RG1 core, by the quantity that will make the core critical. The core loading the fuel assembly of a burnup of 0 having mixed oxide fuel including depleted uranium and the TRUs obtained by the addition is a TRU second generation recycle core (hereinafter referred to as an RG2 core). Hereafter, every repetition of the TRU recycling, the current core discharge TRUs are added to the TRUs obtained by reprocessing the spent fuel assembly taken out from the recycle core of each generation, by the quantity that will make the core critical, and the fuel assembly of a burnup of 0 having mixed oxide fuel of the obtained TRUs and depleted uranium is loaded in the core. TABLE 8RG8 Taken-NuclideRG1RG2RG3RG4RG5RG6RG7RG8out fuelTRU weight (t)3.144.465.486.306.977.558.048.487.57Np-2376.665.775.174.724.374.083.853.662.94Np-2390.000.000.000.000.000.000.000.000.02Pu-2382.765.416.867.868.609.159.579.8911.35Pu-23948.8139.3535.1232.4730.5729.1227.9727.0322.26Pu-24023.0526.0327.0127.5727.9728.2828.5228.7329.47Pu-2416.958.338.318.067.797.567.357.188.12Pu-2425.056.868.008.859.5310.1210.6311.0812.57Am-2414.674.755.105.405.625.795.916.005.22Am-242M0.020.040.060.070.080.080.090.090.11Am-2431.472.082.412.632.792.913.013.093.45Cm-2420.000.000.000.000.000.000.000.000.30Cm-2430.010.020.020.020.020.020.020.020.02Cm-2440.501.201.661.962.182.342.462.553.33Cm-2450.040.130.230.310.370.410.450.470.57Cm-2460.010.030.050.080.100.130.160.180.24Cm-2470.000.000.000.000.010.010.010.020.02Cm-2480.000.000.000.000.000.000.000.010.01 Table 8 shows the TRU composition included in the fuel assembly of a burnup of 0 in the recycle core of each recycle generation from the RG1 core to the RG8 core and the composition of the TRUs included in the spent fuel assemblies taken out from the RG8 core. In FIG. 45, weights of the current core discharge TRUs added to the fuel assembly of a burnup of 0 loaded in the recycle core of each recycle generation from the RG1 core to the RG8 core are indicated in a characteristic 60 and weights of the TRUs included in the spent fuel assemblies taken out from these recycle cores are indicated in a characteristic 59. In FIG. 46, weight rate of Pu-239 included in the TRUs in the fuel assembly of a burnup of 0 loaded in the recycle core of each recycle generation from the RG1 core to the RG8 core is indicated in a characteristic 61 and weight rate of Pu-239 included in the TRUs in the spent fuel assemblies taken out from these recycle cores is indicated in a characteristic 62. The core of each recycle generation from the RG1 core to the RG8 core is loaded with the fuel assemblies including the current core discharge TRUs and having a discharge burnup of 45 GWd/t. In these recycle generation cores, the current core discharge TRUs undergo fission. In the present embodiment, in these recycle generation cores, when the void coefficient is negative like the characteristic 63 shown in FIG. 47, and like the characteristic 64, when the overall core becomes the state of 100% void, which cannot be caused as an initiating event in the BWR and furthermore, even when it is assumed that all the control rods are not operated, no positive reactivity is inserted in up to the RG7 core. The RG8 core has a sufficient negative void coefficient for safety's sake although the positive reactivity is 1 dollar or less. In the present embodiment, the spent fuel assemblies from the RG1 core to the RG7 core are all reprocessed and the discharge TRUs are handed over to the next recycle generation core together with the current core discharge TRUs. Therefore, among the RG1 to the RG8, only 208 fuel assemblies taken out from the RG8 core every year can remain as a spent fuel assembly. On the other hand, about 8000 spent fuel assemblies must be reprocessed in term of the fuel assemblies of slightly enriched uranium currently in use by the ABWR in order to supply about 14 tons of TRUs used in the RG1 to the RG8. The ABWR of the present embodiment and the ABWR using slightly enriched uranium in operation at present are used jointly, thus the number of residual spent fuel assemblies can be greatly reduced to about 2.6% of that when only the ABWR using slightly enriched uranium fuel is operated. A core of a light water reactor according to embodiment 13 which is another embodiment of the present invention will be explained in detail below by referring to FIGS. 48 to 50 and Table 6. The core of the present embodiment is the core 20C similar to that of embodiment 12 and is a core of the ABWR in which the electric power in operation at present is 1350 MW and 872 fuel assemblies having 74 fuel rods per each fuel assembly are loaded. This core is the core of the TRU burner reactor. With respect to the structure of the present embodiment, the portion different from that of embodiment 12 will be explained and the explanation of the same portion as that of embodiment 12 will be omitted. In the core 20C of the present embodiment, the fuel assembly 41M in which the height of the nuclear fuel material zone is 3.71 m is loaded. Further, in the core of the PWR, fuel assemblies including slightly enriched uranium are loaded. Further, in the core of the ABWR, fuel assemblies including slightly enriched uranium are loaded. The core loading a fuel assembly of a burnup of 0 including mixed oxide fuel of the TRUs (hereinafter referred to as current core discharge TRUs) having the composition shown in Table 6 obtained by reprocessing the spent fuel assembly with a discharge burnup of 45 GWd/t taken out from the core of the PWR and thorium is a TRU first generation recycle core (hereinafter referred to as an RG1 core). The current core discharge TRUs having the composition shown in Table 6 are added to the TRUs obtained by reprocessing the fuel assembly taken out from the RG1 core, by the quantity that will make the core critical. The core loading the fuel assembly of a burnup of 0 having mixed oxide fuel of the TRUs obtained by addition and thorium is a TRU second generation recycle core (hereinafter referred to as an RG2 core). Hereafter, every repetition of the TRU recycling, the current core discharge TRUs are added to the TRUs obtained by reprocessing the spent fuel assembly taken out from the recycle core of each generation, by the quantity that the core becomes critical, and the fuel assembly of a burnup of 0 having mixed oxide fuel of the obtained TRUs and thorium is loaded in the core. In FIG. 48, a characteristic 66 indicates weight of the current core discharge TRU added to the fuel assembly of a burnup of 0 loaded in the recycle core of each recycle generation and a characteristic 65 indicates weights of the TRUs in the spent fuel assemblies taken out from these recycle cores. In FIG. 49, a characteristic 67 indicates weight rate of Pu-239 included the TRUs in the fuel assembly of a burnup of 0 loaded in the recycle core of each recycle generation and a characteristic 68 indicates weight rate of Pu-239 included in the TRUs in the spent fuel assemblies taken out from these recycle cores. The core of each recycle generation from the RG1 core to the RG4 core is loaded with the fuel assemblies including the current core discharge TRUs and having a discharge burnup of 45 GWd/t. In these recycle generation cores, the current core discharge TRUs undergo fission. In the present embodiment, in these recycle generation cores, when the void coefficient is negative in up to the RG3 like the characteristic 69 shown in FIG. 50 and like the characteristic 70 shown in FIG. 50, and when the overall core becomes the state of 100% void, which cannot be caused as an initiating event in the ABWR and furthermore, even when it is assumed that all the control rods are not operated, in up to the RG3 core, no positive reactivity is inserted. In the present embodiment, the problems for safety must be solved in the TRU multiple-recycling in and after the RG4 core, but the use quantity of the current core discharge TRUs of the RG1 is large compared with the ABR and other embodiments. Assuming that before the reprocessing technology of fuel assemblies including thorium is established, the reprocessing is not executed in and after the RG2 core for the present, the case that the RG1 core and the current ABWR using slightly enriched uranium are used jointly is evaluated. 208 spent fuel assemblies are taken out every year from the RG1 core. On the other hand, about 3200 spent fuel assemblies of the fuel assemblies of slightly enriched uranium currently in use by the ABWR must be reprocessed to supply about 5.7 tons of TRUs used in the RG1. The ABWR of the RG1 core and the ABWR using slightly enriched uranium in operation at present are used jointly, thus the number of residual spent fuel assemblies can be greatly reduced to about 6.5% of that when only the ABWR using slightly enriched uranium fuel is operated. The present embodiment is one of the methods capable of realizing the great reduction of the number of residual spent fuel assemblies only by changing the fuel assemblies in the ABWR in operation at present. Further, when disposing the spent fuel assemblies straight in the ground, which is considered at present as one of the choices of the TRU disposal, it is considered that mixed oxide fuel pellets of TRUs and thorium are far stable chemically than mixed oxide fuel pellets of TRUs and uranium, so that it is a valid method before the reprocessing technology of fuel assemblies including thorium is established. 1: boiling water reactor, 2, 2A, 2B: plenum, 3, 3A, 3B: neutron absorbing member, 4: neutron absorbing material filling zone, 5, 5A: upper blanket zone, 6, 6A: upper fissile zone, 7, 7A: internal blanket zone, 8, 8A: lower fissile zone, 9, 9A: lower blanket zone, 10: upper reflector zone, 11: lower reflector zone, 12, 16, 16A: nuclear fuel material zone, 14: upper tie-plate, 15: lower tie-plate, 20, 20A: core, 25: core shroud, 27: reactor pressure vessel, 34: fissile zone, 35A, 35C: first zone, 35B, 35D: second zone, 41, 41A-41N, 41Q-41S: fuel assembly, 42, 47: control rod, 44, 44A-44N, 44P-44S: fuel rod.
050227882	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the disposal of waste materials and, more particularly, to the permanent disposal of nuclear and toxic materials by depositing such materials in a subtending tectonic plate adjacent or as near as possible to a subduction zone. 2. Description of the Prior Art The disposal of radioactive wastes from nuclear reactors and other atomic energy activities and of toxic byproducts caused by manufacturing and medical and biologic activities is an area of widespread concern. The long half-life of radioactive waste products and chemical compounds in which radioactivity is found presents a formidable obstacle to storage which will be inherently safe over the years. This is more clearly understood when it is realized that roughly 2.23 cubic meters of solid radioactive nuclear waste are produced annually by a conventional 1000 MW reactor. It is estimated that in the United States, the quantity of high-level radioactive waste generated by reactors to the present time would cover a football field to a height of three feet. Highly toxic Plutonium 239, which is included with this waste, has a half-life of approximately 25,000 years. Ten half-lives are required to reduce this radioactivity by a factor of one-thousand (1,000) which is generally considered to be the required safety level for exposure in the atmosphere. Thus, Plutonium 239 wastes should be isolated for a period of at least 250,000 years. Such toxic material must therefore be disposed in a location where it is impossible for the waste to find its way back into the environment for at least 250,000 years and, preferably, much longer. In respect of chemical wastes such as PCB's, however, they may retain their toxicity indefinitely and, therefore, it is desirable to ensure they remain undisturbed until their eventual destruction. Presently, nuclear wastes are initially removed from a reactor and are placed in large vats of water while a cooling process takes place. Thereafter, they must be stored. Various techniques of storage have been considered including geologic repositioning within the continental crust and the implantation of solidified high-level waste or spent nuclear fuel into stable clay type sediments in low circulation regions in the mid-ocean. In addition, the construction of boreholes having the capability to store such wastes in the tectonic plate adjacent a subduction zone is described in U.S. Pat. No. 5,4,178,109 to Krutenat. Such techniques, however, suffer inherent disadvantages. Nuclear wastes disposed of in a geologic repository on the continental crust have the potential to be tampered with by individuals or countries. Such wastes may accidentally be unearthed in the future by various actions and thereby become exposed to the environment. Wastes in a geologic repository also have the potential for intermingling with and contaminating the water cycle. Earthquake activity is also a problem in that it may fracture the geologic repository and release waste back into the environment. Volcanic activity, an act of war or sabotage, or impact by a celestial body could produce the same result. A lack of international consensus or agreement is a major obstacle to the implantation of high-level radioactive waste containers in clay type sediments in the low circulation regions of the mid-ocean. Waste implanted in ocean sediments would also be subjected to natural upheavals and to mechanical perturbation once they eventually migrated to a subduction zone, as all seabeds are so predestined, as a portion of the sediment would be scraped off along the abutting continental edge. Wastes could then migrate back to the biosphere because of this abrasive action. Even if the sediment and embedded waste were subducted, the waste could return to the environment because of andesitic volcanism adjacent the subduction zone. This is so because it is believed that at a depth of near one hundred (100) kilometers within the earths crust, heat and pressure cause water to be driven from the crystalline structure of the subducted sediments. The heat generated by this phase change combined with the temperature of the rock at that depth causes some of the sediment and overlaying rock to melt and to rise to the surface as volcanoes. Waste melted along with the sediment could thereby return to the biosphere dissolved in the molten rock creating an undesirable environmental condition. In the aforementioned U.S. Pat. No. 4,178,109, there is proposed a technique of disposing of wastes in boreholes at the edge of a subduction zone. While this is an improvement in the location of waste repositories, many problems remain inherent in this solution. Boring a single hole into the seabed from a platform on the surface of the ocean is a difficult and painstaking undertaking and hundreds of such boreholes would be required to accommodate world backlogs of high-level nuclear wastes because of the inherent size limitation caused by drilling. After construction of the borehole in the seabed, it would be difficult to relocate the hole and to deposit the waste into the hole. Such depositing would, apparently, require manipulation of the waste by apparatus located on the sea floor to fill the hole. This could not only be hazardous but an accident while filling the hole could scatter radioactive debris over the seabed. The waste, probably, would also inherently be required to be unshielded when deposited, again because of the diameter of the borehole which would prohibit protective sheathing from being inserted with the waste. Likewise, the problem of scouring mechanical action as the subtending oceanic crust scraped against the non-descending crust would create problems since waste implanted in boreholes in the oceanic crust any distance from the originating ridge would likely be necessarily implanted in the sedimentary layer. This sedimentary layer is, on average, three (3) to four (4) kilometers thick at the subduction zone. In respect of toxic wastes such as chemical, medical and biological wastes, typical previous disposal techniques include incineration and burial or dumping of such wastes in the sea. These are also disadvantageous. Incineration of toxic wastes requires the process to be conducted within exacting tolerances. Otherwise, the potential for generating other poisons, which may be even more hazardous than those originally intended for disposal, exists. Even when carried out under ideal conditions, incineration is inherently atmospheric polluting. Burying toxic wastes and low-level radioactive wastes has also proven disadvantageous. There have been instances where buried wastes have percolated through the overburden meant to isolate it, thereby contaminating the overlaying property such as the Love Canal, in upstate New York, U.S.A. Buried wastes have frequently been inundated by or have themselves seeped into subterranean aquifers thereby fouling the fresh water supply. Medical and other wastes thought to have been eliminated when dumped at sea frequently have washed ashore and have received widespread publicity in doing so. The earth's crust is formed of large solid tectonic plates. These large tectonic plates are formed at ocean ridges and slowly migrate until they reach "subduction" zones at which location they re-enter the earth at an average rate of six (6) cm per year. An objective of the present invention is to place waste material in repositories radiating outwardly from an access tunnel bored into the basaltic layer of the oceanic crust beneath sediments overlaying the basaltic layer at or as near as possible the edge of a subduction zone. The access tunnel would originate from land on the nondescending side of a subduction zone, from the surface of the subducting plate itself, from a man-made or naturally formed island situated over a tectonic plate that is moving towards a subduction zone or from a caisson situated over the subtending tectonic plate. Each repository filled with waste would be sealed from the access and, accordingly, the biosphere, by a plug. The crustal downwards movement of the tectonic plate would carry the waste into the interior of the earth. Many millions of years would be required for the waste to circulate through the earth's mantle before it could reemerge in a diluted, chemically and physically altered form at an oceanic ridge. There are several areas located throughout the world that are favorable locales for the tunnel and repository process described herein. In Canada, the Brooks Peninsula on Vancouver Island in the Province of British Columbia, Canada and the Scott Islands north of Vancouver Island are located on the non-descendlng, North American Plate side of the Cascadia subduction zone. They are located near enough to the subducting Explorer Plate to make accessing the subducting plate by a tunnel with an origin on the North American side of the subduction zone possible. The subduction zone is also shallow enough, in the range of 1 mile, opposite these sites to permit successful tunneling beneath the Pacific Ocean. In the United States, Cape Mendecino north of San Francisco in the State of California is similarly situated but located a greater distance from the subducting zone. A tunnel from Cape Mendecino into the subducting Gorda Plate would likely be of similar dimensions to the one recently completed in Japan to link the islands of Honshu and Hokkaido and to the tunnel between France and Great Britain presently under construction. Accordingly, the feasibility of constructing such a tunnel has been demonstrated. In New Zealand, the subduction of the Pacific Plate beneath the Indo-Australian Plate takes place partially on the North Island. To implement the process according to the invention in New Zealand, a tunnel would only have to be pushed far enough into the Pacific side of the North Island that waste deposited in repositories radiating from it would not be encountered accidentally by mineral or petroleum prospectors in the future. The Hawaiian and Mariana Islands are situated above tectonic plates moving towards subduction zones. Tunnels from these or similar islands could access repositories in an oceanic plate which would be subducted at some predictable time in the future. It may also be feasible to construct a man-made island as near as possible to the subduction zone so that repositories could be accessed via a tunnel, originating on the island, constructed into the subducting plate. Such an island, for example, has been constructed in the Beaufort Sea and used as a base for drilling exploratory oil and gas wells. A caisson could also be used to access a shallow tectonic plate near a subduction zone so that repositories could be radiated from an accessing tunnel constructed from the caisson which would act similar to a man-made island. Once accessed, the subducting plate could yield as many waste repositories as necessary to eliminate current waste backlogs as well as future requirements. Each repository, once filled, would be sealed from the tunnel access and, accordingly, the biosphere by a plug. SUMMARY OF THE INVENTION Briefly, the present invention comprise's a method for the disposal of waste material. The waste material is placed into repositories radiating from an accessing tunnel tunnelled into the tectonic plate adjacent or as near as possible to a subduction zone. The descending tectonic plate carries the waste material into the earth's mantle. Another object of the present invention is to provide a method for disposing nuclear and toxic waste by placing the waste in a repository deep enough in the tectonic plate so that it will not return to the environment as a consequence of the mechanical action as the descending plate scrapes against the non-descending plate or volcanism as a result of a phase change and melting of the sediment taking place at depth. Still another object of the present invention is to provide a method for disposing nuclear waste in a repository in the tectonic plate which is sufficiently large so that nuclear waste can be transported to and placed in the repository in shielded containers. Still another object of the present invention is to provide a method for disposing stockpiled toxic wastes in a repository in the tectonic plate which repository is sufficiently large such that toxic wastes could be transported to and placed in the repository in the containers in which they are stockpiled. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:
	claims	1. A method of determining the magnification Mref for a line scan camera that transports a work piece to be imaged in orthogonal x and y axis directions while at a fixed height along a z axis normal to the x-y plane containing the x and y axes, the method comprising the steps of:(a) transporting at a fixed location zcal along the z axis and in the y axis direction a calibration target having opaque edges parallel to the x and y axes and both opaque edges in a plane parallel to the x-y plane;(b) while performing step (a), illuminating the calibration target with actinic radiation emanating in a generally uniform conical pattern from a point source and in a direction toward the calibration target and then further toward a multiple element detector of the actinic radiation disposed upon a detection plane parallel to the x-y plane, the conical pattern having an axis normal to the detection plane, and the multiple element detector having a plurality of xi detection elements responsive to the actinic radiation along a line parallel to the x axis;(c) while performing step (b), collecting and storing at regular intervals of transport motion in step (a) the plurality of detection element outputs Yjα@Xi that, at successive locations yj Δy apart along the y axis, are the respective outputs α of an ith detection element xi of the multiple element detector having some location along the x axis within the detection plane;(d) while performing step (b), collecting and storing at regular intervals of transport motion in step (a) the plurality of detection element outputs Xiα@Yj that, at successive locations Δx apart along the x axis, are the respective outputs α of each ith detection element xi of the multiple element detector having some location along the y axis within the detection plane;(e) selecting an arbitrary trial magnification value Mi from among a range of possible magnification values;(f) while a trial magnification value Mi is in effect:(f1) subsequent to each instance of step (e), for each zi in a range from a selected zmin along the z axis and by steps of a Δz toward a selected zmax along the z axis, zmin<zcal<zmax, reconstructing the image at the height zi;(f2) subsequent to each instance of step (f1), inspecting the reconstructed image for Mi for a value zx of zi that exhibits a sharp x axis edge and a value zy of zi that exhibits a sharp y axis edge;(f3) subsequent to each associated instances of steps (f1) and (f2), saving a value ei that is indicative of the difference between the associated zx and zy;(f4) subsequent to steps (f1), (f2) and (f3), selecting an unused next value for Mi until a selected number of different Mi have been in effect;(g) fitting a function e=f (M) to the set of data {(ei), (Mi)}; and(h) finding the y intercept Mj of e=f (M) and taking Mj to be the value of Mref. 2. A method as claim 1 wherein step (a) comprises motion in a serpentine pattern having legs parallel to the y direction and that are each a step apart in the x direction. 3. A method of determining the magnification Mref for a line scan camera that transports a work piece to be imaged in orthogonal x and y axis directions while at a fixed height along a z axis normal to the x-y plane containing the x and y axes, the method comprising the steps of:(a) transporting at a fixed location zcal along the z axis and in the y axis direction a calibration target having opaque edges parallel to the x and y axes and both opaque edges in a plane parallel to the x-y plane;(b) while performing step (a), illuminating the calibration target with actinic radiation emanating in a generally uniform conical pattern from a point source and in a direction toward the calibration target and then further toward a plurality of multiple element detectors of the actinic radiation arranged in a detection plane parallel to the x-y plane, the conical pattern having an axis normal to the detection plane, and each multiple element detector having a plurality of xi detection elements responsive to the actinic radiation along a line parallel to the x axis;(c) for each multiple element detector and while performing step (b), collecting and storing at regular intervals of transport motion in step (a) the plurality of detection element outputs Yjα@Xi that, at successive locations yj Δy apart along the y axis, are the respective outputs α of an ith detection element xi of the multiple element detector having some location along the x axis within the detection plane;(d) for each multiple element detector and while performing step (b), collecting and storing at regular intervals of transport motion in step (a) the plurality of detection element outputs Xiα@Yj that, at successive locations Δx apart along the x axis, are the respective outputs α of each ith detection element xi of the multiple element detector having some location along the y axis within the detection plane;(e) selecting an arbitrary trial magnification value Mi from among a range of possible magnification values;(f) while a trial magnification value Mi is in effect;(f1) subsequent to each instance of step (e), for each zi in a range from a selected zmin along the z axis and by steps of a Δz toward a selected zmax along the z axis, zmin<zcal<zmax, reconstructing the image at the height zi;(f2) subsequent to each instance of step (f1), inspecting the reconstructed image for Mi for a value zx of zi that exhibits a sharp x axis edge and a value zy of zi that exhibits a sharp y axis edge;(f3) subsequent to each associated instances of steps (f1) and (f2), saving a value ei that is indicative of the difference between the associated zx and zy;(f4) subsequent to steps (f1), (f2) and (f3), selecting an unused next value for Mi until a selected number of different Mi have been in effect;(g) fitting a function e=f (M) to the set of data {(ei), (Mi)}; and(h) finding the y intercept Mj of e=f (M) and taking Mj to be the value of Mref. 4. A method as in claim 3 wherein step (b) comprises illuminating the calibration target with actinic radiation that comprises x-rays. 5. A method as in claim 4 wherein the calibration target comprises a sheet of tungsten. 6. A method as in claim 5 wherein the sheet of tungsten comprises an orificethat is a right isosceles triangle. 7. A method as in claim 3 wherein steps (a), (b), (c) and (d) further comprise the respective steps of transporting, illuminating, collecting and storing for a workpiece comprising a printed circuit assembly and a step (i) of forming reconstructed images thereof at selected values of zi by using shifts and accumulation upon Yα@Xi and Xαi@Yi that are thus formed. 8. A method as in claim 7 wherein step (b) comprises illuminating the workpiece with actinic radiation that comprises x-rays. 9. A method as in claim 7 wherein the workpiece is transparent to at least some wavelengths of visible light and wherein step (b) comprises illuminating the workpiece with visible light. 10. A method as in claim 3 wherein the plurality of multiple element sensors comprises a generally circular arrangement of multiple element sensors disposed upon the detection plane at known locations relative to each other. 11. A method as in claim 3 wherein the plurality of multiple element sensors comprises a regular arrangement of multiple element sensors disposed upon the detection plane at known locations relative to each other, and wherein the regular arrangement comprises the vertices of a regular geometric figure. 12. A method as in claim 3 wherein the plurality of multiple element sensors comprises an arbitrary arrangement of multiple element sensors disposed upon the detection plane at known locations relative to each other. 13. A method as in claim 3 wherein step (a) comprises motion in a serpentine pattern having legs parallel to the y direction and that are each a step apart in the x direction. 14. A method as in claim 3 wherein the plurality of multiple element sensors comprises time domain integration sensors.
	description	1. Field of the Invention The present invention relates to a device for generating entangled photon pairs. The device is applicable to quantum cryptographic systems, quantum computers, and other quantum information communication systems that exploit quantum correlation of photon pairs. 2. Description of the Related Art In recent years, information technology has reached the quantum mechanical level. Quantum cryptography and quantum computing are attracting attention. In particular, quantum cryptography, in which the security of an encryption key is guaranteed by the principles of quantum mechanics, is now regarded as the ultimate secure cryptographic communication system and has been under active research and development. A source of quantum correlated, that is, entangled photon pairs is an essential element for realizing advanced quantum information communication systems taking advantage of the quantum nonlocality of photon pairs. One known method for generating quantum entangled photon pairs uses spontaneous parametric down-conversion (SPDC) in a second-order nonlinear optical medium. In U.S. Pat. No. 7,211,812 (Japanese Patent Application Publication No. 2003-228091, now Japanese Patent No. 4098530), Takeuchi describes a quantum entangled photon pair generating device using β-BaB2O4 (BBO) crystals as second-order nonlinear optical media. Two BBO crystals are aligned in series with a half-wave plate centered between them. Input of linearly-polarized excitation light (pump light) with a wavelength of 351.1 nm produces spontaneous parametric down conversion in the BBO crystals, generating quantum correlated photon pairs with a wavelength equal to twice the wavelength of the excitation light (equal to 702.2 nm). The two photons in each pair are referred to as the signal photon and the idler photon. The half-wave plate rotates the polarization of the photons generated in the first BBO crystal by 90°. When the intensity of the excitation light is sufficiently weak and the probability of the occurrence of spontaneous parametric down conversion in both BBO crystals simultaneously is negligible, the device outputs a signal photon beam and a spatially separated idler photon beam in which each photon in each beam has an equal probability of having been generated in each of the two BBO crystals, and its polarization state is a superposition of two states with mutually orthogonal polarization planes. The signal and idler photons in each pair are said to be polarization entangled in that both give the same result when their polarization is measured in the same way. Many other systems using similar structures to generate quantum entangled photon pairs with wavelengths in the 700 nm to 800 nm band have been reported. Generating entangled photon pairs with wavelengths in the 1550-nm band, which is the minimum absorption loss wavelength band of optical fibers, would be very useful in anticipation of long-haul quantum information communication systems. In Japanese Patent Application Publication No. 2005-258232, Inoue describes a 1550-nm quantum entangled photon pair generating device using periodically poled lithium niobate (PPLN) waveguides as second-order nonlinear optical media. This device has a fiber loop structure incorporating two PPLN waveguides and a polarizing beam splitter (PBS). The two PPLN waveguides are displaced so that their optical axes are mutually orthogonal. A femtosecond excitation light pulse with a wavelength of 775 nm and 45° plane polarization is input through the PBS, which splits it into photons having equal probabilities of being aligned in polarization with the axis of each PPLN waveguide. Like the BBO crystals described above, the PPLN waveguides generate quantum correlated photon pairs by spontaneous parametric down conversion, but the signal and idler photons have wavelengths of 1550 nm. A 1550-nm wavelength quantum entangled photon pair generating device using a PBS and a polarization maintaining optical fiber loop with a single PPLN element has been described by Lim et al. in Stable source for high quality telecom-band polarization-entangled photon pairs based on a single, pulse-pumped, short PPLN waveguide (Optic Express, vol. 16, No. 17, pp. 12460 to 12468, 2008). The polarization maintaining optical fiber loop also includes a fusion splice with a 90° twist. The PPLN waveguide generates quantum correlated photon pairs including signal photons with a wavelength of 1542 nm and idler photons with a wavelength of 1562 nm by spontaneous parametric down conversion. When the intensity of the excitation light is sufficiently weak, the state of each quantum correlated photon pair output from the PBS is a superposition of a state produced by clockwise travel around the loop and an orthogonally polarized state produced by counterclockwise travel. The essential components of these known devices are a second-order nonlinear optical medium in which the SPDC process takes place, and a source of excitation light with a wavelength approximately half the wavelength of the desired quantum entangled photon pairs. In order to obtain quantum entangled photon pairs with wavelengths in the 1550 nm band for use in optical fiber communication, a 775-nm excitation light source is needed. This leads to the following problems. The devices described by Inoue and Lim et al. require a PBS specially designed to operate similarly at both of two greatly differing wavelengths, e.g., 775 nm and 1550 nm. The lenses and other optical elements needed for internal and external optical coupling must also be specially designed. For example, the focal length of a lens must be selected to achieve optical coupling at both the 775-nm and 1550-nm wavelengths. Anti-reflection coatings that prevent reflection at both wavelengths are also needed. Thus the known art requires optical components capable of operating with excitation light and quantum correlated photon pairs having wavelengths that differ by a factor of two. Generally speaking, a device having equally good performance characteristics for light with greatly differing wavelengths cannot be expected to have characteristics as good as a device optimized for one of the wavelengths. More specifically, the polarization extinction ratio of a PBS and the coupling efficiency of a lens system designed for operation at both 775 nm and 1550 nm are generally inferior to the polarization extinction ratio of a PBS and the coupling efficiency of a lens system optimized for just one of these wavelengths, e.g., 1550 nm. The use of components designed to operate at both wavelengths accordingly entails an excessive loss of both input excitation light and the quantum correlated photon pairs generated for output. A quantum information communication system using quantum entangled photon pairs deals with extremely weak light to begin with, generating single photons or photon pairs or still smaller states and transmitting an average of one photon pair or less per time slot. A structure that leads to excessive loss of light critically impairs system performance, and calls for improvement. It would be preferable for a system that generates entangled photon pairs in, for example, the 1550-nm band to use optical components designed just for operation in the 1550-nm band, including not only passive optical components such as the PBS and lens systems mentioned above but also active components such as light sources. Such optical components are commercially available at comparatively low prices and have proven high reliability, and the active components have excellent controllability. An object of the present invention is to provide a quantum entangled photon pair producing device capable of generating quantum entangled photon pair output of high purity by using simple, readily available optical devices rather than specially designed ones. Another object of the invention is to prevent excessive loss of light. The invention provides a quantum entangled photon pair generating device including a polarization maintaining loop path. A loop input unit receives excitation light from an external source, separates the excitation light into first and second excitation light components with mutually orthogonal polarization planes, feeds the first excitation light component clockwise into the polarization maintaining loop path, and feeds the second excitation light component counterclockwise into the polarization maintaining loop path. An optical conversion generation unit disposed in the polarization maintaining loop path generates up-converted light from each excitation light component by second harmonic generation, and generates down-converted light from the up-converted light by spontaneous parametric down-conversion. The optical conversion generation unit includes a pair of second-order nonlinear optical media disposed on opposite sides of a half-wave plate, which rotates the plane of polarization of the excitation light and the down-converted light. Up-converted light generated in one second-order nonlinear optical medium passes through the half-wave plate without polarization rotation and generates down-converted light in the other second-order nonlinear optical medium. A polarization manipulation unit manipulates the polarization direction of at least one of the excitation light or down-converted light components. The down-converted light propagating in the clockwise and counterclockwise directions on the polarization maintaining loop path is received by a loop output unit that recombines the clockwise and counterclockwise propagating components that have not passed through the half-wave plate in the optical conversion generation unit because they were generated from up-converted light that had already passed through the half-wave plate, and outputs the combined light. The combined down-converted light includes polarization entangled photon pairs having substantially the same wavelength as the excitation light. The loop input unit and loop output unit may be combined into a single polarization splitting-combining module. Since the input excitation light and the output down-converted light have substantially the same wavelength, the optical components of the quantum entangled photon pair generating device can be designed for operation at this wavelength. It is unnecessary to provide guaranteed coupling performance or loss performance at the shorter wavelength of the up-converted light, which is used only within the second-order nonlinear optical media. Since the quantum entangled photon pair generating device can be fabricated from standard optical components optimized for operation at the excitation wavelength, it can be manufactured at a low cost, and can provide output of high purity with comparatively low loss. Embodiments of the invention will now be described with reference to the attached drawings, in which like elements are indicated by like reference characters. Referring to FIG. 1, the quantum entangled photon pair generating device 10 in the first embodiment includes at least a polarization splitting-combining module 101, a first half-wave plate 104, and an optical conversion generation unit 100. Two of the input and output ports of the polarization splitting-combining module 101, the first half-wave plate 104, and the optical conversion generation unit 100 constitute a Sagnac interferometer optical loop LP. The optical conversion generation unit 100 includes a first second-order nonlinear optical medium 102, a second half-wave plate 105, and a second second-order nonlinear optical medium 103, connected in cascade in this order. The quantum entangled photon pair generating device 10 also includes an optical circulator 106, an optical low-pass filter 107, and a wavelength division multiplexing (WDM) filter 108, as optical input/output devices for input of excitation light to the optical loop LP and output of signal and idler photons from the optical loop LP. The optical loop LP is preferably a polarization maintaining optical system. Accordingly, the relationships among the optical axes of the polarization splitting-combining module 101, first and second second-order nonlinear optical media 102, 103, and first and second half-wave plates 104, 105 require particular attention. The optical loop LP may be formed with polarization-maintaining optical fiber, or with free space optics employing only lenses and mirrors. In a fiber loop, if some of the optical components have attached pigtails of conventional optical fiber lacking the polarization maintaining property, a pseudo-polarization-maintaining optical system can still be constructed by using additional optical devices such as polarization controllers. The vacuum wavelength of the input excitation light will be denoted λp. This wavelength λp is near the desired wavelengths of the quantum entangled photon pairs, e.g., near 1550 nm for use in 1550-nm optical communication systems. The wavelengths λp, λs, and λi of the input excitation light, signal photon, and idler photon, satisfy the following equation (1) corresponding to the energy conservation law, where both λs and λi are wavelengths in vacuum. 2 λ p = 1 λ s + 1 λ i ( 1 ) The polarization splitting-combining module 101 has a first input/output port 101-1 coupled to a second input/output port 106-2 of the optical circulator 106, a second input/output port 101-2 disposed opposite the first input/output port 101-1 and coupled to an end of the second second-order nonlinear optical medium 103, a third input/output port 101-3 coupled to an end of the first half-wave plate 104, and a fourth input/output port 101-4 disposed opposite the third input/output port 101-3. No essential light is input to or output from the fourth input/output port 101-4 in the first embodiment, so there is no need to connect optical signal input/output interface devices, such as an optical fiber pigtail or an optical connector. The fourth input/output port 101-4 is shown only for convenience of description. This is also true in the third embodiment. The fourth input/output port 101-4 is used in the second and fourth embodiments. The optical circulator 106 has a first input port 106-1 for receiving input excitation light with wavelength λp, a second input/output port 106-2 for output of the light received at the first input port 106-1 to the first input/output port 101-1 of the polarization splitting-combining module 101, and a third output port 106-3 for output of the light received at the second input/output port 106-2. The polarization splitting-combining module 101 and the optical circulator 106 must provide assured operation at wavelengths equal to or near λp, including λs, and λi, but need not operate correctly at λp/2 or wavelengths near λp/2. If the excitation wavelength λp is 1550 nm, for example, a commercially available 1550-nm polarization splitting and combining module and a commercially available 1550-nm optical circulator may be used. Devices guaranteed to operate at wavelengths of both λp and λp/2, as required by Inoue and by Lim et al., are unnecessary. The components of light entering the polarization splitting-combining module 101 are defined in terms of the direction of oscillation of the electric field vector of the light with respect to the plane of incidence of the light on the polarization selective reflecting surface of the polarization splitting-combining module. The incident light is said to be p-polarized if its electric field vector oscillates parallel to this incidence plane, and s-polarized if its electric field vector oscillates perpendicular to this incidence plane. Incident light may include both p-polarized and s-polarized components. In the polarization splitting-combining module 101, the p-polarized component of light input to the first input/output port 101-1 is output from the second input/output port 101-2, and the s-polarized component is output from the third input/output port 101-3. The p-polarized component of light input to the second input/output port 101-2 is output from the first input/output port 101-1, and the s-polarized component of light input to the third input/output port 101-3 is output from the fourth input/output port 101-4. The polarization splitting-combining module 101 may be a commercially available thin-film polarizing beam splitter, but the invention is not limited to this type of device. For example, a birefringent polarizing prism may be used instead. The input excitation light with a wavelength of λp is input to the first input port 106-1 of the optical circulator 106, output from the second input/output port 106-2, input to the first input/output port 101-1 of the polarization splitting-combining module 101, and split into a p-polarized component which is output from the second input/output port 101-2 and an s-polarized component which is output from the third input/output port 101-3. In the first embodiment, the optical intensities of the p-polarized component and the s-polarized component must be identical. Accordingly, the excitation light input to the first input/output port 101-1 of the polarization splitting-combining module 101 must be polarized so that the intensity ratio of its p-polarized and s-polarized components is 1:1. Such input excitation light will be referred to as 45° polarized excitation light. This excitation light may be prepared by inserting a polarization controller at a position preceding the first input port 106-1 of the optical circulator 106 to assure that the excitation light input to the first input/output port 101-1 of the polarization splitting-combining module 101 includes only light that is linearly polarized at a 45° angle with respect to the p- and s-polarization directions in the polarization splitting-combining module 101. Each of the half-wave plates 104, 105 has mutually orthogonal fast and slow axes that produce an optical phase difference of π radians between the components of the light of wavelength λp polarized parallel to the two axes. In the description below, unless otherwise noted, the term ‘1/n-wave plate’ (n=2, 3, 4, . . . ) will mean a plate producing a phase difference of 1/n at the wavelength λp of the excitation light. The first half-wave plate 104 is aligned as shown in FIG. 2 so that its fast and slow axes A1, A2 are at 45° angles to the polarization direction S of the s-polarized component of the excitation light output from the third input/output port 101-3 of the polarization splitting-combining module 101. The polarization direction of the excitation light output from the third input/output port 101-3 is rotated by 90° by passage through the first half-wave plate 104 to match the polarization direction of the p-polarized component. The optical devices in the optical loop LP are disposed so that this polarization direction matches the optical axis direction (Z-axis direction in the example in the first embodiment) of the first and second-order nonlinear optical media 102, 103. The first and second second-order nonlinear optical media 102, 103 are nonlinear optical media, such as PPLN media, having a second-order nonlinear optical effect. Upon reception of input excitation light with a wavelength of λp, they perform second harmonic generation (SHG) and generate light, referred to as intermediate SHG light or simply as SHG light below, with a wavelength (λp/2) equal to half the input wavelength. Each of the first and second second-order nonlinear optical media 102, 103 receives the SHG light generated by the other one of the two second-order nonlinear optical media 102, 103 and uses the SHG light as seed light for an SPDC process that generates quantum correlated photon pairs, each pair consisting of a signal photon with a wavelength λs and an idler photon with a wavelength λi. In the description of the operation of the first embodiment, for convenience, the excitation light input to the two second-order nonlinear optical media 102, 103, the intermediate SHG light generated therein, and the desired SPDC correlated signal and idler photon pairs are all linearly polarized in the same direction. When PPLN waveguides are used as the second-order nonlinear optical media 102 and 103, for example, this alignment can be obtained by use of the PPLN d33 second-order nonlinear optical coefficient for the SHG and SPDC processes, the excitation light input to the PPLN crystals to generate the intermediate SHG light and the SHG light input to the PPLN crystals to generate the entangled photon pairs by SPDC both being linearly polarized in the Z-axis direction of the PPLN crystals, so that the signal and idler photons are also polarized in the Z-axis direction of the PPLN crystal from which they are output. For this exemplary use of the d33 second-order nonlinear optical coefficient, the optical axes of the first and second second-order nonlinear optical media 102, 103 and the second half-wave plate 105 disposed between them are arranged as shown schematically in FIG. 3. The Z-axes of the first and second second-order nonlinear optical media 102, 103 are aligned with the polarization direction P (p-polarization direction) of the excitation light output from the second input/output port 101-2. The optical axes A1, A2 of the second half-wave plate 105 are at 45° angles to this direction P. Accordingly, when the input excitation light and transient signal and idler photons (described below) are output from one of the second-order nonlinear optical media 102 and 103, polarized in its Z-axis direction, to the second half-wave plate 105, they are converted from polarized light to s-polarized light in the second half-wave plate 105 before entering the other of the first and second second-order nonlinear optical media 102, 103. The optical low-pass filter 107 removes the λp/2 wavelength component of the light output from the third output port 106-3 of the optical circulator 106, thereby removing the intermediate SHG light generated in the first and second second-order nonlinear optical media 102, 103. Ideally, in the first embodiment the optical low-pass filter 107 is transparent only to the signal photon component with wavelength λs and the idler photon component with wavelength λi, and not to the excitation light component with wavelength λp, for a reason that will be described below. Of the light that passes through the optical low-pass filter 107, the WDM filter 108 separates at least the signal photon component with wavelength λs and the idler photon component with wavelength λi and transmits them on separate optical paths. A conventional wavelength division multiplexing filter of the arrayed waveguide grating (AWG) type, transmitting at least the λs and λi wavelength components representing the signal and idler photons, may be used as the WDM filter 108. The signal photon and idler photon wavelength components transmitted through the WDM filter 108 are carried over the optical transmitting paths of, for example, an optical fiber communication network to respective receiving parties A and B. The receiving parties A and B then perform simultaneous measurement and other operations to communicate information by a known quantum information communication protocol. The operation of the quantum entangled photon pair generating device 10 in the first embodiment will be described on the assumption that PPLN crystals are used as the first and second second-order nonlinear optical media 102, 103, and that the component corresponding to their d33 second-order nonlinear optical coefficient is used for the SHG and SPDC processes. Excitation light with wavelength λp is injected from the second and third input/output ports 101-2, 101-3 of the polarization splitting-combining module 101 into the optical loop LP as p-polarized and s-polarized components of identical intensities. The p-polarization direction corresponds to the Z-axis of the PPLN crystals in the first and second second-order nonlinear optical media 102, 103. First, the process that takes place as the p-polarized excitation light output from the second input/output port 101-2 propagates on the optical loop LP in the clockwise direction will be described. Input of the excitation light causes the second second-order nonlinear optical medium (PPLN crystal) 103 to generate intermediate SHG light as seed light. Quantum correlated photon pairs consisting of a signal photon and an idler photon are generated from some of this intermediate SHG light in the same PPLN crystal (the second second-order nonlinear optical medium 103) by the SPDC process. These photon pairs will be referred to as transient signal and idler photons, or simply as transient light, because they do not become part of the final output. The light output from the second second-order nonlinear optical medium 103 includes residual excitation light, intermediate SHG light, and transient signal and idler photons, all of which are p-polarized light, polarized in the Z-axis direction of the PPLN crystal. The excitation light, intermediate SHG light, and transient signal and idler photons then pass through the second half-wave plate 105. The excitation light and the transient signal and idler photons, which have wavelengths equal or nearly equal to λp, have their planes of polarization rotated by substantially 90°, so they enter the first second-order nonlinear optical medium 102 as s-polarized components. The intermediate SHG light, which has a wavelength λp/2, receives a phase shift of one wavelength from the second half-wave plate 105, so its polarization is not rotated. Accordingly, the intermediate SHG light is input to the first second-order nonlinear optical medium 102 as a p-polarized component. In passage through the first second-order nonlinear optical medium 102, the excitation light and the transient signal and idler photons do not trigger the generation of new SHG light because of their s-polarization, and thus there is no subsequent generation of transient signal and idler photons by the SPDC process within the first second-order nonlinear optical medium 102. The intermediate SHG light entering the first second-order nonlinear optical medium 102 as p-polarized light, however, undergoes the SPDC process, generating new signal and idler photons that will become part of the final correlated photon pair output. As a result, the first second-order nonlinear optical medium 102 outputs two orthogonally polarized light groups: an s-polarized group including the excitation light and the transient signal and idler photons generated in the second second-order nonlinear optical medium 103, and a p-polarized group including the intermediate SHG light generated in the second second-order nonlinear optical medium 103 and the desired signal and idler photons generated in the first second-order nonlinear optical medium 102. After leaving the first second-order nonlinear optical medium 102, these s- and p-polarized light components pass through the first half-wave plate 104 and enter the third input/output port 101-3 of the polarization splitting-combining module 101. In passage through the first half-wave plate 104, the polarization planes of all components except the intermediate SHG light component are rotated by 90°. The input excitation light and the transient signal and idler photons generated in the second second-order nonlinear optical medium 103 are input to the third input/output port 101-3 as p-polarized components and output from the fourth input/output port 101-4, which is not used in the first embodiment. The desired signal and idler photons generated in the first second-order nonlinear optical medium 102 are input to the third input/output port 101-3 as s-polarized components and output from the first input/output port 101-1. If the wavelength dependency of the polarization splitting-combining module 101 is ignored, the intermediate SHG light is output from the fourth input/output port 101-4. Accordingly, the excitation light propagating in the clockwise direction around the optical loop LP gives rise to desired correlated photon pairs consisting of s-polarized signal and idler photons which are output from the first input/output port 101-1, while the excitation light itself, and the transient light and intermediate SHG light generated in the second second-order nonlinear optical medium 103, are output form the fourth input/output port 101-4. Next, the processes that take place as the excitation light output from the third input/output port 101-3 as s-polarized light propagates in the counterclockwise direction around the optical loop LP will be described. This excitation light first passes through the first half-wave plate 104, in which it undergoes a polarization rotation of 90°, becoming a p-polarized component. Like the excitation light propagating clockwise on the loop LP, the excitation light propagating counterclockwise triggers SHG and then SPDC processes in the first second-order nonlinear optical medium 102, producing intermediate SHG light and quantum correlated photon pairs consisting of transient signal and idler photons. The counterclockwise-propagating light, now including excitation light, intermediate SHG light, and transient light, is all output from the first second-order nonlinear optical medium 102 as p-polarized light, but then passes through the second half-wave plate 105, which rotates the polarization of the excitation light and transient light by 90°. Accordingly, these components become s-polarized light while the intermediate SHG light remains p-polarized. The s-polarized excitation light and transient light pass through the second second-order nonlinear optical medium 103 without triggering the SHG and SPDC processes, so they produce no additional SHG light or transient signal and idler photons. The p-polarized intermediate SHG light, however, triggers an SPDC process, producing new signal and idler photons that will become another part of the desired output of quantum correlated photon pairs. Accordingly, the second second-order nonlinear optical medium 103 outputs the counterclockwise-propagating excitation light and the transient light generated in the first second-order nonlinear optical medium 102 as s-polarized components, and the counterclockwise-propagating intermediate SHG light and the desired signal and idler photon pairs generated in the second second-order nonlinear optical medium 103 as p-polarized components. The counterclockwise light output from the second second-order nonlinear optical medium 103 enters the second input/output port 101-2 of the polarization splitting-combining module 101. The s-polarized excitation light and transient light are output from the unused fourth input/output port 101-4. The p-polarized desired signal and idler photon pairs are output from the first input/output port 101-1. If the wavelength dependency of the polarization splitting-combining module 101 is ignored, the p-polarized intermediate SHG light is also output from the first input/output port 101-1. Accordingly, as the input excitation light propagates in the counterclockwise direction around the optical loop LP, the desired p-polarized signal and idler photon pairs and the p-polarized intermediate SHG light generated in the first second-order nonlinear optical medium 102 are output from the first input/output port 101-1, while the s-polarized input excitation light and the s-polarized transient signal and idler photon pairs are output from the fourth input/output port 101-4. As in the technique described by Lim et al., photons travel clockwise and counterclockwise around the optical loop LP with equal probability, and when the intensity of the excitation light is sufficiently weak, the polarization state of each signal-idler photon pair output from the first input/output port 101-1 is a superimposition of a p-polarized state produced by clockwise travel and an s-polarized state produced by counterclockwise travel. Although each photon may show either one of the two states when its polarization is measured, the signal and idler photons both show the same state if their polarization is measured simultaneously in the same way. The quantum entangled photon pair generating device 10 therefore generates polarization entangled photon pairs. The components of the light output from the first input/output port 101-1 of the polarization splitting-combining module 101 are shown in FIGS. 4A and 4B. In FIG. 4A, the polarization splitting-combining module 101 is a polarizing beam splitter using a thin film 101R. In FIG. 4B, the polarization splitting-combining module 101 is a conventional polarizing prism using a birefringent crystal. Either of them may be used in the first embodiment. As shown in both FIGS. 4A and 4B, the light components output from the first input/output port 101-1 of the polarization splitting-combining module 101 are the desired polarization entangled signal-idler photon pairs and the intermediate SHG light generated by the excitation light propagating counterclockwise in the optical loop. The excitation light returning as loop output, the clockwise component of the intermediate SHG light, and the transient signal and idler photons are in principle output from the fourth input/output port 101-4 of the polarization splitting-combining module 101. The returning excitation light, which has a relatively strong optical intensity and a wavelength near the wavelength of the entangled photon pairs, is therefore output, together with the unneeded transient light, from a different port from the desired polarization entangled photon pairs The components output from the first input/output port 101-1 are input to the second input/output port 106-2 and output from the third output port 106-3 of the optical circulator 106. For convenience, the wavelength dependency of the optical circulator 106 will be ignored and it will be assumed that the output from the third output port 106-3 includes the intermediate SHG component of wavelength λp/2. The light output from the third output port 106-3 passes through the optical low-pass filter 107, where the intermediate SHG light component is removed. The remaining light is input to the WDM filter 108, from which the signal photon component with wavelength λs and the idler photon component with wavelength λi are output onto separate optical paths. The signal photon wavelength component and idler photon wavelength component that have passed through the optical circulator 106 are carried on their separate optical transmission paths to respective receiving parties A and B, respectively, who use the photon pairs to communicate as described above. The (intermediate) SHG light of wavelength λp/2, which serves as seed light in the SPDC process, is needed only within the first and second second-order nonlinear optical media 102, 103, so its transmission losses in optical devices other than the optical conversion generation unit 100 can be ignored, and when the intermediate SHG light leaves the optical loop LP, it can simply be discarded. In particular, the polarization splitting-combining module 101 and the first half-wave plate 104 can be designed for operation at wavelengths near λp, without having to operate in any particular way at the λp/2 wavelength. The optical couplings that couple light into and out of the second-order nonlinear optical media 102, 103 also have to perform well only at or near the λp wavelength, and not at both wavelengths λp/2 and λp. This can reduce the system cost, as well as reducing optical loss, and produce a higher-purity quantum entangled state. Since the intermediate SHG light of wavelength λp/2 is not needed outside the second-order nonlinear optical media 102, 103, even a potentially great optical loss of this light in the polarization splitting-combining module 101 and its optical couplings causes no problem. A high optical loss is in fact preferable because it helps reduce the requirements placed on the optical low-pass filter 107 that removes the intermediate SHG component from the final output. In the first embodiment, in principle, the returning excitation light component and transient signal and idler photon components, which have wavelengths near the wavelength of the desired quantum entangled photon pairs and optical intensities equal to or greater than the optical intensity of the desired quantum entangled photon pairs, are not output from the first input/output port 101-1 of the polarization splitting-combining module 101. Therefore, since there is in theory no possibility of leakage of high-intensity excitation light into the desired stream of quantum entangled photon pairs at the output port, in principle, the quantum entangled photon pair generating device 10 can operate even if the wavelength of the desired quantum entangled photon pairs is very close or even equal to the wavelength of the input excitation light (λs=λi=λp). This is a great practical advantage, because it means that the full wavelength band of the generated quantum entangled photon pairs can be used effectively. In particular, when the signal and idler photons have identical wavelengths, λs=λi, wavelength nonidintifiability also occurs, which is preferable for advanced quantum information communication techniques. This property is also useful in the high-efficiency generation of quantum entangled photon pairs by use of second-order nonlinear optical media structured so as to narrow the wavelength band of the quantum entangled photon pairs, thereby generating quantum entangled photons with high efficiency per unit wavelength. As the first and second second-order nonlinear optical media 102, 103, a bulk lithium niobate (LiNbO3) crystal or bulk PPLN crystal, a PPLN waveguide formed in such a bulk crystal, or other various second-order nonlinear optical media may be used, depending on the desired wavelengths of the quantum entangled photon pairs. For example, the LiNbO3 crystal described by Lim et al. may be used to produce quantum entangled photon pairs in the 1.5-micrometer waveband. In order to realize the quantum entangled photon pair generating device 10 in the first embodiment, it is of particular significance for industrial use for the SHG and SPDC processes to take place within the first and second second-order nonlinear optical media 102, 103 with high efficiency. For this reason, the phase matching between the input excitation light and the SHG light and between the SHG light and the signal and idler light are both important. For a bulk crystal, angle phase matching is commonly used, but as pointed out by Takeuchi, the resulting spatial separation of the signal and idler photons can lower the purity of the quantum entangled state. Use of a ferroelectric periodic-polarization inverting structure, or other structure in which the second-order nonlinear optical coefficients are spatially modulated has the advantage of producing a quasi-phase matching condition without relying on angle phase matching. A second-order nonlinear optical medium combined with an optical waveguide structure has the advantage of mitigating the loss of purity of the quantum entanglement state due to spatial separation, and also the advantage of strong light confinement, which increases the second-order nonlinear optical coefficients, thereby increasing the probabilities with which the SHG and SPDC processes take place. For the 1.5-micrometer waveband, a PPLN waveguide is therefore thought to be an optimal second-order nonlinear optical medium for use in the optical conversion generation unit 100. The energy conservation law and momentum conservation (phase matching) laws for the SHG and SPDC processes in a PPLN waveguide can be expressed by the following equations (2) to (5). The relationship between wavenumber and wavelength in a PPLN waveguide with an effective refractive index n is given by equation (6). SHG Process: energy ⁢ ⁢ conservation ⁢ ⁢ law 1 λ SHG = 2 λ p ( 2 ) momentum ⁢ ⁢ conservation ⁢ ⁢ law 2 ⁢ k p - k SHG = 2 ⁢ π Λ ⁢ ( 3 ) SPDC Process: energy ⁢ ⁢ conservation ⁢ ⁢ law 1 λ SHG = 2 λ p = 1 λ s + 1 λ i ( 4 ) momentum ⁢ ⁢ conservation ⁢ ⁢ law k s + k i - k SHG = 2 ⁢ π Λ ⁢ ( 5 ) k x = 2 ⁢ π ⁢ ⁢ n x λ x ⁢ ⁢ ( x = p , SHG , s , i ) ( 6 ) In these equations, λ indicates vacuum wavelength, k indicates wavenumber in the PPLN waveguide, Λ indicates the PPLN polarization reversal period, and the subscripts p, SHG, s, and i represent the input excitation light, SHG light, signal photons, and idler photons, respectively. Equations (2) and (4) represent wavelengths and frequency relationships based on the law of conservation of energy. The wavelength of the SHG light is half the wavelength of the input excitation light. The sum of the optical frequencies of the signal and idler photons is equal to the frequency of the SHG seed light from which they are generated and is therefore twice the frequency of the input excitation light, where light of a wavelength λ has a frequency of c/λ, c being the speed of light in a vacuum. Equations (3) and (5) relate to phase matching. If the effective refractive indices np, nSHG are determined from the excitation light wavelength λp and the shape of the PPLN waveguide, the polarization reversal period Λ is determined from equations (3) and (6). If the signal and idler photon wavelengths differ from each other (λs≠λp, λl≠λp), in general, equations (3) and (5) do not both hold. That is, the phase matching conditions for the SHG and SPDC processes are incompatible. From the well-known solution of the coupled-mode equation describing the nonlinear optical effect, however, phase unmatch is expected to decrease the probability of occurrence of the SHG and SPDC processes in proportion to {sin2(δL/2)}/(δL/2)2, where δ is defined by equation (7) and indicates the phase unmatch in the SPDC process, and L indicates the PPLN waveguide length. δ = k s + k i - k SHG - 2 ⁢ π Λ ( 7 ) If the phase unmatch tolerance limit is assumed to be a 50% decrease in the probability of occurrence of the SHG and SPDC processes from the maximum value obtained under phase matching conditions, the value of δ is approximately 2.78, as derived from the following equation: sin 2 ⁡ ( δ ⁢ ⁢ L / 2 ) ( δ ⁢ ⁢ L / 2 ) 2 = 0.5This limits the wavelength band of the correlated photon pairs generated in the SPDC process, and determines the wavelength range of the correlated signal and idler photons. In a vicinity of the excitation light wavelength in which the wavelength dependency of the effective refractive index is substantially linear and can be represented by equation (8), equation (9) is obtained from equations (4), (6), and (8), so the phase matching condition equations (3) and (5) can both be satisfied within this wavelength range. n ⁡ ( λ ) = A + B ⁢ ⁢ λ ( 8 ) 2 ⁢ k p = ⁢ 4 ⁢ π ⁢ ⁢ n p λ p = ⁢ 2 ⁢ π ⁢ 2 λ p ⁢ ( A + B ⁢ ⁢ λ p ) = ⁢ 2 ⁢ π ⁡ [ ( 1 λ s + 1 λ i ) ⁢ A + 2 ⁢ B ] = ⁢ 2 ⁢ π ⁡ [ A + B ⁢ ⁢ λ s λ s + A + B ⁢ ⁢ λ i λ i ] = ⁢ 2 ⁢ π ⁡ [ n s λ s + n i λ i ] = ⁢ k s + k i ( 9 ) From the above description, it will be understood that in order to realize the optical conversion generation unit 100 in the first embodiment, first the polarization reversal period Λ of the PPLN waveguide should be chosen to satisfy equation (3). Generation of correlated signal and idler photons with a wavelength combination (λs, λi) satisfying the SPDC phase matching condition represented by equation (5), or at least having a phase unmatch within an allowed tolerance range, can then can be expected, leading to output of the desired quantum entangled photon pairs. The following effects can be expected from the first embodiment. Unlike the prior art, this invention allows the first and second second-order nonlinear optical media 102, 103 disposed in the optical loop to carry out the SPDC process and also to generate the seed light needed for the SPDC process, so that light of the seed wavelength does not have to be supplied from outside the optical loop. Since the SHG light is needed only in the second-order nonlinear optical media 102, 103, the other system components need not couple or propagate the SHG light with low loss. Therefore, the quantum entangled photon pair generating device and other system components such as coupling lenses do not have to be designed for operation at wavelengths of both λp and λp/2; they can be optimized for operation at and near λp. The result is that the system fabrication cost is reduced, less optical loss occurs at the wavelengths of the excitation light and the output photon pairs, and a quantum entangled optical pair generating device is obtained that can produce a quantum entangled state of improved purity. Three variations of the first embodiment will be described with reference to FIGS. 5, 6, 7A, and 7B. In the first two of these variations, the method of input and output of the excitation light and quantum entangled photon pairs is altered. The variation shown in FIG. 5 dispenses with the optical circulator. The quantum entangled photon pair generating device 10A in FIG. 5 uses an arrayed waveguide grating (AWG) as the WDM filter 108. The AWG 108 has at least three transmission wavelengths: the signal photon wavelength λs, the idler photon wavelength λi, and the excitation wavelength λp. The AWG 108 has wavelength selective input/output ports that transmit light of different wavelengths and a common input/output port that transmits light of all the input/output wavelengths. Light input to the common input/output port is separated into individual wavelength components and output from the corresponding wavelength selective ports. Excitation light from an external source is input to a wavelength selective port that transmits at the excitation wavelength, is then output from the common port to the first input/output port 101-1 of the polarization splitting-combining module 101, and is input bidirectionally (clockwise and counterclockwise) to the second-order nonlinear optical media 102, 103 as in the first embodiment. The light returning from the optical loop LP through the first input/output port 101-1 of the polarization splitting-combining module 101 to the common port of the AWG 108 is separated into a signal photon component and an idler photon component, which are output through the wavelength selective ports for the corresponding wavelengths. If necessary, optical low-pass filters 107-s, 107-i may be inserted downstream of the signal and idler output ports, as shown, to remove the SHG wavelength component. FIG. 6 shows another variation of the first embodiment in which the optical circulator is not used. The quantum entangled photon pair generating device 10B in FIG. 6 uses a narrowly selective optical bandpass filter 110 that selectively reflects light with a wavelength of λp and transmits light of other wavelengths, including the signal and idler wavelengths. Alternatively, an optical bandpass filter 110 that transmits light with a wavelength of λp and reflects light of other wavelengths may be used. The signal and idler wavelengths must be sufficiently separated from the excitation wavelength λp so as not to overlap the reflection or transmission band of the optical bandpass filter 110. The optical bandpass filter 110 in FIG. 7 reflects excitation light of wavelength λp into the first input/output port 101-1 of the polarization splitting-combining module 101. Among the light components that traverse the optical loop LP, return to the polarization splitting-combining module 101, and are output from the first input/output port 101-1, any residual excitation light component that may be present is again reflected by the optical bandpass filter 110, and the other components are transmitted through the optical bandpass filter 110 to an optical low-pass filter 107, which removes the SHG component. The signal photon component and idler photon component are then separated by a WDM filter 108 and output on separate optical paths. The optical conversion generation unit 100 in FIG. 1 includes three discrete devices: the two second-order nonlinear optical media 102, 103 and the second half-wave plate 105. FIGS. 7A and 7B show an alternative optical conversion generation unit 100C in which these three components are integrated into a single crystal substrate. This structure is substantially the same as the structure of the integrated polarization independent quasi-phase-matched difference frequency generation (QPM-DFG) wavelength converter shown in FIG. 7 on page 300 in Bunkyokuhantendebaisu no kiso to oyo (Foundations and Applications of Polarization Inverting Devices) by Shintaro Miyazawa and Tadashi Kurimura, first published by Optronics Co. on Jun. 8, 2005. To fabricate the optical conversion generation unit 100C in FIG. 7, first, a polarization inversion structure (indicated by arrows in the side view in FIG. 7B) and a PPLN waveguide structure (indicated the central stripe 190 in the top plan view FIG. 7A) are formed together in a single LiNbO3 substrate. The second half-wave plate 105 is then embedded in the LiNbO3 substrate, cutting laterally across the PPLN waveguide at its center, separating the PPLN waveguide into two parts that function as a first second-order nonlinear optical medium 102C and a second second-order nonlinear optical medium 103C, corresponding to the first and second second-order nonlinear optical media 102, 103 in FIG. 1. A Zn-diffused waveguide that guides both TE (transverse electric) and TM (transverse magnetic) waves may be used in this structure, but use of a type of waveguide, such as a proton exchange waveguide channel, that guides only one of the two types of waves (e.g., the TM wave for a proton exchange waveguide channel) and does not guide the orthogonally polarized (e.g., TE) wave is more effective because it produces a higher optical insertion loss. The reason is that since the p-polarization direction in this variation matches, for example, the TM polarization direction, the input excitation light and the transient signal and idler photons output from the first-stage second-order nonlinear optical medium suffer a high propagation loss in passing as TE waves through the second-stage second-order nonlinear optical medium. This leaves less residual excitation and transient light to contaminate the output of desired quantum entangled photon pairs at the first input/output port 101-1 of the polarization splitting-combining module 101, which generally has a finite polarization extinction ratio and does not eliminate such contamination completely. In the above description, it is assumed that the input excitation light, the intermediate SHG light generated from the input excitation light, and the correlated photon pairs generated from the intermediate SHG light are all polarized in the same direction, but this is not a necessary condition. If the d31 component of the PPLN second-order nonlinear optical coefficient matrix is used for the SHG and SPDC processes, for example, the same effect as in the first embodiment can be obtained by inserting the first half-wave plate 104 between the optical conversion generation unit 100 and the second input/output port 101-2 of the polarization splitting-combining module 101. The second embodiment dispenses with the optical circulator used in the first embodiment and uses a more complex polarization manipulation unit in the optical loop. Referring to FIG. 8, the quantum entangled photon pair generating device 10C in the second embodiment replaces the first half-wave plate used in the first embodiment with two pairs of nonreciprocal polarization converters 211, 212, each consisting of a Faraday rotator and a half-wave plate. This structure guarantees that the fundamental operations described in the first embodiment can be carried out, and enables the desired quantum entangled photon pairs to be output from a different port of the polarization splitting-combining module 101 than the port at which the excitation light is input. The first nonreciprocal polarization converter 211 includes a first Faraday rotator 207 and a third half-wave plate 208 inserted in cascade on the optical loop LP between the third input/output port 101-3 of the polarization splitting-combining module 101 and the optical conversion generation unit 100. The second nonreciprocal polarization converter 212 includes a second Faraday rotator 209 and a fourth half-wave plate 210 inserted in cascade between the second input/output port 101-2 of the polarization splitting-combining module 101 and the optical conversion generation unit 100. The Faraday rotators 207, 209 each rotate the plane of polarization of incident light by exactly 45° at the excitation wavelength of λp and by approximately 90° at the SHG wavelength of λp/2. The half-wave plates 208, 210, like the half-wave plate in the first embodiment, have fast and slow axes that produce an optical phase difference of π radians at the λp wavelength of the excitation light. The components in the nonreciprocal polarization converters 211, 212 are aligned as shown in FIG. 9. The first nonreciprocal polarization converter 211 and second nonreciprocal polarization converter 212 have the same structure, so FIG. 9 applies to both, although only reference numerals for the first nonreciprocal polarization converter 211 are shown Excitation light linearly polarized in a specific direction may be input from the side of the first Faraday rotator 207 or from the side of the third half-wave plate 208. The specific polarization direction matches either the p-polarization direction or the s-polarization direction in the polarization splitting-combining module 101. The optical axes of the third half-wave plate 208 are oriented at 22.5° angles to the p- and s-polarization directions. The polarization splitting-combining module 101, first and second second-order nonlinear optical media 102, 103, second half-wave plane 105, optical low-pass filter 107, and WDM filter 108 in FIG. 8 function as in the first embodiment, so descriptions will be omitted. Next, the operation of the quantum entangled photon pair generating device 10C with the above structure will be described. As in the first embodiment, when 45° excitation light of wavelength λp is input to the first input/output port 101-1 of the polarization splitting-combining module 101, it is separated into a p-polarized component output from the second input/output port 101-2 and an s-polarized component output from the third input/output port 101-3, each component having the same optical intensity. First, the processes that take place as the s-polarized component of the excitation light output from the third input/output port 101-3 of the polarization splitting-combining module 101 propagates in the counterclockwise direction on the optical loop LP will be described. This component of the excitation light initially encounters the first nonreciprocal polarization converter 211. The variations in its polarization state in this polarization converter 211 will be described with reference to FIG. 9 and FIGS. 9A to 9D. The s-polarized component output from the third input/output port 101-3 is indicated by a rightward-pointing arrow in FIG. 9A. In passing through the first Faraday rotator 207, the polarization of this component is rotated by 45° counterclockwise, as indicated by a 45° upper-right pointing arrow in the center in FIG. 9A. The light then passes through the third half-wave plate 208, the optical axes of which are oriented at angles of 22.5° to the p- and s-polarization directions. The axis near the p-polarization direction is also at an angle of 22.5° to the plane of polarization of the light that has passed through the Faraday rotator 207, so the polarization of this light is rotated by a further 45° and the light output from the third half-wave plate 208 is p-polarized, as indicated by the upward-pointing arrow at the far right in FIG. 9A. In short, the first nonreciprocal polarization converter 211 rotates the polarization of the s-polarized incident light of wavelength λp counterclockwise by 90°. The originally s-polarized but now p-polarized excitation light output from the first nonreciprocal polarization converter 211 is input to the first second-order nonlinear optical medium 102. As explained in the first embodiment, s-polarized excitation light, s-polarized transient light, p-polarized intermediate SHG light, and the desired p-polarized SPDC correlated photon pairs are output from the second second-order nonlinear optical medium 103 in the optical conversion generation unit 100. The now s-polarized excitation component and transient component, the p-polarized intermediate SHG light, and the p-polarized desired SPDC correlated photon pairs generated in the second second-order nonlinear optical medium 103 are input to the second nonreciprocal polarization converter 212. The axes of the fourth half-wave plate 210 of the second nonreciprocal polarization converter 212 are also oriented at angles of 22.5° to the p- and s-polarization directions. Operating in the same way as the first nonreciprocal polarization converter 211, the second nonreciprocal polarization converter 212 rotates the polarization plane of the excitation light component and the transient light component, which have wavelengths equal or near to λp, counterclockwise by 90°. The excitation light and the transient component are thereby converted back to p-polarized light. A similar counterclockwise 90° polarization rotation is effected on the desired SPDC correlated photon pairs, which exit the second nonreciprocal polarization converter 212 in the s-polarized state. The excitation light, the transient component, and the desired SPDC correlated photon pairs propagating on the optical loop LP in the counterclockwise direction now enter the second input/output port 101-2 of the polarization splitting-combining module 101. The s-polarized desired SPDC correlated photon pairs are output from the fourth input/output port 101-4 of the polarization splitting-combining module 101. This contrasts with the first embodiment, in which the excitation light and the desired SPDC correlated photon pair were output from the first input/output port 101-1. The p-polarized excitation light and transient signal-idler photon pairs are output from the first input/output port 101-1 of the optical conversion generation unit 100, to which the original excitation light is input. The p-polarized component of the excitation light output from the second input/output port 101-2 of the polarization splitting-combining module 101 propagates on the optical loop LP in the clockwise direction, passing through the second nonreciprocal polarization converter 212, the optical conversion generation unit 100, and the first nonreciprocal polarization converter 211. The variations in the polarization state in the second nonreciprocal polarization converter 212 can also be described with reference to FIG. 9 by substituting reference characters 209 and 210 for reference characters 207 and 208. In FIG. 9B, the p-polarized component indicated by the far right upward-pointing arrow is input to the fourth half-wave plate 210 and its polarization plane is rotated by 45° in the clockwise direction, as indicated by the 45° upper-right pointing arrow in the center of FIG. 9B, due to the 22.5° angle between its polarization plane and the corresponding optical axis of the fourth half-wave plate 210. The rotated output light then passes through the second Faraday rotator 209, in which its polarization is rotated by 45° in the counterclockwise direction. Accordingly, the originally p-polarized component is output from the second nonreciprocal polarization converter 212 without change as p-polarized light. Similarly, no rotation of polarization of p- or s-polarized light with a wavelength of or near λp occurs in clockwise passage through the first nonreciprocal polarization converter 211, because of the 22.5° angles between the axes of the half-wave plate and the p- and s-polarization directions. The p-polarized excitation light output from the second nonreciprocal polarization converter 212 is input to the second second-order nonlinear optical medium 103. As in the first embodiment, s-polarized excitation light, s-polarized transient signal and idler photons, p-polarized intermediate SHG light, and desired p-polarized SPDC correlated photon pairs are output from the first second-order nonlinear optical medium 102 and enter the first nonreciprocal polarization converter 211. The s-polarized excitation light and transient components and the p-polarized SPDC correlated photon pairs pass through the first nonreciprocal polarization converter 211 with their polarization states unchanged and enter the third input/output port 101-3. The p-polarized SPDC correlated photon pairs are output as polarization entangled photon pairs from the fourth input/output port 101-4, instead of the first input/output port 101-1 to which the original excitation light was input. The s-polarized returning excitation light and the s-polarized transient signal and idler photons are output are output from the first input/output port 101-1. Next the variations in the polarization of the intermediate SHG light output from the second-order nonlinear optical medium 102 when passing through the first nonreciprocal polarization converter 211 and the second nonreciprocal polarization converter 212 will be described. At the wavelength (λp/2) of the SHG light, the third half-wave plate 208 in the first nonreciprocal polarization converter 211 and the fourth half-wave plate 210 in the second nonreciprocal polarization converter 212 are single-wave plates, which cause no rotation of polarization, but a substantially 90° rotation is produced by passage through each of the Faraday rotators 207, 209. The intermediate SHG light therefore emerges from the first nonreciprocal polarization converter 211 and second nonreciprocal polarization converter 212 with its plane of polarization rotated by substantially 90°, regardless of its input direction, as shown in FIGS. 9C and 9D. Consequently, the intermediate SHG light traveling clockwise leaves the optical conversion generation unit 100 with p-polarization, is converted to s-polarized light by the first nonreciprocal polarization converter 211, enters the third input/output port 101-3 of the polarization splitting-combining module 101, and (ignoring the wavelength dependence of the polarization splitting-combining module 101) exits from the first input/output port 101-1. The intermediate SHG light traveling counterclockwise leaves the optical conversion generation unit 100 with p-polarization, is converted to s-polarized light by the second nonreciprocal polarization converter 212, enters the second input/output port 101-2 of the polarization splitting-combining module 101, and (again ignoring the wavelength dependence of the polarization splitting-combining module 101) exits from the fourth input/output port 101-4. The above discussion is summarized in FIG. 10. The desired quantum entangled photon pairs are output from the fourth input/output port 101-4 of the polarization splitting-combining module 101 together with the counterclockwise intermediate SHG light component. The returning excitation light, the transient signal and idler photons, and the clockwise intermediate SHG light component are output from the first input/output port 101-1. The output from the fourth input/output port 101-4 is processed as was the output from the first input/output port 101-1 in the first embodiment. The intermediate SHG light and any residual excitation light that may be mixed with the SPDC correlated photon pairs are removed by the optical low-pass filter 107 and WDM filter 108, and the SPDC correlated photon pairs are separated into signal photons and idler photons and output onto separate optical paths. The effect of the second embodiment is that no optical circulator is needed to separate the output path of the desired quantum entangled photon pairs from the input path of the excitation light. The purity of the desired output is thereby improved, because leakage of excitation light into the output path through the circulator is eliminated. If necessary, however, an optical circulator may be provided on the excitation light input path, as in the first embodiment, to prevent returning excitation light from destabilizing the operation of the excitation light source (not shown). Referring to FIG. 11, the quantum entangled photon pair generating device 10D in the third embodiment is generally similar in structure to the quantum entangled photon pair generating device in the first embodiment, but lacks the optical low-pass filter of the first embodiment and instead includes a polarization converter 314 between the second input/output port 101-2 of the polarization splitting-combining module 101 and the optical conversion generation unit 100. The polarization converter 314 includes a fifth half-wave plate 311, a quarter-wave plate 312, and a sixth half-wave plate 313 coupled in cascade. The optical axes of the fifth half-wave plate 311, quarter-wave plate 312, and sixth half-wave plate 313 are aligned as shown in FIG. 12. The optical axes of the fifth half-wave plate 311 and the sixth half-wave plate 313 are rotated clockwise by angles of 22.5° from the and s-polarization directions (the p-polarization direction is shown in FIG. 12). The optical axes of the quarter-wave plate 312 make 45° angles to the p- and s-polarization directions. The optical conversion generation unit 100, polarization splitting-combining module 101, first half-wave plate 104, optical circulator 106, and WDM filter 108 function as in the first embodiment, so descriptions will be omitted. The operation of the quantum entangled photon pair generating device 10D will now be described. As in the first embodiment, when excitation light of wavelength λp is input to the first input/output port 101-1 of the polarization splitting-combining module 101, linearly polarized at a 45° angle to the p- and s-directions of the polarization splitting-combining module 101, it is separated into a p-polarized component output from the second input/output port 101-2 and an s-polarized component output from the third input/output port 101-3, each component having the same optical intensity. A distinctive effect in the third embodiment, which will be described later, is produced by the wavelength dependency of the polarization converter 314. This will now be described with reference to FIG. 12 and FIGS. 12A to 12D. FIG. 12A shows the variations in the polarization state of the p-polarized component of the excitation light output from the second input/output port 101-2 in passing through the polarization converter 314. From the second input/output port 101-2, the p-polarized component of the excitation light with wavelength λp, indicated by an upward-pointing arrow at the far left in FIG. 12A, first passes through the fifth half-wave plate 311. Because of the orientation of the optical axes of the fifth half-wave plate 311, this excitation light component leaves the fifth half-wave plate 311 with its polarization plane rotated 45° clockwise from the p-polarization direction, as indicated by the first upper-right pointing arrow in FIG. 12A. Next this excitation light component, now polarized at an angle of 45° with respect to the p- and s-directions, enters the quarter-wave plate 312. The optical axes of the quarter-wave plate 312 are also oriented at 45° angles to the p- and s-polarization directions, so no polarization rotation occurs as the light passes through the quarter-wave plate 312. After passing through the quarter-wave plate 312, this excitation light component, still polarized at a 45° angle clockwise from the p-polarization direction, enters the sixth half-wave plate 313. Because of the 22.5° clockwise angle of the optical axes of the sixth half-wave plate 313, the polarization plane of the excitation light is rotated by 45° in the counterclockwise direction and returns to the p-polarization direction, as indicated by the upward-pointing arrow at the far right in FIG. 12A. The p-polarized component of the excitation light is therefore output from the polarization converter 314 with its original polarization unchanged. Because of the symmetrical structure of the polarization converter 314, the same also holds in the passage of p-polarized light in the opposite direction, as indicated by FIG. 12B. Next, the variations in the polarization of the intermediate SHG light with wavelength λp/2 as it passes through the polarization converter 314 will be described with reference to FIGS. 12C and 12D. FIG. 12C shows the variations in the polarization state of hypothetical intermediate SHG light propagating clockwise around the optical loop LP. FIG. 12D shows the variations in the polarization state of the intermediate SHG light propagating counterclockwise. At the λp/2 wavelength of the intermediate SHG light, the half-wave plates 311 and 313 act as single-wave plates, and the quarter-wave plate 312 acts as a half-wave plate. Accordingly, the p-polarized SHG light propagating counterclockwise passes through the sixth half-wave plate 313 with its polarization unchanged, as indicated by the upward-pointing arrows to the right of center in FIG. 12D, has its polarization plane rotated by 90° by the quarter-wave plate 312, as indicated by the rightward-pointing arrow to the left of center in FIG. 12D, and passes through the fifth half-wave plate 311 with its polarization unchanged, as indicated by the rightward-pointing arrow at the far left in FIG. 12D. Therefore, the polarization converter 314 rotates the polarization plane of the intermediate SHG light propagating in the counterclockwise direction around the optical loop LP by 90°, so that the intermediate SHG light is s-polarized when it leaves the polarization converter 314. Similarly, intermediate SHG light propagating clockwise would be changed from p-polarization to s-polarization, as shown in FIG. 12C, if it passed through the polarization converter 314. To summarize, in passage through the polarization converter 314, the polarization of the excitation light, the desired SPDC correlated photon pairs, and the transient photon pairs, all of which have wavelengths equal or near to λp, is not rotated, while the polarization plane of the SHG light, which has a wavelength of λp/2, is rotated by 90°. The 22.5° and 45° angles of the optical axes of the optical elements in the polarization converter 314 are selected for the purpose of accomplishing this polarization conversion. The overall operation of the third embodiment will now be described. The wavelength dependency of the polarization splitting-combining module 101, which affects only the SHG light, will continue to be ignored. Since the polarization converter 314 does not change the polarization of the excitation light, the transient light, and the desired signal and idler photon pairs, these components are output from the optical loop LP as in the first embodiment: the desired signal and idler photon pairs from the first input/output port 101-1 of the polarization splitting-combining module 101; the returning excitation light and the transient light from the fourth input/output port 101-4, which is not used. Since the clockwise-propagating intermediate SHG light generated in the optical conversion generation unit 100 does not pass through the polarization converter 314, the clockwise-propagating intermediate SHG light is also output from the optical loop LP as in the first embodiment, from the fourth input/output port 101-4 of the polarization splitting-combining module 101. The counterclockwise-propagating intermediate SHG light generated in the optical conversion generation unit 100 passes through the polarization converter 314 and is changed from the p-polarization state to the s-polarization state as shown in FIG. 9D. The s-polarized intermediate SHG light then enters the second input/output port 101-2 of the polarization splitting-combining module 101 and exits from the fourth input/output port 101-4. The above operations are summarized in FIG. 13. The first input/output port 101-1 is used only for input of the excitation light to the optical loop LP and output of the desired signal and idler photon pairs from the optical loop LP. All other light exits from the fourth input/output port 101-4. The desired signal and idler photon pairs are separated from the input path by the optical circulator 106 in FIG. 11 and routed to receiving parties A and B by the WDM filter 108. Since the desired quantum entangled photon pairs and the intermediate SHG light are output from separate ports, the optical low-pass filter 107 used in the preceding embodiments to reject the intermediate SHG light can in principle be omitted. The variations of the first embodiment shown in FIGS. 5 and 6 can also be used in the third embodiment. That is, the optical circulator 106 may be eliminated and the excitation light may be input through the WDM filter 108 as in FIG. 5, or by use of an optical bandpass filter 110 as in FIG. 6. The same effects are obtained as in FIG. 11. In addition to the effects produced by the first and second embodiments, the third embodiment produces the following effect. In principle, the optical low-pass filter for removing SHG light can be omitted, thereby reducing optical loss on the final output path. In practice, even if the polarization extinction ratio of the intermediate SHG light is not sufficiently high in the polarization splitting-combining module 101 and an optical low-pass filter 107 must be used to block residual intermediate SHG light, because the polarization splitting-combining module 101 is optimized for wavelength λp and may not provide an assured polarization extinction ratio at wavelength λp/2, there is less residual intermediate SHG light than in the first and second embodiments, so the performance requirements for the optical low-pass filter 105 are relaxed and its cost can be reduced. Referring to FIG. 14, the fourth embodiment combines the structures of the second and third embodiments. Specifically, the quantum entangled photon pair generating device 10E in the fourth embodiment places the polarization converter 314 of the third embodiment between the second Faraday rotator 209 and the optical conversion generation unit 100 in the second embodiment. The half-wave plate 104 disposed between the third input/output port 101-3 of the polarization splitting-combining module 101 and the first Faraday rotator 207 in the third embodiment is not used. The optical low-pass filter 107 disposed between the fourth input/output port 101-4 and the WDM filter 108 in the second embodiment is unnecessary in principle, and is not shown in FIG. 14. The operation of the quantum entangled photon pair generating device 10F in the fourth embodiment can be understood from the descriptions of the second and third embodiments. As in the second embodiment, 45° polarized excitation light is input to the first input/output port 101-1 of the polarization splitting-combining module 101 and returns to the first input/output port 101-1, accompanied by transient signal and idler photon pairs and clockwise-propagating intermediate SHG light, none of which are affected by the polarization converter 314. The desired SPDC correlated photon pairs generated in the optical conversion generation unit 100, which are also unaffected by the polarization converter 314, are output from the fourth input/output port 101-4. The p-polarized intermediate SHG light propagating counterclockwise from the optical conversion generation unit 100 undergoes 90° polarization rotations in both the polarization converter 314 and the second nonreciprocal polarization converter 212, enters the second input/output port 101-2 of the polarization splitting-combining module 101 as p-polarized light, and exits from the first input/output port 101-1. This operation is summarized in FIG. 15. The desired signal and idler photon pairs are output from the fourth input/output port 101-4 of the polarization splitting-combining module 101. All other optical input and output takes place at the first input/output port 101-1. Compared with the third embodiment (FIG. 13), the roles of the first and fourth input/output ports 101-1, 101-4 as output ports are reversed. By combining the effects of the second and third embodiments, in principle, the fourth embodiment eliminates the need for both an optical circulator on the input path and an optical low-pass filter on the desired output path, thereby reducing optical loss in the quantum entangled photon pair generating device. If necessary, however, an optical circulator may be added to block excitation light from returning to its source (not shown), and an optical low-pass filter may be added to improve the purity of the quantum entangled photon pair output. In the preceding embodiments have been described as using PPLN crystals as second-order nonlinear optical media, but as noted above, similar effects can also be produced with other second-order nonlinear optical media, including bulk crystal media, waveguide media having an optical waveguide structure similar to that of a PPLN waveguide, and various other media. The position of the first half-wave plate 104 on the optical loop LP in the first and third embodiments is a design choice. When the d11 component of the second-order nonlinear optical medium is used to produce the effects described in these embodiments, for example, the first half-wave plate 104 may be disposed between the optical conversion generation unit 100 and the second input/output port 101-2 of the polarization splitting-combining module 101. The preferred position of the first half-wave plate 104 depends on the orientation of the optical axes of the second-order nonlinear optical media in relation to the polarization direction of the excitation light. The locations of the polarization converter 314 and the nonreciprocal polarization converters 211 and 212 in the second to fourth embodiments can be selected depending on similar factors. Those skilled in the art will recognize that further variations are possible within the scope of the invention, which is defined in the appended claims.
	description	The present application is a continuation of U.S. patent application Ser. No. 16/507,637 filed Jul. 10, 2019, which is a divisional of U.S. patent application Ser. No. 14/910,433 filed Feb. 5, 2016, which is a U.S. national stage application under 35 U.S.C. § 371 of PCT Application No. PCT/US2014/062094, filed Oct. 24, 2014, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/895,267 filed Oct. 24, 2013. The entireties of foregoing applications are incorporated herein by reference. The present invention relates nuclear steam supply systems, and more particularly to a steam generator used in a modular reactor system having natural gravity driven coolant flow circulation. Pressurized water reactors (PWRs) for nuclear power generation facilities utilize both pumped and natural circulation of the primary coolant (water) to both cool the reactor core and heat the secondary coolant (water) to produce steam which may be working fluid for a Rankine power generation cycle. The existing natural circulation PWRs suffer from the drawback that the heat exchange equipment is integrated with and located within the reactor pressure vessel. Such an arrangement not only makes the heat exchange equipment difficult to repair and/or service, but also subjects the equipment to corrosive conditions and results in increased complexity and a potential increase in the number of penetrations into the reactor pressure vessel. In addition, locating the heat exchange equipment within the reactor pressure vessel creates problems with respect to radiation levels encountered for crews to repair the heat exchange equipment in proximity to the radioactively hot components of the reactor vessel. The general view has also been that the heat exchangers should be located in the reactor vessel to achieve natural circulation in those systems which may utilize this type of flow circulation. The steam generator (SG) is a vitally important tubular heat exchanger in a pressurized water reactor (PWR). It serves to boil the purified Rankine cycle secondary coolant water (also called the “secondary” side water or feedwater) into steam using the heat energy from the reactor primary coolant heated by its circulation through the reactor's core (called the “primary” side). Because of the high operating pressure (typically over 2200 psi) of the reactor coolant, the steam generator is a massive piece of vertically arrayed equipment. The transfer of heat energy occurs from the primary fluid flowing inside the tubes to the secondary water located in the space outside the tubes. Improvements in nuclear steam generators are desired. The present invention provides an improved steam generator for a nuclear steam supply system. According to one embodiment, a nuclear steam supply system with natural gravity-driven coolant circulation includes: a vertically-oriented reactor vessel comprising an elongated cylindrical shell forming an internal cavity configured for containing primary coolant and a nuclear reactor fuel core; a vertically-oriented steam generating vessel comprising an elongated cylindrical shell defining an internal cavity, a top tubesheet, and a bottom tubesheet; a vertical riser pipe extending vertically between the top and bottom tubesheets, the riser pipe fluidly connected to the reactor vessel; a plurality of heat transfer tubes extending vertically between the top and bottom tubesheets; and a fluid coupling comprising an eccentric cone section forming a flow conduit for exchanging primary coolant between the steam generating vessel and reactor vessel. A closed primary coolant loop is formed in which primary coolant flows from the reactor vessel through the eccentric cone into the steam generator vessel and returns from the steam generating vessel to the reactor vessel through the eccentric cone. According to another embodiment, a nuclear steam supply system with natural gravity-driven coolant circulation includes: a vertically-oriented reactor vessel comprising an elongated cylindrical shell forming an internal cavity configured for containing primary coolant and a nuclear reactor fuel core; a vertically-oriented steam generating vessel comprising an elongated cylindrical shell defining an internal cavity configured for containing secondary coolant, a top tubesheet, and a bottom tubesheet; a plurality of heat transfer tubes extending vertically between the top and bottom tubesheets, the tubes including a preheater section, a steam generator section, and a superheater section, wherein secondary coolant in a liquid state enters a shell side of the preheater section at a bottom of the steam generating vessel and flows upward to the steam generator section where a portion of the secondary coolant boils to produce steam which in turn flows upward into the superheater section at a top of the steam generating vessel; a vertical riser pipe extending vertically between the top and bottom tubesheets, the riser pipe fluidly connected to the reactor vessel; a fluid coupling forming a flow conduit for exchanging primary coolant between the steam generating vessel and reactor vessel; and a tubular recirculation shroud surrounding the tubes in the steam generator section, the shroud configured to recirculate a portion of the liquid secondary coolant in the steam generator section to the preheater section. The primary coolant flows upward through the riser pipe and downward through the tubes on the tube side of the steam generating vessel to heat the secondary coolant. According to one embodiment, a steam generator for a nuclear steam supply system includes: a vertically-oriented steam generating vessel comprising an elongated cylindrical shell defining an internal cavity configured for containing secondary coolant, a top tubesheet, a secondary coolant outlet nozzle below the top tubesheet, a bottom tubesheet, and a secondary coolant inlet nozzle above the bottom tubesheet; a plurality of heat transfer tubes extending vertically between the top and bottom tubesheets, the tubes including a preheater section, a steam generator section, and a superheater section, wherein secondary coolant in a liquid state enters a shell side of the preheater section via the inlet nozzle and flows upward to the steam generator section where a portion of the secondary coolant boils to produce steam which in turn flows upward into the superheater section and exits the steam generating vessel through the outlet nozzle; a vertical riser pipe extending vertically between the top and bottom tubesheets, the riser pipe in fluid communication with the tubes and configured for fluid coupling to a reactor vessel containing primary coolant; a double-walled fluid coupling forming a flow conduit for exchanging primary coolant between the steam generating vessel and reactor vessel, the fluid coupling configured so that primary coolant from the reactor vessel flows through the fluid coupling into the steam generator vessel and returns from the steam generating vessel to the reactor vessel through the fluid coupling; a bottom collection plenum formed below the bottom tubesheet by the fluid coupling and configured for fluid coupling to the reactor vessel, the collection plenum in fluid communication with the tubes; a top distribution plenum formed above the top tubesheet, the distribution plenum in fluid communication with the riser pipe and tubes; and a tubular recirculation shroud surrounding the tubes in the steam generator section, the shroud configured to recirculate a portion of the liquid secondary coolant in the steam generator section to the preheater section. Advantages and aspects of the present invention include the following: Core deep underground: The reactor core resides deep underground in a thick-walled Reactor Vessel (RV) made of an ASME Code material that has decades of proven efficacy in maintaining reactor integrity in large PWR and BWR reactors. All surfaces wetted by the reactor coolant are made of stainless steel or Inconel, which eliminates a major source of corrosion and crud accumulation in the RV. Gravity-driven circulation of the reactor coolant: The nuclear steam supply system according to the present disclosure does not rely on any active components (viz., a Reactor Coolant pump) for circulating the reactor coolant through the core. Instead, the flow of the reactor coolant through the RV, the steam generator heat exchangers, and other miscellaneous equipment occurs by the pressure head created by density differences in the flowing water between the hot and cold segments of the primary loop. The reliability of gravity as a motive force underpins its inherent safety. The movement of the reactor coolant requires no pumps, valves, or moving machinery of any kind. Black-start capable (no reliance on off-site power): Off-site power is not essential for starting up or shutting down the nuclear steam supply system. The rejection of reactor residual heat during the shutdown also occurs by gravity-driven circulation. Thus, the need for an emergency shutdown power supply at the site—a major concern for nuclear plants—is eliminated. Indeed, the nuclear steam supply system uses gravity (and only gravity) as the motive force to meet its operational imperatives under both normal and accident conditions. Assurance of a large inventory of water around and over the reactor core: The present nuclear steam supply system reactor vessel (RV) has no penetrations except at its very top, which means that the core will remain submerged in a large inventory of water even under the hypothetical postulated event under which all normal heat rejection paths are lost. No large penetrations in the Reactor Vessel (RV): All penetrations in the RV are located in the top region of the RV and are small in size. The absence of large piping in the reactor coolant system precludes the potential of a “large break” Loss of Coolant Accident (LOCA) event. Easy accessibility to all critical components: In contrast to the so-called “integral” reactor systems, the steam generator and the control rod drive system are located outside the RV at a level that facilitates easy access, making their preventive maintenance and repair a conveniently executed activity. The steam generator consists of a single loop that includes in some embodiments a preheater, steam generator, and a superheater topped off by a pressurizer. The heat exchangers in the loop, namely the preheater, the steam generator, and the superheater have built-in design features to conveniently access and plug tubes such as appropriate placed manholes that provide access to the heat exchanger tubesheets and/or tube bundles. The decision to deploy the heat exchange equipment outside of the harsh environment of the reactor cavity in the nuclear steam supply system has been informed by the poor reliability of PWR steam generators over the past 3 decades and the colossal costs borne by the industry to replace them. The RV flange features a reverse joint to minimize its projection beyond the perimeter of the RV cylinder. This design innovation makes it possible to connect the Stack directly to the RV nozzle—gorging to forging connection-eliminating any piping run between them. This design features eliminates the risk of a large pipe break LOCA. Demineralized water as the reactor coolant: The reactor coolant is demineralized water, which promotes critical safety because of its strong negative reactivity gradient with rise in temperature. Elimination of borated water also simplifies the nuclear steam supply system (NSSS) by eliminating the systems and equipment needed to maintain and control boron levels in the primary coolant. Pure water and a corrosion-resistant primary coolant loop help minimize crud buildup in the RV. Improved steam cycle reliability: The reliability of the steam cycle is improved by dispensing with the high pressure turbine altogether. Rather, the cycle steam is superheated before it is delivered to the low pressure turbine. The loss in the Rankine efficiency is less than 0.5 percent; the rewards in terms of enhanced reliability and simplification of the power cycle are quite substantial. Pressure Control: The pressurizer contains a conventional heating/quenching element (water/steam for pressure control). A bank of electric heaters are installed in the pressurizer section which serve to increase the pressure by boiling some of the primary coolant and creating a steam bubble that resides at the top of the pressurizer near the head. A spray column is located near the top head of the pressurizer which sprays water into the steam bubble thereby condensing the steam and reducing the steam bubble. The increase/decrease in size of the steam bubble serves to increase/decrease the pressure of the primary coolant inside the reactor coolant system. In one exemplary embodiment, the primary coolant pressure maintained by the pressurizer may be without limitation about 2,250 psi. In alternative embodiments, a nitrogen type pressurizer system may be used. In this embodiment, the pressurizer serves to control the pressure in the reactor vessel by the application of controlled nitrogen pressure from external high pressure nitrogen tanks fluidly coupled to the pressurizer. Nitrogen pressure controlled reactors have been used in other reactor types and have years of successful operating experience with a quick response profile. Preventing fuel failures in the reactor: Over 70 percent of all fuel failures in operation are known to occur from fretting (erosion from repetitive impact) damage, which is the result of “pinging” of the fuel rods by the grid straps. The vibration of the grid straps is directly related to the level of turbulence around the fuel. In the present nuclear steam supply system, the Reynolds number is approximately 20 percent of that in a typical operating PWR today. A lower Reynolds number translates into an enfeebled pinging action (erosion rate varies approximately as 4.8 power of velocity of impact!) on the rods and thus a drastically reduced fretting damage rate. Lower burn-up levels selected for present nuclear steam supply system (in the 45 GWD per MTU range) in comparison to around 60 in the presently operating reactors) will also help ameliorate embrittlement of the fuel cladding and thus prevent rod wastage. Increased Self-shielding: The gravity-driven circulation of the primary fluid in the present nuclear steam supply system (NSSS) accrues another significant dividend in the form of a dramatically reduced radiation dose emanating from the NSSS. This is because the Nitrogen (N-16) isotope, produced by the neutron bombardment of oxygen in the reactor water in the core, generates high gamma energy emitting N-16 isotope which is largely responsible for the radiation emanating from the Containment. N-16, however, has a half-life of only 7.4 seconds which is less than one-fourth of the time needed for the primary water to travel to the top of the steam generators. Therefore, the quantity of N-16 is attenuated by over 7 half-lives, which means it is in effect depopulated down to minuscule values. Scoping calculations suggest that the radiation dose from the top of the steam generator in the NSSS can be 3 or more orders of magnitude less than that in a pumped-water PWR of a similar size. Thus, it is not necessary to build a thick concrete containment for present NSSS for radiation shielding. In lieu of building and in situ reinforced concrete containment, a shop fabricated steel containment capable of withstanding a crashing airplane is deployed which is more suitable, and more economical. All drawings are schematic and not necessarily to scale. The features and benefits of the invention are illustrated and described herein by reference to exemplary embodiments. This description of exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. The disclosure expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features. In the description of embodiments disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Steam generators used in modern nuclear power plants fall into two categories: Recirculating Type and Once-Thru Type. Recirculating Type Steam Generators: The recirculating steam generator is the most commonly used design in the industry. It features a vertical U-bundle with a hemi-head integrally welded to the tubesheet and the primary fluid entering the up flow leg of the U-tubes and exiting through the same hemi-head after flowing down the other leg of the tubes. The hemi-head space is divided into two compartments to separate the “hot” and “cooled” primary streams. The secondary side features a shroud that enables the boiling water to recirculate by the thermo-siphon action. Most world suppliers of operating PWRs, including Westinghouse, Siemens, Combustion Engineering, Framatome, and Mitsubishi utilized the Recirculating type U-bundle steam generators in their PWRs. However, the recirculating type steam generators have suffered from massive tube failures in PWRs around the world well before the end of their design life, forcing utilities to spend billions of dollars in replacement costs. Some plants such as Maine Yankee, Trojan, and Connecticut Yankee have shutdown permanently because of the high cost of steam generator replacement. Once-Thru Type Steam Generators: This design employs straight tubes fastened to the tubesheets located at the top and bottom extremities of the tube bundle. The primary water (reactor coolant) and the secondary water (boiler water) flow in a counter-current arrangement with the latter boiling outside the tubes as it extracts heat from the former across the tube walls. The mixture of water and steam in the lower produced in the lower reaches of the tube bundle progressively becomes more dry steam as the secondary flow stream rises inside the steam generator. Babcock & Wilcox was the only reactor supplier who used the once-thru steam generator configuration in its Pressurized Water Reactor (PWR) designs. The disaster at Three Mile Island Unit 2 supplied by B&W in 1979 exposed the flaws of this design. As shown in FIGS. 1 and 2, a nuclear steam supply system 100 (NSSS) of a safe modular underground reactor (SMR) according to the present disclosure comprises a vertical subterranean reactor vessel 200 with the nuclear fuel cartridge (or core) 210 containing the nuclear fuel source standing upright near its bottom. The basic flow or circulation path of the primary coolant or water (i.e. closed primary coolant loop) contained in the reactor vessel through the steam generating vessel 300 and reactor vessel 200 is shown schematically in FIG. 12 and functions as follows. The pressurized reactor primary coolant (at about 2250 psig) is heated by the fission in the core 210, which reduces the coolant density causing it to rise within the tubular reactor shroud 220. The heated reactor coolant (@ about 600 deg. F.) exits the reactor vessel and enters the steam generator 301. Once inside the steam generator, the primary coolant or water flows upward and is delivered to the top distribution plenum 391 by a centrally located tubular riser shell or pipe 337. The primary coolant fluid reverses direction and descends the steam generator flowing inside the bank of tubes (tube side), progressively transmitting its heat energy to the secondary water that flows vertically upwards on the shell side of the steam generator in a countercurrent arrangement to the primary flow stream. The cooled (and thus densified primary stream) re-enters the reactor vessel and flows downward in the annular space between the shroud and reactor vessel walls, reaching the bottom of the fuel core. The primary fluid reverses direction and flows upward resuming its circulation in the primary coolant circuit or loop of the nuclear steam supply system as it is heated by nuclear fission occurring in the reactor. The rate of flow of the primary fluid is set by the balance in the hydrostatic head between its hot up-flowing segment and the cool down-flowing segment (both of which span the reactor vessel and the steam generator) and the hydrodynamic pressure loss governed by what engineers know as the classic Bernoulli's equation. The closed primary coolant flow loop is therefore configured to produce and maintain natural gravity-driven circulation of primary coolant without the assistance of pumps. As the above summary indicates, the design objectives of the steam generator to fulfill the needs of primary side (i.e. primary coolant side) in one embodiment include: Provide for the flow of the primary fluid in it with as little friction loss as possible. Reduced pressure loss will increase the rate of circulation and improve the in-tube heat transfer coefficient, which are both salutary effects. Minimize the lateral distance between the reactor vessel and the steam generator so that the joint between them does not require a pipe (failure of such piping connections from events such as earthquakes, thermal fatigue, and other adverse mechanisms is a matter of safety concern in nuclear plants, which drives the decision to eliminate any large piping in the present SMR). The secondary side (i.e. secondary coolant side) of the steam generator also has several needs that should be addressed to avoid reliability problems that have afflicted prior designs. The design objectives of the secondary side include: In recirculating steam generators, the boiling of water in the shell side space has led to the accumulation of aggressive species on the tubesheet surface and in the crevices where the tubes emerge from the tubesheet, which over time, attack the tube walls causing leakage. The accumulation of solids in the tube support plate crevices has resulted in choking of the tubes in recirculating steam generators. In recirculating, the steam leaving the steam generator must be stripped of its entrained moisture by mechanical means. The effectiveness of the moisture separator (installed above the tube bundle of the steam generator) has been a source of operation problems in PWRs. The once-through steam generators suffered from the demerit of having too little water inventory in the shell side space. In case of an interruption in the in-flow from the feedwater (secondary coolant) line, the steam generator would tend to go dry in a very short time, making it a safety risk. This risk actually materialized at Three Mile Island nuclear generating plant in April 1979. The above deficiencies in the present day steam generator designs have guided the development of a new design disclosed herein. While the novel design features of the new present embodiment of a steam generator can be used in any steam producing boiler (i.e. non-nuclear), its anatomy and features are explained in the context of a nuclear SMR. Referring initially to FIGS. 1-6, a steam supply system 100 for a nuclear pressurized water reactor (PWR) according to the present disclosure is shown. From the thermal-hydraulic standpoint, the system includes reactor vessel 200 and steam generator 301 fluidly coupled thereto. The steam generating vessel 300 and reactor vessel 200 are vertically elongated and separate components which hydraulically and physically are closely coupled, but discrete vessels in themselves that are thermally isolated except for the exchange of primary loop coolant (i.e. reactor coolant) flowing between the vessels. The steam generating vessel 300 is laterally adjacent to, but vertically offset from the reactor vessel 200 to provide access to the reactor vessel internal components and control rods. As further described herein, the steam generating vessel 300 in one embodiment includes three heat transfer zones comprising (from bottom to top) a preheater section 320, main steam generator section 330, and a superheater section 350 which converts a fluid such as water flowing in a secondary coolant loop from a liquid entering the steam generating vessel 300 at feedwater inlet 301 to superheated steam leaving the steam generating vessel at steam outlet 302. The secondary coolant loop water may be a Rankine cycle fluid used to drive a turbine-generator set for producing electric power in some embodiments. Other uses of the steam are possible. The assemblage of the foregoing three heat exchangers may be referred to as a “stack.” Pressurizer 380 maintains a predetermined pressure of the primary coolant fluid. The pressurizer is an all-welded pressure vessel mounted atop the steam generating vessel 300 and engineered to maintain a liquid/gas interface (i.e. primary coolant water/inert gas) that operates to enable control of the primary coolant pressure in the steam generator. Pressurizer 380 may be mounted directly on top of the steam generating vessel 300 above the top tubesheet 333a and hydraulically seals the vessel at the top end. The pressurizer 380 is in fluid communication with the top tubesheet 333a and primary coolant pooling above the tubesheet in the top distribution plenum 391. The top head of the pressurizer 390 may have a hemispherical or an ellipsoidal profile in cross section. The pressurizer 380 is an all-welded pressure vessel with an open flange at its bottom, a curved “false bottom” plate, and a combination of conical and cylindrical shell courses and a top head in the form of a surface of revolution. In one embodiment, as shown, pressurizer 380 has an open flange at its bottom and is removably mounted to the steam generating vessel 300 via a bolted and flanged connection 390 to provide access to the top tubesheet 333a for maintenance, inspection, and/or repair of the tubes (e.g. plugging tubes, checking tubesheet-to-tube joints, etc.). The pressurizer 380 in some embodiments includes a convexly curved false bottom plate 412 that separates the turbulated primary flow underneath it in the top distribution plenum 391 from the water mass in pressurizer space keeping the latter relatively quiescent (see, e.g. FIG. 2). Suitably located small holes or perforations in the false bottom plate 412 provide for fluid communication between the water inventories in the two spaces. Referring to FIG. 11, reactor vessel 200 and steam generating vessel 300 may be housed in a containment vessel 110. Containment vessel 110 may be formed of a suitable shop-fabricated steel comprised of a top 111, bottom 112, and cylindrical sidewall 113 extending therebetween. In some embodiments, portions of the containment vessel which may be located above ground level may be made of ductile ribbed steel to help withstand aircraft impact. A missile shield 117 which is spaced above the top 111 of the containment vessel 110 may be provided as part of the containment vessel or a separate containment enclosure structure (not shown) which encloses the containment vessel 110. A horizontal partition wall 114 divides the containment vessel into an upper portion 114a and a lower portion 114b. Partition wall 114 defines a floor in the containment vessel. In one embodiment, a majority of reactor vessel 200 may be disposed in lower portion 114b and steam generating vessel 300 may be disposed in upper portion 114a as shown. Partition wall 114 may be formed of any suitable material, including without limitation for example concrete or metal. In various embodiments, the containment vessel 110 may be mounted above ground, partially below ground, or completely below ground. In certain embodiments, the containment vessel 110 may be positioned so that at least part or all of lower portion 114b that contains the nuclear fuel reactor core (i.e. fuel cartridge 230) is located below ground level. In one embodiment, the entire reactor vessel 200 and a portion of the steam generating vessel 300 are located entirely below ground level for maximum security. The cylindrical shell or sidewall 113 of containment vessel 110 may be horizontally split into an upper section and lower section which are joined together by a circumferential welded or bolted flanged joint 119 as shown in FIG. 11 to provide a demarcation for portions of the containment vessel which are located essentially above and below ground level. In other embodiments, the upper and lower sections may be welded together without use of a flange. In one embodiment, for example without limitation, the containment vessel 110 may have a representative height of approximately 200 feet or more for a 160 MW (megawatt) modular nuclear electric generation facility. A non-limiting representative diameter for this power generation facility is about 45 feet. Any suitable height and diameter for the containment vessel may be provided depending on system component configuration and dimensions. Containment vessel 110 further includes a wet reactor well 115 defined in one embodiment by a cylindrical circumscribing walled enclosure 116 which is flooded with water to provide enhanced radiation shielding and a back-up reserve of readily accessible coolant for the reactor core. In one embodiment, the walled enclosure 116 may be formed of stainless steel cylindrical walls which extend circumferentially around the reactor vessel 200 as shown. Other suitable materials may be used to construct enclosure 116. The wet reactor well 115 is disposed in the lower portion 114b of the containment vessel 110. Lower portion 114b may further include a flooded (i.e. water) used fuel pool 118 adjacent to the enclosure 116. In one embodiment, both the used fuel pool 118 and walled enclosure 116 are disposed below horizontal partition wall 114 as shown in FIG. 1. Both the reactor vessel 200 and steam generating vessel 300 preferably may be vertically oriented as shown to reduce the footprint and diameter of the containment vessel 110. The containment vessel 110 has a diameter large enough to house both the reactor vessel, steam generating vessel, and any other appurtenances. The containment vessel 110 preferably has a height large enough to completely house the reactor vessel and steam generating vessel to provide a fully contained steam generator with exception of the water and steam inlet and outlet penetrations for second coolant loop fluid flow associated with the Rankine cycle for driving the turbine-generator set for producing electric power. FIG. 12 shows the circulation path of primary coolant (e.g. water) in the primary coolant flow loop (see directional arrows). In one embodiment, the primary coolant flow is gravity-driven relying on the change in temperature and corresponding density of the coolant as it is heated in the reactor vessel 200, and then cooled in the steam generating vessel 300 as heat is transferred to the secondary coolant loop of the Rankine cycle which drives the turbine-generator (T-G) set. The pressure head created by the changing different densities of the coolant (i.e. hot—lower density and cold—higher density) induces flow or circulation through the reactor vessel-steam generating vessel system as shown by the directional flow arrows. Advantageously, the gravity-driven primary coolant circulation requires no coolant pumps or machinery thereby resulting in cost (capital, operating, and maintenance) savings, reduced system power consumption thereby increasing energy conversion efficiency of the PWR system, in addition to other advantages as described herein. Reactor Vessel Reactor vessel 200 may be similar to the reactor vessel with gravity-driven circulation system disclosed in commonly-owned U.S. patent application Ser. No. 13/577,163 filed Aug. 3, 2012, which is incorporated herein by reference in its entirety. Referring to FIGS. 1-3, reactor vessel 200 in one non-limiting embodiment is an ASME code Section III, Class 1 thick-walled cylindrical pressure vessel comprised of a cylindrical sidewall shell 201 with an integrally welded hemispherical bottom head 203 and a removable hemispherical top head 202. Shell 201 defines an internal cavity 208 configured for holding the reactor core, reactor shroud, and other appurtenances as described herein. In one embodiment, the upper extremity of the reactor vessel shell 201 may be equipped with a slightly tapered hub flange 204 (also known as “welding neck” flange in the art) which is bolted to a similar mating flange 205 welded to the top head 202. The bolted connection of the top head 202 provides ready access to the reactor vessel internals such as the reactor core. Two concentric self-energizing gaskets 206 compressed between the two mating flanges 204, 205 provide leak tightness of the reactor vessel 200 at the connection between the top head 202 and shell 201. The leak tightness under operating conditions is assured by an axisymmetric heating of the flanged joint that is provided by the fluid flow arrangement of the primary coolant in the system, as further described herein. The top head 202 may contain vertical penetrations 207 for insertion of the control rods and further may serve as a base for mounting the associated control rod drives, both of which are not depicted but well known in the art without further elaboration. With continuing reference to FIGS. 1-3, the reactor vessel 200 includes a tubular cylindrical reactor shroud 220 which contains the reactor core defined by fuel cartridge 230. Reactor shroud 220 transversely divides the shell portion of the reactor vessel into two concentrically arranged spaces: (1) an outer annulus 221 defining an annular downcomer 222 for primary coolant entering the reactor vessel which is formed between the outer surface of the reactor shroud and the inner surface of the shell 201; and (2) an inner passageway 223 defining a riser column 224 for the primary coolant leaving the reactor vessel heated by fission in the reactor core. The reactor shroud 220 is elongated and extends in an axial direction along vertical axis VA1 of the reactor vessel which defines a height and includes an open bottom 225 and top 226. In one embodiment, the bottom 225 of reactor shroud 220 is vertically spaced apart by a distance from the bottom head 203 of reactor vessel 200 and defines a bottom flow plenum 228. Bottom flow plenum 228 collects primary coolant from annular downcomer 222 and directs the coolant flow into the inlet of the riser column 224 formed by the open bottom 225 of reactor shroud 220 (see, e.g. FIG. 2). On the opposite top end, the top hub flange 204 of reactor vessel 200 ensures that the hot primary coolant water exiting the reactor vessel through outlet nozzle 271 cannot flow back into the downcomer 222 and mix with the incoming cooled primary coolant from the steam generator 301. Both the fuel cartridge 230 and reactor shroud 220 are supported by a core support structure (“CSS”), which in one embodiment includes a plurality of lateral support members 250 that span between and are attached to the reactor shroud and the shell 201 of the reactor vessel 200. Two support members 250 are shown in FIG. 10 for brevity. A suitable number of supports members spaced both circumferentially and vertically apart are provided as needed to support the combined weight of the fuel cartridge 230 and reactor shroud 220. In one embodiment, the bottom of the reactor shroud 220 is not directly attached to the reactor vessel 200 to allow the shroud to grow thermally in a vertical axial direction (i.e. parallel to vertical axis VA1) without undue constraint. A plurality of circumferentially spaced apart flow baffles 251 may be attached to the bottom of shroud 220 which further support the dead weight of the shroud. Baffles 251 are vertically oriented and have a shape configured to complement the curvature of the hemispherical bottom head 203 of the reactor vessel 200 as shown (see, e.g. FIG. 10) on which the baffles are seated. A plurality of lateral perforations 252 may be provided in the baffles 251 to aid in mixing the cooled primary coolant flow descending in the downcomer 222 before rising to enter the fuel cartridge 230. The reactor shroud 220 may be a single-walled open cylinder in one embodiment as shown. In an alternative construction, shroud 220 may be a double-walled cylinder comprising two radially spaced apart single shells with a sealed air gap or insulating material therebetween. This double-wall construction of reactor shroud 220 forms an insulated structure designed to retard the flow of heat across it and forms a smooth vertical riser column 224 for upward flow of the primary coolant (i.e. water) heated by the fission in the fuel cartridge 230 (“core”), which is preferably located at the bottom extremity and inside passageway 224 of the shroud in one embodiment as shown in FIGS. 1-3. The reactor shroud 220 is laterally supported by the reactor vessel by the lateral support members 250 to prevent damage from mechanical flow-induced vibrations resulting in metal fatigue over a period of time. Shroud 220 and other wetted parts of reactor vessel 200 may be made of a corrosion resistant material, such as without limitation stainless steel. Other materials and/or corrosion resistant coatings may be used. Referring to FIGS. 2 and 10, fuel cartridge 230 in one embodiment is a unitary autonomous structure containing upright fuel assemblies, and is situated in a region of the reactor vessel 200 that is spaced above bottom head 203 so that a relatively deep plenum of water lies underneath the fuel cartridge. Fuel cartridge 230 may be located inside reactor shroud 230 at the bottom end of the shroud as shown. The fuel cartridge 230 is insulated by reactor shroud 220 so that a majority of the heat generated by the fission reaction in the nuclear fuel core is used in heating the primary coolant flowing through the fuel cartridge and adjoining upper portions of the riser column 224. Fuel cartridge 230 is an open cylindrical structure including cylindrically shaped sidewalls 231, open top 233, and open bottom 234 to allow the primary coolant to flow upward completely through the cartridge (see directional flow arrows). In one embodiment, the sidewalls 231 may be formed by multiple arcuate segments of reflectors which are joined together by suitable means. The open interior of the fuel cartridge 230 is filled with a support grid 232 for holding the nuclear fuel rods and for insertion of control rods into the core to control the fission reaction as needed. Briefly, in operation, the hot reactor primary coolant exits the reactor vessel 200 through a low flow resistance outlet nozzle 270 to be cooled in the adjacent steam generating vessel 300 (see, e.g. FIGS. 2, 3, and 12). The cooled reactor primary coolant leaves the steam generating vessel 300 and enters the reactor vessel 200 through the inlet nozzle 271. The internal plumbing and arrangement in the reactor vessel directs the cooled reactor coolant down through to the annular downcomer 222. The height of the reactor vessel 200 is preferably selected to support an adequate level of turbulence in the recirculating reactor primary coolant by virtue of the density differences in the hot and cold water columns which is commonly known as the thermo-siphon action (density difference driven flow) actuated by gravity. In one embodiment, the circulation of the reactor primary coolant is driven by over 8 psi pressure generated by the thermo-siphon action, which has been determined to ensure (with adequate margin) a thoroughly turbulent flow and stable hydraulic performance. Referring to FIGS. 2 and 4, the top of the reactor vessel shell 201 is welded to a massive upper support forging which may be referred to as a reactor support flange 280. Support flange 280 supports the weight of the reactor vessel 200 and internal components above the wet reactor well 115. In one embodiment, the support flange is structurally stiffened and reinforced by a plurality of lugs 281 which are spaced circumferentially apart around the reactor vessel and welded to both the reactor vessel and flange, as shown. Support flange 280 contacts and engages horizontal partition wall 114 which transfers the dead weight of the reactor vessel 200 to the containment vessel 110. The reactor vessel's radial and axial thermal expansion (i.e. a majority of growth being primarily downwards from horizontal partition wall 114) as the reactor heats up during operation is unconstrained. However, the portion of containment vessel 110 which projects above partition wall 114 is free to grow upwards in unison with the upwards growth of the steam generating vessel 30 to minimize axial differential expansion between the steam generating vessel and reactor vessel. Because the reactor vessel and steam generating vessel are configured and structured to thermally grow in height at substantially the same rate when heated, this arrangement helps minimize potential thermal expansions stress in the primary coolant fluid coupling 273 between the reactor vessel and steam generating vessel. The support flange 280 is spaced vertically downwards on reactor vessel shell 201 by a distance from top head 202 of reactor vessel 200 sufficient to allow a fluid connection to be made to the steam generating vessel 300 which is above partition wall 114, as shown in FIGS. 2 and 11. When the reactor vessel 200 is mounted inside containment vessel 110, top head 202 of the reactor vessel and the primary coolant fluid coupling 273 (collectively formed by combined inlet-outlet flow nozzle 270/271) are located above reactor well 115. This provides a location for connection to the steam generator plenums and for the engineered safety systems (e.g. control rods, etc.) to deal with various postulated accident scenarios. A majority of the reactor vessel shell 201, however, may be disposed below partition wall 114 and immersed in the wet reactor well 115 as shown in FIG. 11. The bottom region of the reactor vessel 200 is restrained by a lateral seismic restraint system which may be comprised of a plurality of circumferentially and vertically spaced apart lateral restraint members 260 (one of which is shown schematically in FIG. 11 for brevity). Restraint members 260 span the space between the reactor shell 201 and the reactor well 115 inside surface of the cylindrical enclosure 116 to withstand seismic events. The seismic restraint design is configured to allow for free axial (i.e. longitudinal along vertical axis VA1) and diametrical thermal expansion of the reactor vessel 200. The reactor well 115 is flooded during power operations to provide defense-in-depth against a (hypothetical, non-mechanistic) accident that is assumed to produce a rapid rise in the enthalpy of the reactor's contents. Because the reactor is designed to prevent loss of core water by leaks or breaks and the reactor well is flooded, burn-through of the reactor vessel by molten fuel (corium) is not likely. Referring to FIGS. 2-4, the reactor vessel combined inlet-outlet flow nozzle 270/271 (primary coolant fluid coupling 273) is comprised of two concentric flow conduits including an outer inlet nozzle 270 and inner outlet nozzle 271. The outlet nozzle 271 has one end welded to the reactor shroud 220 (internal to the reactor vessel shell 201) and an opposite end welded to the inlet nozzle 371 of the steam generating vessel 300 (at the bottom of riser pipe 337). The reactor vessel inlet nozzle 270 has one end welded to the reactor vessel shell 201 and an opposite end welded to steam generator outlet nozzle 370 defined at least in part by the bottom tubesheet 333b of the steam generating vessel 300. Accordingly, reactor vessel inlet nozzle 270 is essentially welded to the perimeter of bottom tubesheet 333b of the steam generator 301 (best shown in FIG. 4). It should be noted that the inlet nozzle 371 of the steam generating vessel 300 and riser pipe 337 are contiguous in structure. The inlet nozzle 371 is further contiguous with the outlet nozzle 271 of the reactor vessel. Accordingly, the riser pipe 337 may also be viewed from one perspective as physically extending and fluidly connected directly to the internal shroud 220 of the reactor vessel as a single flow conduit in lieu of three separate flow conduit sections. In one embodiment, therefore, the riser pipe 337 may have a constant diameter including portions which are considered to form the primary coolant inlet nozzle 371 and reactor vessel outlet nozzle 271. An annular bottom collection plenum 373 is formed between the inlet and outlet nozzles 270, 271 of primary coolant fluid coupling 273 below the bottom tubesheet 333b (see, e.g. FIG. 4). Collection plenum 373 serves to collect the cooled primary coolant exiting the bottom ends of the tubes 332 through the bottom tubesheet 333b which flows back to the reactor vessel 200 through inlet nozzle 270 into the annular downcomer 222. In the present embodiment, the outlet nozzle 271 of the reactor vessel and inlet nozzle 371 of the steam generating vessel each have a smaller diameter than the inlet nozzle 270 of the reactor vessel and outlet nozzle 370 of the steam generating vessel. The combined inlet-outlet flow nozzle 270/271 is located above partition wall 114 of the containment vessel 110. The inlet nozzle 371 and outlet nozzle 370 of the steam generating vessel 300 collectively define a mating concentrically arranged combined primary coolant inlet/outlet nozzle 371/370 for the steam generating vessel. In one embodiment, the inlet flow nozzle 270 and outlet flow nozzle 271 of the reactor vessel 200 are configured as 90 degree flow conduits or elbows as shown. This allows extremely close horizontal spacing of the reactor vessel and steam generator shells due to the closely coupled primary coolant combined inlet-outlet flow nozzle 270/271 to the steam generator, thereby eliminating a straight horizontal section of piping between the reactor vessel and steam generator. Advantageously, such close coupling of the reactor vessel 200 and steam generator vessel 300 avoids need for long loops of large piping in the reactor primary coolant which creates the potential for a “large break” Loss of Coolant Accident (LOCA) event. Close coupling of the reactor vessel 200 and steam generating vessel 300 are achieved by the minimal radial projection of the combined inlet-outlet flow nozzle 270/271 beyond the reactor vessel shell. The total horizontal length of the inlet/outlet nozzle connection between the reactor vessel 200 and steam generating vessel 300 in certain embodiment is less than or equal to the diameter of the reactor vessel 200, and/or the steam generating vessel 300 to eliminate long runs of large coolant piping between the reactor and steam generating vessels. Concomitantly, the vertical centerline VA2 of the steam generating vessel 300 may be less than two steam generator diameters apart horizontally from the vertical centerline VA1 of the reactor vessel 200 in some embodiments. To achieve the closest possible coupling of the reactor vessel 200 and steam generating vessel 300, the outer reactor vessel inlet nozzle 270 of the primary coolant fluid coupling 273 may be a mitered 90 degree elbow or bend comprising an eccentric cone section 274 joined to a short horizontal stub pipe section 275 using a miter joint 276 (best shown in FIG. 4). The miter joint 276 minimizes the lateral distance between the reactor vessel 200 and steam generating vessel 300. Miter joint 276 is disposed an angle between 0 and 90 degrees (e.g. about 30-60 degrees in some embodiments) with respect to the horizontal plane at the joint. The stub pipe section 275 is disposed at a 90 degree angle to the eccentric cone section 274. The outer reactor vessel inlet nozzle 270 therefore forms an asymmetrically-shaped outer flow jacket which surrounds the inner reactor vessel outlet nozzle 271 as shown. The eccentric cone section 274 has a circular cross section and inside diameter which varies (i.e. narrows) from its inlet end at steam generator outlet nozzle 370 adjacent bottom tubesheet 333b to the stub pipe section 275. Cone section 274 is formed by a straight inner sidewall 274b and an opposing inclined sidewall 274a which is angled with respect to the inner sidewall as shown in FIG. 4. The outlet end of the eccentric cone section at the miter joint 276 has a circular cross section as does the inlet to the stub pipe section 275 which is coupled to the reactor vessel wall 201 (e.g. welded). Steam Generator The steam generator 301 will now be described in further detail. Referring to FIGS. 1-9, the steam generating vessel 300 in one embodiment may a vertically oriented and elongated structure which defines a vertical axis VA2. In one embodiment, the vertical axis VA2 of the steam generating vessel is horizontally offset from the vertical axis VA2 of the reactor vessel 200 so that the steam generating vessel is arranged laterally adjacent to the reactor vessel. In one embodiment, the steam generating vessel 300 has a height which is at least as high as the height of the reactor vessel 200 to achieve the thermo-hydraulic conditions necessary to induce gravity-driven primary coolant circulation through the steam generating vessel 300 and reactor vessel 200. Structurally, steam generating vessel 300 includes a top 310, bottom 311, and a vertically extending hollow cylindrical shell 312 extending therebetween which defines an internal cavity 393 for holding a plurality of heat exchange components. Steam generating vessel 300 further includes a top tubesheet 333a, bottom tubesheet 333b, a plurality of heat transfer tubes 332 extending vertically between the tubesheets, an internal riser pipe 337, and pressurizer 380 disposed on the top 310 of the vessel. The top and bottom tubesheets 333a, 333b are circular in top plan view and of suitable thickness to withstand the operating pressure within the steam generating vessel 300 without undue deformation which could adversely affect the integrity of the joints between the tubes 332 and tubesheets. In one embodiment, the bottom tubesheet 333b may have a convexly rounded top so that any debris accumulating within the steam generating vessel 300 settles to the outside perimeter of the tubesheet inside the shell 312. The tubesheets are preferably formed a thick corrosion resistant steel such as stainless steel in one embodiment. In one embodiment, riser pipe 337 is concentrically aligned with shell 312 and lies on the vertical axis VA2 of the vessel. The tubes 332 are circumferentially arranged around the outside of the riser pipe 337 in any suitable pattern between the riser pipe and shell 312 of steam generating vessel 300. In one embodiment, the tubes 332 of the steam generating vessel 300 may define three heat transfer zones arranged vertically for converting secondary coolant feedwater entering the bottom of the vessel from a liquid phase to a steam phase exiting the top of the vessel. In one embodiment, the steam phase is superheated steam. The three heat transfer zones may include (from bottom up) a preheater section 320 for initial heating of the liquid secondary coolant, main steam generator section 330 which serves as the boiler for heating the secondary coolant to the boiling point temperature where it changes phase to steam, and superheater section 350 for heating the steam to superheated conditions. In certain arrangements and configurations of the steam generator 300, the preheater 320 may be omitted depending on the thermo-hydraulic design of the system. The preheater section 320, steam generator section 330, and superheater section 350 are tubular heat exchangers each including a plurality of parallel straight tubes 332 (i.e. tube bundles) with the top and bottom tubesheets 333a, 333b disposed at the uppermost and lowermost extremities or ends of each tube 332. In one embodiment, the tube bundles are contiguous in structure from top to bottom so that there are no intermediate structures formed between the three different heat transfer sections on the tubeside. Primary coolant therefore flows downwards through each of the tubes 332 which have a continuous structure and height from the top tubesheet 333a to bottom tubesheet 333b. The preheater section 320, steam generator section 330, and superheater section 350 therefore are defined by the phase of the secondary coolant within the three different heat transfer zones as the feedwater changes phase from a liquid state entering the steam generating vessel 300 at the bottom to steam exiting from the top of the vessel. The internal cavity 393 of the steam generating vessel 300 may be contiguous and open between the tubesheets 333a and 333b on the shell side of the steam generating vessel 300 without any intermediate structures which may interrupt the upward flow of secondary coolant. The preheater 320, steam generator 330, and superheater 350 are configured to form a parallel counter-flow type heat exchanger arrangement in which the secondary coolant (Rankine cycle) flows in an opposite, but parallel direction to the reactor primary coolant (see, e.g. FIGS. 4, 5, and 9B). In a certain embodiment, the preheater section 320 may be configured to provide a combination of parallel counter-flow and cross-flow of the secondary coolant with respect to the primary coolant flow via the provision of flow baffles 394 on the shell side of the steam generating vessel 300. Referring to FIGS. 4, 7B, and 9B, two different configurations and sizes of baffle plates may be provided comprising a circular outer baffle 394a attached to steam generator shell 312 and having a central opening 394c, and a circular inner baffle 394b attached to riser pipe 337 and having a central opening 394d. Outer baffle 394a has a central opening 394c (i.e. circular) with a diameter larger than the diameter of the riser pipe 337 forming a lateral outside gap between the riser pipe and baffle, and an outside diameter slightly smaller than the inside diameter of the shell 312 for attachment thereto. Inner baffle 394b has a central opening 394d with a diameter slightly larger than the riser pipe 337 for attachment thereto, and an outside diameter smaller than the inside diameter of the steam generator shell 312 forming a lateral outside gap between the outer baffle. This arrangement advantageously causes the secondary coolant to flow through the preheater section 320 in the circuitous path shown (see directional flow arrows in FIG. 4) which maximizes contact time and heat transfer between the tubes 332 heated on the tube side by the primary coolant and the secondary coolant feedwater flowing on the shell side of the steam generating vessel 300. The inner and outer baffles 394b, 394a are arranged in an alternating pattern in the vertical direction to produce a combination of a perpendicular cross-flow pattern and parallel counter-flow pattern of the liquid secondary coolant with respect to the primary coolant through the preheater section 320 (see, e.g. directional arrows FIGS. 4 and 9B). The baffle plates 394a, 394c in the shell side space are therefore shaped to promote a combination of either radially symmetric cross flow or axially symmetric longitudinal flow of the shell side fluid. In certain embodiments, the steam generator section 330 and/or superheater section 350 may include baffles similar to baffles 394a and 394b shown in FIGS. 4, 7B, and 9B. The tube support system (baffles) in each zone is configured to promote radially symmetric flow. Radially symmetric flow fields are desired to prevent bowing or bending of the steam generator shell 312 from circumferential thermal gradients. Referring to FIGS. 9, 9B, and 9C, the interface between the preheater and the steam generator section 320, 330 zones in one embodiment may be demarcated by a relatively thick interface plate 410 which has a plurality of drilled and polished holes to form an extremely tight fit around the tubes (e.g. radial gap to the tube less than 1/64 inch). In other configurations, the interface plate may be omitted. Both the bottom tubesheet 333b and the interface plate 410 may have slightly convex top surfaces so that any contaminants or debris produced by boiling the secondary coolant that may tend to settle on them are swept to the outer periphery of the steam generating vessel 300 from which they can be evacuated through suitably sized “blow down” openings in the steam generator shell 312 (not shown) periodically. The foregoing tubular heat exchangers (i.e. preheater, steam generator, and superheater) are hydraulically connected in series on both the tube side (reactor primary coolant) and the shellside (the secondary coolant forming the working fluid of the Rankine Cycle which changes phase from liquid to superheated gas). The top 310 of the steam generating vessel 300 may be terminated with flanged connection 390 which couples the pressurizer 380 to the vessel (see, e.g. FIGS. 7A, 7B, and 8). The bottom tubesheet 333b forms the bottom 311 of steam generating vessel 300 and is directly connected to the steam generating vessel shell 312 (see, e.g. FIG. 4). Pressurizer 380 is mounted to top 310 of steam generating vessel 300 and is in fluid communication with both the top or outlet of riser pipe 337 and the inlet to superheater tubes 332. Pressurizer 380 which features a cylindrically-curved shell of revolution includes internal features to maintain a quiescent mass of water therein while ensuring a communicable relationship with the primary coolant water coursing through the top of the steam generating vessel 300 in the top distribution plenum 391 (see, e.g. FIG. 2). The pressurizer 380 has conventional electric heaters and spray nozzles to control primary coolant pressure. The pressurizer 380 may therefore generally include a heating/quenching element (i.e. water/steam) for pressure control of the reactor primary coolant. The element is comprised of a bank of electric heaters which are installed in the pressurizer section that serve to increase the pressure by boiling some of the primary coolant and creating a steam bubble that resides at the top of the pressurizer near the head (above the liquid/gas interface 392 of the primary coolant). A water spray column is located near the top head of the pressurizer which sprays water into the steam bubble thereby condensing the steam and reducing the size of the steam bubble. The increase/decrease in size of the steam bubble serves to increase/decrease the pressure of the primary coolant inside the reactor coolant system. In one exemplary embodiment, a representative primary coolant pressure maintained by the pressurizer 380 and heating/quenching element 381 may be without limitation about 2,250 psi. In alternative embodiments, a liquid/gas interface may be formed between an inert gas, such as nitrogen (N2) supplied by supply tanks connected to the pressurizer 380, and the liquid primary coolant. The pressurizer 380 defines a top distribution plenum 391 which collects reactor primary coolant rising through riser pipe 337 and distributes the primary coolant to the inlet of each of the tubes 332 penetrating the top tubesheet 333a. Plenum 391 resides above the top tubesheet 333a within the pressurizer forming a liquid reserve of primary coolant. Top tubesheet 333a may be recessed below the top 310 of steam generating vessel 300 (best shown in FIG. 8) to facilitate formation of the plenum. The depth of the plenum 391 may vary depending on the exact location of the liquid/gas interface 392; however, the depth of primary coolant in the plenum is preferably sufficient to cover the tubes 332 and tubesheet 333a and evenly distribute the primary coolant from the riser pipe 337 to the inlet ends of each of the tubes 332 penetrating the tubesheet. Referring to FIGS. 1, 4, and 7-9, steam generating vessel 300 includes a secondary coolant inlet nozzle 395 which is fluidly connected to steam generator shell 312 for introducing liquid secondary coolant feedwater into the bottom of the preheater section 320. In one embodiment, the inlet nozzle 395 may be attached to shell 312 at one of two radially projecting expansion joints 396a, 396b formed integrally with the shell in the preheater section 320 as best shown in FIG. 4. The expansion joints may have a box-like configuration in cross-section as shown and encircle the shell 312 of the steam generating vessel 300 for accommodating thermal growth in length/height of the steam generating vessel 300. The risk of high tube stresses due to differential expansion between the tubes 332 and the steam generator shell 312 advantageously is mitigated by the flanged and flued expansion joints 396a, 396b located near the top and bottom tubesheets 333a, 333b. Steam generating vessel 300 also includes a secondary coolant outlet nozzle 397 which is fluidly connected to steam generator shell 312 for withdrawing secondary coolant superheated steam from the superheater section 350. In one embodiment, the outlet nozzle 397 may be attached to shell 312 at the second radially projecting expansion joints 396b formed integrally with the shell in the superheater section 350 as best shown in FIG. 8. Although steam generator 301 includes straight heat transfer tubes 332, the steam generator vessel 300 may be configured to form a recirculating type steam generator. Referring to FIGS. 2 and 7-9, the steam generator section 330 in one embodiment of a steam generator 301 includes a tubular recirculation shroud 398 having a diameter smaller than the inside diameter of the steam generator vessel shell 312 forming an annular downcomer 399 between the shell and shroud for recirculating liquid secondary coolant. The bundle of heat transfer tubes 332 is disposed inside the shroud 398. The top 401 of the shroud is spaced below the water level W in the steam generator 301 forming the steam-liquid interface at the superheater section 350 of the tube bundle (see, e.g. FIG. 9A). Accordingly, the shroud 398 is wetted at all times during normal operation of the steam generator. The water level W may be maintained within a narrow range by a conventional level controller (not shown) such that the shroud 398 in the steam generator section 330 is submerged in water (primary coolant) at all times. The heat transfer surfaces and flow areas are sized such that the re-circulation ratio (ratio of the re-circulation flow rate to the steam generation rate) is approximately 5 in one non-limiting embodiment. On the opposite end, the bottom 402 of the recirculation shroud is disposed above and proximate to the top of the preheater section 320 of the tube bundle above the interface plate 410 (see, e.g. FIG. 9B). In operation, liquid secondary coolant flows upward on the shell side inside the shroud 398 towards the water lever W as it is heated by the tubes 332 (primary coolant flowing downwards therein on the tube side). The fluid rises as it becomes less dense from heating and boils producing steam. The reserve of secondary coolant not converted into steam cools further and flows radially outwards into the top of the annular downcomer 399 and flows downward towards the preheater section 320. The secondary coolant in the downcomer 399 then reverses direction and re-enters the bottom of the shroud mixing and flowing upwards again with the secondary coolant leaving the preheater section 320 to complete the recirculation flow loop. The steam generating vessel 200 may be supported by a gusseted cylindrical flanged support skirt 400. FIGS. 4 and 5 show the support skirt in greater detail. The support skirt 400 is attached to the bottom 311 of the steam generator vessel 300 in one arrangement. Support skirt 400 is structurally robust and may have a double-flanged arrangement comprising a radially projecting top bearing flange 405, radially projecting bottom base flange 404, and a circumferentially extending vertical wall 407 extending between the flanges. Wall 407 forms a circular enclosure (in transverse cross section) at least partially or fully surrounding the primary coolant fluid coupling 273 as shown. In various configurations, the support skirt 400 may be circumferentially continuous for 360 degrees or extend circumferentially less than 360 degrees. The bearing flange 405 and base flange 404 are diametrically enlarged with respect to the wall 407 thereby projecting beyond the wall. Base flange 404 is configured for seating on and attachment to divider wall 114 of the containment vessel 110 to transfer the dead weight of the steam generator 301 to the vessel (see also FIG. 11). Base flange 404 may be attached to divider wall 114 by any suitable means. In one embodiment, the base 404 may be attached with bolting such as a plurality of anchor bolts 408 spaced circumferentially apart. The base flange 404 and vertical wall 407 form an angled flanged arrangement. In one embodiment, the bottom tubesheet 333b includes a diametrically enlarged and radially projecting flange 406 which is configured and dimensioned to engage the top bearing flange 405 of the support skirt 400. Flange 406 is an integral unitary structural part of the tubesheet 333b. Accordingly, the bottom tubesheet 33b serves a dual function as a flow and support device. The flange 406 forms an annular stepped surface 409 around the perimeter of tubesheet 333b to positively engage the top bearing flange 405 and prevent lateral movement of the bottom of the steam generating vessel 300 during a seismic event. The bottom tubesheet flange 406 is therefore machined or formed to serve as the transmission path for the weight of the steam generator unit to the support foundation (e.g. divider wall 114) via the flanged support skirt 400. In other possible embodiments, the tubesheet flange 406 may be formed separately on the steam generating vessel 300 from the tubesheet 333b. The steam generator support skirt 400 further includes a plurality of vertically oriented stiffeners 403 extending between the bearing and base flanges 405, 404. The stiffeners 403 are circumferentially spaced apart and formed of structure plate which may be cut an angle as shown (see, e.g. FIGS. 4 and 5). The support skirt 400 including stiffeners 403, flanges 404, 405, and wall 407 are preferably made of structural steel plate of suitable thickness to bear the weight of a steam generator 301 containing secondary coolant during operating conditions. In one non-limiting embodiment, the steam generating vessel 300 and other components herein described exposed to moisture may be made of a corrosion resistant metal such as stainless steel and/or steel with a corrosion resistant liner or coating. Other types of metals may be used. The flow path of the reactor primary coolant and secondary coolant for the Rankine cycle will now be described. FIG. 12 shows the reactor primary coolant flowpath via directional flow arrows (i.e. primary coolant flow loop). FIGS. 1-4 and 6-9 show the secondary coolant flowpath of the Rankine cycle through steam generating vessel 300 via directional arrows. Primary coolant flows on the tube side of the steam generating vessel 300 and secondary coolant flows on the shell side. Cooled primary coolant (“cold”) leaves steam generating vessel 300 through outlet nozzle 370 and enters reactor vessel 200 through outer inlet nozzle 270. The primary coolant flows downwards through annular downcomer 222 enters the bottom of riser column 224. The primary coolant flows upwards through fuel cartridge 230 and is heated by convection and conduction in the fuel core. The now heated or “hot” primary coolant exits the reactor vessel 200 through outer inlet nozzle 270 and enters steam generating vessel 300 through inlet nozzle 371. The hot primary coolant flows vertically upwards in riser pipe 337 and is directed to the top of the “stack” into the top distribution plenum 391 formed by the pressurizer 380. The hot primary coolant enters the tubes 332 through penetrations in top tubesheet 333a and reverses direction to begin the downwards journey through steam generating vessel 200 in the tubes. The hot primary coolant first flows down through the superheater 350 on the tube side of the tube bundle which has wet saturated steam (secondary coolant) flowing upwards on the shell side from the steam generator 230 below in the stack. The saturated steam becomes superheated and is dried by the primary water inside the tubes, which is flowing in counter flow to the rising steam mass. The counter-flow arrangement permits the steam to be superheated to within a few degree Fahrenheit of the reactor coolant's peak temperature, resulting in maximized thermodynamic efficiency. The superheated steam then leaves the steam generating vessel 300 via outlet nozzle 397. Continuing the process, the now less hot coolant continues to flow down through the steam generating vessel 300 next proceeding through the steam generator 330 on the tube side. On the shell side, liquid secondary coolant undergoes a phase change and is turned to steam as the primary coolant is further cooled in giving up heat to the secondary coolant. The now further cooled primary coolant flows down through the preheater 320 on the tube side which encounters and preheats the cold (e.g. sub-cooled) liquid secondary coolant entering the shell side through the feedwater inlet nozzle 395 of the steam generator. The now cooled primary coolant has completed the closed flow loop through the steam generating vessel 300 and reactor vessel 200, and re-enters the reactor vessel through inlet nozzle 270 to repeat the foregoing flow process in the closed primary coolant flow loop. In one embodiment, an exemplary non-limiting reactor vessel “hot” outlet temperature may be in a range of about and including 575 to 600 degrees F. An exemplary non-limiting reactor vessel “cold” inlet temperature may be in a range of about and including 350 to 385 degrees F. An exemplary reactor vessel operating pressure may be about 2,250 psi (pounds per square inch) which is maintained by pressurizer 380. Other suitable flow temperatures and pressures may be used depending on the heat transfer requirements of the specific application and Rankine cycle side steam production operating parameters. In one embodiment, the reactor vessel primary coolant may be unborated demineralized water. In one exemplary embodiment, the shell 312 of steam generating vessel may be made of steel such as type 508 carbon steel. Tubesheets 333a, 333b may be made of the same steel with an Inconel cladding when the tubes 312 are made of Inconel. In other embodiments, these components may be formed of other suitable metal materials including stainless steel. Other features and aspects of the steam generator 301 may include the following: a. The tubes 332 and the riser shell or pipe 337 may be fastened to the two tubesheets 333a, 333b by conventional methods such as edge welding, butt welding, hydraulic expansion, roller expansion, or a combination thereof. In non-limiting preferred embodiments, the tubes 332 are fastened to the two tubesheets 333a, 333b by a high integrity joining process such as hydraulic expansion or explosion bonding. Roller expansion is not necessarily favored in all situations because it has an adverse effect on the service life of the tubes due to work hardening of the tube material in the rolled zone. b. Either or both the steam generating vessel shell 312 and the riser pipe 337 may incorporate one or more “flexible shell elements” to acquire axial flexibility. c. The tubes 332 and/or the riser pipe 337 may be installed in the tubesheets 333a, 333b such that they are in a prescribed state of pre-tension. d. The shell side inlet and outlet nozzles 301, 302 are located close to the bottom and top tubesheets 333a, 333b, preferably in the shell 312 course of the “flexible shell elements” or expansion joints 396a, 396b. e. A perforated impingement shell 411 is installed in each of the two expansion joints 396a, 396b wherein the inlet and outlet nozzles are situated to provide for an essentially radially symmetric entrance of feedwater secondary coolant and exit of heated steam from the steam generating vessel 300, respectively (see, e.g. FIG. 4). The steam generator vessel 300 and pressurizer 380 may be laterally restrained at the four locations in one embodiment including proximate to the bottom tubesheet 333b, tope tubesheet 333a, near the mid-elevation of the steam generator shell 312, and the top of the pressurizer by lateral supports 420 (see, e.g. FIG. 6). In one embodiment, the support skirt 400 may provide the lateral restraint near the bottom tubesheet 333b. The lateral restraints 420 may be lined with an insulating material at their interface with the steam generating vessel shell 312 so as to prevent excessive heating of the structural material in the body of the restraints. The lateral restraints 420 may be equipped with a spring/damper material to reliably distribute the load on each during a seismic or mechanical loading event. The lateral supports 420 at mid-height of the steam generating vessel 300 and at the top tubesheet 333a location adjacent the flanged joint 390 shown advantageously help increase the beam mode frequency of the steam generator 301 in the rigid range. The lateral restraints further do not interfere with the axial vertical movement of the steam generator 301 along vertical axis VA2 due to thermal expansion. While the invention has been described and illustrated in sufficient detail that those skilled in this art can readily make and use it, various alternatives, modifications, and improvements should become readily apparent without departing from the spirit and scope of the invention.
040509877	abstract	A bearing and seal structure for nuclear reactors utilizing rotating plugs above the nuclear reactor vessel. The structure permits lubrication of bearings and seals of the rotating plugs without risk of the lubricant draining into the reactor vessel below. The structure permits lubrication by utilizing a rotating outer race bearing.
	description	This application claims priority from, and is a 35 U.S.C. §111(a) continuation of, PCT international application number PCT/US2008/083234 filed on Nov. 12, 2008, incorporated herein by reference in its entirety, which claims priority from U.S. provisional patent application Ser. No. 60/987,222 filed on Nov. 12, 2007, incorporated herein by reference in its entirety. This invention was made with Government support from the DOE-NE Nuclear Energy Research Initiative, Contract No. DE-FC07-05ID14669. The Government has certain rights in this invention. This application is also related to PCT International Publication No. WO 2009/097037 published on Aug. 6, 2009, incorporated herein by reference in its entirety. Not Applicable A portion of the material in this patent document is subject to copyright protection under the copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive any of its rights to have this patent document maintained in secrecy, including without limitation its rights pursuant to 37 C.F.R. §1.14. 1. Field of the Invention This invention pertains generally to nuclear reactor design, and more particularly to a liquid-fluoride-salt cooled high-temperature nuclear reactor using pebble fuel that achieves high power density. 2. Description of Related Art Current high temperature reactors, such as the Pebble Bed Modular Reactor (PBMR), use helium as a coolant. Helium-cooled high temperature reactors (HTRs) with prismatic and pebble fuels have been extensively studied and developed, and are well known in the art. Likewise molten fluoride salts were developed in the 1950's as solvents for fluid-fueled nuclear reactors. More recently, reactors using clean liquid fluoride salt as a coolant, and solid prismatic or pebble fuel of similar type to that for helium cooled HTRs, have been proposed Each of the following publications which provides additional background information and is incorporated herein by reference in its entirety: P. Bardet, J. Y. An, J. T. Franklin, D. Huang, K. Lee, M. Toulouse and P. F. Peterson, “The Pebble Recirculation Experiment (PREX) for the AHTR,” submitted to Global 2007, Boise, Id., Sep. 9-13, 2007. M. Fratoni, F. Koenig, E. Greenspan, and P. F. Peterson, “Neutronic and Depletion Analysis of the PB-AHTR,” Global 2007, Boise, Id., Sep. 9-13, 2007. A. Griveau, F. Fardin, H. Zhao, and P. F. Peterson, “Transient Thermal Response of the PB-AHTR to Loss of Forced Cooling,” Global 2007, Boise, Id., Sep. 9-13, 2007. P. Bardet, E. Blandford, M. Fratoni, A. Niquille, E. Greenspan, and P. F. Peterson, “Design, Analysis and Development of the Modular PB-AHTR,” 2008 International Congress on Advances in Nuclear Power Plants (ICAPP '08), Anaheim, Calif., Jun. 8-12, 2008. E. D. Blandford and P. F. Peterson, A Novel Buoyant Shutdown Rod Design for the Passive Reactivity Control of the PB-AHTR,” 4th International Topical Meeting on High Temperature Reactor Technology, Washington, D.C., Sep. 28-Oct. 1, 2008. R. C. Robertson, 6/71 “Conceptual Design Study of a Single-Fluid Molten-Salt Breeder Reactor,” Chapter 3, “Reactor Primary System,” ORNL-4541, June, 1971. C. W. Forsberg, P. Pickard and P. F. Peterson, “Molten-Salt-Cooled Advanced High-Temperature Reactor for Production of Hydrogen and Electricity,” Nuclear Technology, 144, pp. 289-302 (2003). S. J. de Zwann, B. Boer, D. Lathouwers and J. L. Kloosterman, “Static design of a liquid-salt-cooled pebble bed reactor (LSPBR),” Annals of Nuclear Energy 34 (2007) 83-92. Tallackson, J. R., “Thermal Radiation Transfer of Afterheat in MSBR Heat Exchangers,” ORNL-TM-3145, 3/71. McWherter, J. R., “Molten Salt Breeder Experiment Design Bases,” ORNL-TM-3177, pg. 26, 11/70. A practical realization of a liquid-salt cooled high temperature reactor could bring major benefits to nuclear energy by enabling the excellent passive safety and high power conversion efficiency of helium cooled reactors to be achieved, but in a more compact, high power density, low pressure reactor. The present invention pertains to a novel Modular Pebble Bed Advanced High Temperature Reactor (PB-AHTR) design which achieves high power density with greatly reduced reactor size and cost. One aspect of the invention involves using a large number of parallel, pebble filled flow channels in replaceable graphite reflector blocks. Another aspect of the invention involves using pebbles with smaller diameter than used in helium cooled pebble bed reactors to increase the heat transfer surface area and reduce the fuel temperature. A still further aspect of the invention is a method to introduce and remove pebbles from the reactor core, so that the pebbles can be recirculated multiple times through the core and depleted pebbles replaced with fresh pebbles to maintain core reactivity. Advantages of using the channel-core configuration include: (1) a significant reduction of the volume fraction of salt in the core, improving reactivity and discharge burn up; (2) neutron moderation by the reflector graphite, allowing higher heavy metal loading in the pebbles and reducing the number of pebbles requiring manufacture and the spent fuel volume; (3) the capability to recirculate high burn up pebbles to the center of the core to flatten the core power distribution; (4) improved response of the pebble core to seismic loads; and (5) the ability to provide locations in the central, high flux region of the core for the insertion of control and safety rods. Another aspect of the invention involves pebble fuel design and reactivity control for a liquid-cooled pebble-channel nuclear reactor. In one embodiment, the pebble fuel is designed to have an inert graphite kernel, surrounded by an annular fuel region with fuel particles, with a protective coating of graphite on the exterior of the pebble. The use of an inert graphite kernel with an annular fuel region decreases the fuel temperature significantly compared to the conventional homogeneous fuel distribution in a fuel pebble, which brings benefits in the response of the reactor to Anticipated Transient Without Scram (ATWS) transients. Adjustment of the density of the kernel allows the pebble density and buoyancy in the liquid coolant to be controlled. In another embodiment, the reactor uses control and shutdown elements that are neutrally buoyant in the salt at a temperature somewhat above the normal core inlet temperature and below the normal core outlet temperature. Flow through the control channel may come from the core inlet plenum or an intermediate location in the core, so that under transients where the primary pumps stop or the coolant entering the control channel temperature rises above the design temperature, the elements drop into channels in and around the core without external activation. These control elements may be fabricated from a combination of graphite (density of 1.7 g/cc or less) and boron carbide (density of 2.5 g/cc), in appropriate proportion to provide neutral buoyancy in the liquid coolant (nominally 0.1967 g/cc at 640° C.). The buoyant element or elements may have various shapes, including cylinders, spheres, and cruciforms, or combinations thereof. The optimal geometry may consist of a single vertical element with a cruciform cross section in its center and cylindrical cross sections at its ends, with dimensions selected to (1) optimize the cross-sectional area to maximize the terminal drop velocity via the balance between buoyancy forces (increased cross sectional area) and drag forces (decreasing cross sectional area and perimeter), (2) maximize the effectiveness of neutron absorption in the center region of the element (cruciform geometry), (3) facilitate active insertion of the element using an externally activated control rod applying force to the top of element, and (4) facilitate passive stopping of the element upon reaching the bottom of the channel (for example, with a cylindrical section entering into a dash pot at the bottom of the channel). In another embodiment of the invention, the reactor uses a fuel pebble with density lower than the liquid coolant density, and the defueling chute is positioned to remove the pebbles above the core, rather than below the core as is the practice with conventional helium-cooled pebble bed reactors. This configuration takes advantage of the fact that it is easier to fabricate pebbles that are less dense than salt than more dense, and that it is preferred to have the defueling machine above the core for a pool-type reactor configuration. In a further embodiment, the reactor uses water, with plastic spheres fabricated from a material like polyethylene, scaled to approximately 50% of the prototypical scale, to generate experimental data for pebble motion to be used in licensing of liquid-cooled pebble bed reactors. This method for experimental validation for licensing has lower cost than using experiments with the prototypical high-temperature salt and pebbles. Another aspect of the invention is to provide a method to recirculate fuel pebbles in a liquid-salt cooled, high temperature reactor core to permit refueling. Another aspect of the invention is to fabricate pebbles that are positively buoyant in the coolant and have reduced stored energy. Another aspect of the invention is to provide a method to passively or actively insert neutron control elements into the center region of the core to control the reactor power. Another aspect of the invention is to provide a method to increase moderation of neutrons in the core and allow higher pebble heavy metal loading. Another aspect of the invention is to provide a method to prevent ingress of cover gas into the core if the primary salt inventory is reduced. Another aspect of the invention is to provide a method to connect the graphite radial reflector structure to the reactor vessel that sustains the structure in compression, and to provide a method to support the reflector structure during initial assembly, heating, and filling of the reactor vessel with salt. Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. By way of example, and not of limitation, the invention pertains to a compact, liquid salt cooled, modular pebble bed advanced high temperature reactor (PB-AHTR). The reactor preferably uses an annular fuel pebble comprising an inert graphite center kernel, a TRISO fuel particles region, and a graphite outer shell, with an average pebble density lower than the density of the liquid salt so the pebbles float. The pebbles are introduced into a coolant entering the reactor and are carried into the bottom of the reactor core, where they form a pebble bed inside a plurality of vertical channels inside replaceable Pebble Channel Assemblies (PCAs). Pebbles are removed through defueling chutes located at the top of each PCA. Each PCA also includes channels for insertion of neutron control and shutdown elements, and channels for insertion of core flux mapping and other instrumentation. The PCAs are surrounded by a graphite permanent radial reflector to provide neutron shielding to the reactor vessel wall. Vertical buoyancy and pressure loads are transferred to the metallic reactor vessel near the top of the reflector. During assembly of the radial reflector and heating and filling of the reactor vessel, the graphite blocks are held in compression by metal tie rods extending from the top of the reactor to a metal reflector support ring below the reflector. The reactor uses overhung centrifugal primary pumps, with an anti-siphon vent on the pump suction pipes to prevent ingestion of cover gas if the primary salt inventory is reduced. In one beneficial embodiment, the reactor has a nominal power output of 900 MWth and uses a core inlet/outlet temperature of 600° C./704° C., thereby allowing the use of currently available and code-qualified materials for construction. The reactor delivers heat at an average temperature of 652° C., the same average temperature as the General Atomics GT-MHR (core inlet/outlet temperature of 450° C./850° C.), and thus achieves the same power conversion efficiency of ˜46%. Natural circulation of the liquid coolant provides highly effective thermal coupling of the fuel with the large mass of graphite reflector material, so the peak rise in the core outlet temperature is less than 30° C. under loss of forced cooling transients. The modular design achieves a nominal core average power density of 20 MW/m3 to 30 MW/m3, compared to 4.8 MW/m3 for the PBMR and 6.5 MW/m3 for the GT-MHR, which are cooled by high-pressure helium. High power density is achieved due to the effective heat transfer provided by the coolant, and by a novel pebble-channel core configuration and the use of smaller (3-cm diameter) pebbles. The design reduces the spent fuel volume to less than half that of a conventional helium cooled PBMR. Our recent PB-AHTR work has shown that high power densities are possible compared to the typical maximum value of 6.5 MW/m3 for modular helium cooled reactors. In this work that studied a large, cylindrical core configuration, pebble recirculation methods were verified experimentally (P. Bardet, J. Y. An, J. T. Franklin, D. Huang, K. Lee, M. Toulouse and P. F. Peterson, “The Pebble Recirculation Experiment (PREX) for the AHTR,” submitted to Global 2007, Boise, Id., Sep. 9-13, 2007), neutronics simulations demonstrated that negative void reactivity can be achieved by increasing the heavy metal loading of the pebbles (M. Fratoni, F. Koenig, E. Greenspan, and P. F. Peterson, “Neutronic and Depletion Analysis of the PB-AHTR,” Global 2007, Boise, Id., Sep. 9-13, 2007), and RELAP5-3D simulations showed that the increase in the core outlet temperature during a loss of forced cooling (LOFC) transient was quite small (A. Griveau, F. Fardin, H. Zhao, and P. F. Peterson, “Transient Thermal Response of the PB-AHTR to Loss of Forced Cooling,” Global 2007, Boise, Id., Sep. 9-13, 2007). These studies led to the conclusion that the PB-AHTR can achieve power densities between 15 MW/m3 to 30 MW/m3, and that the reduced leakage from the core allows up to a 20% higher discharge burn-up, for the same initial enrichment, compared to an annular MHR core design. Practical embodiments of a liquid-salt cooled high temperature reactor according to the invention will now be described. Beneficially, the reactor employs a novel design using pebble fuel in a pool configuration that provides high intrinsic safety. The design provides several important advances over the state of the art, including, but not limited to, (i) providing a method to recirculate fuel pebbles in the reactor core to permit refueling; (ii) providing a method fabricate pebbles that are buoyant in the coolant and have reduced stored energy; (iii) providing a method to passively or actively insert control elements into the center region of the core to control the reactor power; (iv) providing a method to increase moderation of neutrons in the core and to allow higher pebble heavy metal loading; and (v) providing a method to prevent ingress of cover gas into the core under forced circulation if the primary salt inventory is reduced. In each of these respects the design differs in important ways from the state of the art for helium-cooled pebble bed reactors and other reactor designs. Referring to FIG. 1 through FIG. 5, a generalized embodiment of a modular pebble bed advanced high temperature reactor 10 according to the present invention is shown. This exemplary reactor comprises a reactor vessel 12 with an outer graphite radial reflector 14 and a core formed by one or more replaceable graphite pebble channel assemblies (PCAs) 16 (the embodiment shown in FIG. 1 through FIG. 5 has seven PCAs). The reactor core is formed by fuel pebbles located in one or more pebble channels 18 and in upper plenums 20 and lower plenums 22 located in each PCA. The fuel pebbles are recirculated out of the core using defueling chutes 24 and defueling machines 26 located in each PCA. The recirculated pebbles are inspected for burn up and either replaced or reinjected into the coolant flow entering each of the PCA lower inlet plenums 28. The pebble core is cooled by a liquid fluoride salt circulated vertically upward through the pebble channels 18 into a plurality of exit plenums 30, which collect the coolant flow into one or more hot legs taking the flow to one or more primary pump impellors 32. Under normal operation the coolant level 34 remains above the pump impellor(s). Under a loss of coolant accident where the primary pump(s) continue to operate, the pumping is stopped passively by an anti-siphon vent 36, sustaining the total coolant inventory above the minimum faulted level required for decay heat removal. Decay heat is removed by natural circulation heat transfer to a plurality of direct reactor auxiliary cooling heat exchangers 38. Reactivity control for power is performed by adjusting the rate of fresh fuel pebble injection and by controlling the position of a plurality of control rods located in vertical channels 40 around the periphery of the reactor core. Reactivity control for shut down is performed by inserting a plurality of shut down rods located in vertical channels 42 in the middle region of the reactor core. The graphite outer radial reflector blocks 14 are positively buoyant in the salt coolant under normal high-temperature operating conditions, but must be installed in the reactor under room temperature conditions without the salt coolant. For the initial installation of the these reflector blocks 14 in the cold reactor vessel, a plurality of tie rods 44 hold a lifting plate 46 that in turn carries the weight of the reflector blocks 14 and holds the stack of blocks against an upper hold-down structure 47. The tie rod tensioning system maintains a constant force during heat up of the reactor vessel, correcting for differential thermal expansion between the graphite blocks and the vessel. The lifting plate then holds the blocks in place as the molten salt coolant is added to the vessel, and the blocks then float upward against the upper hold-down structure 48, which transfers up-lift forces into the reactor vessel 12. FIG. 6 shows a vertical cross section through one of the shut down rod channels 42 in FIG. 1 through FIG. 5. Here, channel 42 is shown with a buoyantly activated shut down rod that comprises one or more cylindrical neutrally buoyant control elements 50 containing a neutron absorbing material such as boron carbide or another neutron poison. The control elements 50 preferably comprise a mixture of high density graphite, low density graphite, and neutron poison that results in an average density such that the elements are neutrally buoyant at a coolant temperature above the normal core inlet temperature and below the normal core outlet temperature. Under normal reactor power operation some core inlet flow bypasses through the shutdown channel, maintaining the channel temperature sufficiently low that the elements float out of the core. Under transients and accidents where this temperature rises, the elements sink into the core to provide passive shut down. The bypass flow entering the channel may flow through a fluidic diode, such that hotter coolant enters the channel more rapidly following a loss of forced circulation. Forced insertion of the shut down elements occurs following a SCRAM signal, which causes a heavy activation rod 52 to drop by gravity and force the shut down elements into the core. A cylindrical hole 54 along the center of the activation rod 52 provides access for a laser range finding beam to independently measure the position of the control elements. FIG. 7 shows a vertical cross section through one of the shut down rod channels 42 occupied by an alternative embodiment of a buoyantly activated shut down element. Referring also to FIG. 8, in this embodiment the element has a cylindrical top section 56 and bottom section 58, with the center section 60 having a cruciform geometry to maximize the rod neutron reactivity worth while minimizing the rod drag coefficient. The mass distribution in the element is adjusted so that the center of mass is located below the center of buoyancy to stabilize the rod in the vertical position. In this embodiment, forced insertion is provided by an activation element 62 that has a cylindrical hole along its center that provides access for a laser range finding beam to independently measure the position of the shut down element. Also in this embodiment, the element motion is slowed and kinetic energy dissipated by a hydraulic snubbing channel 64. Upon entering the snubbing channel, the cylindrical bottom end of the element 58 forces coolant to flow through the annular, ribbed gap between the snubbing channel and the rod, dissipating kinetic energy. Furthermore, the bypass coolant flow enters the channel from an opening 66 located above the snubbing channel. FIG. 9 shows a cross section of a spherical fuel pebble according to an aspect of the present invention. The fuel, preferably comprising a mixture of TRISO fuel particles with a high-density, thermally conductive graphite binder, is contained in an annular region 102 and is protected by a high density, inert outer coating of graphite 104. The center kernel of the pebble 106 is a low-density graphite kernel. The density of this kernel is selected to adjust the average density of the fuel pebble to a value that provides an optimal buoyancy force. In particular, the density of the center kernel may be selected so that the ratio of the average density of the pebble to the coolant density is the same as the ratio of the density of polyethylene and the density of water, which may be used for scaled hydrodynamic experiments to verify pebble motion in the reactor core. Referring also to FIG. 10 through FIG. 12, an exemplary 900-MWt Modular PB-AHTR reactor vessel is shown that is 10.5 m high and 6.0 m in diameter. FIG. 10 provides an example of the vertical dimensions for several sections of the reactor vessel as shown. It can be seen that, in this embodiment, the upper reflector structure has a height 200 of 3.60 m, the core channel region has a height 202 of 2.20 m, and the bottom reflector structure has a height 204 of 1.50 m. It can also be seen that the DHX effective height 206 is 2.00 m and that the core effective height 208 is 3.20 m. FIG. 11 provides an example of the vertical dimensions for several sections of the PCA. FIG. 11 also shows additional design details of the PCA such as the locations of DHX distribution plenums 300, 0.10 m φ risers 302, pebble defueling chutes 304, cross-flow openings 306, core outlet collection chambers 308, exit coolant flow channels 310, upper core pebble plenums 312, pebble channels 314, the bottom of the pebble beds 316, lower core pebble plenums 318, and the coolant inlets 320 from the cold legs. In this embodiment, all corners 322 are curved for pebble flow and all corners 324 have a 0.025 m radius. Referring also to FIG. 12A through FIG. 12F, additional exemplary dimensions are illustrated. Also shown in FIG. 12A through FIG. 12F is a shutdown rod channel 42 which is 0.198 m in diameter (FIG. 12C), 756 coolant holes 326 which are 0.015 m in diameter on 0.025 m triangular pitch (FIG. 12D), a 0.30 m φ out-flow openings 328 (FIG. 12E), collection chambers 30 (FIG. 12E), 0.15 m φ cross-flow openings 330 (FIG. 12E), 0.20 m φ cross-flow openings 332 (FIG. 12E), and 0.15 m φ interconnecting cross-flow channels 334 (FIG. 12F). In the exemplary core configuration for the reactor shown in FIG. 2, there are seven hexagonal pebble channel assemblies 16: 1.25 m across (flat to flat), with 0.198-m diameter pebble fuel channels on a 0.250-m center-to-center pitch. The volume fraction of pebble fuel channels is ˜44% and the effective core height is 3.2 m. In the exit plenum configuration shown in FIG. 3, note that radial flow passes through multiple collection chambers to achieve effective mixing. DHX 336, cold legs 338, and core outlet collection channels 340 (0.2 m×0.5 m) can also be seen in these figures. In the embodiment illustrated, the reactor core comprises multiple, replaceable pebble channel assemblies (PCAs) 16 shown in detail in FIG. 4 and FIG. 5. In contrast to prior art, in the inventive liquid cooled high temperature reactor (HTR) design, pebbles are injected into the coolant entering a PCA. More particularly, (i) the pebbles are injected into the coolant flow entering the bottom of each PCA and are carried to the bottom of the pebble bed in the PCA; (ii) the pebbles are removed using a defueling chute located at the top of each PCA; and (iii) the pebbles flow up through a one or more pebble channels in each PCA, with 18 pebble channels used in the exemplary design. The exemplary reactor vessel shown in FIG. 1 and FIG. 10 has an outer radial graphite reflector surrounding the PCA's, which provides neutron shielding to the reactor vessel. Because the graphite blocks have positive buoyancy in the salt and have a different thermal expansion coefficient than the vessel material, in the exemplary reactor the blocks are connected to the reactor vessel near the top of the vessel by an upper hold down structure so that buoyancy forces naturally compress the blocks, in contrast to conventional art for helium cooled reactors where the connection is at the bottom of the vessel and gravity forces compress the blocks. Moreover, in the exemplary reactor metal tie rods are provided, extending from the top of the reactor to a metallic support ring located below the radial reflector. During initial assembly of the radial reflector and subsequent heating and filling of the reactor vessel with salt, these tie rods are used to maintain the reflector in compression as the vessel undergoes thermal expansion and is filled with molten salt coolant. The reactor shown in FIG. 1 and FIG. 10 has one or more primary centrifugal pumps with overhung cantilever shafts and seal bowls. The placement of the pump impellors at a high elevation in the primary loop limits the primary salt inventory loss that could occur due to a leak if the primary pumps continued and maintain a pressure at the leak location higher than the external pressure. In addition, the reactor shown in FIG. 1 and FIG. 10 has an anti-siphon vent line located at an elevation below the primary pump impellor that rapidly injects cover gas into the primary pump if the primary salt inventory drops to the level of the vent line, breaking the siphon and preventing the primary pump from ingesting gas at a lower flow rate, thus operating in a two-phase flow mode and injecting cover gas into the primary loop. In a preferred embodiment, a pebble is manufactured using a combination TRISO fuel particles and normal and reduced density graphite, such that the average pebble density is lower than the salt density and the pebbles have positive buoyancy. In one embodiment of the exemplary pebble shown in FIG. 9, the kernel is approximately 1.98 cm in diameter, the annular region surrounding the kernel is approximately 0.52 cm thick, and the outer coating is approximately 0.5 cm thick. Adjusting the density of the graphite in this kernel allows the density of the pebble to be reduced to provide sufficient buoyancy, and reduces the thermal diffusion length and the pebble centerline temperature to reduce the pebble stored energy. Referring again to FIG. 4 and FIG. 5, each PCA may have multiple pebble channels located between an upper and lower pebble plenum. These pebble channels introduce additional graphite in the center of the reactor core, providing added neutron moderation and reducing the average volume fraction of salt and its contribution to parasitic neutron absorption. These pebble channels also transfer horizontal acceleration forces though the pebble bed in the event of seismic motion, reducing the motion of the pebbles relative to the reactor vessel and the potential to change reactivity due to expansion or compression of the pebble bed. The PCA is fabricated from interlocking hexagonal or nearly hexagonal graphite blocks. To replace a PCA, the reactor may first be defueled by replacing the fuel spheres with inert graphite spheres. Following defueling, metallic connecting rods are inserted through the top cover plate of the PCA, down through the graphite blocks to the metallic bottom plate, where the rods connect using a latching mechanism similar to that designed previously for the MSBR. The PCA can then be lifted out of the reactor into a transfer cask for cooling, graphite disposal, and refurbishment, and a replacement PCA inserted. Each PCA also preferably includes channels for insertion of neutron flux mapping and other instruments, channels for the insertion of temporary metal tie rods for PCA removal and replacement, and channels for insertion of neutron control elements. These cylindrical (or spherical) control elements, shown in FIG. 6 and FIG. 7/FIG. 8, comprise a mixture of graphite and boron carbide, or another neutron poison, in proportions to make the control element neutrally buoyant in the salt at a temperature intermediate between the normal core inlet temperature and the normal core outlet temperature. Under forced circulation operation, bypass flow from the core inlet or an intermediate location maintains the salt temperature in the channel below the neutral buoyancy temperature, so the elements float and remain outside the core. Under conditions where forced circulation stops, or where intermediate heat removal stops, heated salt enters the channel and the elements passively sink when this temperature exceeds the neutral buoyancy temperature. Depending on design of the gap around the elements, additional hydrodynamic forces may be applied to the elements by the bypass flow that can be optimized to further control the passive response of the element. Above the elements a high density control rod provides active insertion of the elements following a scram signal. A laser beam, or other instrument, is used to measure the vertical position of the control elements. In a helium cooled pebble bed reactor, the pebble diameter is limited to a minimum of approximately 6 cm to achieve an acceptably low pressure loss and recirculating power. Because liquid salts have very high volumetric heat capacity, pumping power is far smaller. Based on the earlier PB-AHTR results, therefore, in the exemplary modular PB-AHTR higher power density is achieved without increasing the fuel stored energy by using smaller pebbles (3 cm in diameter). Reducing the pebble diameter by a factor of two doubles the pebble surface area per unit volume, and halves the thermal conduction length scale in the pebble, allowing the power density to be increased by a factor of 4 with the same temperature difference from the surface to the center of the pebble and therefore the same stored energy. In addition, we consider it desirable to have the pebbles flow inside a number of separate channels, inside a set of graphite reflector blocks called a PCA, as shown in FIG. 1 through FIG. 5 and FIG. 10 through FIG. 12. This configuration using PCA's has a number of potential advantages over the large, homogenous pebble core that was studied previously. Advantages of the modular design with pebbles located in large numbers of separate channels include, for example: (a) The moderation provided by the PCA structure allows the heavy metal loading in the pebbles to be increased further, reducing the number of pebbles requiring fabrication and the spent fuel volume. (b) The coolant void fraction in the core is reduced by approximately a factor of two, reducing parasitic neutron absorption in the coolant and increasing the discharge burn up. (c) The heterogenous core configuration, where neutrons are moderated partially in the reflectors, reduces resonance absorption of neutrons and increases discharge burn up. However, the increased surface area of the exterior of the core does increase neutron leakage into the outer radial reflector, reducing the overall increase in discharge burn up. (d) The multiple channel configuration allows a simple approach to a 2-zone core, where pebbles discharged from the six-Pebble Channel Assemblies (PCAs) in the outer zone are then circulated in the one PCA in the inner zone to drive the pebbles to higher burn up, flattening the power distribution in the core. In another embodiment a yet larger number of PCAs could be used to provide additional radial zones and increase the reactor power, for example three zones with nineteen PCAs. (e) The solid reflectors provide locations for insertion of control elements. Passive reserve shutdown can be provided by neutrally buoyant shutdown elements that drop into the core when the coolant temperature in the control element channel exceeds the normal value, Control elements can be fabricated from a mixture of graphite (1700 kg/m3) and boron carbide (2500 kg/m3) to give the desired density. (g) The channel configuration addresses the question of pebble bed motion and expansion or packing under seismic loading (although the PB-AHTR is a seismically base isolated plant). It is simpler to design and qualify for seismic loading than the solid central reflector of the helium-cooled PBMR that does not have horizontal support. In the design shown in FIG. 1 through FIG. 5 and FIG. 10 through FIG. 12, the core-average power density is nominally 30 MW/m3 and the average pebble channel power density is 60 MW/m3. This results in a modular PB-AHTR with a 6.0-m diameter, 10.5-m high reactor vessel that can be more readily transported to the construction site and that operates at atmospheric pressure. This can be compared to the 9-m diameter, 31-m high reactor vessel for the 600 MWt GT-MHR that operates at 7 MPa. Even thought the core outlet temperature of the modular PB-AHTR is 704° C., allowing the use of available ASME code qualified materials, it achieves a similar 46% thermodynamic efficiency in power conversion because the average temperature of delivered heat is 652° C., the same as the average temperature provided by the GT-MHR. The combination of greatly reduced reactor size (a factor of 9 smaller reactor vessel volume than the GT-MHR), high power conversion efficiency (equaling GT-MHR), and effective uranium utilization (20 to 40% greater than a conventional light water reactor) suggest that the modular PB-AHTR could have excellent economics. Table 1 presents results of analysis showing that the pressure losses are larger for a 600 MWth modular PB-AHTR (which was subsequently uprated to 900 MWth), increasing from 0.73 bar for the large core, large pebble design, to 3.2 to 4.3 bar from the modular designs with 4.0 or 3.0 cm diameter pebbles. However the required pumping power is still quite low compared to the circulating power required for a modular helium reactor, and is similar to the pumping power required for pressurized water reactors. The 900 MWt modular PB-AHTR is a convenient power output for initial commercialization, and it is sufficiently small to be attractive for co-generation applications to produce electricity and process steam for tar sands and heavy oil production, coal liquefaction, or ethanol distillation. Also, because the core is comprised of seven pebble channel elements, the AHTR Pilot Plant (APP) can use a single, full scale, full height channel element, operating at 110 MWt, and reproduce all of the steady state and transient phenomena for the full-scale plant. Due to its potential for superior economics, compatibility with the low enriched uranium fuel cycle, and passive safety, the 900 MWt modular and 110 MWt Pilot Plant PB-AHTR also qualify as a candidate competitor to the PBMR and Iris reactors as a small, exportable reactor. RELAP5-3D was used to assess the response of modular PB-AHTR to Forced Cooling (LOFC) and Anticipated Transient Without Scram (ATWS) transients (M. Fratoni, F. Koenig, E. Greenspan, and P. F. Peterson, “Neutronic and Depletion Analysis of the PB-AHTR,” Global 2007, Boise, Id., Sep. 9-13, 2007). In the modular core, individual pebble channels may be modeled as separate flow channels connected by heat structures. FIG. 13 shows a 1/12 sector RELAP5-3D model for the PB-AHTR core. The reactor was modeled as having an inner Pebble Channel Assembly (PCA), consisting of 1/12 of the center PCA, and an outer PCA consisting of ½ of one of the 6 outer PCA's. The inner PCA consisted of 4 pebble channels with common inlet and outlet plenums. The four pebble channels consisted of one 1/12 channel (#1) and three ½ channels (#2, #3, #4). Each channel communicates thermally with its neighboring channels through the PCA reflector graphite. Channels #3 and #4 communicate with the bypass flow in the gap between the inner and outer PCA's. The outer PCA consisted of three ½ channels (#5, #9, and #15) and seven full channels (#7, #8, #10, #11, #12, #13, #14). The safety rod location (#6) was modeled as consisting of ½ of a pebble channel and 2 empty safety rod insertion channels. The outer pebble channels (#11, #13, #14, #15) communicate thermally with the reflector material and bypass flow in the gap between the outer PCA and the outer reflector. Two of the pebble channels (#8, #11) and the safety rod channel location (#6) communicate with the bypass flow in the gap between the outer PCA and its neighboring outer PCA. In the modular PB-AHTR the pebbles move inside pebble channels, and these graphite pebble channel assemblies provide additional moderation of neutrons. The two most important scaling factors affecting neutron transport in the modular core are the age of fission neutrons in graphite and the mean free path (mfp) of thermal neutrons in the pebbles. The latter is a strong function of the heavy metal (HM) loading (packing fraction). The age in graphite (down to 1 eV) is 368 cm2. This means that the mean distance (straight line) a fission neutron travels in graphite until its energy gets below 1 eV is [SQRT(6*Age)]˜47 cm. For comparison, in water it is 12.7 cm and in heavy water 28 cm. The modular PB-AHTR is somewhat similar, from the viewpoint of heterogeneity, to a CANDU type core with heavy-water moderator outside the fuel channels. This heterogeneity provides resonance self shielding which helps increase the achievable fuel discharge burn up. But in the PB-AHTR there is more moderation in the fuel (pebble bed) channel. This extra moderation complicates the estimation of how much macro self-shielding can be achieved in the modular AHTR without performing detailed neutronic calculations. A first estimate of the channel diameter for the modular AHTR can be obtained by requiring that its diameter will be comparable to the diameter of the fuel cluster of the CANDU when measured in terms of the mean free path (MFP) of thermal neutrons. It will vary with the packing fraction. Typical CANDU fuel bundles are 10 cm in diameter, on a 28.6 cm square lattice. The exemplary modular PB-AHTR design has 19.8 cm diameter pebble channels on a (approximately) 25 cm hexagonal lattice. This pebble channel diameter is very close to what one would recommend based on MFP scaling ((10 cm)(47 cm/28 cm))=16.8 cm. But the volume of moderator outside of the pebble channels is much smaller than for the fuel channels in the CANDU. This is necessary due to limits on the power density, pressure loss, and HM loading that can be achieved in the pebble channels. The closer spacing of pebble channels also should be helpful in reducing neutron leakage around the periphery of the reactor core. In the exemplary design the pebble channels occupy approximately 50% of the volume of the core, so the modular core is approximately 30% pebbles, 20% salt, and 50% channel assembly graphite by volume, compared to 60% pebbles and 40% salt for a homogeneous pebble core. To maintain the same ratio of HM to moderator, the HM loading in the pebbles must be approximately doubled. This is reasonable. For a conventional salt cooled pebble core the optimal carbon to heavy metal ratio is C/HM=363 (Table IX, M. Fratoni, F. Koenig, E. Greenspan, and P. F. Peterson, “Neutronic and Depletion Analysis of the PB-AHTR,” Global 2007, Boise, Id., Sep. 9-13, 2007). The corresponding kernel packing factor is 12.5% for homogeneous pebbles or 25% for annular pebbles. To maintain the same HM to moderator ratio the packing factor in the modular PB-AHTR must be doubled, to 50% for the annular pebble configuration, which would in turn halve the spent fuel volume. More commonly a packing factor of 40% is recommended, so the diameter of the internal kernel may be decreased. Kernel diameter, particle power, and uranium enrichment, are also key parameters that are optimized in the detailed design of the fuel. Resonance self shielding at the kernel level has benefits for discharge burn up. For the homogeneous salt cooled pebble bed core, the maximum discharge burn up of 129 GWd/tHM for a 425 micron fuel kernel diameter drops down to 119 GWd/tHM for fuel with 225 micron kernels (FIG. 4, Fratoni, F. Koenig, E. Greenspan, and P. F. Peterson, “Neutronic and Depletion Analysis of the PB-AHTR,” Global 2007, Boise, Id., Sep. 9-13, 2007). The heterogeneous core of the modular PB-AHTR with the higher HM loading in the pebbles should provide some additional resonance self shielding, which may have some further beneficial effect on discharge burn up and fuel utilization. Equally important is the 50% reduction in the volume fraction of the core occupied by salt, which will roughly halve the parasitic absorption of neutrons in the salt. On the other hand, the modular PB-AHTR will have higher neutron leakage due to the smaller size and larger surface area of its core. Detailed analysis is needed to determine what the net impact is on the fuel discharge burn up. The baseline modular PB-AHTR reactor vessel is fabricated from Alloy 800H, with an internal, non-structural cladding of Hastelloy N to assure high corrosion resistance. An exemplary vessel according to FIG. 10 is D=6.0 m in outside diameter and the maximum level of salt in the 10.5-m tall vessel is 10.0 m. For the purpose of estimating the required vessel thickness, the allowable stress is determined by the following logic. The normal operating temperature of the vessel is the core inlet temperature, 600° C. For conservatism to account for gamma heating, the steady state operating temperature of the vessel is taken as 650° C. and the vessel must operate with sufficiently low stress to avoid significant creep over the lifetime of the vessel (60 years). Under LOFC transients and ATWS accidents, the vessel can reach higher temperatures for limited periods of time. Under these conditions the requirement is to maintain stresses below the yield stress, while checking to assure that creep deformation will be small for the anticipated duration of such transients. Under LOFC and ATWS transients the pumps do not operate, so pressures in the vessel arise from hydrostatic loads only. Referring to Table 2, a yield stress of 70 MPa was selected as representative in the temperature range from 850° C. to 900° C. where ATWS transients might reach. LOFC transients are expected to have much lower peak temperatures (under 750° C.). At 650° C., the stress required to provide a creep rate of 0.00001 percent per hour is 90 MPa. At this stress level, 11.4 years is required to provide 1% deformation. Considering yield stress and creep, a maximum stress level of 70 MPa is indicated. For conservatism, a safety factor of 2 is taken, and the average vessel thickness is estimated for a stress level of 35 MPa. For steady, full power operation the pressure P in the vessel is established by the combination of the hydrostatic pressure (190 kPa) and the pressure loss from the core inlet plenum to the primary pump suction (530 kPa). To achieve a principal stress of σp=(σ12σ22)1/2=35 MPa, a vessel wall thickness of t=7 cm is required, to sustain the hoop stress of σ1=PD/2 t=31.0 MPa and axial stress of σ2=PD/4 t=15.5 MPa. This vessel thickness can be compared to the 5 cm thickness of the S-PRISM vessel, which is 9.0 m in diameter and 20 m high. The total mass of the PB-AHTR reactor vessel, not including the top flange, is then approximately 120 metric tons. Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. For example, the present invention is not limited to use with pebble fuel elements. The PCAs could alternatively be loaded with fuel elements have different geometries and density characteristics where the fuel elements may or may not be buoyant in the salt coolant. Where other than pebble fuel elements are used, the PCAs described herein would be more generally referred to as fuel channel assemblies (FCAs). Those skilled in the art will appreciate that different fuel configurations may require modifications to the PCA/FCA which would not depart from the scope of the invention described herein. For example, with pin fuel, the FCA would have channels extending its full length, and the fuel assembly may include a graphite plug above it to fill in the upper portion. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.” TABLE 1Comparison of pressure losses and pumping power for integraland modular PB-AHTR cores based on Ergun equation, for bedvoid fraction of 0.4 and pump efficiency of 0.7.IntegralModularModularPebble diameter (cm)6.04.03.0Thermal power (MWt)2400600600Power density in flow channels10.34040(MW/m3)Number of flow channels1127127Diameter of flow channels (m)6.700.1980.198Average height of core (m)6.613.843.84Core inlet/outlet temperature (° C.)600/704600/704600/704Core mass flow rate (kg/sec)967024172417Average coolant flow velocity (m/s)0.14 m/s0.3150.315Core pressure drop (kPa)73320430Core (only) pumping power (kW)514564756Core (only) specific pumping power0.2140.9401.260(kW/MWt) TABLE 2Tensile Properties And Hardness Of Alloys800H And 800HT At High TemperaturesYield StrengthTemperatureHardnessTensile Strength(0.2% Offset)° F.° C.BHNksiMPaksiMPa802712677.853621.7150800425—67.546518.813010005409062.743213.09012006508454.837813.59313007058247.732915.810914007607434.223613.190
054955114	claims	1. A device for preventing the formation of a flammable mixture of hydrogen and oxygen in a reactor containment of a nuclear power plant, said device comprising one or more inerting elements situated in the reactor containment, each element comprising one or more chemical substances which deliver an inerting gas and/or inerting gas mixture through disintegration and/or chemical reaction at temperatures greater than or equal to a respective temperature of reaction. 2. The device according to claim 1, wherein the inerting gas and/or inerting gas mixture comprises carbon dioxide and/or steam. 3. The device according to claim 2, wherein the proportion of carbon dioxide and/or water of crystallization of at least one of the chemical substances is at least 45% of the respective molecular weight. 4. The device according to claim 1, further comprising one or more hydrogen/oxygen catalytic recombiners situated in the reactor containment, wherein at least one of the inerting elements is arranged to be heated through thermal conduction, radiation and/or convection in response to a catalytic reaction at one or more of the catalytic recombiners. 5. The device according to claim 1, 2 or 4 comprising a plurality of the inerting elements, each of the elements comprising a respective chemical substance, wherein the temperature of reaction of the respective chemical substance of at least one inerting element differs from the temperature of reaction of the respective chemical substance of another of the plurality of inerting elements. 6. The device according to claim 1 or 4, wherein one or more inerting elements have a receptacle containing the one or more chemical substances, the walls of the receptacle being permeable by the inerting gas and/or the inerting gas mixture. 7. The device according to claim 6, wherein a filter layer comprising High Efficiency Particulate Air filter material is located on or near the receptacle wails. 8. The device according to claim 4, wherein at least one of the catalytic recombiners comprises a catalyst plate to which one or more of the inerting elements are connected in a manner having good heat conductivity. 9. The device according to claim 8, wherein the temperature of reaction of a substance lying in the immediate vicinity of the catalyst plate or in contact with it is in the range of 200.degree. to 450.degree. C. 10. The device according to claim 8, wherein the one or more inerting elements are connected at such a distance from the surface of the catalyst plate as to permit free access of the surrounding atmosphere to the surface of the catalyst plate. 11. The device according to claim 8 or 10, wherein at least one of the one or more inerting elements contains a plurality of chemical substances having different temperatures of reaction and arranged in layers, the substance having the highest temperature of reaction in a layer adjacent to the catalyst plate. 12. The device according to claim 1 or 4, wherein at least one of the one or more inerting elements contains a plurality of chemical substances having different temperatures of reaction. 13. The device according to claim 1 or 4, wherein the chemical substance leaves no liquid product of reaction remaining after disintegration or reaction takes place. 14. The device according to claim 1, 2 or 4, wherein at least one of the one or more inerting elements comprise a chemical substance which during disintegration or reaction forms a product capable of combining with oxygen in the gas mixture of the surrounding atmosphere. 15. A device for reducing the risk of deflagration or detonation of a flammable gas in a reactor containment of a nuclear power plant, said device comprising one or more inerting elements situated in the containment, each element comprising one or more chemical substances which deliver an inerting gas and/or inerting gas mixture through disintegration and/or chemical reaction at temperatures greater than or equal to a respective temperature of reaction. 16. The device according to claim 15, further comprising one or more catalytic structures situated in the reactor containment, wherein at least one of the inerting elements is arranged to be heated through thermal conduction, radiation and/or convection in response to oxidation of the flammable gas catalyzed by one or more of the catalytic structures. 17. A device for preventing the formation of a flammable mixture of hydrogen and oxygen in a reactor containment of a nuclear power plant, said device comprising inerting means situated in the reactor containment for inerting the mixture of hydrogen and oxygen in response to a temperature reaching and/or exceeding a temperature of reaction, combiner means for catalytically oxidizing the hydrogen, and means for transferring heat generated at the combiner means to the inerting means. 18. A device according to claim 17, wherein said inerting means comprises means for removing and/or reducing oxygen in the reactor containment.
	summary
	description	1. Field of the Invention The present invention relates to an X-ray optical system for small angle scattering to prepare an X-ray beam incident on a specimen in an X-ray small angle scattering apparatus. 2. Description of the Related Art When an X-ray beam is incident on a specimen, the X-ray scatters with an angle in a range within a small angle (a small angle region) in the vicinity of the travelling direction of the X-ray beam, this being referred to as small angle scattering. Measurement of the small angle scattering provides various pieces of information, including a grain size, a periodic structure and the like, on the specimen material. An apparatus for measuring the above-described small angle scattering is referred to as an X-ray small angle scattering apparatus, and an optical system specific thereto (an optical system for preparing an X-ray beam to be incident on a specimen) is referred to as an X-ray optical system for small angle scattering. FIG. 8 is a conceptual diagram of the conventional X-ray optical system for small angle scattering. It is noted that, in the drawing, the dimension in the direction perpendicular to the optical axis, the vertical direction in the drawing, is exaggerated. This conventional X-ray optical system for small angle scattering is referred to as a three-slit optical system. The first slit 14, the second slit 16 and the third slit 18 are arranged between an X-ray source 10 and a specimen 12 in the described order from the X-ray source side. An X-ray passing through (or reflected at) the specimen 12 is to scatter and reach an X-ray detector 20. Such a three-slit optical system is disclosed in, for example, Harold P. Klug and Leroy E. Alexander, “X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials”, John Wiley & Sons, 1954, p. 638. The X-ray optical system for small angle scattering must satisfy the requirements of: a small angle of divergence (for example, 0.04 degree or less) of the X-ray beam incident on the specimen; and a small width W (for example, 0.1 mm or less) of the X-ray beam (direct beam) at a detection point. The first slit 14 and the second slit 16 serve to restrict the angle of divergence of the X-ray beam and to reduce the width of the X-ray beam (direct beam) at the detection point. The third slit 18 serves to interrupt scattered rays from the edge of the second slit 16. Explaining actual values for realizing the above-described requirements, For example, the aperture width of the first slit 14 is set at 0.04 mm, the aperture width of the second slit 16 is set at 0.03 mm, and the distance L1 between the first slit 14 and the second slit 16 is set at 100 mm. The above-described three-slit optical system is specific to the X-ray small angle scattering apparatus only, and accordingly a specialized X-ray small angle scattering apparatus must be prepared in order to measure the small angle scattering. Since the three-slit optical system is a special optical system, this cannot be easily switched to other X-ray incident optical systems for X-ray analysis. Accordingly, it is an object of the present invention to provide an X-ray optical system for small angle scattering which can be easily switched to other X-ray incident optical systems for X-ray analysis. It is another object of the present invention to provide an X-ray optical system for small angle scattering which can make a monochromatic X-ray beam with an X-ray intensity larger than that of the conventional X-ray optical system for small angle scattering. An X-ray optical system for small angle scattering according to an aspect of the present invention includes a multilayer mirror having a parabolic reflecting surface for collimating an X-ray beam, a narrow slit for restricting the width of the X-ray beam and a scattering slit in the described order from an X-ray source side. The positional relationship between the multilayer mirror and the narrow slit may be reversed. That is, the narrow slit may be arranged nearer to the X-ray source than the multilayer mirror. An X-ray optical system for small angle scattering according to another aspect of the present invention has features described below. (a) A multilayer mirror having a parabolic reflecting surface for collimating an X-ray beam, an optical-path selecting slit device, a small-angle selecting slit device and a specimen-side slit are arranged in the described order from an X-ray source side. (b) The optical-path selecting slit device has an aperture through which the X-ray beam can pass, so that selective switching can be performed between a first state in which a parallel beam having been reflected at the multilayer mirror passes through the aperture and a second state in which the X-ray beam having bypassed the multilayer mirror passes through the aperture. (c) The small-angle selecting slit device has a narrow slit for small angle scattering measurement and a broad aperture, so that switching can be performed between a first state in which the beam width of the parallel beam having been reflected at the multilayer mirror is restricted by the narrow slit and a second state in which the parallel beam having been reflected at the multilayer mirror passes through the broad aperture. (d) The aperture center position and the aperture width of the specimen-side slit are variable. In the above-described configuration, the feature (c) may be modified in a manner that the small-angle selecting slit device may be selectively equipped with a first component having a narrow slit for small angle scattering measurement and a second component having a broad aperture. In the present invention, the first slit of the X-ray optical system for small angle scattering of the conventional three-slit system is omitted, and the multilayer mirror is used in place thereof. Consequently, the X-ray optical system for small angle scattering can be easily switched to other X-ray incident optical systems for X-ray analysis. Furthermore, since the multilayer mirror is used, a monochromatic X-ray beam having X-ray intensity larger than that of the conventional X-ray optical system for small angle scattering can be obtained. Referring to FIG. 1 illustrating the first embodiment of the present invention, a multilayer mirror 24, an optical-path selecting slit device 26, a small-angle selecting slit device 28 and a Soller slit 30 are arranged between an X-ray source 22 and a specimen-side slit 23 in the described order from the X-ray source side. These constituents will be described below in detail. An aperture slit plate 32 is fixed, with screws, on the end surface of the multilayer mirror 24 and has a first aperture 34 and a second aperture 36. An X-ray beam having passed through the first aperture 34 bypasses the multilayer mirror 24 and travels toward a specimen, this condition being to be described in detail below with reference to FIG. 5. The X-ray beam having passed through the second aperture 36 is reflected at a reflecting surface 38 of the multilayer mirror 24 to become a parallel beam 40 and travels toward the specimen. Both of the two apertures 34 and 36 have dimensions of 0.9 mm in width and about 13 mm in height. The aperture slit plate 32 serves to prevent an unnecessary X-ray from entering into the optical system. That is, an X-ray beam 60 for the para-focusing method (see FIG. 3) and an X-ray beam 62 for both the small angle scattering measurement and the parallel beam method (see FIG. 3) can pass through the aperture slit plate 32, whereas other X-rays are prevented from entering into the incident optical system, so that the influence of the scattered X-ray is reduced. The reflecting surface 38 of the multilayer mirror 24 has a parabolic shape, and the relative positional relationship between the multilayer mirror 24 and the X-ray source 22 is adjusted so that the X-ray source 22 is located at the focal point of the parabolic surface. Therefore, the X-ray beam reflected at the reflecting surface 38 becomes the parallel beam 40. The reflecting surface 38 is composed of a synthetic multilayer film in which heavy elements and light elements are alternately laminated and a lamination period thereof continuously varies along the parabolic line, so that an X-ray having a specific wavelength (CuKα X-ray in this embodiment) can satisfy the Bragg's law at every position on the reflecting surface 38. This type of parabolic multilayer mirror is disclosed in, for example, Japanese Patent Publication 11-287773 A (1999). The multilayer mirror 24 selectively reflects an X-ray having a specific wavelength to prepare the parallel beam 40 and, therefore, is a monochromator as well. The parallel beam 40 obtained using the multilayer mirror 24 has an angle of divergence of 0.03 to 0.05 degree or less. Consequently, the parallel beam 40 reflected at the multilayer mirror 24 becomes parallel to have the same level of angle of divergence as that formed by the first slit and the second slit of the conventional three-slit optical system, for example, 0.04 degree. Therefore, the parallel beam 40 reflected at the multilayer mirror 24 can be used as an X-ray beam for small angle scattering measurement with the conventional first slit being omitted. The optical-path selecting slit device 26 is substantially in the shape of a disk and, as shown in FIG. 2a, has one slender aperture 42 at the location deviated from the center of rotation 44 of the disk. This aperture 42 has the dimensions of 3 mm in width and about 12 mm in height. The optical-path selecting slit device 26 can be turned about the center of rotation 44 through an angle of 180 degrees. In a state shown in FIG. 2a (first state), the aperture 42 is located on the left side of the center of rotation 44. When the optical-path selecting slit device 26 in the first state is turned by 180 degrees about the center of rotation 44, it becomes a state shown in FIG. 2c (second state), the aperture 42 being located on the right side of the center of rotation 44. In the state shown in FIG. 2a, only the parallel beam which has been reflected at the multilayer mirror can pass through the aperture 42. On the other hand, in the state shown in FIG. 2c, only the X-ray beam which has bypassed the multilayer mirror (the X-ray beam has a predetermined angle of divergence described below and can be used as the X-ray beam for the para-focusing method) can pass through the aperture 42. The small-angle selecting slit device 28 is substantially in the shape of a disk as well and, as shown in FIG. 2a, has a narrow slit 48 and a broad aperture 50 at diametrically opposed positions with respect to the center of rotation 46 which is in line with the center of rotation 44 of the optical-path selecting slit device 26. The narrow slit 48 serves to restrict the width of the parallel beam 40 which has been reflected at the multilayer mirror 24, and has a width of 0.03 mm and a height of about 12 mm. On the other hand, the broad aperture 50 serves to make the X-ray beam pass through, and has a width of 3 mm and a height of about 12 mm. As shown in FIG. 2a, the narrow slit 48 is located on the left side of the center of rotation 46, which is the first state, so that the beam width of the parallel beam which has been reflected at the multilayer mirror is restricted by the narrow slit 48. On the other hand, as shown in FIG. 2b, the broad aperture 50 is located on the left side of the center of rotation 46, which is the second state, so that the parallel beam which has been reflected at the multilayer mirror can pass through the broad aperture 50 as it is. This small-angle selecting slit device 28 can be modified as described below. That is, a first component having the narrow slit 48 for small angle scattering measurement and a second component having the broad aperture 50 are prepared as separate components, and these components may be selectively mounted to the small-angle selecting slit device 28, these being interchangeable with each other as necessary. With reference to FIG. 1 again, the Soller slit 30 serves to restrict the divergence of the X-ray beam in the vertical direction. A plurality of thin blades, each having a predetermined length in the direction along the optical axis, are arranged with small spacing in the vertical direction. The specimen-side slit 23 is composed of two slit blades 52 and 54, which can be horizontally moved independently of each other, that is, in the direction indicated by arrows 56 and 58, so that the aperture center position (the center position of the aperture in the horizontal direction) and the aperture width can be changed. Alternatively, it may be possible that two slit blades 52 and 54 are of a ganged open-close motion type and the center of the two slit blades (that is, the aperture center position) are horizontally moved by an electric motor independent of another electric motor for the ganged motion. Next, a method for using this X-ray optical system for small angle scattering will be described. FIG. 3 is a plan view of the optical system shown in FIG. 1, viewed from above. The Soller slit is not shown in the drawing. This X-ray optical system for small angle scattering can prepare three types of X-ray beam used for the small angle scattering measurement, for the measurement in the parallel beam method and for the measurement in the para-focusing method by adjusting the optical-path selecting slit device 26, the small-angle selecting slit device 28 and the specimen-side slit 23. FIG. 3 shows a state in which the X-ray beam used for the small angle scattering measurement is obtained. The optical-path selecting slit device 26 and the small-angle selecting slit device 28 are set in the state shown in FIG. 2a. In FIG. 3, of the X-ray generated by the X-ray source 22, an X-ray beam 60 which has passed through the first aperture 34 of the aperture slit plate 32 is interrupted by the optical-path selecting slit device 26. On the other hand, an X-ray beam 62 having passed through the second aperture 36 of the aperture slit plate 32 is reflected at the reflecting surface of the multilayer mirror 24 to become the monochromatic parallel beam 40. This parallel beam 40 passes through the aperture 42 of the optical-path selecting slit device 26. Furthermore, the beam 40 passes through the narrow slit 48 of the small-angle selecting slit device 28 to become the X-ray beam 64 having a small width. Subsequently, the X-ray beam 64 passes through the specimen-side slit 23 and is incident on a specimen 66. The X-ray beam 64 has the angle of divergence which is restricted to, for example, 0.04 degree or less by the effect of the multilayer mirror 24 and the beam width which is restricted to 0.03 mm by the effect of the narrow slit 48. The scattered X-ray generated at the edge of the narrow slit 48 is interrupted by the specimen-side slit 23. The aperture center position and the aperture width of the specimen-side slit 23 can be adjusted in an optimum state by independently moving each of the slit blades 52 and 54 in the horizontal direction indicated by arrows 56 and 58. In this embodiment, each of the slits 52 and 54 are driven in the horizontal direction by an electric motor. This specimen-side slit 23 serves as a scattering slit when the X-ray beam for the small angle scattering measurement is prepared. Comparing such an X-ray optical system for small angle scattering with the conventional three-slit optical system, the following can be said. In the conventional three-slit optical system shown in FIG. 8, the angle of divergence of the X-ray beam is restricted (collimated) by the first slit 14 and the second slit 16. In the present invention, the multilayer mirror serves for collimation. Therefore, in the present invention, the first slit in the conventional three-slit optical system is unnecessary. In the conventional three-slit optical system, a combination of the first slit 14 and the second slit 16 also serve to reduce the beam width of the X-ray beam. In the present invention, on the other hand, the narrow slit 48 serves to restrict the beam width. As a result, in the present invention, the X-ray beam for the small angle scattering measurement can be obtained with the use of a combination of the multilayer mirror 24, the narrow slit 48 and the specimen-side slit 23. If the conventional optical system is referred to as a three-slit optical system, the optical system of the present invention can be referred to as a mirror plus two-slit optical system. Next, the setting of the parallel beam method will be described. FIG. 4 shows the setting of the parallel beam method. The optical-path selecting slit device 26 and the small-angle selecting slit device 28 are set in the state shown in FIG. 2b. In FIG. 4, of the X-ray generated by the X-ray source 22, an X-ray beam 60 having passed through the first aperture 34 of the aperture slit plate 32 is interrupted by the optical-path selecting slit device 26. On the other hand, an X-ray beam 62 having passed through the second aperture 36 of the aperture slit plate 32 is reflected at the reflecting surface of the multilayer mirror 24 to become the monochromatic parallel beam 40. This parallel beam 40 passes through the aperture 42 of the optical-path selecting slit device 26. Furthermore, the parallel beam 40 passes through also the broad aperture 50 of the small-angle selecting slit device 28 as it is. Subsequently, the parallel beam 40 passes through the specimen-side slit 23 and is incident on a specimen 66. As a result, the X-ray beam which is incident on the specimen 66 is the parallel beam 40 which has been reflected at the multilayer mirror 24. The aperture 42 of the optical-path selecting slit device 26, the broad aperture 50 of the small-angle selecting slit device 28 and the specimen-side slit 23 all impose no restriction on the parallel beam 40. When the beam width of the parallel beam 40 must be reduced to a predetermined value, it would be enough that the aperture width of the specimen-side slit 23 may be set at the desired value. Next, the setting of the para-focusing method will be described. FIG. 5 shows the setting of the para-focusing method. The optical-path selecting slit device 26 and the small-angle selecting slit device 28 are set in the state shown in FIG. 2c. In FIG. 5, of the X-ray generated by the X-ray source 22, an X-ray beam 62 having passed through the second aperture 36 of the aperture slit plate 32 is reflected at the reflecting surface of the multilayer mirror 24 to become the parallel beam 40. The beam 40 is, however, interrupted by the optical-path selecting slit device 26. On the other hand, an X-ray beam 60 having passed through the first aperture 34 of the aperture slit plate 32 passes through the aperture 42 of the optical-path selecting slit device 26. Furthermore, this divergent beam 60 passes through also the broad aperture 50 of the small-angle selecting slit device 28 as it is. Subsequently, the divergent beam 60 is restricted to have a desired angle of divergence by the specimen-side slit 23 and is incident on a specimen 66. In this case, the specimen-side slit 23 serves as a divergence slit. It is noted that the aperture center position of the specimen-side slit 23 is shifted from the state shown in FIGS. 3 and 4 and the aperture width is adjusted so that a predetermined angle of divergence is obtained. As described above, in the X-ray optical system for small angle scattering of the present invention, the first slit, which is specific to the small angle scattering measurement, of the conventional three-slit optical system can be omitted, and the multilayer mirror, which is usable for purposes other than the small angle scattering measurement, can be used in place of the first slit. Consequently, the switching from the small angle scattering optical system to the optical system of the parallel beam method or the para-focusing method can be easily performed. FIG. 6 is a graph showing the angle dependence of the X-ray intensity with respect to an X-ray beam for small angle scattering measurement. The horizontal axis indicates a diffraction angle 2θ and the vertical axis (logarithmic scale) indicates the X-ray intensity detected with an X-ray detector (the number of counts per second in a scintillation counter). A slender slit having an aperture width of 0.1 mm is arranged in front of the X-ray detector, this slit is made to scan in the horizontal direction and, thereby, the position of the diffraction angle 2θ is changed. The graph of “three-slit” is obtained by the measurement of the X-ray beam prepared by the conventional X-ray optical system for small angle scattering shown in FIG. 8 as a direct beam, that is, no specimen is arranged. The graph of “mirror+two-slit” is obtained by the measurement of the direct beam of the X-ray beam 64 prepared by the setting for the small angle scattering measurement shown in FIG. 3. In each graph, the X-ray intensity shows a sharp decrease as the diffraction angle 2θ exceeds 0.10 degree, and substantially no influence of the direct beam is shown in the range where 2θ is 0.12 degree or more. Therefore, with respect to both the optical systems, the measurement of the scattered ray from the specimen (small angle scattering measurement) can be performed under no influence of the direct beam in the range where 2θ is 0.12 degree or more. FIG. 7 is a graph showing the results of an actual measurement of the small angle scattering. The graph of “mirror+two-slit” is obtained by the measurement of the small angle scattering while the setting is in the state of the small angle scattering measurement shown in FIG. 3 and a PET (polyethylene terephthalate) sheet is used as the specimen. The graph of “three-slit” is obtained by the measurement of the small angle scattering with the conventional optical system shown in FIG. 8 for the same specimen. In the graph of “mirror+two-slit”, a clear peak is observed and, in addition, a secondary peak is also observed although its peak is low. The measurement result is thus excellent because the X-ray beam prepared by “mirror+two-slit” has an intensity larger than that of the three-slit system (the intensity is 5 times or more than that of the three-slit system) and, in addition, the X-ray beam is made monochromatic. The conditions of the measurement with respect to the graph shown in FIG. 7 will be briefly described. In FIG. 3, the distance from the X-ray source 22 to the specimen 66 is 100 mm, and the distance from the specimen 66 to the X-ray detector (scintillation counter) is 300 mm. A slender slit having an aperture width of 0.1 mm is arranged in front of the X-ray detector. This slit is made to scan in the horizontal direction, so that the position of the diffraction angle 2θ is changed. Next, the second embodiment of the present invention will be described. In the second embodiment, referring to FIG. 1, the small-angle selecting slit device 28 may be arranged between the X-ray source 22 and the multilayer mirror 24. Even under such a configuration, the X-ray optical system for small angle scattering can be prepared in a manner similar to that in the optical system shown in FIG. 1 and, in addition, this optical system can be easily switched to the optical system for the parallel beam method and the para-focusing method. The third embodiment of the present invention will be described. In the third embodiment, the small-angle selecting slit device 28 may be removed, and a scattering slit is arranged between the specimen-side slit 23 and the specimen in the optical system shown in FIG. 1. When the small angle scattering measurement is performed, the aperture width of the specimen-side slit 23 is reduced so as to serve as a narrow slit. The fourth embodiment of the present invention will be described. In the fourth embodiment, the conventional three-slit optical system shown in FIG. 8 may be used provided that the first slit 14 is replaced by a multilayer mirror. In this case, switching to the optical systems for the parallel beam method and the para-focusing method is impossible. However, as indicated in the graph shown in FIG. 7, an improvement in measurement precision is expected because of the performance of the multilayer mirror.
	description	This application claims priority to U.S. Provisional Application No. 60/605,080 which was filed on Aug. 27, 2004 and U.S. Provisional Application No. 60/635,523 which was filed on Dec. 13, 2004. The present invention relates to heating, ventilation and cooling (HVAC) systems, and more particularly to fault diagnostics associated with early detection and isolation of failures in HVAC systems. HVAC systems often do not function as well as expected due to faults developed during routine operation. While these faults are indicative of a failure mode, many faults do not result in immediate system shut down or costly damages. However, most faults, if unnoticed for a long period of time, could adversely affect system performance, life, and lifecycle cost. While diagnostics refer to detection and isolation of faults, prognostic typically refers to predicting faults before they occur. In many applications, however, early detection and diagnostics may serve the same end as prognostics. This is the case when failure propagation happens at a reasonably slow pace. Small changes in system parameters typically do not have a substantial adverse effect initially. As such, accurate prediction of the time between detection of a fault, that is, a small change to one or more system parameters, to full system deterioration or shutdown is not crucial. For instance, detection of HVAC system refrigerant charge leakage and air filter plugging are examples of failure modes for which early detection of changes provides adequate information to take timely maintenance action. Approaches to diagnostics may be divided into two broad categories. One category deals with direct measurement of monitored quantities and another category combines sensing technologies with mathematical algorithms. The technical emphasis in these approaches is the development of dedicated sensors for measurement of crucial system parameters. While such approaches may be more accurate, they are typically costly as they involve adding dedicated hardware for each failure mode of interest. In the combined approach, algorithms play the major role since they allow inference about the health of the system from indirect measurements provided by the sensors. Because the addition of new sensors is more expensive and more difficult to manufacture, algorithms alone are incorporated to utilize available sensors that are configured for a control purpose. Design of failure detection and diagnostics algorithms have been subject of extensive research ranging from statistical approaches and reviews to techniques derived from artificial intelligence and reasoning, graph theory, and bond graphs. Several diagnostics techniques have been applied to the problem of chiller and HVAC fault isolation. Among known approaches, “black-box” or data-driven techniques (such as neural networks) have received considerable attention. Such approaches are well suited to domains where data is abundant but physical knowledge about the phenomenon is scarce. However, one problem with such approaches is that recalibrating the parameters of the black-box model typically requires extensive re-experimentation even if the system changes slightly as there is no direct linkage between model parameters and physical system quantities. As such, there is a desire for an analytical approach to detect faults which reconciles the results of known data driven techniques with a physical understanding of the HVAC system and provides a direct linkage between model parameters and physical system quantities to arrive at classification rules that are easy to interpret, calibrate and implement. The present invention is directed to an analytical approach to detect faults by reconciling known data driven techniques with a physical understanding of the HVAC system and providing a direct linkage between model parameters and physical system quantities to arrive at classification rules that are easy to interpret, calibrate and implement. The present invention focuses on two of the most common problems encountered a multi-modular split HVAC system, which are detecting low refrigerant conditions and air filter plugging. A method for refrigerant charge leak detection is disclosed that relies on a systematic technique for analysis of experimental data, extraction of fault signatures, formulation of fault detection principals, and development and implementation of diagnostic algorithms. A method of detecting air filter plugging is also disclosed that relies on reduced physics-based relationships in heat exchangers to estimate air mass flow through the heat exchangers. Both methods incorporate data filtering techniques to determine which portions of data carry the most information regarding the underlying failure, variable sub-selection based upon available sensors, calculation of a distance between faulty and normal data sets, and maximization of this distance with respect to filtering parameters and variable sub-selection. The sub-selected variables are then processed by classification techniques to generate easy to interpret and easy to implement classification rules. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. FIG. 1 is a schematic illustration of an example HVAC system 10 according to the present invention. In this example, the HVAC system 10 is a duct-free heat pump system known as a multi-modular split system (MMS). The MMS 10 includes one outdoor unit 12 and two indoor units 14A and 14B, which operate in a cooling mode to provide cool air to an interior space during a warm or hot season and a heating mode to provide warm air to the interior space during a cool or cold season. The outdoor unit 12 includes a pair of parallel compressors 16, which are variable speed, an outdoor expansion valve 18 to control a sub-cool in the cooling mode and to control a superheat in the heating mode, an outdoor heat exchanger 20, which behaves as a condenser in the cooling mode and as an evaporator in the heating mode, and an outdoor fan 22. Each of the two indoor units 14A and 14B includes an indoor expansion valve 24, to control the sub-cool in the cooling mode and superheat in the heating mode, and an indoor heat exchanger 26, which behaves as an evaporator in the cooling mode and as a condenser in the heating mode, and an indoor fan 28. A 4-way valve 30 controls the mode of operation from the cooling mode to the heating mode and vice versa. The MMS 10 also includes a receiver tank 32 for storage of refrigerant charge that is operable to change the amount of refrigerant charge circulated depending on the conditions. The speed of the compressors 16 and the indoor fan 28 are adjusted in response to a deviation between a room temperature and a set point. The speed of the compressors 16 is further adjusted to match the total cooling or heating demand. Expansion valves are disposed throughout the MMS 10. In the illustrated example, the expansion valves are pulse modulated valves 34 that are actuated via pulse modulation. The pulse modulated valves 34 are controlled by an actuation signal that adjusts an opening of the pulse modulated valves 34 to control a flow of refrigerant through the MMS 10. Pulse modulated valves 34A and 34B are positioned in-line proximate to the indoor heat exchangers 26. A pair of pulse modulated valves 35 is positioned in-line between a coil 36 and the receiver tank 32. Multiple sensors are also disposed throughout the MMS 10. In the illustrated example, the sensors include a plurality of refrigerant-side temperature sensors 38, air-side temperature sensors 40, and pressure sensors 42. Refrigerant-side temperature sensors 38A–38D are positioned near each end of each of the indoor heat exchangers 26. Refrigerant-side temperature sensors 38E and 38F are positioned near one end of each of the compressors 16. Refrigerant-side temperature sensor 38G is positioned between the 4-way valve 30 and an accumulator 44. Refrigerant-side temperature sensor 38H is positioned between the pair of pulse modulated valves 35 and the receiver tank 34. Refrigerant-side sensor 381 is positioned between the outdoor heat exchanger 20 and the coil 36. Air-side temperature sensors 40A and 40B are positioned between the indoor fans 28 and the indoor heat exchangers 26 and air-side temperature sensor 40C is positioned proximate to the outdoor fan 20. Pressure sensor 42A is positioned proximate to the accumulator 44 and pressure sensor 42B is positioned between the compressors 16 and an oil separator 46. The present invention focuses on developing algorithms to detect faults within the MMS 10 by utilizing existing system sensors and data. An analytical method of diagnosing at least one system fault utilizing existing system sensors is disclosed. The analytical method includes identifying sensors that are available within a given system, analyzing sensor data to determine which of the available sensors generate data indicative of a system fault based upon a maximum separation/minimum overlap between no-fault data and full-fault data for each available sensor, determining a fault relationship based on the analysis, comparing at least one measured system characteristic to the fault relationship and generating at least one fault code indicative of a failure mode when a system fault is identified. However, the system fault identified is not necessarily the system characteristic directly monitored by the sensor generating the data that is being analyzed. For example, the sensor may generate data associated with a pressure within the system, however, the failure code generated may be indicative of a low system refrigerant charge or an air filter plugging condition. The following discusses the development of both a low system refrigerant charge indicator and an air filter plugging indicator of the present invention. Development of a Low System Refrigerant Charge Indicator. A total MMS refrigerant charge is roughly proportional to a total volume filled with liquid refrigerant at any given point in time. Low system refrigerant charge occurs when the total system liquid volume drops. When the MMS 10 operates in the cooling mode, a total MMS refrigerant mass drops and the total MMS volume increases resulting in an overall increase in a volume of vapor refrigerant relative to a volume of liquid refrigerant. The overall increase in total MMS volume causes an increase in temperature of refrigerant exiting the indoor and outdoor heat exchangers 20 and 26 to a temperature above the boiling point of the refrigerant when the refrigerant is in a vapor state or a decrease in temperature of refrigerant exiting the indoor and outdoor heat exchangers 20 and 26 to a temperature below the boiling point of the refrigerant when the refrigerant is in a liquid state. These phenomena are known as superheat and sub-cool respectively. Under these conditions, the MMS 10 will tend to increase the vapor quality at those temperatures if saturated, thereby controlling the superheat. In most systems, the superheat is controlled by actuating an expansion valve. An increase in superheat requires a greater opening of the expansion valve to allow an increased flow of refrigerant to pass through the indoor and outdoor heat exchangers 20 and 26 to maintain the desired superheat. In the example illustrated, the expansion valve 34 is a pulse modulated valve (PMV) and actuation pf the PMV is controlled via pulse modulation. As such, an increase in superheat translates into a higher pulse actuation which in turn correlates to low system refrigerant charge. In addition, low system refrigerant charge is also associated with lower system suction pressures. While the present invention focuses on the cooling mode, the principles discussed are not limited to the cooling mode and may also extend to the heating mode. The present invention includes a fault detection principal for identifying low system refrigerant charge which may be summarized as follows: Low refrigerant charge indicator uses larger average PMV opening of the indoor units OR smaller values of suction pressure observed during the first few minutes (e.g. 10–20 minutes) after the compressor speed (rpm) exceeds a threshold (e.g. 40%–50% of its maximum rpm) excluding first 0–2 minutes of transient data. This fault detection principle is the result of a systematic approach for identification of fault principles and decision rules for low refrigerant charge detection. This approach applies several statistical classification techniques to pre-processed field trial data as described below. The pre-processing involves application of a data filtering process whose objective is to zoom into parts of the data that carry most information about the fault event of interest. The data filtering process decomposes a time-axis into time intervals during which “interesting” transient or steady state behavior occurs. Compressor speed (rpm), denoted by ν(t) at time t, is used as the base-signal for filtering. The base signal is the signal whose temporal behavior is used to decompose the time axis as explained more closely below. The major step in the data filtering process is to decompose the time axis into a sequence of intervals F={Ik}. This decomposition is a function of three filtering parameters κ≧0,Δ≧0, ν≧0 i.e. F=F(κ,Δ, ν) where ν is a threshold value, κ is a pre-determined time period during which an actual value measured by a sensor must remain above the threshold value ν before a fault can be generated, and Δ defines a start-up time period during which the data collected is not considered. F={Ik} is constructed from another sequence {I′k}. Each element, Ik′, is a closed time interval with the following three properties: (1) the length I′k is larger than or equal to κ, (2) ν(t)≧ ν for all t in I′k, (3) I′k is the superset of all other overlapping closed intervals that possess the first two properties. Furthermore, I′k∩I′j=Ø for k≈j. The sequence {I′k}, k=1, 2, 3, . . . , is ordered in such a way that the supremum of all t belonging to I′k, denoted by e(I′k), is smaller than the infimum of all t belonging to I′k+1 denoted by b(I′k+1). {Ik} is constructed by letting b(Ik)=b(I′k) while e(Ik)=max(e(I′k),b(Ik)+Δ). As illustrated in FIG. 2, the following example illustrates show how data filtering can be used to zoom in data depending on a transient response of the base signal: 1. HP(Δ, ν)=F(0,Δ, ν) where Δ is small to medium, constructs a high-pass filter. Points A, B, and D are segmented out by HP(0,100%). 2. BP(κ,Δ, ν)=F(κ,Δ, ν)−F(κ,κ, ν) where κ is small to medium and Δ is medium to large, constructs a band-pass filter. Intervals C and E are segmented out by BP(1,2,100%). 3. LP(κ, ν)=BP(κ,∞, ν)=F(κ,∞, ν)−F(κ,κ, ν) where κ is medium, constructs a low-pass filter. An interval F is segmented out by LP(4,100%). Also note that if the data in FIG. 2 is sampled with a sampling interval 1, then a union of intervals segmented by mutually exclusive sets HP(0,100%), BP(1,2,100%), and LP(4,100%) span all the data points for which the base signal is at 100% of its full operation range. For example, suppose the data are sampled at a sampling interval ΔT. The union of the mutually exclusive sets HP(i×ΔT, ν), BP((i+1)×(ΔT+1), j×ΔT, ν), and LP((i+j+2)×ΔT, ν), where i, j are integers, spans all the data points for which the base signal is larger than or equal to ν. Φ is used to generically refer to a union of all time intervals picked by the filter. To develop the fault detection principal, the time-axis is repeatedly decomposed into three disjoint sets of intervals characterized by high-pass, band-pass, and low-pass conditions using average speed of base compressors as the base signal and various filtering parameters. Each filtering results in a decomposition of time similar to the illustration in FIG. 2. For each repetition of the filtering process, the three disjointed data sets were analyzed based upon a set of statistical techniques consisting of sensor (variable) selection, calculation of distance between no-fault and full-fault data sets, and fault pattern discovery. The data filtering process resulted in selection of an opening associated with the PMV and a suction pressure as the variables carrying most information about system refrigerant charge leakage. An optimal filter was found to be BP(κ,Δ, ν) with κ≦2, 10≦Δ≦20, and ν≈50% of full compressor speed. Combining these results led to the low system refrigerant charge fault detection principle stated above. The fault detection principal for low system refrigerant charge is converted into an algorithm for low system refrigerant charge detection and implemented by calculating a low system refrigerant charge indicator over a batch of data of fixed length. The batch of data contains the most recent data points that have passed through the filter up to a point determined by its fixed length. As more data points become available, they replace the oldest data points, keeping the length of the data batch fixed. To illustrate, consider FIG. 2 again. Suppose that the filter used in the calculations is BP(1,2,100%), segmenting intervals C and E. Also suppose that the sampling time is 1 and the fixed data length is 3. The batches of data in chronological order for this example will be {9,10,15}, {10,15,16}, and {15,16,17}. A time calculated as an average (or median) time of the batches member points is assigned to each data batch. In this example, the times associated with {9,10,15}, {10,15,16}, and {15,16,17} will be 11.3, 13.7, and 16 respectively using averaging over the time points in the batch. A low system charge indicator within each batch is calculated by finding the fraction of points within the batch for which the PMV opening is above a threshold or the suction pressure is below a threshold. The calculated low system charge indicator is assigned to the time associated with the batch. FIG. 3 is a flow chart detailing an example charge leakage calculation. In this flow chart: Φ(t) is a binary indicator that assumes one or zero. Φ(t) is equal to one only if t belongs to an analysis period of interest, a set of all intervals picked by the designed filter, and under a cooling mode operating condition (excluding compressor protection conditions). A batch of data, B, always keeps the most recent time points for which Φ(t)=1. A fixed number of points NB in the batch are set by a user. Typical values for the MMS application are 24×60 or 12×60. C(B) denotes a number of elements of B. δ represents a sampling time. δ should be larger than the data collection sampling time (in MMS case 1 minute), but may be selected larger to accelerate computations.Development of an Air Filter Plugging Indicator. An air filter plugging algorithm uses simple physical relations to estimate a mass flow of air through each heat exchanger. Due to lack of sufficient airside measurements, these relations are based on several simplifying assumptions as described below: Log-mean temperature and energy balance equations are applied to estimate the mass flow of air in the heat exchanger. The mass flow of air is inversely proportional to air filter resistance. A portion of the heat exchanger where refrigerant superheats has large UA. Refrigerant flow is proportional to an opening associated with the PMV. Air latent cooling is negligible. Based on these assumptions, the inverse of air mass flow in each heat exchanger is estimated via: F = ( T a - Tc j ) PMV ⁡ ( Tc 1 - Tc j ) As illustrated in FIG. 1, Ta is an indoor air temperature, Tcj is a middle of an indoor coil temperature (measuring a saturation temperature of the refrigerant in the heat exchanger), Tc1 is a temperature of the superheated refrigerant flowing out of the indoor unit heat exchangers 26, and PMV is an actuation signal of the pulse modulated expansion valves 34A and 34B. In FIG. 1, the measurement points Ta,Tc1,Tcj are respectively marked/numbered by TA-A, TC1-A, and 11 for indoor unit 14A and TA-B, TC1-B, and 13 for indoor unit 14B. Because these assumptions ignore several sources of variability such as latent cooling, an analysis is performed over longer periods to “average out” possible unknown effects. Similar to the development of the low system refrigerant charge indicator discussed above, batches of data are processed for calculation of the air filter plugging indicator. From this point of view, the algorithm is identical to the calculation of the low system refrigerant charge indicator for data batches of certain size. Because the air filter plugging algorithm estimates the inverse of air mass flow in each indoor heat exchanger 26 while the indoor fan 28 runs at various speeds, it is recommended that calculation of the air filter plugging indicator and its comparison to a threshold be performed for each fan speed separately. Although the fan speed data is not directly available, a set-point for the speed (FANTAP) is available and may be used as a proxy for the fan speed. The data filtering process for calculation of the air filter plugging indicator is much simpler than the data filtering process for low system refrigerant charge indicator calculation. The calculation of the air filter plugging indicator involves capturing sensor data that satisfies basic regularity principles needed for application of log mean temperature and energy balance in the cooling mode operations. The filter Φ is set to one at each time point if Ta>Tcj,Tc1>Tcj, PMV larger than a threshold (a value of about 100 is appropriate), and FANTAP is equal to a mode for which the calculation is performed. FIG. 4 is a flow chart detailing an example air filter plugging calculation. In this flow chart: Φ(t) is a binary indicator that assumes one or zero. Φ(t) is equal to one only if t belongs to an analysis period of interest, a set of all intervals picked by the designed filter, and under a cooling mode operating condition (excluding compressor protection conditions). A batch of data, B, always keeps the most recent time points for which Φ(t)=1. A fixed number of points NB in the batch are set by a user. Typical values for the MMS application are 24×60 or 12×60. C(B) denotes a number of elements of B. δ represents a sampling time. δ should be larger than the data collection sampling time (in MMS case 1 minute), but may be selected larger to accelerate computations. FIG. 5 and FIG. 6 show an algorithm response to induced low system refrigerant charge conditions for a first example MMS and a second example MMS respectively. Both example MMS's include one outdoor unit and five indoor units which were designed to meet the cooling and heating demands of two office rooms and two conference rooms. In calculating the results, the thresholds that were optimized for the first system were directly applied to a data set of the second system without any further tuning. In other words, the first system data set was used for “algorithm training” while the second system data was used for validation. In regard to the low system refrigerant charge, the plots illustrated in FIG. 5 and FIG. 6 show the value of a low system refrigerant charge indicator as a function of the number of data batches processed by the algorithm. The data batches are ordered chronologically. The low system refrigerant charge indicator for each batch of data is calculated by finding a percentage of points within the batch for which an opening associated with the PMV is larger than a pre-determined threshold or a suction pressure is smaller than a pre-determined threshold. The variation in intensity of the plot line represents an actual charge averaged over all the points in the batch of data. For instance, if 40% of the points within the batch have 30% charge loss while the rest have full charge (0% charge loss), the average actual charge loss for that batch of data will be 12%, which is referred to as an average actual fault (AAF). From this plot, one may deduce that a value of indicator above 10–15% would flag low charge condition (>25% AAF). FIG. 7 plots a receiver operating characteristic (ROC) of the low system refrigerant charge detection algorithm. ROC is a widely used tool for assessment of the performance of detection algorithms independent from a detection threshold. ROC plots detection rate (hit rate) of an algorithm as a function false alarms (false positives) generated by the algorithm. Detection rate or hit rate measures the probability of the low system refrigerant charge indicator raising an alarm given a failure event actually happens. False alarm or false positive measures the probability of indicating a failure when no failure is actually present. An ideal ROC curve will have 100% detection rate for any positive false alarm. Conceptually, ROC may be calculated by changing the detection threshold from its minimum to its maximum possible value, calculating a false alarm-detection rate pair for each chosen detection threshold, and plotting the calculated pairs. In other words, each point on the ROC curve is associated with one threshold value. When generating the ROC in FIG. 7, presence of a faulty condition for a batch of data is defined as AAF>15% for that data batch. The absence of a fault for the data batch is defined as AAF<5%. FIG. 8 and FIG. 9 show an algorithm response to induced air filter plugging at a high wall unit and a 4-way unit respectively. The presented results are based on data collected from a first system at a high fan speed. The plots show a value of an air filter plugging indicator as a function of a number of data batches processed by the algorithm (ordered chronologically). A variation in intensity of the plot line represent the actual average fault (AAF), defined similarly above. For instance, if 40% of the points within the batch have 50% plugging while the rest have no plugging (0% plugging), the AAF for that batch will be 20%. From this plot, one may deduce that a value of the air filter plugging indicator above 15 would flag plugging conditions. FIG. 10 plots a ROC for the air filter plugging detection algorithm. When generating the ROC in FIG. 10, presence of a faulty condition for a batch of data is defined as AAF>25%. The absence of fault for the data batch is defined as AAF<5%. Although preferred embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
044505787	claims	1. A variable aperture energy beam collimator apparatus comprising: a frame member having a central aperture therethrough; a block assembly which includes a plurality of beam-opaque blocks and variable aperture adjustment means, said adjustment means comprising guide means carried by the frame member and including an individual guide member for slidably carrying each block, each said block having interfacing edges in sliding contact with adjacent blocks and forming a completely beam-opaque surface when in a closed position; and a first operator member carried by the frame member and first linkage means operably connected between the first operator member and the block assembly for simultaneously sliding all of the blocks along their respective guide members with respect to each other while maintaining the sliding interfaces in contact for providing an aperture of desired size. a second in-line block assembly; second variable aperture adjustment means for adjusting said second block assembly thereby defining a second aperture, said second aperture being in congruent alignment with the first aperture to define a beam confining channel; said second block assembly and adjustment means being inverted front-to-back with respect to the first block assembly and first aperture adjustment means, whereby the contacting edge interfaces of said opaque blocks of said second block assembly are not in alignment with the contacting edge interfaces of said opaque blocks of the first block assembly so as to prevent energy leakage from emerging from the collimator apparatus. a second in-line block assembly; second variable aperture adjustment means for adjusting said second block assembly thereby defining a second aperture, said second aperture being in congruent alignment with the first aperture to define a beam confining channel; said seccond block assembly and adjustment means being inverted front-to-back with respect to the first block assembly and first aperture adjustment means, wherein the contacting edge interfaces of said opaque blocks of said second block assembly are not in alignment with the contacting edge interfaces of said opaque blocks of the first block assembly so as to prevent energy leakage from emerging from the collimator apparatus. 2. A variable aperture beam collimator as described in claim 1 wherein said blocks converge at apexes adjacent the center of said block assembly, said block assembly including n-blocks where n is greater than two and the apex angle of each block being 360/n degrees and where the guide member for each block is aligned perpendicular to a line bisecting the apex angle thereof. 3. A variable aperture beam collimator as described in claim 2 wherein said blocks are four in number. 4. A variable aperture beam collimator as described in claim 2 wherein each guide member comprises a guide rod and each block member is provided with a slide bracket for guiding the blocks therealong, said linkage means comprising an elongated cable connected between at least one slide bracket and the operator member and including cooperating support pulleys such that rotation of the operator member imparts movement to said at least one slide bracket and associated block, the interface surfaces of said block imparting motion to the other blocks forcing the other blocks to move along their respective guide rods. 5. A variable aperture beam collimator as described in claim 4 and including means for selectively translating said guide rods with respect to the frame member to provide a change in shape of said variable aperture. 6. A variable aperture beam collimator as described in claim 5 wherein said means for translating said guide rods comprises a plurality of pivotal actuators connecting the adjacent ends of the guide rods, a second operator member carried by the frame member and second linkage means operably connected between the actuators and the second operator members such that rotation of the second operator member imparts pivotal movement to all of the actuators simultaneously such that the blocks are skewed from one another in the closed position and provide a nonequalateral aperture in the open position. 7. A variable aperture beam collimator as described in claim 1, further comprising: 8. A variable aperture beam collimator as described in claim 7 wherein said first and second block assemblies are adjusted unequally providing unequal size first and second apertures providing a divergent beam confining channel. 9. A variable aperture beam collimator as described in claim 1 wherein is included: 10. A variable aperture beam collimator as described in claim 9 and including means for translating the guide members of each block assembly said means for translating comprising a pinion member operably connected to each block assembly and a worm gear mounted between said pinions for simultaneously translating the guide members of each block assembly in opposite directions, wherein the edge interfaces of each of the block assemblies are noncongruent.
052456439	claims	1. In a fuel bundle having a matrix of upstanding vertical fuel rods, a lower tie plate for supporting said fuel rods and permitting the entry of water into the bottom single phase region of said fuel bundle, an upper tie plate for permitting at least some of said fuel rods to extend to said upper tie plate and to permit the exit of water and generated steam from the upper two phase region of said fuel bundle; and, an enclosing channel having said lower tie plate at the bottom end, said upper tie plate at the upper end, and surrounding said fuel rod matrix between said tie plates to permit the flow of water and vapor moderator between said tie plates; the improvement to said fuel bundle comprising: at least some of said matrix of upstanding vertical fuel rods being part length fuel rods commencing at said lower tie plate and extending into the two phase region of said fuel bundle below said upper tie plate so as to define between the end of said part length fuel rods and said upper tie plate a spatial interval; and, means for defining at least one water region occupying at least one interval between one of said part length fuel rods and said upper tie plate, said means for defining at least one water region having sides and a closing bottom for maintaining a volume of liquid water within said region; means at the top of said water region for permitting the exit and entry of water to and exit of steam from said water region whereby said water region accumulates water moderator from said passing two phase water and steam mixture adjacent said water region. a matrix of upstanding vertical fuel rods, a lower tie plate for supporting said fuel rods and permitting the entry of water into the bottom of said fuel bundle, an upper tie plate for permitting at least some of said fuel rods to extend to said upper tie plate and to permit the exit of water and generated steam from the upper two phase region of said fuel bundle; an enclosing channel having said lower tie plate at the bottom end, said upper tie plate at the upper end, and surrounding said fuel rod matrix between said tie plates to permit the flow of water and vapor moderator between said tie plates; at least some of said matrix of upstanding vertical fuel rods being part length fuel rods commencing at said lower tie plate and extending into the two phase region of said fuel bundle below said upper tie plate so as to define between the end of said part length fuel rods and said upper tie plate a spatial interval; means for defining at least one water region occupying the interval between said part length fuel rod and said upper tie plate; said means for defining at least one water region having sides and a closing bottom; means at the top of said water region for permitting the exit and entry of water and steam to said water region whereby said water region accumulates water moderator from said passing two phase water and steam mixture adjacent said water region. a discrete top filled water region overlies a discrete part length fuel rod. a discrete top filled water region overlies more than one part length fuel rods. 2. The invention of claim 1 and wherein said means for defining said at least one water region includes a single chamber overlying a plurality of side-by-side part length fuel rods. 3. The invention of claim 1 and wherein said means for defining said at least one water region defines a cruciform shaped cross sectional water region transversely across a region of said fuel bundle, said cruciform cross sectional water region overlying part length fuel rods placed in a corresponding cruciform cross sectional region underlying said part length water region. 4. The invention of claim 1 and wherein said means at the top of said water region for permitting the entry and exit of water and steam includes means extending into the two phase flow region of said fuel bundle for diverting water into the top of said water region. 5. The invention of claim 4 and wherein said means extending into the two phase flow region of said fuel bundle for diverting water into the top of said water region overlies a surface along which water flows during normal operation of said fuel bundle. 6. The invention of claim 4 and wherein said means extending into the two phase flow region of said fuel bundle for diverting water into the top of said water region is recessed with respect to the cross sectional profile of said water region. 7. In a fuel bundle for a boiling water nuclear reactor comprising: 8. The invention of claim 7 and wherein: 9. The invention of claim 7 and wherein: 10. The invention of claim 7 and wherein said means at the top of said water region for permitting the entry of water and exit of steam includes means extending into the two phase flow region of said fuel bundle for diverting water into the top of said water region.
	claims	1. A SPECT apparatus comprising:a two-dimensional detector that detects radiations from RIs in a patient via a collimator;a correction processing unit that corrects, in order to reduce a fall in spatial resolution having dependency on distances between the respective RIs and the detector, plural two-dimensional projection distributions with different projection angles, which are detected by the detector, on a three-dimensional frequency space according to plural correction functions corresponding to plural distances, respectively; anda reconfiguring unit that reconfigures a three dimensional RI distribution from the plural two-dimensional projection distributions corrected;wherein the correction processing unit includes:a coordinate transforming unit that transforms the plural two-dimensional projection distributions into a three-dimensional projection distribution represented by a three-dimensional actual space formed by a projection angle axis, a slice axis and a channel axis;a transforming unit that transforms the three-dimensional projection distribution into a representation of a frequency space according to three-dimensional Fourier transformation;a correcting unit that corrects values of respective points of the transformed three-dimensional projection distribution according to any one of the plural correction functions corresponding to distances of the respective points; anda transforming unit that transforms the corrected three-dimensional projection distribution into a representation of the actual space according to the three-dimensional Fourier transformation. 2. A SPECT apparatus comprising:a two-dimensional detector that detects radiations from RIs in a patient via a collimator;a correction processing unit that corrects, in order to reduce a fall in spatial resolution having dependency on distances between the respective RIs and the detector, plural two-dimensional projection distributions with different projection angles, which are detected by the detector, on a three-dimensional frequency space according to plural correction functions corresponding to plural distances, respectively; anda reconfiguring unit that reconfigures a three dimensional RI distribution from the plural two-dimensional projection distributions corrected;wherein the correction function is an inverse function of a point spread function represented by the frequency space. 3. A SPECT apparatus according to claim 2, further comprising a storing unit that stores the plural correction functions. 4. A SPECT apparatus according to claim 2, wherein the point spread function is a modulation transfer function. 5. A SPECT apparatus according to claim 2, wherein the collimator is a parallel hole collimator. 6. A SPECT apparatus according to claim 2, further comprising a storing unit that stores data of the plural correction functions. 7. A SPECT apparatus according to claim 6, wherein the distances are associated with the data of each of the plural correction functions. 8. A SPECT apparatus according to claim 6, wherein parameters concerning the distances and filter characteristics are associated with the data of each of the plural correction functions. 9. A SPECT apparatus according to claim 8, wherein the reconfiguring unit reconfigures plural three-dimensional RI distributions on the basis of two-dimensional projection distributions corrected for each of the correction functions with the different filter characteristics. 10. A SPECT apparatus according to claim 9, further comprising a display unit that displays the plural three-dimensional RI distribution as a list. 11. A processing method for a SPECT comprising:correcting plural two-dimensional projection distributions with different projection angles concerning RIs in a patient, which are detected by a two-dimensional detector, on a three-dimensional frequency space according to plural correction functions corresponding to plural distances between the RIs and the detector, respectively; andreconfiguring a three-dimensional RI distribution from the plural two-dimensional projection distributions corrected;wherein the correction function is an inverse function of a point spread function represented by the frequency space. 12. A processing method for a SPECT according to claim 11, whereinin the correcting,the plural two-dimensional projection distributions are transformed into a three-dimensional projection distribution represented by a three-dimensional actual space formed by a projection angle axis, a slice axis and a channel axis,the three-dimensional projection distribution is transformed into representation of a frequency space according to three-dimensional Fourier transformation,values of respective points of the transformed three-dimensional projection distribution are corrected according to any one of the plural correction functions corresponding to distances of the respective points, andthe corrected three-dimensional projection distribution is transformed into representation of the actual space according to the three-dimensional inverse Fourier transformation. 13. A processing method for a SPECT according to claim 11, wherein the point spread function is a modulation transfer function. 14. A program for SPECT processing for causing a computer to realize:means for correcting plural two-dimensional projection distributions with different projection angles concerning RIs in a patient, which are detected by a two-dimensional detector, on a three-dimensional frequency space according to plural correction functions corresponding to plural distances between the RIs and the detector, respectively; andmeans for reconfiguring a three-dimensional RI distribution from the plural two-dimensional projection distributions corrected;wherein the correction function is an inverse function of a point spread function represented by the frequency space.
051942178	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to equipment for cleaning steam generators, and particularly to an improved articulated fluid lance having an extension nozzle that is movable for bringing the fluid jet into close proximity with the broached holes in the support plates for a nuclear steam generator for more efficiently cleaning sludge from steam generators. 2. Description of the Related Art In nuclear power stations, steam generators, such as recirculating steam generators and once-through steam generators, are used for heat exchange purposes in the generation of steam to drive the turbines. Primary fluid which is heated by the core of the nuclear reactor passes through a bundle of tubes in the steam generator. The secondary fluid, generally water, which is fed into the space surrounding the tubes receives heat from the tubes and is converted into steam for driving the turbines. After cooling and condensation has occurred, the secondary fluid is directed back into the space around the tubes to provide a continuous steam generation cycle. Due to the constant high temperature and severe operating conditions, sludge accumulates on the lower portions of the tubes, support plates, and on the tube sheet which supports same. The sludge which is mainly comprised of an iron oxide, such as magnetite, reduces the heat transfer efficiency of the tubes and can cause corrosion. Thus, the tubes must be cleaned periodically to remove the sludge and various types of apparatus and method are available to accomplish this task. U.S. Pat. No. 4,980,120 which is assigned to the Assignee of the present invention, and hereby incorporated by reference, discloses an articulated sludge lance. In addition, U.S. Pat. No. 4,980,120 in the background art section describes various other techniques found in U.S. Pat. Nos. 4,566,406; 4,079,701 and 4,700,662. In addition to those references, U.S. Pat. No. 4,407,236 to Schukei, et al discloses a thin strip of spring steel which enters a tube lane for sludge lance cleaning for nuclear steam generators. The forward ends of the capillary tubes are directed downward for the jetting of fluid under high pressure. U.S. Pat. No. 4,827,953 to Lee is directed to a flexible lance for steam generator secondary side sludge removal. This patent discloses a flexible lance having a plurality of hollow, flexible tubes extending lengthwise along the flexible member. There are a plurality of nozzles at an end of the flexible members with the flexible member being configured to go into the difficult to access geometry of the steam generator. When using the articulated sludge lance, penetration into the steam generator must be at least seven inches below the individual support plates due to stress considerations. This means jetting water from seven inches away while moving the articulated sludge lance parallel to the support plate. It has been found that the effectiveness of the cleaning diminishes considerably with distance from the support plate. Of particular concern is the deposits blocking broached holes. Because of the foregoing, it has become desirable to develop an improved articulated sludge lance which jets the fluid at close proximity to the broached support plate taking into consideration the stress factors. SUMMARY OF THE INVENTION The present invention solves the aforementioned problems associated with the prior art as well as others by providing a movable extension nozzle on an articulated sludge lance. The extension nozzle can be moved elastically with a tension cable to a predetermined curvature and height so as to place the nozzle in close proximity to a support plate. The improved articulated sludge lance of the present invention includes a bumper member attached to the flexible conduit of the nozzle to interact with the tubes in the tube lane as the lance moves therethrough creating a side-to-side motion so that the path of the fluid jet intersects as many of the broached holes as possible. In an alternate embodiment, the improved articulated sludge lance includes actuating means to allow the extension nozzle to extend from a retracted position in the fluid distribution member after it is inserted in place in a tube lane. This facilitates the movement of the improved articulated sludge lance into a specific tube lane in a steam generator for cleaning thereof. Accordingly, an object of the present invention is to provide an improved articulated sludge lance with a movable extension nozzle. Another object of the present invention is to provide an improved articulated sludge lance with an extension nozzle that can be moved to a predetermined curvature and height so as to place the nozzle in close proximity to a support plate for more efficient cleaning. A further object of the present invention is to provide an improved articulated sludge lance with a bumper member that causes the water jet from the lance to intersect as many broached holes as possible in a support plate by means of a side-to-side motion imparted to the extension nozzle. Yet a further object of the present invention is to provide a retractable, movable extension nozzle for an articulated sludge lance. Still, a further object of the present invention is to provide a device which is simple in design, rugged in construction, and economical to manufacture. The various features of novelty characterizing the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, and the operating advantages attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.
	claims	1. An electromagnetic wave-shielding coating dispersion material, comprising a polyaniline (ES) with a solid contents of about 1% to about 50%, a matrix polymer with a solid content of about 1% to about 50%, and additives having a thickener at a predetermined amount, wherein the thickener is selected from the group consisting of modified hydroxyethylcellulose, polymer hydroxyethylcellulose, acrylic acid ester copolymer, ammonium polyacrylate, and mixtures thereof. 2. The electromagnetic wave-shielding coating dispersion material as set forth in claim 1 , wherein the matrix polymer is selected from the group consisting of a vinyl emulsion and an acrylic emulsion resin. claim 1 3. The electromagnetic wave-shielding coating dispersion material as set forth in claim 1 , wherein the additives comprise a wetting agent which is selected from the group consisting of polyoxyethylene nonylphenyl ether (ethylene oxide: about 4 to about 10 mol), polyoxyethylene octylphenyl ether (ethylene oxide: about 5 to about 10 mol), ditridecyl sodium sulfosuccinate, polyethylene glycol laurate (HLB=about 6 to about 15) and mixtures thereof. claim 1 4. The electromagnetic wave-shielding coating dispersion material as set forth in claim 1 , wherein the additives comprise a coalescing agent which is selected from the group consisting of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, butyl carbitol acetate, butyl cellosolve, butyl cellosolve acetate, diethyleneglycol bytyl ether acetate, and mixtures thereof. claim 1 5. The electromagnetic wave-shielding coating dispersion material as set forth in claim 1 , wherein the additives comprise a freezing/thawing stabilizer which is selected from the group consisting of propylene glycol, ethylene glycol, 2,2,4-trimethyl-1,3-pentanediol monoisobutylate, and mixtures thereof. claim 1 6. The electromagnetic wave-shielding coating dispersion material as set forth in claim 1 , wherein the additives comprise a deformer which is selected from the group consisting of PEG-2 tallowate, isooctylalcohol, disodium tallow sulfosuccinamate, and mixtures thereof. claim 1 7. An electromagnetic wave-shielding coating dispersion material, prepared by mixing a polyaniline, an acrylic resin (ES, 100%) and additives having a thickener at predetermined amounts, wherein the thickener is selected from the group consisting of modified hydroxyethylcellulose, polymer hydroxyethylcellulose, acrylic acid ester copolymer, ammonium polyacrylate, and mixtures thereof. 8. The electromagnetic wave-shielding coating dispersion material as set forth in claim 7 , wherein the additives comprise a deformer which is selected from the group consisting of methylalkylsiloxane, sodium salt of an acrylic acid copolymer, and mixture thereof. claim 7 9. The electromagnetic wave-shielding coating dispersion material as set forth in claim 7 , wherein the additives comprise a deformer which is selected from the group consisting of methylalkylsiloxane, sodium salt of an acrylic acid copolymer, and mixtures thereof. claim 7 10. The electromagnetic wave-shielding coating dispersion material as set forth in claim 7 , wherein the additives comprise a leveling agent which is selected from the group consisting of a polyacrylate, a polyester modified methylalkyl polysiloxane copolymer, and mixtures thereof. claim 7 11. The electromagnetic wave-shielding coating dispersion material as set forth in claim 7 , wherein the additives comprise benzotriazole derivatives as a UV stabilizer. claim 7 12. The electromagnetic wave-shielding coating dispersion material as set forth in claim 7 , wherein the additives comprise a UV absorber which is selected from the group consisting of a benzophenone derivative, 2-2xe2x80x2-diethoxy acetophenone, and mixtures thereof. claim 7 13. The electromagnetic wave-shielding coating dispersion material as set forth in claim 7 , wherein the additives comprise a catalyst which is selected from the group consisting of organic tin compound, dibutyltinoxide, dibutyltindisulfide, stannous octoate, tetraisobutyltitanate, and mixtures thereof. claim 7 14. The electromagnetic wave-shielding coating dispersion material as set forth in claim 7 , wherein the hardener is selected from the group consisting of hexamethylene diisocyanate isocyanurate, hexamethylene diisocyanate biuret, hexamethylene diisocyanate uredione, isophorone diisocyanate isocyanurate, and mixtures thereof. claim 7 15. The electromagnetic wave-shielding coating dispersion material as set forth in claim 1 , wherein the polyaniline has the formula: claim 1 16. The electromagnetic wave-shielding coating dispersion material as set forth in claim 7 , the step of adding the mixture of a polyaniline, an acrylic resin (ES, 100%) and additives to a hardener is just before use. claim 7 17. The electromagnetic wave-shielding coating dispersion material as set forth in claim 7 , wherein the polyaniline has the formula: claim 7 18. The electromagnetic wave-shielding coating dispersion material as set forth in claim 7 , wherein the matrix polymer is selected from the group consisting of vinyl emulsion and acrylic emulsion. claim 7
	description	The present application claims priority from Japanese Patent application serial no. 2008-169831, filed on Jun. 30, 2008, the content of which is hereby incorporated by reference into this application. The present invention relates to a method for carrying out a reactor internal and, more particularly, to a method for carrying out a reactor internal suitable for carrying out a core shroud in a reactor pressure vessel (hereinafter referred to as an RPV) in a boiling water reactor nuclear power plant (hereinafter referred to as a BWR plant). In the BWR plant, a nuclear reactor has a core disposed in the RPV. A plurality of fuel assemblies including nuclear fuel material are loaded in the core, and an annular core shroud provided in the RPV surrounds the core. In the BWR plant, operation of the BWR plant is periodically shut down for maintenance and inspection. The core shroud, which is a reactor internal, is also is an object of the maintenance and inspection. If damage such as a crack is found in the core shroud or if replacement of the core shroud is desired from the viewpoint of preventive maintenance, the core shroud in the RPV is replaced to a new core shroud. Japanese Patent Laid-open No. 8-240693 states one way to carry an existing core shroud out of a RPV to replace with a new core shroud. In the method for carrying out a core shroud disclosed in Japanese Patent Laid-open No. 8-240693, the core shroud is coarsely cut up in the RPV filled with cooling water, these cut pieces are further cut up into finer pieces in a reactor well filled with the cooling water, then, the fine pieces are packed into a container, and this container is carried out. However, the method for carrying out the core shroud disclosed in Japanese Patent Laid-open No. 8-240693 requires two steps of coarse cutting and fine cutting of the core shroud, and takes long time to carry out the core shroud. Methods for carrying out a core shroud to solve this problem are described in Japanese Patent Laid-open No. 2000-46983 and WO 00/60607. These methods for carrying out a core shroud deal with a core shroud inside a RPV in a BWR plant. In Japanese Patent Laid-open No. 2000-46983, a cut core shroud is, without being cut up into small pieces, carried out through an opening portion formed in a ceiling of a reactor building by using a crane. This method for carrying out the core shroud will be more precisely explained. After operation of the reactor was shut down, a top head of the RPV is removed and a steam dryer and a stream separator in the RPV are taken out from the RPV into an equipment pool. Furthermore, fuel assemblies in the core are taken out into a fuel storage pool. The core shroud is cut below a core plate, and surrounded by a cask which is a radiation shield. The cask storing the core shroud is lifted by the crane, and carried out of the reactor building through the opening portion formed in the ceiling of the reactor building. Afterward, a new core shroud hoisted by the crane is carried inside the reactor building through the opening portion in the ceiling, and disposed to a predetermined position in the RPV. WO 00/60607 also states a method for carrying out a core shroud in which method, a core shroud cut below a core plate and surrounded by a radiation shield is carried out of a reactor building through an opening portion formed in a ceiling of a reactor building. In this carry method, various parts such as removed jet pumps and cut pipes to be carried out are stored inside the core shroud above the core plate disposed in the core shroud, and the core shroud along with these parts are carried out of the reactor building. Japanese Patent Laid-open No. 2002-131483 discloses a carry method in which a reactor including a core shroud is hoisted by a crane and carried out of a reactor building through an opening portion formed in a ceiling of the reactor building. In this method for carrying out a reactor, a protection device is disposed inside a reactor well to prevent the upset of the reactor being carried out of the reactor building to the fuel storage pool side, and the reactor is carried out through the protection device. The methods for carrying out a core shroud disclosed in Japanese Patent Laid-open No. 2000-46983 and WO 00/60607 do not require fine cutting of the core shroud. Thus, their methods can reduce the time required for carrying out the core shroud than the carry method disclosed in Japanese Patent Laid-open No. 8-240693. However, in the methods for carrying out a core shroud disclosed in Japanese Patent Laid-open No. 2000-46983 and WO 00/60607, safety must be improved to prevent the core shroud from falling into the fuel storage pool storing the fuel assemblies when the core shroud is being carried out. This would be expected to carry out the core shroud through a protection device set up in a reactor well or on an operation floor by applying the protection device disclosed in Japanese Patent Laid-open No. 2002-131483 to the method for carrying out a core shroud disclosed in Japanese Patent Laid-open No. 2000-46983 or WO 00/60607. There is an idea of transferring all the fuel assemblies in the fuel storage pool to a fuel storage pool in another BWR plant to avoid the fuel assemblies in the fuel storage pool from being damaged by the hoisted core shroud falling on them. This idea requires about 30 days for transferring the fuel assemblies. Thus, the preparatory operation for carrying out the core shroud takes long time, and consequently, it requires long time to complete the carrying out of the core shroud. The method for carrying out a core shroud described in Japanese Patent Laid-open No. 2000-46983 or WO 00/60607 with the above-mentioned protection device applied to the method, can reduce the time required for carrying the core shroud out of the reactor building than the method in which the fuel assemblies are transferred to a fuel storage pool in another BWR plant. However, it takes time to set up a strong protection device for preventing the core shroud from falling. An object of the present invention is to provide a method for carrying out a reactor internal for being able to increase safety during carrying out the reactor internal and further reduce the time required for carry operation. A feature of the present invention to achieve the above object comprises steps of: forming an opening portion in a ceiling of a reactor building at a position directly above an equipment pool in the reactor building; cutting a cylindrical reactor internal surrounding a core in a reactor pressure vessel at one position in an axial direction; surrounding the cut cylindrical reactor internal with a radiation shield; and carrying the cylindrical reactor internal surrounded by the radiation shield out of the reactor building through the opening portion. Since the cut cylindrical reactor internal is carried out through the opening portion formed directly above the equipment pool which is far from a fuel storage pool, the cylindrical reactor internal can be prevented from falling into the fuel storage pool storing fuel assemblies during carrying out the cylindrical reactor internal. This improves safety during carrying out the cylindrical reactor internal. In addition, since neither transfer of the fuel assemblies in the fuel storage pool nor the setting of the protection device for preventing the cylindrical reactor internal from falling into the fuel storage pool is necessary when the cylindrical reactor internal is carried out, the time period required for carrying out the cylindrical reactor internal can be further reduced. A feature of another invention comprises steps of: cutting a cylindrical reactor internal surrounding a core in a reactor pressure vessel installed in a reactor building, at one position in the axial direction; taking out the cut cylindrical reactor internal from the reactor pressure vessel; supporting the taken out cylindrical reactor internal by a flange portion of the reactor pressure vessel; surrounding the cylindrical reactor internal supported by the flange portion by the radiation shield; and carrying out the cylindrical reactor internal surrounded by the radiation shield from the reactor building. Since the cylindrical reactor internal supported by the flange portion is surrounded by the radiation shield, the weight of the cylindrical reactor internal and the radiation shield can be supported by the reactor pressure vessel. This eliminates the need of setting up a new support member for supporting the weight of the radiation shield. Thus, the time period required for carrying out the cylindrical reactor internal can be further reduced. According to the present invention, safety during the carrying out the cylindrical reactor internal in the reactor pressure vessel can be improved and the time required for the carry operation can be further reduced. Various embodiments of the present invention will now be described below. A method for carrying out a reactor internal according to the first embodiment, which is a preferred embodiment of the present invention, will be described below with reference to figures. First, general structure of a BWR plant to which the carry method is applied will be explained with reference to FIGS. 2, 3, and 4. The BWR plant has a reactor containment vessel (hereinafter referred to as a PCV) 26 installed in a reactor building 25 and a reactor provided in the PCV 26. This reactor is a boiling water reactor. A reactor well 28, an equipment pool 29, and a fuel storage pool 30 are disposed above the PCV 26 in the reactor building 25. The reactor well 28 is located directly above the reactor. The equipment pool 29 and the fuel storage pool 30 are located on both sides of the reactor well 28, and each of these pools is connected to the reactor well 28. An operation floor 27 is formed in the upper portion of the reactor building 25, surrounding the reactor well 28, the equipment pool 29, and the fuel storage pool 30. A ceiling crane 33 is disposed above the operation floor 27 inside the reactor building 25. A fuel exchanger 32 is movably installed on the operation floor 27 over the reactor well 28. The reactor of the BWR plant has a reactor pressure vessel (hereinafter referred to as an RPV) 1, a core loaded with a plurality of fuel assemblies 10, a core shroud (a cylindrical reactor internal) 4 surrounding the core, and a plurality of control rods 11 to be inserted between the fuel assemblies 10 and withdrawn from between the fuel assemblies 10. The core, the core shroud 4, and the control rods 11 are disposed in the RPV 1. A core plate 8 and a top guide 9 disposed in the core shroud 4 are attached to the core shroud 4. The core plate 8 supports the lower end portions of the fuel assemblies 10, and the top guide 9 supports the upper end portions of the fuel assemblies 10. A plurality of control rod guide pipes 22 provided below the core plate 8 function as a guide for each control rod 11. A plurality of in-core flux monitor guide pipes 23 disposed between the control rod guide pipes 22 are connected by in-core stabilizers 24. The core shroud 4 is fixed to a shroud support cylinder 5, and the shroud support cylinder 5 is installed on the inside bottom surface of the RPV 1 by shroud support legs 6. A baffle plate 7 installed to the inner surface of the RPV 1 in the horizontal direction is also fixed to the shroud support cylinder 5. A plurality of jet pumps 12 are disposed in an annular space formed between the RPV 1 and the core shroud 4, and installed to the baffle plate 7. Each jet pump 12 has a jet pump riser 13, an inlet mixer 14, and a diffuser 15. Each diffuser 15 is installed to the baffle plate 7. A shroud head 21 above the core is installed to the upper end portion of the core shroud 4. A steam separator 16 extends upward from the shroud head 21, and a steam dryer 17 is disposed above the steam separator 16. The steam separator 16 and the steam dryer 17 are disposed in the RPV 1. A core spray sparger 20 is installed to the shroud head 21. The method for carrying out a reactor internal of the present embodiment is described using, as an example, a carrying out operation of the core shroud 4, which is performed as part of a replacement operation of the core shroud 4. This method for carrying out a reactor internal is performed based on the steps shown in FIG. 1, and each operation of steps S1 to S19 is sequentially executed. A crane is installed (step S1). A crane (a first transfer apparatus) 18 for hoisting the steam dryer 17, the steam separator 16, the core shroud 4, and so on provided in the RPV 1, out of the reactor building 25 (see FIG. 7) is installed on the ground (or on a road) outside the reactor building 25. An opening portion is formed in a ceiling of the reactor building 25 (step S2). An opening portion 34 for carrying out the core shroud 4 (see FIGS. 2 and 7) is formed in a ceiling 37 of the reactor building 25 directly above the equipment pool 29 (see FIG. 7). An openable and closable shutter 35 covers the opening portion 34, and is movably attached to the ceiling (see FIG. 7). The shutter 35 is opened when equipment is carried in or out through the opening portion 34, or else it is closed. In addition, the opening portion 34 is provided with an air curtain to prevent radioactive material from escaping outside the reactor building 25 through the opening portion 34 when the shutter 35 is open. A top head of the RPV is transferred onto the operation floor (step S3). A top head 3 is attached with a plurality of bolts to a flange 2 located at the upper part of the RPV 1. Before the top head 3 is removed, the reactor well 28 and the equipment pool 29 are filled with water to shield radiation. The bolts are removed, and the top head 3 is hoisted by the ceiling crane (a second transfer apparatus) 33 to be transferred onto the operation floor 27 through the reactor well 28. The top head 3 is covered with a sheet to prevent any radioactive material from scattering, and kept on the operation floor 27. The steam dryer is transferred (step S4). The steam dryer 17 in the RPV 1 is hoisted by the ceiling crane 33 and removed from the RPV 1. This steam dryer 17 is transferred into the equipment pool 29 by the ceiling crane 33 and temporarily placed on the bottom of the equipment pool 29. The steam separator is transferred (step S5). The shroud head 21 on which the steam separator 16 is fixed is removed from the core shroud 4. The steam separator 16 together with the shroud head 21 is hoisted by the ceiling crane 33, removed from the RPV 1, and transferred to the equipment pool 29. This steam separator 16 and the shroud head 21 are placed on the bottom of the equipment pool 29 at a corner of the equipment pool 29. This corner is one of the corners farthest from the reactor well 28 among the four corners of the equipment pool. The steam dryer 17 placed inside the equipment pool 29 is stacked on top of the steam separator 16. Then, a separation wall 78 having two orthogonal sides (see FIG. 2) is disposed by the ceiling crane 33 around the stacked steam separator 16 and steam dryer 17. The top head 3, the steam dryer 17, the steam separator 16, etc. are surrounded by two sides of the equipment pool 29 and the two sides of the separation wall 78. A radiation shield provided to the separation wall 78 (not shown) covers the upper part of the steam separator 16 disposed in the separation wall 78. This radiation shield extends from the top end of the two side walls of the separation walls 78 to the half of the height of each side wall. The fuel assemblies are transferred to the fuel storage pool (step S6). A gripper (not shown) of the fuel exchanger 32 grips the fuel assembly 10 loaded to the core. The fuel assembly 10 taken out of the RPV 1 by the fuel exchanger 32 is lifted inside the reactor well 29, transferred into the fuel storage pool 30, and stored in a storage rack 31 in the fuel storage pool 30. All the fuel assemblies in the core are stored in the storage rack 31. The control rods and the control rod guide pipes are carried out (step S7). The control rods 11 inserted into the core are stored in the equipment rack (not shown) disposed in the fuel storage pool 30 by the fuel exchanger 32 in the same manner as the fuel assemblies 10. The control rod guide pipes 22 in the RPV 1 are also removed from the RPV 1 by the fuel exchanger 32 and stored in the above equipment rack. A hole is formed in the top guide (step S8). As shown in FIG. 5, a part of a guide member of the top guide 9 provided to the core shroud 4 is removed, and a hole 19 is formed in the top guide 9. The hole 19 should be large enough for putting the removed jet pumps 12, the spray sparger 20, etc. into the core shroud 4. Reactor internal equipments are stored in the core shroud (step S9). The jet pumps 12 provided in the RPV 1 are taken out by separately removing the jet pump risers 13, the inlet mixers 14 and the diffusers 15, and the removed pieces of the jet pump 12 are stored in the core shroud 4 through the hole 19. The core spray sparger 20 is also removed and stored in the core shroud 4. Piping connected to the core spray sparger 20 is also cut and stored in the core shroud 4 through the hole 19. FIG. 6 shows a state in which these reactor internal equipments and piping are stored in the core shroud 4. The ceiling crane 33 is used to store the removed jet pump risers 13, the core spray sparger 20, etc. into the core shroud 4. A radiation shield plate is installed on an upper end of the core shroud (step S10). The shutter 35 is opened as shown in FIG. 7, and a radiation shield plate 36 is carried, using the crane 18, in the reactor building 25 through the opening portion 34 in the ceiling 37 ((a) of FIG. 7). The radiation shield 36 has, as shown in FIG. 8, a plurality of hoist bolts 39 protruding upward and a plurality of ribs 38, each having a through-hole, around the shield 36. The radiation shield 36 is hoisted by the crane 18 with wires attached to the hoist bolts 39. This radiation shield 36 is temporarily placed in the equipment pool 29 ((b) of FIG. 7). The radiation shield 36 is then lifted by the ceiling crane 33 ((c) of FIG. 7), transferred from the equipment pool 29 to the reactor well 28 ((d) of FIG. 7), and lowered in the reactor well 28 ((e) of FIG. 7) to be set on the upper end of the core shroud 4 in the RPV 1. FIG. 9 shows a state in which the radiation shield 36 is set on an upper end ring 40 that is the upper end of the core shroud. The radiation shield 36 is attached to the upper end ring 40 with hoist bolts 41. Preparation for lifting the core shroud is performed (step S11). Wires are removed from the hoist bolts 39 attached to the radiation shield 36 and re-attached to the hoist bolts 41 attached to the radiation shield 36. The hoist bolts 41 combines the radiation shield 36 with the core shroud 4. The wires are attached to the ceiling crane 33 in order to hang the core shroud 4 (see FIG. 10). The ceiling crane 33 is operated to pull the wires to the extent that they are not slack. The core shroud is cut (step S12). While the wires are stretched, the core shroud 4 is cut from outside. The cutting position of the core shroud 4 is lower than the core plate 8, higher than the baffle plate 7 and at one position in the axial direction of the core shroud 4. Preferably, the cutting position is close to the baffle plate 7. At this cutting position, the core shroud 4 is cut in a circumferential direction. Since the wires are stretched, the core shroud 4 is prevented from tipping or falling during or after the cutting of the core shroud 4. A cask bottom lid is carried into the equipment pool (step S13). A bottom lid (a bottom portion of the radiation shield) 42 of a cask hoisted by the crane 18 is carried into the reactor building 25 through the opening portion 34 and placed outside the separation wall 78 in the equipment pool 29 (see FIG. 11). The bottom lid 42 is made up of a radiation shield. A structure of the bottom lid 42 is described using FIGS. 12 and 13. The bottom lid 42 has jacks 44 and a jack supporting member 45. The center portion of the bottom lid 42 caves in. The jacks 44, each upper end of which is fixed to the bottom lid 42, are provided to the jack supporting member 45. The jacks 44 are attached to the under surface of the bottom lid 42. A plurality of guiding pins 43, whose form is thinner toward the upper end, are fixed to the side walls of the bottom lid 42. Instead of the guiding pins 43, bolts 43A may be attached to the side walls of the bottom lid 42 in the direction that the screw portion of each bolt faces upward (see FIG. 14). The bottom lid 42 is carried into the equipment pool 29 during the time period before the step S14 to be described later is started and after the radiation shield 36 carried into the equipment pool 29 in the step S10 is started to be transferred toward the reactor well 28 while being hoisted by the ceiling crane 33. Preferably, the bottom lid 42 is carried into the equipment pool 29 during the period between the time when the radiation shield 36 is started to be transferred toward the reactor well 28 by the ceiling crane 33 in the step 10 and the time when the operation of the step S12 is completed. This allows the operation of the step S14 to be started immediately after the operation of Step S12 is completed. Therefore, the time required for carrying out the core shroud 4 can be reduced. The core shroud is transferred to the equipment pool (step S14). As shown in FIG. 15, the core shroud 4 cut at the above-described position is lifted by the ceiling crane 33 and transferred from the RPV 1 into the reactor well 28. Then, the core shroud 4 is transferred into the equipment pool 29 by the ceiling crane 33 and put on top of the bottom lid 42 placed on the bottom of the equipment pool 29. A cask shell is carried into the equipment pool (step S15). A cask shell (the shell portion of the radiation shield) 46 hoisted by the crane 18 is, as shown in FIG. 16, carried into the reactor building 25 through the opening portion 34 and lowered into the equipment pool 29. The annular cask shell 46 is a radiation shield, and its upper end portion is closed while its lower end portion is open. The cask shell 46 is lowered in such a way that it covers the core shroud 4 placed on top of the bottom lid 42. The cask shell 46 is stopped from being lowered just before its bottom end contacts the top end of the bottom lid 42 and is kept being hoisted by the crane 18 with wires (see FIG. 17). A water surface 47 of the cooling water inside the equipment pool 29 is maintained at the upper end portion of the equipment pool 29. The bottom lid is attached to the cask shell (step S16). After the cask shell 46 is stopped from being lowered, the bottom lid 42 is raised by operation of the jacks 44. When an upper end of the bottom lid 42 touches a lower end of the cask shell 46, the bottom lid 42 is stopped from being raised by the jacks 44. At this point, the guiding pins 43 are inserted into holes formed in a flange provided at the lower end portion of the cask shell 46. A nut is placed to an upper end portion of each guiding pin 43, and the bottom lid 42 is joined to the cask shell 46 by fastening each nut (see FIG. 18). The contacting portions of the bottom lid 42 and the cask shell 46 engage with each other to prevent radiation leakage from inside. A cask 48, which is a radiation shield surrounding the core shroud 4, is made up by attaching the bottom lid 42 to the cask shell 46 in this way. Water is drained from the cask (Step S17). A gas supplying pipe 51 provided with a valve 52 is, as shown in FIG. 19, disposed between a side wall of the cask 48 and the core shroud 4. A lower end of the gas supplying pipe 51 extends to the bottom of the cask 48, that is, near a top surface of the bottom lid 42. A water drainage pipe 49 provided with a valve 50 is also disposed between a side wall of the cask 48 and the core shroud 4. A lower end of the water drainage pipe 49 is positioned higher than the lower end of the gas supplying pipe 51, and disposed in the upper portion of the cask 48. The crane 18 is operated to pull the cask 48 up so that the cask 48 is lifted above the water surface 47. While the cask 48 hoisted by the crane 18 is held above the water surface 47, the valves 50 and 52 are opened. Nitrogen gas (or rare gas) is supplied from the gas supplying pipe 51 into the cask 48. The water in the cask 48 is discharged from the water drainage pipe 49 to the outside of the cask 48 due to the supply of this nitrogen gas. After the water is drained from the cask 48, the valves 50 and 52 are closed. The core shroud is carried out (Step S18). After the water is drained, the cask 48 is lifted by the crane 18, and the core shroud 4 shielded by the cask 48 is carried out of the reactor building 25 through the opening portion 34 (see FIG. 20). The jacks 44 and the jack supporting member 45 are also carried out with the cask 48. After the cask 48 is carried out, the shutter 35 is closed, closing the opening portion 34. The cask 48 including the core shroud 4 is carried out of the reactor building 25 by the crane 18, and stored in a storage provided in the nuclear power plant (step S19). The whole operation of carrying out the core shroud 4 in the RPV 1 out of the reactor building 25 is completed by the above operations. In the present embodiment, since the core shroud 4 covered by the radiation shield (the cask 48) is carried out of the reactor building 25 through the opening portion 34 formed in the ceiling 37 of the reactor building 25 at the position directly above the equipment pool 29, it can prevent the core shroud 4 from tipping and falling into the fuel storage pool 30 storing the fuel assemblies 10 during the carrying out. For this reason, the fuel assemblies 10 in the fuel storage pool 30 will not be damaged in the present embodiment, and safety during the carrying out of the core shroud 4 is significantly improved. When the cut core shroud 4 is transferred from the RPV 1 to the equipment pool 29, the core shroud 4 is transferred only through the reactor well 28 and does not transferred above the operation floor 27. This ensures that the core shroud 4 does not fall into the fuel storage pool 30. Since the cut core shroud 4 does not fall into the fuel storage pool 30 during the transfer, the core shroud 4 can be transferred while the fuel assemblies 10 are stored in the fuel storage pool 30. This eliminates the need of transferring the fuel assemblies 10 in the fuel storage pool 30 to a fuel storage pool in another BWR plant when the core shroud 4 is to be transferred. This contributes to a significant reduction in the time period required for completing the carry operation of the core shroud 4. Furthermore, since the present embodiment requires no protection device 59 for preventing the carrying out core shroud 4 from falling into the fuel storage pool 30, as in fourth embodiment described later, the time period required for completing the carry operation of the core shroud 4 can be further reduced. Since the radiation shield 36 is installed onto the upper end portion of the core shroud 4 in the RPV 1, radiation from the core shroud 4 can be shielded by the radiation shield 36. When the core shroud 4 is pulled up into the reactor well 28, the upper end of the core shroud 4 comes close to the water surface in the reactor well 28. However, since the radiation shield 36 is installed on the upper end of the core shroud 4, the radiation released above the water surface can be greatly reduced. After the core shroud 4 is transferred into the equipment pool 29, the radiation from the core shroud 4 reaching above the water surface in the equipment pool 29 can also be significantly reduced by the radiation shield 36. The radiation shield 36 is provided with the hoist members (the hoist bolts 41) so that, by attaching the radiation shield 36 to the core shroud 4, the cut core shroud 4 can be easily lifted by the ceiling crane 33. The cut core shroud 4 can be transferred from the RPV 1 to the equipment pool 29 using the ceiling crane 33 because the cask 48, which is a very heavy radiation shield, is attached to the core shroud 4 in the equipment pool 29. In the present embodiment, the bottom lid 42 of the cask 48 is attached to the cask shell 46 after the core shroud 4 and the bottom lid 42 are raised by operation of the jacks 44. This allows the bottom lid 42 to contact the cask shell 46 easily and quickly. In addition, since the bottom lid 42 is raised by the jacks 44 while the cask shell 46 is hoisted by the crane 18, the bottom lid 42 can be attached to the cask shell 46 without the weight of the cask shell 46 pressed on the bottom of the equipment pool 29. If the cask shell 46 is put on the bottom lid 42 placed on the bottom of the equipment pool 29, all the weight of the core shroud 4, the bottom lid 42, and the cask shell 46 concentrates on one part of the bottom of the equipment pool 29 supporting the bottom lid 42. When these loads concentrate on one part of the bottom of the equipment pool 29, the bottom of the equipment pool 29 may not be able to support the weight unless reinforcement work is done to it. The present embodiment has no such concern since the weight of the cask shell 46 is not on the bottom of the equipment pool 29. In the present embodiment, the top head 3 of the RPV 1, and the stream dryer 17, the steam separator 16, and the shroud head 21 taken out from the RPV 1 are disposed on top of the other at one corner in the equipment pool 29 so that a space to put the core shroud 4 is ensured in the equipment pool 29. Therefore, the bottom lid 42 and the cask shell 46 can be attached to the core shroud 4 in the equipment pool 29. In the present embodiment, since the cask 48 which is a radiation shield, is attached to the core shroud 4 in the equipment pool 29, a long opening portion 54 is not required to be formed in the ceiling 37 as in second embodiment. This reduces the time required for forming the opening portion in the ceiling. Furthermore, no shutter 55 is needed. Reactor internal equipments and piping stored in the core shroud 4 can be carried out of the reactor building 25 with the core shroud 4. This reduces the time required for carrying out the removed reactor internal equipments and cut piping. If the reactor internal equipments and piping are carried out of the reactor building 25 separately from the core shroud 4, it takes longer to complete the carry operation of the core shroud 4, reactor internal equipments, and piping. However, the present embodiment can reduce such time. Since the cut core shroud 4 is surrounded by the cask 48, when the core shroud 4 is carried out of the reactor building 25, radiation from the core shroud 4 to a worker can be prevented. After the cut core shroud 4 is carried out of the reactor building 25, a newly manufactured core shroud 4 is carried into the reactor building 25 through the opening portion 34 by the crane 18 and transferred into the equipment pool 29. This new core shroud 4 is hoisted by the ceiling crane 33, transferred to the reactor well 28, and lowered to the predetermined position in the RPV 1. This new core shroud 4 is joined to the shroud support cylinder 5 by welding. Jet pumps are installed in the RPV 1, and the fuel assemblies 10 in the fuel storage pool 30 are loaded in the core. The steam separator 16 and the steam dryer 17 placed in the equipment pool 29 are installed in the RPV 1, and the top head 3 is attached to the RPV 1. After that, operation of the BWR plant is started. If the cask shell 46 is to be put on the bottom lid 42 placed on the bottom of the equipment pool 29 in the step S15 of the present embodiment, load dispersion members 53 are spread over a wide range of the bottom of the equipment pool 29 in the step S13. Then, the bottom lid 42 carried into the reactor building 25 is put on the load dispersion members 53 (see FIG. 21). The load dispersion members are made up of a plurality of rectangular blocks as shown in FIG. 22. The load dispersion members 53 are placed across a plurality of beams making up the bottom portion of the equipment pool 29 and work to disperse the load of the core shroud 4 and the cask shell 46 over a wide range of the bottom of the equipment pool 29. In the step S15, the core shroud 4 taken out from the RPV 1 is put on the bottom lid 42 placed on the bottom of the equipment pool 29. Then, in the step S16, the cask shell 46 carried into the reactor building 25 is lowered by the crane 18 and put on the bottom lid 42. After that, the bottom lid 42 and the cask shell 46 are joined as described above. When the load dispersion members 53 are used, neither the jacks 44 nor the jack supporting member 45 is needed. Since the load of the core shroud 4, the bottom lid 42, and the cask shell 46 can be dispersed over a wide range of the bottom of the equipment pool 29 by the load dispersion members 53, no reinforcement work is necessary to the bottom of the equipment pool 29. A method for carrying out a reactor internal according to second embodiment, which is another embodiment of the present invention, will now be described below with reference to FIG. 23. The present embodiment provides a method for carrying out a reactor internal applicable to a BWR plant, in which method, a core shroud is an object carried out. In the present embodiment, the operations of the steps S13 and S14 in the steps S to S19 executed in the first embodiment, are replaced by those of steps S20 to S22. Each operation of the steps S1 to S12 and S15 to S19 executed in the present embodiment is practically the same as that in the first embodiment. Each operation of the steps S20 to S22, which is different from the first embodiment, will be described. In order to execute the carry method of the present embodiment, a long opening portion 54 other than the opening portion 34, extending from the opening portion 34 to the position directly above the reactor well 28, is formed in the ceiling 37 of the reactor building 25 in the step S2 (see FIG. 24). The opening portion 54 has a narrow width through which only wires hanging from the crane 18 can pass. The opening portion 54 can be closed by a shutter 55 (see FIG. 25). Since the opening portion 54 is formed in the present embodiment, the core shroud 4, the steam dryer 17, the stream separator 16, the bottom lid 46, and the cask shell 46, which are transferred within the reactor building 25 using the ceiling crane 33 in the first embodiment, can be carried using the crane 18. After each operation of the steps S1 to S12 is executed, the operation of the step S20 is performed. However, in the step S10 in the present embodiment, the radiation shield 36 carried into the reactor building 25 through the opening portion 34 hoisted by the crane 18 is transferred to the position directly above the RPV 1 in the reactor well 28 by the crane 18. At this point, the wires hanging the radiation shield 36 run through the opening portion 54. Then, the radiation shield 36 is lowered to the upper end portion of the core shroud 4 by operation of the crane 18 and attached to the upper end portion of the core shroud 4. The core shroud is transferred into the equipment pool (step S20). The cut core shroud 4 is lifted by the crane 18, carried from the RPV 1 into the equipment pool 29, and put on the bottom of the equipment pool 29 (see FIG. 25). The cask bottom lid is carried into the reactor building and transferred onto the RPV (step S21). The bottom lid 42 hoisted by the crane 18 is carried into the reactor building 25 through the opening portion 34, and transferred in the horizontal direction above the operation floor 27 by operation of the crane 18. Then, this bottom lid 42 is carried to the position directly above the reactor well 28. Further, the bottom lid 42 is lowered by the crane 18 and directly put on the flange 2 of the RPV 1 (see FIG. 26). The bottom lid 42 used in the present embodiment is provided with neither the jacks 44 nor the jack supporting member 45. FIG. 27 shows a state in which the bottom lid 42 is placed on the flange 2. The ceiling crane 33 may be used for carrying the cut core shroud 4 into the equipment pool 29 and for carrying the bottom lid 42 within the reactor building 25. The core shroud is transferred onto the bottom lid (step S22). The core shroud 4 in the equipment pool 29 is hoisted by the crane 18, transferred into the reactor well 28, and then, lowered in the reactor well 28. This core shroud 4 is put on the bottom lid 42 placed on the flange 2 (see FIG. 28). In the carry operation of the step S15 in the present embodiment, the cask shell 46 is transferred into the reactor well 28 by the crane 18. The cask shell 46 hoisted by the crane 18 is carried into the reactor building 25 through the opening portion 34, and transferred in the horizontal direction above the operation floor 27 to the position directly above the reactor well 28 (see FIG. 29). This cask shell 46 is lowered into the reactor well 28 by operation of the crane 18 almost to the core shroud 4 placed on the bottom lid 42 put on the flange 2. The cask shell 46 is further lowered in such a way that it covers the core shroud 4, and when the bottom end of the cask shell 46 contacts the upper end of the bottom lid 42, the cask shell 46 is stopped from being lowered (see FIG. 29). In the step S16 of the present embodiment, the bottom lid 42 is attached to the cask shell 46 while the bottom lid 42 is put on the flange 2 of the RPV 1 (see FIG. 30). In this way, the cask 48 is attached to the core shroud 4. Water is drained from the cask 48 in the step S17 while the cask 48 is hoisted by the crane 18. Then, the core shroud 4 surrounded by the cask 48, storing reactor internal equipments and piping inside, is hoisted by the crane 18 with wires attached to the cask 48 and carried from the reactor well 28 into the equipment pool 29 (see FIG. 31). The cask 48 storing the core shroud 4 is lifted by the crane 18 and carried out of the reactor building 25 through the opening portion 34. In the present embodiment, each effect produced in the first embodiment can be obtained except for the one produced by that the bottom lid 42 raised by the jacks 44 is attached to the cask shell 46 while the cask shell 46 is hoisted by the crane 18. In the present embodiment, since the opening portion 54 is formed in the ceiling 37 of the reactor building 25, which opening portion extends from the opening portion 34 formed directly above the equipment pool 29 to the position directly above the reactor well 28, there is no need to switch between the crane 18 and the ceiling crane 33 for hoisting carrying objects (for example, the core shroud 4 and the radiation shield 36) as in the first embodiment. This can reduce the time required for carrying these objects. In the present embodiment, the bottom lid 42 and the cask shell 46 are joined while the bottom lid 42 is put on the flange 2 of the RPV 1, the cut core shroud 4 is put on the bottom lid 42, and in addition, the cask shell 46 is put on the bottom lid 42. In the present embodiment such as this, all the weight of the core shroud 4, the bottom lid 42 and the cask shell 46 put on the bottom lid 42 are supported by the RPV 1. Since the RPV 1 is installed on a pedestal (not shown) set up on a base mat, it can sufficiently support all the weight of the core shroud 4, the bottom lid 42, and the cask shell 46. This eliminates the need of setting up a new support member for supporting the cask 48 which is a radiation shield. Thus, the time required for carrying out the cut core shroud 4 can be reduced. A method for carrying out a reactor internal according to third embodiment, which is another embodiment of the present invention, will now be described below with reference to FIG. 32. The present embodiment also provides a method for carrying out a reactor internal applicable to a BWR plant, in which method, a core shroud is an object carried out. In the present embodiment, the operations of the steps S13 to S15 in the steps S1 to S19 executed in the first embodiment, are replaced by those of steps S20, S21, S23, and S24. Each operation of the steps S1 to S12 and S16 to S19 executed in the present embodiment is practically the same as that in the first embodiment. The operations of the steps S21, S23, and S24, which are different from the first embodiment, will be described. The operation of the step S20 is the same as that in the second embodiment. In the present embodiment, the opening portion 54, other than the opening portion 34, is formed on the ceiling 37 of the reactor building 25 in the step S2 in the same manner as in the second embodiment. After each operation of the steps S3 to S12 and S20 are executed, the cask bottom lid is carried into and transferred onto the RPV (step S21). The operation of this the step S21 is the same as that of the step S21 in the second embodiment. Then, the cask shell is carried into the reactor building to be joined with the core shroud (step S23). A cask shell 46A hoisted by the crane 18 is carried into the reactor building 25 through the opening portion 34. This cask shell 46A is lowered and covers the core shroud 4 placed in the equipment pool 29 (see FIG. 33). The cask shell 46A is provided with a couple of joining members (for example, bolts or pins) 56 extending toward the axis of the cask shell 46A from positions opposing the side walls. Each joining member 56 engages with a side wall of the cask shell 46A with a screw, and is turned to be moved toward the core shroud 4. When the tips of both joining members 56 touch the outer surface of the core shroud 4 in the cask shell 46A, the joining members 56 are stopped from being turned. The tip portions of the two joining members 56, contacting the outer surface of the cask shell 46A, are located below an upper flange 77 of the core shroud 4 (see FIG. 34). The cask shell and the core shroud are transferred onto the bottom lid on the RPV (Step S24). The cask shell 46A in the equipment pool 29 is hoisted by the crane 18. The core shroud 4 in the cask shell 46A is supported by the two joining members 56 and lifted with the cask shell 46A. The cask shell 46A and the core shroud 4 are transferred from the equipment pool 29 into the reactor well 28 (see FIG. 35). The core shroud 4 is put on the bottom lid 42 placed on the flange 2 of the RPV 1. The bottom lid 42 is attached to the cask shell 46A in the same manner as in the second embodiment (step S16), and water is drained from the cask 48 (step S17). The core shroud 4 surrounded by the cask 48 is carried out of the reactor building 25 (step S18), and stored in the storage (step S19). In the present embodiment, each effect produced in the second embodiment can be obtained. In the present embodiment, since the core shroud 4 and the cask shell 46A are carried from the equipment pool 29 onto the RPV 1 together, the time required for carrying the core shroud 4 and the cask shell 46A can be reduced compared to the second embodiment in which the cask shell 46, and the core shroud 4 placed in the equipment pool 29 are separately carried onto the RPV 1. For this reason, the present embodiment can reduce the time required for carrying the core shroud 4 out of the reactor building 25 compared to the second embodiment. A method for carrying out a reactor internal according to fourth embodiment, which is another embodiment of the present invention, will now be described below with reference to FIG. 36. The present embodiment also provides a method for carrying out a reactor internal applicable to a BWR plant, in which method, a core shroud is an object carried out. In the present embodiment, the operation of step S25 is added to the operations of the steps S1 to S12, S20 to S22, and S15 to S19 executed in the second embodiment. The step S25 is executed between the steps S9 and S10. In the present embodiment, each operation except for the operation of the step S25, which is an essentially different operation, is practically the same as that in the second embodiment. After the installation of the crane 18 is completed in the step S1, an opening portion 57 is formed in the ceiling 37 of the reactor building 25 directly above the reactor well 28, that is, the RPV 1, as in FIG. 37 (step S2). A shutter 58 for opening and closing the opening portion 57 is installed to the ceiling 37. In the steps S3 to S5, the crane 18 is used to carry relevant equipment out of the reactor building 25 through the opening portion 57. After that, the operations of the steps S6 to S9 are executed. A protection device is set up on the operation floor (step S25). A protection device 59, as shown in FIGS. 38 and 39, comprises a protection wall 60, support members 61, and a plurality of pulleys 62. A couple of support members 61 are attached to the protection wall 60 to prevent the protection wall from falling. The plurality of pulleys 62 are rotatably attached to the protection wall 60 along the height direction. Two protection devices 59 are set up on the operation floor 27 in such a way that each protection wall 60 faces the reactor well 28 (see FIG. 38). The radiation shield plate 36 hoisted by the crane 18 is carried into the reactor building 25 through the opening portion 57 as shown in FIG. 40, and attached to the upper end portion of the core shroud 4 in the RPV 1 (step S10). The steps S11 and S12 are executed. The cut core shroud 4, to the upper end portion of which the radiation shield plate 36 is attached, is transferred into the equipment pool 29 by the ceiling crane 33 as shown in FIG. 41 (step S20). The bottom lid 42 hoisted by the crane 18 is carried into the reactor building 25 through the opening portion 57 and put on the flange 2 of the RPV 1 as shown in FIG. 42 (step S21). The core shroud 4 in the equipment pool 29 is hoisted by the crane 33 and transferred onto the bottom lid 42 on the RPV 1 as shown in FIG. 43 (step S22). The cask shell 46 hoisted by the crane 18 is carried into the reactor building 25 through the opening portion 57 as shown in FIG. 44 and covers the core shroud 4 placed on the bottom lid 42 (step S15). After that, the cask shell 46 are attached to the bottom lid 42 in the step S16, and water is drained from the cask 48 (step S17). Then, the core shroud 4 surrounded by the cask 48 is lifted by the crane 18 as shown in FIG. 45 and carried out of the reactor building 25 through the opening portion 57 (step S18). The core shroud 4 carried out is stored in the storage (step S19). In the present embodiment, the bottom lid 42 and the cask shell 46 are joined while the cut core shroud 4 is put on the bottom lid 42 placed on the flange 2 of the RPV 1, and the cask shell 46 is put on the bottom lid 42, in the same manner as in the second embodiment. In the present embodiment also, all the weight of the core shroud 4, the bottom lid 42, and the cask shell 46 can be supported by the RPV 1 installed on the pedestal. Since this eliminates the need of setting up a new support member for supporting the cask 48 which is a radiation shield, the time required for carrying out the cut core shroud 4 can be reduced. In the present embodiment, since the protection devices 59 are set up on the operation floor 27 between the reactor well 28 and the fuel storage pool 30, the core shroud 4 transferred from the reactor well 28 over the operation floor 27 can be prevented from falling into the fuel storage pool 30. No damage will occur to the fuel assemblies 10 in the fuel storage pool 30 when the core shroud 4 is carried out, and safety during the carry operation of the core shroud 4 is significantly improved. Since there is no need to transfer the fuel assemblies 10 to a fuel storage pool in another BWR plant, the time period for completing the carry operation of the core shroud 4 can be significantly reduced. The radiation shield 36 installed on the upper end portion of the core shroud 4 can shield radiation from the core shroud 4 as described in the first embodiment. Furthermore, by using the hoist members (the hoist bolts 41) provided to the radiation shield 36, the cut core shroud 4 can be easily transferred. The reactor internal equipments and piping to be disposed of along with the core shroud 4 can be carried out of the reactor building 25. This can reduce the time required for carrying out the removed reactor internal equipments and cut piping. Since the cut core shroud 4 is surrounded by the cask 48 which is a radiation shield, radiation to a worker can be prevented. In the present embodiment, since the opening portion 57 in the ceiling 37 is formed directly above the RPV 1, the objects to be carried into the reactor building 25 or out of the reactor building 25 can be carried into or out by the crane 18. Since this eliminates the need of switching between the crane 18 and the ceiling crane 33 for hoisting these objects as in Embodiment 1, the time required to carry these objects can be reduced. A method for carrying out a reactor internal according to fifth embodiment, which is another embodiment of the present invention, will now be described below with reference to FIG. 46. The present embodiment also provides a method for carrying out a reactor internal applicable to a BWR plant, in which method, a core shroud is an object e carried out. In the present embodiment, steps S22 and S15 in all the steps executed in fourth embodiment are replaced by steps S23 and S24 executed in the third embodiment. In the present embodiment, each operation in the steps except for the steps S23 and S24 is the same as that in the fourth embodiment. After the step S1 is finished, the opening portion 57 and the long opening portion 54 are formed in the ceiling 37 of the reactor building 25 as shown in FIG. 47, which long opening portion 54 extends from the opening portion 57 to the position directly above the equipment pool 29 (step S2). The shutter 58 for opening and closing the opening portion 57 and the shutter 55 for opening and closing the opening portion 54 are provided to the ceiling 37 (see FIG. 48). In the present embodiment, the cask shell 46A and the core shroud 4 are carried into the reactor building 25 and out of the reactor building 25 not through the opening portion 54 but through the opening portion 57. Each operation of the steps S3 to S9, S25, S10 to S12, S20 and S21 is sequentially executed in the same manner as in the fourth embodiment. In the step 25, the two protection devices 59 are set up on the operation floor 27 as shown in FIG. 47. After the operation of the step S21 is finished, the cask shell 46A is carried into the reactor building 25 and joined with the core shroud 4 (step S23). The cask shell 46A hoisted by the crane 18 is carried into the reactor building 25 through the opening portion 57 and covers the core shroud 4 placed in the equipment pool 29 (see FIG. 48). The cask shell 46A and the core shroud 4 are joined with the two joining members (for example, bolts or pins) 56 in the same manner as in the third embodiment. The jointed cask shell 46A and core shroud 4 are transferred from the equipment pool 29 into the reactor well 28 as shown in FIG. 49, and put on the bottom lid 42 placed on the flange 2 of the RPV 1 (step S24). After that, each operation of the steps S16 to S19 is executed. In the present embodiment, each effect produced in the fourth embodiment can be obtained. In addition, since the core shroud 4 and the cask shell 46A are carried from the equipment pool 29 onto the RPV 1 together, the present embodiment can reduce the time required for carrying the core shroud 4 and the cask shell 46A in the same manner as in the third embodiment. For this reason, the present embodiment can reduce the time required for carrying the core shroud 4 out of the reactor building 25 compared to the second embodiment. A method for carrying out a reactor internal according to sixth embodiment, which is another embodiment of the present invention, will now be described below with reference to FIGS. 50 to 53. The present embodiment also provides a method for carrying out a reactor internal applicable to a BWR plant, in which method, a core shroud is an object carried out. In the present embodiment, the operations of all the steps in the first embodiment are executed. In the present embodiment, a hoist balance device 63 shown in FIG. 50 is used in the steps S10 to S19, and a shield wall (a shield member) 75 is set up on the operation floor 27, surrounding the reactor well 28 and the equipment pool 29. The hoist balance device 63 comprises a balance member 64 made up of two crossing I-shaped beams, a disk-shaped radiation shield 65, compact cranes 69, and load cells 70 (see FIG. 50). The radiation shield 65 is hanged from the balance member 64 by attaching four wires 68 provided to the balance member 64 to four hoist rings 67 provided to the top surface of the shield 65. The diameter of the radiation shield 65 is larger than the diameter of the core shroud 4 to reduce radiation to a worker who stands on the radiation shield 65. The compact crane (for example, a chain block) 69 is provided to each under surface of the both end portions of the I-shaped beams of the balance member 64. The compact crane 69 is an elevating device. The load cell 70 is provided to each compact crane 69. A wire 72 attached to the load cell 70 extends below the radiation shield 65 through a sleeve 71 penetrating the radiation shield 65. The four wires 72 are attached to the respective hoist bolts (the hanging members) 41 provided to the radiation shield 36. Although not shown in FIGS. 50 and 51, a fence 79, shown in FIG. 54, is provided to the outer edge portion of the radiation shield 65 to prevent the worker standing on the radiation shield 65 from falling off. The load cells 70 measure the weight of the core shroud 4 to hoist. The shield wall 75 is made of radiation shielding material and set up on the operation floor 27 around the reactor well 28 and the equipment pool 29 (see FIGS. 52 and 53). The shield wall 75 is supported by support members 76 to prevent the shield wall 75 from falling. The shield wall 75 is set up on the operation floor 27 while, for example, when the opening portion is being formed in the step S2. The hoist balance device 63 is hoisted by the ceiling crane 33 (or the crane 18) with wires attached to four hoist rings 66 provided on the top surface of the balance member 64. The core shroud 4 is lifted using the hoist balance device 63 in the step S14. The radiation shield 65 is also used as a scaffold for a worker. Cooling water in the reactor well 28 is drawn, and a water surface 74 of the cooling water is lower than the radiation shield 65. The worker standing on the radiation shield 65 operates the four compact cranes 69 to reel each wire 72, and the core shroud 4 is lifted (see FIG. 51). Then, the core shroud 4 is transferred to the equipment pool 29 (Step S14). In the present embodiment also, each effect produced in the first embodiment can be obtained. In the present embodiment, since the shield wall 75 surrounds the reactor well 28 and the equipment pool 29, radiation to the worker standing on the operation floor 27 can be restrained when the core shroud 4 is transferred from the reactor well 28 to the equipment pool 29. The hoist balance device 63 can be used in the step S20 of the second, fourth, and fifth embodiments, and in the step S14 of the third embodiment. The installation of the shield wall 75 can also be applied to any of the second, third, fourth, and fifth embodiments. A method for carrying out a reactor internal according to seventh embodiment, which is another embodiment of the present invention, will now be described below with reference to FIG. 54. The present embodiment also provides a method for carrying out a reactor internal applicable to a BWR plant, in which method, a core shroud is an object carried out. In the present embodiment, the operations of all the steps in the first embodiment are executed. In the present embodiment, a hoist balance device 63A shown in FIG. 54 is used in the steps S10 to S19. The hoist balance device 63A has hoist bolts (hanging members) 41A instead of the hoist bolts 41 in the hoist balance device 63 used in the sixth embodiment. Although FIG. 54 does not show everything, the other structure of the hoist balance device 63A is the same as the hoist balance device 63. The fence 79 is provided to the outer edge portion of the radiation shield 65 to prevent a worker standing on the radiation shield 65 from falling off. The hoist bolts 41A used in the present embodiment are longer than the hoist bolts 41. The hoist bolts 41A set up on the top surface of the cask 48 which is supported by the jacks 44 put on the bottom of the equipment pool 29, more specifically, on the top surface of the cask shell 46 of the cask 48, protrude upward above the water surface in the equipment pool 29. Furthermore in the present embodiment, a radiation shield plate 36A is placed on the upper end of the core shroud 4. While the radiation shield plate 36 used in each of the above embodiments is flat, the radiation shield plate 36A has a cylindrical portion protruding downward from the outer edge portion. When the radiation shield 36A is placed on top of the core shroud 4, the cylindrical portion of the radiation shield 36A surrounds the upper end portion of the side wall of the core shroud 4. In the present embodiment, each effect produced in the first embodiment can be obtained. In the present embodiment, since the hoist bolts 41A protrude above the water surface in the equipment pool 29, the wires hanged from the compact cranes 69, attached to the hoist bolts 41A can be prevented from being submerged in the water. Since the wires are prevented from being submerged in the water, tiny gaps between the numerous thin lines of each wire will not be contaminated by radioactive material contained in the water. If the radioactive material gets into the space between those thin lines of the wire, removal of the radioactive material will be difficult. In addition, in the present invention which uses the radiation shield plate 36A, not only that the top of the core shroud 4 is covered by the radiation shield plate 36A but also that the upper end portion of the side wall of the core shroud 4 is surrounded by the cylindrical portion of the radiation shield 36A. Therefore, the radiation released from the side wall portion of the core shroud 4 toward the operation floor 27 near the water surface can be shielded. The radiation shield plate 36A may be used in place of the radiation shield plate 36 in previously-described the first, second, third, fourth, fifth, and sixth embodiments and the eighth, ninth, tenth embodiments to be described later. The cask 48 having the hoist bolts 41A can be applied to the first, second, third, fourth, fifth, and sixth embodiments. A method for carrying out a reactor internal according to eighth embodiment, which is another embodiment of the present invention, will now be described below with reference to FIG. 55. The present embodiment also provides a method for carrying out a reactor internal applicable to a BWR plant, in which method, a core shroud is an object carried out. The present embodiment includes the operation steps in which, steps S26 to S28 are executed instead of the steps S9 and S10 in the steps executed in the first embodiment, and new steps S29 to S32 are added after the step S19. Each operation of the steps S1 to S19 in the present embodiment is the same as that in the first embodiment. Only the operations different from the first embodiment are described below. After the operation of the step S7 is finished, an equipment storage container is carried into the equipment pool (step S26). An equipment storage container 85 (see FIG. 56) hoisted by the crane 18 is carried into the equipment pool 29 through the opening portion 34 formed in the ceiling 37 of the reactor building 25. This equipment storage container 85 is put outside the separation wall 78 in the equipment pool 29. A reactor internal equipment is stored in the equipment storage container (step S27). The top guide 9, the core spray sparger 20, and the core plate 8 provided in the core shroud 4 are removed and sequentially taken out from the RPV 1 by the ceiling crane 33. At this time, no jet pump 12 is removed. The top guide 9, the core spray sparger 20, and the core plate 8 provided in the core shroud 4 are a reactor internal equipment 80 respectively. Each of the reactor internal equipments 80 taken out from the RPV 1 is sequentially stored in the equipment storage container 85 in the equipment pool 29. The equipment storage container 85 storing the relevant reactor internal equipments 80 is hermetically sealed with a lid. The equipment storage container is carried out (Step S28). The equipment storage container 85 is hoisted by the crane 18 using hoist bolts 41A, and the equipment storage container 85 is hoisted from the equipment pool 29 by the crane 18 (see FIG. 56). This equipment storage container 85 is carried out of the reactor building 25 through the opening portion 34 and stored in the storage. After that, each operation of Steps S10 to S19 performed in Embodiment 1 is executed. The operation of Step S13 may be executed concurrently with Steps S11 and S12 in the same manner as in Embodiment 1. However, in Step S18 of the present embodiment, the core shroud 4 containing no reactor internal equipment including a jet pump inside is carried out of the reactor building 25. After the operation of the step S19 is finished, each operation of the steps S29 to S32 is sequentially executed. An equipment storage container is carried into the equipment pool (step S29). An equipment storage container 81 for storing the jet pumps 12 is carried into the equipment pool 29 through the opening portion 34 formed in the ceiling 37 using the crane 18 (see FIG. 57). This equipment storage container 81 is put outside the separation wall 78 in the equipment pool 29 in the same manner as the equipment storage container 85. The jet pumps are stored in the equipment storage container (step S30). The jet pumps 12 provided in the RPV 1 are removed, and the removed jet pumps 12 are taken out from the RPV 1 in the upward direction by the ceiling crane 33. These jet pumps 12 are transferred from the reactor well 28 into the equipment pool 29, and stored in the equipment storage container 81 from the horizontal direction (see FIG. 58). As shown in FIG. 59, one of the side walls and the top side of the equipment storage container 81 are open. This allows the jet pumps 12 hoisted by the ceiling crane 33 to be transferred horizontally and to be easily stored in the equipment storage container 81 through the open side of the side walls. Since the top side is open, wires from the ceiling crane 33 hanging the jet pumps 12 do not touch the equipment storage container 81. In addition, since the jet pumps 12 can be stored in the equipment storage container 81 from the horizontal direction, radiation released from the jet pumps 12 can be significantly suppressed from reaching above the water surface in the equipment pool 29. A plurality of jet pumps 12 provided in the RPV 1 are sequentially stored in the equipment storage container 81 (see FIGS. 59 and 60). The jet pumps 12 provided in the RPV 1 are the reactor internal equipments. The equipment storage container is hermetically sealed (step S31). After the jet pumps 12 in the RPV 1 are all stored in the equipment storage container 81, the equipment storage container 81 is hermetically sealed. In order to hermetically seal the equipment storage container 81, a side wall 82 hoisted by the ceiling crane 33 is first installed to the open portion of the side walls of the equipment storage container 81. A top cover 83 hoisted by the ceiling crane 33 is installed to the upper end portion of the equipment storage container 81 with the side wall 82 already installed (see FIG. 61). When the top cover 83 is installed to the equipment storage container 81, hoist bolts 84 provided to the top cover 83 are hoisted by the ceiling crane 33. When the top cover 83 is installed to the equipment storage container 81, a hole for passing a wire in each of the hoist bolts 84 extending upward is above the liquid surface in the equipment pool 29. The equipment storage container is carried out of the reactor building (step S32). Wires attached to the crane 18 are passed through the holes in the hoist bolts 84 of the equipment storage container 81 placed in the equipment pool 29. The crane 18 lifts the equipment storage container 81 and carries it out of the reactor building 25 through the opening portion 34 (see FIG. 62). The carried-out equipment storage container 81 is stored in the storage in the same manner as the core shroud 4. In the present embodiment, each effect produced in the first embodiment can be obtained except for the one produced by that the reactor internal equipments including the jet pumps 12 are stored in the core shroud 4. Since the reactor internal equipment 80 is stored in the equipment storage container 81 and carried out, the present embodiment eliminates the need of the hole forming operation to the top guide 9 executed in the step S8 in the first embodiment for carrying the core spray sparger 20 into the core shroud 4. In addition, in the present embodiment, the jet pumps 12 are removed from the RPV 1 and stored in the equipment storage container 81 after the core shroud 4 is carried out. This allows the jet pumps 12 to be easily removed from the RPV 1 because the core shroud 4 is not in the RPV 1. The steps S26 to S32 executed in the present embodiment can be applied to each of previously-described the second, third, fourth, fifth, and sixth embodiments. In other words, the steps S26 to S28 can be executed instead of the steps S8 and S9, and the steps S29 to S32 can be added after the step S19 in each of the second, third, fourth, fifth, and sixth embodiments. A method for carrying out a reactor internal according to ninth embodiment, which is another embodiment of the present invention, will now be described below with reference to FIG. 63. The present embodiment also provides a carry method for a reactor internal applicable to a BWR plant, in which method, a core shroud is an object carried out. The present embodiment includes the operation steps in which, the steps S29 to S32 executed in the eighth embodiment are added to the steps executed in the first embodiment. Each operation of the steps S1 to S19 in the present embodiment is the same as that in the first embodiment. However, in the step S9, each of the reactor internal equipments (the top guide 9, core spray sparger 20, etc.) except for the jet pumps 12 is stored in the core shroud 4. The core shroud 4 storing these reactor internal equipments is carried out in the step S18. In the present embodiment, each effect produced in the first embodiment can be obtained. The present embodiment also allows the jet pumps to be easily removed in the same manner as in the eighth embodiment. The steps S29 to S32 can be applied to each of previously-described the second, third, fourth, fifth, and sixth embodiments in the same manner as in the present embodiment. In other words, the steps S29 to S32 can be added after the step S19 in each of the second, third, fourth, fifth, and sixth embodiments. A method for carrying out a reactor internal according to tenth embodiment, which is another embodiment of the present invention, will now be described below with reference to FIG. 64. The present embodiment also provides a method for carrying out a reactor internal applicable to a BWR plant, in which method, a core shroud is an object carried out. In the present embodiment, each of the operations in the eighth embodiment is executed except for the operations of the steps S29 to S32. In the step 27 in the present embodiment, the reactor internal equipments 80 stored in the step S27 of the eighth embodiment and the jet pumps 12 which are the other reactor internal equipments, are stored in the equipment storage container 85. The equipment storage container 85 storing the jet pumps 12 and the reactor internal equipments 80 is carried out of the reactor building 25 in the step S28. In the present embodiment, each effect produced in the first embodiment can be obtained. The steps S29 to S32 can be applied to each of previously-described the second, third, fourth, fifth, and sixth embodiments in the same manner as in the present embodiment. In other words, the steps S26 to S28 can be executed in place of Steps S8 and S9 in each of the second, third, fourth, fifth, and sixth embodiments.
058898301	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS The figures of the drawings show an exemplary embodiment of a containment chamber of the invention that is a crucible-like catch basin but is analogously applicable to a containment chamber constructed as a propagation chamber. Referring now in detail to the figures of the drawings, in which identical reference numerals identify identical components, and first, particularly, to FIG. 1 thereof, there is seen a fragmentary, longitudinal section through a nuclear power plant having a cooling system 1 for cooling a containment or retention chamber 2 constructed to receive core melt. A reactor pressure vessel 3 which is largely rotationally symmetrical about its primary axis 5 is disposed in a reactor cavern 48 formed by a supporting structure 36. The reactor pressure vessel 3 contains a reactor core 4. The containment chamber 2 is formed in the reactor cavern 48 below the reactor pressure vessel 3 through the use of a catch basin 28 for a core melt. The catch basin 28 has a floor 24 and a wall 25. A free space remains between the support structure 36 on one hand and the wall 25 and the floor 24 on the other hand, for an external cooling device 23 of the catch basin 28. In the interior of the catch basin 28, the floor 24 and the wall 25 are adjoined by a lining 38, for instance of zirconium oxide (ZrO.sub.2) tiles. A layer of sacrificial concrete 27, especially for lowering the melting point of a core melt, is disposed on the lining 38 toward the floor 24. A cooling pipe 6 for coolant fluid 7 is constructed as a flood pipe 31 which passes from a flooding container 8 through both the wall 25 and the adjoining support structure 36, with a slight inclination from the horizontal, into the catch basin 28. In the catch basin 28, the flood pipe 31 is closed by a closure element 15, in particular a closure element that opens as a function of temperature. In the flooding container 8, the flood pipe 31 is closed by a closure element 9 that opens as a function of a fluid level and in particular has a float 10. A compensator 29 which surrounds the flood pipe 31 between the wall 25 and the support structure 36, seals off the wall 25 from the external cooling device 23 and absorbs thermal expansion of the catch basin 28. The float 10 that seals the flood pipe 31 has an interior 11. A filler pipe 12, which has an inlet opening 13 geodetically above the flood pipe 31, is introduced into the interior 11. The inlet opening 13 is likewise located above an operative level 14 of the coolant fluid 7, in particular coolant water, that is located in the flooding container. The external cooling device 23 of the catch basin 28 communicates with the flooding container 8 through a supply line 26 that extends through the support structure 36 substantially horizontally below the reactor cavern 48. In the flooding container 8, the supply line 26 is likewise closed by a closure element 9 having a float 10. The closure element 9 of the supply line 26 also has a filler pipe 12 which extends into the interior 11 of the float 10, leads out of the coolant fluid 7 above the operative level 14 and is bent back in a U to enter the coolant fluid 7 again, where it ends in an inlet opening 13. A return 20 for internal cooling which is disposed above the operative level 14 and thus above the flood pipe 31, extends from the reactor cavern 48 into the flooding container 8. Inside the flooding container 8, this return 20 is closed by a further closure element 21, which has a further float 10 that is immersed approximately half-way into the coolant water 7. A ball valve 22 with a float ball is disposed between the further closure element 21 and the return 20. Each of the closure elements 9, 21 has a respective condensed water suction removal device 19. The return 20 extends in the reactor cavern 48 above the catch basin 28 through both the support structure 36 and an insulation 37 adjoining the support structure 36. The return 20 communicates with the interior of the catch basin 28. During normal operation of the nuclear power plant, the cooling system 1, which includes the external cooling device 23, the flood pipe 31, the return 20 and the closure elements 9, 21, 15, is closed. In particular, both the external cooling device 23 and the flood pipe 31 are filled with air. During normal operation of the nuclear power plant, the external cooling device 23 serves the purpose of operative air cooling, which prevents heating up of the support structure. Cooling air is fed from below through airshafts that are located outside the support structure 36, into the supply line 26, which is constructed as an annular channel and communicates with eight horizontal channels, to the outside of the catch basin 28. The cooling air rises on the outside of the catch basin 28 and the support structure 36 as it heats up and can escape into a non-illustrated reactor building of the nuclear power plant. The annular channel likewise communicates through eight pipes with the flooding container 8. During an accident involving melting of the reactor core 4, the flooding container 8 is flooded with additional coolant fluid, in particular coolant water 7, so that the level rises from the operative level 14 to an elevated level that is located above the inlet opening 13 of the float 10. The additional coolant fluid in this case is primary coolant water emerging from the primary coolant loop of the reactor core 4. The additional coolant fluid can optionally be fed from a separate, additional coolant fluid supply. The floats 10, which close the flood pipe 31 and the external cooling device 23, are filled with coolant water 7 and sink downward because of the decreasing buoyancy. As a result, both the flood pipe 31 and the external cooling device 23 are filled with coolant water. When the operative level 14 is exceeded, the external cooling 23 comes into operation first. A return of coolant water 7 through the external cooling device 23 takes place through six horizontally extending, non-illustrated channels above the operative level 14 into the flooding container 7. The return through the external cooling device 23 and the return 20 of the internal cooling are separate from one another. The core melt that emerges as the reactor core 4 melts down leads to heat development in the catch basin 28, as a result of which the closure element 15 of the flood pipe 31 likewise opens, since it opens as a function of temperature. As a result, the coolant fluid 7 flows into the interior of the catch basin 28 to cool the core melt. The elevated level inside the flooding container 8 thereupon drops, for instance by 30 cm to 60 cm, to a flooding level 32, so that the level of the coolant water 7 is at the same height in both the reactor cavern 48 and the flooding container 8. The coolant fluid 7 flowing into the catch basin 28 through the flood pipe 31 is heated and rises by natural circulation as is indicated by flow arrows 30 and flows back through the return 20 into the flooding container 8, as is also represented by the flow arrows 30. Opening of the closure element 9 of the external cooling device 23 causes the coolant water 7 to pass out of the flooding container 8 through the supply line 26, as is represented by flow arrows 44, so that it can reach the outside of the catch basin 28. The coolant water 7 evaporates there and is returned into the flooding container 8 through non-illustrated channels. As a result of the evaporation, cooling of the catch basin 28 from the outside occurs as well. The evaporated coolant water 7 rises inside the nuclear power plant, condenses, and passes back into the flooding container 8. Effective cooling of any core melt occurring in the catch basin 28 is assured over a long period of time through the use of the closure elements 9 for both the flood pipe 31 and the external cooling device 23, which elements open upon a rise of the level in the flooding container 8. In FIG. 2, the further closure element 21 of FIG. 1, having a float 10 and a ball valve 22 with a floatable ball, is shown on a larger scale. At the operative level 14, the float 10 is immersed approximately halfway in the coolant water 7. The floatable ball of the ball valve 22 rests on a ball position holder 33 that extends downward from the return 20 to the float 10. Even in the event of a pressure wave arising in the reactor cavern 48 and propagating through the return 20, the ball valve 22 seals off the float 10, so that the float remains protected. The float 10 is guided in guides 35, and it is thus displaceable along an axis 49. The ball valve 22 has a vent 34. During a normal operating state of the nuclear power plant, the return 20 is dry and in particular is filled with air. If the level inside the flooding container 8 rises from the operative level 14 to a flooding level 32, which is located geodetically above the further closure element 21, then the coolant water 7 reaches the ball valve 22 through the return 20. After the entry of the coolant water 7 into the ball valve 22, the floatable ball rises and uncovers an opening 50, through which the coolant water 7 can flow out of the return 20 into the float 10. As a result of the inflowing coolant water 7, the buoyancy of the float 10 decreases, and it sinks along the axis 49 in the flooding container 8, and therefore the coolant water 7 can flow out of the return 20 into the flooding container 8 in natural circulation. The flood pipe 31 of FIG. 1 is shown on a larger scale in FIG. 3. Inside the catch basin 28, the flood pipe 31 is closed by the closure element 15 that opens as a function of temperature and has a bale closure 16. The flood pipe 31 is surrounded between the support structure 36 and the catch basin 28 by the compensator 29, which rests sealingly on the catch basin 28 in a ball sealing seat 38. On a larger scale, FIG. 4 shows the closure element 15 of FIG. 3 that opens as a function of temperature. The bale or hoop closure 16 acts through a bale or hoop 42 to press a cap 40 firmly into a ball sealing seat 39 of the flood pipe 31. The bale 42 is firmly connected to the flood pipe 31 through a tightening screw 17, which has a melting bolt 43. The melting bolt 43 is formed of silver with a melting temperature of about 960.degree. C. A splash protector 41 between the melting bolt 43 and the cap 40 is disposed parallel to the flood pipe 31, to protect the melting bolt 43 against escaping coolant water 7. As a result, it is assured that melt-through of the melting bolt 43 is not delayed by evaporating coolant water 7, even if the ball sealing seat 39 should leak. FIG. 5 shows an alternative embodiment of a closure element 15, which opens as a function of temperature, for the flood pipe 31. The closure element 15 has a closure cap 18, which is soldered to the flood pipe 31 at two solder strips 45 through a silver strip 46 that surrounds the flood pipe 31. An insulator 47 having an air cushion is introduced between the silver strip 46 and abutting portions of the flood pipe 31 and the closure cap 18. If high heat develops in the containment chamber 2, the solder strips 45 and if applicable the silver strip 46 melt open, so that the closure cap 18 falls off and the flood pipe 31 opens. The closure elements 15 shown in FIG. 4 and FIG. 5 each have only one melting element 43, 46. As a result, the danger of unequal melting open of two melting elements that close the closure element, with the possibility of belated opening of the closure element, is averted. The invention is distinguished by a cooling system with a cooling pipe for cooling a containment chamber constructed to receive a core melt. The cooling is tripped through the use of a passive closure element. The closure element opens as a function of the level of coolant water in a flooding container, so that coolant water flows into the containment chamber or along its outside surfaces. The closure element preferably has a float which due to its buoyancy closes off the cooling pipe. The float is constructed in such a way that when a level of cooling water that is above an operative level is reached, the float is filled with coolant water through a filler pipe, and the cooling pipe sinks downward into the flooding container, thereby opening. The cooling system has a return that is extended above the fluid pipe that feeds coolant water into the containment chamber. Through the use of the return and the fluid pipe, a natural circulation of the coolant water develops, thereby assuring effective cooling of the containment chamber and the core melt caught therein.
H00006890	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1-4 depict several different embodiments of the fuel design of the present invention. In all, the effective smear density of the fuel is significantly less than that of a conventional fuel stack. Standard metallic reactor fuels are utilized, such as U-Zr and U-Pu-Zr. Other metallic fuels may alternatively be included. The invention does not have any applicability to nonmetallic, ceramic fuels because those fuels exhibit far less thermal conductivity than metallic fuels (2.5 W/m-k versus 20 W/m-k), and have much higher melting points (5000.degree. F. versus 2200.degree. F.). Ceramic fuels exhibit very little swelling, so the need for the porosity included in the present invention does not exist. FIG. 1 depicts a fuel form 110 including a longitudinally or axially extending channel 112. Channel 112 is typically formed when the fuel form 110 is cast. As will be explained more fully below, fuel form 110 completely fills the space defined within the cladding, but the presence of axial channel 112 results in the effective smear density of the fuel being less than if the channel was not included Total smear density will now be in the range of about 70 to 75%. Fuel form 110 is normally cast so that axial channel 112 is formed at that time. Alternatively, axial channel may be drilled or formed by other methods. FIG. 2 depicts another fuel form 210, which includes a plurality of peripheral, axially extending flutes 212. Again, like the axial channel 112 in fuel form 110, the flutes 212 result in a decreased smear density. FIG. 3 depicts a third fuel form 310 which is homogeneously porous and is comprised of powdered fuel. As the powdered fuel is loaded, such as with a vibrating feeder, it may be permeated with tag gas, which would then permit the elimination of a tag gas capsule in the fuel pin. Binary uranium zirconium powder would be one such powder that may be utilized for this embodiment. FIG. 4 depicts a fourth fuel form 410 which includes a plurality of gas voids 412 therein, created by the injection of gas into a molten fuel rod during the molding process. The gas may take the form of tag gas, which would eliminate the requirement of a tag gas capsule. The voids 412 within fuel form 410 are relatively evenly distributed in radial directions. However, fuel form 410 has been shown in section to show that the depicted form is not axially homogeneous. This aspect of the invention permits the fuel to be more concentrated at the ends of the form than at the central regions. The variation in the axial power profile would normally be in the neighborhood of about 50%, peak to minimum. This is a desirable feature because typically fission is more efficient in the axially central region of the pins. By concentrating more fuel adjacent the end regions, the axial pin power distribution curve can be flattened, with the potential of dramatically increasing power output. This is accomplished without decreasing the total amount of fuel in the fuel pin because, except for the voids 412, fuel form 410 extends outwardly all the way to the cladding. In prior designs, the fuel was more concentrated, but the requirement of the sodium thermal barrier between the fuel and the cladding reduced, by as much as 25% or more, the available space for the fuel. This axial variation of fuel density may also be achieved with fuel form 310 of FIG. 3 by compressing the ends thereof. The forces of compression typically would not pass entirely through the powdered fuel material, so that the fuel would be more compressed adjacent the end regions. FIGS. 5-7 schematically depict various fuel pin configurations made possible by the present invention. The basic difference between these three configurations is the number and position of the fission gas plenums. FIG. 5 illustrates a fuel pin, indicated generally with the numeral 114. Fuel pin 114 includes a single, lower fission gas plenum 116 disposed below fuel form or fuel material 110. Although fuel form 110, with axial channel 112, has been included in fuel pin 114 for illustration, it should be understood that any one of the other fuel forms, 210, 310 or 410 could alternatively be provided. With each of these fuel forms, at least a portion of the fuel material extends radially outwardly to the cladding member. Of course, depending upon the fuel form used, there may be slight manufacturing clearances in the range of 0.008 inch or so. However, for the purposes of this description, such fuel forms will still be considered to be extending out to the cladding. Also included in fuel pin 114 are a top end cap 120 and an upper blanket filled with fertile material such as depleted uranium, which enhances fission in the fuel region. Alternatively, a reflector, such as Inconel 600, may be used to reflect neutrons back into the fuel material. Both of these components are positioned above fuel material 110. A lower blanket 124 is disposed immediately below fuel material 110, and is held in position against fuel material 118 by a lower lock plug 126. A tag gas capsule 130, the details of which will be explained, is disposed in the lower portion of plenum 116, and is mounted against a bottom end cap 132 of fuel pin 114. Cladding 134 is provided to cover fuel pin 114. The fuel pin 114 is shown to be mounted to an attachment rail 36. Top and bottom end caps 120 and 132, upper and lower blankets 122 and 124, cladding 134, and attachment rail 36 are all of conventional design. Unlike conventional designs, fuel form 110 extends radially outwardly to the cladding 134, and does not include a sodium thermal barrier. In conventional designs, the thermal barrier serves to fix the position of the fuel material. In the depicted fuel pin 114, fuel form 110 is fixed in position by lower lock plug 126. As depicted, lower lock plug 126 is substantially cup-shaped, and fits against the inner walls of cladding 134. A swage tool (not shown) is used to push lower lock plug 126 into position and form dimples 128 in the lock plug and the adjacent cladding 134. The fit between lower lock plug 126 and cladding 134 is such that fission gases which are generated in fuel material 110 can pass through lower blanket material 124 and through the interface between the lock plug and the cladding, and into plenum 116. The configuration of the fuel pin of FIG. 6 is very similar to that of FIG. 5 except for the position of the fission gas plenum; therefore, the components have been numbered with corresponding numbers in the 200 series. While fuel form 210, having axial flutes 212, is shown to be included, the other fuel forms 110, 310 and 410 alternatively may be used. Fuel pin 214 includes a top end cap 220 and a tag gas capsule 230, the details of which will be explained, disposed at the upper end of an upper fission gas plenum 240. An upper lock plug 238, having swaged dimples 228, is disposed against an upper blanket 222, which is positioned immediately above the fuel material 210. A lower blanket 224 is disposed below the fuel, immediately above a bottom end cap 232. Conventional cladding 234 covers fuel pin 214, and it is mounted to an attachment rail 36. The configuration of the fuel pin 314 of FIG. 7 is also similar except that it includes both a lower and an upper fission gas plenum chamber 316 and 340. Fuel form 310 is depicted although again, the other forms may alternatively be included. Fuel pin 314 includes a top end cap 320, lower and upper lock plugs 326 and 338 with swaged dimples 328, upper and lower blankets 322 and 324, cladding 334, and a bottom end cap 332 which is adapted to be mounted to an attachment rail 36. FIG. 8 is a simplified schematic depiction of a liquid metal fast reactor, prototypic of a pool-type of reactor. While FIG. 8 does not depict any of the preferred embodiments of the invention, the figure will be used to describe the operation of the depicted designs. The reactor has been generally identified with the numeral 850. It includes a primary vessel 852 of heavy stainless steel which is contained in a reinforced concrete protective housing 854. The active core region, indicated generally at 856, contains nuclear fuel or fissile material and is disposed within primary vessel 852. Fuel is deposited in the previously-described fuel pins, indicated generally and schematically in FIG. 8 as 814. The fuel pins are then spaced inside fuel assemblies, although such assemblies have not been shown in FIG. 8. The fuel assemblies are surrounded by rows of reflector assemblies (not shown). Interspersed among the fuel assemblies are movable control rods 857, which are made of neutron absorptive material, and are used to control the rate at which fission occurs in the reactor 850. Only a few of these control rods 857 have been depicted, for simplification purposes. A coolant system, such as liquid sodium 858, is drawn from a pool in primary vessel 852 and is pumped through the core by a pump 860. This coolant 858 flows through each fuel assembly and between the fuel pins 814, traveling in an upward direction. The liquid sodium coolant 858 then passes from the top of core 856 through intermediate heat exchangers 862, where it releases its heat to a secondary sodium coolant system, shown generally at 864. Secondary sodium coolant system 864 is used to generate steam in a steam generator system 866. In the fuel pin designs depicted in FIGS. 5 and 6, tag gas capsules, such as capsules 130 and 230, are included. While a conventional tag gas capsule may be used in those designs, in one preferred embodiment of the invention, a novel tag gas capsule, shown generally at 910 in FIGS. 9-11, is included. As best seen in FIGS. 9 and 10, tag gas capsule 910 includes a tube 912 which has a top end 912a and a bottom end 912b. Tube 912 also includes a top end cap 914 and a bottom end cap 916. Bottom end cap 916 has a centrally disposed inner well 918 which comprises an undercut portion of the bottom end cap and is capable of being ruptured. Capsule 910 further includes an axially extending, centrally disposed penetrator member or rod 920 having an upper end 922 fixedly mounted centrally in a bore 921 disposed in top end cap 914. Although rod 920 is shown in FIGS. 9-11 as being cylindrical, it may also be rectangular or polyhedral. Rod 920 has a lower end 924 which may be pointed or angled as depicted in FIGS. 9-11, or it may be flat. The external configuration of inner well 918 of bottom end cap 916 is generally complementary to the external configuration of penetrator member 920, and the width of well 918 is at least as large as the width of penetrator member 920. While FIG. 11 illustrates a loose fit between penetrator 920 and well 918, in certain applications a closer fit may be desired in order to assist in the lateral support of penetrator 920. Penetrator member 920 is constructed of an alloy or material with a relatively high coefficient of thermal expansion, and tube 912 is constructed of an alloy or material with a relatively low coefficient of thermal expansion. For example, with a 3.12 inch long tube, it is anticipated that a differential thermal expansion of 0.009 inches could be achieved using a 20% CW 316 stainless steel penetrator member and a 2.25% Cr/1% Mo steel tube. This expansion difference is more than adequate to insure penetration of inner well 918. Assembly of capsule 910 is performed by positioning bottom end cap 916 on tube 912 and seal welding the tube bottom end. End 922 of penetrator member 920 is then inserted into bore 921, and brazed into place. Top end cap 914 with penetrator 920 is then inserted into tube 912 with end cap 916 so that the penetrator seats in well 918 of bottom end cap 916. A known preload is applied between the top end cap and the bottom end cap, and the top end of tube 12 is seal welded. Capsule 910 is inserted into a gas pressure chamber (not shown) and laser drilled at one end. The gas pressure in the capsule is then depressurized, back filled and pressurized with tag gas, and laser welded. When the capsule is placed in a fuel pin during reactor start up, an increase in fuel temperature will cause penetrator member 920 to expand axially more than tube 912 causing penetrator end 924 to rupture well 918 of the end cap thereby releasing tag gas into the fuel pin. Rupture of end cap 916 will occur at the peak of the fuel pin operating temperature profile (approximately 800.degree. F.), which is after the fuel slug-to-cladding-gap closure has begun. By delaying the release of a gas until peak operating temperatures are reached, the power to melt characteristics are improved. First, xenon, a widely used tag gas, has a low heat transfer coefficient. Therefore, when xenon is present in the gap in the fuel pin between the fuel slug and the cladding prior to fuel slug restructuring and closure of the gap, there is a reduction of the heat transport capabilities from the fuel to the sodium coolant. Consequently, a lower power to melt characteristic is obtained by releasing tag gas into the fuel pin prior to fuel utilization. By delaying the injection of the tag gas as disclosed in the present invention, there is an improvement in the heat transport characteristics from the fuel to the sodium coolant and a concomitant increase in the power to melt characteristics during initial start up. Also, by delaying tag gas injection until after the closure of the fuel slug-to-cladding-gap has begun, the power to melt characteristics during reactor start up is further improved. Improvement in the power to melt characteristics during reactor start up can result in significant cost savings. Moreover, use of this novel tag gas capsule which ruptures in-core eliminates the need to use verification equipment during fabrication, such as with conventional tag gas capsules which are ruptured in the fuel pin and then verified prior to insertion in the reactor. It is important to note that although we have disclosed this novel tag gas capsule in connection with use in a liquid metal reactor, this aspect of the invention could also be used in other types of fast reactors. OPERATION OF THE DEPICTED EMBODIMENT The operation of the fuel pin 114 of FIG. 5 will first be described, although it will be appreciated that the operation of the embodiments of FIGS. 6 and 7 are quite similar. When the control rods 857 (see FIG. 8) are partially withdrawn and fission begins within the fuel material 110, heat begins to build up. Because the radial periphery of fuel material 110 is in abutment with the inner diameter of cladding 134, substantial amounts of heat are conveyed through the cladding and into the liquid sodium coolant 858 (FIG. 8). Thus, even in the initial stages of fission, heat is being transferred to the secondary coolant system 864 and to the steam generator system 866. As fission continues in fuel pin 114, the fuel material 110 swells, and this swelling begins to fill axial channel 112 in fuel form or material 110. If other fuel forms 210, 310 or 410 are utilized, such swelling would correspondingly fill the channels or voids in those forms. As fission progresses, fission gases are generated. These gases leach downwardly through the lower blanket 124 and pass through the cladding/lower lock plug interface, and into lower plenum 116. These gases are quite hot so it is a very real advantage of the present invention that the plenum can be located adjacent the lower portion of fuel pin 114. Because liquid sodium coolant 858 is passing upwardly between the fuel pins 814, that coolant will be much cooler as it passes a lower plenum than if it passed the fuel region of the fuel pin prior to flowing past an upper plenum. This results in lower temperatures and gas pressures in a lower plenum, which, in turn, increases the effective capacity of the lower plenum or may even permit reduction in plenum size. In conventional fuel pins (not shown), the presence of the sodium thermal bond normally requires that the plenum be disposed above the fuel region. As discussed above, the presence of the sodium thermal bond in such systems also has the drawback of taking up as much as 25% or more of the space in the fuel region, and during fission will also be taking up valuable space in the plenum as the sodium melts and is forced into the plenum by the swelling fuel material. The operation of the fuel pin 214 in FIG. 6 is similar to that of 114 except for the fact that there is an upper plenum 240, rather than a lower plenum. Therefore, the plenum lengths would be equal to that of the sodium bonded fuel pin, except that the sodium no longer is present to take up space in the plenum. An advantage of fuel pin 214, however, is that it shows that the invention permits retrofitting in existing reactors. Therefore, the design of the entire reactor would not have to be substantially modified to adopt the fuel forms of FIGS. 1-4. In fact, the reactor could be upgraded to increase power production. Fuel pin 314 of FIG. 7 also operates in a similar fashion except that the fission gases will flow into both an upper and a lower plenum, 340 and 316, respectively. A particular advantage with this embodiment is that it includes both an upper and a lower lock plug 338 and 326, which can be exerting pressure against both sides of the fuel material 310. This construction has the advantage of concentrating fuel adjacent the axial ends of the fuel, which increases fission and power production at those regions. This construction also tends to flatten out the axial power distribution curve, which can dramatically increase the efficiency and productivity of the reactor. It should be appreciated that this axial compression of the ends of the fuel material can also be performed in fuel pins 114 and 214, but is probably most efficiently done with the design of fuel pin 314. One other difference in fuel pin 314 is that it deletes the tag gas capsules shown in other depicted embodiments. This deletion is possible when fuel form 310 has been impregnated with tag gas. Thus, if there is a leak in fuel pin 314, the impregnated tag gas will pass out of the fuel pin during fission just as if a tag gas capsule were included. Elimination of the tag gas capsules in the other depicted fuel pin designs is also possible if tag gas has been impregnated into the fuel forms of those pins as well. Finally, fuel form 410 of FIG. 4 permits the concentration of fuel adjacent the axial ends without requiring any axial compression. Thus, fuel form 410 may be used in any one of the depicted fuel pins equally well. The other advantages of fuel form 410 is that it readily facilitates the impregnation of tag gas into its voids 412, which permits elimination of the tag gas capsule. It should be understood that various changes and modifications to the preferred embodiment described herein will be apparent to those skilled in the art. These and other changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is, therefore, intended that such changes and modifications be covered by the following claims.
	summary
046631127	description	DETAILED DESCRIPTION OF THE INVENTION The conductivity differences between pure and doped material in a fuel rod are evaluated by means of an eddy current measuring method. To this end, the impedance of a test coil surrounding the fuel rod is measured. The frequency of the a-c voltage feeding this test coil method is chosen so low that conductivity differences due to different doping of the fuel pellets within the tube can be measured. The position of a test coil concentrically surrounding the fuel rod is changed from the beginning to the end of the testing range. In the process, the impedance of the test coil is measured as a function of its position. The test coil is fed with an a-c voltage, the frequency of which is so low that the measured value in the region of a fuel pellet of pure uranium dioxide differs distinctly from that which is measured in the region of the doped fuel pellet. The method according to the invention is based on the finding that the conductivity of the fuel pellets increases steeply even with slight doping and small differences in the conductivity can be measured with a magnetic field penetrating an electrically conducting tube. At a suitably low frequency, sufficiently large impedance differences occur at the test coil. Preferably, the measured values are recorded by a recorder as a function of the position of the test coil. For this purpose, the measured values can be digitalized in a transient recorder and stored in this form and optionally evaluated simultaneously or later by a computer. In this manner, fast changes of the measured value, for instance at the pellet boundaries, which are not displayed by a measuring recorder which is too sluggish, become visible. This procedure makes it possible to select a value sufficiently high for practical requirements (for instance 10 cm/sec) for the passage velocity of the fuel rod through the test coil. As a result of measuring the impedance of a test coil surrounding the fuel rod in accordance with the invention, a profile typical of the contents of the fuel rod is produced. This allows not only the determination of the doping concentration of the fuel pellets and thereby a distinction of pellets with different dopings, even if the differences between pellets is only 1%. In addition, metallic occlusions in the pellet, undesirable spacings between adjacent pellets and their skewed position can be determined, as well as the location of structural material, for instance, of springs or aluminum oxide pellets. Finally, the length of the pellet column can also be measured in this manner. Observing the proper radiation protection measures, the invention can also be used, of course, for measuring fuel rods which have been irradiated. The invention utilizes the well-known eddy current method and the test equipment and apparatus known for carrying it out. In this method, the change of the impedance of a test coil is evaluated if a test piece is introduced into the latter. The change in impedance depends here on quality features of the test piece such as material faults, dimensional deviations, etc. Here, however, the test piece was always of metal throughout. With the invention, however, ceramic or semiconducting material is measured which is surrounded by an electrically conducting metal tube. As in the known cases, the absolute value of the impedance can be measured and indicated with the invention; higher sensitivity, however, is obtained with a reference value method, in which the difference between the measured value of the test piece and the measured value of a comparison object is evaluated. The comparison object is preferably a tube which is surrounded by a comparison coil and is advantageously filled with a fuel pellet, the data of the tube and the fuel pellet being the same as the reference data of the fuel rods to be measured. However, the comparison coil can also surround the fuel rod to be measured physically next to the test coil. Preferably, the test coil or an additional auxiliary coil is subjected to at least one additional a-c voltage of higher frequency and the impedance so determined is measured and evaluated. In this manner, other properties of the test piece such as, for instance, thickness, eccentricity and homogeneity of the tube wall of the fuel rod can be measured at the same time by appropriate choice of the frequencies. The invention is particularly well suited for an automated test in which the measured profile of the test pieces is compared with the desired profile of a good fuel rod and from the result of this comparison, a switch setting for sorting the test pieces is controlled. An embodiment example of the invention will be explained in greater detail with reference to the drawings. In the measuring arrangement of FIG. 1 is shown a fuel rod generally designated with 1 and its cladding tube 10.1. A spring 11, two pellets 12 of aluminum oxide, 36 fuel pellets 13 with different doping and a further pellet 12 of aluminum oxide are arranged between two closures 14 in the cladding tube 10.1. This fuel rod is moved through a test coil 2.1 in the direction of the arrow x, the measured impedance being recorded according to FIG. 2 by a recorder 4. Recorder 4 is controlled by an eddy current test equipment 3 to which an additional comparison coil 2.2 is connected which surrounds an empty comparison tube section 10.2. The comparison coil and the test coil are fed from the eddy current test equipment with an a-c voltage of correspondingly low frequency, and the impedance difference between the auxiliary coil 2.2 and the test coil 2.1 is measured and, after suitable amplification, is recorded by the recorder 4 over the length x of the fuel rod. In FIG. 2 can clearly be seen the individual fuel pellets since they meet at the end faces not over the full areas but only over a circular ring. Each pellet is therefore imaged by a half-wave. The height level of these half-waves is in addition a measure for the doping, in this case for the Gd.sub.2 O.sub.3 content in percent, of a fuel pellet which consists otherwise of UO.sub.2. With this profile therefore one can without problem distinguish pure UO.sub.2 pellets (Gd.sub.2 O.sub.3 content=0%) from doped pellets; with suitable calibration, the degree of doping can even be measured. The profile indicates furthermore the location of structural material, where the branch a images the two aluminum oxide pellets 12 and branch b, the spring 11. With the invention, the frequency of the a-c voltage at the test coil is below 10 kHz; in the known eddy current measuring methods, on the other hand, it is usually above 50 kHz. With a rod diameter of 12.5 mm and a wall thickness of 0.98 mm of the cladding tube, a frequency between 6.6 and 7.5 kHz has primarily been found to be particularly advantageous. With a thinner rod diameter of 9.7 mm and a wall thickness of 0.7 mm, 9 to 9.5 kHz have been used. The air gap between the individual pellets and the cladding tube is about 190 .mu.m. The foregoing is a description corresponding, in substance, to German application P 33 10 755.6, dated Mar. 24, 1983, international priority of which is being clamped for the instant application, and which is hereby made part of this application. Any material discrepancies between the foregoing specification and the specification of the aforementioned corresponding German application are to be resolved in favor of the later.
050283804	description	DESCRIPTION OF PREFERRED EMBODIMENTS The method for the identification the leakiness of a neutron-capturing pencil of a nuclear reactor, according to the invention, shall be described firstly in relation to FIG. 2. As shown schematically in the above-mentioned figure, the pencil, or control rod, marked Cr is placed in an impervious chamber marked 1. This chamber is filled with an aggressive solution called an analyzing solution. The aggressive solution may be formed by a solution of an acid taken from one of the following groups: nitric acid, sulphuric acid, hydrochloric acid. The concentration of this solution ranges between N/100 and 10.sup.N. As a non-exhaustive example, it may be N/30 where N designates the normality of the solution. The above-mentioned analyzing solution is then put under pressure, marked HP, in order to make this solution penetrate the pencil Cr through the leakiness of this presumably defective pencil. The pressure is then relaxed and the solution is brought to a low pressure level (marked LP) so that the solution, which has penetrated the defective radius, can go out of it and return to the impervious chamber 1. The solution is then analyzed in order to show up, in this solution, metallic salts of metals forming the core of the pencil. For a pencil Cr, with a core formed by an alloy of cadmium Cd, indium In and silver Ag, the metallic salts are silver, indium and cadmium salts. In addition to showing up nitrocompounds, the method according to the invention may advantageously consist in detecting, in the solution contained in the chamber 1 after the pressure is relaxed, a radioactive isotope of the alloy, more especially that of silver, marked Ag 110 m, with reference to a threshold value of concentration of this isotope. Advantageously, the radioactive isotope of silver Ag 110 m is detected by gamma spectrometry. In order to improve the detection of the above-mentioned radioactive isotope of silver Ag 110 m, prior to the step in which the pencil Cr is placed in the impervious chamber 1, filled with acid solution, this solution then forming the starting solution, the method according to the invention may also consist in determining, by spectrometry, the concentration in radioactive isotopes, including Ag 110 m, of the starting solution mentioned above. The concentration of the starting solution in radioactive isotopes, including Ag 110 m, is then chosen as the threshold value of concentration to measure the concentration in radioactive isotopes, notably silver. The chemical concentration of silver in water may also be measured. According to a particularly advantageous aspect of the method according to the invention, the pressure (HP) applied to the analyzing solution in order to make this solution penetrate the pencil Cr is maintained for a period of about 10 minutes at least. This pressure may advantageously be equal to several bars. Furthermore, in order to accelerate the chemical reaction of the solution on the metals forming the core of the pencil Cr, the solution may be subjected, before or after the introduction of the pencil in the impervious chamber 1, to heating. Furthermore, the method according to the invention may include a step consisting in the measurement of the chemical concentration of silver, indium and cadmium in the water before the pencil is placed in the chamber, said step being repeated after the pressurizing and heating operations. A more detailed description of a device enabling the implementing of the method according to the invention shall be given with reference to FIG. 2. According to the above-mentioned figure, the device includes the above-mentioned impervious chamber, marked 1, capable of receiving at least one pencil Cr to be analyzed. Of course, it will be understood that the device according to the invention can be advantageously implemented so that the impervious chamber 1 is capable of taking not one pencil Cr, but an entire cluster in order to make checks on it. The impervious chamber 1 is provided with a circuit 2 for the supply of analyzing solution. The circuit for the supply of analyzing solution has a high pressure conduit provided with a valve V1 and a low pressure conduit provided with a valve V2. It will be understood, of course, that the actuation of the valves V1 and V2, with the HP conduit being connected, for example, to a compressor system, makes it possible, firstly, to pressure the analyzing solution in the impervious chamber 1 and to keep it under pressure by opening the valve V1, the valve V2 being closed or, on the contrary, by the closing of the valve V1 and the opening of the valve V2, the valve V2 being installed on the low pressure conduit, to bring the pressure down to a sufficiently low value, to enable the solution that has penetrated the pencil Cr, after chemical attack on the constituent elements of its core, to come out in the solution contained in the impervious chamber 1. The high pressure circuit HP may be connected, for example, to a compressor delivering pressure ranging from 1 to 15 bars. As a non-restrictive example, this pressure may be in the region of 12 bars. The low pressure circuit LP may, on the contrary, be connected to a circuit used to set up, in the impervious chamber 1, pressure close to that of the environment of this chamber or equal to a few bars. As will be further seen in FIG. 2, the device according to the invention also has an analysis circuit 3 connected to the impervious chamber 1. This analysis circuit 3 has at least one circulation pump 32 for the analyzing solution and a counting vessel 30 for the counting of radioactive particles, including the silver isotope Ag 110 m. Means 31 for the counting of the radioactive particles are also planned, these means being associated with the counting vessel 30. Advantageously, the counting vessel 30 and the counting means 31 may be formed by a system, normally available in the market, for the counting of gamma rays. Of course, the counting vessel 30 and the counting means 31 are advantageously complemented by a display system 33 enabling the display of the result of the above-mentioned counting measurements. Furthermore, the analysis circuit 3 also has a valve V3 for taking samples of the analyzing solution. With reference to FIG. 2, the sequence of operations enabling the application of the method is as follows: According to a particularly advantageous mode, and prior to the pressurizing of the impervious chamber 1 and before the introduction of the pencils Cr to be tested in the impervious chamber 1, a sample of the analyzing solution is taken by means of the valve V3 in order to measure the residual content of the solution in metallic salts, notably, silver salts. In the same way, a count is done, using the means 31 for the counting of radioactive particles in this starting solution, in order to determine the threshold value corresponding to the presence of the radioactive isotopes, including the above-mentioned Ag 110 m. After the pencil Cr to be tested is introduced into the impervious chamber 1, the opening of the valve V1 enables the pressurizing of the chamber, and this pressurizing is done at a value ranging from 1 to 15 bars. This pressure is maintained for at least ten minutes, then the valve V1 is again closed and the valve V2 is opened, thus enabling a depressurization to be done. The display means 33 can be used to follow the development of the on-line count signal delivered by the counting means 31. A sampling of the analyzing solution through the valve V3 then makes it possible to make an evaluation of the material in the fluid and a quantitative analysis of the silver, indium or cadmium ions or their radioactive isotopes therein. The comparison of the values measured, in nitrocompounds, of the constituent elements of the core of the pencil with their value in the starting solution, taken as a threshold value, then makes it possible to identify the pencil Cr or the leaky cluster. As is further shown in FIG. 2, the analysis circuit 3 also has, connected as a bypass to this analysis circuit, a circuit 4 to heat the solution. Advantageously, the solution heating circuit 4 may be formed by any circuit for the electrical heating of a thermostat controlled chamber used to carry the analyzing solution, put into circulation by the circulation pump 32, to a temperature ranging from 30.degree. to 90.degree. C. As a non-restrictive example, this temperature may be 75.degree. C. FIG. 3 shows the diagram of a complete installation of a device according to the invention. Of course, the pencil or pencils and the corresponding cluster have a non-negligible degree of radioactivity, and the manipulation of the latter can be contemplated only in immersion in the water of the pool of the corresponding nuclear reactor. To this end, and although the tools used to manipulate the pencil or pencils and the cluster have not been shown in FIG. 3, the device according to the invention, and especially the impervious chamber 1, is immersed in the pool P of the nuclear reactor. Of course, the set of circuits formed by the high pressure circuit HP, the low pressure circuit LP, the impervious chamber 1 and the analysis circuit 3 is impervious to the water of the pool. FIG. 3 also shows the valve V3 in a chamber shielded against ionizing radiation, it being possible to perform the analysis of chemical derivatives of the constituent elements of the core of each pencil in the above-mentioned chamber. We have thus described a method and device enabling the detection or identification the leakiness of one or more neutron-capturing pencils of a nuclear reactor. The method and device according to the invention are particularly advantageous inasmuch as they enable systematic checking of parts essential to the working of a pressurized-water nuclear reactor, namely essential parts such as neutron-capturing pencils and the corresponding clusters for the checking of the working of the reactor.
	claims	1. A method for automatically adjusting a radiation diaphragm having a plurality of individually adjustable diaphragm elements, for subsequently obtaining a diagnostic radiation image, with a diagnostic radiation dose, of a subject, comprising the steps of:irradiating the subject with a radiation dose substantially lower than said diagnostic radiation dose passing through said diaphragm with said diaphragm elements open to generate a non-diagnostic localization exposure of the subject from radiation striking a radiation detector, having a detector surface in a detector plane comprised of a plurality of pixels, said exposures being composed of image points respectively formed by combining a plurality of adjacent pixels into a group;electronically, non-manually analyzing said localization exposure for determining only an exterior contour of the subject projected into said detector plane; andusing said contour, automatically electronically calculating respective positions for the individual diaphragm elements at which the individual diaphragm elements substantially abut the exterior contour, and, before obtaining said diagnostic radiation image, automatically electronically moving the individual diaphragm elements to the respective calculated positions to substantially prevent direct irradiation of said radiation detector by radiation unattenuated by the subject when subsequently obtaining the diagnostic radiation image. 2. A method as claimed in claim 1 wherein said localization exposure contains at least one direct radiation region struck by radiation unattenuated by the subject, and a subject region struck by radiation attenuated by the subject, and wherein the step of analyzing said localization exposure comprises converting said localization exposure into a representation wherein said direct radiation region is designated with a first value and said subject region is designated with a second value. 3. A method as claimed in claim 1 wherein said radiation propagates in a primary beam direction, and wherein said diaphragm elements are disposed in a diaphragm plane, and wherein the step of calculating the respective positions of the individual diaphragm elements comprises calculating said positions using coordinates of at least one point on the contour of the subject in the localization exposure, a position of the detector plane relative to said primary beam direction, and a position of the diaphragm plane relative to said primary beam direction. 4. A method as claimed in claim 3 comprising calculating the respective positions using coordinates of said at least one point on the contour that, in said projection in the detector plane, form an outermost point of the contour in a direction of the diaphragm element whose position is being calculated. 5. A method as claimed in claim 3 wherein said diaphragm radiation image is subsequently obtained with radiation emitted from a focal spot of a radiation source, and wherein said radiation detector has a detector surface containing a plurality of detector elements disposed in rows and columns of a matrix, said detector surface being disposed perpendicularly to said primary beam direction, said method comprising the further steps of:generating said localization exposure with radiation originating from said focal spot; andcalculating the respective positions of the individual diaphragm elements using a coordinate system for defining said coordinates of said at least one point on the contour, said position of the detector plane, and said position of the diaphragm plane, having an origin at said focal spot and coordinate axes respectively proceeding in said primary beam direction and parallel to said rows and columns. 6. A method as claimed in claim 5 wherein said diaphragm plane is disposed perpendicularly to said primary beam direction, and wherein the step of calculating the respective positions of the individual diaphragm elements comprises, for each diaphragm element:determining, as intermediate coordinates, coordinates of a point on the contour of the subject in the detector plane at which the diaphragm element would initially contact the contour as the diaphragm element is moved toward the contour; andmultiplying said intermediate coordinates with a quotient of coordinates in said coordinate system representing the position of the diaphragm plane and coordinates in said coordinate system representing the position of the detector plane, for obtaining final coordinates for the diaphragm element. 7. A method for automatically adjusting a radiation diaphragm having a plurality of individual adjustable diaphragm elements, for subsequently obtaining a diagnostic radiation image, with a diagnostic radiation dose, of a subject, comprising the steps of:irradiating the subject with a radiation dose substantially lower than said diagnostic radiation dose passing through said diaphragm with said diaphragm elements open to generate a non-diagnostic localization exposure of the subject from radiation striking a radiation detector, having a detector surface in a detector plane comprised of a plurality of pixels;electronically, non-manually analyzing said localization exposure for determining only an exterior contour of the subject projected into said detector plane;using said contour, automatically electronically calculating respective positions for the individual diaphragm elements at which the individual diaphragm elements substantially abut the exterior contour, and, before obtaining said diagnostic radiation image, automatically electronically moving the individual diaphragm elements to the respective calculated positions to substantially prevent direct irradiation of said radiation detector by radiation unattenuated by the subject when subsequently obtaining the diagnostic radiation image; andadding said localization exposure pixel-by-pixel to the subsequently obtained diagnostic radiation image. 8. A method as claimed in claim 7 wherein said localization exposure contains at least one direct radiation region struck by radiation unattenuated by the subject, and a subject region struck by radiation attenuated by the subject, and wherein the step of analyzing said localization exposure comprises converting said localization exposure into a representation wherein said direct radiation region is designated with a first value and said subject region is designated with a second value. 9. A method as claimed in claim 7 wherein said radiation propagates in a primary beam direction, and wherein said diaphragm elements are disposed in a diaphragm plane, and wherein the step of calculating the respective positions of the individual diaphragm elements comprises calculating said positions using coordinates of at least one point on the contour of the subject in the localization exposure, a position of the detector plane relative to said primary beam direction, and a position of the diaphragm plane relative to said primary beam direction. 10. A method as claimed in claim 9 comprising calculating the respective positions using coordinates of said at least one point on the contour that, in said projection in the detector plane, form an outermost point of the contour in a direction of the diaphragm element whose position is being calculated. 11. A method as claimed in claim 9 wherein said diaphragm radiation image is subsequently obtained with radiation emitted from a focal spot of a radiation source, and wherein said radiation detector has a detector surface containing a plurality of detector elements disposed in rows and columns of a matrix, said detector surface being disposed perpendicularly to said primary beam direction, said method comprising the further steps of:generating said localization exposure with radiation originating from said focal spot; andcalculating the respective positions of the individual diaphragm elements using a coordinate system for defining said coordinates of said at least one point on the contour, said position of the detector plane, and said position of the diaphragm plane, having an origin at said focal spot and coordinate axes respectively proceeding in said primary beam direction and parallel to said rows and columns. 12. A method as claimed in claim 11 wherein said diaphragm plane is disposed perpendicularly to said primary beam direction, and wherein the step of calculating the respective positions of the individual diaphragm elements comprises, for each diaphragm element:determining, as intermediate coordinates, coordinates of a point on the contour of the subject in the detector plane at which the diaphragm element would initially contact the contour as the diaphragm element is moved toward the contour; andmultiplying said intermediate coordinates with a quotient of coordinates in said coordinate system representing the position of the diaphragm plane and coordinates in said coordinate system representing the position of the detector plan, for obtaining final coordinates for the diaphragm element.
	summary
	claims	1. A nail lamp comprising:an upper housing, comprising a light diffusing material;a lower housing, adapted to mate with the upper housing, wherein when the upper and lower housings are mated, an enclosed space is formed between the upper and lower housings; anda printed circuit board, coupled to the lower housing and positioned in the enclosed space between the upper and lower housings, wherein the printed circuit board comprises a plurality of exterior-facing light emitting diodes and interior-facing emitting diodes,wherein exterior-facing light emitting diodes are positioned on a first surface of the printed circuit board, while the interior-facing emitting diodes are on a second surface of the printed circuit board that is opposite to the first surface,light emitted by the exterior-facing light emitting diodes strike a surface of the light diffusing material,light emitted by the interior-facing light emitting diodes does not strike a surface of the light diffusing material, but rather are directed through apertures formed in the lower housing into a treatment chamber below the enclosed space and the lower housing, where the treatment chamber will receive a hand or foot of a user of the nail lamp, and the hand or foot of a user will be exposed to light emitted by the interior-facing light emitting diodes. 2. The nail lamp of claim 1 wherein the light diffusing material scatters light received from the exterior-facing light emitting diodes to provide a relatively uniform illumination on an exterior surface of the upper housing. 3. The nail lamp of claim 1 wherein the treatment chamber comprises sufficient width to accommodate five fingers of a human hand placed on a relatively flat surface. 4. The nail lamp of claim 1 further comprising a base plate wherein the base plate is removably coupled to a lower housing of the nail lamp. 5. The nail lamp of claim 1 further comprising sensors coupled to a printed circuit board enclosed in the enclosed space, wherein when the sensors detect a hand or foot is not present in the treatment chamber, the nail lamp is automatically turned off. 6. The nail lamp of claim 1 wherein the lower housing comprises:a first wall, wherein the first wall forms an upper boundary of the treatment chamber;a second wall and a third wall, wherein the second and third walls are angled with respect to the first wall;a fourth wall adjacent to the second wall; anda fifth wall adjacent the third wall. 7. The nail lamp of claim 1 wherein the circuitry further comprises a button coupled to a timer. 8. The nail lamp of claim 1 wherein the exterior-facing light emitting diodes emit light of wavelengths ranging from 390 nanometers to 700 nanometers, and the treatment chamber facing light emitting diodes emit light of wavelengths ranging from 100 nanometers to 400 nanometers. 9. The nail lamp of claim 1 wherein the light diffusing material of the upper housing is translucent. 10. The nail lamp of claim 1 wherein the exterior-facing light emitting diodes emit light having a different wavelength range from the interior-facing light emitting diodes. 11. The nail lamp of claim 1 wherein the exterior-facing light emitting diodes emit light having a wavelength in a range from about 620 nanometers to about 740 nanometers. 12. The nail lamp of claim 1 wherein the exterior-facing light emitting diodes emit light having a wavelength in a range from about 495 nanometers to about 570 nanometers. 13. The nail lamp of claim 1 wherein the interior-facing light emitting diodes emit light having a wavelength of 400 nanometers or less, and the exterior-facing light emitting diodes emit light having a wavelength of 450 nanometers or greater. 14. The nail lamp of claim 1 wherein the interior-facing emitting diodes emit light in a first direction, the exterior-facing light emitting diodes emit light in a second direction, and the first direction is opposite of the second direction. 15. A nail lamp comprising:an upper housing, comprising a shell, an opening for a power input and a plurality of exterior facing light emitting diodes, wherein the exterior facing light emitting diodes can emit light through the shell;the shell comprises a light diffusing material that scatters light from the exterior facing light emitting diodes to provide a more uniform illumination across an exterior surface of the shell compared to an uneven illumination without the light diffusing material;a lower housing that forms a cavity, coupled to the upper housing, comprising openings through which a plurality of cavity facing light emitting diodes can emit light through, wherein the cavity comprises sufficient width to accommodate five fingers of a human hand placed on a flat surface;circuitry, enclosed between the upper and lower housing, comprising at least one printed circuit board comprising the cavity facing and exterior facing light emitting diodes;a button,a control circuit, coupled to the button and the power input,a timer, coupled to the control circuit; anda rechargeable battery coupled to the control circuit. 16. The nail lamp of claim 15 wherein the battery is external to the nail lamp and can removably couple to a power supply to recharge the battery, and when the battery is not coupled to the power supply, the battery can be removably coupled to the power input of the nail lamp to provide power to operate the nail lamp. 17. The nail lamp of claim 15 wherein the battery is external to the nail lamp and the nail lamp further comprises a charging dock, wherein the charging dock comprises a first port that can be coupled to the external battery, and a second port that can be coupled to the power input of the nail lamp. 18. The nail lamp of claim 15 wherein the battery is external to the nail lamp and the nail lamp further comprises a battery port, wherein the battery can be removably coupled to the battery port. 19. The nail lamp of claim 15 wherein the light diffusing material of the upper housing is translucent. 20. The nail lamp of claim 15 wherein the exterior-facing light emitting diodes emit light having a different wavelength range from the interior-facing light emitting diodes. 21. The nail lamp of claim 15 wherein the printed circuit board comprises a plurality of exterior-facing light emitting diodes and interior-facing emitting diodes, the exterior-facing light emitting diodes are on a first surface of the printed circuit board, and the interior-facing emitting diodes are on a second surface of the printed circuit board that is opposite to the first surface. 22. The nail lamp of claim 15 wherein the interior-facing emitting diodes emit light in a first direction, the exterior-facing light emitting diodes emit light in a second direction, and the first direction is opposite of the second direction. 23. A nail lamp comprising:an upper housing, comprising a translucent light-diffusing material;a lower housing, adapted to mate with the upper housing, wherein when the upper and lower housings are mated, an enclosed space is formed between the upper and lower housings; anda printed circuit board, coupled to the lower housing and positioned in the enclosed space between the upper and lower housings, wherein the printed circuit board comprises a plurality of exterior-facing light emitting diodes and interior-facing emitting diodes,the exterior-facing light emitting diodes emit visible light comprising a visible, non-ultraviolet wavelength, and the interior-facing emitting diodes emit ultraviolet light,the exterior-facing light emitting diodes are positioned on a first surface of the printed circuit board, while the interior-facing emitting diodes are on a second surface of the printed circuit board that is opposite to the first surface,the interior-facing emitting diodes emit light in a first direction, the exterior-facing light emitting diodes emit light in a second direction, and the first direction is opposite of the second direction,light emitted by the exterior-facing light emitting diodes strike a surface of the translucent light-diffusing material,light emitted by the interior-facing light emitting diodes does not strike a surface of the translucent light-diffusing material, but rather are directed through apertures formed in the lower housing into a treatment chamber below the enclosed space and the lower housing, where the treatment chamber will receive a hand or foot of a user of the nail lamp, and the hand or foot of a user will be exposed to light emitted by the interior-facing light emitting diodes. 24. The nail lamp of claim 23 wherein the exterior-facing light emitting diodes emit light having a different wavelength range from the interior-facing light emitting diodes. 25. The nail lamp of claim 23 wherein the interior-facing light emitting diodes comprises ultraviolet LEDs, and the exterior-facing light emitting comprises non-ultraviolet LEDs. 26. The nail lamp of claim 23 wherein the interior-facing light emitting diodes emit light having an ultraviolet wavelength, and the exterior-facing light emitting diodes do not emit light having an ultraviolet wavelength.
	claims	1. A method for ablating hyaluronan-based hydrogels, the method comprising the steps of:(a) preparing hyaluronan-based hydrogels; and(b) performing X-ray irradiation to the hyaluronan-based hydrogels to induce a degradation of the hyaluronan-based hydrogels by a gel-to-sol transition during the X-ray irradiation. 2. The method according to claim 1, wherein the X-ray irradiation is performed using hard X-rays. 3. The method according to claim 1, wherein the X-ray irradiation is performed using X-rays in the range of 10-60 keV. 4. The method according to claim 1, wherein the degradation kinetics of the hyaluronan-based hydrogels is determined by total X-ray dose during the X-ray irradiation. 5. The method according to claim 4, wherein the total X-ray dose to initiate the transition is in the range of 0.2˜1 J g−1. 6. The method according to claim 4, wherein the total X-ray dose to complete the transition is in the range of 2˜4 J g−1. 7. A method for fabricating three-dimensional microchannels of hyaluronan-based hydrogels with X-ray ablation, the method comprising the steps of:(a) preparing hyaluronan-based hydrogels; and(b) performing X-ray irradiation to the hyaluronan-based hydrogels via a mask transmitting X-rays locally to induce a degradation of the hyaluronan-based hydrogels by a gel-to-sol transition during the X-ray irradiation. 8. The method according to claim 7, wherein the X-ray irradiation is performed using hard X-rays. 9. The method according to claim 7, wherein the X-ray irradiation is performed using X-rays in the range of 10-60 keV. 10. The method according to claim 7, wherein the depth and the width of the microchannels are tunable by adjusting the X-ray dose and the mask width, respectively. 11. The method according to claim 7, wherein the degradation kinetics of the hyaluronan-based hydrogels is determined by the total X-ray dose during the X-ray irradiation. 12. The method according to claim 7, wherein the total X-ray dose to initiate the transition is in the range of 0.2˜1 J g−1. 13. The method according to claim 7, wherein the total X-ray dose to complete the transition is in the range of 2˜4 J g−1.
	summary
	claims	1. A drawing apparatus configured to perform drawing on a substrate with a plurality of charged particle beams, the drawing apparatus comprising:an irradiation optical system including a collimator lens on which a diverging charged particle beam is incident;an aperture array configured to split the charged particle beam from the irradiation optical system into a plurality of charged particle beams;a converging lens array configured to form a plurality of crossovers of the plurality of charged particle beams from the aperture array; anda projection optical system including an element in which a plurality of apertures corresponding to the plurality of crossovers are formed, and a plurality of projection lenses corresponding to the plurality of apertures and configured to project charged particle beams from the plurality of apertures onto the substrate,wherein the converging lens array includes converging lenses disposed such that each of the plurality of crossovers, which are formed by the converging lenses from the charged particle beam incident on the aperture array at incidence angles associated with aberration of the irradiation optical system, is aligned with corresponding one of the plurality of apertures in the element, andthe converging lenses include a converging lens eccentric relative to corresponding one of the plurality of apertures in the element. 2. The drawing apparatus according to claim 1, wherein the eccentric converging lenses is eccentric so as to compensate for the aberration of the irradiation optical system. 3. The drawing apparatus according to claim 1, wherein the collimator lens has a front focal plane located at a position deviating from a position of a crossover from which a charged particle beam diverges and is incident on the collimator lens. 4. The drawing apparatus according to claim 1, wherein the aperture array includes an aperture eccentric relative to corresponding one of the plurality of apertures in the element with the eccentric converging lens. 5. The drawing apparatus according to claim 1, wherein the aperture array is disposed at a front focal plane of the converging lens array, and includes an aperture eccentric relative to corresponding one of the plurality of apertures in the element with the eccentric converging lens by the same amount as the eccentric converging lens. 6. The drawing apparatus according to claim 1, wherein the aperture array is disposed at a position deviating from a front focal plane of the converging lens array, and includes an aperture which is eccentric relative to corresponding one of the plurality of apertures in the element with the eccentric converging lens by an amount different from that by which the eccentric converging lens is eccentric. 7. The drawing apparatus according to claim 1, wherein the drawing apparatus comprises a plurality of groups arranged in parallel, each group including the irradiation optical system, the aperture array, the converging lens array, and the projection optical system. 8. The drawing apparatus according to claim 1, wherein the element includes a blanker array. 9. The drawing apparatus according to claim 1, wherein the element includes a stop aperture array. 10. A drawing apparatus configured to perform drawing on a substrate with a plurality of charged particle beams, the drawing apparatus comprising:an irradiation optical system including a collimator lens on which a diverging charged particle beam is incident;an aperture array configured to split the charged particle beam from the irradiation optical system into a plurality of charged particle beams;a converging lens array configured to form a plurality of crossovers of the plurality of charged particle beams from the aperture array; anda projection optical system including an element in which a plurality of apertures corresponding to the plurality of crossovers are formed, and a plurality of projection lenses corresponding to the plurality of apertures and configured to project charged particle beams from the plurality of apertures onto the substrate,wherein the converging lens array includes a converging lens eccentric relative to corresponding one of the plurality of apertures in the element,wherein the irradiation optical system is configured to adjust an aberration thereof such that each of the plurality of crossovers, which are formed by the converging lenses from the charged particle beam incident on the aperture array at incidence angles associated with the aberration of the irradiation optical system, is aligned with corresponding one of the plurality of apertures in the element. 11. The drawing apparatus according to claim 10, wherein the collimator lens includes a plurality of charged particle lenses, andwherein the irradiation optical system is configured to adjust at least one of a power and position of each of the plurality of charged particle lenses so as to change the aberration with a front focal plane position and a front principal plane position of the collimator lens kept. 12. The drawing apparatus according to claim 10, wherein the irradiation optical system is configured to form an irradiation optical system crossover at a front-side position of the collimator lens, andwherein the irradiation optical system is configured to adjust the aberration by adjusting a focal length of the collimator lens, and adjusts a position of the irradiation optical system crossover in accordance with the adjusted focal length. 13. The drawing apparatus according to claim 12, wherein the irradiation optical system includes a charged particle source, andwherein the irradiation optical system is configured to adjust the position of the irradiation optical system crossover by displacement of the charged particle source. 14. The drawing apparatus according to claim 12, wherein the irradiation optical system includes a crossover adjustment optical system arranged at a front side of the irradiation optical system crossover, andwherein the irradiation optical system is configured to adjust the positions of the irradiation optical system crossover by adjustment of a power of the crossover adjustment optical system. 15. The drawing apparatus according to claim 10, wherein the eccentric converging lens is eccentric so as to compensate for the aberration of the irradiation optical system. 16. The drawing apparatus according to claim 10, wherein the collimator lens has a front focal plane located at a position deviating from a position of a crossover from which a charged particle beam diverges and is incident on the collimator lens. 17. The drawing apparatus according to claim 10, wherein the aperture array includes an aperture eccentric relative to corresponding one of the plurality of apertures in the element with the eccentric converging lens. 18. The drawing apparatus according to claim 10, wherein the aperture array is disposed at a front focal plane of the converging lens array, and includes an aperture eccentric relative to corresponding one of the plurality of apertures in the element with the eccentric converging lens by the same amount as the eccentric converging lens. 19. The drawing apparatus according to claim 10, wherein the aperture array is disposed at a position deviating from a front focal plane of the converging lens array, and includes an aperture which is eccentric relative to corresponding one of the plurality of apertures in the element with the eccentric converging lens by an amount different from that by which the eccentric converging lens is eccentric. 20. The drawing apparatus according to claim 10, wherein the drawing apparatus includes a plurality of groups arranged in parallel, each group including the irradiation optical system, the aperture array, the converging lens array, and the projection optical system. 21. The drawing apparatus according to claim 10, wherein the element includes a blanker array. 22. The drawing apparatus according to claim 10, wherein the element includes a stop aperture array. 23. A method of manufacturing an article, the method comprising:performing drawing on a substrate using a drawing apparatus;developing the substrate on which the drawing has been performed; andprocessing the developed substrate to manufacture the article,wherein the drawing apparatus is configured to perform drawing on the substrate with a plurality of charged particle beams, the drawing apparatus including:an irradiation optical system including a collimator lens on which a diverging charged particle beam is incident;an aperture array configured to split the charged particle beam from the irradiation optical system into a plurality of charged particle beams;a converging lens array configured to form a plurality of crossovers of the plurality of charged particle beams from the aperture array; anda projection optical system including an element in which a plurality of apertures corresponding to the plurality of crossovers are formed, and a plurality of projection lenses corresponding to the plurality of apertures and configured to project charged particle beams from the plurality of apertures onto the substrate,wherein the converging lens array includes converging lenses disposed such that each of the plurality of crossovers, which are formed by the converging lenses from the charged particle beam incident on the aperture array at incidence angles associated with aberration of the irradiation optical system, is aligned with corresponding one of the plurality of apertures in the element, andthe converging lenses includes a converging lens eccentric relative to corresponding one of the plurality of apertures in the element. 24. A method of manufacturing an article, the method comprising:performing drawing on a substrate using a drawing apparatus;developing the substrate on which the drawing has been performed; andprocessing the developed substrate to manufacture the article,wherein the drawing apparatus is configured to perform drawing on the substrate with a plurality of charged particle beams, the drawing apparatus including:an irradiation optical system including a collimator lens on which a diverging charged particle beam is incident;an aperture array configured to split the charged particle beam from the irradiation optical system into a plurality of charged particle beams;a converging lens array configured to form a plurality of crossovers of the plurality of charged particle beams from the aperture array; anda projection optical system including an element in which a plurality of apertures corresponding to the plurality of crossovers are formed, and a plurality of projection lenses corresponding to the plurality of apertures and configured to project charged particle beams from the plurality of apertures onto the substrate,wherein the converging lens array includes a converging lens eccentric relative to corresponding one of the plurality of apertures in the element,wherein the irradiation optical system is configured to adjust an aberration thereof such that each of the plurality of crossovers, which are formed by the converging lenses from the charged particle beam incident on the aperture array at incidence angles associated with the aberration of the irradiation optical system, is aligned with corresponding one of the plurality of apertures in the element.
042773067	abstract	Methods and apparatus for plasma impurity control in toroidal plasma systems such as Tokamak plasma systems is disclosed which utilize an axisymmetrical plasma diffusion pump system.
	description	This application is a divisional of U.S. patent application Ser. No. 10/150,894, filed on May 17, 2002 now abandoned, which claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application Ser. No. 60/292,109, filed on May 18, 2001, entitled “3He Reactor With Direct Electrical Conversion.” 1. Field of the Invention The present invention relates to electrical current generation from nuclear fusion. More particularly, the invention concerns improvements in a Helium-3 (3He) fusion device, and particularly a (3He—3He) fusion device with electrostatic reaction confinement. 2. Description of Prior Art By the year 2050 AD, the Earth may have run out of all economically recoverable fossil fuels, such as oil and natural gas. There should still be plenty of coal, but only if mankind is willing to put up with its associated greenhouse gasses. Also, there may be no place to put the toxic residues of present nuclear fission reactors. West Valley N.Y. doesn't want them and neither does Nevada. Worse yet, in 2050 AD all the alternate sources of energy, like hydroelectric, wind, wood, tidal, geothermal and solar, will not supply even 25% of the energy mankind will need to feed the 10 billion people that will populate Earth by that time. Present day nuclear fission reactors operate like a slow atomic (“A”) bomb, splitting heavy plutonium or uranium atoms into smaller elements and giving off power. American and Russian nuclear engineers and physicists have succeeded in slowing down the fission reaction to produce useful power, as exemplified by Three-Mile Island and Chernobyl, (a mixed blessing!). Others have accomplished this more successfully. France generates a significant part of its energy requirements from fission reactors and has achieved a perfect safety record. Their reactors are all of the same design and are run by nuclear engineers. In the U.S., the reactors are built differently and their operation is left mostly to technicians. But France still has the same problem that the U.S. has in regard to the disposal of the toxic residues. Mankind may have no alternative but to develop the ability to harness useful energy from nuclear fusion. To date, however, it has not been feasible to produce a controlled, sustainable nuclear fusion reaction, at least not to the point of producing useful power. Nuclear fusion devices must operate like a slow hydrogen (“H”) bomb, fusing light weight atoms such as hydrogen or helium. Present nuclear fusion devices are classified by the methods used to support the nuclear fusion reaction, which takes place at a temperature much hotter than the surface of the Sun. No container on Earth can hold it. The reaction must therefore be suspended by either electromagnetic, gravitational (inertial) or electrostatic fields. A fusion device known as the “TOKAMAK” at Princeton, N.J. operates by magnetic confinement in a huge 250 ton supercooled electromagnet. The electromagnet exquisitely controls and shapes a magnetic field, which physically supports the reaction. As far as known, the TOKAMAK device has never operated longer than a few seconds at a time and the federal government has withdrawn its support. With inertial confinement, hundreds of powerful lasers are pointed concentrically at a gold capsule containing a small amount of hydrogen. The pressure and the temperature of the capsule are raised to fusion levels and produce a burst of energy. This process must then be repeated, perhaps 100 times per second, to provide a reasonably continuous flow of power. Two such devices exist in the USA, one in Rochester, N.Y. and one in Livermore, Calif. As far as known, neither has ever approached “break-even” in power generation. U.S. Pat. No. 4,826,646 of Bussard, the contents of which are incorporated herein by this reference, discloses a fusion device using electrostatic confinement of the reaction. The fusion reaction is confined by electrostatic forces in a large potential well within a vacuum chamber. The potential well is created by confining electrons using a quasi-spherical-cusp magnetic field to form a highly negatively charged virtual anode. Positive ions, such as Deuterium (D), Tritium (T), and/or 3He are introduced into the vacuum chamber and pulled into the well, where they have an opportunity to fuse according to fusion reactions involving D-T, D-D, and D-3He. Dr. Gerald Kulcinski and co-investigators at the Fusion Technology Institute at the University of Wisconsin/Madison are seeking to demonstrate nuclear fusion energy using inertial electrostatic confinement (IEC) and combinations of 3He and D ion starting materials. The fusion reaction is confined in a 1000 pound cylindrical aluminum vacuum chamber. This chamber has an inner diameter of 91 cm and an inner height of 65 cm. It contains a pair of concentric, tungsten alloy spherical grids with a very strong electrostatic field inside them. The outer grid is 45 cm in diameter and is grounded. The inner grid is 10 cm in diameter and is connected to a large negative potential via a ceramic insulated electrode that feeds through a small opening in the vacuum chamber. When positive ions (e.g., 3He or D ions) are introduced into the vacuum chamber, they fall into the potential well created by the electrostatic field within the grids and oscillate backwards and forward at increasing speed until two ions collide, fusing into a 4He ion and releasing high energy protons. This device has been used to successfully demonstrate D-3He and D-D fusion with significant high-velocity proton generation at 40 kV acceleration voltages across the two grids. Although these are significant achievements, no provision has been made to recover useful energy from the device in excess of the input power required to sustain the reactions. Moreover, as far as known, the foregoing device has produced no successful reaction based on the fusion of two 3He ions into one 4He ion with the release of a stream of high velocity protons in the 1 to 10 MeV range. To achieve 3He—3He fusion will require a 200 kV grid voltage. However, the investigators at the Fusion Technology Institute have not been able to use voltages over 80 kV because of arcing between the ceramic insulated electrode and the vacuum chamber. A fusion reaction using 3He alone would be desirable because the fuel (He-3) is non-radioactive, the process is non-radioactive, and the residue (He-4) is non-radioactive. In fact, the residue, He-4, is used to inflate childrens' balloons. Thus, He-3 may be the perfect fuel for fusion-based nuclear reactions. On the other hand, the D-3He and D-D fusion reaction generates a steady stream of neutrons, protons, electrons, helium-4 (He-4), tritium, gamma and x-rays. Accordingly, improvements are indicated in the construction and implementation of fusion devices. A fusion device that is especially adapted for 3He reactions (particularly 3He—3He reactions) includes two concentric high-voltage spherical grids, preferably of a tungsten alloy. Both grids are positioned in a vacuum chamber that is relatively large in size (e.g., at least about 3 ft. in diameter). The outer grid is grounded and the inner grid can be held at a high negative DC voltage, such as −200,000 volts. The high voltage ceramic insulated electrode that feeds through the vacuum chamber outer wall of the prior art IEC fusion device is also replaced with a wide spaced hermetic feed-through insulator, which depends on air separation rather than ceramic insulation so as to provide a long air leakage path sufficient to suppress any sparking. For an 3He—3He reaction, the grids are maintained in a 3He ion environment within the vacuum chamber at a pressure of about one Torr (1 mm Hg). Positive 3He ions are attracted to the grounded outer grid and move toward it. As each 3He ion approaches the outer grid, it passes through the grid and comes under the attraction of the high negative voltage of the inner grid. The 3He ion accelerates across the inner grid and passes though the opposite wall at high (but not relativistic) speed. It then comes under the influence of the grounded outer grid, decelerates, turns around and progresses back through both grids. This oscillatory motion continues until finally one 3He ion going across the grids collides with a similar ion returning from the other side. The collision results in a nuclear reaction whereby the two neutrons in the two 3He ions combine into a He-4 ion. Two protons from one of the 3He ions joins the He-4 ion, completing it, and the other two protons for the other 3He ion come off at relativistic speeds, and fly out through both grids. Traveling at a sizable fraction of the speed of light (relativistic speeds), they have very large energies in a band ranging from 1 to 10 MeV, with a peak at about 5 MeV. These protons would normally impact the outer case of the vacuum chamber enclosure, creating heat, which could be used to form steam, but the device would then represent a heat engine, subject to the classic 40% maximum efficiency of all heat engines. Instead, another embodiment of the invention is proposed for use in a fusion device having a potential well formed by either a spherical grid anode or a virtual anode according to the Bussard patent described above. According to this embodiment of the invention, one or more concentric spherical cages (with optional proton diverters) are added outside the potential well of the device to slow down the speeding protons, collect them, and produce an electrical output. A voltage divider arrangement can be used to obtain a desired electrical output. In a further alternative embodiment, a magnetron coverts proton energy directly into microwave energy. As summarized above, a basic device according to the invention consists of a vacuum chamber enclosure containing two concentric spheres made of tungsten wire grid material and carrying a voltage differential of 200 kV for a 3He—3He fusion reaction, with the inner grid being negative. The tungsten wires are quite fine (0.8 mm in diameter) compared to the separation between the wires to insure good transparency to the proton stream output. The vacuum is a “soft” vacuum of about 0.1 to 1.0 Torr of 3He. This is about the atmospheric pressure seen at 100 km altitude above sea level. This means that at this altitude, and above, a vacuum chamber should not be needed, for example in a nuclear rocket engine. For a 3He—3He fusion reaction, positive 3He ions are injected into the area near the grounded outer grid. Each 3He ion slides down the potential hill and passes through the outer grid, falls under the influence of the negative inner grid (−200 kV), where it picks up speed until it passes through the inner grid. The 3He ion will have then achieved maximum velocity (prior to fusion) and will continue through the center of the inner grid at the same velocity, pass through the far side of the inner grid, and enter the influence of the far side of the outer grid, which is at ground potential. The 3He ion slows, stops, and then reverses and goes back through both grids in an oscillating pattern. Eventually the 3He ion will meet another 3He ion traveling in the opposite direction and collide with it. The collision will result in a 4He ion, and two fusion protons. The major portion of the energy will be in the two 5 MeV protons, but the fusion is a three-body reaction which produces a spread of energies between 1 MeV and 10 MeV, with a broad peak at about 5 MeV. The energy is ½ mv2. The proton has a single charge, so the velocity is very high, about a tenth of the speed of light. The proton travels out through both grids and, if unimpeded, impacts on the case of the vacuum enclosure, giving up its energy in the form of heat. One could potentially put some coils of tubing in the vacuum chamber outer shell and generate steam as the power output of the device, but this would then be a heat engine and would be subject to the usual Carnot Cycle efficiency limit of all heat engines of about 40%. While such a nuclear fusion device would still be a great breakthrough, it is preferable to find some way of direct electrical conversion of the proton stream into an electron current, to avoid the limitations of the Carnot Cycle. The output energy is in the form of a stream of high-velocity protons. To recover this energy, two things must be done. First, the proton stream must be slowed down, or stopped, to recover the momentum energy. Second, the proton stream must be converted into an electron current. Both objects can be accomplished by inserting an additional positively charged wire cage well outside the grounded high-voltage grid. If this cage is charged to +5 MV, it will slow down 5 MeV protons to a stop and permit them to drift over to the nearest wire of the cage and discharge. Neutralizing some of these protons by inserting electrons from an outside source (a very high resistor to ground) will produce an electron current at the 5 MV voltage level. Reduction of this voltage to a 1 MV level will permit direct connection to high-voltage DC transmission lines. Because the stream of protons has a spread of energies all the way from 1 MeV through 10 MeV, use of a number of tungsten wire cages, as many as ten (or more), and respectively charged with 1, 2, 3, 4 - - - to 10 MV, is proposed. This will produce ten energy sources at various levels of voltage, each requiring a separate voltage reduction scheme to arrive at the 1 MV level of the transmission lines. These voltage reduction elements may further include a device for periodically reversing the polarity of the DC current 60 times per second so as to permit the production of conventional AC power for the National Grid. However, waveform modification to go to a sinusoidal wave will probably be necessary. The presence of a 10 MV voltage level on one of the cages raises some interesting problems. At sea-level 5000 volts will jump across a distance of 0.25 inches (more or less, depending on the shape of the electrodes). Thus, 200 kV will jump an arc of 10 inches, 1 MV will jump an arc of 50 inches, and 10 MV will jump an arc of 500 inches, or more than 40 ft. Fortunately, the arcing voltage limits are much higher at 100 km of altitude. As one goes up from sea level, the voltage necessary to jump one inch, halves in Quito, Ecuador, but then gradually approaches an inversion point at about 30,000 ft. of altitude. From then on it increases more or less linearly with the reciprocal of pressure. Thus, allowing a generous safety factor, a safe spacing of the 10 MV cage from its low voltage neighbors and from the grounded grid, might be as low as 15 ft. in the vacuum of space (or within a vacuum chamber). However, a ground-based device operating at sea level atmospheric pressure might well require a 100 ft. diameter high-vacuum chamber enclosure (providing a 50 foot spacing around the 10 MV cage). The presence of so many spherical cages might give some concern about loss of transparency to the proton stream. In such a case, one may employ diversion of the proton stream slightly away from each wire, but still keeping it within the slowing influence of the wire. In post WW II vacuum tube technology, power pentodes were displaced from some of their market share by the advent of the 6L6 “beam” tetrode. This tube dispensed with the normal suppresser grid and substituted a “beam-forming” extension of the grid, which diverted the electron beam slightly to one side and counteracted the space-charge, but without the detrimental effect of the suppresser grid which it replaced. A similar technique is used here, whereby an extra diverter grid wire is placed in front of each collector wire (and given a charge slightly more positive than that on the collector wire. This would divert the proton stream slightly aside to avoid hitting the wire. However the protons destined to strike the wire would still be slowed to a stop but would circle around the wire before landing on it. The faster portions of the proton stream will travel right through, unencumbered, with but a slight bend in their path around the collector wire rather than hitting it. Thus transparency can be improved. Based on the voltage-pressure dependent electrical arcing characteristics discussed above, the first inventive embodiment calls for a relatively large device (e.g., a vacuum chamber diameter of at least about 3 ft.), and a feed electrode passing through the vacuum chamber with a large space gap so as to provide a long air leakage path sufficient to suppress any sparking when carrying high voltages (e.g., −200 kV). In particular, as shown in FIGS. 1 and 1A, the 3He fusion device (2) includes a vacuum chamber (4) having a cylindrical outer shell (6) (other shapes could be used). The vacuum chamber (4) contains a spherical outer grid (8) that is connected to ground potential (9) and a spherical inner grid (10) that is connected via a shielded electrode (12) to a voltage source (13) capable of producing −200 kV. The electrode is fed through a large opening (14) in the vacuum chamber outer shell (6). This opening is preferably large enough to provide an air gap of at least about 10 inches between the electrode (12) and the outer shell. This is the air gap required at sea level to prevent arcing of the −200 kV electrode as it enters the vacuum chamber at full atmospheric pressure. The gap between the opening in the vacuum chamber outer shell and the −200 kV electrode is hermetically sealed with a suitable material, such as an acrylic spacer (14). To initiate a 3He—3He fusion reaction, the inner grid (10) is charged to −200 kV and 3He ions (+) are dropped into the outermost space between the grounded outer grid (8) and the outer shell (6) of the vacuum chamber (4). Each 3He ion drifts toward the center and passes through the grounded grid (8). The ion then comes under the influence of the −200 kV inner grid (10) and accelerates, achieving maximum speed (not relativistic) as it passes through the −200 kV grid. The 3He ion then proceeds at constant speed across the inner grid (10) until it passes through the interior of this grid. The 3He ion then decelerates under the influence of the far side of the outer (grounded) grid (8) until it stops, reverses and travels back towards where it came from. The 3He ion again accelerates, decelerates and oscillates back and forth. Eventually, the ion in returning will strike another ion coming across. The collision will generate a nuclear fusion reaction, generating a 4He ion and two relativistic protons. A neutron from each 3He will form the two neutrons of the 4He ion. Two protons from one 3He ion will complete the 4He ion. The remaining two protons will come off the remaining 3He ion at relativistic speed and will randomly race through any grid (if unimpeded) and impact the outer shell (6) of the vacuum chamber (4), producing heat. This heat could be used to produce steam, but energy production efficiency would be limited by the limitation of the Carnot cycle efficiency to about 40%. As shown in FIG. 2, one or more isolated concentric collector cages (20) are located outside of the potential well created by the high-voltage outer and inner grids (8, 10) of FIG. 1. Although not shown, the collector cages (20) could be similarly located outside the potential well formed by a virtual anode in a fusion device constructed according to the Bussard patent described above. Each cage (20) attracts protons until the potential at the cage (20) equals that of the immediately surrounding space. Protons that are near the potential of a cage (20) will impact on the cage. If a small stream of electrons is now supplied to the cage (20) (not sufficient to significantly change the cage potential) an electron current, at the cage potential, will be obtained. Thus, the energy contained in the relativistic speed of the protons will be given up and transformed into a small electron current but at MV levels. Insofar as each proton has a unit charge, each proton with an energy of “n” MeV will have an electrical potential of “n” MV. The collector cages (20) will thus provide direct electrical conversion, circumventing the Carnot cycle efficiency of all heat engines. If ten such isolated cages (20) are located beyond the high-voltage grids (8, 10), then ten electron currents can be obtained at 1, 2, 3, 4 - - - 7, 8, 9, 10 MV voltage levels. Now, if capacitor banks (30) are placed across each collector cage (20), to ground (9), and if each capacitor bank (30) comprises multiple series elements, the series-charged capacitors representing each capacitor bank (30) can discharge in parallel, resulting in a voltage divider. Each collector cage (20) will then have its voltage level (DC) transformed down to a common 1 MV level for cross-country power transport. Also, if the discharges are simultaneous, and the polarity of each discharge is sequentially reversed, 60 times per second, the output will be AC. FIG. 2 shows that there may be as many as ten collector cages (20), distributed across the distance from the outer grounded grid to the vacuum chamber outer shell. The energy of the fusion protons will be distributed over a range of 1 to 10 MeV. As indicated above, given that the protons are particles having a unit charge, the voltage distribution of these particles (due to the varying speeds of the relativistic protons, will vary between 1 MV and 10 MV. Thus, a 5 MeV proton will tear randomly through both of the high-voltage grids (8, 10) without slowing appreciably, and if brought to rest half way out the voltage gradient to the outermost cage (20), would be at a potential of 5 MV. As many such protons accumulate at this point, they will come to rest on the isolated collector cage (20) located there, bringing the cage to an equilibrium potential of 5 MV if no current is drawn from it. If a small number of electrons are drawn from a collector cage (20) (not enough to disturb the field potential at that pointy, useful current at 5 MV can be produced. If, at this point, a capacitor bank (30) having five 1 MV capacitors is connected in series across this cage (20) to ground, the capacitors will eventually charge to 5 MV. If the five capacitors are periodically discharged in parallel, rather than in series, the output will be 1 MV, which can be directly attached to an existing 1 MV inter-city power transmission grid. Similarly, ten such collector cages (20), equally distributed (potential-wise) across the space between the outer (grounded) grid (8) and the vacuum chamber outer shell (6), and charging to 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 MV, can be series-connected to ground (9) across 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 1 MV capacitors, respectively, for each cage. Discharging these individual capacitors in parallel will produce a multiple 1 MV power (DC) supply. A possible objection to the previous embodiments is that some of the relativistic protons will hit the high-voltage grids (8, 10) and the collector cages (20), thereby immediately coming to a stop and giving up their energy in heat. This problem can be minimized (1) by having the grids (8, 10) and cages (20) be a small percentage of the area traversed by the relativistic protons and (2) by positioning an extra grid diverter wire (40) in front of each collector cage wire (42), charged slightly more positive than the collector wire itself This arrangement, which is shown in FIG. 3, will split the stream (50) of relativistic protons, sending them to each side of the collector wire (42), avoiding the impact (or minimizing it) and reducing the losses from this source. As noted above, a somewhat analogous technique was used in the old W.W. II 6L6 “beam tetrode,” which shaped the emission from the cathode to avoid the space charge near the plate (anode) and eliminate the need for an extra “suppression” grid which otherwise would have been necessary. In a related embodiment, the diverter wires (40) are not separately charged, but are connected (see 44) to the next more positive collector cage wire (42). Because this system depends for its diversion on the voltage developed by the proton stream on the collector cage wires (42), it should be self-adjusting. Varied placement of the diverter wires (40) themselves would produce some control. In this embodiment, the collector cage (20) having the highest expected voltage (10 MV) has a fixed voltage applied to it to locate the outer voltage of the energy limit of the highest expected energy field (about 10 MeV), and thus set the distribution pattern for all the collector cage voltages. In this embodiment, the current through each collector cage (20) is controlled such as to adjust the voltage level of the cage, so that the divided voltage will be close to the desired level of 1 MV. In this embodiment, shown in FIG. 4, a proton stream (50) is injected at high velocity radially into a magnetic field (52) in the open center of a magnetron cavity (54). The magnetron's magnetic field (52) bends the proton stream (50) into a circular path. As the proton stream (50) passes the cusps (56) in the magnetron structure, a voltage will be induced in each of the four magnetron cavities (58). As the proton element approaches the other side of the cavity (58), another voltage will be induced, augmenting the original voltage pulse which will arrive a fraction of a microsecond later, having had to navigate the circumference of the magnetron (54). This will happen at all four cavities (58) simultaneously. A single inductive loop (60) inserted into any cavity (58) will draw energy from the proton stream (50), thus drawing energy from all four cavities (58) simultaneously, as is done in military radar magnetrons. In this way, the energy in high-velocity proton stream (50) from the device is directly electrically converted into microwave energy, without having to go through the wasteful loss of the Carnot Cycle efficiency limit common to all heat engines. In each of the foregoing seven embodiments, a fusion device with direct electrical conversion has been shown and described. Unlike current energy production techniques, the fusion device of the invention is not a heat engine. It generates electricity directly and is not limited by the “Carnot cycle” efficiency. More importantly, the fusion device does not generate carbon dioxide or any of the other “greenhouse” gasses. Additionally, the fuel (3He) is non-radioactive. A 3He—3He fusion reaction process produces no residual radioactivity and the residue (4He) is non-radioactive. In fact, the residue, 4He, is used to inflate childrens' balloons. Thus, 3He may be the perfect fuel and a 3He—3He reaction may be the perfect reaction process. However, there are a couple of caveats. The first is that the reaction takes place at a temperature much hotter than the surface of the Sun. The other is that there is practically no 3He on Earth. More particularly, there is a tiny bit of 3He deep in the Earth, from when the Earth was first formed. It comes up to the Earth's surface as a tiny percentage of natural gas. There is also a small additional supply of He-3 in old nuclear bombs in the form of radioactive tritium gas (3H), which decays into, of all things, 3He in about 13 years (half-life). Substantially more 3He comes from the Sun in an ionized form on the solar wind. The ions hit the Earth's magnetic field and get diverted away. Because the ions cannot land on Earth, they drift around and eventually land on the Moon. They have been landing there for four billion years. It is estimated that there is more 3He energy on the Moon than mankind has ever had in the form of fossil fuels on Earth. 3He on the Moon is contained in an ore called ilmenite (iron titanate), which contains titanium dioxide. 3He comes adsorbed on the titanium dioxide. The ilmenite must be scraped off the Moon surface and refined to obtain the titanium dioxide. The recovered titanium dioxide may then be placed under a large transparent plastic hood and held there two weeks, until the Moon rotates around towards the Sun. It will become very hot under the hood and boil off the 3He. Then the process needs to wait two weeks until the Moon rotates around away from the Sun. This will result in very cold temperatures under the hood, which should go a long way toward liquefying the 3He. It is estimated that a single shuttle load (25 tons) of 3He brought back from the Moon would supply all of the energy needs of the USA for a year. The cost of the 3He, including the shuttle, the Moon colony, and the ilmenite refinery, amortized over a suitable number of decades, has been calculated to be an equivalent oil cost of about $8 per equivalent barrel of oil. The current price for a barrel of oil is about $22 (in early 2000 AD). The generation of 3He fusion power is thus not only technically feasible, it is economically feasible. In fact, in the opinion of applicant, it is inevitable. Accordingly, fusion device has been disclosed with provision for direct electric conversion of a relativistic proton stream into electric current at a voltage level of one million V DC. While various embodiments of the invention have been shown and described, it should be apparent that many variations and alternative embodiments could be implemented in accordance with the invention. For example, although 3He—3He reactions have been discussed in the foregoing detailed description, it will be appreciated that other fusion reactions using 3He and other materials, such as Deuterium, could be implemented. Non-3He fusion reactions, such as D-D, may also be possible. It is understood, therefore, that the invention is not to be in any way limited except in accordance with the spirit of the appended claims and their equivalents.
050858238	summary	TECHNICAL FIELD The present invention relates generally to control rod drives used in nuclear reactors and, more specifically, to a latch assembly effective for preventing rotation of the control rod drive when actuated. BACKGROUND ART In one type of nuclear reactor, control rods are selectively inserted and withdrawn from a nuclear reactor vessel for controlling the operation thereof. Each of the control rods is typically positioned by a conventional control rod drive which includes a ball screw or spindle threadingly engaging a ball nut for raising and lowering the ball nut as the spindle is rotated either clockwise or counterclockwise. A hollow piston rests upon the ball nut at one end thereof and at its other end is conventionally joined to the control rod. Displacement of the ball nut provides displacement of the piston which in turn inserts or withdraws the control rod in the reactor vessel. In order to achieve faster insertion of the control rod than could be obtained by normal rotation of the ball spindle, which is conventionally referred to as a scram operation, a rapid flow of high-pressure water is injected through the control rod drive past the piston for lifting the piston off the ball nut in a relatively short time for quickly inserting the control rod into the reactor vessel. The high-pressure water is channeled to the control rod drive through a scram line pipe attached to a high-pressure water accumulator. In one type of occurrence which allows for rapid backflow of the water past the piston, due to, for example, a break in the scram line, the backflow may cause a large reverse pressure on the piston which in turn provides a back force on the control rod ball nut. This back force can cause reverse rotation of the ball spindle with corresponding withdrawal of the control rod. Withdrawal of one of the control rods due to such a backflow occurrence may cause damage to adjacent fuel in the reactor vessel, requiring replacement thereof leading to undesirable down time of the reactor and economic losses. In order to prevent the above occurrence, a conventional electromechanical brake is provided in the control rod drive for holding the ball spindle from rotating unless the brake is energized. The brake is sized for restraining rotation of the ball spindle against such forces due to backflow of water over the piston when the control rod drive motor is not operating. And, when the control rod drive motor is operating, the motor itself is sized for providing adequate torque for resisting the forces due to the backflow of water in the event of the above-described occurrence. To ensure operability of the brake, the brake is periodically tested. However, the brakes are located adjacent to the reactor vessel, which is inaccessible during operation of the reactor due to the radiation field emanating from the reactor vessel. The radiation field continues at reduced levels also during shutdown of the reactor, which would require inspectors to wear suitable protective clothing and limit their time in the area. In one nuclear reactor embodiment, there are about 205 control rod drives, including a respective number of brakes, which would necessarily require a substantial amount of time for testing all of the brakes. Testing of the brakes during reactor shutdown would, therefore, be relatively costly to accomplish, which is additionally economically undesirable since the reactor is not operating for producing power. Since conventional electromechanical brakes typically utilize braking pads for restraining rotation of a rotor disc, they are subject to slippage. Slippage can result in undesirable partial withdrawal of the control rod during backflow occurrence, and also requires additional means for effectively testing the torque-resisting capability of the brake. OBJECTS OF THE INVENTION Accordingly, one object of the present invention is to provide a new and improved latch assembly for preventing rotation of a shaft. Another object of the present invention is to provide a latch assembly effective for providing a positive rotational restraint of the shaft. Another object of the present invention is to provide a relatively simple and compact latch assembly for a shaft. Another object of the present invention is to provide a latch assembly which is relatively easily testable. Another object of the present invention is to provide a latch assembly for preventing rotation of a control rod drive for a nuclear reactor and which may be actuated and tested remotely therefrom. DISCLOSURE OF INVENTION A latch assembly is disclosed for selectively preventing rotation of a shaft, such as a shaft used in a control rod drive for a nuclear reactor. The latch assembly includes a stationary housing for receiving the shaft, and a gear fixedly joined to the shaft. The gear includes a plurality of circumferentially spaced gear teeth. A latch arm is pivotally joined to the housing and has at least one latch tooth facing the gear teeth. Means are provided for selectively positioning the latch arm in an engaged position wherein the latch and gear teeth prevent rotation of the shaft in a first direction, and in a disengaged position for allowing the shaft to rotate without obstruction between the gear teeth and the latch tooth.
055235158	claims	1. A method of separating and purifying a spent solvent generated in a nuclear fuel cycle and containing a higher hydrocarbon and a phosphate, said method comprising; applying to the spent solvent a pressure high enough for allowing the crystallization of the higher hydrocarbon to thereby crystallize the higher hydrocarbon, and separating under pressure a resulting solid mainly composed of the higher hydrocarbon from a remaining solution containing the phosphate in a higher concentration. 2. The method according to claim 1, wherein the higher hydrocarbon is n-dodecane and the phosphate is tributyl phosphate. 3. The method according to claim 2, wherein the pressure crystallization step is carried out at a temperature not below about -10.degree. C. and not above 15.degree. C. 4. The method according to claim 1, which further comprising subjecting the remaining solution containing the phosphate to the pressure crystallization step to repeat the crystallization treatment. 5. The method according to claim 1, which further comprising subjecting the remaining solution containing the phosphate to low-temperature vacuum distillation to thereby separate the solution into the phosphate and a deterioration product thereof contained in the solution, said deterioration product being formed as a result of degradation of a portion of the phosphate. 6. The method according to claim 1, wherein a pressure higher than a solid/liquid transformation pressure of the higher hydrocarbon is applied to crystallize the higher carbon and the crystallization is carried out at a temperature not below -10.degree. C. and not above 15.degree. C.
041486870	description	DETAILED DESCRIPTION OF EMBODIMENTS FIG. 1 shows the neutron multiplication factor versus lattice pitch as calculated by a Monte Carlo code, HWCOR-SAFE, for a typical CANDU 19-rods fuel element used in the Douglas Point Nuclear Power Station in Canada. In the original Douglas Point fuel element, all 19 rods are made of natural UO.sub.2 with Zircaloy-2 cladding and the square lattice pitch is 22.86 cm. In the proposed fuel element of the present invention including a beryllium containing rod, the central rod is replaced by a Zircaloy-2 sheathed beryllium rod of the same size. The calculation results as given in FIG. 1 show that the beryllium-embedded fuel with a pitch of 22 cm has about the same neutron multiplication value as that of the original Douglas Point fuel. A reduction of 0.86 cm in pitch here is equivalent to saving of about 9% of the D.sub.2 O moderator inventory. As a second illustration of the use of an (n, 2n) scatterer in the heavy water reactor fuel, the coolant of the above-mentioned fuel is changed from D.sub.2 O to H.sub.2 O and the central fuel rod is replaced by an unfuelled tubular central supporting rod with the lattice pitch enlarged to about 27 cm to simulate a CANDU-BLW fuel such as that used in the Gentilly Nuclear Power Station in Canada. The reactivities calculated by Monte Carlo method for this fuel with and without the central tubular tie-rod replaced by a beryllium rod of the same size are shown in FIG. 2. It is seen from this figure that by inserting a beryllium rod in the center of the fuel element the lattice pitch can be reduced by about 2 cm without a decrease in reactivity, thus giving a saving of approximately 16.5% of the D.sub.2 O moderator inventory for the present case. FIG. 3 is a drawing on the CANDU 28-pins fuel element as used in the Pickering Generating Station in Canada with twelve additional beryllium rods embedded at positions as shown. From the calculated results of reactivity as given in FIG. 4, it is seen that with the twelve beryllium rods embedded in the fuel the pitch can be reduced from the original 28.58 cm to 27.4 cm without diminishing the reactivity of the original no-beryllium-embedded fuel. This, in turn, yields a saving of about 9.78% of the D.sub.2 O moderator inventory. For light water reactors, in order to simplify the calculations by Monte Carlo method, a concentrically arranged fuel element may be utilized. FIG. 5 gives an example of the proposed LWR (light water reactor) fuel element with beryllium inserted therein. Each fuel element consists of bundle of 19 enriched UO.sub.2 fuel rods and 6 smaller beryllium rods. Here, the fuel rod dimension was set to be the same as that of a typical boiling water reactor (BWR). To illustrate what achievement can be obtained by embedding beryllium rods into the fuel element as shown in FIG. 5, the reactivity calculations were done for the fuel with various uranium enrichment values and the results were plotted in FIG. 6. The uranium enrichment chosen for the fuel element with the six beryllium rods removed was 1.95 weight percent of .sup.235 U which is typical for a boiling water reactor. A square lattice pitch of 9.5 cm was used in the Monte Carlo calculations here. It is seen from FIG. 6 that the uranium enrichment of a beryllium-embedded fuel can be lessened by about 0.1 weight percent and still yields the same neutron multiplication factor as compared to the fuel without beryllium embedded.
045335133	claims	1. In a water cooled nuclear reactor having a core and an enclosing means housing said core, said enclosing means comprising an elongated concrete body and a pressure chamber within said concrete body, said pressure chamber being substantially defined by a solid of revolution about a vertical, longitudinal axis of rotation, said pressure chamber having an opening directed to the axial direction and a cover arranged at said opening so as to give a pressure-tight sealing of said pressure chamber, said pressure chamber constituting only part of a larger cavity within said concrete body, said cavity in addition to said pressure chamber comprising a space located above said opening and connected with the outside of said concrete body by means of at least one transversal tunnel provided in said concrete body, said enclosing means being further characterized in that said space is defined in an upwards direction by means of a transversely extending limiting surface belonging to an integral portion of said concrete body, in that most of said limiting surface is disposed vertically above said cover, in that a gap extends vertically between said limiting surface and said cover, in that a plurality of compressive-force transmitting elements are arranged so as to bridge said gap, in that said cover is arranged relative to said space and dimensioned so as to be removable from said opening for maintenance of equipment associated with said core, and in that said at least one tunnel is dimensioned to permit transport of said cover through said tunnel upon removal of said cover from said opening. 2. Enclosing means according to claim 1 which further includes means for transporting said cover through said transversal tunnel. 3. Enclosing means as claimed in claim 1, wherein said concrete body comprises a plurality of pre-stressed loops of metallic material arranged in the concrete and completely surrounding said cavity, each of said loops substantially lying in a corresponding axial plane. 4. Enclosing means as claimed in claim 3, wherein each one of said loops comprises a first straight portion arranged axially outside said limiting surface, said first portion extending transversely from an outer limiting surface of said concrete body to an imaginary axial plane oriented perpendicularly to said first portion, a second portion connected to said first portion which approximately forms a circular arc of 90.degree., an axially extending third portion connected to said second portion, a semicircular fourth portion connected to said third portion (20), an axially extending fifth portion connected to said fourth portion, a sixth portion connected to said fifth portion and arranged along a circular arc of approximately 90.degree., and a straight transversely extending seventh portion connected to said sixth portion and extending to an outer limiting surface of said concrete body. 5. Enclosing means as claimed in claim 3, wherein said loops are each arranged in a loop-formed channel cast in said concrete body.
	claims	1. A radiation source comprising: an outer housing having a fastener, said outer housing configured to be opened; a substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope wherein said substrate is flexible. 2. The radiation source according to claim 1 , wherein said substrate is made of one of paper and plastic. claim 1 3. A radiation source comprising: an outer housing having a fastener, said outer housing configured to be opened; a substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, wherein said substrate is flexible, said substrate has a first form factor when contained within said outer housing, and said substrate is manipulable to have a second form factor smaller than said first form factor when said substrate is removed from said outer housing. 4. A radiation source comprising: an outer housing having a fastener, said outer housing configured to be opened; a substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, wherein at least a portion of said radioactive deposit has at least two layers. 5. The radiation source according to claim 4 , wherein an activity density of each of said at least two layers is the same. claim 4 6. A radiation source comprising; an outer housing having a fastener, said outer housing configured to be opened; a substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, wherein said substrate is radiopaque. 7. A radiation source comprising: an outer housing having a fastener, said outer housing configured to be opened; a substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, wherein said radioactive deposit includes a colorant. 8. The radiation source according to claim 7 , wherein a color of a portion of said radioactive deposit corresponds to an activity level of said portion of said radioactive deposit. claim 7 9. A radiation source comprising: an outer housing having a fastener, said outer housing configured to be opened; a substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, wherein said radioactive deposit includes a binding agent for fixedly depositing said radioactive deposit on said front surface. 10. A radiation source comprising: an outer housing having a fastener, said outer housing configured to be opened; a substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, wherein said radioactive deposit is fixedly deposited upon said front surface by covering said radioactive deposit and said front surface with a sealing layer. 11. A radiation source comprising: an outer housing having a fastener, said outer housing configured to be opened; a substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, further including a second substrate with a second radioactive deposit deposited thereon, said second substrate being contained within said outer housing. 12. The radiation source according the claim 11 , wherein the combination of said radioactive deposit and said second radioactive deposit produces a desired radioactive deposit. claim 11 13. A radiation source comprising: an outer housing having a fastener, said outer housing configured to be opened; a substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, wherein said radioactive deposit has a substantially uniform activity distribution. 14. A radiation source for calibration of nuclear imaging equipment, said radiation source comprising: an outer housing having a fastener, said outer housing configured to be opened; a flexible substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, a binding agent, and a colorant, wherein at least a portion of said radioactive deposit has at least two layers, each layer having substantially the same activity density, and a color of a second portion of said radioactive deposit indicates the activity level of said portion of said radioactive deposit. 15. A radiation source for calibration of nuclear imaging equipment, said radiation source comprising: an outer housing having a fastener, said outer housing configured to be opened; a flexible substrate removably contained within said outer housing, said substrate having a front surface; a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, and a colorant; and a sealing layer covering said radioactive deposit and said front surface of said substrate, wherein at least a portion of said radioactive deposit has at least two layers, each layer having substantially the same activity density, and a color of a second portion of said radioactive deposit indicates an activity level of said second portion of said radioactive deposit. 16. A nuclear imaging system, comprising: a piece of nuclear imaging equipment to be calibrated; and a radiation flood source to calibrate the piece of nuclear imaging equipment including, an outer housing having a fastener, said outer housing configured to be opened, a substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, further including a second substrate with a second radioactive deposit deposited thereon, said second substrate being contained within said outer housing. 17. A nuclear imaging system, comprising: a piece of nuclear imaging equipment to be calibrated; and a radiation flood source to calibrate the piece of nuclear imaging equipment including, an outer housing having a fastener, said outer housing configured to be opened, a substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, wherein the combination of said radioactive deposit and said second radioactive deposit produces a desired radioactive result. 18. A radiation source for calibration of nuclear imaging equipment, said radiation source comprising: an outer housing having a fastener, said outer housing configured to be opened; a flexible substrate removably contained within said outer housing, said substrate having a front surface; and a radioactive deposit fixedly deposited upon said front surface within said outer housing, said radioactive deposit having a radioisotope, a binding agent, and a colorant, wherein said substrate has a first form factor when contained within said outer housing, and said substrate is manipulable to have a second form factor smaller than said first form factor when said substrate is removed from said outer housing; at least a portion of said radioactive deposit has at least two layers, each layer having substantially the same activity density, and the color of a portion of said radioactive deposit indicates the activity level of said portion of said radioactive deposit.
050376039	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 prior art 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 removably attached to the upper ends of the guide thimbles 14, in a manner fully described below, to form an integral assembly capable of being 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 24 and the opposite ends of the rod are closed by upper and lower end plugs 26,28 to hermetically seal the rod. Commonly, a plenum spring 30 is disposed between the upper end plug 26 and the pellets 24 to maintain the pellets in a tight, stacked relationship within the rod 18. The fuel pellets 24 composed of fissile material are responsible for creating the reactive power of the nuclear reactor. A liquid moderator/coolant such as water, or water containing boron, is pumped upwardly through the fuel assemblies of the core in order to extract heat generated therein for the production of useful work. To control the fission process, a number of control rods 32 are reciprocally movable in the guide thimbles 14 located at predetermined positions in the fuel assembly 10. Specifically, the top nozzle 22 includes a rod cluster control mechanism 34 having an internally threaded cylinder member 36 with a plurality of radially extending flukes or arms 38. Each arm 38 is interconnected to a control rod 32 such that the control mechanism 34 is operable to move the control rods 32 vertically in the guide thimbles 14 to thereby control the fission process in the fuel assembly 10, all in a well-known manner. Prior Art Top Nozzle Attaching Structure As illustrated in FIGS. 1, 2 and 7, the top nozzle 22 has a lower adapter plate 40 with a plurality of control rod passageways 42 (only one being shown) formed through the adapter plate. The control rod guide thimbles 14 have their uppermost end portions 44 coaxially positioned within the passageways 42 in the adapter plate 40. For gaining access to the fuel rods 18, the adapter plate 40 of the top nozzle 22 is removably connected to the upper end portions 44 of the guide thimbles 14 by a prior art attaching structure, generally designated 46. The prior art attaching structure 46 is generally the same as described in above-cited U.S. Pat. No. 4,631,168, the disclosure of which is hereby incorporated by reference thereto. Thus, the attaching structure 46 will be described herein only to the extent necessary to facilitate a complete understanding of the improved tool 48 of the present invention, to be described later on in reference to FIGS. 8-18, which is employed in removing and replacing the top nozzle 22 of the fuel assembly 10. Referring to FIGS. 2-7, the top nozzle attaching structure 46 of the reconstitutable fuel assembly 10 includes a plurality of outer sockets 50 (only one being shown) defined in the top nozzle adapter plate 40 by the plurality of passageways 42 (also only one being shown) which each contains an annular circumferential groove 52 (only one being shown), a plurality of inner sockets 54 (only one being shown) defined on the upper end portions 44 of the guide thimbles 14, and a plurality of locking tubes 56 (only one being shown) inserted in the inner sockets 54 to maintain them in locking engagement with the outer sockets 50. Each inner socket 54 of the attaching structure 46 is defined by an annular circumferential bulge 58 on the hollow upper end portion 44 of one guide thimble 14 only a short distance below its upper edge. A plurality of elongated axial slots 60 are formed in the upper end portion 44 of each guide thimble 14 to permit inward elastic collapse of the slotted end portion to a compressed position so as to allow the circumferential bulge 58 thereon to be inserted within and removed from the annular groove 52 via the adapter plate passageway 42. The annular bulge 58 seats in the annular groove 52 when the guide thimble end portion 44 is inserted in the adapter plate passageway 42 and has assumed an expanded position. In such manner, the inner socket 54 of each guide thimble 14 is inserted into and withdrawn from locking engagement with one of the outer sockets 50 of the adapter plate 40. More particularly, the axially extending passageway 42 in the adapter plate 40 which defines the outer socket 50 is composed of an upper bore 62 and a lower bore 64. The lower bore 64 is of considerably greater axial length than the upper bore 62 and contains the annular groove 52 which is spaced a short distance below a ledge 66 formed at the intersection of the upper and lower bores 62,64. The lower bore 64 has a diameter which is greater than that of the upper bore 62, therefore, the ledge 66 faces in a downward direction. The primary purpose of the ledge 66 is to serve as a stop or an alignment guide for proper axial positioning of the upper end portion 44 in the passageway 42 when the inner socket 54 is inserted into the outer socket 50. As seen in FIG. 7, the upper edge of the guide thimble upper end portion 44 abuts the ledge 66. The locking tube 56 is inserted from above the top nozzle 22 into its respective locking position in the hollow upper end portion 44 of one guide thimble 14 forming one inner socket 54. When the locking tube 56 is inserted in its locking position, as seen in FIG. 7, it retains the bulge 58 of the inner socket 54 in the latter's expanded locking engagement with the annular groove 52 and prevents the inner socket 54 from being moved to its compressed releasing position in which it could be withdrawn from the outer socket 50. In such manner, each locking tube 56 maintains its respective one inner socket 54 in locking engagement with the outer socket 50 and thereby the attachment of the top nozzle 22 on the upper end portion 44 of each guide thimble 14. Additionally, securing means in the form of a slightly outwardly flared (for instance 1-2 degrees) upper peripheral marginal edge portion 68 and a plurality of small dimples 70 located along the exterior of the locking tube 56 are provided to secure the locking tube 56 at the locking position. Thus, when the locking tube 56 is inserted into the inner socket 54, a tight frictional fit is formed with the inner socket. Although the flared upper marginal edge portion 68 does not provide a positive securement, the dimples 70 do. The dimples 70 are preformed by any suitable method, such as by die forming or being coined, and so configured to have a generally pyramidal shape such that the metal forming the dimples substantially resists yielding and dimensional change regardless of the number of insertions and withdrawals of the locking tube 56 into and from the locking position. Also, when the locking tube 56 is inserted into the upper end portion 44 of the guide thimble 14, the dimples 70 are located at the elevation of the circumferential bulge 58 and are spaced in alignment circumferentially about the exterior of the locking tube so as to extend into the bulge 58. In such manner, the dimples 70 provide a positive interference fit with the guide thimble upper end portion 44 at the bulge 58 thereof which prevents inadvertent withdrawal of the locking tube 56 from the locking position. Improved Hand Held Tool of the Present Invention Referring to FIGS. 8-17, there is illustrated the improved tool 48 of the present invention for removing and replacing the locking tube 56 from a locking position in the upper end portion 44 of the guide thimble 14. In its basic components, the tool 48 includes an elongated hollow tubular assembly 72, an actuator assembly 74, a bail assembly 76, a force-imparting member 78, and a hand-operated actuating mechanism 80. The tubular assembly 72 of the tool 48 has upper and lower opposite end portions 72A, 72B. The bail assembly 76 of the tool 48 is fixedly attached to the upper end portion 72A of the tubular assembly 72, whereas the lower end portion 72B of the tubular assembly 72 is insertable in the locking tube 56. The bail assembly 76 includes a generally flat plate 82 fixed to the upper end portion 72A of the tubular assembly 72 and a U-shaped handle 84 connected to and extending upwardly from the plate 82 for a user to use in gripping the tool 48. The plate 82 serves as a member for receiving a force impacted thereon by the force-imparting member 78. The force-imparting member 78 is disposed about the upper end portion 72A of the tubular assembly 72 and is slidably movable therealong in a reciprocating manner for delivering any number of desired forceful impacts against the force-receiving plate 82 of the bail assembly 76. The force-imparting member 78 is a cylindrical body having an exterior knurled surface 78A for gripping by a user. More particularly, the tubular assembly 72 is composed of an upper elongated hollow tube 86, a lower guide member 88 and a plurality of lifting members 90. The lower guide member 88 and lifting members 90 are connected to and extend axially from a common tubular base portion 92. The tubular base portion 92 has a male end fitting 92A which is threadably connected to a female end fitting 86A in a lower end of the upper tube 86 of the tubular assembly 72. The lower guide member 88 is composed of a elongated hollow tubular element 94 having an open lower end 94A and a guide element 96 interfitting the open end 94A of the tubular element 94. The guide element 96 has a body portion projecting from the tubular element 94 which defines an upper cylindrical segment 96A and a lower conical nose 96B. The upper cylindrical segment 96A has a section 96C of reduced diameter which is inserted into and attached to the end 94A of the tubular element 94. Further, the end 94A of the tubular element 94 and the cylindrical segment 96A of the guide element body portion 96 have substantially the same outside diameter so as to provide a continuous smooth transition 98 from the tubular element end 94A to the guide element body portion 96. The conical nose 96B and the smooth transition 98 on the guide member 88 facilitates ease of alignment and insertion of the guide member 88 into the hollow locking tube 56 without catching on the upper edge 56A of the locking tube 56 at the transition 98 of the guide member 88. Also, the tubular element 94 at a region thereof spaced above its lower end 94A has a plurality of apertures 100 (best seen in FIGS. 16 and 18) defined at circumferentially spaced locations about the tubular element. The locking tube lifting members 90 extend within and in concentric relation with the hollow tubular element 94 of the guide member 88. Each lifting member 90 is composed of an elongated finger element 90A rigidly attached at its upper end to the tubular base portion 92 and having a tapered tip 90B at its lower end and a barb-shaped catch element 90C projecting radially outwardly from a central axis A (FIG. 8) of the tubular assembly 72 and tubular element 94 and aligned with the apertures 100 (FIGS. 16 and 18) in the tubular element 94. The finger elements 90A are normally disposed in a contracted condition, as seen in FIGS. 8-10 and 19, and are resiliently yieldable to deflect radially outwardly to an expanded condition, as seen in FIGS. 20 and 21 upon application of radially outwardly directed forces thereon. Upon removal of such forces, the finger elements 70A will return to the contracted condition. In the expanded condition of the finger elements 90A, the catch elements 90C defined on the respective finger elements 90A project from the tubular element 94 through the apertures 100 so as to underlie and engage a lower edge 56B of the locking tube 56, as seen in FIGS. 20, 21 and 23. On the other hand, in the contracted condition of the finger elements 90A, the catch elements 90C are retracted from the apertures 100 and disposed inside of the tubular element 94 so as to be disengaged from the lower edge 56B of locking tube 56, as seen in FIG. 19. The actuator assembly 74 of the tool 48 is mounted through the tubular assembly 72 for axial movement therealong and has upper and lower end portions 74A, 74B. The actuating mechanism 80 has a pivotal lever 102 pivotally mounted by a bracket 103 attached to the plate 82 of the bail assembly 76. The lever 102 is coupled to the upper end portion 74A of the actuator assembly 74. Pivoting of the lever 102 between its solid and dashed line positions, as seen in FIG. 8, causes axial movement of the actuator assembly through a stroke of a precise length downwardly and upwardly relative to the stationarily-held tubular assembly 72. More particularly, the actuator assembly 74 includes elongated upper and lower shaft members 104, 106 threadably connected together in a tandem arrangement. The upper shaft member 104 at the upper end portion 74A of the actuator assembly 74 is connected to the lever 102, whereas the lower shaft member 106 at the lower end portion 74B of the actuator assembly 74 extends between the lifting members 90 of the tubular assembly 72. The upper shaft member 104 is movably mounted within the upper hollow tube 86 of the tubular assembly 72 by annular bushings 105 attached in and spaced axial along the tube 86. The lower shaft member 106 has upper and lower tandemly-arranged shaft segments 106A, 106B. The upper shaft segment 106A is larger in outside diameter than the lower shaft segment 106B. Pivotal movement of the lever 102 from the solid to dashed line position of FIG. 8 pushes the actuator assembly 74 downwardly along the central axis A, inserting the upper shaft segment 106A between and removing the lower shaft segment 106B from between the lifting members 90. The larger diameter upper shaft segment 106A forces the lifting members 90 to deflect radially outward from the contracted condition of FIG. 19 to the expanded condition of FIG. 20 which extends the catch elements 90C through the apertures 100 into underlying relation and engagement with the lower edge 56B of the locking tube 56. On the other hand, pivotal movement of the lever 102 from the dashed to solid line position of FIG. 8 pulls the actuator assembly 74 upwardly along the central axis A, removing the upper shaft segment 106A from between and inserting the lower shaft segment 106B between the lifting members 90. The smaller diameter lower shaft segment 106B permits the lifting members 90 to deflect radially inward back to their contracted condition of FIG. 19, which retracts the catch elements 90C from the apertures 100 and out of engagement with the lower edge 56B of the locking tube 56. The actuator assembly 74 also includes a retractor member 108 attached to a lower end 106C of the lower shaft member 106. The retractor member 108 is a cylindrical body having a tapered recessed portion 108A for engaging the tapered tips 90B of the lifting members 90 when the actuator assembly 74 is moved in the upward direction. The inwardly and downwardly inclined configuration of the tapered recessed portion 108A of the retractor member 108 ensures that the lifting members 90 are forced to deflect from the expanded to contracted condition and their catch elements 90C are disengaged from the lower edge 56B of the locking tube 56. As seen in FIG. 21, with the lifting members 90 in their expanded condition, the removed locking tube 56 is captured on the outer tubular element 94 between the lifting member catch elements 90C and a downwardly-facing ledge 110 defined on the outer tubular element 94 by an enlarged tubular head 112 formed on the upper end of the tubular element. When the lifting members 90 are deflected back to their contracted condition, the locking tube 56 is released and can drop off the lower end portion 72B of the tubular assembly past the guide member 88. 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 or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof.
041349415	summary	The invention concerns a new type of pressed spherical fuel element made of graphite for high temperature reactors consisting of a graphite nucleus (or core) containing only fertile (breeder) particles, a graphite shell containing only fuel particles and a further outer shell of pure graphite and an especially advantageous process for reprocessing this fuel element after the irradiation in the reactor. The three layers of the fuel element are concentric. Spherical graphite fuel elements are necessary for gas cooled high temperature reactors. They usually consist of a fuel and fertile material containing spherical nucleus which is surrounded by a fuel free shell (Hrovat German Offenlegungsschrift 1,646,783). The graphite matrix, i.e., the graphite material of the nucleus and shell is identical. The fuel element diameter generally is 60 mm and the thickness of the shell 5 mm. In the known spherical graphite fuel elements the spherical nucleus contains in homogeneous distribution the fuel or fertile material in the form of spherical particles. To retain fission products the particles are surrounded by a multiple layer of pyrolytic carbon, in a given case with an intermediate layer of silicon carbide. There is added as fuel Uranium 235 and as fertile material Thorium 232 in the form of the carbide or oxide. Thereby in the so-called THTR-element, the standard spherical fuel element of the thorium high temperature reactor, fuel and fertile material jointly are provided for in the same particles, in the so-called feed-breed-element, however, they are separated in discrete particles which are distributed mixed together in the nucleus of the sphere. In the uranium-thorium cycle there is sought to be obtained from the thorium the especially valuable Uranium 233 in as pure as possible condition and without being admixed with other uranium isotopes because of its high fission neutron yield. For this reason there has been tried the separation from each other of the fuel and fertile material particles in the reprocessing of the irradiated fuel elements. As the best suited process for reprocessing graphite HTR-fuel elements there has proven conbustion (Atomwirtschaft Vol. 18 (1973) page 294 and Kerntechnik Vol. 15 (1973) page 249.) According to the state of the art today there cannot be satisfactorily attained a separation of fuel and fertile material. The processes which depend upon a sieve separation of the smaller fuel particles from the larger fertile material particles after burning off of the pyrolytic carbon coatings still have the danger of a contact contamination of the different particles with each other. Furthermore a part of the material is lost for the separation because weakened by the burning off and irradiation are broken. Also the possibility of protecting one of the types of particle (preferably the burned off particles) by an unburnable SiC intermediate layer still includes a number of disadvantages, namely, the increase in expense of fabricating the fuel element through additional coating costs, the deterioration of the neutron economy in the reactor, the danger of the Uranium 233 contamination with Uranium 235 in the particle breaking and the increase of the radioactive waste. Especially there cannot be avoided in the burning that a part of the irradiation weakened, SiC-coated particles disintegrate after burning off the outer pyrolytic carbon layer and thereby there occurs a mixing of Uranium 235 and Uranium 233. These disadvantages are avoided by the spherical fuel element of graphite of the invention which is characterized by a nucleus (core) which only contains fertile material particles, surrounded by a graphite zone which only contains fuel particles and an outer shell of pure graphite.
	abstract	A system that select tests to exercise a given computer system is described. During operation, the system tests the given computer system using a set of tests, where a given test includes a given load and a given cycling time selected from a range of cycling times. Moreover, for the given test, the system monitors a stress metric in the given computer system. Additionally, the system selects at least one of the tests from the set of tests to exercise the given computer system based on the monitored stress metric.
050646060	abstract	A channel box removing apparatus which permits a removal of the channel box from a nuclear fuel assembly while being placed on a fuel rack in a spent fuel storage pool without transferring to a preparation machine. The apparatus includes a pair of pivotally mounted, releasable hooks movable between a latched position where the hooks are in lifting engagement with the undersurfaces of clips provided on a pair of diagonally opposed top corners of the channel box and an unlatched position where the hooks are out of engagement with the associated clips. The apparatus also includes a bail cap mounted thereon for vertical movement and adapted to cooperate with a bail of the fuel assembly to guide the apparatus into an operative position with the fuel assembly during lowering of the apparatus. A locking mechanism is provided for preventing accidental disengagement of the hooks from the associated clips when the channel box is being lifted. A first indicator mechanism is also provided for providing a visual indication that the hooks are in the latched position. The apparatus also includes a second indicator mechanism for providing a visual indication that the hooks are in the latched position and also that the channel box alone can be lifted as it has been separated from the fuel assembly.
	abstract	Methods and devices enable shaping of a charged particle beam. A modified dielectric wall accelerator includes a high gradient lens section and a main section. The high gradient lens section can be dynamically adjusted to establish the desired electric fields to minimize undesirable transverse defocusing fields at the entrance to the dielectric wall accelerator. Once a baseline setting with desirable output beam characteristic is established, the output beam can be dynamically modified to vary the output beam characteristics. The output beam can be modified by slightly adjusting the electric fields established across different sections of the modified dielectric wall accelerator. Additional control over the shape of the output beam can be excreted by introducing intentional timing de-synchronization offsets and producing an injected beam that is not fully matched to the entrance of the modified dielectric accelerator.
06207962&	abstract	Methods and apparatus are disclosed for reducing thermal deformation of "upstream" marks (as used for alignment and/or calibration) situated on a reticle or on a reticle plane (e.g., on the reticle stage), thereby facilitating more accurate transfer of the reticle pattern to a sensitized substrate (e.g., semiconductor wafer) using a charged particle beam (e.g., electron beam). The charged particle beam illuminates an upstream mark situated on the reticle or on a reticle plane and projects an image of the illuminated upstream mark onto a corresponding "downstream" mark situated on a substrate plane. A shield is situated upstream of the upstream mark and serves to block downstream passage of the charged particle beam except to illuminate the upstream mark or a portion of the upstream mark. The upstream mark can be situated on the reticle or on a mark member situated in the reticle plane.
	abstract	A charged particle beam irradiation system includes a synchrotron which accelerates an ion beam, an irradiation apparatus for irradiating an object with the ion beam introduced from the synchrotron, detection means for measuring an amount of accumulated charge of the ion beam that orbits in the synchrotron immediately before an extraction control period in an operating cycle of the synchrotron, and beam extraction control means for controlling extraction of the ion beam based on the measurement result of the accumulated beam charge amount so that extraction of a total amount of the ion beam is to be completed with an expiration of an extraction control time, the extraction control time representing a length of the extraction control period of the synchrotron and being set in advance.
	abstract	The invention comprises an ion beam focusing method and apparatus used as part of an ion beam injection system, which is used in conjunction with multi-axis charged particle or proton beam radiation therapy of cancerous tumors. The ion beam focusing system includes two or more electrodes where one electrode of each electrode pair partially obstructs the ion beam path with conductive paths, such as a conductive mesh. In a given electrode pair, electric field lines, running between the conductive mesh of a first electrode and a second electrode, provide inward forces focusing the negative ion beam. Multiple such electrode pairs provide multiple negative ion beam focusing regions.
048624900	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGS. 1 and 2, a vacuum window 10, in accordance with the present invention, includes a support substrate 12, a front membrane 14, and a back membrane 16. Substrate 12 can be made from many different types of materials including silicon, glass, quartz, sapphire, or tungsten, and is provided with a window aperture 18 which, in the illustrated embodiment, is substantially cylindrical. The front membrane 14 has a perimeter portion 20 attached to a front surface of substrate 12, and a window portion 22 aligned with window aperture 18. The window portion 22 has a number of pane openings 24 surrounded by a plurality of ribs 26, and a plurality of pane sections 28 formed within pane openings 24. The back membrane 16 is preferably made from the same material as the front membrane 14, and has a perimeter portion 30 attached to a back surface of substrate 12. Second thick membrane 16 is provided with a cylindrical aperture 32 which is aligned with the window aperture 18. Three materials that have been found to be suitable membrane material are boron nitride, boron carbide, and silicon carbide. All three of these materials have low atomic numbers and permit the formation of the thin pane sections 28 and thick ribs 26. Taking boron nitride as an example for the membrane material, a 37% transmission rate for soft x-rays can be obtained by making front membrane 14 four micrometers thick at the ribs 26, 0.1 micrometers thick at the pane sections 28, and by making the pane sections 68 micrometers square. A method for producing a vacuum window in accordance with the present invention starts with the selection and preparation of a suitable substrate material. As mentioned previously, a clean, polished silicon wafer has been found to be a suitable substrate. A relatively thick boron nitride membrane is grown on both sides of the silicon wafer using low-pressure chemical vapor deposition (LPCVD) techniques that are well known to those skilled in the art of integrated circuit manufacturing. For example, in a preferred embodiment, the boron nitride is deposited on the silicon wafers in a furnace tube at 470.degree. C. at a pressure of 900 m Torr with a flow of 11 standard cubic centimeters per minute (SCCM), of NH.sub.3 mixed with 145 SCCM of 10% diborane (B.sub.2 H.sub.6) in hydrogen dilution gas plus 345 SCCM of hydrogen carrier gas. The silicon wafers are serially arranged relative to axial flow of reactant gases within the furnace tube with the normals to their major face axially aligned with each other and parallel to the axis of revolution of the tube with 2 cm spacing between wafers. The deposition rate is approximately 1 .mu.m per hour and the deposition time is 6 to 8 hours to form a 6 to 8 .mu.m thick layer having a tensile stress of 1.times.10.sup.9 dynes/cm.sup.2. Thereafter, in a preferred embodiment, the wafer is coated by evaporation on both sides with a thin layer, as of 1000 .ANG. of Ni masking material. Next, a photolithographic process is used to pattern the thick boron nitride on the back side of the substrate to make a window aperture mask. The photolithographic process preferably includes the steps of applying a layer of photoresist to the boron nitride, curing the photoresist in a soft-bake cycle, exposing the photoresist through a suitable mask, developing the photoresist. The exposed nickel mask is patterned by etching in standard aluminum etch. Then, the remaining photoresist is removed. The photolithographic process is, once again, well known to those skilled in the art of integrated circuit manufacturing. After the window aperture mask is created on the back surface of the wafer, the relatively thick boron nitride on the front surface of the wafer is patterned to produce the pane opening sections and the ribs. At this point, the pane openings extend through the relatively thick front membrane to the upper surface of the silicon substrate. For example, in a preferred embodiment, a 1 .mu.m thickness of photoresist is spun onto the back side of the nickel-coated wafer. The photoresist is patterned to expose the nickel. Photoresist 1 .mu.m thick is then spun onto the front side of the nickel-coated wafer and patterned with the front side mask to expose the front side nickel through the photoresist. The wafer is then immersed in a wet etch for the nickel, as of conventional wet aluminum etchant commercially available from KTI of Sunnyvale, California, to expose the boron nitride on both sides of the wafer through the patterned openings in the nickel and photoresist masks. The boron nitride layers 16 and 14 are then plasma etched to expose the silicon through the boron nitride, Ni and photoresist masks. A suitable plasma etch is 96% CF.sub.4 and 4% O.sub.2 at 75 watts and 200 m Torr. The front side etch is stopped immediately upon etching through the boron nitride to the silicon so as not to pit or significantly etch the polished silicon surface. A residual gas analyzer is employed for analyzing the gaseous reaction products of the plasma etching process to determine when the silicon starts to be etched. Etching is terminated when these products are detected. The resist and nickel masks are then stripped, and the wafer is cleaned in boiling sulfuric peroxide, to assure particle-free pane openings. Next, a thin layer of boron nitride is deposited over the front layer of boron nitride to form thin layers or pane sections against the front surface of the wafer at the bottom of the pane openings. The pane sections are very uniform in nature, and are free of such defects as particles, pinholes and fractures because they were formed by deposition rather than by some other, less controllable process such as being etched down from a thicker deposition. For example, in a preferred embodiment, the thin layer of boron nitride, which forms the pane portions 28 of the x-ray window, is deposited in essentially the same manner as the aforedescribed thick membranes 14 and 16, except that the flow conditions are varied slightly to reduce the tensile stress of the deposited layer to about 2.times.10.sup.8 dynes/cm.sup.2. Suitable flow conditions into the furnace tube are 15 SCCM of NH.sub.3, 100 SCCM 10% diborane and hydrogen and 385 SCCM hydrogen. The deposition rate is about 1 .mu.m per hour and the deposition time is chosen to deposit between 1000 and 2500 .ANG. boron nitride onto the front surface covering the ribs 26 and exposed silicon at the bottom of the recesses defined between intersecting ribs 26. Thereafter, the wafer is diced, as by sawing to separate individual x-ray windows 10 from the wafer. The silicon substrate portion remaining under the pane portion 28 supports the pane 28 during the sawing operation and prevents fracture thereof by the sawing slurry and shock and vibration associated with sawing. Next, a silicon etching acid mixture is used to etch a window aperture through the wafer as defined by the window aperture pattern mask of the back layer of thick boron nitride. Finally, the vacuum window is cleaned and mounted in a suitable holder. For example, in a preferred embodiment, the individual window die are placed in a holder and immersed in a wet silicon etchant which will not etch the boron nitride. A suitable room temperature silicon etchant is the conventional isotropic silicon etchant consisting of 1 part nitric acid, 1 part hydrofluoric acid, and 2 parts of acetic acid, all by volume and of industry standard concentration. A preferred etchant is the same as above, except without the acetic acid constituent. The industry standard concentration of nitric, HF and acetic are 69-71%, 48-51% and 99.7%, respectively. In a preferred method for mounting the x-ray window in a suitable holder, the wafer, before dicing, is coated, as by evaporation, on its back side, overlaying the boron nitride layer 16, through a suitable mask with 300-500 .ANG. of either Cr, Ti or Ni, followed by 5000 .ANG. of aluminum. This back side metallization is confined by the mask to the periphery of the window frame portion. After dicing, individual die are anodically, i.e., thermoelectrically, or electric field assisted, bonded to a Pyrex glass holder having an opening aligned with the back side recess 18 of the x-ray window 10. Typical anodic bonding conditions are 3000 V negative applied to the glass relative to the potential of the silicon substrate 12 for 10 to 20 minutes at 250.degree. to 300.degree. C. While this invention has been described with reference to a single preferred embodiment, it is contemplated that various alterations and permutations of the invention will become apparent to those skilled in the art upon reading of the preceding descriptions and a study of the drawing. For example, another suitable membrane material for membranes 14 and 16 and panes 28 is silicon nitride. The etchants employed for the boron nitride examples above are also suitable for etching boron carbide, silicon carbide and silicon nitride. The silicon etchants above are also suitable for use with membranes of boron carbide, silicon carbide and silicon nitride.
	description	Firstly referring to FIG. 1, a segmented rack is observed which integrates several intermediate lattices (3) to (9), coinciding with the active part of the stored radioactive component and another two assemblies (1)(2) and (10)(11) coinciding with the non-active part of said stored component, all supported by a base (12) provided with adjustable support legs (13). According to the present invention, the intermediate components (3) to (9) which coincide with the active part of the stored radioactive component, consist of plates of a material formed from neutronic poisons, the most common being: a) A single plate of boron treated steel as shown in FIG. 2. b) Two plates of normal steel (18-19) forming a double wall, inside of which there is boron treated water or Boral laminates (20). Boral is a dispersion of boron carbide in an aluminium matrix. See FIG. 3. c) Two adjacent plates, one of normal stainless steel (21) and the other of boron treated steel (22) as shown in FIG. 4. However, the assemblies (1)(2) and (10)(11) are carried out with normal stainless steel plates, not treated with boron and with a low carbon content, having a greater thickness than material integrating the central lattices. The coupling between one of these intermediate lattices (4) with that located immediately above (3) and/or below (5) is carried out by dovetailing across the grooves (16) on both sides of the plates (15) which integrate each mesh as shown in FIG. 2. The joint is finally carried out by angle welding (17), if this is necessary for the design conditions, forming very stable, rigid assemblies; and in those applications where due to the mechanical design conditions, it is not necessary to weld, or the internal material comprising each one of these lattices were not welded or were not weldable, or in countries where welding is not authorized, a vertical tying of the different meshes is performed by thin, pretensioned strips (14), welded to the lower and upper stainless steel meshes. All the intermediate components (4) to (9) are formed by plates (15) grooved on both sides, forming at least one line in one direction and another perpendicular to the former at a different level, being joined across said grooves (16) to form a reticulated volume in which extended and parallel conduits are formed by piling successive lattices. The end units of the rack, shown in the figure with references (3) and (9), are formed by parallel plates with a width equivalent to the difference in height between the two plates conforming the central units, in such a way that arranged in the suitable plane, they overlap the protruding part of the former to form an extremely flat lattice unit, or in other words, terminating the corresponding part which in any of the previous configurations was drawn in with respect to the most protruding plates. The materials, shape and arrangement of the components may vary provided this does not involve a change of the essential features of the invention claimed below:
	claims	1. A steam dump control system for controlling a response of a nuclear reactor to a transient, comprising:at least one steam dump valve having a positioner operable to open said valve;a coolant sensor system for monitoring an average temperature of a coolant of the nuclear reactor and providing a temperature error signal when the average temperature of the coolant exceeds a reference temperature;a nuclear power plant power sensing system for monitoring power of the reactor and power of a turbine, and providing a power error signal when the power of the turbine is reduced and the power of the turbine changes relative to the power of the reactor at a rate that exceeds a preselected rate; anda control means having an input from the coolant sensor system and an input from the nuclear power plant power sensing system, for combining the temperature error signal and the power error signal to produce a valve control signal to control said valve positioner. 2. The system of claim 1 wherein said nuclear reactor is a pressurized water reactor. 3. The system of claim 1 wherein said steam dump valves are selected from the group consisting of condenser dump valves and atmospheric steam dump valves. 4. The system of claim 1 wherein a summator is provided for summing said temperature error signal and said power error signal. 5. A system for controlling a response of a nuclear reactor to a load rejection transient, comprising:a coolant sensor system for monitoring an average temperature of a coolant of the nuclear reactor and generating a temperature error when the average temperature of the coolant exceeds a reference temperature;a power sensing system for monitoring power of the nuclear reactor and power of a turbine and generating a power error when the power of the turbine is reduced and the power of the turbine changes relative to the power of the reactor at a rate that exceeds a preselected rate;a conversion means to convert the power error to a corresponding temperature error;a summator to add the temperature error from the coolant sensor system and the temperature error corresponding to the power error from the power sensing system to generate a resultant temperature error;a control means to provide a valve control signal based on the resultant temperature error; andat least one steam dump valve which is operable to open on receipt of the valve control signal. 6. The system of claim 5 wherein the nuclear reactor comprises a Reactor Coolant System having a hot leg with a temperature, Thot, and a cold leg with a temperature, Tcold, said average temperature determined from an average of Thot and Tcold. 7. The system of claim 5 wherein the nuclear reactor comprises a turbine having an impulse chamber and said reference temperature is determined from a pressure measured in the impulse chamber of the turbine. 8. The system of claim 5 wherein the at least one steam dump valve has a valve positioner and the valve positioner enables opening of the at least one steam dump valve.
	description	1. Field of the Invention The present invention relates to a wavelength-dispersive X-ray spectrometer used in an electron probe microanalyzer (EPMA) or other similar instrument and, more particularly, to a technique for improving the performance of an X-ray spectrometer equipped with analyzing crystals curved in the direction of angular dispersion. 2. Description of Related Art EPMAs are widely used as instruments for qualitatively and quantitatively analyzing a sample by sharply focusing an accelerated electron beam, directing the beam toward a surface of the sample, dispersing the generated characteristic X-rays, and analyzing the sample from the wavelengths and intensities of the dispersed X-rays. Generally, an EPMA is equipped with a wavelength-dispersive (WD) spectrometer designed to collect X-rays while moving the crystal along a straight path. This X-ray spectrometer may be hereinafter referred to as the WD spectrometer of the straight moving ray-collection type. Fundamental instrumentation of such an X-ray spectrometer is shown in the cross section of FIG. 1. When a focusing electron beam EB hits a sample 2, X-rays are produced. Electron optics for generating, accelerating, and focusing the electron beam EB are not shown. An X-ray spectrometer 1 holds an analyzing crystal 3 whose center C moves on a straight line SC that is tilted at an angle of an X-ray takeoff angle α from a point of source S of X-rays. At this time, the point of source S, the center C of the analyzing crystal 3, and the center F of a slit 5 in an X-ray detector 4 are always present on the circumference of a Rowland circle 6 having a constant radius R. The position of the X-ray detector 4 and the center Q of the Rowland circle 6 move such that line segments SC and CF are kept equal in length. The curved crystalline lattice plane of the analyzing crystal 3 that extends along arc C2 always faces the center Q of the Rowland circle. The curved crystalline lattice plane is curved about a point D with a curvature of 2R. The point D is the intersection of an extension of a straight line CQ and the Rowland circle 6, the straight line CQ connecting the center C of the analyzing crystal 3 and the center Q of the Rowland circle 6. The length of the line segment SC is referred to as a spectral position L. Let θ be the angle of incidence of X-rays on the center C of the analyzing crystal. The angle θ is made between straight lines C1 and SC. The straight line C1 passes through the center C of the analyzing crystal and is tangent to the Rowland circle 6. The spectral position L is given byL=2R·sin θ (1)Meanwhile, from the Bragg condition, the diffraction conditions for the analyzing crystal are given by2d·sin θ=n·λ (2)where n is the order of diffraction and a positive integer, λ is the wavelength of X-rays, and d is the lattice spacing of the analyzing crystal. From Eqs. (1) and (2), we can obtain: L = 2 ⁢ R 2 ⁢ d · n · λ ( 3 ) It is possible to know the wavelength γ of the diffracted characteristic X-rays by measuring the spectral position L. Since the characteristic X-rays have a wavelength intrinsic to the element, the element contained in the sample can be identified. Furthermore, the concentration of the element contained in the sample can be known from the measured intensity of the characteristic X-rays. Curved analyzing crystals have two types: Johansson type and Johann type. The differences between the Johansson and Johann types are shown in FIGS. 7(a) and 7(b) and FIGS. 8(a) and 8(b). FIG. 7(a) is a perspective view of a Johansson analyzing crystal, as viewed from inside a Rowland circle. First, the flat crystal is curved about a point D with curvature 2R such that the direction of angular dispersion of the analyzing crystal agrees with arc C2. Then, the curved crystal is polished with the same curvature R as the radius of the Rowland circle 6. Thus, X-rays incident on an arc of the analyzing crystal 3 in contact with the circumference of the Rowland circle 6 are diffracted while completely satisfying the requirement of Eq. (2) as shown in FIG. 7(b). However, the condition of Eq. (2) is satisfied less with going away from the arc in contact with the Rowland circle in a lateral direction perpendicular to the direction of angular dispersion. The double-dot-dash lines in FIG. 7(b) indicate positions with equal incident angle error. The double-dot-dash lines are referred to as equal incident-angle error lines. This tendency becomes more conspicuous with reducing the incident angle θ. Consequently, the wavelength resolution of the detected X-rays and the ratio of the intensity of the characteristic X-rays to the background intensity are deteriorated. Techniques for alleviating these problems are shown in Japanese Patent Laid-Open No. H10-239495. The diffractive surfaces of Johansson crystals are physically polished. Therefore, some analyzing crystals for relatively long wavelengths have deteriorated performance and thus cannot be easily put into practical use. In this case, the following Johann type is used. FIG. 8(a) is a perspective view of an analyzing crystal in a Johann geometry, as viewed from the inside of a Rowland circle. In the Johann type, the direction of angular dispersion of the analyzing crystal is curved with curvature 2R about a point D such that the crystalline lattice plane extends along an arc C2. Under this curved condition, the crystal is used. In this type of analyzing crystal, X-rays incident on mutually crossing lines about the center C of the analyzing crystal are diffracted while completely satisfying Eq. (2) as shown in FIG. 8(b). Solid lines or dashed lines in FIG. 8(b) like the letter X expand in the direction of angular direction according to increasing the value of the incident angle θ. The double-dot-dash lines in FIG. 8(b) indicate positions with equal incident-angle error. The double-dot-dash lines are referred to as equal incident-angle error lines. The geometry of the mutually crossing lines varies with the value of L. As the incident angle θ decreases, the geometry approaches the center C of the analyzing crystal as shown as dashed lines in FIG. 8(b). Where it is difficult to polish the surface of an analyzing crystal or deterioration of performance with polishing should be avoided, a Johann geometry is used. LB (Langmuir-Blodgett) films often used as an analyzing element for X-ray spectroscopy for analysis of ultralight elements and analyzing elements using layered synthetic microstructures are difficult to polish and, therefore, they are used only in Johann geometry. Organic crystals synthetically produced from RAP (Rubidium acid phthalate), TAP (Thallium acid phthalate), or PET (Pentaerythritol) can be polished to make Johansson crystals, but they are often used to make Johann crystals because of a compromise with performance deterioration. A layered synthetic microstructure is created by artificially stacking a layer of high X-ray scattering capabilities and a spacer layer for securing lattice spacing on a substrate alternately. This microstructure is also referred to as an artificial superlattice. Analyzing elements of LB films and layered synthetic microstructures are not crystals in proper meaning but they are herein conveniently referred to as analyzing crystals. An analyzing crystal is curved such that larger parts of X-rays emitted from a point X-ray source S are diffracted. However, both Johansson and Johann crystals of FIGS. 7(a) and 7(b) and FIGS. 8(a) and 8(b), respectively, are curved in only the direction of angular dispersion. In this case, the opening of the slit 5 in the X-ray detector 4 needs to have a length of 2W in a direction parallel to the widthwise direction of the analyzing crystal 3 as shown in FIG. 9. However, there is the problem that spatial restrictions are inevitably imposed when a wide slit is placed. Especially, the Johann analyzing crystal is affected greatly by limitation on the length of the slit, because the completely diffracted region is an X-shaped form and thus the width of the analyzing crystal can be increased with desirable results. In an attempt to avoid this problem and to obtain a high-intensity X-ray spectrometer, a two-directional curved analyzing crystal that is curved even in the widthwise direction of a Johann analyzing crystal has been fabricated. A two-directionally curved analyzing crystal having spherically-curved concave surfaces both in the direction of angular dispersion of the curved analyzing crystal and in a direction perpendicular to the direction of angular dispersion is herein referred to as a spherically-curved, Johann-type analyzing crystal, the concave surfaces having the same curvature as the diameter of the Rowland circle. In a curved analyzing crystal fitted to an X-ray spectrometer mounted in an EPMA, the effective diffraction area actually contributing to diffraction differs depending on whether it is a Johansson or Johann crystal, on the spectral position L, and on the kind of analyzing crystal used. In some cases, the effective diffraction area is only about a half of the total area of the analyzing crystal. The aforementioned spherically-curved Johann analyzing crystal has an optimum angular dispersion direction length according to the wavelength of the selected X-ray. That is, the length in the direction of angular dispersion is relatively small for shorter wavelengths of X-rays. The length in the direction of angular dispersion is relatively large for longer wavelengths of X-rays. Therefore, a spherically-curved, Johann-type analyzing crystal fabricated to match the length suitable for one wavelength of characteristic X-rays of interest within the analyzed range cannot be suitably used for spectral analysis of other characteristic X-rays which are widely different in wavelength from the X-ray to be selected. For example, the spectral waveform of the characteristic X-rays at wavelengths shorter than the X-rays to be spectrally selected has a tail on the lower diffraction angle side (on the shorter wavelength side), deteriorating the wavelength resolution. In very bad cases, lumpy hills appear on the waveform. This may impair the reliability of the waveform itself. Furthermore, there is the problem that the total area of the analyzing crystal is narrower than the effective diffraction area for characteristic X-rays longer than the X-rays to be spectrally selected, giving rise to a loss of the detectable X-ray intensity. In an ordinary curved crystal, there is the problem that X-rays enter even those portions which do not contribute to diffraction, deteriorating the wavelength resolution of the detected X-rays and the ratio of the intensity of the characteristic X-rays to the background intensity. In an attempt to solve this problem, Japanese Patent Laid-Open No. S52-27695 discloses a technique using a disk having various sizes of X-ray takeoff windows between a source of X-rays and an analyzing crystal. An operator can select an X-ray takeoff window matched with the effective diffraction area by manipulating the disk from outside the vacuum. However, it is not easy for the operator to select an X-ray takeoff window of appropriate size. Consequently, there is the problem that it is laborious to switch the X-ray takeoff window by manual manipulations. Furthermore, it is impossible to cope with continuous variation of X-ray wavelength. It is an object of the present invention to provide a wavelength-dispersive X-ray spectrometer which is free of the foregoing problems. That is, only X-rays diffracted in ever optimum effective diffractive regions on the curved analyzing crystal are guided to an X-ray detector at all times without the need for the operator to make any decision. This object is achieved in accordance with the teachings of the present invention by a wavelength-dispersive X-ray spectrometer fitted to an X-ray microarea-analyzer, such as an electron probe microanalyzer, the X-ray spectrometer being designed to collect X-rays diffracted by the curved analyzing crystal while moving the crystal straight. The X-ray spectrometer has analyzing crystals each having a crystalline lattice plane. The direction of angular dispersion of the crystalline lattice plane is so curved that it has a curvature equal to the diameter of a Rowland circle. A limitation device for limiting an incident region and/or an exit region of the surface of the curved analyzing crystal is mounted integrally with the curved analyzing crystal. Incident X-rays enter the incident region or exit from the exit region of the surface of the crystal after being diffracted and go toward an X-ray detector such that only X-rays diffracted by the effective diffractive regions of the surface of the curved analyzing crystal are detected by the X-ray detector in response to variation of the effective diffractive regions of the surface of the analyzing crystal contributing to actual diffraction when the spectral position of the X-ray spectrometer varies. In one feature of the present invention, the limitation device is made of an X-ray blocking plate upstanding toward the inside of the Rowland circle from the position of the surface of the analyzing crystal at the end of the analyzing crystal in the direction of angular dispersion. The X-ray blocking plate blocks parts of at least one of incident X-rays going from a point source of X-rays toward the curved analyzing crystal and X-rays diffracted by the analyzing crystal toward the X-ray detector. In another feature of the present invention, the limitation device is made of an X-ray blocking plate upstanding toward the center of the Rowland circle in the X-ray spectrometer from an end of a crystal support member that supports the analyzing crystal in the direction of angular dispersion of the crystal or toward the center of curvature of the curved analyzing crystal. The X-ray blocking plate blocks parts of at least one of incident X-rays going from a point X-ray source toward the analyzing crystal and X-rays diffracted by the analyzing crystal toward the X-ray detector. In a further feature of the present invention, the limitation device is made of an X-ray blocking plate upstanding perpendicularly to the plane of the Rowland circle in the X-ray spectrometer and parallel to a straight line from an end of a crystal support member that supports the curved analyzing crystal in the direction of angular dispersion of the crystal. The straight line passes through the center of the curved analyzing crystal and through the center of the Rowland circle. The X-ray blocking plate blocks parts of at least one of incident X-rays going from a point X-ray source toward the analyzing crystal and X-rays diffracted by the analyzing crystal toward the X-ray detector. In yet another feature of the present invention, the limitation device has an X-ray blocking plate disposed at an end of a crystal support member that supports the curved analyzing crystal in the direction of angular dispersion of the crystal. A part of the X-ray blocking plate provides cover over an appropriate, substantially rectangular region at an end portion of the surface of the analyzing crystal. A front-end portion of the X-ray blocking plate is made to upstand toward the center of the Rowland circle in the X-ray spectrometer or toward the center of curvature of the analyzing crystal. The upstanding portion of the X-ray blocking plate blocks parts of at least one of incident X-rays going from a point X-ray source toward the curved analyzing crystal and X-rays diffracted by the analyzing crystal toward the X-ray detector. In an additional feature of the present invention, the limitation device has an X-ray blocking plate disposed at an end of a crystal support member that supports the curved analyzing crystal in the direction of angular dispersion of the crystal. A part of the X-ray blocking plate provides cover over an appropriate, substantially rectangular region at an end portion of the surface of the curved analyzing crystal. A front-end portion of the X-ray blocking plate is made to upstand perpendicularly to the plane of the Rowland circle in the X-ray spectrometer and parallel to a straight line passing through the center of the crystal and through the center of the Rowland circle. The upstanding portion of the X-ray blocking plate blocks parts of at least one of incident X-rays going from a point X-ray source toward the curved analyzing crystal and X-rays diffracted by the analyzing crystal toward the X-ray detector. In one embodiment of the present invention, the analyzing crystal is a spherically-curved, Johann-type analyzing crystal. The crystal has a concave surface curved into a spherical form having the same curvature as the diameter of the Rowland circle in the direction of angular dispersion of the curved analyzing crystal and in a direction perpendicular to the angular dispersion. The shape of the portion of the X-ray blocking plate which upstands toward the inside of the Rowland circle from an end of a crystal support member that supports the spherically-curved, Johann-type analyzing crystal in the direction of angular dispersion of the crystal is substantially rectangular. The present invention also provides a wavelength-dispersive X-ray spectrometer designed such that radiations going straight are collected, the X-ray spectrometer using curved analyzing crystals mounted therein. Each of the curved analyzing crystals has an X-ray blocking plate upstanding from the position of the surface of the analyzing crystal toward the inside of the Rowland circle. The height of the X-ray blocking plate is so determined that a region thereof contributing to diffraction is set based on data indicating error in incident angle of X-rays incident on the surface of the curved analyzing crystal. In yet an additional feature of the present invention, the curved analyzing crystal is an analyzing element made of a layered synthetic microstructure having a lattice spacing of less than 2 nm. The limitation device is formed integrally with the analyzing element made of layered synthetic microstructure. According to the present invention, when an analysis is made using a curved analyzing crystal which is mounted in a wavelength-dispersive X-ray spectrometer designed to collect X-rays diffracted by the curved analyzing crystal while moving the crystal straight, a limitation device is mounted integrally with the curved analyzing crystal. The direction of angular dispersion of the crystalline lattice plane of the analyzing crystal has a curvature equal to the diameter of the Rowland circle. The surface of the curved analyzing crystal has an effective diffractive region contributing to actual diffraction. As the spectral position of the X-ray spectrometer varies, the effective diffractive region varies. Correspondingly, the limitation device limits at least one of the incident regions of the surface of the curved analyzing crystal from which incident X-rays enter and the exit region of the surface of the analyzing crystal from which X-rays are diffracted toward the X-ray detector such that only X-rays diffracted by the effective diffractive region of the surface of the analyzing crystal are detected by the X-ray detector. Consequently, only the X-rays diffracted by the effective diffractive region of the surface of the curved analyzing crystal can be guided to the X-ray detector at all times for every wavelength of X-rays within the spectral range without the need for the operator to make any decision or perform any manipulation. As a result, X-rays on portions not contributing to diffraction can be prevented; otherwise, abnormal waveforms would be produced and the spectrally selective performance would be deteriorated. Hence, the wavelength resolution of characteristic X-rays used for analysis and the ratio of the intensity of the characteristic X-rays to the background intensity can be improved. Other objects and features of the invention will appear in the course of the description thereof, which follows. Embodiments of the present invention are hereinafter described with reference to the accompanying drawings. It is to be understood that the scope of the present invention is not limited thereto. Components operating identically or similarly are indicated by the same reference numerals in various figures and their repeated description will be avoided. When a spherically-curved Johann analyzing crystal is used as a curved analyzing crystal, effective diffractive regions should be discussed. The effective diffractive regions are first described. FIG. 2 illustrates incident angle error Δθ on a spherically-curved Johann analyzing crystal under a Bragg condition given by Eq. (2). Incident angle error Δθ at an arbitrary point P on the crystal is given byΔθ=θp−θ (4)where θ is the incident angle of X-rays to the center C of the analyzing crystal and θp is the incident angle of X-rays on the point P. FIGS. 3(a)-3(d) show examples of calculation of incident angle error Δθ on the surface of the spherically-curved Johann analyzing crystal fitted to a wavelength-dispersive X-ray spectrometer of the straight moving ray-collection type having a Rowland circle with a radius of 140 mm. The values of incident angle error Δθ obtained when the incident angle θ is 18.48°, 28.74°, 43.04°, and 54.59°, respectively, are shown in FIGS. 3(a), 3(b), 3(c), and 3(d), respectively. Regions G1-G10 are indicated by different degrees of concentration and denote various magnitudes of incident angle error Δθ. The regions G1-G10 have relationship shown in Table 1, where K=0.0005 radian. TABLE 1regioncorresponding incident angle error ΔθG1−K < Δθ < KG2 K ≦ Δθ < 2KG32K ≦ Δθ < 3KG43K ≦ Δθ < 4KG54K ≦ Δθ < 5KG65K ≦ Δθ < 6KG76K ≦ Δθ < 7KG87K ≦ Δθ < 8KG98K ≦ Δθ < 9KG109K ≦ Δθ It can be considered that in a normal effective diffractive region of the Johann analyzing crystal, incident angle error Δθ is in the range of about ±3 to 4 K. As can be seen from FIGS. 3(a)-3(d), the incident angle error Δθ on the surface of the spherically-curved Johann analyzing crystal fitted to the WD spectrometer of the straight moving ray-collection type increases with going away from the center position in the direction of angular dispersion. Furthermore, it can be seen that the magnitude of the incident angle error Δθ depends on the incident angle θ and increases with reducing the incident angle θ and vice versa. On the other hand, at positions moved away from the widthwise center vertically to the Rowland circle in the X-ray spectrometer, the magnitude of the incident angle error Δθ is substantially the same as the magnitude at the widthwise center. Accordingly, the effective diffractive region on the surface of the spherically-curved Johann analyzing crystal fitted to the WD spectrometer of the straight moving ray-collection type is determined by the length in the direction of angular dispersion. This length depends on the incident angle θ. It can be seen that the length increases with increasing the incident angle θ and vice versa. Based on the above-described findings, a spherically-curved, Johann-type analyzing crystal fitted to a WD spectrometer of the straight moving ray-collection type is so fabricated that it has an optimum length in the direction of angular dispersion for X-rays close to the longest wavelength limit (i.e., maximum value of incident angle θ) within the spectral range determined by the fitted WD spectrometer. When shorter wavelengths of X-rays within the spectrometer spectral range are spectrally diffracted, if the effective diffractive region in the direction of angular dispersion is limited according to the spectral position L without limiting the widthwise length of the analyzing crystal, only X-rays diffracted by the effective diffractive region of the surface of the analyzing crystal are detected by the X-ray detector for every wavelength of X-rays within the spectral range; otherwise, the spectral resolving performance would be deteriorated. Consequently, the wavelength resolution of the characteristic X-rays used for analysis and the ratio of the intensity of characteristic X-rays to the intensity of background can be improved. In the present invention, as a method of limiting the effective diffractive region of an analyzing crystal in the direction of angular dispersion according to the spectral position L, an X-ray blocking plate is mounted near each end of the curved analyzing crystal in the direction of angular dispersion. The blocking plate is made to upstand from the position of the surface of the crystal toward the inside of a Rowland circle. The X-ray blocking plate blocks parts of at least one of incident X-rays going from a point X-ray source toward the analyzing crystal and X-rays diffracted by the analyzing crystal toward the X-ray detector. However, the thickness and mechanical strength of the analyzing crystal are not sufficient. Therefore, it is difficult to mount the X-ray blocking plate directly to the analyzing crystal. Consequently, in practice, the X-ray blocking plate is mounted to a crystal support member that supports the analyzing crystal. At this time, it is only necessary that the only portions of the blocking plates that upstand from the position of the surface of the crystal are located close to the ends of the crystal in the direction of angular dispersion. Furthermore, the crystal support member to which the X-ray blocking plate is mounted is not limited to a member to which the analyzing crystal can be directly mounted. Any member can be used which is located close to the end of the analyzing crystal in the direction of angular dispersion and which has a mechanical positional relationship with the analyzing crystal, the positional relationship not being varied if the incident angle θ is varied, i.e., the member moving together with the analyzing crystal. A method of mounting the X-ray blocking plate to the crystal support member consists of using adhesive or fixing the blocking plate with small screws. FIGS. 4(a) and 4(b) show examples of X-ray blocking plates, each of which is made to upstand directly from an end of a crystal support member in the direction of angular dispersion of a curved angular crystal. If the X-ray blocking plate upstanding toward the inside of a Rowland circle is directed toward the center Q of the Rowland circle in the spectrometer or toward a point D as shown in FIG. 4(a), or if the blocking plate is made perpendicularly to the plane of the Rowland circle in the X-ray spectrometer and parallel to a straight line which passes through the center C of the analyzing crystal and the center Q of the Rowland circle as shown in FIG. 4(b), it is easy to find the necessary height by geometrical computations as described later. During the process where an analyzing crystal in the form of a flat plate is curved or further bent into a spherical form, end portions of the crystal tend to be curved non-uniformly. If so, X-rays are not correctly diffracted in these regions. This leads to a deterioration of the performance. Therefore, a part of the X-ray blocking plate may first cover a substantially rectangular appropriate region of an end portion of the surface of the curved analyzing crystal and then a front-end portion of the X-ray blocking plate may be made to upstand toward the inside of a Rowland circle in the X-ray spectrometer as shown in FIGS. 5(a) and 5(b) without causing the X-ray blocking plate to upstand directly from an end of the crystal support member in the direction of angular dispersion of the analyzing crystal. Also, in this case, it is easy to calculate the height if the X-ray blocking plate upstanding toward the inside of the Rowland circle is directed toward the center Q of the Rowland circle in the spectrometer or point D as shown in FIG. 5(a) or if the plate is made perpendicularly to the plane of the Rowland circle in the X-ray spectrometer and parallel to a straight line passing through the center C of the analyzing crystal and through the center Q of the Rowland circle as shown in FIG. 5(b). FIG. 6 illustrates the manner in which non-contributing regions H1 and H2 are created by X-ray blocking plates, each of which is made to upstand perpendicularly to the plane of the Rowland circle in the X-ray spectrometer and parallel to a straight line passing through the center C of an analyzing crystal and the center Q of a Rowland circle in the case of FIG. 4(b). Of incident X-rays X1 emitted from a point X-ray source S toward an analyzing crystal 3, X-ray components going toward the non-contributing region H1 on the crystal near side of the point X-ray source S are blocked by an X-ray blocking plate Ai from reaching the surface of the crystal. Of incident X-rays X2, X-ray components hitting the non-contributing region H2 on the crystal farther side of the point X-ray source S are diffracted by the surface of the crystal but blocked by an X-ray blocking plate Ad from reaching the X-ray detector. That is, the region which is located between the non-contributing regions H1 and H2 and which permits the incident X-rays to hit the crystal surface and the exiting diffracted X-rays to reach the X-ray detector contributes to diffraction. Appropriate height of the X-ray blocking plates that are made to upstand from the position of the surface of the curved analyzing crystal is determined by the size of the Rowland circle in the X-ray spectrometer and the length of the crystal in the direction of angular dispersion. A method of calculating the height of an X-ray blocking plate is described by taking the case in which the X-ray blocking plate is made to upstand perpendicularly to the plane of the Rowland circle in the X-ray spectrometer and parallel to a straight line passing through the center C of the analyzing crystal and the center Q of the Rowland circle as an example by referring to FIG. 10. For the sake of convenience, the center C of the analyzing crystal is taken as the origin of coordinates in FIG. 10. Since the input side and output side of the crystal are symmetrical, only the input side is shown. The surface 3a of the crystal is on an arc C2 of curvature 2R. Let a be the horizontal distance from the center C of the analyzing crystal to the X-ray blocking plate. Let h be the height of the X-ray blocking plates from the height of the center C of the analyzing crystal in a direction parallel to the direction directed toward the center Q of the Rowland circle. Let h0 be the height from the height of the center C of the crystal to the position of the crystal surface in the longitudinal end of the crystal. Let h1 be the height from the position of the crystal surface in the longitudinal end of the crystal to the front end of the X-ray blocking plate. Let b be the horizontal distance from the center C of the analyzing crystal to the front end of the shadow created by the X-ray blocking plate (intersection of the crystal surface 3a and X1). Let k be the height from the height of the center C of the analyzing crystal to the intersection of the crystal surface 3a and X1. Let R be the radius of the Rowland circle. Let θ be the incident angle. Angles γ0 and γ shown in the figure are given by γ 0 = arctan ⁢ a 2 ⁢ R ( 5 ) γ = arcsin ⁢ b 2 ⁢ R ( 6 ) Therefore, from Eqs. (5) and (6), the heights k and h0 are given by k = 2 ⁢ R · ( 1 - cos ⁢ ⁢ γ ) ( 7 ) h 0 = 2 ⁢ R · ( 1 - cos ⁢ ⁢ γ 0 ) ( 8 ) An angle β is given by β = arctan ⁢ cos ⁡ ( θ - γ ) - cos ⁢ ⁢ θ sin ⁡ ( θ - γ ) ( 9 ) Alternatively, the angle β is approximately given by β ≅ γ · sin ⁢ ⁢ θ sin ⁢ ⁢ θ - γ · cos ⁢ ⁢ θ ( 10 ) Therefore, using k in Eq. (7) and β in Eq. (9) or (10), the height h is given byh=(a−b)·tan(θ+β)+k (11)From Eqs. (8) and (11), the height h1 is found from the equation:h1=h−h0 (12) Although the height of the X-ray blocking plate can be found similarly in the case of FIGS. 4(a) and 5(a), its detailed description is omitted. An example in which the height of the X-ray blocking plate was found under the conditions where R=140 mm and α=20 mm by the aforementioned method is described below. b is the distance on the side of the X-ray generation point S in the direction of angular dispersion under the actual conditions where the incident angle error Δθenables regions G1-G3 and where region G4 and the following regions are shielded by the X-ray blocking plate. The results of calculation are shown in Table 2. TABLE 2incident angle θ (in degrees)18.4828.7443.0454.59averageb (mm)8.310.814.317.9—h (mm)4.45.76.34.05.1h1 (mm)3.75.05.63.34.4 As shown in Table 2, the required height of the X-ray blocking plate can be determined from data obtained by calculating the incident angle error Δθ. Meanwhile, the results shown in Table 2 indicate that if the height h of the X-ray blocking plate or h1 is determined such that effective diffractive regions having similar levels of incident angle error Δθ are set, the value of the height h varies depending on the incident angle θ and is not always kept constant. Although this tendency somewhat varies depending on the size of the Rowland circle, on the length of the analyzing crystal in the direction of angular dispersion, and on the direction in which the X-ray blocking plate is made to upstand, the value of the height h generally tends to increase when the incident angle θ is relatively close to the midpoint of the spectral range as shown in Table 2. Accordingly, if the average value of the values of the height h corresponding to different values of the incident angle θ is taken as the height of the X-ray blocking plate, an optimum or nearly optimum average effective diffractive region can be set over the whole spectral range. Alternatively, if an element that is most important or used most frequently within the spectral range, the height h may be set according to the incident angle θ of the characteristic X-rays of that element. Where limitations are imposed on the mechanism of the X-ray spectrometer, it is not always necessary that an X-ray blocking plate be mounted at each of the opposite ends of the analyzing crystal. An X-ray blocking plate may be mounted at any one end. Furthermore, as can be seen from FIGS. 3(a)-3(d), the spread of the region in which the magnitude of the incident angle error Δθ is constant is not symmetrical in the direction of angular dispersion with respect to the center C of the analyzing crystal. The spread is somewhat narrower on the side of the point X-ray source S of X-rays. Therefore, the height h found from the value of the horizontal distance b on the side of the point X-ray source S, the value of b on the opposite side or the average value may be taken as the height of the X-ray blocking plate at each end. The height on the side of the point X-ray source S of X-rays and the height on the opposite side may be set to different appropriate values. In the description of the embodiments of the present invention provided so far, a spherically-curved, Johann-type analyzing crystal is taken as an example. As shown in FIGS. 3(a)-3(d), the region of the spherically-curved, Johann-type analyzing crystal to be blocked is substantially rectangular. Therefore, as shown in FIGS. 4(a) and 4(b) and FIGS. 5(a) and 5(b), the shape of the X-ray blocking plate that is made to upstand may be substantially rectangular. However, in the case of an ordinary analyzing crystal in a Johann geometry curved only in the direction of angular dispersion, the shape of the region in which the incident angle error Δθ increases as shown in FIG. 8(b) does not assume a simple rectangular form. Even in this case, the fully diffractive region while completely satisfying Eq. (2) like the letter X expands and contracts in the direction of angular dispersion according to the value of the incident angle θ (the letter X expands in the direction of angular dispersion according to increasing the value of θ) and so certain advantages can be obtained even if the shape of the X-ray blocking plate made to upstand is substantially rectangular. In addition, if the X-ray blocking plate is shaped like a triangle or an arc directed toward the front end, such as X-ray blocking plates A5 and A6 as shown in FIGS. 11(a) and 11(b), it is obvious that the regions not contributing to diffraction can be more effectively shielded at least in the direction of angular dispersion. The present invention is implemented in an analyzing element made of a layered synthetic microstructure in the manner described below. Where a layered synthetic microstructure is used, an analyzing element adapted for the purpose of use can be fabricated by appropriately selecting a combination of materials used for the stacked layers and the spacing between the stacked layers (i.e., the lattice spacing). One typical example of layered synthetic microstructure analyzing element that has been put into practical use is an element using layers of tungsten and silicon at a lattice spacing of about 3 nm. Another example is an element using layers of nickel and carbon at a lattice spacing of about 5 nm. A further example is an element using layers of molybdenum and carbon tetraboride at a lattice spacing of about 10 nm. In recent years, with improvement of the technique for fabricating layered synthetic microstructure, attempts have been made to fabricate layered synthetic microstructure having smaller lattice spacing than heretofore. FIGS. 12(a)-12(d) show characteristic X-ray spectra derived by an analyzing element mounted to a wavelength-dispersive X-ray spectrometer of the straight moving ray-collection type without using any X-ray blocking plate. The analyzing element has a layered synthetic microstructure having a lattice spacing of about 1.5 nm, which has a curvature equal to the diameter of the Rowland circle in the direction of angular dispersion. In the graphs of FIGS. 12(a)-(d), X-ray intensity is plotted on the vertical axis on an arbitrary scale. The spectral position L when the radius of the Rowland circle is 140 mm is plotted on the horizontal axis. The position L is given by Eq. (3) and represented in millimeters. Spectra of FIGS. 12(a)-12(d) are close to Si—Kα (wavelength of 0.713 nm), Al—Kα (wavelength of 0.834 nm), Mg—Kα (wavelength of 0.989 nm), and F—Kα (wavelength of 1.832 nm), respectively. In this analyzing element of layered synthetic microstructure, the incident angle θ when each characteristic X-ray is diffracted is about 13.7° for Si—Kα, about 16.1° for Al—Kα, about 19.2° for Mg—Kα, and about 37.6° for F—Kα. In each spectrum, the left side on the paper indicates the lower angle side having smaller incident angle θ (the same as the shorter wavelength side). In the spectrum of FIG. 12(a), an abnormal bumpy hill appears clearly on the lower angle side of Si—Kα. In the spectrum FIG. 12(b), an abnormal bumpy hill appears slightly and an abnormally long tail appears on the lower angle side of Al—Kα. In the spectrum of FIG. 12(c), no abnormal bumpy hill is observed but the lower angle side of Mg—Kα has an abnormally long tail. The spectrum of FIG. 12(d) in which only satellite lines of F—Kα are observed is normal. That is, it can be seen that the waveform becomes more abnormal with reducing the incident angle θ of X-rays. Spectra of FIGS. 13(a)-13(d) are close to Si—Kα, Al—Kα, Mg—Kα, and F—Kα, respectively, and have been obtained by using the analyzing element of layered synthetic microstructure from which the spectra of FIGS. 12(a)-12(d) have been taken. The X-ray blocking plate shown in FIG. 11(a) was attached to the analyzing elements. In each spectrum, Kβ-line or satellite line(s) are observed other than Kβ-line. An abnormal bump or tailing on the lower angle side is not observed unlike in the spectra of FIGS. 12(a)-12(d). The results indicate that when X-rays enter at a small incident angle θ, a normal waveform is obtained by the action of the X-ray blocking plate. We conducted similar experiments on curved analyzing elements made of layered synthetic microstructure having lattice spacing of about 2 nm and about 3 nm, respectively. We have confirmed that in the case of the curved analyzing element of the layered synthetic microstructure having a lattice spacing of about 2 nm, the X-ray blocking plate works effectively. However, in the case of the curved analyzing element of the layered synthetic microstructure having a lattice spacing of about 3 nm, the full width at half maximum (FWHM) of the F—Kα line decreases only by several percent even if a large X-ray blocking plate that reduces the intensity of F—Kα line to about 60 to 70% is mounted. Consequently, an X-ray blocking plate is not necessary. Accordingly, our experiment reveals that in the case of a curved analyzing element of a layered synthetic microstructure fitted to an X-ray spectrometer of the straight moving ray-collection type, if the lattice spacing of the analyzing element is less than 2 nm, the X-ray blocking plate for using only an effective diffractive region of the analyzing element removes abnormal waveform portions and thus works effectively to produce a normal waveform. In other words, in cases where an X-ray analysis is performed using an analyzing element of layered synthetic microstructure having a lattice spacing of less than 2 nm, the X-ray blocking plate mentioned above is necessary to carry out the analysis reliably. A layered synthetic microstructure analyzing element producing the spectra shown in FIGS. 12(a)-12(d) and FIGS. 13(a)-13(d) is fabricated by stacking multiple synthetic layers of film on the surface of a flat substrate, and curving the film into a Johann geometry. One method of fabricating an analyzing element with a layered synthetic microstructure consists of shaping the substrate itself into a curved geometry, such as Johann geometry or spherically-curved Johann geometry, and then stacking multiple synthetic layers of film on the substrate. With respect to an analyzing element having a layered synthetic microstructure formed on a previously curved surface, abnormal waveforms can be removed using an X-ray blocking plate in the same way as in the foregoing embodiment and a normal waveform can be obtained. Having thus described my invention with the detail and particularity required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.
	description	This application is a continuation of U.S. Ser. No. 13/024,027, filed on Feb. 9, 2011, which is a continuation-in-part of U.S. Ser. No. 12/166,918, filed on Jul. 2, 2008, now U.S. Pat. No. 7,989,786, which is a continuation-in-part of U.S. Ser. No. 11/695,348, filed on Apr. 2, 2007, now U.S. Pat. No. 7,786,455, which is a continuation-in-part of U.S. Ser. No. 11/395,523, filed on Mar. 31, 2006, now U.S. Pat. No. 7,435,982, the entire disclosures each of which are hereby incorporated by reference herein. This application claims the benefit of, and priority to U.S. Provisional Patent Application No. 61/302,797, filed on Feb. 9, 2010, the entire disclosure of which is incorporated by reference herein. The invention relates to methods and apparatus for providing a laser-driven light source. High brightness light sources can be used in a variety of applications. For example, a high brightness light source can be used for inspection, testing or measuring properties associated with semiconductor wafers or materials used in the fabrication of wafers (e.g., reticles and photomasks). The electromagnetic energy produced by high brightness light sources can, alternatively, be used as a source of illumination in a lithography system used in the fabrication of wafers, a microscopy system, or a photoresist curing system. The parameters (e.g., wavelength, power level and brightness) of the light vary depending upon the application. The state of the art in, for example, wafer inspection systems involves the use of xenon or mercury arc lamps to produce light. The arc lamps include an anode and cathode that are used to excite xenon or mercury gas located in a chamber of the lamp. An electrical discharge is generated between the anode and cathode to provide power to the excited (e.g., ionized) gas to sustain the light emitted by the ionized gas during operation of the light source. During operation, the anode and cathode become very hot due to electrical discharge delivered to the ionized gas located between the anode and cathode. As a result, the anode and/or cathode are prone to wear and may emit particles that can contaminate the light source or result in failure of the light source. Also, these arc lamps do not provide sufficient brightness for some applications, especially in the ultraviolet spectrum. Further, the position of the arc can be unstable in these lamps. Accordingly, a need therefore exists for improved high brightness light sources. A need also exists for improved high brightness light sources that do not rely on an electrical discharge to maintain a plasma that generates a high brightness light. The properties of light produced by many light sources (e.g., arc lamps, microwave lamps) are affected when the light passes through a wall of, for example, a chamber that includes the location from which the light is emitted. Accordingly, a need therefore exists for an improved light source whose emitted light is not significantly affected when the light passes through a wall of a chamber that includes the location from which the light is emitted. The present invention features a light source for generating a high brightness light. The invention, in one aspect, features a light source having a chamber. The light source also includes an ignition source for ionizing a gas within the chamber. The light source also includes at least one laser for providing energy to the ionized gas within the chamber to produce a high brightness light. In some embodiments, the at least one laser is a plurality of lasers directed at a region from which the high brightness light originates. In some embodiments, the light source also includes at least one optical element for modifying a property of the laser energy provided to the ionized gas. The optical element can be, for example, a lens (e.g., an aplanatic lens, an achromatic lens, a single element lens, and a fresnel lens) or mirror (e.g., a coated mirror, a dielectric coated mirror, a narrow band mirror, and an ultraviolet transparent infrared reflecting mirror). In some embodiments, the optical element is one or more fiber optic elements for directing the laser energy to the gas. The chamber can include an ultraviolet transparent region. The chamber or a window in the chamber can include a material selected from the group consisting of quartz, Suprasil® quartz (Heraeus Quartz America, LLC, Buford, Ga.), sapphire, MgF2, diamond, and CaF2. In some embodiments, the chamber is a sealed chamber. In some embodiments, the chamber is capable of being actively pumped. In some embodiments, the chamber includes a dielectric material (e.g., quartz). The chamber can be, for example, a glass bulb. In some embodiments, the chamber is an ultraviolet transparent dielectric chamber. The gas can be one or more of a noble gas, Xe, Ar, Ne, Kr, He, D2, H2, O2, F2, a metal halide, a halogen, Hg, Cd, Zn, Sn, Ga, Fe, Li, Na, an excimer forming gas, air, a vapor, a metal oxide, an aerosol, a flowing media, or a recycled media. The gas can be produced by a pulsed laser beam that impacts a target (e.g., a solid or liquid) in the chamber. The target can be a pool or film of metal. In some embodiments, the target is capable of moving. For example, the target may be a liquid that is directed to a region from which the high brightness light originates. In some embodiments, the at least one laser is multiple diode lasers coupled into a fiber optic element. In some embodiments, the at least one laser includes a pulse or continuous wave laser. In some embodiments, the at least one laser is an IR laser, a diode laser, a fiber laser, an ytterbium laser, a CO2 laser, a YAG laser, or a gas discharge laser. In some embodiments, the at least one laser emits at least one wavelength of electromagnetic energy that is strongly absorbed by the ionized medium. The ignition source can be or can include electrodes, an ultraviolet ignition source, a capacitive ignition source, an inductive ignition source, an RF ignition source, a microwave ignition source, a flash lamp, a pulsed laser, or a pulsed lamp. The ignition source can be a continuous wave (CW) or pulsed laser impinging on a solid or liquid target in the chamber. The ignition source can be external or internal to the chamber. The light source can include at least one optical element for modifying a property of electromagnetic radiation emitted by the ionized gas. The optical element can be, for example, one or more mirrors or lenses. In some embodiments, the optical element is configured to deliver the electromagnetic radiation emitted by the ionized gas to a tool (e.g., a wafer inspection tool, a microscope, a metrology tool, a lithography tool, or an endoscopic tool). The invention, in another aspect, relates to a method for producing light. The method involves ionizing with an ignition source a gas within a chamber. The method also involves providing laser energy to the ionized gas in the chamber to produce a high brightness light. In some embodiments, the method also involves directing the laser energy through at least one optical element for modifying a property of the laser energy provided to the ionized gas. In some embodiments, the method also involves actively pumping the chamber. The ionizable medium can be a moving target. In some embodiments, the method also involves directing the high brightness light through at least one optical element to modify a property of the light. In some embodiments, the method also involves delivering the high brightness light emitted by the ionized medium to a tool (e.g., a wafer inspection tool, a microscope, a metrology tool, a lithography tool, or an endoscopic tool). In another aspect, the invention features a light source. The lights source includes a chamber and an ignition source for ionizing an ionizable medium within the chamber. The light source also includes at least one laser for providing substantially continuous energy to the ionized medium within the chamber to produce a high brightness light. In some embodiments, the at least one laser is a continuous wave laser or a high pulse rate laser. In some embodiments, the at least one laser is a high pulse rate laser that provides pulses of energy to the ionized medium so the high brightness light is substantially continuous. In some embodiments, the magnitude of the high brightness light does not vary by more than about 90% during operation. In some embodiments, the at least one laser provides energy substantially continuously to minimize cooling of the ionized medium when energy is not provided to the ionized medium. In some embodiments, the light source can include at least one optical element (e.g., a lens or mirror) for modifying a property of the laser energy provided to the ionized medium. The optical element can be, for example, an aplanatic lens, an achromatic lens, a single element lens, a fresnel lens, a coated mirror, a dielectric coated mirror, a narrow band mirror, or an ultraviolet transparent infrared reflecting mirror. In some embodiments, the optical element is one or more fiber optic elements for directing the laser energy to the ionizable medium. In some embodiments, the chamber includes an ultraviolet transparent region. In some embodiments, the chamber or a window in the chamber includes a quartz material, suprasil quartz material, sapphire material, MgF2 material, diamond material, or CaF2 material. In some embodiments, the chamber is a sealed chamber. The chamber can be capable of being actively pumped. In some embodiments, the chamber includes a dielectric material (e.g., quartz). In some embodiments, the chamber is a glass bulb. In some embodiments, the chamber is an ultraviolet transparent dielectric chamber. The ionizable medium can be a solid, liquid or gas. The ionizable medium can include one or more of a noble gas, Xe, Ar, Ne, Kr, He, D2, H2, O2, F2, a metal halide, a halogen, Hg, Cd, Zn, Sn, Ga, Fe, Li, Na, an excimer forming gas, air, a vapor, a metal oxide, an aerosol, a flowing media, a recycled media, or an evaporating target. In some embodiments, the ionizable medium is a target in the chamber and the ignition source is a pulsed laser that provides a pulsed laser beam that strikes the target. The target can be a pool or film of metal. In some embodiments, the target is capable of moving. In some embodiments, the at least one laser is multiple diode lasers coupled into a fiber optic element. The at least one laser can emit at least one wavelength of electromagnetic energy that is strongly absorbed by the ionized medium. The ignition source can be or can include electrodes, an ultraviolet ignition source, a capacitive ignition source, an inductive ignition source, an RF ignition source, a microwave ignition source, a flash lamp, a pulsed laser, or a pulsed lamp. The ignition source can be external or internal to the chamber. In some embodiments, the light source includes at least one optical element (e.g., a mirror or lens) for modifying a property of electromagnetic radiation emitted by the ionized medium. The optical element can be configured to deliver the electromagnetic radiation emitted by the ionized medium to a tool (e.g., a wafer inspection tool, a microscope, a metrology tool, a lithography tool, or an endoscopic tool). The invention, in another aspect relates to a method for producing light. The method involves ionizing with an ignition source an ionizable medium within a chamber. The method also involves providing substantially continuous laser energy to the ionized medium in the chamber to produce a high brightness light. In some embodiments, the method also involves directing the laser energy through at least one optical element for modifying a property of the laser energy provided to the ionizable medium. The method also can involve actively pumping the chamber. In some embodiments, the ionizable medium is a moving target. The ionizable medium can include a solid, liquid or gas. In some embodiments, the method also involves directing the high brightness light through at least one optical element to modify a property of the light. In some embodiments, the method also involves delivering the high brightness light emitted by the ionized medium to a tool. The invention, in another aspect, features a light source having a chamber. The light source includes a first ignition means for ionizing an ionizable medium within the chamber. The light source also includes a means for providing substantially continuous laser energy to the ionized medium within the chamber. The invention, in another aspect, features a light source having a chamber that includes a reflective surface. The light source also includes an ignition source for ionizing a gas within the chamber. The light source also includes a reflector that at least substantially reflects a first set of predefined wavelengths of electromagnetic energy directed toward the reflector and at least substantially allows a second set of predefined wavelengths of electromagnetic energy to pass through the reflector. The light source also includes at least one laser (e.g., a continuous-wave fiber laser) external to the chamber for providing electromagnetic energy to the ionized gas within the chamber to produce a plasma that generates a high brightness light. A continuous-wave laser emits radiation continuously or substantially continuously rather than in short bursts, as in a pulsed laser. In some embodiments, at least one laser directs a first set of wavelengths of electromagnetic energy through the reflector toward the reflective surface (e.g., inner surface) of the chamber and the reflective surface directs at least a portion of the first set of wavelengths of electromagnetic energy toward the plasma. In some embodiments, at least a portion of the high brightness light is directed toward the reflective surface of the chamber, is reflected toward the reflector, and is reflected by the reflector toward a tool. In some embodiments, at least one laser directs a first set of wavelengths of electromagnetic energy toward the reflector, the reflector reflects at least a portion of the first wavelengths of electromagnetic energy towards the reflective surface of the chamber, and the reflective surface directs a portion of the first set of wavelengths of electromagnetic energy toward the plasma. In some embodiments, at least a portion of the high brightness light is directed toward the reflective surface of the chamber, is reflected toward the reflector, and passes through the reflector toward an output of the light source. In some embodiments, the light source comprises a microscope, ultraviolet microscope, wafer inspection system, reticle inspection system or lithography system spaced relative to the output of the light source to receive the high brightness light. In some embodiments, a portion of the high brightness light is directed toward the reflective surface of the chamber, is reflected toward the reflector, and electromagnetic energy comprising the second set of predefined wavelengths of electromagnetic energy passes through the reflector. The chamber of the light source can include a window. In some embodiments, the chamber is a sealed chamber. In some embodiments, the reflective surface of the chamber comprises a curved shape, parabolic shape, elliptical shape, spherical shape or aspherical shape. In some embodiments, the chamber has a reflective inner surface. In some embodiments, a coating or film is located on the outside of the chamber to produce the reflective surface. In some embodiments, a coating or film is located on the inside of the chamber to produce the reflective surface. In some embodiments, the reflective surface is a structure or optical element that is distinct from the inner surface of the chamber. The light source can include an optical element disposed along a path the electromagnetic energy from the laser travels. In some embodiments, the optical element is adapted to provide electromagnetic energy from the laser to the plasma over a large solid angle. In some embodiments, the reflective surface of the chamber is adapted to provide electromagnetic energy from the laser to the plasma over a large solid angle. In some embodiments, the reflective surface of the chamber is adapted to collect the high brightness light generated by the plasma over a large solid angle. In some embodiments, one or more of the reflective surface, reflector and the window include (e.g., are coated or include) a material to filter predefined wavelengths (e.g., infrared wavelengths of electromagnetic energy) of electromagnetic energy. The invention, in another aspect, features a light source that includes a chamber that has a reflective surface. The light source also includes an ignition source for ionizing a gas within the chamber. The light source also includes at least one laser external to the chamber for providing electromagnetic energy to the ionized gas within the chamber to produce a plasma that generates a high brightness light. The light source also includes a reflector positioned along a path that the electromagnetic energy travels from the at least one laser to the reflective surface of the chamber. In some embodiments, the reflector is adapted to at least substantially reflect a first set of predefined wavelengths of electromagnetic energy directed toward the reflector and at least substantially allow a second set of predefined wavelengths of electromagnetic energy to pass through the reflector. The invention, in another aspect, relates to a method for producing light. The method involves ionizing with an ignition source a gas within a chamber that has a reflective surface. The method also involves providing laser energy to the ionized gas in the chamber to produce a plasma that generates a high brightness light. In some embodiments, the method involves directing the laser energy comprising a first set of wavelengths of electromagnetic energy through a reflector toward the reflective surface of the chamber, the reflective surface reflecting at least a portion of the first set of wavelengths of electromagnetic energy toward the plasma. In some embodiments, the method involves directing at least a portion of the high brightness light toward the reflective surface of the chamber which is reflected toward the reflector and is reflected by the reflector toward a tool. In some embodiments, the method involves directing the laser energy comprising a first set of wavelengths of electromagnetic energy toward the reflector, the reflector reflects at least a portion of the first wavelengths of electromagnetic energy toward the reflective surface of the chamber, the reflective surface directs a portion of the first set of wavelengths of electromagnetic energy toward the plasma. In some embodiments, the method involves directing a portion of the high brightness light toward the reflective surface of the chamber which is reflected toward the reflector and, electromagnetic energy comprising the second set of predefined wavelengths of electromagnetic energy passes through the reflector. The method can involve directing the laser energy through an optical element that modifies a property of the laser energy to direct the laser energy toward the plasma over a large solid angle. In some embodiments, the method involves directing the laser energy through an optical element that modifies a property of the laser energy to direct the laser energy toward the plasma over a solid angle of approximately 0.012 steradians. In some embodiments, the method involves directing the laser energy through an optical element that modifies a property of the laser energy to direct the laser energy toward the plasma over a solid angle of approximately 0.048 steradians. In some embodiments, the method involves directing the laser energy through an optical element that modifies a property of the laser energy to direct the laser energy toward the plasma over a solid angle of greater than about 2π (about 6.28) steradians. In some embodiments, the reflective surface of the chamber is adapted to provide the laser energy to the plasma over a large solid angle. In some embodiments, the reflective surface of the chamber is adapted to collect the high brightness light generated by the plasma over a large solid angle. The invention, in another aspect, relates to a method for producing light. The method involves ionizing with an ignition source a gas within a chamber that has a reflective surface. The method also involves directing electromagnetic energy from a laser toward a reflector that at least substantially reflects a first set of wavelengths of electromagnetic energy toward the ionized gas in the chamber to produce a plasma that generates a high brightness light. In some embodiments, the electromagnetic energy from the laser first is reflected by the reflector toward the reflective surface of the chamber. In some embodiments, the electromagnetic energy directed toward the reflective surface of the chamber is reflected toward the plasma. In some embodiments, a portion of the high brightness light is directed toward the reflective surface of the chamber, reflected toward the reflector and passes through the reflector. In some embodiments, the electromagnetic energy from the laser first passes through the reflector and travels toward the reflective surface of the chamber. In some embodiments, the electromagnetic energy directed toward the reflective surface of the chamber is reflected toward the plasma. In some embodiments, a portion of the high brightness light is directed toward the reflective surface of the chamber, reflected toward the reflector and reflected by the reflector. The invention, in another aspect, features a light source that includes a chamber having a reflective surface. The light source also includes a means for ionizing a gas within the chamber. The light source also includes a means for at least substantially reflecting a first set of predefined wavelengths of electromagnetic energy directed toward the reflector and at least substantially allowing a second set of predefined wavelengths of electromagnetic energy to pass through the reflector. The light source also includes a means for providing electromagnetic energy to the ionized gas within the chamber to produce a plasma that generates a high brightness light. The invention, in another aspect, features a light source that includes a sealed chamber. The light source also includes an ignition source for ionizing a gas within the chamber. The light source also includes at least one laser external to the sealed chamber for providing electromagnetic energy to the ionized gas within the chamber to produce a plasma that generates a high brightness light. The light source also includes a curved reflective surface disposed external to the sealed chamber to receive at leas a portion of the high brightness light emitted by the sealed chamber and reflect the high brightness light toward an output of the light source. In some embodiments, the light source includes an optical element disposed along a path the electromagnetic energy from the laser travels. In some embodiments, the sealed chamber includes a support element that locates the sealed chamber relative to the curved reflective surface. In some embodiments, the sealed chamber is a quartz bulb. In some embodiments, the light source includes a second curved reflective surface disposed internal or external to the sealed chamber to receive at least a portion of the laser electromagnetic energy and focus the electromagnetic energy on the plasma that generates the high brightness light. The invention, in another aspect, features a light source that includes a sealed chamber and an ignition source for ionizing a gas within the chamber. The light source also includes at least one laser external to the sealed chamber for providing electromagnetic energy. The light source also includes a curved reflective surface to receive and reflect at least a portion of the electromagnetic energy toward the ionized gas within the chamber to produce a plasma that generates a high brightness light, the curved reflective surface also receives at least a portion of the high brightness light emitted by the plasma and reflects the high brightness light toward an output of the light source. In some embodiments, the curved reflective surface focuses the electromagnetic energy on a region in the chamber where the plasma is located. In some embodiments, the curved reflective surface is located within the chamber. In some embodiments, the curved reflective surface is located external to the chamber. In some embodiments, the high brightness light is ultraviolet light, includes ultraviolet light or is substantially ultraviolet light. The invention, in another aspect, features a light source that includes a chamber. The light source also includes an energy source for providing energy to a gas within the chamber to produce a plasma that generates a light emitted through the walls of the chamber. The light source also includes a reflector that reflects the light emitted through the walls of the chamber. The reflector includes a reflective surface with a shape configured to compensate for the refractive index of the walls of the chamber. The shape can include a modified parabolic, elliptical, spherical, or aspherical shape. In some embodiments, the energy source is at least one laser external to the chamber. In some embodiments, the energy source is also an ignition source within the chamber. The energy source can be a microwave energy source, an AC arc source, a DC arc source, a laser, or an RF energy source. The energy source can be a pulse laser, a continuous-wave fiber laser, or a diode laser. In some embodiments, the chamber is a sealed chamber. The chamber can include a cylindrical tube. In some embodiments, the cylindrical tube is tapered. The chamber can include one or more seals at one or both ends of the cylindrical tube. The chamber can include sapphire, quartz, fused quartz, Suprasil quartz, fused silica, Suprasil fused silica, MgF2, diamond, single crystal quartz, or CaF2. The chamber can include a dielectric material. The chamber can include an ultraviolet transparent dielectric material. The chamber can protrude through an opening in the reflector. In some embodiments, the light source also includes an ignition source for ionizing the gas within the chamber. The ignition source can include electrodes, an ultraviolet ignition source, a capacitive ignition source, an inductive ignition source, a flash lamp, a pulsed laser, or a pulsed lamp. The ignition source can include electrodes located on opposite sides of the plasma. In some embodiments, the light source also includes a support element that locates the chamber relative to the reflector. The support element can include a fitting to allow at least one of pressure control or filling of the chamber. In some embodiments, the light source includes at least one optical element. The optical element can modify a property of the light emitted through the walls of the chamber and reflected by the reflector. The optical element can be a mirror or a lens. The optical element can be configured to deliver the light emitted through the walls of the chamber and reflected by the reflector to a tool (e.g. a wafer inspection tool, a microscope, an ultraviolet microscope, a reticle inspection system, a metrology tool, a lithography tool, or an endoscopic tool). The invention, in another aspect, features a method for producing light. The method involves emitting a light through the walls of a chamber. The method also involves using a reflective surface of a reflector to reflect the light, wherein the reflective surface has a shape configured to compensate for the refractive index of the walls of the chamber. In some embodiments, the method also involves flowing gas into the chamber. In some embodiments, the method also involves igniting the gas in the chamber to produce an ionized gas. In some embodiments, the method also involves directing energy to the ionized gas to produce a plasma that generates a light (e.g. a high brightness light). In some embodiments, the method also involves directing laser energy into the chamber from at least one laser external to the chamber. In some embodiments, the method also involves directing the laser energy through an optical element that modifies a property of the laser energy. In some embodiments, the method also involves directing the reflected light through an optical element to modify a property of the reflected light. In some embodiments, the method also involves directing the reflected light to a tool. In some embodiments, the method also involves controlling the pressure of the chamber. In some embodiments, the method also involves expressing the shape as a mathematical equation. In some embodiments, the method also involves selecting parameters of the equation to reduce error due to the refractive index of the walls of the chamber below a specified value. In some embodiments, the method also involves configuring the shape to compensate for the refractive index of the walls of the chamber. In some embodiments, the method also involves producing a collimated or focused beam of reflected light with the reflective surface. In some embodiments, the method also involves modifying a parabolic, elliptical, spherical, or aspherical shape to compensate for the refractive index of the walls of the chamber to produce a focused, reflected high brightness light. The invention, in another aspect, features a light source including a chamber. The light source also includes a laser source for providing electromagnetic energy to a gas within the chamber to produce a plasma that generates a light emitted through the walls of the chamber. The light source also includes a reflector that reflects the electromagnetic energy through the walls of the chamber and the light emitted through the walls of the chamber, the reflector includes a reflective surface with a shape configured to compensate for the refractive index of the walls of the chamber. The invention, in another aspect, features a light source having a chamber. The light source also includes means for providing energy to a gas within the chamber to produce a plasma that generates a light emitted through the walls of the chamber. The light source also includes means for reflecting the light emitted through the walls of the chamber, the reflecting means including a reflective surface with a shape configured to compensate for the refractive index of the walls of the chamber. The invention, in another aspect, features a light source having a chamber. The light source also includes an ignition source for ionizing a medium (e.g., a gas) within the chamber. The light source also includes a laser for providing energy to the ionized medium within the chamber to produce a light. The light source also includes a blocker suspended along a path the energy travels to block at least a portion of the energy. In some embodiments, the blocker deflects energy provided to the ionized medium that is not absorbed by the ionized medium away from an output of the light source. In some embodiments, the blocker is a mirror. In some embodiments, the blocker absorbs the energy provided to the ionized medium that is not absorbed by the ionized medium. The blocker can include graphite. In some embodiments, the blocker reflects energy provided to the ionized medium that is not absorbed by the ionized medium. In some embodiments, the reflected energy is reflected toward the ionized medium in the chamber. In some embodiments, the blocker is a coating on a portion of the chamber. In some embodiments, the light source includes a coolant channel disposed in the blocker. In some embodiments, the light source includes a coolant supply (e.g., for supplying coolant, for example, water) coupled to the coolant channel. In some embodiments, light source includes a gas source that blows a gas (e.g., nitrogen or air) on the blocker to cool the blocker. In some embodiments, the light source includes an arm connecting the blocker to a housing of the light source. In some embodiments, the energy provided by the laser enters the chamber on a first side of the chamber and the blocker is suspended on a second side of the chamber opposite the first side. The invention, in another aspect, relates to a method for producing light. The method involves ionizing with an ignition source a medium within a chamber. The method also involves providing laser energy to the ionized medium in the chamber to produce a light. The method also involves blocking energy provided to the ionized medium that is not absorbed by the ionized medium with a blocker suspended along a path the energy travels. In some embodiments, blocking the energy involves deflecting the energy away from an output of the light source. In some embodiments, the blocker includes a mirror. In some embodiments, blocking the energy includes absorbing the energy. In some embodiments, blocking the energy includes reflecting the energy. In some embodiments, reflecting the energy includes reflecting the energy towards the ionized medium in the chamber. In some embodiments, the method also involves cooling the blocker. In some embodiments, cooling the blocker includes flowing a coolant through a channel in or coupled to the blocker. In some embodiments, the method involves blowing a gas on the blocker to cooler the blocker. The invention, in another aspect, relates to a method for producing light. The method involves ionizing with an ignition source a gas within a chamber. The method also involves providing laser energy to the ionized gas in the chamber at a pressure of greater than 10 atmospheres to produce a high brightness light. In some embodiments, the gas within the chamber is at a pressure of greater than 30 atmospheres. In some embodiments, the gas within the chamber is at a pressure of greater than 50 atmospheres. In some embodiments, the high brightness light is emitted from a plasma having a volume of about 0.01 mm3. The invention, in another aspect, relates to a light source having a chamber with a gas disposed therein, and ignition source and at least one laser. The ignition source excites the gas. The excited gas has at least one strong absorption line at an infrared wavelength. The at least one laser provides energy to the excited gas at a wavelength near a strong absorption line of the excited gas within the chamber to produce a high brightness light. In some embodiments, the gas comprises a noble gas. The gas can comprise xenon. In some embodiments, the excited gas comprises atoms at a lowest excited state. The gas can be absorptive near the wavelength of the at least one laser. The strong absorption line of the excited gas can be about 980 nm or about 882 nm. In some embodiments, the excited gas is in a metastable state. The invention, in another aspect, relates to a method for producing light. An ignition source excites a gas within a chamber. A laser is tuned to a first wavelength to provide energy to the excited gas in the chamber to produce a high brightness light. The excited gas absorbs energy near the first wavelength. The laser is tuned to a second wavelength to provide energy to the excited gas in the chamber to maintain the high brightness light. The excited gas absorbs energy near the second wavelength. In some embodiments, the laser is tuned to the first and second wavelengths by adjusting the operating temperature of the laser. In some embodiments, the laser is a diode laser and the laser is tuned approximately 0.4 nm per degree Celsius of temperature adjustment. The operating temperature of the laser can be adjusted by varying a current of a thermoelectric cooling device. The gas within the chamber can have atoms with electrons in at least one excited atomic state. The gas within chamber can be a noble gas, and in some embodiments, the gas within the chamber is xenon. In some embodiments, the first wavelength is approximately 980 nm. The second wavelength can be approximately 975 nm. The second wavelength can be approximately 1 nm to approximately 10 nm displaced from the first wavelength. The invention, in another aspect, relates to a light source. The light source includes a chamber having one or more walls and a gas disposed within the chamber. The light source also includes at least one laser for providing a converging beam of energy focused on the gas within the chamber to produce a plasma that generates a light emitted through the walls of the chamber, such that a numerical aperture of the converging beam of energy is between about 0.1 to about 0.8. In some embodiments, the numerical aperture is about 0.4 to about 0.6. The numeral aperture can be about 0.5. The light source can also include an optical element within a path of the beam. The optical element can be capable of increasing the numerical aperture of the beam. In some embodiments, the optical element is a lens or a mirror. The lens can be an aspheric lens. In some embodiments, a spectral radiance of the plasma increases with an increase in numerical aperture of the beam. The invention, in another aspect, relates to a method of pre-aligning a bulb for a light source. The bulb, having two electrodes, is coupled to a mounting base. The bulb and mounting base structure are inserting into a camera assembly. The camera assembly includes at least one camera and a display screen. At least one image of the bulb from the at least one camera is displays on the display screen. A position of the bulb within the mounted base is adjusted such that a region of the bulb between the two electrodes aligns with a positioning grid on the display screen. In some embodiments, a lamp for a light source is pre-aligned using the method described herein. In some embodiments, the method also includes toggling between the at least two cameras to align the bulb. The camera assembly can include two cameras. Images from the two cameras can be displayed in different colors. In some embodiments, the two cameras are positioned to capture images of the bulb from two orthogonal directions. The position of the bulb can be adjusted vertically and horizontally. The position of the bulb can be adjusted by a manipulator. The manipulator can be positioned above the bulb and can be capable of moving the bulb vertically and horizontally. The method can also include securing the bulb to a base after the region of the bulb between the two electrodes aligns with the positioning grid on the display screen. In some embodiments, the positioning grid is pre-determined such that when the center area of the bulb between the two electrodes aligns with the positioning grid on the display screen, the region is aligned relative to a focal point of a laser when the bulb and mounting base are inserted into a light source. The invention, in another aspect, relates to a method for decreasing noise within a light source. The light source includes a laser. A sample of light emitted from the light source is collected. The sample of light is converted to an electrical signal. The electrical is compared to a reference signal to obtain an error signal. The error signal is processed to obtain a control signal. A magnitude of a laser of the light source is set based on the control signal to decrease noise within the light source. These steps can be repeated until a desired amount of noise is reached. In some embodiments, the sample of light emitted from the light source is collected from a beam splitter. The beam splitter can be a glass beam splitter or a bifurcated fiber bundle. In some embodiments, the error signal is the difference between the reference sample and the converted sample. The error signal can be processed by a control amplifier. The control amplifier is capable of outputting a control signal proportional to at least one of a time integral, a time derivative, or a magnitude of the error signal. The sample can be collected using a photodiode. In some embodiments, the sample is collected using a photodiode within a casing of the light source. In some embodiments, the sample is collected using a photodiode external to a casing of the light source. In some embodiments, two samples are collected. One sample can be collected using a first photodiode within a casing of the light source and another sample can be collected using a second photodiode external to the casing of the light source. The invention, in another aspect, relates to a light source. The light source includes a chamber having one or more walls and a gas disposed within the chamber. The light source also includes at least one laser for providing energy to the gas within the chamber to produce a plasma that generates a light emitted through the walls of the chamber. A dichroic mirror is positioned within a path of the at least one laser such that the laser energy is directed toward the plasma. The dichroic mirror selectively reflects at least one wavelength of light such that the light generated by the plasma is not substantially reflected toward the at least one laser. The invention, in another aspect, relates to a light source. The light source has a chamber with a gas disposed therein and an ignition source for exciting the gas. The light source also has at least one laser for providing energy to the excited gas within the chamber to produce a high brightness light having a first spectrum. An optical element is disposed within the path of the high brightness light to modify the first spectrum of the high brightness light to a second spectrum. The optical element can be a prism, a weak lens, a strong lens, or a dichroic filter. In some embodiments, the second spectrum has a greater proportion of intensity of light in the ultraviolet range than the first spectrum. In some embodiments, the first spectrum has a greater proportion of intensity of light in the visible range than the second spectrum. The invention, in another aspect, relates to a method for decreasing noise of a light source within a predetermined frequency band. The light source includes a laser diode. A current of the laser diode is modulated at a frequency greater than the predetermined frequency band causing the laser to rapidly switch between different sets of modes to decrease noise of the light source within the predetermined frequency band. The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims. FIG. 1 is a schematic block diagram of a light source 100 for generating light that embodies the invention. The light source 100 includes a chamber 128 that contains an ionizable medium (not shown). The light source 100 provides energy to a region 130 of the chamber 128 having the ionizable medium which creates a plasma 132. The plasma 132 generates and emits a high brightness light 136 that originates from the plasma 132. The light source 100 also includes at least one laser source 104 that generates a laser beam that is provided to the plasma 132 located in the chamber 128 to initiate and/or sustain the high brightness light 136. In some embodiments, it is desirable for at least one wavelength of electromagnetic energy generated by the laser source 104 to be strongly absorbed by the ionizable medium in order to maximize the efficiency of the transfer of energy from the laser source 104 to the ionizable medium. In some embodiments, it is desirable for the plasma 132 to be small in size in order to achieve a high brightness light source. Brightness is the power radiated by a source of light per unit surface area into a unit solid angle. The brightness of the light produced by a light source determines the ability of a system (e.g., a metrology tool) or an operator to see or measure things (e.g., features on the surface of a wafer) with adequate resolution. It is also desirable for the laser source 104 to drive and/or sustain the plasma with a high power laser beam. Generating a plasma 132 that is small in size and providing the plasma 132 with a high power laser beam leads simultaneously to a high brightness light 136. The light source 100 produces a high brightness light 136 because most of the power introduced by the laser source 104 is then radiated from a small volume, high temperature plasma 132. The plasma 132 temperature will rise due to heating by the laser beam until balanced by radiation and other processes. The high temperatures that are achieved in the laser sustained plasma 132 yield increased radiation at shorter wavelengths of electromagnetic energy, for example, ultraviolet energy. In one experiment, temperatures between about 10,000 K and about 20,000 K have been observed. The radiation of the plasma 132, in a general sense, is distributed over the electromagnetic spectrum according to Planck's radiation law. The wavelength of maximum radiation is inversely proportional to the temperature of a black body according to Wien's displacement law. While the laser sustained plasma is not a black body, it behaves similarly and as such, the highest brightness in the ultraviolet range at around 300 nm wavelength is expected for laser sustained plasmas having a temperature of between about 10,000 K and about 15,000 K. Most conventional arc lamps are, however, unable to operate at these temperatures. It is therefore desirable in some embodiments of the invention to maintain the temperature of the plasma 132 during operation of the light source 100 to ensure that a sufficiently bright light 136 is generated and that the light emitted is substantially continuous during operation. In this embodiment, the laser source 104 is a diode laser that outputs a laser beam via a fiberoptic element 108. The fiber optic element 108 provides the laser beam to a collimator 112 that aids in conditioning the output of the diode laser by aiding in making laser beam rays 116 substantially parallel to each other. The collimator 112 then directs the laser beam 116 to a beam expander 118. The beam expander 118 expands the size of the laser beam 116 to produce laser beam 122. The beam expander 118 also directs the laser beam 122 to an optical lens 120. The optical lens 120 is configured to focus the laser beam 122 to produce a smaller diameter laser beam 124 that is directed to the region 130 of the chamber 128 where the plasma 132 exists (or where it is desirable for the plasma 132 to be generated and sustained). In this embodiment, the light source 100 also includes an ignition source 140 depicted as two electrodes (e.g., an anode and cathode located in the chamber 128). The ignition source 140 generates an electrical discharge in the chamber 128 (e.g., the region 130 of the chamber 128) to ignite the ionizable medium. The laser then provides laser energy to the ionized medium to sustain or create the plasma 132 which generates the high brightness light 136. The light 136 generated by the light source 100 is then directed out of the chamber to, for example, a wafer inspection system (not shown). Alternative laser sources are contemplated according to illustrative embodiments of the invention. In some embodiments, neither the collimator 112, the beam expander 118, or the lens 120 may be required. In some embodiments, additional or alternative optical elements can be used. The laser source can be, for example, an infrared (IR) laser source, a diode laser source, a fiber laser source, an ytterbium laser source, a CO2 laser source, a YAG laser source, or a gas discharge laser source. In some embodiments, the laser source 104 is a pulse laser source (e.g., a high pulse rate laser source) or a continuous wave laser source. Fiber lasers use laser diodes to pump a special doped fiber which then lases to produce the output (i.e., a laser beam). In some embodiments, multiple lasers (e.g., diode lasers) are coupled to one or more fiber optic elements (e.g., the fiber optic element 108). Diode lasers take light from one (or usually many) diodes and direct the light down a fiber to the output. In some embodiments, fiber laser sources and direct semiconductor laser sources are desirable for use as the laser source 104 because they are relatively low in cost, have a small form factor or package size, and are relatively high in efficiency. Efficient, cost effective, high power lasers (e.g., fiber lasers and direct diode lasers) are recently available in the NIR (near infrared) wavelength range from about 700 nm to about 2000 nm. Energy in this wavelength range is more easily transmitted through certain materials (e.g., glass, quartz and sapphire) that are more commonly used to manufacture bulbs, windows and chambers. It is therefore more practical now to produce light sources that operate using lasers in the 700 nm to 2000 nm range than has previously been possible. In some embodiments, the laser source 104 is a high pulse rate laser source that provides substantially continuous laser energy to the light source 100 sufficient to produce the high brightness light 136. In some embodiments, the emitted high brightness light 136 is substantially continuous where, for example, magnitude (e.g. brightness or power) of the high brightness light does not vary by more than about 90% during operation. In some embodiments, the ratio of the peak power of the laser energy delivered to the plasma to the average power of the laser energy delivered to the plasma is approximately 2-3. In some embodiments, the substantially continuous energy provided to the plasma 132 is sufficient to minimize cooling of the ionized medium to maintain a desirable brightness of the emitted light 136. In this embodiment, the light source 100 includes a plurality of optical elements (e.g., a beam expander 118, a lens 120, and fiber optic element 108) to modify properties (e.g., diameter and orientation) of the laser beam delivered to the chamber 132. Various properties of the laser beam can be modified with one or more optical elements (e.g., mirrors or lenses). For example, one or more optical elements can be used to modify the portions of, or the entire laser beam diameter, direction, divergence, convergence, numerical aperture and orientation. In some embodiments, optical elements modify the wavelength of the laser beam and/or filter out certain wavelengths of electromagnetic energy in the laser beam. Lenses that can be used in various embodiments of the invention include, aplanatic lenses, achromatic lenses, single element lenses, and fresnel lenses. Minors that can be used in various embodiments of the invention include, coated mirrors, dielectric coated mirrors, narrow band mirrors, and ultraviolet transparent infrared reflecting mirrors. By way of example, ultraviolet transparent infrared reflecting mirrors are used in some embodiments of the invention where it is desirable to filter out infrared energy from a laser beam while permitting ultraviolet energy to pass through the mirror to be delivered to a tool (e.g., a wafer inspection tool, a microscope, a lithography tool or an endoscopic tool). In this embodiment, the chamber 128 is a sealed chamber initially containing the ionizable medium (e.g., a solid, liquid or gas). In some embodiments, the chamber 128 is instead capable of being actively pumped where one or more gases are introduced into the chamber 128 through a gas inlet (not shown), and gas is capable of exiting the chamber 128 through a gas outlet (not shown). The chamber can be fabricated from or include one or more of, for example, a dielectric material, a quartz material, Suprasil quartz, sapphire, MgF2, diamond or CaF2. The type of material may be selected based on, for example, the type of ionizable medium used and/or the wavelengths of light 136 that are desired to be generated and output from the chamber 128. In some embodiments, a region of the chamber 128 is transparent to, for example, ultraviolet energy. Chambers 128 fabricated using quartz will generally allow wavelengths of electromagnetic energy of as long as about 2 microns to pass through walls of the chamber. Sapphire chamber walls generally allow electromagnetic energy of as long as about 4 microns to pass through the walls. In some embodiments, it is desirable for the chamber 128 to be a sealed chamber capable of sustaining high pressures and temperatures. For example, in one embodiment, the ionizable medium is mercury vapor. To contain the mercury vapor during operation, the chamber 128 is a sealed quartz bulb capable of sustaining pressures between about 10 to about 200 atmospheres and operating at about 900 degrees centigrade. The quartz bulb also allows for transmission of the ultraviolet light 136 generated by the plasma 132 of the light source 100 through the chamber 128 walls. Various ionizable media can be used in alternative embodiments of the invention. For example, the ionizable medium can be one or more of a noble gas, Xe, Ar, Ne, Kr, He, D2, H2, O2, F2, a metal halide, a halogen, Hg, Cd, Zn, Sn, Ga, Fe, Li, Na, an excimer forming gas, air, a vapor, a metal oxide, an aerosol, a flowing media, or a recycled media. In some embodiments, a solid or liquid target (not shown) in the chamber 128 is used to generate an ionizable gas in the chamber 128. The laser source 104 (or an alternative laser source) can be used to provide energy to the target to generate the ionizable gas. The target can be, for example, a pool or film of metal. In some embodiments, the target is a solid or liquid that moves in the chamber (e.g., in the form of droplets of a liquid that travel through the region 130 of the chamber 128). In some embodiments, a first ionizable gas is first introduced into the chamber 128 to ignite the plasma 132 and then a separate second ionizable gas is introduced to sustain the plasma 132. In this embodiment, the first ionizable gas is a gas that is more easily ignited using the ignition source 140 and the second ionizable gas is a gas that produces a particular wavelength of electromagnetic energy. In this embodiment, the ignition source 140 is a pair of electrodes located in the chamber 128. In some embodiments, the electrodes are located on the same side of the chamber 128. A single electrode can be used with, for example, an RF ignition source or a microwave ignition source. In some embodiments, the electrodes available in a conventional arc lamp bulb are the ignition source (e.g., a model USH-200DP quartz bulb manufactured by Ushio (with offices in Cypress, Calif.)). In some embodiments, the electrodes are smaller and/or spaced further apart than the electrodes used in a conventional arc lamp bulb because the electrodes are not required for sustaining the high brightness plasma in the chamber 128. Various types and configurations of ignition sources are also contemplated, however, that are within the scope of the present invention. In some embodiments, the ignition source 140 is external to the chamber 128 or partially internal and partially external to the chamber 128. Alternative types of ignition sources 140 that can be used in the light source 100 include ultraviolet ignition sources, capacitive discharge ignition sources, inductive ignition sources, RF ignition sources, a microwave ignition sources, flash lamps, pulsed lasers, and pulsed lamps. In one embodiment, no ignition source 140 is required and instead the laser source 104 is used to ignite the ionizable medium and to generate the plasma 132 and to sustain the plasma and the high brightness light 136 emitted by the plasma 132. In some embodiments, it is desirable to maintain the temperature of the chamber 128 and the contents of the chamber 128 during operation of the light source 100 to ensure that the pressure of gas or vapor within the chamber 128 is maintained at a desired level. In some embodiments, the ignition source 140 can be operated during operation of the light source 100, where the ignition source 140 provides energy to the plasma 132 in addition to the energy provided by the laser source 104. In this manner, the ignition source 140 is used to maintain (or maintain at an adequate level) the temperature of the chamber 128 and the contents of the chamber 128. In some embodiments, the light source 100 includes at least one optical element (e.g., at least one mirror or lens) for modifying a property of the electromagnetic energy (e.g., the high brightness light 136) emitted by the plasma 132 (e.g., an ionized gas), similarly as described elsewhere herein. FIG. 2 is a schematic block diagram of a portion of a light source 200 incorporating principles of the present invention. The light source 200 includes a chamber 128 containing an ionizable gas and has a window 204 that maintains a pressure within the chamber 128 while also allowing electromagnetic energy to enter the chamber 128 and exit the chamber 128. In this embodiment, the chamber 128 has an ignition source (not shown) that ignites the ionizable gas (e.g., mercury or xenon) to produce a plasma 132. A laser source 104 (not shown) provides a laser beam 216 that is directed through a lens 208 to produce laser beam 220. The lens 208 focuses the laser beam 220 on to a surface 224 of a thin film reflector 212 that reflects the laser beam 220 to produce laser beam 124. The reflector 212 directs the laser beam 124 on region 130 where the plasma 132 is located. The laser beam 124 provides energy to the plasma 132 to sustain and/or generate a high brightness light 136 that is emitted from the plasma 132 in the region 130 of the chamber 128. In this embodiment, the chamber 128 has a paraboloid shape and an inner surface 228 that is reflective. The paraboloid shape and the reflective surface cooperate to reflect a substantial amount of the high brightness light 136 toward and out of the window 204. In this embodiment, the reflector 212 is transparent to the emitted light 136 (e.g., at least one or more wavelengths of ultraviolet light). In this manner, the emitted light 136 is transmitted out of the chamber 128 and directed to, for example, a metrology tool (not shown). In one embodiment, the emitted light 136 is first directed towards or through additional optical elements before it is directed to a tool. By way of illustration, an experiment was conducted to generate ultraviolet light using a light source, according to an illustrative embodiment of the invention. A model L6724 quartz bulb manufactured by Hamamatsu (with offices in Bridgewater, N.J.) was used as the chamber of the light source (e.g., the chamber 128 of the light source 100 of FIG. 1) for experiments using xenon as the ionizable medium in the chamber. A model USH-200DP quartz bulb manufactured by Ushio (with offices in Cypress, Calif.) was used as the chamber of the light source for experiments using mercury as the ionizable medium in the chamber. FIG. 3 illustrates a plot 300 of the UV brightness of a high brightness light produced by a plasma located in the chamber as a function of the laser power (in watts) provided to the plasma. The laser source used in the experiment was a 1.09 micron, 100 watt CW laser. The Y-Axis 312 of the plot 300 is the UV brightness (between about 200 and about 400 nm) in watts/mm2 steradian (sr). The X-Axis 316 of the plot 300 is the laser beam power in watts provided to the plasma. Curve 304 is the UV brightness of the high brightness light produced by a plasma that was generated using xenon as the ionizable medium in the chamber. The plasma in the experiment using xenon was between about 1 mm and about 2 mm in length and about 0.1 mm in diameter. The length of the plasma was controlled by adjusting the angle of convergence of the laser beam. A larger angle (i.e., larger numerical aperture) leads to a shorter plasma because the converging beam reaches an intensity capable of sustaining the plasma when it is closer to the focal point. Curve 308 is the UV brightness of the high brightness light produced by a plasma that was generated using mercury as the ionizable medium in the chamber. The plasma in the experiment using mercury was about 1 mm in length and about 0.1 mm in diameter. By way of illustration, another experiment was conducted to generate ultraviolet using a light source according to an illustrative embodiment of the invention. A model USH-200DP quartz bulb manufactured by Ushio (with offices in Cypress, Calif.) was used as the chamber of the light source for experiments using mercury as the ionizable medium in the chamber (e.g., the chamber 128 of the light source 100 of FIG. 1). The laser source used in the experiment was a 1.09 micron, 100 watt ytterbium doped fiber laser from SPI Lasers PLC (with offices in Los Gatos, Calif.). FIG. 4 illustrates a plot 400 of the transmission of laser energy through a plasma located in the chamber generated from mercury versus the amount of power provided to the plasma in watts. The Y-Axis 412 of the plot 400 is the transmission coefficient in non-dimensional units. The X-Axis 416 of the plot 400 is the laser beam power in watts provided to the plasma. The curve in the plot 400 illustrates absorption lengths of 1 mm were achieved using the laser source. The transmission value of 0.34 observed at 100 watts corresponds to a 1/e absorption length of about 1 mm. FIG. 5 is a schematic block diagram of a portion of a light source 500 incorporating principles of the present invention. The light source 500 includes a chamber 528 that has a reflective surface 540. The reflective surface 540 can have, for example, a parabolic shape, elliptical shape, curved shape, spherical shape or aspherical shape. In this embodiment, the light source 500 has an ignition source (not shown) that ignites an ionizable gas (e.g., mercury or xenon) in a region 530 within the chamber 528 to produce a plasma 532. In some embodiments, the reflective surface 540 can be a reflective inner or outer surface. In some embodiments, a coating or film is located on the inside or outside of the chamber to produce the reflective surface 540. A laser source (not shown) provides a laser beam 516 that is directed toward a surface 524 of a reflector 512. The reflector 512 reflects the laser beam 520 toward the reflective surface 540 of the chamber 528. The reflective surface 540 reflects the laser beam 520 and directs the laser beam toward the plasma 532. The laser beam 516 provides energy to the plasma 532 to sustain and/or generate a high brightness light 536 that is emitted from the plasma 532 in the region 530 of the chamber 528. The high brightness light 536 emitted by the plasma 532 is directed toward the reflective surface 540 of the chamber 528. At least a portion of the high brightness light 536 is reflected by the reflective surface 540 of the chamber 528 and directed toward the reflector 512. The reflector 512 is substantially transparent to the high brightness light 536 (e.g., at least one or more wavelengths of ultraviolet light). In this manner, the high brightness light 536 passes through the reflector 512 and is directed to, for example, a metrology tool (not shown). In some embodiments, the high brightness light 536 is first directed towards or through a window or additional optical elements before it is directed to a tool. In some embodiments, the light source 500 includes a separate, sealed chamber (e.g., the sealed chamber 728 of FIG. 7) located in the concave region of the chamber 528. The sealed chamber contains the ionizable gas that is used to create the plasma 532. In alternative embodiments, the sealed chamber contains the chamber 528. In some embodiments, the sealed chamber also contains the reflector 512. FIG. 6 is a schematic block diagram of a portion of a light source 600 incorporating principles of the present invention. The light source 600 includes a chamber 628 that has a reflective surface 640. The reflective surface 640 can have, for example, a parabolic shape, elliptical shape, curved shape, spherical shape or aspherical shape. In this embodiment, the light source 600 has an ignition source (not shown) that ignites an ionizable gas (e.g., mercury or xenon) in a region 630 within the chamber 628 to produce a plasma 632. A laser source (not shown) provides a laser beam 616 that is directed toward a reflector 612. The reflector 612 is substantially transparent to the laser beam 616. The laser beam 616 passes through the reflector 612 and is directed toward the reflective surface 640 of the chamber 628. The reflective surface 640 reflects the laser beam 616 and directs it toward the plasma 632 in the region 630 of the chamber 628. The laser beam 616 provides energy to the plasma 632 to sustain and/or generate a high brightness light 636 that is emitted from the plasma 632 in the region 630 of the chamber 628. The high brightness light 636 emitted by the plasma 632 is directed toward the reflective surface 640 of the chamber 628. At least a portion of the high brightness light 636 is reflected by the reflective surface 640 of the chamber 628 and directed toward a surface 624 of the reflector 612. The reflector 612 reflects the high brightness light 636 (e.g., at least one or more wavelengths of ultraviolet light). In this manner, the high brightness light 636 (e.g., visible and/or ultraviolet light) is directed to, for example, a metrology tool (not shown). In some embodiments, the high brightness light 636 is first directed towards or through a window or additional optical elements before it is directed to a tool. In some embodiments, the high brightness light 636 includes ultraviolet light. Ultraviolet light is electromagnetic energy with a wavelength shorter than that of visible light, for instance between about 50 nm and 400 nm. In some embodiments, the light source 600 includes a separate, sealed chamber (e.g., the sealed chamber 728 of FIG. 7) located in the concave region of the chamber 628. The sealed chamber contains the ionizable gas that is used to create the plasma 632. In alternative embodiments, the sealed chamber contains the chamber 628. In some embodiments, the sealed chamber also contains the reflector 612. FIG. 7 is a schematic block diagram of a light source 700 for generating light that embodies the invention. The light source 700 includes a sealed chamber 728 (e.g., a sealed quartz bulb) that contains an ionizable medium (not shown). The light source 700 provides energy to a region 730 of the chamber 728 having the ionizable medium which creates a plasma 732. The plasma 732 generates and emits a high brightness light 736 that originates from the plasma 732. The light source 700 also includes at least one laser source 704 that generates a laser beam that is provided to the plasma 732 located in the chamber 728 to initiate and/or sustain the high brightness light 736. In this embodiment, the laser source 704 is a diode laser that outputs a laser beam via a fiberoptic element 708. The fiber optic element 708 provides the laser beam to a collimator 712 that aids in conditioning the output of the diode laser by aiding in making laser beam rays 716 substantially parallel to each other. The collimator 712 then directs the laser beam 716 to a beam expander 718. The beam expander 718 expands the size of the laser beam 716 to produce laser beam 722. The beam expander 718 also directs the laser beam 722 to an optical lens 720. The optical lens 720 is configured to focus the laser beam 722 to produce a smaller diameter laser beam 724. The laser beam 724 passes through an aperture or window 772 located in the base 724 of a curved reflective surface 740 and is directed toward the chamber 728. The chamber 728 is substantially transparent to the laser beam 724. The laser beam 724 passes through the chamber 728 and toward the region 730 of the chamber 728 where the plasma 732 exists (or where it is desirable for the plasma 732 to be generated by the laser 724 and sustained). In this embodiment, the ionizable medium is ignited by the laser beam 724. In alternative embodiments, the light source 700 includes an ignition source (e.g., a pair of electrodes or a source of ultraviolet energy) that, for example, generates an electrical discharge in the chamber 728 (e.g., the region 730 of the chamber 728) to ignite the ionizable medium. The laser source 704 then provides laser energy to the ionized medium to sustain the plasma 732 which generates the high brightness light 736. The chamber 728 is substantially transparent to the high brightness light 736 (or to predefined wavelengths of electromagnetic radiation in the high brightness light 736). The light 736 (e.g., visible and/or ultraviolet light) generated by the light source 700 is then directed out of the chamber 728 toward an inner surface 744 of the reflective surface 740. In this embodiment, the light source 700 includes a plurality of optical elements (e.g., a beam expander 718, a lens 720, and fiber optic element 708) to modify properties (e.g., diameter and orientation) of the laser beam delivered to the chamber 732. Various properties of the laser beam can be modified with one or more optical elements (e.g., mirrors or lenses). For example, one or more optical elements can be used to modify the portions of, or the entire laser beam diameter, direction, divergence, convergence, and orientation. In some embodiments, optical elements modify the wavelength of the laser beam and/or filter out certain wavelengths of electromagnetic energy in the laser beam. Lenses that can be used in various embodiments of the invention include, aplanatic lenses, achromatic lenses, single element lenses, and fresnel lenses. Minors that can be used in various embodiments of the invention include, coated mirrors, dielectric coated mirrors, narrow band mirrors, and ultraviolet transparent infrared reflecting mirrors. By way of example, ultraviolet transparent infrared reflecting mirrors are used in some embodiments of the invention where it is desirable to filter out infrared energy from a laser beam while permitting ultraviolet energy to pass through the mirror to be delivered to a tool (e.g., a wafer inspection tool, a microscope, a lithography tool or an endoscopic tool). FIGS. 8A and 8B are schematic block diagrams of a light source 800 for generating light that embodies the invention. The light source 800 includes a chamber 828 that contains an ionizable medium (not shown). The light source 800 provides energy to a region 830 of the chamber 828 having the ionizable medium which creates a plasma. The plasma generates and emits a high brightness light that originates from the plasma. The light source 800 also includes at least one laser source 804 that generates a laser beam that is provided to the plasma located in the chamber 828 to initiate and/or sustain the high brightness light. In some embodiments, it is desirable for the plasma to be small in size in order to achieve a high brightness light source. Brightness is the power radiated by a source of light per unit surface area into a unit solid angle. The brightness of the light produced by a light source determines the ability of a system (e.g., a metrology tool) or an operator to see or measure things (e.g., features on the surface of a wafer) with adequate resolution. It is also desirable for the laser source 804 to drive and/or sustain the plasma with a high power laser beam. Generating a plasma that is small in size and providing the plasma with a high power laser beam leads simultaneously to a high brightness light. The light source 800 produces a high brightness light because most of the power introduced by the laser source 804 is then radiated from a small volume, high temperature plasma. The plasma temperature will rise due to heating by the laser beam until balanced by radiation and other processes. The high temperatures that are achieved in the laser sustained plasma yield increased radiation at shorter wavelengths of electromagnetic energy, for example, ultraviolet energy. In one experiment, temperatures between about 10,000 K and about 20,000 K have been observed. The radiation of the plasma, in a general sense, is distributed over the electromagnetic spectrum according to Planck's radiation law. The wavelength of maximum radiation is inversely proportional to the temperature of a black body according to Wien's displacement law. While the laser sustained plasma is not a black body, it behaves similarly and as such, the highest brightness in the ultraviolet range at around 300 nm wavelength is expected for laser sustained plasmas having a temperature of between about 10,000 K and about 15,000 K. Conventional arc lamps are, however, unable to operate at these temperatures. It is desirable in some embodiments of the invention to deliver the laser energy to the plasma in the chamber 828 over a large solid angle in order to achieve a plasma that is small in size. Various methods and optical elements can be used to deliver the laser energy over a large solid angle. In this embodiment of the invention, parameters of a beam expander and optical lens are varied to modify the size of the solid angle over which the laser energy is delivered to the plasma in the chamber 828. Referring to FIG. 8A, the laser source 804 is a diode laser that outputs a laser beam via a fiberoptic element 808. The fiber optic element 808 provides the laser beam to a collimator 812 that aids in conditioning the output of the diode laser by aiding in making laser beam rays 816 substantially parallel to each other. The collimator 812 directs the laser beam 816 to an optical lens 820. The optical lens 820 is configured to focus the laser beam 816 to produce a smaller diameter laser beam 824 having a solid angle 878. The laser beam 824 is directed to the region 830 of the chamber 828 where the plasma 832 exists. In this embodiment, the light source 800 also includes an ignition source 840 depicted as two electrodes (e.g., an anode and cathode located in the chamber 828). The ignition source 840 generates an electrical discharge in the chamber 828 (e.g., the region 830 of the chamber 828) to ignite the ionizable medium. The laser then provides laser energy to the ionized medium to sustain or create the plasma 832 which generates the high brightness light 836. The light 836 generated by the light source 800 is then directed out of the chamber to, for example, a wafer inspection system (not shown). FIG. 8B illustrates an embodiment of the invention in which the laser energy is delivered to the plasma in the chamber 828 over a solid angle 874. This embodiment of the invention includes a beam expander 854. The beam expander 854 expands the size of the laser beam 816 to produce laser beam 858. The beam expander 854 directs the laser beam 858 to an optical lens 862. The combination of the beam expander 854 and the optical lens 862 produces a laser beam 866 that has a solid angle 874 that is larger than the solid angle 878 of the laser beam 824 of FIG. 8A. The larger solid angle 874 of FIG. 8B creates a smaller size plasma 884 than the size of the plasma in FIG. 8A. In this embodiment, the size of the plasma 884 in FIG. 8B along the X-axis and Y-axis is smaller than the size of the plasma 832 in FIG. 8A. In this manner, the light source 800 generates a brighter light 870 in FIG. 8B as compared with the light 836 in FIG. 8A. An experiment was conducted in which a beam expander and optical lens were selected to allow operation of the light source as shown in FIGS. 8A and 8B. A Hamamatsu L2273 xenon bulb (with offices in Bridgewater, N.J.) was used as the sealed chamber 828. The plasma was formed in the Hamamatsu L2273 xenon bulb using an SPI continuous-wave (CW) 100 W, 1090 nm fiber laser (sold by SPI Lasers PLC, with offices in Los Gatos, Calif.)). A continuous-wave laser emits radiation continuously or substantially continuously rather than in short bursts, as in a pulsed laser. The fiber laser 804 contains laser diodes which are used to pump a special doped fiber (within the fiber laser 804, but not shown). The special doped fiber then lases to produce the output of the fiber laser 804. The output of the fiber laser 804 then travels through the fiberoptic element 808 to the collimeter 812. The collimeter 812 then outputs the laser beam 816. The initial laser beam diameter (along the Y-Axis), corresponding to beam 816 in FIG. 8A, was 5 mm. The laser beam 816 was a Gaussian beam with a 5 mm diameter measured to the 1/e2 intensity level. The lens used in the experiment, corresponding to lens 820, was 30 mm in diameter and had a focal length of 40 mm. This produced a solid angle of illumination of the plasma 832 of approximately 0.012 steradians. The length (along the X-Axis) of the plasma 832 produced in this arrangement was measured to be approximately 2 mm. The diameter of the plasma 832 (along the Y-Axis), was approximately 0.05 mm. The plasma 832 generated a high brightness ultraviolet light 836. Referring to FIG. 8B, a 2× beam expander was used as the beam expander 854. The beam expander 854 expanded beam 816 from 5 mm in diameter (along the Y-Axis) to 10 mm in diameter, corresponding to beam 858. Lens 862 in FIG. 8B was the same as lens 820 in FIG. 8A. The combination of the beam expander 854 and the optical lens 862 produced a laser beam 866 having a solid angle 874 of illumination of approximately 0.048 steradians. In this experiment, the length of the plasma (along the X-Axis) was measured to be approximately 1 mm and the diameter measured along the Y-Axis remained 0.05 mm. This reduction of plasma length by a factor of 2, due to a change in solid angle of a factor of 4, is expected if the intensity required to sustain the plasma at its boundary is a constant. A decrease in plasma length (along the X-Axis) by a factor of 2 (decrease from 2 mm in FIG. 8A to 1 mm in FIG. 8B) resulted in an approximate doubling of the brightness of the radiation emitted by the plasma for a specified laser beam input power because the power absorbed by the plasma is about the same, while the radiating area of the plasma was approximately halved (due to the decrease in length along the X-Axis). This experiment illustrated the ability to make the plasma smaller by increasing the solid angle of the illumination from the laser. In general, larger solid angles of illumination can be achieved by increasing the laser beam diameter and/or decreasing the focal length of the objective lens. If reflective optics are used for illumination of the plasma, them the solid angle of illumination can become much larger than the experiment described above. For example, in some embodiments, the solid angle of illumination can be greater than about 2π (about 6.28) steradians when the plasma is surrounded by a deep, curved reflecting surface (e.g., a paraboloid or ellipsoid). Based on the concept that a constant intensity of light is required to maintain the plasma at its surface, in one embodiment (using the same bulb and laser power described in the experiment above) we calculated that a solid angle of 5 steradians would produce a plasma with its length equal to its diameter, producing a roughly spherical plasma. FIG. 9 is a schematic diagram of a light source 900 for generating light. The light source 900 includes a sealed chamber 928 (e.g., a sealed quartz bulb, sealed sapphire tube) that contains an ionizable medium (not shown). The light source 900 also includes an energy source (not shown). The energy source provides energy to a region of the chamber 928 to produce a plasma 932. The plasma 932 generates and emits a light 936 that originates from the plasma 932. The light 936 generated by the light source 900 is directed through the walls 942 of the chamber 928 toward the reflective surface 944 of the reflector 940. The reflective surface 944 reflects the light generated by the light source 900. The walls 942 of the chamber 928 allow electromagnetic energy (e.g., light) to pass through the walls 942. The refractive index of the walls is a measure for how much the speed of the electromagnetic energy is reduced inside the walls 942. Properties (e.g., the direction of propagation) of the light ray 936 generated by the plasma 932 that is emitted through the walls 942 of the chamber 928 are modified due to the refractive index of the walls 942. If the walls 942 have a refractive index equal to that of the medium 975 internal to the chamber 928 (typically near 1.0), the light ray 936 passes through the walls 942 as light ray 936′. If, however, the walls have a refractive index greater than that of the internal medium 975, the light ray 936 passes through the walls as light ray 936″. The direction of the light represented by light ray 936 is altered as the light ray 936 enters the wall 942 having an index of refraction greater than the medium 975. The light ray 936 is refracted such that the light ray 936 bends toward the normal to the wall 942. The light source 900 has a medium 980 external to the chamber 928. In this embodiment, the medium 980 has an index of refraction equal to the index of refraction of the medium 975 internal to the chamber 928. As the light ray 936 passes out of the wall 942 into the medium 980 external to the chamber 928, the light ray 936 is refracted such that the light ray (as light ray 936″) bends away from the normal to the wall 942 when it exits the wall 942 The light ray 936″ has been shifted to follow a route parallel to the route the light ray 936′ would have followed had the refractive index of the wall 942 been equal to the refractive indices of the internal medium 975 and external medium 980. This refractive shift of direction and the resulting position of the light ray 936 (and 936′ and 936″) is described by Snell's Law of Refraction:n1 sin θ1=n2 sin θ2 EQN. 1where, according to Snell's Law, n1 is the index of refraction of the medium from which the light is coming, n2 is the index of refraction of the medium into which the light is passing, θ1 is the angle of incidence (relative to the normal) of the light approaching the boundary between the medium from which the light is coming and the medium into which the light is passing, and θ2 is the angle of incidence (relative to the normal) of the light departing from the boundary between the medium from which the light is coming and the medium into which the light is passing (Hecht, Eugene, Optics, M. A., Addison-Wesley, 1998, p. 99-100, QC355.2.H42). If the internal medium 975 does not have an index of refraction equal to that of the external medium 980, the light ray 936 refracts to follow a route according to Snell's Law. The route the light ray 936 follows will diverge from the route that light ray 936′ follows when the internal medium 975, wall 942, and external medium 980 do not have equal indices of refraction. If the refractive index of the walls 942 of the chamber 928 is equal to the internal medium 975 and external medium 980, the reflective surface 944 reflects light ray 936′ and produces a focused beam of light 956. If, however, the refractive index of the walls 942 is greater than the internal medium 975 and external medium 980, the reflective surface 944 reflects light ray 936″ and does not produce a focused beam (the light ray 936″ is dispersed producing light 960). Accordingly, it is therefore desirable to have a light source that includes a chamber and a reflective surface with a shape configured to compensate for the effect of the refractive index of the walls of the chamber. In alternative embodiments, the reflective surface 940 is configured to produce a collimated beam of light when the refractive index of the walls 942 of the chamber 928 is equal to that of the internal medium 975 and external medium 980. However, if the refractive index of the walls 942 of the chamber 928 is greater than that of the internal medium 975 and external medium 980, the reflective surface 940 would produce a non-collimated beam of light (the reflected light would be dispersed, similarly as described above). In other embodiments, aspects of the invention are used to compensate for the effect of the refractive index of the walls 942 of the chamber 928 for laser energy directed in to the chamber 928. Laser energy is directed toward the reflective surface 944 of the reflector 940. The reflective surface 944 reflects the laser energy through the walls 942 of the chamber 928 toward the plasma 932 in the chamber 928 (similarly as described herein with respect to, for example, FIGS. 5 and 6). If the walls 942 of the chamber 928 have a refractive index greater than that of the internal 975 and external 980 media, the direction of the laser energy is altered as the energy enters the walls 942. In these embodiments, if the reflective surface 944 of the reflector 942 has a shape configured to compensate for the effect of the refractive index of the walls of the chamber, the laser energy entering the chamber 928 will not diverge. Rather, the laser energy entering the chamber 928 will be properly directed to the location of the plasma 932 in the chamber 928, similarly as described herein. In this manner, principles of the invention can be applied to electromagnetic energy (e.g., laser energy) that is directed in to the chamber 928 and electromagnetic energy (e.g., light) produced by the plasma 932 that is directed out of the chamber 928. FIG. 10A is a schematic block diagram of a light source 1000a for generating light. The light source 1000a includes a sealed chamber 1028a (e.g., a sealed quartz tube or sealed sapphire tube) that contains an ionizable medium (not shown). The light source 1000a also includes an energy source 1015a. In various embodiments, the energy source 1015a is a microwave energy source, AC arc source, DC arc source, or RF energy source. The energy source 1015a provides energy 1022a to a region 1030a of the chamber 1028a having the ionizable medium. The energy 1022a creates a plasma 1032a. The plasma 1032a generates and emits a light 1036a that originates from the plasma 1032a. The light source 1000a also includes a reflector 1040a that has a reflective surface 1044a. The reflective surface 1044a of the reflector 1040a has a shape that is configured to compensate for the refractive index of the walls 1042a of the chamber 1028a. The walls 1042a of the chamber 1028a are substantially transparent to the light 1036a (or to predefined wavelengths of electromagnetic radiation in the light 1036a). The light 1036a (e.g., visible and/or ultraviolet light) generated by the light source 1000a is directed through the walls 1042a of the chamber 1028a toward the inner reflective surface 1044a of the reflector 1040a. If the refractive index of the walls 1042a is not equal to that of the media internal and external (not shown) to the chamber 1028a, the position and direction of the light ray 1036a is changed by passing through the walls 1042a of the chamber 1028a unless the reflective surface 1044a has a shape that compensates for the refractive index of the walls 1042a of the chamber 1028a. The light 1036a would disperse after reflecting off the surface 1044a of the reflector 1040a. However, because the shape of the reflective surface 1044a of the reflector 1040a is configured to compensate for the refractive index of the walls 1042a of the chamber 1028a, the light 1036a does not disperse after reflecting off the surface 1044a of the reflector 1040a. In this embodiment, the light 1036a reflects off the surface 1044a of the reflector 1040a to produce a collimated beam of light. FIG. 10B is a schematic block diagram of a light source 1000b for generating light. The light source 1000b includes a sealed chamber 1028b (e.g., a sealed quartz tube or sealed sapphire tube) that contains an ionizable medium (not shown). The light source 1000b also includes an energy source 1015b. The energy source 1015b is electrically connected to electrodes 1029 located in the chamber 1028b. The energy source 1015b provides energy to the electrodes 1029 to generate an electrical discharge in the chamber 1028b (e.g., the region 1030b of the chamber 1028b) to ignite the ionizable medium and produce and sustain a plasma 1032b. The plasma 1032b generates and emits a light 1036b that originates from the plasma 1032b. The light source 1000b also includes a reflector 1040b that has a reflective surface 1044b. The reflective surface 1044b of the reflector 1040b has a shape that is configured to compensate for the refractive index of the walls 1042b of the chamber 1028b. The walls 1042b of the chamber 1028b are substantially transparent to the light 1036b (or to predefined wavelengths of electromagnetic radiation in the light 1036b). The light 1036b (e.g., visible and/or ultraviolet light) generated by the light source 1000b is directed through the walls 1042b of the chamber 1028b toward the inner reflective surface 1044b of the reflector 1040b. If the refractive index of the walls 1042b is not equal to that of media internal and external (not shown) to the chamber 1028b, the direction and position of the light ray 1036b is changed by passing through the walls 1042b of the chamber 1028b unless the reflective surface 1044b has a shape that compensates for the refractive index of the walls 1042b of the chamber 1028b. The light 1036b would disperse after reflecting off the surface 1044b of the reflector 1040b. However, because the shape of the reflective surface 1044b of the reflector 1040b is configured to compensate for the refractive index of the walls 1042b of the chamber 1028b, the light 1036b does not disperse after reflecting off the surface 1044b of the reflector 1040b. In this embodiment, the light 1036b reflects off the surface 1044b of the reflector 1040b to produce a collimated beam of light. FIG. 11 is a schematic block diagram of a light source 1100 for generating light that embodies the invention. The light source 1100 includes a sealed chamber 1128 (e.g., a sealed, cylindrical sapphire bulb) that contains an ionizable medium (not shown). The light source 1100 provides energy to a region 1130 of the chamber 1128 having the ionizable medium which creates a plasma 1132. The plasma 1132 generates and emits a light 1136 (e.g., a high brightness light) that originates from the plasma 1132. The light source 1100 also includes at least one laser source 1104 that generates a laser beam that is provided to the plasma 1132 located in the chamber 1128 to initiate and/or sustain the high brightness light 1136. In this embodiment, the laser source 1104 is a diode laser that outputs a laser beam 1120. The optical lens 1120 is configured to focus the laser beam 1122 to produce a smaller diameter laser beam 1124. The laser beam 1124 passes through an aperture or window 1172 located in the base 1124 of a curved reflective surface 1140 and is directed toward the chamber 1128. The chamber 1128 is substantially transparent to the laser beam 1124. The laser beam 1124 passes through the chamber 1128 and toward the region 1130 of the chamber 1128 where the plasma 1132 exists (or where it is desirable for the plasma 1132 to be generated by the laser 1124 and sustained). In this embodiment, the ionizable medium is ignited by the laser beam 1124. In alternative embodiments, the light source 1100 includes an ignition source (e.g., a pair of electrodes or a source of ultraviolet energy) that, for example, generates an electrical discharge in the chamber 1128 (e.g., in the region 1130 of the chamber 1128) to ignite the ionizable medium. The laser source 1104 then provides laser energy to the ionized medium to sustain the plasma 1132 which generates the light 1136. The chamber 1128 is substantially transparent to the light 1136 (or to predefined wavelengths of electromagnetic radiation in the light 1136). The light 1136 (e.g., visible and/or ultraviolet light) generated by the light source 1100 is then directed out of the chamber 1128 toward an inner surface 1144 of the reflective surface 1140. The reflective surface 1144 of the reflector 1140 has a shape that compensates for the refractive index of the walls 1142 of the chamber 1128. If the refractive index of the walls 1142 is not equal to that of the media internal and external (not shown) to the chamber 1128, the speed of the light 1136 would be changed by passing through the walls 1142 of the chamber 1128 if the reflective surface 1144 does not have a shape that compensates for the refractive index of the walls 1142 of the chamber 1128 (similarly as described above with respect to FIG. 9). FIG. 12 is a cross-sectional view of a light source 1200 incorporating principles of the present invention. The light source 1200 includes a sealed cylindrical chamber 1228 that contains an ionizable medium. The light source 1200 also includes a reflector 1240. The chamber 1228 protrudes through an opening 1272 in the reflector 1240. The light source 1200 includes a support element 1274 (e.g. a bracket or attachment mechanism) attached to the reflector 1240. The support element 1274 is also attached to a back end 1280 of the chamber 1228 and locates the chamber 1228 relative to the reflector 1240. The light source 1200 includes electrodes 1229a and 1229b (collectively 1229) located in the chamber 1228 that ignite the ionizable medium to produce a plasma 1232. The electrodes 1229a and 1229b are spaced apart from each other along the Y-Axis with the plasma 1232 located between opposing ends of the electrodes 1229. The light source 1200 also includes an energy source that provides energy to the plasma 1232 to sustain and/or generate a light 1236 (e.g., a high brightness light) that is emitted from the plasma 1232. The light 1236 is emitted through the walls 1242 of the chamber 1228 and directed toward a reflective surface 1244 of a reflector 1240. The reflective surface 1244 reflects the light 1236. In some embodiments, the electrodes 1229 also are the energy source that provides energy to the plasma 1232 sustain and/or generate the light 1236. In some embodiments, the energy source is a laser external to the chamber 1228 which provides laser energy to sustain and/or generate the light 1236 generated by the plasma 1232, similarly as described herein with respect to other embodiments of the invention. For example, in one embodiment, the light source 1200 includes a laser source (e.g., the laser source 104 of FIG. 1) and associated laser delivery components and optical components that provides laser energy to the plasma 1232 to and/or generate the light 1236. If the refractive index of the walls 1242 of the chamber is equal to that of the media internal and external (not shown) to the chamber 1228, and the reflective surface 1244 of the reflector 1240 is a parabolic shape, the light 1236 reflected off the surface 1244 produces a collimated beam of light 1264. If the refractive index of the walls 1242 of the chamber is equal to that of the media internal and external to the chamber 1228, and the reflective surface 1244 of the reflector 1240 is an ellipsoidal shape, the light 1236 reflected off the surface 1244 produces a focused beam of light 1268. If the refractive index of the walls 1242 of the chamber 1228 is greater than that of the media internal and external to the chamber 1228, the direction and position of the light ray 1236 is changed by passing through the walls 1242 of the chamber 1228 unless the reflective surface 1244 of the reflector 1240 has a shape that compensates for the refractive index of the walls 1242 of the chamber 1228. The light ray 1236 would disperse after reflecting off the surface 1244 of the reflector 1240. However, because the shape of the reflective surface 1244 of the reflector 1240 is configured to compensate for the refractive index of the walls 1242 of the chamber 1228, the light 1236 does not disperse after reflecting off the surface 1244 of the reflector 1240. In this embodiment, the refractive index of the walls 1242 of the chamber 1228 is greater than that of the internal and external media and the reflective surface 1242 has a modified parabolic shape to compensate for the refractive index of the walls 1242. The modified parabolic shape allows for the reflected light 1236 to produce the collimated beam of light 1264. If a parabolic shape was used, the reflected light 1236 would not be collimated, rather the reflected light would be dispersed. A modified parabolic shape means that the shape is not a pure parabolic shape. Rather, the shape has been modified sufficiently to compensate for the aberrations that would otherwise be introduced into the reflected light 1236. In some embodiments, the shape of the reflective surface 1242 is produced to reduce the error (e.g., dispersing of the reflected light 1236) below a specified value. In some embodiments, the shape of the reflective surface 1242 is expressed as a mathematical equation. In some embodiments, by expressing the shape of the reflective surface 1242 as a mathematical equation, it is easier to reproduce the shape during manufacturing. In some embodiments, parameters of the mathematical equation are selected to reduce error due to the refractive index of the walls 1242 of the chamber 1228 below a specified value. The light source 1200 includes a seal assembly 1250 at the top of the chamber 1228. The light source 1200 also includes a fitting 1260 at the bottom end of the chamber 1228. The seal assembly 1250 seals the chamber 1228 containing the ionizable medium. In some embodiments, the seal assembly 1250 is brazed to the top end of the chamber 1228. The seal assembly 1250 can include a plurality of metals united at high temperatures. The seal assembly 1250 can be, for example, a valve stem seal assembly, a face seal assembly, an anchor seal assembly, or a shaft seal assembly. In some embodiments the seal assembly 1250 is mechanically fastened to the top end of the chamber 1228. In some embodiments, there are two seal assemblies 1250, located at the two ends of the chamber 1228. The fitting 1260 allows for filling the chamber with, for example, the ionizable medium or other fluids and gases (e.g., an inert gas to facilitate ignition). The fitting 1260 also allows for controlling the pressure in the chamber 1228. For example, a source of pressurized gas (not shown) and/or a relief valve (not shown) can be coupled to the fitting to allow for controlling pressure in the chamber 1228. The fitting 1260 can be a valve that allows the ionizable medium to flow into the chamber 1228 through a gas inlet (not shown). FIG. 13 is a graphical representation of a plot 1300 of the blur or dispersal produced by a reflective surface (e.g., the reflective surface 1244 of FIG. 12) for a reflective surface having various shapes that are expressed as a mathematical expression having the form of EQN. 2. The blur or dispersal is the radius by which light rays reflected off of the reflective surface miss the desired remote focus point for the reflected light (e.g., the reflected light 1268 of FIG. 12 in the situation where the shape of the reflective surface 144 is a modified elliptical shape). r ⁡ ( z ) = a 1 ⁢ z + a 2 ⁢ z 2 + a 3 ⁢ z 3 + … + a n ⁢ z n 1 + b 1 ⁢ z + b 2 ⁢ z 2 + … + b m ⁢ z m EQN . ⁢ 2 The X-axis 1304 of the plot 1300 is the position along the optical axis (in millimeter units) where a particular ray of light reflects from the reflective surface (e.g. the reflective surface 1244) of FIG. 12). The Y-Axis 1308 of the plot 1300 is the radius (i.e., blur or dispersal) in millimeter units. The cylindrical chamber has an outer diameter (along the X-axis) of 7.11 mm and an inner diameter of 4.06 mm. Curve 1312 shows the radius by which light rays reflected off of the location along the optical axis of the reflective surface miss the desired remote focus point for the reflected light, in which the reflective surface is expressed as a mathematical equation (EQN. 2) in which n=2 and m=0. Curve 1316 shows the radius by which light rays reflected off of the location along the optical axis of the reflective surface miss the desired remote focus point for the reflected light, in which the reflective surface is expressed as a mathematical equation (EQN. 2) in which n=3 and m=1. Curve 1320 shows the radius by which light rays reflected off of the location along the optical axis of the reflective surface miss the desired remote focus point for the reflected light, in which the reflective surface is expressed as a mathematical equation (EQN. 2) in which n=4 and m=4. Curve 1324 shows the radius by which light rays reflected off of the location along the optical axis of the reflective surface miss the desired remote focus point for the reflected light, in which the reflective surface is expressed as a mathematical equation (EQN. 2) in which n=5 and m=5. In this embodiment, a ray tracing program was used to select (e.g., optimize) the parameters of the mathematical equation so the shape of the reflective surface compensates for the refractive index of the walls of the chamber containing the ionizable medium. Referring to FIG. 13 and EQN 2, the parameters are the order and coefficients of the mathematical equation. In this embodiment, a ray tracing program was used to determine the paths of the light rays emitted through the walls of a chamber in which the walls had a refractive index greater than that of the media internal and external to the chamber, and reflected off a reflective surface with a shape described according to EQN. 2 with selected order and coefficients. In this embodiment, the ray tracing program graphs the radii by which light rays originating at points along the optical path of the reflective surface miss the desired remote focus point. In this embodiment, the order and coefficients of the rational polynomial (EQN. 2) are adjusted until the radii by which light rays miss the remote focus point are within a threshold level of error. In other embodiments, the order and/or coefficients are adjusted until the full width at half maximum (FWHM) of the light rays emitted by the plasma converge within a specified radius of the remote focus point. In one embodiment, the specified radius is 25 μm. In other embodiments, the ray tracing program graphs the radii by which light rays originating at points along the optical path of the reflective surface miss a target collimated area at a specified distance from the vertex of the reflective surface. The parameters of the mathematical equation expressing the shape of the reflective surface are adjusted until the radii by which light rays miss the target collimated area are within a threshold level of error. In other embodiments, the order and/or coefficients are adjusted until the full width at half maximum (FWHM) of the light rays emitted by the plasma is located within a specified radii of a target collimated area at a specified distance from the vertex of the reflective surface. In alternative embodiments of the invention, alternative forms of mathematical equations can be used to describe or express the shape of the reflective surface of the reflector (e.g., reflective surface 1244 of reflector 1240 of FIG. 12). The principles of the present invention are equally applicable to light sources that have different chamber shapes and/or reflective surface shapes. For example, in some embodiments, the reflective surface of the reflector has a shape that is a modified parabolic, elliptical, spherical or aspherical shape that is used to compensate for the refractive index of the walls of the chamber. FIG. 14 is a schematic block diagram of a portion of a light source 1400, according to an illustrative embodiment of the invention. The light source 1400 includes a sealed chamber 1428 that includes an ionizable medium. The light source 1400 also includes a first reflector 1440 that has a reflective surface 1444. The reflective surface 1444 can have, for example, a parabolic shape, elliptical shape, curved shape, spherical shape or aspherical shape. In this embodiment, the light source 1400 has an ignition source (not shown) that ignites an ionizable gas (e.g., mercury or xenon) in a region 1430 within the chamber 1428 to produce a plasma 1432. In some embodiments, the reflective surface 1444 can be a reflective inner or outer surface. In some embodiments, a coating or film is located on the inside or outside of the chamber to produce the reflective surface 1444. A laser source (not shown) provides a laser beam 1416 that is directed toward a surface 1424 of a second reflector 1412. The second reflector 1412 reflects the laser beam 1420 toward the reflective surface 1444 of the first reflector 1440. The reflective surface 1444 reflects the laser beam 1420 and directs the laser beam toward the plasma 1432. The refractive index of the walls 1442 of the chamber 1430 affects the laser beam 1416 as it passes through the walls 1442 in to the chamber 1430 similarly as light passing through the walls 1442 of the chamber 1430 is affected as described previously herein. If the shape of the reflective surface 1444 is not selected to compensate for the refractive index, the laser energy disperses or fails to focus after entering the chamber 1430 and is not focused on the plasma 1432. Accordingly, in this embodiment, the reflective surface 1444 of the reflector has a shape that is selected to compensate for the refractive index of the walls 1442 of the chamber 1430 (similarly as described previously herein with respect to, for example, FIGS. 12 and 13). The laser beam 1416 provides energy to the plasma 1432 to sustain and/or generate a high brightness light 1436 that is emitted from the plasma 1432 in the region 1430 of the chamber 1428. The high brightness light 1436 emitted by the plasma 1432 is directed toward the reflective surface 1444 of the first reflector 1440. At least a portion of the high brightness light 1436 is reflected by the reflective surface 1444 of the first reflector 1440 and directed toward the second reflector 1412. Because the reflective surface 1444 of the reflector has a shape that is selected to compensate for the refractive index of the walls 1442 of the chamber 1430, the light 1436 reflected by the reflective surface 1444 produces the desired collimated beam of light 1436 that is directed towards the second reflector 1412. The second reflector 1412 is substantially transparent to the high brightness light 1436 (e.g., at least one or more wavelengths of ultraviolet light). In this manner, the high brightness light 1436 passes through the second reflector 1412 and is directed to, for example, a metrology tool (not shown). In some embodiments, the light 1436 is directed to a tool used for photoresist exposure, conducting ellipsometry (e.g., UV or visible), thin film measurements. In some embodiments, the high brightness light 1436 is first directed towards or through a window or additional optical elements before it is directed to a tool. FIG. 15A is a cross-sectional view of a light source 1500 incorporating principles of the present invention. FIG. 15B is a sectional view (in the Y-Z plane) of the light source 1500 of FIG. 15A. The light source 1500 includes a housing 1510 that houses various elements of the light source 1500. The housing 1510 includes a sealed chamber 1522 and has an output 1580 which includes an optical element 1520 (e.g., a quartz disk-shaped element) through which light can exit the housing 1510. The light source 1500 includes a sealed chamber 1528 that contains an ionizable medium (not shown). The light source 1500 also includes a reflector 1540. The light source 1500 also includes a blocker 1550. The light source 1500 includes electrodes 1529a and 1529b (collectively 1529) located in part in the chamber 1528 that ignite the ionizable medium to produce a plasma (not shown). The electrodes 1529a and 1529b are spaced apart from each other (along the Y-Axis) with the plasma located between opposing ends of the electrodes 1529. In some embodiments, the electrodes 1529 also are the energy source that provides energy to the plasma to sustain and/or generate the light. In this embodiment, the energy source is a laser (not shown) external to the chamber 1528 which provides laser energy 1524 (e.g., infrared light) to sustain and/or generate the light 1530 (e.g., a high brightness light including ultraviolet and/or visible wavelengths) generated by the plasma, similarly as described herein with respect to other embodiments of the invention. The laser energy 1524 enters the chamber 1528 on a first side 1594 of the chamber 1528. In some embodiments, the light source 1500 also includes associated laser delivery components and optical components that provide laser energy to the plasma to sustain and/or generate the light 1530. In this embodiment, the light source 1500 includes an optical element 1560 to delivery the laser energy 1524 from the laser to the plasma to sustain and/or generate the light 1530 that is emitted from the plasma. The light 1530 is emitted through the walls of the chamber 1528. Some of the light 1530 emitted through the walls of the chamber 1528 propagates toward a reflective surface 1532 of the reflector 1540. The reflective surface 1532 reflects the light through the optical element 1520 in the housing 1510 to a focal point 1525 of the reflector 1540. Some of the light 1536 propagates toward the optical element 1560. The optical element 1560 absorbs the light 1536, and the light 1536 is not reflected through the optical element 1520. As a result, the light reflected to the focal point 1525 is the light 1530 emitted from the plasma that is reflected by the reflector 1540 along paths shown as the regions 1540 and 1541. Consequently, the light source 1500 includes dark region 1542 due to the light that is radiated toward the optical element 1560 and therefore not reflected to the focal point 1525 of the reflectors 1540. Some of the laser energy delivered to the plasma is not absorbed by the plasma. The laser energy that is not absorbed (laser energy 1556) continues to propagate along the positive X-Axis direction towards the end of the housing 1510. The blocker 1550 is suspended on a second side 1596 of the chamber 1528. The blocker 1550 is suspended along a path 1562 the laser energy 1556 travels. The blocker 1550 is coupled to an arm 1555 that suspends the blocker 1550 in the chamber 1522 of the light source 1500. The blocker 1550 blocks the laser energy 1556 to prevent it from propagating toward the end of the housing and through an output 1580 of the light source 1500. In this embodiment, the blocker 1550 is a mirror that deflects the laser energy 1556 that is not absorbed by the plasma away from the opening 1520 and towards the walls of the housing 1510 (illustrated as laser energy 1584). The blocker 1550 reflects the laser energy 1556 toward a wall 1588 of the housing 1510. The housing 1510 absorbs part of the reflected laser energy 1584 and reflects part of the laser energy 1584 toward the opposite wall 1592 of the housing 1510. A portion of the laser energy 1584 is absorbed each time it impacts a wall (e.g., wall 1588 or 1592) of the housing 1510. Repetitive impact of the laser energy 1584 with the walls of the housing 1510 causes the laser energy 1584 to be substantially (or entirely) absorbed by the walls of the housing 1510. The blocker 1550 prevents laser energy (e.g., infrared wavelengths of electromagnetic energy) from exiting the housing 1510 through the opening 1580 by deflecting the laser energy 1556 using the blocker 1550. As a result, only the light produced by the plasma (e.g., ultraviolet and/or visible wavelengths) exits the housing 1510 through the opening 1580. The blocker 1550 is suspended in the housing 1510 in a location where the blocker 1550 would not deflect light 1530 reflected by the reflector 1540 through the opening 1580 to the focal point 1525. The blocker 1550 does not deflect the light 1530 because the blocker 1550 is located in the dark region 1542. In addition, the arm 1555 coupled to the blocker 1550 also does not deflect the light 1530 because the arm is positioned in the housing 1510 in a location that is aligned with the electrode 1529a along the positive X-Axis direction relative to the electrode 1529a. In this manner, the blocker 1550 and arm 1555 are positioned to minimize their blocking of the light 1530. The dark region 1542 tapers as the region 1542 approaches the opening 1580. To prevent the blocker 1550 from deflecting light reflected by the reflector 1540, the laser energy blocker 1550 is positioned at a location along the X-Axis where the cross-sectional area (in the Y-Z plane) of the blocker 1550 is equal to or less than the cross sectional area (in the Y-Z plane) of the dark region 1542. As a result, the smaller the cross-sectional area (in the Y-Z plane) of the blocker 1550, the closer along the X-Axis the blocker 1550 can be placed to the opening 1580. In some embodiments, the laser energy blocker 1550 is made of any material that reflects the laser energy 1556. In some embodiments, the blocker 1550 is configured to reflect the laser energy 1556 back toward the ionized medium in the chamber 1528. In some embodiments, the blocker 1550 is a coating on a portion of the chamber 1528. In some embodiments, the blocker is a coating on the optical element 1520 at the opening 1580. In some embodiments, the laser energy blocker 1550 is made of a material that absorbs, rather than reflects, the laser energy 1556 (e.g., graphite). In some embodiments in which the blocker absorbs the laser energy 1556, the blocker 1550 heats up because it absorbs the laser energy 1556. In some embodiments, the blocker 1550 is cooled. The blocker 1550 can include one or more coolant channels in the blocker 1550. The light source can also include a coolant supply coupled to the coolant channel which provides coolant to the coolant channel to cool the blocker 1550. In some embodiments, the light source 1500 includes a gas source (e.g., a pressurized gas canister or gas blower) to blow gas (e.g., air, nitrogen, or any other gas) on the blocker 1550 to cool the blocker 1550. In some embodiments, the light source 1500 includes one or more tubes (e.g., copper tubes) that wind around the laser energy blocker 1550. The light source 1500 flows a coolant (e.g., water) through the tubes to cool the blocker 1550. By way of illustration, an experiment was conducted to generate ultraviolet light using a light source, according to an illustrative embodiment of the invention. A specially constructed quartz bulb with a volume of 1 cm3 was used as the chamber of the light source (e.g., the chamber 128 of the light source 100 of FIG. 1) for experiments using xenon as the ionizable medium in the chamber. The bulb was constructed so that the chamber formed within the quartz bulb was in communication with a pressure controlled source of xenon gas. FIG. 16 is a graphical representation of brightness as a function of the pressure in a chamber of a light source, using a light source according to the invention. FIG. 16 illustrates a plot 1600 of the brightness of a high brightness light produced by a plasma located in the chamber as a function of the pressure in the chamber. The laser source used in the experiment was a 1.09 micron, 200 watt CW laser and it was focused with a numerical aperture of 0.25. The resulting plasma shape was typically an ellipsoid of 0.17 mm diameter and 0.22 mm length. The Y-Axis 1612 of the plot 1600 is the brightness in watts/mm2 steradian (sr). The X-Axis 1616 of the plot 1600 is the fill pressure of Xenon in the chamber. Curve 1604 is the brightness of the high brightness light (between about 260 and about 400 nm) produced by a plasma that was generated. Curve 1608 is the brightness of the high brightness light (between about 260 and about 390 nm) produced by the plasma. For both curves (1604 and 1608), the brightness of the light increased with increasing fill temperatures. Curve 1604 shows a brightness of about 1 watts/mm2 sr at about 11 atmospheres which increased to about 8 watts/mm2 sr at about 51 atmospheres. Curve 1608 shows a brightness of about 1 watts/mm2 sr at about 11 atmospheres which increased to about 7.4 watts/mm2 sr at about 51 atmospheres. An advantage of operating the light source with increasing pressures is that a higher brightness light can be produced with higher chamber fill pressures. To start a laser-driven light source (“LDLS”), the absorption of the laser light by the gas within the chamber (e.g., chamber 128 of FIG. 1) is strong enough to provide sufficient energy to the gas to form a dense plasma. However, during operation, the same absorption that was used to start the LDLS can be too strong to maintain the brightness of the light because the light can be prematurely absorbed before the light is near the laser focus. These criteria often come into conflict and can create an imbalance in the absorption needed to start a LDLS and the absorption needed to maintain or operate the LDLS. When starting a LDLS, the plasma density is generally low and hence, other things being equal, the absorption is weak. This can cause most of the laser light to leave the plasma region without being absorbed. Such a situation can lead to an inability to sustain the plasma by the laser alone. One solution to this problem is to tune the laser to a wavelength near a strong absorption line of the excited working gas within the chamber (e.g., chamber 128 of FIG. 1). However, after ignition this same strong absorption can become a liability because the laser energy can be absorbed too easily before the laser power reaches the core of the plasma near the laser focus. This latter condition can lead to a low brightness light source radiating from a large volume. One solution to this problem is to tune the laser wavelength away from the strong absorption line until a condition is reached where the maximum radiance is achieved. The optimum operating state can be a balance between small plasma size and sufficiently high power absorption. This scenario leads to a light source and a method of operation where the laser is first tuned to a wavelength nearer the absorption line and then tuned to another wavelength further away from the strong absorption line for optimum operation. A light source can use an excited gas that has at least one strong absorption line at an infrared wavelength to produce a high brightness light. For example, referring to FIG. 1, the light source 100 includes a chamber 128 that has a gas disposed therein. The gas can comprise a noble gas, for example, xenon, argon, krypton, or neon. An ignition source 140 can be used to excite the gas within the chamber 128. The ignition source 140 can be, for example, two electrodes. The excited gas has electrons at an energy level that is higher than the energy of the gas at its ground state, or lowest energy level. The excited gas can be in a metastable state, for example, at an energy that is higher than the ground state energy of the gas but that lasts for an extended period of time (e.g., about 30 seconds to about one minute). The specific energy level of the excited state can depend on the type of gas that is within the chamber 128. The excited gas has at least one strong absorption line at an infrared wavelength, for example at about 980 nm, 895 nm, 882, nm, or 823 nm. The light source 100 also includes at least one laser 104 for providing energy to the excited gas at a wavelength near a strong absorption line of the excited gas within the chamber 128 to produce a high brightness light 136. The gas within the chamber 128 can be absorptive near the wavelength of the laser 104. Operation of the light source to balance the conflicting criteria for starting and maintaining the high brightness light can comprise tuning a laser (e.g., laser 104 of FIG. 1) to a first wavelength to produce a high brightness light and then tuning the laser to a second wavelength to maintain the high brightness light. The first wavelength can be at an energy level that is capable of forming and sustaining a dense plasma, thus creating a high brightness light, and the second wavelength can be at an energy level such that the laser energy is not substantially absorbed by the plasma prior to the laser reaching its focus point. For example, a gas within a chamber (e.g., chamber 128 of FIG. 1) can be excited with an ignition source. In some embodiments, a drive laser at a power below 1000 W can be used to ignite the plasma. In other embodiments, a drive laser at a power above or below 1000 W can be used to ignite the plasma. To ignite the plasma and/or the excited gas within the chamber, a LDLS can be operated near the critical point of the gas within the chamber. The critical point is the pressure above which a gas does not have separate liquid and gaseous phases. For example, the critical point of xenon is at a temperature of about 290 Kelvin and at a pressure of about 5.84 MPa (about 847 psi). In some embodiments, other gases are used, for example neon, argon or krypton can be used. In other embodiments, combinations of gases can be used, for example, a mixture of neon and xenon. After the gas within the chamber is ignited, a laser (e.g., laser 104 of FIG. 1) can be tuned to a first wavelength to provide energy to the excited gas in the chamber to produce a high brightness light. The excited gas within the chamber absorbs energy near the first wavelength. After the high brightness light is initiated, the laser can be tuned to a second wavelength to provide energy to the excited gas within the chamber to maintain the high brightness light. The second wavelength can either be less than or greater than the first wavelength. The excited gas within the chamber absorbs energy near the second wavelength. The gas within the chamber can be, for example, a noble gas and can have atoms with electrons in at least one excited atomic state. Noble gases such as xenon, argon, krypton or neon can be transparent in the visible and near infrared range of the spectrum, but this is not the case when the gas is at high temperature or in the presence of excited molecular states, such as excimers. Any condition of the gas which results in population of high energy electronic states, such as the lowest excited state (e.g., the excited state closest in energy to the ground state) in xenon, will also result in the appearance of strong absorption lines due to transitions between the relatively high energy state and any of the several higher level states which lie at a level of order 1 eV above it. FIG. 17 shows a simplified diagram of the relevant energy levels in xenon. Each of the horizontal bars represents an energy level which can be occupied by an electron in the xenon atom or molecule (dimer). When an electron moves between two levels, a photon can be emitted or absorbed, e.g. a 980 nm photon. The groups of close together horizontal bars on the “Molecular Levels,” or left, side of the diagram show that the close association of xenon atoms in the molecule leads to broadening of the energy levels of the atom into bands. Transitions between these bands then allow for a broadened range of absorption, which explains the enhanced absorption even at wavelengths some distance (e.g., several nanometers) away from the exact atomic transition of 980.0 nm. Still referring to FIG. 17, an example of such an absorption line is the one at about 980 nm and about 882 nm in xenon which is a transition from the metastable atomic 5p5(2P°3/2)6s level to the 5p5(2P°3/2)6p level. The molecules have a corresponding set of transitions yielding a broadened 980 nm or 882 nm line. Such lines are also observed in emission due to the reverse transition. Other examples of suitable absorption lines in xenon are, for example, 881.69 nm, 823.1 nm, and 895.2 nm. Table 1 shows emission and absorption measurements and average temperature of the cathode spot of a xenon arc in the stationary mode. As shown, xenon in the plasma form has multiple absorbance lines in the IR spectrum. As shown by the high percentage of energy that can be absorbed at multiple wavelengths, 881.69 nm, 823.1 nm, and 895.2 nm, as well as 980 nm, are good wavelengths that can be used within a LDLS to initiate a high brightness light. TABLE 1(as measured by Lothar Klein (April 1968/Vol.7, No. 4/APPLIED OPTICS 677)).Nλ0Absorptionλ(Å)(W cm−1 sr−1 μ−1)(%) T(° K)XeI82325,9008910,020cont85001,6152310,750XeI8819 (peak)4,390979,160(wing)4,9609010,500XeI98003,400899,820XeI99233,340909,840XeI1052889228.59,950XeI1174290642.59,400XeI12623640379,920cont13100213178,870XeI147335755510,060XeI15418317379,840 FIG. 18 shows simplified spectral diagrams of the relevant energy levels in neon, argon, krypton and xenon. Each horizontal bar represents an energy level which can be occupied by an electron in the neon, argon, krypton, or xenon atom or molecule (dimer). The transition between these energy levels in the noble gases, allow for a broadened range of absorption. Therefore, these noble gases can be used in a LDLS to start and maintain a high brightness light in accordance with the systems and methods described herein. Tuning the laser several nanometer, as can be needed to adjust the wavelength of the laser from a first wavelength to initiate a high brightness light to a second wavelength to sustain the high brightness light, can be accomplished by adjusting the operating temperature of the laser. FIG. 19 shows a graph of laser output wavelength versus temperature for xenon, which can be used as a tuning mechanism for a laser of a LDLS. The laser bandwidth is approximately 5 nm and the xenon absorption lines 1905 are shown, for example, at about 980 nm. For example, the wavelength of a typical diode laser operating near the 980 nm absorption line of xenon can be tuned approximately 0.4 nm per degree Celsius of temperature change. The specific temperature or range of temperatures depends on the particular laser. The effect is that thermal expansion of the laser material causes the length of the laser cavity to increase with temperature, thereby shifting the resonant wavelength of the cavity to a longer wavelength. The temperature of the laser can be set by a thermoelectric cooling device (e.g., a Peltier cooling device) and quickly tuned by varying the current to the thermoelectric cooler (“TEC”). Electronic fan speed control of a cooling fan is another option for laser temperature control. Also, electric heating of the laser can be used to control the temperature. Temperature of the laser can be monitored by a sensor and controlled by a feedback circuit driving the cooling and/or heating means. The second wavelength that the laser of the LDLS is tuned to can be approximately 1 nm to approximately 10 nm displaced from the first wavelength. In some embodiments, the second wavelength is less than the first wavelength and in some embodiments the second wavelength is greater than the first wavelength. For example, to start a LDLS, the laser can be tuned to a wavelength of about 980 nm using xenon gas within the chamber of the light source. After a high brightness light is initiated, the laser can be tuned to a wavelength of about 975 nm to maintain the high brightness light. In some embodiments, the second wavelength is about 985 nm. Several different methods can be used to start and maintain the light source. In some embodiments, a high voltage pulse is applied to the ignition electrodes in the lamp. A DC current of about 1 to about 5 Amps can initially flow through the resulting plasma from an ignition power supply. The current can decay exponentially with a time constant of about 2 milliseconds. During this time the resulting plasma is illuminated by a focused laser beam at a wavelength of, for example, about 980 nm where the laser temperature is about 35 (see, e.g., FIG. 19, which shows that when the laser temperature is at about 35° C. the laser will emit energy at a wavelength of about 980 nm). The laser plasma is then sustained after the DC current decays to zero. A plasma light sensor can be used to determine that the plasma is sustained by the laser and then the laser is cooled to a temperature about 25° C. and the resulting wavelength of about 975 nm, or a desired predetermined operating wavelength, which can be determined by active feedback on the properties of the laser driven light source, such as radiance (e.g., brightness) (see, e.g., FIG. 19, which shows that when the laser temperature is at about 25° C. the laser will emit energy at a wavelength of about 975 nm). This method can rely on direct electron heating by the laser, and therefore, can require sufficient electron density to couple the laser power. This method can be used for a LDLS that operates at about 60 W. In some embodiments, a different starting scheme can be used, which is suitable for low laser powers, for example, laser powers between about 10 W and about 50 W. For example, a laser wavelength can be deliberately tuned to rely on direct absorption of the laser power by the neutral gas, which is absorptive at or near the laser wavelength. However, since laser photon energy is low (approximately 1.26 eV for 980 nm), compared to atomic excited states (e.g., the lowest xenon excited state is about 8.31 eV), this method cannot not rely on absorption from the ground state. In addition, multi-photon effects can require high power and usually a pulsed laser. Since the starting scheme cannot rely on absorption from the ground state, the starting scheme can instead rely on absorption from an excited state. However, this requires that at least one excited state of the gas within a chamber of a LDLS be populated with electrons. Some excited states have long life times, for example, the lifetime of metastable xenon is approximately 40 seconds. Due to the long lifetime, the metastable states tend to be preferentially populated. When choosing absorption lines of a gas near the laser wavelength, it can be preferred to choose those with lower level on a metastable state. In addition, at high pressures (e.g., pressures greater than about 0.1 bar), pressure and molecular effects broaden the absorption lines. A certain level of DC arc current can be required to start the LDLS, but less DC arc current can be required for a laser at higher power and operating closer to an absorption line of the gas within the chamber of the light source. A peak DC current can be varied by changing the resistance of a current limiting resistor after a booster capacitor. Threshold current is the laser driving current above which the plasma can be started when well aligned. Laser output power is proportional to laser current. Higher laser driving current can also make the laser center wavelength closer to an atomic line, for example, closer to 980 nm. FIG. 20 is a graph 2000 of power 2100 versus pressure 2200 for argon 2300 and xenon 2400. See Keefer, “Laser-Sustained Plasmas,” Laser-Induced Plasmas and Applications, published by Marcel Dekker, edited by Radziemski et al., 1989, pp. 169-206, at page 191. The graph 2000 shows the minimum power (about 30 W, with minimum power occurring below 20 atm.) required to sustain plasmas in argon and xenon as well as the maximum pressure that can be obtained. In addition, at points 2500 and 2600, the prior art laser sustained plasma can not be operated at any higher pressure when the laser sustained plasma is operated according to the prior art. For instance, the highest pressure that can be achieved for xenon 2400 is about 21 atm and the highest pressure that can be achieved for argon 2300 is about 27 atm. At these pressures, the prior art laser sustain plasma requires about 50 W of power to sustain a xenon plasma and about 70 W of power to sustain an argon plasma. Operating at higher pressure is beneficial because plasmas for the purpose of light generation can be obtained with higher brightness while lower powers are required when operated according to the present invention. To obtain lower powers the LDLS can be operated at a wavelength of about 980 nm. When the LDLS is operated at 980 nm, a higher maximum pressure is observed than the maximum pressures shown in FIG. 20. In addition, a maximum pressure, similar to that shown in FIG. 20, has not been achieved when a LDLS is operated at 980 nm. Therefore, when the LDLS is operated at the 980 nm wavelength, the LDLS can be operated at substantially higher pressures than prior art laser sustained plasmas. For example, the LDLS can be operated at pressures greater than about 30 atm. When the LDLS is operated at these high pressures and at a wavelength of about 980 nm, the power needed to sustain the plasma drops dramatically. For example, when the LDLS is operated at a pressure greater than about 30 atm, the power need to sustain the plasma can be as low as about 10 W. FIG. 21 shows different sized laser beams 2105, 2110, 2115 focused on a small plasma 2120. Each laser beam 2105, 2110, 2115 has a different numerical aperture (“NA”), which is a measure of the half angle of a cone of light. The NA is defined to be the sine of the half angle of the cone of light. For example, laser beam 2105 has a smaller NA than laser beam 2110, which has a smaller NA than laser beam 2115. As shown in FIG. 21, a laser beam with a larger NA, for example, laser beam 2115, can have an intensity that converges more quickly on plasma 2120 (e.g., it can converge more quickly to the laser focal point) than a laser beam with a smaller NA, for example, laser beam 2105. In addition, laser beams with a larger NA can rapidly decrease in intensity as the laser beam leaves the focus point and thus will have less of an effect on the high brightness light than a laser beam with a smaller NA. For example, laser beam 2105′ corresponds to laser beam 2105, laser beam 2110′ corresponds to laser beam 2110, and laser beam 2115′ corresponds to laser beam 2115. As shown by FIG. 21, the intensity of laser beam 2115 decreases more rapidly (2115′) after the focus point than laser beam 2105 due to the larger NA of beam 2115, which also results in less interference of the laser beam with the high brightness light. Referring to FIG. 1, a light source 100 can utilize the NA property of a beam of light to produce a high brightness light. The light source 100 can include a chamber 128 having one or more walls. A gas can be disposed within the chamber 128. At least one laser 104 can provide a converging beam of energy focused on the gas within the chamber 128 to produce a plasma that generates a light emitted through the walls of the chamber 128. The NA of the converging beam of energy can be between about 0.1 or about 0.8, or between about 0.4 to about 0.6, or about 0.5. In some embodiments, the laser 104 is a diode laser. A diode laser can include optical elements and can emit a converging beam of energy without any other optical elements present in the optical system. In some embodiments, an optical element is positioned within a path of the laser beam, for example, referring to FIG. 1, an optical element can be positioned between the laser 104 and the region 130 where the laser beam energy is provided. The optical element can increase the NA of the beam of energy from the laser. The optical element can be, for example, a lens or a mirror. The lens can be, for example, an aspheric lens. In FIG. 1, the combination of beam expander 118 and lens 120 serves to increase the NA of the beam. For example, a NA of 0.5 can be achieved when the illuminated diameter of lens 120 is equal to its focal length multiplied by 1.15. These conditions correspond to a beam half angle of 30 degrees. A laser beam having a large numerical aperture can be beneficial because a laser beam with a large NA can converge to obtain a high intensity in a small focal zone while having an intensity which rapidly decreases outside the small focal zone. This high intensity can sustain the plasma. In some embodiments, it is beneficial to have the plasma be in a sphere. A laser beam with a large NA can help to maintain the plasma in a spherical shape because of the convergence and focus of the laser beam on the plasma. In addition, a laser beam with a large NA can increase the spectral radiance or brightness of the emitted light because a high intensity light is emitted from a small, spherical plasma. In some embodiments it is beneficial to have the plasma be in any other geometric shape, including but not limited to an oval. In some embodiments, an aspheric lens for laser focus is used to achieve high NA and small plasma spot size. FIG. 22 is a graph 2200 showing spectral radiance on the y-axis and NA on the x-axis. As shown on FIG. 22, spectral radiance of the plasma increases with an increase in numerical aperture of the beam. For example, for a laser tuned to approximately 975 nm, as NA increases up to 0.55, the spectral radiance also increases. For example, when the NA is about 0.4, the spectral radiance is about 15 mW/nm/mm2/sr. When the NA is increased to about 0.5, the spectral radiance increases to about 17 mW/nm/mm2/sr. Therefore, when the NA was increased by about 0.1, the spectral radiance increased by about 2 mW/nm/mm2/sr. A laser beam having an NA of about 0.5 can produce a higher brightness light than a laser beam having a smaller NA. FIG. 23A shows a bulb 2300 having a chamber 2305 that can be used in a LDLS. To assure reliable ignition of a LDLS, a high degree of alignment can be achieved between the focus of the laser and a point 2315 within the bulb 2300 which lies on a line between the tips of the electrodes 2310, 2311 used for ignition and is approximately equidistant from the tips of the electrodes 2310, 2311. This line is important because the initial arc used for ignition of the laser plasma follows close to this line. In addition to this requirement, there can also be a need for simple replacement of a bulb at the point of use of the LDLS without complex alignment procedures. In the case of prior art aligned bulbs, the purpose of pre-alignment is to provide alignment of the light source zone with an optical system. That goal can be met in the LDLS by alignment of the laser beam, not the bulb, which assures alignment of the light emitting zone during operation and which alignment remains fixed independent of the replacement of a bulb. Therefore the purpose achieved by pre-aligning the bulb in the LDLS is primarily that of LDLS ignition, not optical alignment of the light emitting zone. In some embodiments, the lamps or bulbs can be pre-aligned. In one embodiment, the electrodes are positioned within a tolerance of about 0.01 to about 0.8 mm, and more specifically that the electrodes are within a tolerance of about 0.1 to about 0.4 mm. In some embodiments, the center of the plasma should be within about 0.001 to 0.02 mm of the center of the gap between the electrodes. With these tight tolerances, it can be beneficial to have the lamps/bulbs pre-aligned so that the end user does not have to align the lamps/bulbs upon replacement. A bulb for a light source can be pre-aligned so that an operator of the light source does not have to align the bulb prior to use. The bulb 2300 having two electrode 2310, 2311 can be coupled to a mounting base 2320, as shown in FIG. 23B. The bulb 2300 can be coupled to the mounting base 2320 by a dog-point set screw, a nail, a screw, or a magnet. The bulb and mounting based structure can be inserted into a camera assembly, for example, camera assembly 2400 of FIG. 24. The camera assembly includes at least one camera, for example, cameras 2405, 2410 and a display screen (not shown). The camera assembly 2400 can include more than two cameras. In some embodiments, a master pin 2415 is placed in an alignment base 2420. The alignment base 2420 and master pin 2415 can be placed into the camera assembly 2400 for use as a bulb centering target. After the camera assembly 2400 is initially set up with the alignment base 2420 and master pin 2415, the bulb 2300 and mounting base 2320 of FIG. 23B can be inserted into the camera assembly 2400 in place of the alignment base 2420 and master pin 2415. The two cameras 2405, 2410 can be arranged to look at the bulb from two orthogonal directions to allow a high accuracy (25 to 50 microns) when the bulb is positioned correctly with respect to the mounting base. The mounting base can be made of metal or any other suitable material. FIG. 25 shows a display screen 2500 that can be displayed from at least one of the cameras (e.g., cameras 2405, 2410 of FIG. 24) when a bulb (e.g., bulb 2300 of FIG. 23B) is mounted in the camera assembly (e.g., camera assembly 2400 of FIG. 24). The display screen can show two electrodes 2505, 2510 that are within a bulb. The arrows 2515, 2520 can be used to help position the electrodes 2505, 2510 and thus the bulb in a mounting base. The center point 2525 can be positioned equidistant from the tips of the electrodes 2505, 2510 when the tip of the electrodes 2505, 2510 is aligned with the arrows 2515, 2520, respectively. The arrows 2515, 2520 and the center grid 2530 can comprise a positioning grid with which the electrodes are aligned. If the bulb assembly is not positioned correctly within the mounting base (and thus the electrodes do not align properly in the display screen 2500), the position of the bulb within the mounting base can be adjusted such that a region of the bulb between the two electrode (e.g., center point 2525) aligns with a positioning grid on the display screen 2500. The position of the bulb can be adjusted either vertically or horizontally within the mounting base to align the electrodes 2505, 2510 with the positioning grid. The position of the bulb can be adjusted by a manipulator that is positioned above the bulb when the bulb is in the camera assembly. The manipulator can be capable of moving the bulb vertically and horizontally. For example, the manipulator can be a robotized arm that can clamp to the bulb. The robotized arm can be moved, for example, by a computer program. In some embodiments, the method of pre-aligning the bulb includes toggling between the two cameras (e.g., cameras 2405, 2410 of FIG. 24) to align the bulb. The display screen 2500 and a predetermined grid can change based on what camera is being displayed. In some embodiments, the images from the cameras are displayed side-by-side on the display screen. In some embodiments, the images from the two cameras are displayed in different colors, for example, one camera can display an image in red while another camera can display an image in green. The positioning grid on the display screen can be pre-determined such that when the center area 2525 of the bulb between the two electrodes 2505, 2510 aligns with the positioning grid on the display screen, the region 2525 is aligned relative to a focal point of a laser when the bulb and mounting base are inserted into a light source. When the bulb has been aligned, the bulb can be secured to the mounting base. In some embodiments, cement is cured to fix the bulb position permanently in the base. In some embodiments any other type of securing or fastening agent/material can be used to secure the bulb position permanently in the base. This pre-aligned bulb can be used by inserting the pre-aligned bulb into a light source. The user does not have to align the bulb in any way. The user can simply insert the pre-aligned bulb into a LDLS without having to make any adjustments for alignment. The mounting base can guarantee the alignment of the bulb when the bulb is placed into the LDLS. In one embodiment the base has one or more alignment features to guarantee the alignment of the bulb when it is placed into the LDLS. In another embodiment, the base has one or more mating features, for example, apertures, grooves, channels, or protuberances, to guarantee the alignment of the bulb when it is placed into the LDLS. A feedback loop can be installed in the LDLS to decrease the amount of noise within the LDLS. Noise can occur due to gas convection within the bulb or outside the bulb. Noise can also occur due to mode changes within the laser, and especially within laser diodes or due to mechanical vibration generated within or outside the LDLS. One solution to decrease the amount of noise is to install a feedback loop. Another solution to decrease the amount of noise is to tilt the laser to 90 degrees from a horizontal plane of the plasma. Another solution is to precisely stabilize the temperature of the laser, for example by sensing the laser temperature and using a feedback control system to maintain a constant temperature. Such a temperature stabilization system can utilize a thermoelectric cooler controlled by the feedback system. In some embodiments, the amount of noise increases as the laser is tilted closer to horizontal. FIG. 26 shows a flow chart 2600 for a method of decreasing noise within a light source. A sample of light that is emitted from the light source can be collected (step 2610). The sample of light that is collected from the light source can be collected from a beam splitter. The beam splitter can be a glass beam splitter or a bifurcated fiber bundle. The sample of light can be collected using a photodiode. The photodiode can be within a casing of the light source or the photodiode can be external to the casing of the light source. In some embodiments, two samples of light are collected. One sample can be collected by a first photodiode within the casing of the light source and one sample can be collected by a second photodiode external to the casing of the light source. The sample of light can be converted to an electrical signal (step 2620). The electrical signal can be compared to a reference signal to obtain an error signal (step 2630). The error signal can be the difference between the reference signal and the electrical signal. The error signal can be processed to obtain a control signal (step 2640). In some embodiments, the error signal is processed by a control amplifier. The control amplifier can be capable of outputting a control signal proportional to at least one of a time integral, a time derivative, or a magnitude of the error signal. A magnitude of a laser of the light source can be set based on the control signal to decrease noise within the light source (step 2650). Steps 2610-2650 can be repeated until a desired amount of noise is reached. Once the desired amount of noise is reached, steps 2610-2650 can continue to be repeated to maintain the amount of noise within the system. Steps 2610-2650 can be carried out by analog or digital electronics in a manner whereby the steps are not discrete, but rather form a continuous process. FIG. 27 shows a schematic illustration of a functional block diagram 2700 of an embodiment of a feedback loop. The circuit can consist of one or more modules 2705, 2706. In one embodiment, the circuit consists of two modules, for example, a lamp controller module 2705 and a lamp house module 2706. In one embodiment, universal AC 2710 is put into an AC to DC converter 2715. In one embodiment the AC power input is about 200 W. The AC to DC converter 2715 converts AC power to DC power. In some embodiments, the DC power is provided to a Laser Drive 2720. The laser drive 2720 can then operate the laser 2725, for example an IPG diode laser. In some embodiments, the laser 2725 is operated at about 975 nm and in other embodiments the laser is 2725 operated at about 980 nm. The laser 2725 can be coupled to a fiber 2730, for example a fiber optic cable, which transmits the laser beam to a bulb 2735. In some embodiments the bulb 2735 is a quartz bulb that is greater than 180 nm. In some embodiments, output light from the LDLS is stabilized so that the noise over a bandwidth of greater than 1 KHz is substantially reduced and long term drift is prevented. In some embodiments, a sample of the output beam is obtained by a beam splitter, or other means, so that the sample of light is taken effectively from the same aperture and the same NA or solid angle as the output light is taken from. As an example, a glass beam splitter can be placed in the beam. A few percent of the output power can be deflected from the beam, but it retains all the angular and spatial character of the actual output beam. Then, this sample is converted to electrical current by a detector and compared to a preset or programmable reference level. A signal representing the difference between the reference and actual detector current, e.g., an error signal, can then be processed by a control amplifier having, for example, the capability to produce an output control signal proportional to any or all of the time integral, the time derivative, and the magnitude of the error signal. The output of this control amplifier then sets the magnitude of the current flowing in the laser diode. The variation in laser output produced in this way can cancel out any fluctuation or drift in the output beam power. In some embodiments, one or more modules are connected to a tool 2740. The tool 2740 can be any device that can utilize a LDLS, for example, a high pressure/performance liquid chromatography machine (“HPLC”). In some embodiments, the tool 2740 contains a photodiode 2745 that converts the light emitted from the LDLS into either current or voltage. In some embodiments, the photodiode 2745 sends a signal 2746 to a control board 2750 that contains a closed loop control. This signal 2746 can then be compared with a reference signal and the resulting error signal can be used to adjust the LDLS so that the light monitored by the photodiode 2745 remains at a constant value over time. In some embodiments, water is used to cool the lamp control module 2705. In some embodiments, purge gas and/or room air are used to cool the lamp house module 2706. In some embodiments, other coolants are used to cool the lamp control module 2705 or the lamp house module 2706. In some embodiments the laser module is cooled by a thermoelectric cooler. The lamp house module 2706 can also include an igniter module 2755 that can be used to excite a gas within a chamber of the light source. The lamp house module 2706 can include a photodiode 2760 and a photodiode conditioning circuit 2765. The photodiode 2760 can provide a current signal proportional to the intensity of the high brightness light. Photodiode conditioning circuit 2765 can provide a robust, buffered electrical signal suitable for transmitting the photodiode signal to remotely located electronic control circuits. The photodiode signal can be used to establish that the lamp is ignited and operating properly and it can be used in an internal feedback loop as described herein. FIG. 28 shows a control system block diagram 2800 that employs two feedback loops. For example, one feedback loop can use an external photodiode (see the bolded boxes of FIG. 28) and another feedback loop can use an internal photodiode (see the bolded, dashed boxes of FIG. 28). In some embodiments, the external diode feedback loop results in a 0.3% pk-pk noise level. In some embodiments, the external photodiode feedback loop is a closed loop control (“CLC”) system with feedback from a sample of the output beam, sampled with the same aperture and NA as the output beam. The control system block diagram 2800 employing two feedback loops includes three modules, a lamp controller module 2805, a lamp house module 2806, and a fixture module 2807. Within the lamp controller module 2805 an internal reference 2810 is provided to a comparison tool 2815. The comparison tool can be a summing junction. The lamp controller module 2805 also includes a power supply 2820 to the laser that can obtain a signal from an external feedback PI controller 2825, an internal feedback PI controller 2830 or a fixed set point 2835 depending on the circuit 2840. For example, as shown in FIG. 28, the power supply 2820 is receiving a signal from the internal feedback PI controller 2830. The power supply 2820 sends power to a bulb 2845 within the lamp house module 2806. Light 2850 is emitted from the bulb 2845. A portion of the light 2850 can be used for the internal feedback loop. The internal feedback loop within the lamp house module 2806 includes optics 2855, a detector 2860, and a pre-amplified calibration, noise and power feedback 2865. The internal feedback loop can be send a signal to the comparison tool 2815 to be compared to the internal reference 2810 to obtain an error signal. The light 2850 emitted from the bulb 2845 can be sent to optics 2870. The light 2875 emitted from the optics 2870 can be the high brightness light that is used in a variety of applications, for example, an HPLC device. A portion of the light 2870 can be used for the external feedback loop. The internal feedback loop within the fixture module 2807 includes optics 2880, a detector 2885, and a pre-amplified calibration, noise and power feedback 2890. The external feedback loop can send a signal to the comparison tool 2815 to be compared to the internal reference 2810 or the internal feedback loop signal to obtain an error signal. In some embodiments, the feedback system can correct the laser drive current to maintain a constant intensity of light as measured in a sample of the output beam sampled from the same spatial region of the emitting area and from the same solid angle used in the application. In some embodiments, a beam splitter is used to obtain such a sample and deliver the sample of light to a photodetector, which generates the feedback signal. FIG. 29 shows an optical system 2900 of a light source with a noise measurement system and feedback loop. The optical system includes a collimator and focusing lens 2905 that focuses a beam of light 2910 from a laser (not shown) on a chamber 2915 of a bulb 2920. The light 2910 is emitted from the plasma 2925 within the chamber 2915 toward an off axis parabolic mirror (“OAP”) 2930. The light continues though an iris 2935, for example a 10 mm iris, and an optical filter 2940 to a second OAP 2945. The light 2910 passes through an aperture 2950, for example a 200 μm aperture. A beam sampler 2955 can be used to deflect a portion of the light 2910 to a feedback detector photodiode 2960 to be used as a sample in the feedback loop. The remaining light 2910 continues to an output beam detector photodiode 2965. The optical system 2900 simulates an application of the light source and allows measurement of the noise level achieved in the light reaching the output beam detector photodiode 2965, which light and noise level are representative of the light entering a users optical system, such as an HPLC detector. The use of a feedback loop or closed loop control (“CLC”) can decrease the amount of noise within a light source. Table 2 shows noise measurement data with and without a CLC circuit. Averaged for many scans, the Pk-Pk/Mean in a 20 second period is 0.74% without using a CLC system, and 0.47% with a CLC system. Even for a 200 second period the noise is 0.93% without CLC, and 0.46% with a CLC. TABLE 2Pk-Pk/Mean noise for LDLS with or without CLCLDLS withoutLDLS withPk-Pk/Mean (%)CLCCLC200ms0.390.332s0.610.4420s0.740.47200s0.930.46 As shown in FIG. 29 the plasma 2925 is imaged by the second OAP 2945 reflector onto a 200 μm aperture at the front end of a lens tube. A quartz lens (1″ diameter, 25 mm focusing length, Edmund Optics, NT48-293) is mounted in the same lens tube and forming a 1:1 image of the aperture 2950 to a noise measurement photodiode 2965 (Thorlabs DET25K) through a beam sampler 2955 (fused silica, 0.5° Wedged, Thorlabs, BSF10-A1). The beam reflected by the beam sampler 2955 is focused to a second photodiode 2960 (Thorlabs DET25K) which is the detector for a closed-loop control system. There is no aperture in front of the photodiodes so the photodiodes were under-filled by the image of the 200 μm aperture. In some embodiments, the LDLS noise is caused by the laser mode hopping. The output spectrum of a semiconductor laser employed for a LDLS has a discrete set of frequencies i.e., modes. Small fluctuation of the current running through the laser diode or laser temperature can cause the laser diode to switch to the different set of modes. The instantaneous switching between modes is called mode hopping. The mode hopping can cause rapid changes in the laser output spectrum and output power. As the plasma emission intensity depends on these parameters, the mode hopping also causes changes of the LDLS radiance and therefore can compromise the LDLS stability. This effect is undesirable as high stability is required for LDLS used for absorption detectors in chromatography applications. To eliminate the negative impact of the mode hopping on the LDLS stability, the current of the semiconductor laser can be modulated at a frequency of a few tens of kHz. The amplitude of modulation is about 10-20% of the total laser current. The modulation of the current can cause intentional switching of the laser diode between different sets of modes. If this switching occurred slowly it can be observed and measured as noise by instruments having a certain bandwidth, or a predetermined frequency band. However, a rapid modulation of the laser current, at a frequency greater than the predetermined frequency band, and corresponding rapid mode hopping, can have effects which are averaged out when measured within the predetermined frequency band. As an example of an application requiring low noise, the measurement in the chromatography application is relatively slow and takes about 0.1-2.0 seconds and therefore the frequency band of interest when measuring noise in that case is primarily about 0.5 Hz to 10 Hz and secondarily about 0.1 Hz to 100 Hz to allow for digital sampling of the data. The frequency of the modulation imposed on the laser current can then be a frequency higher than about 100 Hz and preferably about 10 kHz to 100 kHz. Multiple oscillations of the laser current can occur during the period of the measurement. The contribution of different modes averaged during the period of the measurement leads to effective reduction of noise in chromatographic measurements. Some applications, for which the LDLS can be used, for example a spectrometer, have light detectors that are sensitive in a specific wavelength range. A LDLS can output a high brightness light that is about 20 times as bright in the most sensitive wavelength range of the detector as previous light sources. This dramatic increase in spectral radiance can saturate the detector of the application, which can result in the application not being able to take advantage of light outside the detector's most sensitive wavelength range, even though the LDLS can have its greatest practical advantage outside the detector's most sensitive range, e.g., in the deep ultraviolet range. In other words, the high radiance in a less useful part of the wavelength spectrum can result in an inability to use the high radiance in the useful part of the spectrum. One solution to this problem is to use a light source that has a chamber with a gas disposed therein, an ignition source of exciting the gas and at least one laser for providing energy to the excited gas within the chamber to produce a high brightness light. The high brightness light has a first spectrum. The light source also includes an optical element disposed within the path of the high brightness light to modify the first spectrum of the high brightness light to a second spectrum. The optical element can be, for example, a prism, a weak lens, a strong lens, or a dichroic filter. The second spectrum can have a relatively greater intensity of light in the ultraviolet range than the first spectrum. The first spectrum can have a relatively greater intensity of light in the visible range than the second spectrum. The optical element can increase the intensity of the light at certain wavelengths relative to the intensity of light at certain other wavelengths. FIG. 30 shows a schematic illustration of a weak lens method 3000 for modifying a spectrum of a high brightness light. High brightness light from a LDLS 3005 is sent via a delivery fiber 3010 to a filter 3015. A weak lens 3020, which can focus certain, pre-determined wavelengths because the refractive index of the lens material is dependent on wavelength modifies the spectrum of the high brightness light. The lens can be made of glass or fused quartz or other materials whose refractive index is wavelength dependent. The spectrum is modified because the chromatic aberration of the weak lens causes some wavelengths of the light to focus at the aperture of the application 3050, while other wavelengths fail to focus there and are lost from the system. The high brightness light with a modified spectrum then goes to two OAPs 3025, 3030 and then to a beam splitter 3035. The beam splitter 3035 can send a portion of the high brightness light with the modified spectrum to a feedback fiber 3040. This sample of the light can be sent to a photodiode and PID controller 3045. The PID controller 3045 can control the current to the LDLS 3005 to maintain a constant output of high brightness light. The remainder of the high brightness light can be sent to an application 3050, for example a spectrometer. The light sent to the application can have a modified spectrum from the original high brightness light emitted from the LDLS 3005 due to the light passing through the weak lens 3020. FIG. 31 shows a schematic illustration of a strong lens method 3100 for modifying a spectrum of a high brightness light. Similar to the weak lens method of FIG. 30, high brightness light from a LDLS 3005 is sent via a delivery fiber 3010 to a filter 3015. The high brightness light then goes to an OAP 3025. A strong lens 3027 exhibiting chromatic aberration, as for the weak lens above, is positioned between the OAP 3025 and a beam splitter 3035. The strong lens 3027 can focus certain, pre-determined wavelengths to modify the spectrum of the high brightness light. After the high brightness light is modified, the light can be sent to an application 3050, for example a spectrometer. The light sent to the application can have a modified spectrum from the original high brightness light emitted from the LDLS 3005 due to the light passing through the strong lens 3020. The beam splitter 3035 can send a portion of the high brightness light with the modified spectrum to a feedback fiber 3040. This sample of the light can be sent to a photodiode and PID controller 3045. The PID controller 3045 can control the current to the LDLS 3005 to adjust the current to maintain a constant output of high brightness light. FIG. 32 shows a schematic illustration of a filter method 3200 for modifying a spectrum of a high brightness light. High brightness light from a LDLS 3005 is sent via a delivery fiber 3010 to a filter 3015. The high brightness light then goes to two OAPs 3025, 3030. A reflective filter 3205 is positioned between OAP 3030 and application 3050. The reflective filter 3205 can filter certain, pre-determined wavelengths to modify the spectrum of the high brightness lights. The light sent to the application 3050 can have a modified spectrum from the original high brightness light emitted from the LDLS 3005 due to the light passing through the reflective filter 3205. For example, the reflective filter can use many layers of materials having differing refractive indexes and be designated so that shorter wavelengths are efficiently reflected whereas longer wavelengths are at least partially transmitted or absorbed by the filter. A transmissive filter can also be applied. FIG. 33 shows a schematic illustration of a prism method 3300 for modifying a spectrum of a high brightness light. High brightness light from a LDLS 3005 is sent via a delivery fiber 3010 to a filter 3015. The high brightness light then goes to two OAPs 3025, 3030. A prism 3305, for example a 20° quartz prism, is positioned between the output OAP 3030 and the application 3050. The prism disperses the light according to wavelength and produces an elongated focus spot that contains a short wavelength enhanced spectrum at one end and a long wavelength enhanced spectrum at the other end. The light sent to the application 3050 can have a modified spectrum from the original high brightness light emitted from the LDLS 3005 due to the light passing through the prison 3305. For example, if the position of the elongated focus spot is adjusted so that the aperture leading into the application 3050 receives light from one end of the elongated focus spot the spectrum of light in the application will be primarily short wavelength light and long wavelengths will be suppressed. In some embodiments, it is desirable to minimize the laser power in the light source output to reduce the amount of safety procedures that are required to operate the LDLS. FIG. 34 is a schematic illustration of a laser-driven light source 3400. To minimize the laser power in the light source output, the laser beam 3410 is positioned to contact a mirror 3430. The mirror 3430 re-directs the laser beam at a 90° angle to the plasma 3420. Light output from the laser-driven light source 3400 is emitted from the system horizontally. In some embodiments, an absorbing structure or coating is placed on the inside of the enclosure 3470 where the residual laser beams (e.g., laser beams that are unabsorbed by the plasma) will strike after transiting the bulb. In some embodiments the mirror 3430 selectively reflects the laser wavelength. The mirror 3430 can be used to deliver the laser beam 3410 to the plasma 3420 as well as reduce the back reflection of light from the plasma to the laser and/or the laser delivery fiber 3440. For example, the mirror can be a dichroic mirror positioned within the path of the laser such that the laser energy is directed toward the plasma. The dichroic mirror can selectively reflect at least one wavelength of light such that the light generated by the plasma is not substantially reflected toward the at least one laser. The dichroic mirror can comprise glass with multiple layers of dielectric optical coatings. The optical coating can reflect energy at one wavelength and transmit energy at a different wavelength. Therefore, the dichroic mirror can reflect the wavelength energy of the laser to the plasma 3420. The high brightness light that is produced by the plasma can have a different wavelength than the laser energy. The high brightness light can pass through the mirror 3430 instead of being reflected back to the laser. In some embodiments, the mirror 3430 helps keep the fiber end and/or the connector from being damaged. In other embodiments, the mirror is used to change the direction of the laser beam 3410. A LDLS has numerous applications. For example, a LDLS can be used to replace D2 lamps, xenon arc lamps, and mercury arc lamps. In addition, a LDLS can be used for HPLC, UV/VIS spectroscopy/spectrophotometry, and endoscopy. Furthermore, a LDLS can be used in a microscope illuminator for protein absorption at 280 nm and DNA at 260 nm. A LDLS can also be used for general illumination in a microscope and for fluorescence excitation in a fluorescence based instrument or microscope. A LDLS can also be used in a confocal microscope. A LDLS can also be used for circular dichroism (“CD”) spectroscopy. A LDLS can provide brighter light at shorter wavelengths with lower input power, as compared to high wattage xenon arc lamps currently used. In addition, a LDLS can be used in atomic absorption spectroscopy to provide a brighter light source than arc lamps currently used. In addition, a LDLS can be used spectrometers or spectrographs to provide lower noise than arc lamps currently used. In some embodiments, a LDLS can be used with an absorption cell. A system using a LDLS with an absorption cell has the advantage that a very small cell can be used while still maintaining a high rate of photon flux through the cell due to the very high radiance, high brightness, of the LDLS. Thus, smaller volumes of material are needed to carry out an analysis in the cell, and for a given time resolution, lower flow rates are required. FIG. 35 is a schematic illustration of an absorption cell 3500. An absorption cell has a vessel 3505 with transparent walls 3506. The vessel 3505 can hold a gas or a liquid. The absorptivity or absorption spectrum of the gas or liquid can be measured. The absorption cell 3500 can contain one or more optical windows, 3510. In some embodiments the optical windows 3510 can let in light from a light source 3520. In some embodiments the light source 3520 is a LDLS. One of the windows 3510 can be illuminated by light 3530 from the LDLS which is delivered to the window 3510 by an optical system (not shown). The optical system can include a combination of lenses, mirrors, gratings and other optical elements. The system can be a focusing mirror to focus the LDLS light into the absorption cell 3500 while avoiding the chromatic aberration which can occur if a lens is used. The light 3530 can be detected by a detector 3540. The absorption cell 3500 can be used as the sample cell 3680 in FIG. 36 In some embodiments, a LDLS can be used with a UV detector. FIG. 36 is a schematic illustration of a UV detector 3600. The UV detector 3600 contains a light source 3610. In some embodiments the light source 3610 is a LDLS. Light 3615 from the light source 3610 follows the path of the arrows in FIG. 36. For example, the light 3615 emitted from the light source 3610, contacts a first curved mirror 3620 and then a second curved mirror 3630. The light 3615 then contacts a diffraction grating 3640 and returns to the second curved mirror 3630. The light 3615 then contacts a first plane mirror 3650 and then a second plane mirror 3660. The light 3615 passes through a first lens 3670. In some embodiments, the first lens 3670 is a quartz lens. The light 3615 then enters a sample cell 3680 and passes through a second lens 3690. In some embodiments, the second lens 3690 is a quartz lens. The light 3615 then enters a photo cell 3695. In some embodiments, a LDLS can be used with a diode array detector. FIG. 37 is a schematic illustration of a diode array detector 3700, according to an illustrative embodiment of the invention. In some embodiments, the diode array detector contains a light source 3710. In some embodiments, the light source 3710 is a LDLS. In some embodiments the light 3715 from the light source 3710 passes through an achromatic lens system 3720 and then a shutter 3730. The light 3715 then enters a flow cell 3740 and then entrance aperture 3745. The light 3715 exits the entrance aperture 3745 and contacts a holographic grating 3750. The holographic grating 3750 directs the light 3770 into a photo diode array 3760. In some embodiments, a LDLS can be used with a fluorescence detector. FIG. 38 is a schematic illustration of a fluorescence detector 3800, according to an illustrative embodiment of the invention. In some embodiments the fluorescence detector contains a light source 3810. In one embodiment the light source 3810 is a LDLS. The light 3815 from the light source 3810, passes through a first lens 3820. In some embodiments, the first lens 3820 is a quartz lens. The light 3815 then passes through a first window 3840 and enters chamber 3830. Some of the light 3815 exits the chamber 3830 through a second window 3845. In some embodiments the first and second windows 3840, 3845 are made of quartz. Some of the light 3815 exits through a transparent wall of the chamber 3830 and contacts a second lens 3850. The lens 3850 focuses the light 3815. The light 3815 then enters photo cell 3860. Variations, modifications, and other implementations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the invention is to be defined not by the preceding illustrative description but instead by the spirit and scope of the following claims.
	abstract	When a scintillator and a reinforcing member are bonded by using an adhesive, scattering and reflection occur at interfaces between the scintillator and the adhesive and between the adhesive and the reinforcing member. Due to this, a blurred image is formed on a sensor, and the resolution deteriorates. A radiation detecting element comprises: a substrate transparent to visible light; and a fluorescent screen that emits fluorescence in response to radiation by a dopant added to a material that is the same as a material of the substrate, wherein the fluorescent screen is thinner than the substrate, and the substrate and the fluorescent screen are bonded while maintaining continuity of a refractive index.
	summary
051739305	description	DETAILED DESCRIPTION OF THE INVENTION Referring now in detail to the drawing, there is shown a monochromator which includes a housing 10 having therein a plurality of mirrors 11, 12, 13 and 14 having opposed pairs of mirror faces 18, 19 and 20, with the housing being provided with inlet and outlet windows 24 and 25, respectively for each of the mirror pairs. Filters 26 mounted on the windows 24 reject visible and ultraviolet light. The mirrors 11-14 are mounted in channels 28 which are provided with pivot pins 30 which extend through apertures (not shown) in the housing to allow the mirrors to pivot in the housing. The channels 28 are also provided with other pivot pins 33 which extend through apertures in a pair of links 35 which serve to hold the mirrors in a parallel relationship. The housing 11, the pivot pins 30 and 33 and the links 35 are precisely made to accurately hold the opposed mirror faces 18, 19 and 20 to within less than 1 arc second from absolute parallel. Also, the opposite surfaces of each of the mirrors 11-14 are parallel to each other to within less than 1 arc second. All of the mirror surfaces should be superpolished to a smoothness of less than about 3 Angstroms RMS. When tested with visible light, the mirror surfaces should be flat to better than 1/20th wave. Materials which can be used for the mirrors and which can be polished to this degree are known. Each pair of opposed or facing mirror faces 18, 19 and 20 is coated with a multilayer coating such that the pairs 18, 19 and 20 each have different coatings but the coatings on any given pair are identical. These coatings are made up of alternating layers of high-Z diffractor material of a thickness d1 separated by layers of low-Z spacer material of thickness d2. Such coatings and the methods of making them are known. The multilayer coatings constitute synthetic Bragg crystals, with x-ray reflection taking place by Bragg diffraction. The wavelength at which the peak of the reflected flux occurs is given by the Bragg relation: n(.lambda.)=2DSin.theta., where n is the order of the diffraction (usually taken to be unity), D is the multilayer diffractor and spacer thickness parameter and .theta. is the angle at which the radiation strikes the mirror surface. One skilled in the art will be aware of which high Z materials will give the best diffraction performance at any desired wave length and which low Z spacer materials should be used with the selected high Z diffractor layers. He will also be aware of how to select the desired thicknesses d1 and d2 to obtain the desired diffractor and spacer thickness parameter. Inasmuch as each pair of opposed mirror faces has its own multilayer coating, different from the coatings on the other pairs of faces, it can readily be seen that each pair of opposed faces will have a peak reflection of x-rays at some wavelength which is different from the peak reflection of the other pairs of faces. This allows one to select the pair of mirror faces which provides the greatest reflection of x-rays at the wavelength desired. The housing is mounted for sliding movement between a plurality of guides 40, as best shown in FIG. 2. The guides 40 are mounted on a base 41 (FIG. 1) and are precisely made and positioned to very accurately position the housing as it is moved from one position to another in the guides 40. A driving mechanism of a known type 44 mounted on the base 41 is connected to the housing by a rod 45 for moving the housing 11 within the guides 40. From the above, it will readily be apparent that the wavelength of peak reflectivity of x-rays by a multilayer mirror is dependent on the angle at which the x-ray beam strikes the mirror, so that one can vary the wavelength at which maximum reflectivity occurs by adjusting the angle of incidence. This is accomplished in this apparatus by pivoting the mirrors on the pivot pins 30. A traversing mechanism 50 of a known type is mounted on the top of the housing and is adapted to traverse a rod 51 which is secured to one of the links 35 to pivot the mirrors to adjust the angle at which a polychromatic x-ray beam 54 strikes the mirror. It can be seen that upward movement of the rod 51 increases the angle of incidence, while downward movement of the rod 51 lowers the angle of incidence. In operation, the driving mechanism 44 is actuated to move the housing 10 in the guides 40 to bring into the path of the polychromatic x-ray beam 54 that pair of mirror faces, 18, 19 or 20 which offer the best reflection over the desired wavelength range. The traversing mechanism 50 is then actuated to pivot the mirrors to change the angle of incidence to select the desired wavelength in the output beam 55. The polychromatic beam 54 reflects off the surface 20 of the mirror 14 (when the housing is positioned as shown in FIG. 1) to strike the surface 20 of the mirror 13 at the same angle of incidence. A monochromatic beam 55 is reflected out of the housing 10 through the outlet window 25 associated with the mirror pair 13 and 14.
047175290	summary	BACKGROUND OF THE INVENTION The present invention relates to a guide for directing a thimble into a fuel assembly in a nuclear power plant, and more particularly to a thimble guide whose length can readily be changed. A typical pressurized water reactor includes a reactor vessel which contains nuclear fuel, a coolant (water) which is heated by the nuclear fuel, and means for monitoring and controlling the nuclear reaction. The reactor vessel is cylindrical, and is provided with a hemispherical bottom and a hemispherical top which is removable. Hot water is conveyed from and returned to the vessel by a reactor coolant system which includes one or more reactor coolant loops (usually as three or four loops, depending upon the power-generating capacity of the reactor). Each loop includes a pipeline to convey hot water from the reactor vessel to a steam generator, a pipeline to convey the water from the steam generator back to the reactor vessel, and a pump. The steam generator is essentially a heat exchanger which transfers heat from the reactor coolant system to water from a source that is isolated from the reactor coolant system; the resulting steam is conveyed to a turbine to generate electricity. During operation of the reactor, the water within the vessel and the coolant system is maintained at a high pressure to keep it from boiling as it is heated by the nuclear fuel. Nuclear fuel is supplied to the reactor in the form of a number of fuel assemblies. Each fuel assembly includes a base element called a bottom nozzle and a bundle of fuel rods and tubular guides which are supported on the bottom nozzle. The fuel rods have cylindrical housings which are filled with pellets of fissionable material enriched with U-235. The tubular guides accommodate measuring instruments and movably mounted control rods of neutron-moderating material. A typical fuel assembly for a pressurized water reactor is about 4.1 meters long, about 19.7 centimeters wide, and has a mass of about 585 kg, and a typical four loop reactor might contain 196 such fuel assemblies supported parallel to one another on a core plate within the reactor vessel. After a service life during which the U-235 enrichment of the fuel assemblies is depleted, the reactor is shut down, the pressure within the vessel is relieved, the hemispherical upper cap of the vessel is removed, and the old fuel assemblies are replaced by new ones. A number of measuring instruments are employed to promote safety and to permit proper control of the nuclear reaction. Among other measurements, a neutron flux map is generated periodically, such as every 28 days, using data gathered by neutron flex detectors which are moved through a number of randomly selected fuel assemblies. To guide the flux detectors during their periodic journeys, closed stainless steel tubes known as flux thimbles extend through the bottom of the reactor vessel and into the fuel assemblies which have been selected as measuring sites. This will be explained in more detail with reference to FIG. 1. In FIG. 1, a core plate 10 that is 17.5 inches (44.5 cm) thick is horizontally mounted within a reactor vessel having wall 12, the portion of wall 12 which is illustrated being at the hemispherical bottom end cap of the vessel. A number of fuel assemblies, including fuel assembly 14, are supported in an orderly array on plate 10. Fuel assembly 14 includes a bottom nozzle 16 having four legs 18 which are joined to a platform portion 20 with a centrally disposed aperture 22 in it. For purposes of the present application aperture 22 will be deemed to be located in the plane of the lower surface of plateform portion 20. A number of fuel rods 23 are bundled together and supported on platform portion 20. Within this bundle is an instrumentation tube 24 which is aligned with aperture 22 and which extends to the top nozzle (not illustrated) of fuel assembly 14. A bore 26 having a threaded region 28 extends through core plate 10 in alignment with aperture 22. A conventional thimble guide 30 is provided with a threaded portion and with a recessed wrench-engaging region 32 which permits technicians to screw guide 30 into threaded region 28 of plate 10 during fabrication of the reactor. After guide 30 is attached in this way, welds 34 are added for additional security. Typically guide 30 is 3.38 inches (8.58 cm) high, from the upper surface of plate 10 to the upper lip 35 of guide 30, and there is a gap of 1.37 inches (3.48 cm) between upper lip 35 and aperture 22. A bore 36 extends through wall 12 of the reactor vessel in alignment with bore 26. A vessel-penetration sleeve 38 having an outer diameter of about 1.5 inches (3.81 cm) extends through bore 36 and is welded at 40 to provide a seal which is resistant to high pressure. A bottom mounted instrumentation column 42 mounted on plate 10 extends between bore 26 and sleeve 38. Column 42 includes a fitting 44 which is attached to plate 10 by bolts 46, an upper pipe element 48 which is joined to fitting 44 by welds 50, and a lower pipe element 52 which is joined coaxially to element 48 at a tie plate (not illustrated). Lower pipe element 52 has an inner diameter of 2 inches (5.08 cm), so that there is a gap between sleeve 38 and element 52. In a typical four-loop pressurized water reactor (having 196 fuel assemblies 14), 58 of the fuel assemblies 14 would be randomly selected for neutron flux monitoring. Accordingly, in such a reactor it will be apparent that there would be 58 guides 30, each communicating via a respective bore 26 and bottom mounted instrumentation column 42 with a respective vessel-penetration sleeve 38. During fabrication, sleeves 38 would be installed in the reactor vessel wall 12 and guides 30 and bottom mounted instrumentation columns 42 would be installed on core plate 10, the columns 42 being secured to one another by tie plates (not illustrated). Then the core plate 10 and attached structures would be lowered into the vessel, with the sleeves 38 fitting into elements 52. In the resulting structure, the upper ends (not illustrated) of sleeves 38 are spaced apart from the lower ends (not illustrated) of upper pipe elements 48, so that sleeves 38 are not in fluid-tight communication with bottom mounted instrumentation columns 42. The bore 54 of upper pipe element 48 typically has a diameter of 0.468 inches (1.189 cm) and terminates in a flared region 56. The bore 58 of fitting 44 is typically 0.68 inches (1.73 cm) in diameter and has flared regions at either end. The bore 26 typically has a diameter of 0.75 inches (1.91 cm). The thing to note is that the channel provided by bores 54, 58, and 26 becomes progressively wider from upper pipe element 48, to fitting 44, to bore 26. This construction facilitates manufacture of the reactor and provides guidance for thimble 60 (to be discussed shortly) while avoiding the possibility that it might become stuck in the channel. Thimble 60 is a long stainless steel tube which begins at a plate (known as a seal table, not illustrated) outside the reactor vessel and which has a closed end (not illustrated) that is normally disposed inside a fuel assembly. Thimble 60 slidably extends through tube 24, guide 30, bore 26, bottom mounted instrumentation column 42, and sleeve 38. A stainless steel guide tube (not illustrated) is welded to the outer end of sleeve 36, and thimble 60 extends within the guide tube to the seal table, which is typically located in a shielded position near the top of the reactor vessel. Since the interior of the reactor vessel is in fluid communication with the interior of sleeve 38, it will be apparent that the guide tube provides a pressure boundary which extends around thimble 60 from wall 12 to the seal table, where a high pressure seal (not illustrated) is provided between the inner wall of the guide tube (not illustrated) and the outer wall of thimble 60. The net result is that thimble 60 provides a low-pressure access channel into the reactor from a shielded position outside of the reactor. A flux detector (not illustrated), about 2 inches (5 cm) long, is slidably accommodated within thimble 60 and is attached to a flexible push-pull cable (not illustrated) which extends through thimble 60 to flux-mapping equipment (not illustrated) located beyond the seal table (not illustrated). At periodic intervals, typically once every 28 days, the flux detectors are pushed to the tops of thimbles 60 and are then slowly withdrawn through the fuel assemblies 14 as flux measurements are taken at different heights to provide a neutron flux map of the interior of the reactor. Normally thimbles 60 remain inserted in the instrumentation tubes 24 of the randomly selected fuel assemblies 14 between the periodic flux mapping operations. Thimbles 60 must be withdrawn from fuel assemblies 14, however, at intervals of 12-18 months when the reactor is shut down for refueling and fuel shuttling. During the refueling operation the nuclear reaction is terminated, the pressure within the reactor vessel is relieved, and the guide tubes (not illustrated) are unsealed from the thimbles 60 at the seal table (not illustrated). The thimbles 60 (which are somewhat flexible) are then withdrawn by a distance of about 14 feet (4.27 meters) to free them from the spent fuel assemblies 14, which are thereupon removed via remote control and replaced by fresh fuel assemblies 14. Thimbles 60 are then driven into the fresh fuel assemblies 14, the reactor vessel and seal table are sealed, and power generation begins anew. The conventional thimble guide 30 of FIG. 1 has several shortcomings. It has been found that considerable turbulence exists during operation of a reactor in the region between the upper surface of core plate 10 and the lower surfaces of platform portions 20 of fuel assemblies 14. Guides 30 expose a significant portion of thimbles 60 to this turbulence, which vibrates thimbles 60 and increases wear to an undesirable extent. Simply increasing the length of guides 30 would be undesirable because fuel assembly designs may change, including the lengths of legs 18. Since guides 30 are permanently installed at the time the reactor is built, any particular length for guides 30 that is selected at that time might make it impossible to take advantage of future design improvements in fuel assemblies. Furthermore, it has been found that fluid flow in the gaps around thimbles 60 due to the progressively widening channels from elements 48 to fittings 44 to bores 26 is sufficient to cause vibrations which increase wear. Finally, the flared regions at upper lips 35 appear to increase turbulence. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide the thimble guide assembly having a length which can be varied in order to reduce the exposed length of the thimble. Another object of the present invention is to provide a thimble assembly whose length can be adjusted, by remote control, after initial fabrication of the reactor. Another object of the present invention is to provide a thimble assembly having a lower sleeve to improve the flow path through the bore in the core plate and through the bottom mounted instrumentation column attached to the core plate. Another object of the present invention is to provide a thimble assembly having an upper lip which is configured to minimize the effects of fluid discharge. These and other objects are attained by providing a thimble guide assembly which includes an elongated first element having a thimble channel and means for mounting the first element on the core plate so that the thimble channel is coaxial with the bore of the core plate, and an elongated second element having a thimble channel and means for connecting the first element to the second element so that the thimble channels thereof are coaxial.
	summary
050248073	claims	1. In a nuclear reactor having fuel assemblies including an upper end fitting and a lower end fitting and spaced nuclear fuel rod spacer grids therebetween for supporting and spacing a plurality of elongated nuclear fuel rods, each of which includes a hollow active portion of nuclear fuel filled cladding intermediate the rod ends and a tapering end cap of solid material with a circumferential groove on the rod end which first encounters reactor coolant flow, a tall spacer grid relative to the grids adjacent the active portion being means for capturing and retaining deleterious debris carried by reactor coolant before it enters the active region of a fuel assembly through solid end caps compartments' corners and creates fuel rod cladding damage, comprising in combination: a polygonal perimeter, a plurality of fuel end cap compartments defined by pairs of first and second intersection and slottedly interlocked grid-forming strips attached to said perimeter and to each other, fuel rod end caps each extending into a respective one of said end cap compartments, at least some of said end cap compartments defined by two pairs of intersecting and slottedly interlocked strips which include integral springs for contact with said end caps in said circumferential grooves and for cooperation with opposing arched portions of said strips also in contact with said end caps, leaves projecting out of said strips intermediate their intersections, each of said leaves being spaced from the fuel rod end caps and extending into the solid end caps compartments' corners and each of said leaves being means for enhancing the spacer grid's ability to capture and retain debris in the regions of said solid end caps compartments' corners so that before said debris passing into said regions engages the active portion of the fuel rods it is captures. 2. The spacer grid of claim 1 in which the arched portions of said strips are formed by the bends of the strips which make the strips have a wavy structure. 3. The spacer grid of claim 2 in which the arched portions of said strips contact said end caps above and below but not in said circumferential grooves. 4. The spacer grid of claim 1 in which the leaves of the individual strips are substantially symmetrical about the slotted intersections when the slottedly interlocked strips are viewed edgewise in the direction of coolant flow. 5. The spacer grid of claim 1 in which the circumferential grooves include tapered surfaces to assist in rod insertion and removal. 6. The spacer grid of claim 1 in which the springs include curved surfaces to assist in rod insertion and removal.
	abstract	A transmission electron microscope comprises a high-voltage source for outputting a high voltage at two high-voltage outputs and outputting a control signal at a controller output; a focusing lens for focusing a beam; a monochromator which allows only those particles of the particle beam to pass whose kinetic energy is within an adjustable energy interval; an energy-dispersive component which deflects particles of different kinetic energies differently; a detector; and a controller connected to the controller output, which controls a beam deflector, arranged between the energy-dispersive component and the detector, the monochromator, or the energy-dispersive component in dependence on the control signal, or superposes plural of intensity distributions detected by the detector with an offset relative to one another, which offset is set in dependence on the control signal.
048896845	summary	BACKGROUND OF THE INVENTION This invention relates to the fuel bundles of boiling water nuclear reactors and more particularly relates to an improved interface between the lower tie-plate and fuel bundle channel. Outline of the Problem Boiling water nuclear reactors generate steam in their core. This core is composed of an array of side-by-side vertically upstanding square sectioned fuel bundles. These fuel bundles divide the core region of the reactor into the so-called core bypass region, exterior of the fuel bundles, and the core region interior of the fuel bundles. The flow region interior of the fuel bundles is at a higher pressure than the bypass region. Typically, water is forced to circulate through the fuel bundles by pumping. The flow region exterior of the fuel bundles is the core bypass region. This region contains nonboiling water and is used to provide increased presence of water for the moderation of high speed neutrons to low speed neutrons so that the chain reaction in the boiling water reactor can continue. In order for this invention to be completely understood, the construction of a typical fuel bundle must be understood. Thereafter, the operation of such a fuel bundle during normal online operation of the reactor will be set forth. The problem of creep and pressure induced deflection of the channel in the vicinity of the lower tie-plate will be set forth. It is this deflection problem to which this invention is addressed. Then the problem of reflood of the core during a loss of coolant accident will be discussed. The participation of the lower tie-plate in such reflood will be set forth in preparation for an improvement in reflood of the disclosed invention. Fuel bundle construction can be summarized in a simplified format sufficient for the understanding of this invention. A fuel bundle consists of a group of fuel rods between an upper tie-plate and a lower tie-plate. The upper tie-plate and the lower tie-plate and the fuel rods extending therebetween are provided with a polygon section, which section is preferably square. This section is surrounded by a water impervious channel which forms a water tight boundary from the lower tie-plate to the upper tie-plate. The lower tie-plate consists of a plate which supports the lower ends of the fuel rods and an integral tubular structure which channels flow from below the lower tie-plate to the bottom of the lower tie-plate. The plate has openings between the fuel rods, and flow passes through these openings and into the fuel bundle. The lower tie-plate has four purposes. First, it supports the heavy fuel rods. Second, it forms a mechanical connection between the upper tie-plate and the lower tie-plate by threaded connection between some of the fuel rods. Third, the lower tie-plate allows water inflow from below the fuel bundle into the interior of the fuel bundle. Finally, the lower tie-plate in cooperation with the fuel bundle channel restricts leakage flow from the interior of the fuel bundle to the bypass region. This invention provides an improved method for restricting the leakage flow. There are two avenues of water flow through the lower tie-plate. The first avenue of flow is through openings between the fuel rod locations, which allow water used for both neutron moderation and steam generation to flow under pressure upwardly through the fuel bundle. This flow enters and passes from the lower tie-plate in the form of pure water. Steam is generated within the fuel bundle and passes out through the upper tie-plate in the form of a steam water mixture. The second avenue of flow is from the major aperture in the tie-plate through the side of the tie-plate to the so-called core bypass region. This flow occurs through small metering apertures, some of which are formed in the side of the lower tie-plate. During normal operation, these apertures supply the core bypass region with low pressure water. During a loss of coolant accident, these same apertures in the lower tie-plate permit so-called "reflood" of the interior of the fuel bundles from the core bypass region. Having discussed in general terms the construction of the fuel bundle and its relation to the core, the function of the fuel bundle during normal operation can be set forth. The problem of pressure acting on the channel of the lower tie-plate can be understood. During normal operation, water is introduced in forced circulation from the reactor and in effect pumped through the lower tie-plate of the fuel bundle. Water around the fuel rods is confined along a path by the fuel channel. A water steam mixture exits the top of the fuel bundle. After exit at the top of the fuel bundle, the water steam mixture passes on to steam separators with the water being recirculated and the steam being separated for power generation. The core bypass region also has a flow. This flow occurs among other places through the collective apertures in the sides of the lower tie-plates of all of the fuel bundles. Water is metered to the core bypass region at a reduced pressure. Thus, there is a substantial pressure differential at the lower tie-plate across the fuel bundle channel. The effect of this pressure differential on the fuel channel is easy to understand. The high water pressure from the inside of the fuel bundle acts towards the low water pressure in the core bypass region to the outside of the fuel bundle through the fuel channel wall. The square section channel is subjected to pressure forces that in the absence of resistance would cause the square sectioned channel to become cylindrical. Responsive to this pressure difference, the channel deflects away from the lower tie-plate. During reactor operation, the channel is subject to a neutron flux. The neutron flux, in combination with the stresses due to the pressure loading, causes the channel to creep so that the channel deflection increases with time. It is known to place a reinforcing band around the bottom of the channel at the lower tie-plate to prevent leakage. It will be appreciated that the interstitial volume between fuel bundles defines the volume for control rod excursion and control of the reaction. As far as bands used for channel reinforcement extend into this region, their added dimension is not desired. Further, insofar as such reinforcement adds to the neutron absorbing mass of the channel, the resultant reaction causes a loss of efficiency. SUMMARY OF THE PRIOR ART In the prior art, the lower tie-plate has been provided with indentations passing along the area of overlap of the channel. These indentations accommodate side-by-side spring biased fingers. These fingers are spring biased from the tie-plate outwardly to and towards the channel. These spring biased fingers occupy the interstitial volume between the channel and the tie-plate. As the channel deflects away from the tie-plate, the fingers move into the increasing interstitial volume and block fluid flow. Thus, the expansion due to both pressure differential and radiation induced creep does not cause excessive leakage. Unfortunately, such springs are themselves a contributor to the undesired expansion of the channel at the lower tie-plate, since the springs apply a load to the channel. SUMMARY OF THE INVENTION In a nuclear boiling reactor, an improved lower tie-plate and fuel channel interface for a boiling water reactor fuel bundle is disclosed. The fuel bundle has a lower tie-plate for supporting fuel rods and permitting the introduction of fluid interior of the fuel bundle. An upper tie-plate maintains the lower tie-plate supported rods in side-by-side relation and has apertures for discharging a mixture of water and steam. The fuel rods extend between the tie-plates for the generation of steam with some of the fuel rods forming a threaded connection fastening the tie-plates together. A polygon sectioned channel, preferably square, surrounds the tie-plates and fuel rods for the confining of fluid flow between the tie-plates interior of the bundle. The interface of the channel as it surrounds the lower tie-plate is reconfigured. This reconfiguration includes means for inducing a rapid pressure drop from the interior juncture of the lower tie-plate and channel to and towards the exterior juncture of the lower tie-plate and channel. This rapid pressure drop leaves the bottom portion of the square sectioned channel without a pressure load. In one embodiment, a labyrinth seal configuration is made in the lower tie-plate consisting of intermittent interruptions of an otherwise constant flow area between the lower tie-plate channel. The labyrinth seal is disclosed as configured either in the lower tie-plate or channel. In a preferred embodiment, a venturi flow configuration with diffuser is provided so that pressure drop in accordance with Bernoulli's principle effects reduced pressure between the lower tie-plate and channel. This reduced pressure reinforces the unstressed and lower portion of the channel with a (negative) hydraulic force applied to counter the (positive) force of outward channel bowing. Reverse venturi flow channel with diffusers are configured at the corners of the channel and adjacent lower tie-plate. These reversed venturi flow channels provide a resricted metered flow during reactor operation from the interior of the fuel bundle to the exterior core bypass region. At the same time and during a loss of coolant accident, a low pressure flow path for reflood of the fuel bundles is provided. Other Objects, Features, and Advantages An object to this invention is to disclose a reconfiguration of the lower tie-plate at the tie-plate channel juncture which hydraulically reinforces the channel at the tie-plate. According to a first embodiment of this invention, a labyrinth seal is configured to the periphery of the lower tie-plate. This labyrinth seal consists of intermittent horizontal pockets interrupting an otherwise constant section flow path configured between the tie-plate on one hand and the channel on the other hand. This labyrinth seal effects an immediate drop in pressure of water trying to pass from the relatively high pressure region interior of the fuel bundle to the low pressure region in the core bypass region exterior of the fuel bundle. An advantage of the labyrinth seal configuration is that the lowermost portion of the channel is left in an unloaded configuration. In this unloaded configuration, it suitably reinforces the overlying portion of the channel subjected to a hydraulic differential force. Thus, the overlying portion of the channel subjected to a high pressure interior from within the fuel bundle and a low pressure exterior in the core bypass region is in effect reinforced by the lower unloaded portion of the channel. According to a second and preferred embodiment of this invention, a venturi flow region is deliberately configured in the lower tie-plate immediate the lower portion of the fuel bundle channel. This venturi channel includes a diffuser for inducing a favorable pressure distribution over the lower portion of the fuel bundle channel. An advantage of this aspect of the invention is that the lower portion of the fuel channel experiences a (negative) hydraulic force with respect to the core bypass volume. This negative hydraulic force in addition to the unloaded portion of the fuel channel coacts upon the channel to maintain improved proximity to the lower tie-plate. A further advantage of this latter configuration is that the greater the tendency of the channel to bow away from the lower tie-plate, the greater the velocity of the flow through the venturi. The greater the velocity of the flow through the venturi, the stronger the hydraulic forces acting on the lower portion of the fuel channel. Thus, the increased hydraulic forces on the fuel channel maintain its proximity to the lower tie-plate. An improved seal results under all conditions. A serendipitous effect follows the reinforcement of the channel by fluid flow. Since most reactors at the lower tie-plate contemplate a small amount of flow from the interior of the channel at the lower tie-plate to the exterior of the channel in the core bypass region, the required leakage for the channel reinforcement provides this required flow. Such provision of required flow to the core bypass region has the supplemental result of the hydraulic reinforcement as set forth above. A further advantage of this invention is that no reconfiguration of the channel at the lower tie-plate is required. Rather, by reconfiguration of the lower tie-plate alone, the flow as set forth in this invention can be achieved. A further object to this invention is to illustrate a reconfiguration of the lower tie-plate which permits fuel bundle reflood from the core bypass region in the event of a loss of coolant accident. According to this aspect of the invention, the lower tie-plate at the corner is configured to form a passage having a venturi and a diffuser. The diffuser is aligned to provide energy efficient water flow in the direction of the interior of the fuel bundle from the core bypass region. In normal operation and due to reverse flow through the diffuser only a small and metered flow is experienced from the interior of the fuel bundle to the core bypass region. During reflood, a venturi diffuser assisted low friction flow path is established from the core bypass region to the interior of the fuel bundle. Consequently, efficient reflood can easily occur.
	abstract	Radioactive laundry liquid wastes are supplied in a liquid waste heating vessel. Hydrogen peroxide and an alkali solution are supplied to the liquid waste heating vessel. pH of radioactive laundry liquid wastes is adjusted to 7 or higher by the alkali solution. The radioactive laundry liquid wastes are heated to 50xc2x0 C. or higher by a heating device. The heated radioactive laundry liquid wastes are introduced to first and second aeration vessels. Ozone is supplied from an ozone generator by way of an ozone gas discharge port to the first aeration vessel. Ozone discharged from the first aeration vessel is introduced from the ozone gas discharge port to the second aeration vessel. Therefore, the amount of ozone dissolved into the radioactive laundry liquid wastes is increased so that the amount of hydroxy radicals formed for decomposing organic substances increases, since the laundry liquid wastes are heated to 50xc2x0 C. or higher under the presence of hydrogen peroxide.
	abstract	A method for immobilizing liquid radioactive waste is provided, the method having the steps of mixing waste with polymer to form a non-liquid waste; contacting the non-liquid waste with a solidifying agent to create a mixture, heating the mixture to cause the polymer, waste, and filler to irreversibly bind in a solid phase, and compressing the solid phase into a monolith. The invention also provides a method for immobilizing liquid radioactive waste containing tritium, the method having the steps of mixing liquid waste with polymer to convert the liquid waste to a non-liquid waste, contacting the non-liquid waste with a solidifying agent to create a mixture, heating the mixture to form homogeneous, chemically stable solid phase, and compressing the chemically stable solid phase into a final waste form, wherein the polymer comprises approximately a 9:1 weight ratio mixture of styrene block co-polymers and cross linked co-polymers of acrylamides.
044180357	abstract	The faster acting junction of a difference junction thermocouple associated with a gamma sensor is located vertically above the other junction to ordinarily monitor local power generation in the fuel core of a nuclear reactor and in response to a reversal in the signal voltage polarity indicate a drop in level of coolant to thereby also function as a coolant monitor. An internal electrical heater enhances the coolant monitoring capability of the sensor, which may also be extended into the dome of the reactor vessel for monitoring conditions therein.
	abstract	An instrumented capsule for material irradiation tests in research reactors. The instrumented capsule performs an optimum material irradiation test under a testing environment similar to the operational environment of a real reactor. The capsule minimizes the influence of flow-induced vibration caused by forced-circulation-type coolant flow in a research reactor, and overcomes the problems experienced in the conventional breakable parts of instrumented capsules which may be broken during the process of loading/unloading the capsules in vertical irradiation holes of reactor pools. The instrumented capsule includes a capsule main body installed in the vertical irradiation hole. The capsule main body consists of a shell and several instruments, such as thermocouples, dosimeters, a vacuum control pipe, and heaters housed in the shell. The capsule main body also includes heat media, specimens set in the heat media, insulators interposed between adjacent heat media, upper and lower end plugs to seal the ends of the shell, an upper guide spring unit to vertically place the capsule main body in the irradiation hole, and a reinforced lower fixing unit assembled with the lower end plug. The instrumented capsule also includes a connecting means for connecting the capsule main body to a capsule control system installed outside the reactor pool.
	abstract	Disclosed are methods and apparatus for characterizing defects by using X-ray emission analysis techniques. The X-rays are emitted in response to an impinging beam, such as an electron beam, directed towards the sample surface where a defect resides. It may also be used to help determine where the void(s) are with respect to the interconnect structure. Methods disclosed are for spatially locating defects in or on integrated circuits. Also disclosed are methods for identifying the elemental composition of defects and spatially locating different elemental components of defects.
	claims	1. A method of fabricating a grid of a fuel assembly of a nuclear reactor, comprising:providing a plurality of interconnected straps, said straps forming a lattice pattern defining a plurality of cells;providing a sleeve, said sleeve having a cylindrical portion and a flared portion;inserting said sleeve into one of said cells such that at least a portion of said cylindrical portion resides in said one of said cells and said flared portion extends above a top end of said one of said cells and overhangs a perimeter of said one of said cells; andwelding said flared portion and causing said weldment flared portion to flow over and fuse to the straps defining said one of said cells. 2. A method according to claim 1, one or more of the straps defining said one of said cells having a weld tab, said welded flared portion flowing over and fusing to said weld tabs. 3. A method according to claim 1, said welding step comprising directing a heat source at said flared portion. 4. A method according to claim 3, said heat source being a laser beam. 5. A method according to claim 1, one or more of the straps defining said one of said cells being loose straps, said welding step attaching said loose straps to said sleeve.
	claims	1. A method of operating a cone-beam CT scanning system, the system having a two-dimensional pixel array having a first dimension, a second dimension, a number Xpix of pixels in the first dimension, and number of Ypix pixels in the second dimension, Xpix being greater than one hundred and Ypix being greater than ten, the system further having a source of radiation that emits a cone-beam of radiation that normally covers all of the pixels of the pixel array, the method comprising:determining an extent of the pixel array that the cone-beam radiation will receive direct-path radiation passing through a target volume of an object during a rotational scan of the object, the rotation scan including a plurality of projections of the object taken at a corresponding plurality of relative angles between the object and the source of radiation, the extent of the angles being equal to or greater than 180 degrees, the target volume being smaller than the volume of the object; andobscuring a portion of the cone beam of radiation such that direct rays of the radiation cover at least the determined extent, but less than 85 percent of the pixel array. 2. The method of claim 1 wherein obscuring a portion of the cone beam further comprises obscuring a portion of the cone beam such that direct unobscured rays of the radiation span at least 15 percent of the second dimension over at least a portion of the pixel array. 3. The method of claim 1 wherein obscuring a portion of the cone beam further comprises obscuring a portion of the cone beam such that direct unobscured rays of the radiation span at least 20 percent of the second dimension over at least a portion of the pixel array. 4. The method of claim 1 wherein obscuring a portion of the cone beam further comprises obscuring a portion of the cone beam such that direct unobscured rays of the radiation cover 50 percent or less of the area of the pixel array. 5. The method of claim 1 wherein obscuring a portion of the cone beam further comprises obscuring a portion of the cone beam such that direct unobscured rays of the radiation cover 35 percent or less of the area of the pixel array. 6. The method of claim 1 wherein obscuring a portion of the cone beam further comprises obscuring one or more bands of the cone beam radiation, each band being parallel to the second dimension. 7. The method of claim 1 wherein determining the extent of the pixel array that the cone-beam radiation will receive direct-path radiation passing through a target volume of the object during a rotational scan of the object comprises receiving one or more prior projections of the object, locating the target volume in at least one prior projection, and determining the extent of the target volume from the location of the region in the at least one prior projection. 8. The method of claim 1 wherein the system has a projection axis from the source of radiation to the pixel array and a scan axis about which either or both of the object and radiation source rotate, the scan axis intersecting the projection axis at a center point, the center point being located a distance d from the source of radiation, the pixel array being located a distance D from the source of radiation, the first dimension of the pixel array being perpendicular to the scan axis, the second dimension of the pixel array being parallel to the scan axis, the projection axis intersecting the pixel array at a point (Xc,Yc) where Xc is a location in the first dimension of the pixel array and Yc is a location in the second dimension of the pixel array, wherein the target volume is located within a cube defined by values z1 and z2measured relative to the center point along the dimension of the projection axis, values y1 and y2 measured relative to the center point along the dimension of the scan axis, and values x1 and x2 measured relative to the center point along the dimension of an axis that is perpendicular to both the projection axis and the scan axis, wherein determining an extent of the pixel array that the cone-beam radiation will receive direct-path radiation passing through the target volume comprises:determining the extent along the first dimension of the pixel array substantially as (Xc−ΔX) to (Xc+ΔX), where ΔX=rD/d, where r=[Δx 2+Δz2]1/2, where Δx is the maximum of the absolute values of x1 and x2, and Δz is the maximum of the absolute values of z1 and z2; anddetermining the extent along the second dimension of the pixel array substantially as (Yc−ΔY+ΔB) to (Yc+ΔY+ΔB), where ΔY=ΔyD/(d-r), ΔB=ΔbD/(d-r), Δy is the absolute value of the difference between y1 and y2, and Δb=(y1 +y2)/2. 9. The method of claim 1 further comprising obtaining a plurality of projections of the object with the portion of the cone beam obscured, the plurality of projections being taken at a corresponding plurality of relative angles between the object and the source of radiation. 10. The method of claim 9 wherein obtaining a plurality of radiographic projections of the object with the portion of the cone beam obscured comprises obtaining at least 250 projections. 11. A method of reconstructing projection data comprising:acquiring a first set of radiographic projections of an object that has been taken by a system having a pixel array with a plurality of pixels and a radiation source, the radiation source capable of covering all of the pixels of the pixel array with direct rays of radiation, wherein each radiographic projection has been taken with a portion of the pixels of the pixel array obscured from direct rays of radiation from the radiation source, wherein each radiographic projection of the first set comprises image values for all of pixels of the pixel array;acquiring an indication of which pixels of the pixel array have been obscured from direct rays of radiation from the radiation source;generating estimates of scattered radiation from the image values that are from the first set of radiographic projections and that are for pixels of the pixel array that have been obscured from direct rays of radiation from the radiation source;generating corrected radiographic projections from the first set of radiographic projections and the estimates of the scattered radiation; andperforming a truncated reconstruction of the object using the first set of the radiographic projections and the indication of which pixels have been obscured from direct rays of radiation from the radiation source; wherein performing the truncated reconstruction generates a reconstruction from the corrected radiographic projections. 12. The method of claim 11 wherein acquiring an indication of which pixels have been obscured from direct rays of radiation from the radiation source comprises receiving the indication. 13. The method of claim 11 wherein acquiring an indication of which pixels have been obscured from direct rays of radiation from the radiation source comprises analyzing the image values of at least one of the radiographic projections of the first set of radiographic projections to determine which pixels have been obscured. 14. The method of claim 11 wherein acquiring the first set of radiographic projections of the object comprises receiving the first set of radiographic projections. 15. The method of claim 11 wherein acquiring the first set of radiographic projections of the object comprises obtaining the first set of radiographic projections from a cone-beam CT system. 16. The method of claim 11 wherein the first set of radiographic projections are from a scan of the object taken about a scan axis with the pixel array having a first dimension perpendicular to the scan axis, a second dimension parallel to the scan axis, a plurality of pixels in the first dimension, and a plurality of pixels in the second dimension, and further taken with direct rays of the radiation from the radiation source covering less than 85 percent of the pixel array and spanning at least three percent of the second dimension of the pixel array in a portion of the pixel array;wherein the method further comprises acquiring a second set of radiographic projections of a scan of the object taken about the scan axis with direct rays of the radiation from the radiation source covering at least 85 percent of the pixel array; andwherein performing the truncated reconstruction of the object further uses the second set of radiographic projections. 17. A computer-program product that directs a data processor to reconstruct projection data, the product comprising:a tangible non-transitory computer-readable medium;a first set of instructions embodied on the computer-readable medium that directs a data processor to acquire a first set of radiographic projections of an object that has been taken by a system having a pixel array with a plurality of pixels and a radiation source, the radiation source normally covering all of the pixels of the pixel array with direct rays of radiation, wherein each radiographic projection has been taken with a portion of the pixels of the pixel array obscured from direct rays of radiation from the radiation source, wherein each radiographic projection of the first set comprises image values for all of pixels of the pixel array;a second set of instructions embodied on the computer-readable medium that directs the data processor to acquire an indication of which pixels of the pixel array have been obscured from direct rays of radiation from the radiation source;a third set of instructions embodied on the computer-readable medium that directs the data processor to perform a truncated reconstruction of the object using the first set of the radiographic projections and the indication of which pixels have been obscured from direct rays of radiation from the radiation source; anda fourth set of instructions embodied on the computer-readable medium that directs the data processor to store the results of the truncated reconstruction on a tangible computer-readable memory; anda fifth set of instructions embodied on the computer-readable medium that directs the data processor to generate estimates of scattered radiation from the image values that are from the first set of radiographic projections and that are for pixels of the pixel array that have been obscured from direct rays of radiation from the radiation source, and to generate corrected radiographic projections from the first set of radiographic projections and the estimates of the scattered radiation; andwherein the third set of instructions directs the data processor to perform the truncated reconstruction using the corrected radiographic projections. 18. The computer-program product of claim 17 wherein the second set of instructions directs the data processor to acquire the indication of which pixels have been obscured from direct rays of radiation from the radiation source comprises receiving the indication. 19. The computer-program product of claim 17 wherein the second set of instructions directs the data processor to analyze the image values of at least one of radiographic projections to generate the indication of which pixels have been obscured. 20. The computer-program product of claim 17 wherein the second set of instructions directs the data processor to generate a histogram of the image values of at least one of radiographic projections. 21. The computer-program product of claim 17 wherein the second set of instructions directs the data processor to convolve the image values of a radiographic projection with a derivative operator. 22. The computer-program product of claim 17 wherein the third set of instructions directs the data processor to generate a set of truncated radiographic projections that only include image values for pixels of the pixel array that have not been obscured from direct rays of radiation from the radiation source, and to perform the truncated reconstruction from the truncated radiographic projections. 23. The computer-program product of claim 17 wherein the first set of instructions directs the data processor to obtain the projections from a computer-readable medium. 24. The computer-program product of claim 17 wherein the first set of instructions directs the data processor to obtain the projections from a cone-beam CT system. 25. The computer-program product of claim 17 wherein the first set of radiographic projections are from a scan of the object taken about a scan axis with the pixel array having a first dimension perpendicular to the scan axis, a second dimension parallel to the scan axis, a plurality of pixels in the first dimension, and a plurality of pixels in the second dimension, and further taken with direct rays of the radiation from the radiation source covering less than 85 percent of the pixel array and spanning at least three percent of the second dimension of the pixel array in a portion of the pixel array;wherein the computer-program product further comprises a fifth set of instructions embodied on the computer-readable medium that directs the data processor to acquire a second set of radiographic projections of a scan of the object taken about the scan axis with direct rays of the radiation from the radiation source covering at least 85 percent of the pixel array; andwherein the third set of instructions directs the data processor to perform the truncated reconstruction of the object further using the second set of radiographic projections.
055106650	description	DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the preferred embodiment of the present invention will be described. An optoelectronic active circuit element 10 in accordance with the present invention comprises a light source means 12, an optical control means 14 and a photocell means 16. The optical control means 14 is a photorefractive material that is intimately interposed between a light emitting surface of the light source means 12 and a light receiving surface of the photocell means 16. Unlike the prior art secondary or intermediary electrical/optical hybrid devices having optical inputs and outputs with an electrical intermediary, the optoelectronic active circuit element 10 of the present invention is an electrical/optical hybrid device that has an electrical input 20 and an electrical output 22 with an optical intermediary in the form of light source means 12 and optical control means 14. Also, unlike the prior art photodetectors and photochoppers, the optoelectronic active circuit element 10 of the present invention is capable of emulating a traditional active circuit element (i.e., a transistor or a diode) by operating in the active range of an I-V curve. The optoelectronic active circuit element 10 operates as an active circuit element by providing an input voltage V.sub.input 20 that controls the transmissivity of the optical control means 14. As a result, the photons 22 emitted by the light emitting surface of the light source means 12 are modulated before striking the light receiving surface of the photocell means 16. In the embodiment as shown in FIG. 1, the photons 22 are amplitude modulated to decrease the number of photons 24 that are allowed to pass through to the light receiving surface of the photocell means 16. In an alternative embodiment described in greater detail hereinafter, the photons 22 may also be frequency modulated by the optical control means 14 to produce the desired effect of the optoelectronic active circuit element 10. The photons 24 striking the light receiving surface of the photocell means 16, in this case a photovoltaic cell, generate an open circuit voltage V.sub.output that is dependent upon the frequency and intensity of the photon energy absorbed by the photo detector means 16. As such, the optoelectronic active circuit element 10 behaves like a traditional active circuit element (i.e., a triode vacuum tube, a transistor or a diode) in that the output voltage or current is a function of the input voltage or current. Unlike conventional semiconductor transistors or diodes, the optoelectronic active circuit element 10 exhibits the characteristic of a vacuum tube in that the energy source can be completely independent from the input voltage or current. This isolation of the input signal from the energy source results in a favorable signal-to-noise ratio (SNR) for the optoelectronic active circuit element 10 of the present invention. Self-Powered Active Circuit Element In the preferred embodiment of the present invention shown in FIG. 2 and described in the previously identified parent application entitled LIGHT EMITTING POLYMER ELECTRICAL ENERGY SOURCE, the light source means 12 is a light emitting polymer (LEP) material 60 and the photocell means 16 are photovoltaic cells 62. By using the LEP material 60, the preferred embodiment of the present is self-powered in that the energy for the light source means 12 is contained within the light source itself. The LEP material 60 is optically separated from the photovoltaic cells 62 by an optical control means 64 for controlling the amount of light that may be absorbed by the photovoltaic cells 62. The optical control means 64 is a photorefractive material, such as a liquid crystal display (LCD) or lead lantium zirconium titinate (PLZT) or similar material, that is either transparent or opaque, depending upon the voltage or current applied to the material. By controlling the amount of light that may be absorbed by the photovoltaic cells 62, the optical control means 64 also controls the output of the photovoltaic cells 62 and, hence, operates as either a voltage or current regulator depending upon the particular circuit that utilizes the electrical energy source of the present invention. In the preferred embodiment, the LEP material 60 is a tritiated organic polymer to which an organic phosphor or scintillant is bonded. Such an LEP material was obtained from Amersham International plc, Amersham Place, Little Chalfont, Buckinghamshire, England, and, pending NRC regulatory approval, may be available from Amersham International plc. Such an LEP material is described in the United Kingdom patent application, Ser. No. 890,5297.1 by Colin D. Bell, entitled TRITIATED LIGHT EMITrING POLYMER COMPOSITION, filed in the British Patent Office on Mar. 8, 1989, the disclosure of which is hereby incorporated by reference herein. It should be recognized that other types of LEP material known in the prior art may also be utilized with the present invention. (e.g., U.S. Pat. Nos. 3,033,797, 3,325,420 and 3,342,743). Those aspects of the LEP material 60 that allow it to be used effectively in the present invention are discussed in greater detail in the previously identified parent application. Light Source Means Although the preferred embodiment of the light source means 12 is described in terms of the LEP material 60, it will be recognized that a variety of light sources are contemplated for use with the present invention. For example, the light source means 12 might be comprised of a light emitting diode or a semiconductor laser powered by an external power supply. Another variation on the self-powered aspect of the LEP material 60 is to provide a chemoluminiscient material that would be activated to operate the optoelectronic active circuit element 10 for a short period of time, for example, as an emergency transmitter. As discussed in greater detail hereinafter, the frequency bandwidth of the emitted light energy may also be used by the present invention, both in terms of its effect on the efficiency of the present invention and on the modulation of the photon energy by the optical control means 14. The preferred embodiment of the light source means 12 is described in terms of a light source having at least one light emitting surface. As will be appreciated by a person skilled in the art, the preferred embodiment of the present invention is well-suited for the type of planar construction techniques used with integrated circuits. The materials of the preferred embodiment are capable of being integrated using well-known deposition and sputtering techniques for constructing the integral combination of the LEP material 60, the photocell 62 and the photorefractive material 64. These techniques allow the optoelectronic active circuit element 10 to be miniaturized. It will also be seen that this embodiment of the present invention may be incorporated with traditional semiconductor integrated circuit devices. Although the preferred embodiment of the light source means 12 utilizes a planar light emitting surface, other shapes and configurations of light source may also be within the scope of the present invention. For example, the LEP material 60 may be cast as an entire volume about the combination of one or more photovoltaic cells 62 having a photorefractive optical control means 64 sputtered thereon. Alternatively, the light source may be optical intimate, but physically remote from the optical control means, provided that there is suitable optical mating means (e.g., bundled optical fibers, light pipes or light channels) to transport the known photon energy from the light source to the optical control means. Photocell Means In the preferred embodiment as described in the previously identified parent application, the photovoltaic cells 62 are amorphous thin-film silicon solar cells, Model No. 035-01581-01, available from ARCO Solar, Inc., Chatsworth, Calif., or their equivalent. These cells have their highest efficiency conversion (greater than 20%) in the blue range of the spectrum of visible light to match the frequency bandwidth of the emitted light of LEP material incorporating a phosphor that emits in the blue range. While the particular photovoltaic cells 62 in the preferred embodiment have been selected to match the blue range of the spectrum of visible light, it should be apparent that other photovoltaic cells may be selected to match the bandwidth of light emitted at other frequencies. In particular, as discussed below, it is known that a new solar cell, known as the Sunceram II (trademark), available from Panasonic's Industrial Battery Sales Div., is claimed to more efficient than conventional amorphous silicon solar cells, especially in the red range of the spectrum of visible light. A standard type of photovoltaic cell having a p-n junction is shown in FIG. 6. An incoming photon of energy hv creates an electron-hole pair and the junction field accelerates the electron toward the n-side of the junction and the hole toward the p-side of the junction. The separation of charge leads to a voltage across the junction, the maximum value of which is V.sub.oc. The ideal bandgap energy E.sub.g for a given photon energy should be one which is just a few tenths of an eV below the photon energy. Because the absorption coefficient for the photon increases as the photon energy increases above E.sub.g, the photon energy should be somewhat greater than E.sub.g to obtain good absorption of the photons. Referring to FIG. 7, an equivalent circuit for a photovoltaic cell and the diode equation which describes the operation of the photovoltaic cell are shown. As can be seen from the descriptive equation in FIG. 7, the current in the photovolatic cell at the operating point is the difference between the light generated current and oppositely direct currents because of diode currents and shunt currents. Clearly, the photovolatic cell will perform most efficiently when these oppositely-directed currents are minimized. This is especially important for the small light-generated currents that are experienced at low light intensities. Using the photovoltaic cell descriptive equation with the assumed diode parameters, the equation can be solved for the maximum power point parameters. This solution should yield an upper limit for the efficient of the photovoltaic cell with the given operating parameters. With the considerations understood, one embodiment of photocell mans 16 of the present invention is an amorphous silicon photovoltaic cell comprised of an intrinsic layer sandwiched between a p-layer and an n-layer. The emitted light energy enters through the p-layer. The entire photovoltaic cell is sandwiched between two conductive layers, one of which is transparent and forms the light absorbing surface of the photocell means 16. A 1/4".times.1/2" amorphous silicon cell was constructed and I-V curves were measured for a number of intensities at different wavelengths. The results of these measurements are shown in FIG. 8. From the I-V curves in FIG. 8, the quantum efficiency of the photovoltaic cell is plotted as a function of wavelength as shown in FIG. 9. Given the curve of FIG. 9, the cell current density J.sub.L can be integrated to predict a total short circuit current for a given intensity of each of the desired spectra. The cell power output can then be found from a characteristic curve for that cell. FIG. 10 shows the results of this determination indicating the incident intensity of the preferred embodiment of the present invention. The result for the cell shown in FIGS. 7-10 had a relatively thick i-layer in order to absorb the longer wavelengths in that spectrum. Further enhancement in efficiency may be achieved by reducing the cell i-layer thickness to a value more appropriate for the wavelengths of the preferred embodiment (615 nm). FIG. 11 shows the construction of such a cell for the 615 nm spectrum. The layer thickness in this cell which would provide the best efficiency for the 615 nm spectrum can be determined by experiment using the criteria just outlined. The applicant estimates that, when properly optimized, this cell should proved for a 12% or higher quantum efficiency. Although the preferred embodiment of the photocell means 16 is described in terms of the photovoltaic cells 62, it will be recognized that a variety of photovoltaic and photoconductive devices are contemplated for use with the present invention. For example, the photocell means 16 might be comprised of a semiconductor avalanche photodiode or phototransistor; or the photocell means 16 might be made of a metal-semiconductor type photocell or a Schottky-barrier type photocell. As will be appreciated by one skilled in the art, the selection of the type of photocell means 16 will depend upon numerous factors, including: the band gap energy, the material selected, the construction techniques, the desired efficiency. For a more detailed discussion of these considerations reference is made to J. Wilson and J. Hawkes, Optoelectronics: An Introduction, pgs. 286-327, Prentice Hall (1983). One of the more interesting alternative embodiments of the present invention involves the use of a phototransistor for the photocell means 16. In addition to the gain introduced by the optical control means 14, the phototransistor can provide an additional gain for the optoelectronic active circuit element 10. The net effect is a cascaded two-stage gain device that greatly increase the magnitude of the gain swing of the active circuit element. Equivalent Circuit Referring now to FIG. 3, the equivalent circuit for the optoelectronic active circuit element 10 will be described. The light source means 12 is shown as a voltage source and a transformer for isolating the energy source from the remaining portions of the equivalent circuit. The optical control means 14 acts as a transistor with the base current being supplied by the input voltage V.sub.input 20. The photocell means 16 is shown as its series resistance value connected to the emitter of the transistor with the output voltage V.sub.output 26 being measured across this resistance. In the equivalent circuit as shown, an external capacitor 30 is used to decouple the D.C. components of the output voltage V.sub.output 26. In general, the characteristic function of the optoelectronic active circuit element 10 is driven by the change in the refractive index of the optical control means 14 and the corresponding change in intensity, frequency or both of the photon energy incident upon the optical control means 14. The change in the index of refraction of a photorefractive material may be expressed in terms of the applied electric field as: EQU l/.DELTA.n.sup.2 =r.epsilon.+P.epsilon..sup.2 where r is the linear electro-optic coefficient and P is the quadratic electro-optic coefficient. In solids, the linear variation in the refractive index is known as the Pockels effect and the non-linear variations in the refractive index is referred to as the Kerr effect. For a more detailed discussion of the implications of the Pockel and Kerr effects on the index of refraction of a photorefractive material, reference is made to J. Wilson and J. Hawkes, Optoelectronics: An Introduction, pgs. 85-124, Prentice Hall (1983). It will be appreciated that the characteristic function of any particular embodiment of the present invention will be a complex function dependent ultimately upon the atomic level interaction of the photons and electrons within the photorefractive material, as well as the optical relationships among each of the component materials of the optoelectronic active circuit element 10. Although the applicant has not provided a representative example of the various types of characteristic functions of the optoelectronic active circuit element of the present invention, it is believed that the characteristic function of the device will include, at least, a linear region, an active region and a saturation or cutoff region. The precise nature of the characteristic equation will depend upon the particular materials chosen for the device and the manner in which these material are fabricated, the mathematical representation of which is beyond the scope of the present application. Although the optoelectronic active circuit element of the present invention has been described in terms of an active circuit element, it will be recognized by one skilled in the art that the circuit element of the present invention is capable of emulating many types of active circuit elements such as a transistor/switch, a transistor/amplifier, a diode/rectifier, a diode/detector, and a Schmidt trigger, as well as numerous types of logic elements such as AND gates, OR gates, inverters, and memory cells. Optical Control Means The optical control means 14 of the preferred embodiment is comprised of a photorefractive material that modulates the light incident upon the surface of the optical control means adjacent the light emitting surface of the light source means 12. When an electrical field is applied across a photorefractive medium, the distribution of electrons within the medium is distorted so that the polarizability and hence the refractive index of the medium changes anisotropically. In the present invention, the electrical field is applied in the form of an input voltage or an input signal to the optical control means 14. As will be appreciated by one skilled in the art, the physical application of the electrical signal to the photorefractive medium (i.e., which surfaces are the electrical contacts applied to and the thickness of the dimension across which the electric field will propagate) will effect the photorefractive effect obtained from the medium. In the preferred embodiment, a high impedance device is used to drive the input signal to modulate optical control means 14, thereby decreasing the switching capacitance and the switching time of the optical control means 14. In the preferred embodiment, a small PLZT optical control means having dimensions of approximately 0.05".times.0.05" will have a capacitance in the 10 pF range. This device would be capable of switching speeds on the order of 400 MHz for input signals of 5 volts. The normal index of refraction of PLZT is on the order of 2.5. The index of refraction of thin film PLZT 280-100 is 2.6. These indices of refraction are desirable in that the typical index of refraction of the preferred polymer light source is in the range of 1.5 and the typical index of refraction of the preferred amorphous silicon photocell is in the range of 3.5. For a typical PLZT material, the photorefractive capabilities of the material are such that it can modulate 65% of the photon energy transmitted through the material in response to relatively low electrical fields. The switching speeds of the PLZT are also very fast, with modulation capabilities on the order of 10-20 GHz. Referring now to FIG. 4, a frequency plot of the frequency distribution of a frequency modulated embodiment of the present invention is shown. This plot demonstrates how the index of refraction of the optical control means 14 of the present invention could be used to alter the frequency of the transmitted light. Assuming that the photocell means 16 is responsive only to the narrow frequency band 50, the change in the frequency of the light passing through the optical control means 14 will produce a corresponding change in the voltage output of the photocell means 16. In this embodiment, the optical control means 14 is comprised of an interference filter 52 in combination with a photorefractive material 54. The interference filter means 52 polarizes the incident photon energy such that relatively small changes in the index of refraction of the photorefractive material 54 allow the optical control means 14 to function as a frequency bandpass filter. The interference filter means 52 may be any type of well-known polarizing filter, including an interdigitated grid. The PLZT material of the preferred embodiment may be capable of frequency modulation down to as fine a resolution as 2 nm wavelengths. Although the photorefractive material that comprises the optical control means 14 of the preferred embodiment is shown as being responsive to an electrical signal, it will also be recognized that other types of input signals may be used to activate a change in the index of refraction of certain types of photorefractive materials. For example, certain photorefractive materials may operate as magneto-optical devices, responding to a Farrady magnetic effect. Other types of photorefractive materials may be sensitive to pressure or to acoustical signals. Still other types of photorefractive materials may be sensitive to temperature variations. As a result, the present invention has numerous applications as a sensing device and, in particular, a self-powered sensing device that is capable of amplifying the sensed condition to enable easier detection. Optical Mating Materials Because the characteristic function of the optoelectronic active circuit element 10 is dependent upon the index of refraction of the optical control means 14, the optical mating of the light source means 12, the photocell means 16 and the optical control means 14 is an important consideration in both the efficiency of the device, as well as the characteristic function exhibited by the device. Although it would be possible to factor multiple changes in the indices of refraction of the various components into the characteristic function of the device, it is preferable to minimize the impact of any changes introduced into the device by changes in the indices of refraction of all materials other than the photorefractive material. To accomplish this, the preferred embodiment can include a first optical mating means optically interposed between the light emitting surface of the light source means 12 and the optical control means 14 and a second optical mating means optically interposed between the optical control means 14 and the light collecting surface of the photocell means 16. The purpose of the optical mating means is to maximize the transmisivity of the emitted light energy by minimizing the boundary condition reflections among the various materials. In the preferred embodiment, the first and second optical mating means are comprised of an optical gel, such as Rheogel 210C or Dow Corning Optical Fluid. The first optical gel should have an index of refraction equal to the square root of the product of the index of refraction of the light source means 12 and the index of refraction of the optical control means 14. The second optical gel should have an index of refraction to the square root of the product of the index of refraction of the optical control means 14 and the index of refraction of the photocell means 16. As an alternative to the use of a separate optical mating means, a first and second sputtering material may also be used. The first sputtering material should have an index of refraction equal to the square root of the product of the index of refraction of the light source means 12 and the index of refraction of the optical control means 14 and the second sputtering material should have an index of refraction to the square root of the product of the index of refraction of the optical control means 14 and the index of refraction of the photocell means 16. Another variation on the sputtering material is to define a sputtering region having a defined sputtering depth in the deposited material that comprise the light source means 12, the optical control means 14 or the photocell means 16 that will produce an equivalent effect as an optical mating means. Maximum absorption of the emitted light energy from the light source means is achieved by the intimate optical contact between the light emitting surface of the light source means and the light collecting surface of the photocell means, by matching the maximum absorption frequency bandwidth of the photovoltaic cell with the specified frequency bandwidth of the emitted light energy from the light emitting polymer material, and by the structural arrangement of the light emitting polymer material itself. To maximize the surface area between the light emitting polymer and the photovoltaic cell, the light emitting surface and the light collecting surface are preferably arranged so that they are generally parallel to and in intimate contact with each other. In addition, the light emitting polymer material and the photovoltaic cell may be arranged to allow the photovoltaic cell to be constructed in manner so as to absorb light energy at more than a single surface. Another feature that may be used to increase the efficiency of the present invention is to include a focal means optically interposed between the light emitting surface of the light source means 12 and the light collecting surface of the photocell means 16 for focusing the emitted light energy on the photocell means 16. The focal means may be interposed either prior to, or after, the optical control means 14. Example Applications Referring now to FIGS. 5a and 5b, two sample applications of the optoelectronic active circuit element of the present invention are shown. In FIG. 5a, the optoelectronic active circuit element 10 is used as both an amplifier and power source for the microphone 70 and voltage amplifier 72 of a sound detection device, the output of which may be fed to a transmitter logic, for example. In FIG. 5b, a frequency feedback control 82 is used in conjunction with a frequency modulated optical control means 14 to produce an oscillator 80 having a sinusoidal output signal. Although the description of the preferred embodiment has been presented, it is contemplated that various changes could be made without deviating from the spirit of the present invention. Accordingly, it is intended that the scope of the present invention be dictated by the appended claims rather than by the description of the preferred embodiment.
	claims	1. A method comprising:arranging a shipping container comprising a tubular or cylindrical shell having a closed end, an open end, and elastomeric sidewalls into a vertical orientation in which the tube or cylinder axis of the cylindrical shell is oriented vertically with the closed end oriented down and the open end oriented up;loading an unirradiated nuclear fuel assembly comprising 235U enriched fuel through the open end of the tubular or cylindrical shell into a fuel assembly compartment defined inside the tubular or cylindrical shell; andafter the loading, closing off the open end of the tubular or cylindrical shell by securing the top end-cap to the open end of the tubular or cylindrical shell,wherein the loading causes compression of the elastomeric sidewalls of the fuel assembly compartment. 2. The method of claim 1 further comprising:after the closing off, rearranging the shipping container into a horizontal orientation;after rearranging the shipping container into the horizontal orientation, arranging the shipping container back into the vertical orientation in which the tube or cylinder axis of the cylindrical shell is oriented vertically with the closed end oriented down and the open end oriented up;removing the end-cap to re-open the open end of the tubular or cylindrical shell; andunloading the unirradiated nuclear fuel assembly from the fuel assembly compartment through the re-opened open end of the tubular or cylindrical shell. 3. The method of claim 1 wherein the shipping container includes N fuel assembly compartments defined inside the tubular or cylindrical shell where N is greater than or equal to two, and the loading is repeated N times to load N unirradiated nuclear fuel assemblies into the N respective fuel assembly compartments.
047073250	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and in particular FIG. 1, there is shown an elongated, generally cylindrically shaped nuclear reactor vessel 1 of conventional design for use in a pressurized water nuclear reactor system. Vessel 1 has the usual hemispherical bottom 3, at least one cooling water inlet nozzle 5, and at least one cooling water outlet nozzle 7. As is conventional, vessel 1 forms a pressurized container when sealed at its open and 9 by a head assembly (not shown). Disposed within the vessel 1 is a cylindrical core barrel 11 which is suspended from an inwardly extending flange 13 of vessel 1. Core barrel 11 includes a bottom forging 15 having a plurality of projections 17 disposed about its circumference for engaging a corresponding number of key members 19 on the vessel 1 for stablizing the position of the core barrel 11 in the circumferencial and radial directions. Mounted within the core barrel 11 near its lower end, and connected to the inner wall of the core barrel 11 by connecting elements 21, is a lower core plate 23 on which the nuclear reactor core (not shown) and the lower internals structure of the reactor normally rest. Of the lower internals structure, the only element shown in Figure 1 is the baffle plate arrangement or baffle structure 25 formed of a plurality of individual interconnected baffle plates 27. The baffle plate structure 25 is connected to the core barrel 11 by a plurality of separater plates or spacers 29, and normally contains and surrounds the nuclear reactor core. As is more clearly shown in FIG. 2, the baffle plate structure 25 has a shape corresponding to the arrangement of the generally rectangular configurations of the fuel rod assemblies which make up the nuclear reactor core. Normally, the space within the core barrel 11 above the baffle plate arrangement 25 contains the upper internals structural unit which, in a conventional manner, is simply suspended within the core barrel 11 in that its upper end, which is constituted by an upper support plate (not shown) is supported on the upper flange 31 of the core barrel 11. To accurately align the upper internals structural unit with the lower internals in both the circumferential and radial directions, the upper core plate (not shown in FIG. 1), which forms the lower end or bottom of the upper internals structural unit, is provided with a plurality of symmetrically disposed peripheral grooves, which engage with a like plurality of radially inwardly directed guide pins 33 fastened to the inner wall of the core barrel 11 at the normal elevation of the upper core plate. The guide pins 33 are fixed to the inner wall of the core barrel 11 so that they have a defined relationship to the lower internals structure of the reactor vessel, and in particular a defined relationship to the baffle structure 25. As indicated above, in order to provide compensation for the various possible machining and positioning tolerance values and in order to provide accurate alignment between the upper internals structural unit and the lower internals structure, the peripheral guide or alignment grooves in the large upper core plate are machined to relatively large tolerance values, and a respective relatively small insert, which is machined to the actual required tolerance values on the basis of actual measurements, is provided and fastened in each of the peripheral guide slots or grooves and forms the actual bearing or guide surfaces between the guide pins 33 and the upper core plate. Such an insert is shown, for example, in FIG. 3. As shown in FIG. 3, the upper core plate 35 has a peripheral groove 37 which extends between the two major surfaces of the core plate 35. The dimensions of this groove 37 are substantially larger than the dimensions of the corresponding guide pin 33 (FIG. 1) in both the circumferential and the radial directions. To provide the close tolerances required, a core plate insert 39 is secured within each groove 37 by means of a flange portion 41 which extends laterally beyond the dimensions of the groove 37 along the bottom surface of the upper core plate 35 and is fastened to same by means of four screws 43. The remaining portion of the core plate insert 39, which is actually within the groove 37, extends upwardly from the flange portion 41 between the two major surfaces of the upper core plate 35 and is provided with a U-shaped groove formed by two accurately machined guide surfaces 45 and 49 whose dimensions are determined on the basis of actual measurements of a respective guide pin 33 relative to a respective slot 37. The two opposed surfaces 45 and 49 are dimensioned to bear against the side surfaces of generally rectangular shaped guide pin 33 so as to accurately position the core plate 35 in the circumferential direction, while similar surfaces oriented at 90.degree. to the surfaces 45 and 49 serve to accurately position the upper core plate 35 in the radial direction. Of course, although only one such peripheral guide groove 37 with its insert 39 is shown, it is to be understood that the upper core plate 35 has a plurality of such grooves 37 which are symmetrically disposed about its circumference, and in particular contains four such guide grooves 37 and inserts 39 disposed on the orthogonal or cardinal axes of the upper core plate 35, i.e. each groove 37 is displaced from the two adjacent grooves by 90.degree. relative the center of the plate 35. To take the measurements necessary to customize the inserts 39 for a replacement upper core plate, according to the invention, a gauge plate 51, as shown in section in FIG. 1 and in plan view in FIG. 2, is provided, with the gauge plate 51 being formed of metal, for example, of 304 stainless steel. The gauge plate 51 has an outer diameter which corresponds to that of the upper core plate which is to be replaced, but has a substantially reduced thickness in order to reduce the weight of the gauge plate 51 during use. For example, whereas the actual upper core plate may have a thickness of 7.62 cm (3 in.), the gauge plate 51 may have a thickness in the order of 1.9 cm (3/4 in.). Moreover, in order to further reduce the weight of the gauge plate 51 and so as to permit it to be more easily lowered through the body of water in which the reactor vessel of FIG. 1 is normally submerged during the replacement of refitting period, the interior portion of the circular engaged plate 51 is provided with a number of cut out sections 53. As shown in FIG. 2, the gauge plate 51 is provided with four U-shaped peripheral gauging slots 55 which are located on the cardinal axes of the gauge plate 51 and are positioned to coincide with the locations of the guide pins 33 for the lower internal structure. The gauging slots 55 are of a known size and location relative to one another and sufficiently wide so that the guide pins 33 can enter these gauging slots 55 with sufficient clearance. For example, the slots 55 may be approximately 7.16 cm (2.82 in) wide which, in a typical installation, would allow for an approximately 0.15 cm (0.06 in) radial gap on each side of the respective guide pin 33. Since, as indicated above, the gauge plate 51 is substantially thinner than the upper core plate, it is necessary to provide some arrangement for postioning the gauge plate 51 at the elevation of the guide pins 33 within the core barrel 11. According to the preferred illustrated embodiment of the invention, this is achieved by providing the lower surface of the gauge plate 51 with a plurality, and preferably at least three, of pads 57 which are formed of metal, for example, stainless steel, and which are positioned so that they will rest on the top ends of the baffle plates 27 when the gauge plate 51 is inserted into the core barrel 11. The pads 57 are of a thickness, for example, 2.86 cm (11/8 in), sufficient to cause the gauge plate 51, and in particular the gauging slots 55, to be at the elevation of the guide pins 33 when the pads 57 are resting on the top surface of the baffle plate structure 25 as shown in FIG. 1. In addition to generally positioning the gauge plate 51 relative to the guide pins 33, it is likewise necessary to accurately position the gauge plate 51 relative to the baffle plate arrangement 25. For this purpose, the gauge plate 51 is provided with a plurality of positioning pins 59 which extend downwardly perpendicular to the lower major surface of the gauge plate 51, i.e. the same major surface containing the pads 57. The positioning pins 59 are located on the plate 51 at positions corresponding to the outboard or outer most positions of the fuel assembly top nozzle locations in the upper core plate so as to simulate such positions, and are of sufficient length, for example 10.16 cm (4 in) so that they can extend into the area delimited by the baffle plate arrangement 25 when the gauge plate 51 is resting on the top or end surfaces of the baffle plates 25. As shown, eight such positioning pins 59 are provided in four pairs, with two pairs of positioning pins 59 being diametrically oppositely disposed along each of the cardinal or orthogonal axes of the gauge plate 51, and with the positioning pins 59 of each pair being symmetrically disposed with respect to its associated cardinal axis. As shown in FIG. 2, the eight positioning pins 59 are in fact disposed in the respective outer most corners 61 formed between two adjacent baffle plates 27, with the individual positioning pins 59 being located on the gauge plate 51 so that they will, based on the original drawings of the particular nuclear reactor being gauged, provided an expected very small nominal clearance, for example in the order of 0.028 to 0.03 cm (0.011 to 0.014 in) with each of the associated baffle plates 27 forming the respective corner 61. Finally, in order to determine the actual position of the existing baffle plate arrangement 25, relative to the gauge plate 51, the gauge plate is provided with a plurality of gauging holes 63, which are located at positions corresponding to the expected actual as-built locations of respective baffle plates 27. The gauging holes 63 extend completely through the gauge plate 51 and are of a sufficient diameter so that a gauging device can be inserted through each of the respective gauging holes 63 to accurately locate the actual position of the inner surface of the associated baffle plate 27. Although it is possible to provide such gauging holes 63 for a substantial plurality of the individual baffle plates 27, preferably a minimum of three such gauging holes 63 distributed as shown in FIG. 2 are provided. In particular, as shown in FIG. 2, two of the gauging holes 63' and 63" are associated with the individual baffle plates 27 forming one outer most corner 61, while third gauging hole 63 is associated with the baffle plate 27 diametrically opposed to one of the two baffle plates 27 associated with the pair of gauging holes 63' and 63". Preferably, as shown, the single gauging hole 63 is associated with a radially extending baffle plate 27. According to the preferred embodiment of the invention, the gauging device used with the gauging holes 63 in order to determine the actual position of the inner surface of the respective baffle plates 27 is a step gauge pin 65 as shown in FIG. 4, which includes a cap 67, a collar 69 of the same diameter as the gauging hole 63, and a lower pin portion 70 of a know gauging diameter. To take the measurements, a plurality of pins 65 with different known diameter portions 70 are provided. Alternatively, a single step gauge pin 65 with a plurality of successive different diameter portions 70 may be utilized. In any case, in order to utilize the step gauge pin 65 as a go, no-go type gauge, each of the gauging holes 63 is positioned relative to its associated baffle plate 27 so that the center line of the gauging hole 63 is displaced or offset by a given known amount from the expected location of the inner surface of the associated baffle plate 27 in a direction perpendicular to this inner surface. More particularly, the center line of each gauging hole 63 is offset by a distance equal to the radius of a desired size step gauge pin portion 70 so that if, for example, the center line of the gauging hole 63 is offset by 1.27 cm (0.50 in), the gauge plate 51 will be in the optimum or best position relative to the associated baffle plate 27 if a gauge pin with a portion 70 having a diameter of 2.54 cm (1 in) can be inserted into a gauging hole 63, but a gauge pin with a diameter of 2.67 cm (1.05 in) cannot be inserted. To utilize the above described gauge plate 51 for its intended purpose, the gauge plate 51 is lowered into the core barrel 11, for example, by means of an overhead crane, until its pads 57 rest on the upper end surfaces of the baffle plate arrangement 25. During the lowering procedure the gauge plate 51 is oriented so that, when the plate 51 is at rest the respective guide pins 33 extend into the respective gauging slots 55 and the plurality of positioning pins 59 extend into the respective corners 61 formed by adjacent baffle plates 27. Thereafter, the desired measurements at each of the gauging slots 55 and at each of the gauging holes 63 is carried out with the gauge plate 51 in the same position. Preferably, in order to clearly establish a reference position for the gauge plate 51 relative to the baffle plate arrangement 25, the measurements at the respective gauging holes 63 are carried out before the measurements at the respective gauging slots 55. More specifically, at each of the gauging holes 53, a step gauge pin 65 with the standard or desired diameter portion 71 is inserted into a respective gauging hole 63, and if it can be inserted, an attempt is made to insert the next larger diameter step gauge pin 65 until the step gauge pin with the largest diameter which can be inserted into the gauging hole 67 is determined and noted. This procedure is repeated for each of the gauging holes 63 with the largest diameter step gauge pin 65 which can be inserted preferably being allowed to remain in the respective gauging holes 63 so as to firmly fix the position of the gauging plate 51 relative to the baffle plate arrangement 25. Thereafter, the desired measurements are taken at each of the gauging slots 55. As illustrated in FIG. 5, four measurements are taken at each of the gauging slots 55. More specifically, using the known outer diameter of the gauge plate 51 as a reference, the inner diameter of the core barrel 11 at the elevation where it interfaces with the upper core plate is determined by measuring the gap or distance 71 between the periphery of the gauge plate 51 and the inner surface of the core barrel 11. Additionally, the two radial gaps 73 and 75 between the respective radially extending surfaces 77 and 79 of the generally U-shaped gauging slot 55 and the respective facing adjacent side surfaces of the guide pin 33 are measured and recorded. Finally the circumferential gap 81 between the circumferential gauging surface 83 of the gauging slot 55 and the end surface of the guide pin 33 is measured and recorded. The measurement of the gaps 71, 73, 75 and 81 are carried out at each of the four gauging slots 55 of the gauge plate 51. Since all of the dimensions of the gauge plate 51 are accurately known, the measured data, as indicated above, can be used to customize the replacement upper core plate inserts so that the replacement upper internals structural unit will be compatible with the existing lower internals structure in an operating nuclear reactor plant. Moreover, as can easily be appreciated, since all of the dimensions of the gauge plate 51 are accurately known prior to the measurements, the gauge plate 51 itself need not even be returned to the factory where the replacement parts are being manufactured. That is, all that need be sent to the factory is the results of the various measurements. As indicated above, during the replacement or refitting period of the nuclear reactor, as well as during the measuring process with the gauge plate 51, the reactor vessel 1 is normally submerged in water in order to provide protection against radioactivity. Accordingly, it is desirable for all of the measurements indicated above to be controlled and/or read out from a remote location. This can be accomplished, for example, by means of remotely controlled robot arms (not shown) as are well known in this art and/or by conventional remotely controlled linear measuring instruments disposed on the gauge plate 51 or on a remotely controlled robot arm. According to the preferred mode of carrying out the method according to the invention, the insertion of the step gauge pins 65 is carried out by a remotely controlled robot arm, while the respective measurements of the gaps 71, 73, 75 and 81 at each gauging slot 55 are carried out by respective sets of four measuring devices which are appropriately mounted at known positions on a major surface of the gauge plate 51. More particularly, as shown in FIGS. 1 and 2, respective sets of measuring devices 85, 87, 89 and 91 are mounted at known positions on the upper surface of the gauge plate 51 adjacent each of the gauging slots 55. Each of the measuring devices 85, 87 and 89 is disposed adjacent, and has its longitudinal axis perpendicular, to a respective one of the surfaces 77, 83 and 79 of the associated slot 55 so as to measure the respective gaps 73, 81 and 75 between the respective slot surfaces and the adjacent surfaces of the guide pin 33. The remaining measuring device 91 of each set is disposed adjacent the peripheral surface of the gauge plate 51 and has its longitudinal axis extending in a raidal direction so as to measure the gap 71 between the peripheral surface of the gauge plate 51 and the adjacent inner surface of the core barrel 11. The measuring devices 85, 87, 89 and 91 may, for example, each simply be a spring loaded plunger which, when released from a remote location, will move forward until it rests against a respective one of the three measuring surfaces of the associated guide pin 33 (devices 85, 87, 89) and against the inner surfaces of the core barrel 11 (device 91) and reamin locked in that position. The actual dimensions of the various gaps are then determined by manually measuring the positions of sixteen plungers, for example, by means of a micrometer, after the gauging plate 51 has been removed from the reactor vessel 1. Preferably, however, measuring devices 85, 87, 89, 91 are provided which can be remotely controlled and will additionally produce a direct remote readout of the measured clearances. For example, each of the measuring devices 85, 87, 89 and 91 can be a spring loaded plunger which is provided with an electrical position sensor which produces an electrical signal proportional to the distance moved by the respective plunger and which is individually connected to a remotely located control and indicator circuit 93 via respective wires of a multi-conductor cable 95 (shown schmatically in FIG. 1). It is of course understood, that the position of the circuit 93 in FIG. 1 is schematic only and in reality would be located outside of the reactor vessel 1 and at a safe distance from same. It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.
	claims	1. A beam blocking array positioned along a path of an ion ribbon beam in an ion implanter, said ion ribbon beam having beam profile, said beam blocking array comprising:a drive motor;a drive wheel rotated by said drive motor; anda plurality of profile wheels disposed along an axle connected to said drive wheel, at least one of said plurality of profile wheels configured to rotate when said drive wheel rotates, each of said profile wheels disposed across a width of said ribbon beam and having a position corresponding to a location of said beam. 2. The beam blocking array of claim 1 wherein each of said profile wheels having a first position configured to block at least a portion of said ion beam at a respective beam profile location and a second position configured to allow said beam to pass along said beam path. 3. The beam blocking array of claim 1 wherein each of said profile wheels has an elliptical shape defined by a first and second parallel surfaces. 4. The beam blocking array of claim 3 wherein each of said profile wheels has a drive pin extending substantially perpendicular from said first surface away from said drive motor and substantially parallel to and spaced from said axle. 5. The beam blocking array of claim 3 wherein each of said profile wheels has a pick-up pin extending substantially perpendicular from said second surface toward said drive motor and substantially parallel to and spaced from said axle. 6. The beam blocking array of claim 1 wherein each of said plurality of profile wheels has a first and second perimeter and a first interior wall surface spaced a distance from said first perimeter and a second interior wall surface spaced a distance from said second perimeter. 7. The beam blocking array of claim 6 wherein each of said profile wheels has a drive pin extending substantially perpendicular from said first surface away from said drive motor and substantially parallel to and spaced from said axle. 8. The beam blocking array of claim 6 wherein each of said profile wheels has a pick-up pin extending substantially perpendicular from said second surface toward said drive motor and substantially parallel to and spaced from said axle. 9. The beam blocking array of claim 4 further comprising a drive wheel disposed on said axle and between said drive motor and a first of said plurality of profile wheels, said drive wheel configured to rotate about said axle and force rotation of said plurality of profile wheels. 10. The beam blocking array of claim 9 wherein said drive wheel is defined by a first and second parallel surfaces, said drive wheel further comprising a drive pin extending substantially perpendicular from said first surface away from said drive motor toward said plurality of profile wheels and substantially parallel to and spaced from said axle. 11. The beam blocking array of claim 1 wherein said plurality of profile wheels are spaced along said axle. 12. An ion ribbon beam uniformity control system comprising:a plurality of profile wheels disposed along a transverse axle, each of said profile wheels configured to rotate when said axle rotates, each of said profile wheels disposed across a width of said ion ribbon beam and having a position corresponding to a location of said beam profile; anda single drive motor configured to rotate each of said plurality of profile wheels at an angle with respect to said ion ribbon beam. 13. The ion ribbon beam uniformity control system of claim 10 further comprising an encoder disposed between said single drive motor and said plurality of profile wheels, said encoder configured to provide position information for each of said plurality of profile wheels. 14. The ion ribbon beam uniformity control system of claim 10 wherein each of said profile wheels has an elliptical shape defined by a first and second parallel surfaces. 15. The ion ribbon beam uniformity control system of claim 12 wherein each of said profile wheels has a drive pin extending substantially perpendicular from said first surface away from said drive motor and substantially parallel to and spaced from said axle. 16. The beam blocking array of claim 12 wherein each of said profile wheels has a pick-up pin extending substantially perpendicular from said second surface toward said drive motor and substantially parallel to and spaced from said axle. 17. An ion implanter comprising:an ion source chamber configured to generate ions;an extraction electrode assembly disposed adjacent to said ion source chamber, said extraction electrode assembly configured to extract said generated ions and forming an ion beam having a beam path;a beam blocking array assembly disposed along said ion beam path, said beam blocking array assembly having a plurality of profile wheels configured to block at least a portion of said ion beam corresponding to a location along a width of said beam, said beam blocking array including a drive assembly defined by a single drive motor and an axle along which said profile wheels are disposed and rotate. 18. A method for controlling ion beam uniformity comprising:measuring the profile of an ion beam generated by an ion source;supplying said measured beam profile to a controller;comparing the measured beam profile with the position of a drive wheel obtained;calculating a degree of the current density of the profile to be reduced across the ion beam profile;rotating a plurality of profile wheels utilizing a single drive motor; andblocking a portion of the ion beam at one or more locations corresponding to a respective one of the plurality of profile wheels.

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