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	description	This application is a national stage filing under 35 U.S.C. 371 of International Application No. PCT/US2011/023024, filed Jan. 28, 2011, which claims priority to U.S. Provisional Patent Application No. 61/299,258, filed Jan. 28, 2010, and are incorporated herein by reference in their entireties. The invention relates to a device and method for producing isotopes. More particularly, the invention relates to a device and method for producing neutron generated medical isotopes with or without a sub-critical reactor and low enriched uranium (LEU). Radioisotopes are commonly used by doctors in nuclear medicine. The most commonly used of these isotopes is Mo-99. Much of the supply of Mo-99 is developed from highly enriched uranium (HEU). The HEU employed is sufficiently enriched to make nuclear weapons. HEU is exported from the United States to facilitate the production of the needed Mo-99. It is desirable to produce the needed Mo-99 without the use of HEU. In certain embodiments, provided is a reactor operable to produce an isotope, the reactor comprising a region for containing a controlled nuclear fission reaction, the region segmented into a plurality of independent compartments, each of the compartments for containing a parent material in an aqueous solution that interacts with neutrons to produce the isotope via a fission reaction. The region may be segmented into n independent compartments, wherein n is an integer greater than or equal to 2. In other embodiments, provided is a reactor operable to produce an isotope, the reactor comprising a fusion portion including a target path disposed within a target chamber that substantially encircles a space, the fusion portion operable to produce a neutron flux within the target chamber; and a fission portion for containing a controlled nuclear fission reaction, the fission portion segmented into a plurality of independent compartments and positioned within the space for containing a parent material in an aqueous solution that reacts with a portion of the neutron flux to produce the isotope during a fission reaction. In other embodiments, provided is a method of producing an isotope, the method comprising: positioning a parent material in an aqueous solution within a region for containing a controlled nuclear reaction, the region segmented into a plurality of independent compartments; reacting, in at least one of the compartments over a time period y, neutrons with the parent material to produce the isotope; and extracting the aqueous solution comprising the isotope from the compartment. Other aspects and embodiments of the invention will become apparent by consideration of the detailed description and accompanying drawings. Segmented Reaction Chamber Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. Before explaining at least one embodiment, it is to be understood that the invention is not limited in its application to the details set forth in the following description as exemplified by the Examples. Such description and Examples are not intended to limit the scope of the invention as set forth in the appended claims. The invention is capable of other embodiments or of being practiced or carried out in various ways. Throughout this disclosure, various aspects of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity, and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, as will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof, as well as all integral and fractional numerical values within that range. As only one example, a range of 20% to 40% can be broken down into ranges of 20% to 32.5% and 32.5% to 40%, 20% to 27.5% and 27.5% to 40%, etc. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third, and upper third, etc. Further, as will also be understood by one skilled in the art, all language such as “up to,” “at least,” “greater than,” “less than,” “more than” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. In the same manner, all ratios disclosed herein also include all subratios falling within the broader ratio. These are only examples of what is specifically intended. Further, the phrases “ranging/ranges between” a first indicate number and a second indicate number and “ranging/ranges from” a first indicate number “to” a second indicate number are used herein interchangeably. Terms such as “substantially,” “about,” “approximately” and the like are used herein to describe features and characteristics that can deviate from an ideal or described condition without having a significant impact on the performance of the device. For example, “substantially parallel” could be used to describe features that are desirably parallel but that could deviate by an angle of up to 20 degrees so long as the deviation does not have a significant adverse effect on the device. Similarly, “substantially linear” could include a slightly curved path or a path that winds slightly so long as the deviation from linearity does not significantly adversely effect the performance of the device. Provided is a segmented reaction chamber for a reactor operable to produce an isotope. The reactor may comprise a region for containing a controlled nuclear fission reaction, the region segmented into a plurality of independent compartments. Each of the compartments may contain a parent material in an aqueous solution. The parent material may interact with neutrons to produce an isotope via a fission reaction. The isotope produced may comprise at least one of the isotopes including, but not limited to, Mo-99, I-131, I-125, Xe-133, Cs-137, Co-60, Y-90, Sr-90, and Sr-89. In certain embodiments, a reaction chamber 405 comprises an activation cell 410 that may be segmented, forming a segmented activation cell 600, as shown in FIGS. 32-35. It is envisioned that the principles of a segmented approach for a subcritical reactor for isotope production is also applicable to any aqueous reactor system. In certain embodiments, the invention provides an aqueous reaction chamber (ARC), filled with an aqueous solution, such as one found in a critical or subcritical aqueous isotope production system. The activation cell may be segmented into multiple pieces or a plurality of compartments by dividers 605. The segmented activation cell 600 may be divided or segmented into n independent compartments by dividers 605. The independent compartments n may be any integer from 2 to 10, from 3 to 8, or from 4 to 6. The compartments may be assembled or positioned proximate to the target chamber in any suitable orientation. For example, the compartments may be radially symmetrically disposed about a central axis of the activation cell. In certain embodiments, the compartments may be disposed linearly along a central axis, disposed concentrically about a central axis, or disposed radially asymmetrically about a central axis of the activation cell. The compartments of the activation cell may independently contain a parent material for interacting with the protons or neutrons generated in the target chamber to produce an isotope. 1-3 solution extraction/fill lines 610 may connect each chamber to an exterior reservoir (not shown) to transport parent material and isotope. A plurality of water cooling pipes 615 may flow fluid to supply a cooling jacket 620 proximal to or surrounding the segmented activation cell 600. A lid 625 may cap the segmented activation cell 600 to retain the fluid materials within. A segmented activation cell may allow for the extraction of isotopes at different periods of time. Separations in the reaction region may also be used to control instabilities that might develop in the solution. In some embodiments, the parent material in at least one compartment may be reacted over a time period y with at least a portion of the neutrons or protons generated in the target chamber. The time period y may be about the half life of the isotope produced. For example, the half life of Mo-99 is about 66 h. As such, the time period y may be about 60 h to about 70 h. The time period y may be at least about at least about 12 h, at least about 18 h, 24 h, at least about 36 h, at least about 48 h, at least about 72 h, or at least about 96 h. The time period y may be less than about 2 weeks, less than about 1.5 weeks, less than about 1 week, less than about 5 days, less than about 100 h, less than about 96 h, less than about 72 h, or less than about 48 h. The time period y may be about 12 h to about 2 weeks, about 24 h to about 1 week, about 36 h to about 96 h, or about 48 h to about 80 h. Existing systems describing the production of medical isotopes in ARCs may utilize a single volume to contain the aqueous solution. In such systems, the ARC may be operated from periods of minutes to months to produce various isotopes. When the device has operated for sufficient time to produce the desired quantity of an isotope, the fluid may be drained and the isotope separated. Suitably, optimal production will have occurred after a period of time equal to approximately one half-life of the material being created. Many markets for radioisotopes require a continuous supply of material; oversupply may not be sold and undersupply may result in lost revenue. If an oversupply is generated early in a period of time and cannot be sold, it may decay away in storage. In order to supply constant market demand, an excess of material may be produced early in the cycle, so that there may be ample supply while waiting for the next batch. FIG. 30 illustrates the decay of a particularly useful isotope, Mo-99 as created in a 5 day batch process. The dashed line represents hypothetical demand (x-axis reads days, y axis reads supply units). In this system, it may take 5 days to produce 10 units of Mo-99. Once the isotope is extracted, irradiation may start on the next 5 day batch. This may result in a tremendous variation in the amount of material available. Due to requirements for high purity isotopes, the ARC may irradiate its solution to near saturation, so shorter batches may not be performed to distribute the production of isotopes over time. In other embodiments, the ARC may be cut into physically different sections within the same device. If a device has x regions in it, the entire system could be irradiated to saturation (which occurs at time y), and then one cell may have its isotopes extracted after a period of time proportional to the saturation time. Then, every period of time that passes equal to y/x, another cell may have its isotopes extracted. As soon as isotope extraction is performed on any given cell, the irradiation process on that cell may begin anew. As such, each cell may always be irradiated to nearly saturation before it is empty. Again, considering the case of Mo-99, it may be desirable to have approximately a 5 day irradiation period. In this case, the ARC may be split into 5 cells. Every day in the 5 day period, 2 units of Mo-99 may be extracted. This may lead to a more uniform supply of the radioisotope, as shown in FIG. 31. FIG. 31 shows the amount of Mo-99 available during a 5 day batch process with a segmented reaction chamber in arbitrary units. The dashed line represents hypothetical demand (x-axis reads days, y axis reads supply units). In FIG. 30, shown is the hypothetical ARC described may create an oversupply early in the 5 day period, and may not be able to meet demand later. As shown in FIG. 31, the same ARC, segmented into 5 pieces, may continuously meet demand, which may result in less wasted product and eliminate the shortage previously experienced. A similar effect may be created by producing multiple smaller units, but there may be significantly greater expense involved in doing so. The segmented design may offer almost no additional cost, but may improve performance dramatically. In addition to the utility for smoothing supply to meet demand, the segmented aqueous system may serve to disrupt instabilities that may arise in critical or near critical aqueous systems. These instabilities may lead to control problems that may result in a failure to properly operate. Previous experiments with critical aqueous reactors resulted in instabilities that led to control problems as well as destructive behaviors that caused radiological spills. These instabilities were the result of the solution moving around in unpredictable ways, in some cases forming vortices in the solution. The addition of segmentation to the reaction chamber may minimize the extent to which these instabilities can propagate, which may greatly increase the controllability of the reaction chamber. A segmented reaction chamber may be used with any suitable critical or subcritical fission reactor with an aqueous reaction chamber. For example, a segmented reaction chamber may be used with a hybrid reactor described below. Example of a Hybrid Reactor for Production of Isotopes FIG. 22 illustrates an arrangement of a hybrid reactor 5a that is well suited to the production of medical isotopes. Before proceeding, the term “hybrid reactor” as used herein is meant to describe a reactor that includes a fusion portion and a fission portion. In particular, the illustrated reactor 5a is well suited to the production of Mo-99 from Mo-98 or from a solution of LEU. The hybrid reactor 5a includes a fusion portion 10 and a fission portion 8 that cooperate to produce the desired isotopes. In the construction illustrated in FIG. 22, ten distinct fusion portions 10 are employed. Each fusion portion 10 is arranged as a magnetic fusion portion 10 and acts as a neutron source as will be discussed with regard to FIGS. 1 and 2. Of course other arrangements could use fewer fusion portions 10, more fusion portions 10, or other arrangements of fusion portions as desired. FIG. 23 illustrates another arrangement of a hybrid reactor 5b that is well suited to the production of medical isotopes. In the construction of FIG. 23, linear fusion portions 11 act as neutron sources as will be discussed with regard to FIGS. 3 and 4. In the construction of FIG. 23, the linear fusion portions 11 are arranged such that five fusion portions 11 are positioned at one end of the fission portion 8 and five fusion portions 11 are positioned on the opposite end of the fission portion 8. Of course other arrangements that employ other quantities of fusion portions 11, or other arrangements of fusion portions could be employed if desired. As illustrated in FIGS. 1-3, each fusion portion 10, 11 provides a compact device that may function as a high energy proton source or a neutron source. In one embodiment, the fusion portions 10, 11 utilize 2H-3He (deuterium-helium 3) fusion reactions to generate protons, which may then be used to generate other isotopes. In another embodiment, the fusion portions 10, 11 function as neutron sources by changing the base reactions to 2H-3H, 2H-2H, or 3H-3H reactions. In view of the disadvantages inherent in the conventional types of proton or neutron sources, the fusion portions 10, 11 provide a novel high energy proton or neutron source (sometimes referred to herein generically as an ion source but also considered a particle source) that may be utilized for the production of medical isotopes. Each fusion portion 10, 11 uses a small amount of energy to create a fusion reaction, which then creates higher energy protons or neutrons that may be used for isotope production. Using a small amount of energy may allow the device to be more compact than previous conventional devices. Each fusion portion 10, 11 suitably generates protons that may be used to generate other isotopes including but not limited to 18F, 11C, 15O, 13N, 63Zn, 124I and many others. By changing fuel types, each fusion portion may also be used to generate high fluxes of neutrons that may be used to generate isotopes including but not limited to I-131, Xe-133, In-111, I-125, Mo-99 (which decays to Tc-99m) and many others. As such, each fusion portion 10, 11 provides a novel compact high energy proton or neutron source for uses such as medical isotope generation that has many of the advantages over the proton or neutron sources mentioned heretofore. In general, each fusion portion 10, 11 provides an apparatus for generating protons or neutrons, which, in turn, are suitably used to generate a variety of radionuclides (or radioisotopes). With reference to FIGS. 1 and 2, each magnetic fusion portion 10 includes a plasma ion source 20, which may suitably include an RF-driven ion generator and/or antenna 24, an accelerator 30, which is suitably electrode-driven, and a target system including a target chamber 60. In the case of proton-based radioisotope production, the apparatus may also include an isotope extraction system 90. The RF-driven plasma ion source 20 generates and collimates an ion beam directed along a predetermined pathway, wherein the ion source 20 includes an inlet for entry of a first fluid. The electrode-driven accelerator 30 receives the ion beam and accelerates the ion beam to yield an accelerated ion beam. The target system receives the accelerated ion beam. The target system contains a nuclear particle-deriving, e.g. a proton-deriving or neutron-deriving, target material that is reactive with the accelerated beam and that, in turn, emits nuclear particles, i.e., protons or neutrons. For radioisotope production, the target system may have sidewalls that are transparent to the nuclear particles. An isotope extraction system 90 is disposed proximate or inside the target system and contains an isotope-deriving material that is reactive to the nuclear particles to yield a radionuclide (or radioisotope). It should be noted that while an RF-driven ion generator or ion source is described herein, other systems and devices are also well-suited to generating the desired ions. For example, other constructions could employ a DC arc source in place of or in conjunction with the RF-driven ion generator or ion source. Still other constructions could use hot cathode ion sources, cold cathode ion sources, laser ion sources, field emission sources, and/or field evaporation sources in place of or in conjunction with a DC arc source and or an RF-driven ion generator or ion source. As such, the invention should not be limited to constructions that employ an RF-driven ion generator or ion source. As discussed, the fusion portion can be arranged in a magnetic configuration 10 and/or a linear configuration 11. The six major sections or components of the device are connected as shown in FIG. 1 and FIG. 2 for the magnetic configuration 10, and FIG. 3 for the linear configuration 11. Each fusion portion, whether arranged in the magnetic arrangement or the linear arrangement includes an ion source generally designated 20, an accelerator 30, a differential pumping system 40, a target system which includes a target chamber 60 for the magnetic configuration 10 or a target chamber 70 for the linear configuration 11, an ion confinement system generally designated 80, and an isotope extraction system generally designated 90. Each fusion portion may additionally include a gas filtration system 50. Each fusion portion may also include a synchronized high speed pump 100 in place of or in addition to the differential pumping system 40. Pump 100 is especially operative with the linear configuration of the target chamber. The ion source 20 (FIG. 4 and FIG. 5) includes a vacuum chamber 25, a radio-frequency (RF) antenna 24, and an ion injector 26 having an ion injector first stage 23 and an ion injector final stage 35 (FIG. 6). A magnet (not shown) may be included to allow the ion source to operate in a high density helicon mode to create higher density plasma 22 to yield more ion current. The field strength of this magnet suitably ranges from about 50 G to about 6000 G, suitably about 100 G to about 5000 G. The magnets may be oriented so as to create an axial field (north-south orientation parallel to the path of the ion beam) or a cusp field (north-south orientation perpendicular to the path of the ion beam with the inner pole alternating between north and south for adjacent magnets). An axial field can create a helicon mode (dense plasma), whereas a cusp field may generate a dense plasma but not a helicon inductive mode. A gas inlet 21 is located on one end of the vacuum chamber 25, and the first stage 23 of the ion injector 26 is on the other. Gas inlet 21 provides one of the desired fuel types, which may include 1H2, 2H2, 3H2, 3H2, 3He, and 11B, or may comprise 1H, 3H, 3He, and 11B. The gas flow at inlet 21 is suitably regulated by a mass flow controller (not shown), which may be user or automatically controlled. RF antenna 24 is suitably wrapped around the outside of vacuum chamber 25. Alternatively, RF antenna 24 may be inside vacuum chamber 25. Suitably, RF antenna 24 is proximate the vacuum chamber such that radio frequency radiation emitted by RF antenna 24 excites the contents (i.e., fuel gas) of vacuum chamber 25, for example, forming a plasma. RF antenna 24 includes a tube 27 of one or more turns. RF tube or wire 27 may be made of a conductive and bendable material such as copper, aluminum, or stainless steel. Ion injector 26 includes one or more shaped stages (23, 35). Each stage of the ion injector includes an acceleration electrode 32 suitably made from conductive materials that may include metals and alloys to provide effective collimation of the ion beam. For example, the electrodes are suitably made from a conductive metal with a low sputtering coefficient, e.g., tungsten. Other suitable materials may include aluminum, steel, stainless steel, graphite, molybdenum, tantalum, and others. RF antenna 24 is connected at one end to the output of an RF impedance matching circuit (not shown) and at the other end to ground. The RF impedance matching circuit may tune the antenna to match the impedance required by the generator and establish an RF resonance. RF antenna 24 suitably generates a wide range of RF frequencies, including but not limited to 0 Hz to tens of kHz to tens of MHz to GHz and greater. RF antenna 24 may be water-cooled by an external water cooler (not shown) so that it can tolerate high power dissipation with a minimal change in resistance. The matching circuit in a turn of RF antenna 24 may be connected to an RF power generator (not shown). Ion source 20, the matching circuit, and the RF power generator may be floating (isolated from ground) at the highest accelerator potential or slightly higher, and this potential may be obtained by an electrical connection to a high voltage power supply. RF power generator may be remotely adjustable, so that the beam intensity may be controlled by the user, or alternatively, by computer system. RF antenna 24 connected to vacuum chamber 25 suitably positively ionizes the fuel, creating an ion beam. Alternative means for creating ions are known by those of skill in the art and may include microwave discharge, electron-impact ionization, and laser ionization. Accelerator 30 (FIG. 6 and FIG. 7) suitably includes a vacuum chamber 36, connected at one end to ion source 20 via an ion source mating flange 31, and connected at the other end to differential pumping system 40 via a differential pumping mating flange 33. The first stage of the accelerator is also the final stage 35 of ion injector 26. At least one circular acceleration electrode 32, and suitably 3 to 50, more suitably 3 to 20, may be spaced along the axis of accelerator vacuum chamber 36 and penetrate accelerator vacuum chamber 36, while allowing for a vacuum boundary to be maintained. Acceleration electrodes 32 have holes through their centers (smaller than the bore of the accelerator chamber) and are suitably each centered on the longitudinal axis (from the ion source end to the differential pumping end) of the accelerator vacuum chamber for passage of the ion beam. The minimum diameter of the hole in acceleration electrode 32 increases with the strength of the ion beam or with multiple ion beams and may range from about 1 mm to about 20 cm in diameter, and suitably from about 1 mm to about 6 cm in diameter. Outside vacuum chamber 36, acceleration electrodes 32 may be connected to anti-corona rings 34 that decrease the electric field and minimize corona discharges. These rings may be immersed in a dielectric oil or an insulating dielectric gas such as SF6. Suitably, a differential pumping mating flange 33, which facilitates connection to differential pumping section 40, is at the exit of the accelerator. Each acceleration electrode 32 of accelerator 30 can be supplied bias either from high voltage power supplies (not shown), or from a resistive divider network (not shown) as is known by those of skill in the art. The divider for most cases may be the most suitable configuration due to its simplicity. In the configuration with a resistive divider network, the ion source end of the accelerator may be connected to the high voltage power supply, and the second to last accelerator electrode 32 may be connected to ground. The intermediate voltages of the accelerator electrodes 32 may be set by the resistive divider. The final stage of the accelerator is suitably biased negatively via the last acceleration electrode to prevent electrons from the target chamber from streaming back into accelerator 30. In an alternate embodiment, a linac (for example, a RF quadrapole) may be used instead of an accelerator 30 as described above. A linac may have reduced efficiency and be larger in size compared to accelerator 30 described above. The linac may be connected to ion source 20 at a first end and connected to differential pumping system 40 at the other end. Linacs may use RF instead of direct current and high voltage to obtain high particle energies, and they may be constructed as is known in the art. Differential pumping system 40 (FIG. 8 and FIG. 9) includes pressure reducing barriers 42 that suitably separate differential pumping system 40 into at least one stage. Pressure reducing barriers 42 each suitably include a thin solid plate or one or more long narrow tubes, typically 1 cm to 10 cm in diameter with a small hole in the center, suitably about 0.1 mm to about 10 cm in diameter, and more suitably about 1 mm to about 6 cm. Each stage comprises a vacuum chamber 44, associated pressure reducing barriers 42, and vacuum pumps 17, each with a vacuum pump exhaust 41. Each vacuum chamber 44 may have 1 or more, suitably 1 to 4, vacuum pumps 17, depending on whether it is a 3, 4, 5, or 6 port vacuum chamber 44. Two of the ports of the vacuum chamber 44 are suitably oriented on the beamline and used for ion beam entrance and exit from differential pumping system 40. The ports of each vacuum chamber 44 may also be in the same location as pressure reducing barriers 42. The remaining ports of each vacuum chamber 44 are suitably connected by conflat flanges to vacuum pumps 17 or may be connected to various instrumentation or control devices. The exhaust from vacuum pumps 17 is fed via vacuum pump exhaust 41 into an additional vacuum pump or compressor if necessary (not shown) and fed into gas filtration system 50. Alternatively, if needed, this additional vacuum pump may be located in between gas filtration system 50 and target chamber 60 or 70. If there is an additional compression stage, it may be between vacuum pumps 17 and filtration system 50. Differential pumping section is connected at one end to the accelerator 30 via an accelerator mating flange 45, and at the other at beam exit port 46 to target chamber (60 or 70) via a target chamber mating flange 43. Differential pumping system 40 may also include a turbulence generating apparatus (not shown) to disrupt laminar flow. A turbulence generating apparatus may restrict the flow of fluid and may include surface bumps or other features or combinations thereof to disrupt laminar flow. Turbulent flow is typically slower than laminar flow and may therefore decrease the rate of fluid leakage from the target chamber into the differential pumping section. In some constructions, the pressure reducing barriers 42 are replaced or enhanced by plasma windows. Plasma windows include a small hole similar to those employed as pressure reducing barriers. However, a dense plasma is formed over the hole to inhibit the flow of gas through the small hole while still allowing the ion beam to pass. A magnetic or electric field is formed in or near the hole to hold the plasma in place. Gas filtration system 50 is suitably connected at its vacuum pump isolation valves 51 to vacuum pump exhausts 41 of differential pumping system 40 or to additional compressors (not shown). Gas filtration system 50 (FIG. 10) includes one or more pressure chambers or “traps” (13, 15) over which vacuum pump exhaust 41 flows. The traps suitably capture fluid impurities that may escape the target chamber or ion source, which, for example, may have leaked into the system from the atmosphere. The traps may be cooled to cryogenic temperatures with liquid nitrogen (LN traps, 15). As such, cold liquid traps 13, 15 suitably cause gas such as atmospheric contaminants to liquefy and remain in traps 13, 15. After flowing over one or more LN traps 15 connected in series, the gas is suitably routed to a titanium getter trap 13, which absorbs contaminant hydrogen gasses such as deuterium that may escape the target chamber or the ion source and may otherwise contaminate the target chamber. The outlet of getter trap 13 is suitably connected to target chamber 60 or 70 via target chamber isolation valve 52 of gas filtration system 50. Gas filtration system 50 may be removed altogether from device 10, if one wants to constantly flow gas into the system and exhaust it out vacuum pump exhaust 41, to another vacuum pump exhaust (not shown), and to the outside of the system. Without gas filtration system 50, operation of apparatus 10 would not be materially altered. Apparatus 10, functioning as a neutron source, may not include getter trap 13 of gas filtration system 50. Vacuum pump isolation valves 51 and target chamber isolation valves 52 may facilitate gas filtration system 50 to be isolated from the rest of the device and connected to an external pump (not shown) via pump-out valve 53 when the traps become saturated with gas. As such, if vacuum pump isolation valves 51 and target chamber isolation valves 52 are closed, pump-out valves 53 can be opened to pump out impurities. Target chamber 60 (FIG. 11 and FIG. 12 for magnetic system 10) or target chamber 70 (FIG. 13 and FIG. 14 for the linear system 11) may be filled with the target gas to a pressure of about 0 to about 100 torr, about 100 mtorr to about 30 torr, suitably about 0.1 to about 10 torr, suitably about 100 mtorr to about 30 torr. The specific geometry of target chamber 60 or 70 may vary depending on its primary application and may include many variations. The target chamber may suitably be a cylinder about 10 cm to about 5 m long, and about 5 mm to about 100 cm in diameter for the linear system 14. When used in the hybrid reactor, the target chamber is arranged to provide an activation column in its center. The fusion portions are arranged to direct beams through the target chamber but outside of the activation column. Thus, the beams travel substantially within an annular space. Suitably, target chamber 70 may be about 0.1 m to about 2 m long, and about 30 to 50 cm in diameter for the linear system 14. For the magnetic system 12, target chamber 60 may resemble a thick pancake, about 10 cm to about 1 m tall and about 10 cm to about 10 m in diameter. Suitably, the target chamber 60 for the magnetic system 12 may be about 20 cm to about 50 cm tall and approximately 50 cm in diameter. For the magnetic target chamber 60, a pair of either permanent magnets or electromagnets (ion confinement magnet 12) may be located on the faces of the pancake, outside of the vacuum walls or around the outer diameter of the target chamber (see FIG. 11 and FIG. 12). The magnets are suitably made of materials including but not limited to copper and aluminum, or superconductors or NdFeB for electromagnets. The poles of the magnets may be oriented such that they create an axial magnetic field in the bulk volume of the target chamber. The magnetic field is suitably controlled with a magnetic circuit comprising high permeability magnetic materials such as 1010 steel, mu-metal, or other materials. The size of the magnetic target chamber and the magnetic beam energy determine the field strength according to equation (1):r=1.44√{square root over (E)}/B (1)for deuterons, wherein r is in meters, E is the beam energy in eV, and B is the magnetic field strength in gauss. The magnets may be oriented parallel to the flat faces of the pancake and polarized so that a magnetic field exists that is perpendicular to the direction of the beam from the accelerator 30, that is, the magnets may be mounted to the top and bottom of the chamber to cause ion recirculation. In another embodiment employing magnetic target chamber 60, there are suitably additional magnets on the top and bottom of the target chamber to create mirror fields on either end of the magnetic target chamber (top and bottom) that create localized regions of stronger magnetic field at both ends of the target chamber, creating a mirror effect that causes the ion beam to be reflected away from the ends of the target chamber. These additional magnets creating the mirror fields may be permanent magnets or electromagnets. It is also desirable to provide a stronger magnetic field near the radial edge of the target chamber to create a similar mirror effect. Again, a shaped magnetic circuit or additional magnets could be employed to provide the desired strong magnetic field. One end of the target chamber is operatively connected to differential pumping system 40 via differential pumping mating flange 33, and a gas recirculation port 62 allows for gas to re-enter the target chamber from gas filtration system 50. The target chamber may also include feedthrough ports (not shown) to allow for various isotope generating apparatus to be connected. In the magnetic configuration of the target chamber 60, the magnetic field confines the ions in the target chamber. In the linear configuration of the target chamber 70, the injected ions are confined by the target gas. When used as a proton or neutron source, the target chamber may require shielding to protect the operator of the device from radiation, and the shielding may be provided by concrete walls suitably at least one foot thick. Alternatively, the device may be stored underground or in a bunker, distanced away from users, or water or other fluid may be used a shield, or combinations thereof. Both differential pumping system 40 and gas filtration system 50 may feed into the target chamber 60 or 70. Differential pumping system 40 suitably provides the ion beam, while gas filtration system 50 supplies a stream of filtered gas to fill the target chamber. Additionally, in the case of isotope generation, a vacuum feedthrough (not shown) may be mounted to target chamber 60 or 70 to allow the isotope extraction system 90 to be connected to the outside. Isotope extraction system 90, including the isotope generation system 63, may be any number of configurations to provide parent compounds or materials and remove isotopes generated inside or proximate the target chamber. For example, isotope generation system 63 may include an activation tube 64 (FIGS. 12 and 14) that is a tightly wound helix that fits just inside the cylindrical target chamber and having walls 65. Alternatively, in the case of the pancake target chamber with an ion confinement system 80, it may include a helix that covers the device along the circumference of the pancake and two spirals, one each on the top and bottom faces of the pancake, all connected in series. Walls 65 of activation tubes 64 used in these configurations are sufficiently strong to withstand rupture, yet sufficiently thin so that protons of over 14 MeV (approximately 10 to 20 MeV) may pass through them while still keeping most of their energy. Depending on the material, the walls of the tubing may be about 0.01 mm to about 1 mm thick, and suitably about 0.1 mm thick. The walls of the tubing are suitably made of materials that will not generate neutrons. The thin-walled tubing may be made from materials such as aluminum, carbon, copper, titanium, or stainless steel. Feedthroughs (not shown) may connect activation tube 64 to the outside of the system, where the daughter or product compound-rich fluid may go to a heat exchanger (not shown) for cooling and a chemical separator (not shown) where the daughter or product isotope compounds are separated from the mixture of parent compounds, daughter compounds, and impurities. In another construction, shown in FIG. 15, a high speed pump 100 is positioned in between accelerator 30 and target chamber 60 or 70. High speed pump 100 may replace the differential pumping system 40 and/or gas filtration system 50. The high speed pump suitably includes one or more blades or rotors 102 and a timing signal 104 that is operatively connected to a controller 108. The high speed pump may be synchronized with the ion beam flow from the accelerator section, such that the ion beam or beams are allowed to pass through at least one gap 106 in between or in blades 102 at times when gaps 106 are aligned with the ion beam. Timing signal 104 may be created by having one or more markers along the pump shaft or on at least one of the blades. The markers may be optical or magnetic or other suitable markers known in the art. Timing signal 104 may indicate the position of blades 102 or gap 106 and whether or not there is a gap aligned with the ion beam to allow passage of the ion beam from first stage 35 of accelerator 30 through high speed pump 100 to target chamber 60 or 70. Timing signal 104 may be used as a gate pulse switch on the ion beam extraction voltage to allow the ion beam to exit ion source 20 and accelerator 30 and enter high speed pump 100. When flowing through the system from ion source 20 to accelerator 30 to high speed pump 100 and to target chamber 60 or 70, the beam may stay on for a time period that the ion beam and gap 106 are aligned and then turn off before and while the ion beam and gap 106 are not aligned. The coordination of timing signal 104 and the ion beam may be coordinated by a controller 108. In one embodiment of controller 108 (FIG. 18), controller 108 may comprise a pulse processing unit 110, a high voltage isolation unit 112, and a high speed switch 114 to control the voltage of accelerator 30 between suppression voltage (ion beam off; difference may be 5-10 kV) and extraction voltage (ion beam on; difference may be 20 kv). Timing signal 104 suitably creates a logic pulse that is passed through delay or other logic or suitable means known in the art. Pulse processing unit 110 may alter the turbine of the high speed pump to accommodate for delays, and high speed switch 114 may be a MOSFET switch or other suitable switch technology known in the art. High voltage isolation unit 112 may be a fiber optic connection or other suitable connections known in the art. For example, the timing signal 104 may indicate the presence or absence of a gap 106 only once per rotation of a blade 102, and the single pulse may signal a set of electronics via controller 108 to generate a set of n pulses per blade revolution, wherein n gaps are present in one blade rotation. Alternatively, timing signal 104 may indicate the presence or absence of a gap 106 for each of m gaps during a blade rotation, and the m pulses may each signal a set of electronics via controller 108 to generate a pulse per blade revolution, wherein m gaps are present in one blade rotation. The logic pulses may be passed or coordinated via controller 108 to the first stage of accelerator section 35 (ion extractor), such that the logic pulse triggers the first stage of accelerator section 35 to change from a suppression state to an extraction state and visa versa. If the accelerator were +300 kV, for example, the first stage of accelerator 35 may be biased to +295 kV when there is no gap 106 in high speed pump 100, so that the positive ion beam will not flow from +295 kV to +300 kV, and the first stage of accelerator 35 may be biased to +310 kV when there is a gap 106 in high speed pump 100, so that the ion beam travels through accelerator 30 and through gaps 106 in high speed pump 100 to target chamber 60 or 70. The difference in voltage between the suppression and extraction states may be a relatively small change, such as about 1 kV to about 50 kV, suitably about 10 kV to about 20 kV. A small change in voltage may facilitate a quick change between suppression (FIG. 17) and extraction (FIG. 16) states. Timing signal 104 and controller 108 may operate by any suitable means known in the art, including but not limited to semiconductors and fiber optics. The period of time that the ion beam is on and off may depend on factors such as the rotational speed of blades 102, the number of blades or gaps 106, and the dimensions of the blades or gaps. The isotopes 18F and 13N, which are utilized in PET scans, may be generated from the nuclear reactions inside each fusion portion using an arrangement as illustrated in FIGS. 12 and 14. These isotopes can be created from their parent isotopes, 18O (for 18F) and 16O (for 13N) by proton bombardment. The source of the parent may be a fluid, such as water (H218O or H216O), that may flow through the isotope generation system via an external pumping system (not shown) and react with the high energy protons in the target chamber to create the desired daughter compound. For the production of 18F or 13N, water (H218O or H216O, respectively) is flowed through isotope generation system 63, and the high energy protons created from the aforementioned fusion reactions may penetrate tube 64 walls and impact the parent compound and cause (p,α) reactions producing 18F or 13N. In a closed system, for example, the isotope-rich water may then be circulated through the heat exchanger (not shown) to cool the fluid and then into the chemical filter (not shown), such as an ion exchange resin, to separate the isotope from the fluid. The water mixture may then recirculate into target chamber (60 or 70), while the isotopes are stored in a filter, syringe, or by other suitable means known in the art until enough has been produced for imaging or other procedures. While a tubular spiral has been described, there are many other geometries that could be used to produce the same or other radionuclides. For example, isotope generation system 63 may suitably be parallel loops or flat panel with ribs. In another embodiment, a water jacket may be attached to the vacuum chamber wall. For 18F or 13N creation, the spiral could be replaced by any number of thin walled geometries including thin windows, or could be replaced by a solid substance that contained a high oxygen concentration, and would be removed and processed after transmutation. Other isotopes can be generated by other means. With reference to FIGS. 1 and 3, the operation of the fusion portions will now be described. Before operation of one of the fusion portions, the respective target chamber 60 or 70 is suitably filled by first pre-flowing the target gas, such as 3He, through the ion source 20 with the power off, allowing the gas to flow through the apparatus 10 and into the target chamber. In operation, a reactant gas such as 2H2 enters the ion source 20 and is positively ionized by the RF field to form plasma 22. As plasma 22 inside vacuum chamber 25 expands toward ion injector 26, plasma 22 starts to be affected by the more negative potential in accelerator 30. This causes the positively charged ions to accelerate toward target chamber 60 or 70. Acceleration electrodes 32 of the stages (23 and 35) in ion source 20 collimate the ion beam or beams, giving each a nearly uniform ion beam profile across the first stage of accelerator 30. Alternatively, the first stage of accelerator 30 may enable pulsing or on/off switching of the ion beam, as described above. As the beam continues to travel through accelerator 30, it picks up additional energy at each stage, reaching energies of up to 5 MeV, up to 1 MeV, suitably up to 500 keV, suitably 50 keV to 5 MeV, suitably 50 keV to 500 keV, and suitably 0 to 10 Amps, suitably 10 to 100 mAmps, by the time it reaches the last stage of the accelerator 30. This potential is supplied by an external power source (not shown) capable of producing the desired voltage. Some neutral gas from ion source 20 may also leak out into accelerator 30, but the pressure in accelerator 30 will be kept to a minimum by differential pumping system 40 or synchronized high speed pump 100 to prevent excessive pressure and system breakdown. The beam continues at high velocity into differential pumping 40 where it passes through the relatively low pressure, short path length stages with minimal interaction. From here it continues into target chamber 60 or 70, impacting the high density target gas that is suitably 0 to 100 torr, suitably 100 mtorr to 30 torr, suitably 5 to 20 torr, slowing down and creating nuclear reactions. The emitted nuclear particles may be about 0.3 MeV to about 30 MeV protons, suitably about 10 MeV to about 20 MeV protons, or about 0.1 MeV to about 30 MeV neutrons, suitably about 2 MeV to about 20 MeV neutrons. In the embodiment of linear target chamber 70, the ion beam continues in an approximately straight line and impacts the high density target gas to create nuclear reactions until it stops. In the embodiment of magnetic target chamber 60, the ion beam is bent into an approximately helical path, with the radius of the orbit (for deuterium ions, 2H) given by the equation (2): r = 204 * E i B ( 2 ) where r is the orbital radius in cm, Ei is the ion energy in eV, and B is the magnetic field strength in gauss. For the case of a 500 keV deuterium beam and a magnetic field strength of 7 kG, the orbital radius is about 20.6 cm and suitably fits inside a 25 cm radius chamber. While ion neutralization can occur, the rate at which re-ionization occurs is much faster, and the particle will spend the vast majority of its time as an ion. Once trapped in this magnetic field, the ions orbit until the ion beam stops, achieving a very long path length in a short chamber. Due to this increased path length relative to linear target chamber 70, magnetic target chamber 60 can also operate at lower pressure. Magnetic target chamber 60, thus, may be the more suitable configuration. A magnetic target chamber can be smaller than a linear target chamber and still maintain a long path length, because the beam may recirculate many times within the same space. The fusion products may be more concentrated in the smaller chamber. As explained, a magnetic target chamber may operate at lower pressure than a linear chamber, easing the burden on the pumping system because the longer path length may give the same total number of collisions with a lower pressure gas as with a short path length and a higher pressure gas of the linac chamber. Due to the pressure gradient between accelerator 30 and target chamber 60 or 70, gas may flow out of the target chamber and into differential pumping system 40. Vacuum pumps 17 may remove this gas quickly, achieving a pressure reduction of approximately 10 to 100 times or greater. This “leaked” gas is then filtered and recycled via gas filtration system 50 and pumped back into the target chamber, providing more efficient operation. Alternatively, high speed pump 100 may be oriented such that flow is in the direction back into the target chamber, preventing gas from flowing out of the target chamber. While the invention described herein is directed to a hybrid reactor, it is possible to produce certain isotopes using the fusion portion alone. If this is desired, an isotope extraction system 90 as described herein is inserted into target chamber 60 or 70. This device allows the high energy protons to interact with the parent nuclide of the desired isotope. For the case of 18F production or 13N production, this target may be water-based (16O for 13N, and 18O for 18F) and will flow through thin-walled tubing. The wall thickness is thin enough that the 14.7 MeV protons generated from the fusion reactions will pass through them without losing substantial energy, allowing them to transmute the parent isotope to the desired daughter isotope. The 13N or 18F rich water then is filtered and cooled via external system. Other isotopes, such as 124I (from 124Te or others), 11C (from 14N or 11B or others), 15O (from 15N or others), and 63Zn, may also be generated. In constructions that employ the fission portion to generate the desired isotopes, the isotope extraction system 90 can be omitted. If the desired product is protons for some other purpose, target chamber 60 or 70 may be connected to another apparatus to provide high energy protons to these applications. For example, the a fusion portion may be used as an ion source for proton therapy, wherein a beam of protons is accelerated and used to irradiate cancer cells. If the desired product is neutrons, no hardware such as isotope extraction system 90 is required, as the neutrons may penetrate the walls of the vacuum system with little attenuation. For neutron production, the fuel in the injector is changed to either deuterium or tritium, with the target material changed to either tritium or deuterium, respectively. Neutron yields of up to about 1015 neutrons/sec or more may be generated. Additionally, getter trap 13 may be removed. The parent isotope compound may be mounted around target chamber 60 or 70, and the released neutrons may convert the parent isotope compound to the desired daughter isotope compound. Alternatively, an isotope extraction system may still or additionally be used inside or proximal to the target chamber. A moderator (not shown) that slows neutrons may be used to increase the efficiency of neutron interaction. Moderators in neutronics terms may be any material or materials that slow down neutrons. Suitable moderators may be made of materials with low atomic mass that are unlikely to absorb thermal neutrons. For example, to generate Mo-99 from a Mo-98 parent compound, a water moderator may be used. Mo-99 decays to Tc-99m, which may be used for medical imaging procedures. Other isotopes, such as I-131, Xe-133, In-111, and 1-125, may also be generated. When used as a neutron source, the fusion portion may include shielding such as concrete or a fluid such as water at least one foot thick to protect the operators from radiation. Alternatively, the neutron source may be stored underground to protect the operators from radiation. The manner of usage and operation of the invention in the neutron mode is the same as practiced in the above description. The fusion rate of the beam impacting a thick target gas can be calculated. The incremental fusion rate for the ion beam impacting a thick target gas is given by the equation (3): d ⁢ ⁢ f ⁡ ( E ) = n b * I ion e * σ ⁡ ( E ) * d ⁢ ⁢ l ( 3 ) where df(E) is the fusion rate (reactions/sec) in the differential energy interval dE, nb is the target gas density (particles/m3), Iion is the ion current (A), e is the fundamental charge of 1.602210−19 coulombs/particle, σ(E) is the energy dependent cross section (m2) and dl is the incremental path length at which the particle energy is E. Since the particle is slowing down once inside the target, the particle is only at energy E over an infinitesimal path length. To calculate the total fusion rate from a beam stopping in a gas, equation (2) is integrated over the entire particle path length from where its energy is at its maximum of Ei to where it stops as shown in equation (4): F ⁡ ( E i ) = ∫ 0 E i ⁢ n b I ion e * σ ⁡ ( E ) ⁢ ⁢ d ⁢ ⁢ l = n b ⁢ I ion e ⁢ ∫ 0 E i ⁢ σ ⁡ ( E ) ⁢ ⁢ d ⁢ ⁢ l ( 4 ) where F(Ei) is the total fusion rate for a beam of initial energy Ei stopping in the gas target. To solve this equation, the incremental path length dl is solved for in terms of energy. This relationship is determined by the stopping power of the gas, which is an experimentally measured function, and can be fit by various types of functions. Since these fits and fits of the fusion cross section tend to be somewhat complicated, these integrals were solved numerically. Data for the stopping of deuterium in 3He gas at 10 torr and 25° C. was obtained from the computer program Stopping and Range of Ions in Matter (SRIM; James Ziegler, www.srim.org) and is shown in FIG. 19. An equation was used to predict intermediate values. A polynomial of order ten was fit to the data shown in FIG. 19. The coefficients are shown in TABLE 1, and resultant fit with the best-fit 10th order polynomial is shown in FIG. 20. TABLE 1OrderCoefficient10−1.416621E−2793.815365E−248−4.444877E−2172.932194E−186−1.203915E−1553.184518E−134−5.434029E−1135.847578E−092−3.832260E−0711.498854E−050−8.529514E−05 As can be seen from these data, the fit was quite accurate over the energy range being considered. This relationship allowed the incremental path length, dl, to be related to an incremental energy interval by the polynomial tabulated above. To numerically solve this, it is suitable to choose either a constant length step or a constant energy step, and calculate either how much energy the particle has lost or how far it has gone in that step. Since the fusion rate in equation (4) is in terms of dl, a constant length step was the method used. The recursive relationship for the particle energy E as it travels through the target is the equation (5):En+1=En−S(E)dl (5)where n is the current step (n=0 is the initial step, and Eo is the initial particle energy), En+1 is the energy in the next incremental step, S(E) is the polynomial shown above that relates the particle energy to the stopping power, and dl is the size of an incremental step. For the form of the incremental energy shown above, E is in keV and dl is in μm. This formula yields a way to determine the particle energy as it moves through the plasma, and this is important because it facilitates evaluation of the fusion cross section at each energy, and allows for the calculation of a fusion rate in any incremental step. The fusion rate in the numerical case for each step is given by the equation (6): f n ⁡ ( E ) = n b I ion e * σ ⁡ ( E n ) * d ⁢ ⁢ l ( 6 ) To calculate the total fusion rate, this equation was summed over all values of En until E=0 (or ndl=the range of the particle) as shown in equation (7): F ⁡ ( E o ) = ∑ n = 0 n d ⁢ ⁢ l = range ⁢ f n ⁡ ( E ) ( 7 ) This fusion rate is known as the “thick-target yield”. To solve this, an initial energy was determined and a small step size dl chosen. The fusion rate in the interval dl at full energy was calculated. Then the energy for the next step was calculated, and the process repeated. This goes on until the particle stops in the gas. For the case of a singly ionized deuterium beam impacting a 10 torr helium-3 gas background at room temperature, at an energy of 500 keV and an intensity of 100 mA, the fusion rate was calculated to be approximately 2×1013 fusions/second, generating the same number of high energy protons (equivalent to 3 μA protons). This level is sufficient for the production of medical isotopes, as is known by those of skill in the art. A plot showing the fusion rate for a 100 mA incident deuterium beam impacting a helium-3 target at 10 torr is shown in FIG. 21. The fusion portions as described herein may be used in a variety of different applications. According to one construction, the fusion portions are used as a proton source to transmutate materials including nuclear waste and fissile material. The fusion portions may also be used to embed materials with protons to enhance physical properties. For example, the fusion portion may be used for the coloration of gemstones. The fusion portions also provide a neutron source that may be used for neutron radiography. As a neutron source, the fusion portions may be used to detect nuclear weapons. For example, as a neutron source the fusion portions may be used to detect special nuclear materials, which are materials that can be used to create nuclear explosions, such as Pu, 233U, and materials enriched with 233U or 235U. As a neutron source, the fusion portions may be used to detect underground features including but not limited to tunnels, oil wells, and underground isotopic features by creating neutron pulses and measuring the reflection and/or refraction of neutrons from materials. The fusion portions may be used as a neutron source in neutron activation analysis (NAA), which may determine the elemental composition of materials. For example, NAA may be used to detect trace elements in the picogram range. As a neutron source, the fusion portions may also be used to detect materials including but not limited to clandestine materials, explosives, drugs, and biological agents by determining the atomic composition of the material. The fusion portions may also be used as a driver for a sub-critical reactor. The operation and use of the fusion portion 10, 11 is further exemplified by the following examples, which should not be construed by way of limiting the scope of the invention. The fusion portions 10, 11 can be arranged in the magnetic configuration 10 to function as a neutron source. In this arrangement, initially, the system 10 will be clean and empty, containing a vacuum of 10−9 torr or lower, and the high speed pumps 17 will be up to speed (two stages with each stage being a turbomolecular pump). Approximately 25-30 standard cubic centimeters of gas (deuterium for producing neutrons) will be flowed into the target chamber 60 to create the target gas. Once the target gas has been established, that is, once the specified volume of gas has been flowed into the system and the pressure in the target chamber 60 reaches approximately 0.5 torr, a valve will be opened which allows a flow of 0.5 to 1 sccm (standard cubic centimeters per minute) of deuterium from the target chamber 60 into the ion source 20. This gas will re-circulate rapidly through the system, producing approximately the following pressures: in the ion source 20 the pressure will be a few mtorr; in the accelerator 30 the pressure will be around 20 μtorr; over the pumping stage nearest the accelerator, the pressure will be <20 μtorr; over the pumping stage nearest the target chamber, the pressure will be approximately 50 mtorr; and in the target chamber 60 the pressure will be approximately 0.5 torr. After these conditions are established, the ion source 20 (using deuterium) will be excited by enabling the RF power supply (coupled to the RF antenna 24 by the RF matching circuit) to about 10-30 MHz. The power level will be increased from zero to about 500 W creating a dense deuterium plasma with a density on the order of 1011 particles/cm3. The ion extraction voltage will be increased to provide the desired ion current (approximately 10 mA) and focusing. The accelerator voltage will then be increased to 300 kV, causing the ion beam to accelerate through the flow restrictions and into the target chamber 60. The target chamber 60 will be filled with a magnetic field of approximately 5000 gauss (or 0.5 tesla), which causes the ion beam to re-circulate. The ion beam will make approximately 10 revolutions before dropping to a negligibly low energy. While re-circulating, the ion beam will create nuclear reactions with the target gas, producing 4×1010 and up to 9×1010 neutrons/sec for D. These neutrons will penetrate the target chamber 60, and be detected with appropriate nuclear instrumentation. Neutral gas that leaks from the target chamber 60 into the differential pumping section 40 will pass through the high speed pumps 17, through a cold trap 13, 15, and back into the target chamber 60. The cold traps 13, 15 will remove heavier gasses that in time can contaminate the system due to very small leaks. The fusion portions 11 can also be arranged in the linear configuration to function as a neutron source. In this arrangement, initially, the system will be clean and empty, containing a vacuum of 10−9 torr or lower and the high speed pumps 17 will be up to speed (three stages, with the two nearest that accelerator being turbomolecular pumps and the third being a different pump such as a roots blower). Approximately 1000 standard cubic centimeters of deuterium gas will be flowed into the target chamber 70 to create the target gas. Once the target gas has been established, a valve will be opened which allows a flow of 0.5 to 1 sccm (standard cubic centimeters per minute) from the target chamber 70 into the ion source 20. This gas will re-circulate rapidly through the system, producing approximately the following pressures: in the ion source 20 the pressure will be a few mtorr; in the accelerator 30 the pressure will be around 20 μtorr; over the pumping stage nearest the accelerator, the pressure will be <20 μtorr; over the center pumping stage the pressure will be approximately 50 mtorr; over the pumping stage nearest the target chamber 70, the pressure will be approximately 500 mtorr; and in the target chamber 70 the pressure will be approximately 20 torr. After these conditions are established, the ion source 20 (using deuterium) will be excited by enabling the RF power supply (coupled to the RF antenna 24 by the RF matching circuit) to about 10-30 MHz. The power level will be increased from zero to about 500 W creating a dense deuterium plasma with a density on the order of 1011 particles/cm3. The ion extraction voltage will be increased to provide the desired ion current (approximately 10 mA) and focusing. The accelerator voltage will then be increased to 300 kV, causing the ion beam to accelerate through the flow restrictions and into the target chamber 70. The target chamber 70 will be a linear vacuum chamber in which the beam will travel approximately 1 meter before dropping to a negligibly low energy. While passing through the target gas, the beam will create nuclear reactions, producing 4×1010 and up to 9×1010 neutrons/sec. These protons will penetrate the target chamber 70, and be detected with appropriate nuclear instrumentation. Neutral gas that leaks from the target chamber 70 into the differential pumping section 40 will pass through the high speed pumps 17, through a cold trap 13, 15, and back into the target chamber 70. The cold traps 13, 15 will remove heavier gasses that in time can contaminate the system due to very small leaks. In another construction, the fusion portions 10 are arranged in the magnetic configuration and are operable as proton sources. In this construction, initially, the system will be clean and empty, containing a vacuum of 10−9 torr or lower, and the high speed pumps 17 will be up to speed (two stages with each stage being a turbomolecular pump). Approximately 25-30 standard cubic centimeters of gas (an approximate 50/50 mixture of deuterium and helium-3 to generate protons) will be flowed into the target chamber 60 to create the target gas. Once the target gas has been established, that is, once the specified volume of gas has been flowed into the system and the pressure in the target chamber 60 reaches approximately 0.5 torr, a valve will be opened which allows a flow of 0.5 to 1 sccm (standard cubic centimeters per minute) of deuterium from the target chamber 60 into the ion source 20. This gas will re-circulate rapidly through the system, producing approximately the following pressures: in the ion source 20 the pressure will be a few mtorr; in the accelerator 30 the pressure will be around 20 μtorr; over the pumping stage nearest the accelerator 30, the pressure will be <20 μtorr; over the pumping stage nearest the target chamber 60, the pressure will be approximately 50 mtorr; and in the target chamber 60 the pressure will be approximately 0.5 torr. After these conditions are established, the ion source 20 (using deuterium) will be excited by enabling the RF power supply (coupled to the RF antenna 24 by the RF matching circuit) to about 10-30 MHz. The power level will be increased from zero to about 500 W creating a dense deuterium plasma with a density on the order of 1011 particles/cm3. The ion extraction voltage will be increased to provide the desired ion current (approximately 10 mA) and focusing. The accelerator voltage will then be increased to 300 kV, causing the ion beam to accelerate through the flow restrictions and into the target chamber 60. The target chamber 60 will be filled with a magnetic field of approximately 5000 gauss (or 0.5 tesla), which causes the ion beam to re-circulate. The ion beam will make approximately 10 revolutions before dropping to a negligibly low energy. While re-circulating, the ion beam will create nuclear reactions with the target gas, producing 1×1011 and up to about 5×1011 protons/sec. These protons will penetrate the tubes of the isotope extraction system, and be detected with appropriate nuclear instrumentation. Neutral gas that leaks from the target chamber 60 into the differential pumping section 40 will pass through the high speed pumps 17, through a cold trap 13, 15, and back into the target chamber 60. The cold traps 13, 15 will remove heavier gasses that in time can contaminate the system due to very small leaks. In another construction, the fusion portions 11 are arranged in the linear configuration and are operable as proton sources. In this construction, initially, the system will be clean and empty, containing a vacuum of 10−9 torr or lower and the high speed pumps 17 will be up to speed (three stages, with the two nearest that accelerator being turbomolecular pumps and the third being a different pump such as a roots blower). Approximately 1000 standard cubic centimeters of about 50/50 mixture of deuterium and helium-3 gas will be flowed into the target chamber 70 to create the target gas. Once the target gas has been established, a valve will be opened which allows a flow of 0.5 to 1 sccm (standard cubic centimeters per minute) from the target chamber 70 into the ion source 20. This gas will re-circulate rapidly through the system, producing approximately the following pressures: in the ion source 20 the pressure will be a few mtorr; in the accelerator 30 the pressure will be around 20 μtorr; over the pumping stage nearest the accelerator 30, the pressure will be <20 μtorr; over the center pumping stage the pressure will be approximately 50 mtorr; over the pumping stage nearest the target chamber 70, the pressure will be approximately 500 mtorr; and in the target chamber 70 the pressure will be approximately 20 torr. After these conditions are established, the ion source 20 (using deuterium) will be excited by enabling the RF power supply (coupled to the RF antenna 24 by the RF matching circuit) to about 10-30 MHz. The power level will be increased from zero to about 500 W creating a dense deuterium plasma with a density on the order of 1011 particles/cm3. The ion extraction voltage will be increased to provide the desired ion current (approximately 10 mA) and focusing. The accelerator voltage will then be increased to 300 kV, causing the ion beam to accelerate through the flow restrictions and into the target chamber 70. The target chamber 70 will be a linear vacuum chamber in which the beam will travel approximately 1 meter before dropping to a negligibly low energy. While passing through the target gas, the beam will create nuclear reactions, producing 1×1011 and up to about 5×1011 protons/sec. These neutrons will penetrate the walls of the tubes of the isotope extraction system, and be detected with appropriate nuclear instrumentation. Neutral gas that leaks from the target chamber 70 into the differential pumping section 40 will pass through the high speed pumps 17, through a cold trap 13, 15, and back into the target chamber 70. The cold traps 13, 15 will remove heavier gasses that in time can contaminate the system due to very small leaks. In another construction, the fusion portions 10, 11 are arranged in either the magnetic configuration or the linear configuration and are operated as neutron sources for isotope production. The system will be operated as discussed above with the magnetic target chamber or with the linear target chamber 70. A solid sample, such as solid foil of parent material Mo-98 will be placed proximal to the target chamber 60, 70. Neutrons created in the target chamber 60, 70 will penetrate the walls of the target chamber 60, 70 and react with the Mo-98 parent material to create Mo-99, which may decay to meta-stable Tn-99m. The Mo-99 will be detected using suitable instrumentation and technology known in the art. In still other constructions, the fusion portions 10, 11 are arranged as proton sources for the production of isotopes. In these construction, the fusion portion 10, 11 will be operated as described above with the magnetic target chamber 60 or with the linear target chamber 70. The system will include an isotope extraction system inside the target chamber 60, 70. Parent material such as water comprising H216O will be flowed through the isotope extraction system. The protons generated in the target chamber will penetrate the walls of the isotope extraction system to react with the 16O to produce 13N. The 13N product material will be extracted from the parent and other material using an ion exchange resin. The 13N will be detected using suitable instrumentation and technology known in the art. In summary, each fusion portion 10, 11 provides, among other things, a compact high energy proton or neutron source. The foregoing description is considered as illustrative only of the principles of the fusion portion 10, 11. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the fusion portion 10, 11 to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to as required or desired. As illustrated in FIGS. 22 and 23, the fission portions 400a, 400b of the hybrid reactor 5a, 5b are positioned adjacent the target chambers 60, 70 of a plurality of fusion portions 10, 11. The fusion portions 10, 11 are arranged such that a reaction space 405 is defined within the target chambers 60, 70. Specifically, the ion trajectories within the target chambers 60, 70 do not enter the reaction space 405, and so materials to be irradiated can be placed within that volume. In order to further increase the neutron flux, multiple fusion portions 10, 11 are stacked on top of one another, with as many as ten sources being beneficial. As illustrated in FIG. 22, the hybrid reactor 5a includes the fission portion 400a and fusion portions 10 in the magnetic arrangement to produce a plurality of stacked target chambers 60 that are pancake shaped but in which the ion beam flows along an annular path. Thus, the reaction space 405 within the annular path can be used for the placement of materials to be irradiated. FIG. 23 illustrates a linear arrangement of the fusion portions 11 coupled to the fission portion 400b to define the hybrid reactor 5b. In this construction, the ion beams are directed along a plurality of substantially parallel, spaced-apart linear paths positioned within an annular target chamber 70. The reaction space 405 (sometimes referred to as reaction chamber) within the annular target chamber 70 is suitable for the placement of materials to be irradiated. Thus, as will become apparent, the fission portions 400a, 400b described with regard to FIGS. 24-29 could be employed with either the magnetic configuration or the linear configuration of the fusion portions 10, 11. With reference to FIGS. 22 and 23 the fission portion 400a, 400b includes a substantially cylindrical activation column 410 (sometimes referred to as an activation cell) positioned within a tank 415 that contains a moderator/reflector material selected to reduce the radiation that escapes from the fission portion 400a, 400b during operation. An attenuator may be positioned proximate the activation cell and selected to maintain the fission reaction at a subcritical level, a reflector may be positioned proximate the target chamber and selected to reflect neutrons toward the activation cell, and a moderator may substantially surround the activation cell, the attenuator, and the reflector. The activation column 410 is positioned within the target chamber 60, 70 where the fusion reactions occur. The target chamber 60, 70 is about 1 m tall. A layer of beryllium 420 may surround the target chamber 60, 70. The moderating material is typically D2O or H2O. In addition, a gas regeneration system 425 is positioned on top of the tank 415. An aperture 430 in the center of the gas regeneration system 425 extends into the activation column 410 where a sub-critical assembly 435 including a LEU mixture and/or other parent material may be located. In preferred constructions, the aperture 430 has about a 10 cm radius and is about 1 m long. Each fusion portion 10, 11 is arranged to emit high energy neutrons from the target chamber. The neutrons emitted by the fusion portions 10, 11 are emitted isotropically, and while at high energy those that enter the activation column 410 pass through it with little interaction. The target chamber is surrounded by 10-15 cm of beryllium 420, which multiplies the fast neutron flux by approximately a factor of two. The neutrons then pass into the moderator where they slow to thermal energy and reflect back into the activation cell 410. It is estimated that the neutron production rate from this configuration is about 1015 n/s (the estimated source strength for a single fusion portion 10, 11 operating at 500 kV and 100 mA is 1014 n/s and there are ten of these devices in the illustrated construction). The total volumetric flux in the activation cell 410 was calculated to be 2.351012 n/cm2/s with an uncertainty of 0.0094 and the thermal flux (less than 0.1 eV) was 1.341012 n/cm2/s with an uncertainty of 0.0122. This neutron rate improves substantially with the presence of LEU as will be discussed. As discussed with regard to FIGS. 1 and 3, the fusion portion 10, 11 can be arranged in the magnetic arrangement or the linear arrangement. The real advantage of the magnetic arrangement of the fusion portions 10, 11 is that they allow for a long path length in a relatively low pressure gas. To effectively use the linear configuration, the target gas must be cooled and must be maintained at a higher pressure. One example of such a configuration would have several deuterium beam lines shooting axially into the target chamber 70 from above and below the device as illustrated in FIG. 23. While the target chambers 70 may need to operate at up to 10 torr for this to be successful, it may be a simpler and more efficient approach for the fusion portion 10, 11. The primary simplification in the linear configuration is the elimination of the components needed to establish the magnetic field that guides the beam in the spiral or helical pattern. The lack of the components needed to create the field makes the device cheaper and the magnets do not play a role in attenuating the neutron flux. However, in some constructions, a magnetic field is employed to collimate the ion beam produced by the linear arrangement of the fusion portions 11, as will be discussed. In order to produce Mo-99 of high specific activity as an end product, it should be made from a material that is chemically different so that it can be easily separated. The most common way to do this is by fission of 235U through neutron bombardment. The fusion portions 10, 11 described previously create sufficient neutrons to produce a large amount of Mo-99 with no additional reactivity, but if 235U is already present in the device, it makes sense to put it in a configuration that will provide neutron multiplication as well as providing a target for Mo-99 production. The neutrons made from fission can play an important role in increasing the specific activity of the Mo-99, and can increase the total Mo-99 output of the system. The multiplication factor, keff is related to the multiplication by equation 1/(1−keff). This multiplication effect can result in an increase of the total yield and specific activity of the end product by as much as a factor of 5-10. keff is a strong function of LEU density and moderator configuration. Several subcritical configurations of subcritical assemblies 435 which consist of LEU (20% enriched) targets combined with H2O (or D2O) are possible. All of these configurations are inserted into the previously described reaction chamber space 405. Some of the configurations considered include LEU foils, an aqueous solution of a uranium salt dissolved in water, encapsulated UO2 powder and others. The aqueous solutions are highly desirable due to excellent moderation of the neutrons, but provide challenges from a criticality perspective. In order to ensure subcritical operation, the criticality constant, keff should be kept below 0.95. Further control features could easily be added to decrease keff if a critical condition were obtained. These control features include, but are not limited to control rods, injectable poisons, or pressure relief valves that would dump the moderator and drop the criticality. Aqueous solutions of uranium offer tremendous benefits for downstream chemical processes. Furthermore, they are easy to cool, and provide an excellent combination of fuel and moderator. Initial studies were performed using a uranium nitrate solution-UO2(NO3)2, but other solutions could be considered such as uranium sulfate or others. In one construction, the salt concentration in the solution is about 66 g of salt per 100 g H2O. The solution is positioned within the activation cell 410 as illustrated in FIGS. 24 and 25. In addition to the solution, there is a smaller diameter cylinder 500 in the center of the activation cell 410 filled with pure water. This cylinder of water allows the value of keff to be reduced so that the device remains subcritical, while still allowing for a large volume of LEU solution to be used. In the aqueous solution layout illustrated in FIGS. 24 and 25, the central most cylinder 500 contains pure water and is surrounded by an aqueous mixture of uranium nitrate that is contained between the tube and a cylindrical wall 505 that cooperate to define a substantially annular space 510. The target chamber 60, 70 is the next most outward layer and is also annular. The pure water, the aqueous mixture of uranium nitrate, and the target chamber 60, 70 are surrounded by the Be multiplier/reflector 420. The outermost layer 520 in this case is a large volume of D2O contained within the tank 415. The D2O acts as a moderator to reduce radiation leakage from the fission portion 400a, 400b. FIGS. 26-29 illustrate similar structural components but contain different materials within some or all of the volumes as will be discussed with those particular figures. A common method to irradiate uranium is to form it into either uranium dioxide pellets or encase a uranium dioxide powder in a container. These are inserted into a reactor and irradiated before removal and processing. While the UO2 powders being used today utilize HEU, it is preferable to use LEU. In preferred constructions, a mixture of LEU and H2O that provides Keff<0.95 is employed. FIGS. 26 and 27 illustrate an activation column 410 that includes UO2 in a homogeneous solution with D2O. The center cylinder 500 in this construction is filled with H2O 525, as is the outermost layer 530 (only a portion of which is illustrated). The first annular space 535 contains a solution of 18% LEU (20% enriched) and 82% D2O. The second annular layer 540 is substantially evacuated, consistent with the fusion portion target chambers 60, 70. The center cylinder 500, the first annular space 535, and the second annular space 540 are surrounded by a layer of Be 420, which serves as a multiplier and neutron reflector. In another construction, Mo-99 is extracted from uranium by chemical dissolution of LEU foils in a modified Cintichem process. In this process, thin foils containing uranium are placed in a high flux region of a nuclear reactor, irradiated for some time and then removed. The foils are dissolved in various solutions and processed through multiple chemical techniques. From a safety, non-proliferation, and health perspective, a desirable way to produce Mo-99 is by (n,γ) reactions with parent material Mo-98. This results in Mo-99 with no contamination from plutonium or other fission products. Production by this method also does not require a constant feed of any form of uranium. The disadvantage lies in the difficulty of separating Mo-99 from the parent Mo-98, which leads to low specific activities of Mo-99 in the generator. Furthermore, the cost of enriched Mo-98 is substantial if that is to be used. Still, considerable progress has been made in developing new elution techniques to extract high purity Tc-99m from low specific activity Mo-99, and this may become a cost-effective option in the near future. To implement this type of production in the hybrid reactor 5a, 5b illustrated herein, a fixed subcritical assembly 435 of LEU can be used to increase the neutron flux (most likely UO2), but can be isolated from the parent Mo-98. The subcritical assembly 435 is still located inside of the fusion portion 10, 11, and the Mo-99 activation column would be located within the subcritical assembly 435. In preferred constructions, Mo-98 occupies a total of 20% of the activation column 410 (by volume). As illustrated in FIGS. 28 and 29, the centermost cylinder 500 contains a homogeneous mixture of 20% Mo-98 and H2O. The first annular layer 555 includes a subcritical assembly 435 and is comprised of an 18% LEU (20% enriched)/D2O mixture. The second annular layer 560 is substantially evacuated, consistent with the fusion portion target chambers 60, 70. The center cylinder 500, the first annular space 555, and the second annular space 560 are surrounded by the layer of Be 420, which serves as a multiplier and neutron reflector. The outermost layer 570 (only a portion of which is illustrated) contains water that reduces the amount of radiation that escapes from the fission portion 5a, 5b. For the LEU cases, the production rate and specific activity of Mo-99 was determined by calculating 6% of the fission yield, with a fusion portion 10, 11 operating at 1015 n/s. Keff was calculated for various configurations as well. Table 1 summarizes the results of these calculations. In the case of production from Mo-98, an (n,γ) tally was used to determine the production rate of Mo-99. The following table illustrates the production rates for various target configurations in the hybrid reactor 5a, 5b. Mo-99 yield/Total Mo-99 yieldg U (or Mo-98)@ saturation (6Target ConfigurationKeff(Ci)day kCi)Aqueous UO2(NO3)20.9471.512.93UO2 powder0.9452.9222Natural Mo (w subcritical)0.9430.682.69Mo-98 (w subcritical)0.9432.8311.1Natural Mo (w/o subcritical)—0.0850.44Mo-98 (w/o subcritical)—0.351.8 While the specific activity of Mo-99 generated is relatively constant for all of the subcritical cases, some configurations allow for a substantially higher total production rate. This is because these configurations allow for considerably larger quantities of parent material. It is also worth noting that production of Mo-99 from Mo-98 is as good a method as production from LEU when it comes to the total quantity of Mo-99 produced. Still, the LEU process tends to be more favorable as it is easier to separate Mo-99 from fission products than it is to separate it from Mo-98, which allows for a high specific activity of Mo-99 to be available after separation. In constructions in which Mo-98 is used to produce Mo-99, the subcritical assembly 435 can be removed altogether. However, if the subcritical assembly 435 is removed, the specific activity of the end product will be quite a bit lower. Still, there are some indications that advanced generators might be able to make use of the low specific activity resulting from Mo-98 irradiation. The specific activity produced by the hybrid reactor 5a, 5b without subcritical multiplication is high enough for some of these technologies. Furthermore, the total demand for U.S. Mo-99 could still be met with several production facilities, which would allow for a fission free process. For example, in one construction of a fusion only reactor, the subcritical assembly 435 is omitted and Mo-98 is positioned within the activation column 410. To enhance the production of Mo-99, a more powerful ion beam produced by the linear arrangement of the fusion portion 11 is employed. It is preferred to operate the ion beams at a power level approximately ten times that required in the aforementioned constructions. To achieve this, a magnetic field is established to collimate the beam and inhibit the undesirable dispersion of the beams. The field is arranged such that it is parallel to the beams and substantially surrounds the accelerator 30 and the pumping system 40 but does not necessarily extend into the target chamber 70. Using this arrangement provides the desired neutron flux without the multiplicative effect produced by the subcritical assembly 435. One advantage of this arrangement is that no uranium is required to produce the desired isotopes. Thus, the invention provides, among other things, a segmented activation cell 600 for use in producing medical isotopes. The segmented activation cell may be used, for example, with a hybrid reactor 5a, 5b. The constructions of the hybrid reactor 5a, 5b described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the invention.
	abstract	A method for preparing a powder of a solid solution of dioxide of uranium and of at least one other actinide and/or lanthanide element comprising combusting a solution that comprises uranyl nitrate and at least one nitrate of the other actinide and/or lanthanide element and glycine, with the glycine being used in a predetermined amount so as to form, at the end of the combustion, the solid solution.
042645409	abstract	In the production of nuclear fuel pellets consisting essentially of oxides of uranium, or mixtures of these oxides with oxides of thorium or plutonium, by granulating the oxide powder, pressing the granulated powder into compacts and sintering the compacts, niobium pentoxide is added to the oxide power in sufficient quantity to encourage grain growth in the oxide compact during sintering and the sintering and other process parameters are adjusted so that no impurities are trapped in the sintering pellets which would prevent a high matrix density and grain size being obtained.. Adjustment and control of the oxygen potential of the sintering atmosphere is proposed.
039416526	description	The localising apparatus diagrammatically illustrated in FIG. 1 comprises a source 10 of gas (for instance, argon) at a pressure P.sub.1 slightly higher than the pressure P.sub.2 of the coolant (liquid sodium) at the outlet of assemblies 12. A distributor 14 enables any of tubes 16, each connected to an emulsion pump associated with one of the assemblies 12, to be connected to the source 10. Clearly, the term "assembly" covers both a group of fuel pencils in the same envelope, and a single fuel element. The emulsion coming from that pump which is supplied with gas rises into a collecting and degasifying tank 18 via a vertical tube 20 (one tube 20 is provided for each assembly 12). The level of the tank 18 above the free surface 22 of the sodium is such that a separation is established therein between the liquid sodium, which returns to the mass of sodium in the core via the tubes 20 to which emulsion is not supplied, and the gas. The return of the sodium from the degasifying tank via the tubes 20 not supplied with emulsion might have the disadvantage of polluting such tubes with sodium charged with fission products by their passage through the tube corresponding to the faulty assembly, so that the signal might be slightly difficult to detect. One possible solution to this is illustrated in FIG. 3, which shows how the sodium is returned from the degasifying tank 18 to the reactor via a special tube 20' provided for this purpose and disposed at a lower level than the other tubes. The gas is sucked in by a pump 24 which sends it to an analysing installation 26. For the sake of clarity, FIG. 1 shows in solid arrows the flow paths followed by the gas, the emulsion and the coolant on its way back from the tank 18, broken arrows showing the normal flow of the sodium coolant. The emulsion pump operates on the following principle: the gas injected at the base of a vertical tube 20 at pressure P.sub.1 produces an emulsion whose mean density is lower than that of the liquid coolant. The emulsion rises in the tube 20 and reaches a level higher than that of the surface. The gas flow required for pump operation being low in relation to the total liquid flow for each assembly, supply tubes 16 of small section are enough. Clearly, the volume of the tank 18 is selected to keep the time required for checking an assembly within reasonable limits. The degasifying tank can have a volume of the order of 30 liters for an analysing installation 26 adapted to deliver a signal when it receives a total flow of the order of 0.1 - 0.2 liters per second coming from an assembly 12. FIG. 2 shows an emulsion pump which can be used in the installation illustrated in FIG. 1, in which the pump is associated with an assembly 12. The outlet of the assembly 12 is placed in line with an upwardly flared passage 30 of generally frusto-conical shape with which the core cover plate 32 is formed. The pump diffusor is formed by a perforate cone 34 inserted in a bore 38 in a plate 36 which on the one hand acts as a support for the tubes 20 and on the other co-operates with the cones 34 to bound gas distribution chambers 40 into which the tubes 16 discharge. An identical sodium flow does not pass through all the assemblies 12 of a nuclear reactor, since the dynamic pressures diminish from the centre to the periphery by a factor often of the order of 2. To allow for this, the cone 34 is continued by a bottom tip 42 whose end is obturated and whose side wall is formed with slots or apertures 44 of a size adequate to prevent them being clogged by impurities. By this method the liquid admitted to the cone 34 will be at the same pressure in all tubes, such pressure being the height of the sodium in the reactor vessel and therefore all the emulsion pumps will be identical for any given reactor. Clearly, the tips 42 must penetrate into the passages 30 deeply enough for each diffuser to collect only sodium coming from the assembly 12 to be checked. The flared shape of the passages 30 compensates for the reduction in section due to the introduction of the tip 42 and prevents any increase in speed which might result from such reduction. Disposed in the tank 18 of flat shape, opposite each tube 20 and at a level 28, are anti-splash plates 46 (FIG. 2) adapted to encourage the separation of the gas from the liquid and limit its level locally. The gas pump 24 and the analysing installation 26 disposed outside the reactor screening enclosure 48 are connected to the tank via a conduit 50. The following numerical data, given by way of example, are those of an apparatus adapted for use with a fast neutron 250 MWe reactor in which the outlet temperature of the assemblies under normal operating conditions is 833.degree.K: Inside diameter of tube 20: 25 mm Inside diameter of tip 42: 16 mm Pressure P.sub.1 of the gas in the emulsifier: 1.175 bar sodium flow in the pump: 0.28 l/s Gas flow in the emulsifier at pressure P.sub.1 and normal opera- ting temperature: 0.45 l/s Gas flow at outlet of tube 20: 0.53 l/s Speed of the emulsion in center of tube 20: 2 m/s proportion of gas by volume at the center of the tube 20: 0.5 Delivery of the pump: 0.45 Emersion ratio: x/H = 1.8 Clearly, the emersion ratio must be so selected that the level of the emulsion does not drop below the tank 18. The value of 1.8 shown above takes account of this fact, whose importance is clear if it is remembered that for this particular reactor the outlet temperature of the assemblies on stoppage (corresponding to minimum level 28) is 453.degree.K, while such temperature is 833.degree.K during operation. The main advantages afforded by the invention can be gathered from the foregoing description: the apparatus is very simply constructed and there is very little risk of breakdown (pumps without moving members, switching distributor disposed in the gas circuit); sensitivity is increased by the intimate mixing of the gas and liquid during the formation of the emulsion. The use of pumps with tips enables standard diffusers to be used throughout the installation.
	summary
047553324	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of and an apparatus for pelletizing a radioactive waste, and more particularly, to a method of and an apparatus for pelletizing a radioactive waste in which it is possible to shorten the compressing time required when a waste powder is to be compressed or press-molded into a pellet, and to prevent environmental pollution from being caused by the waste powder which may be scattered during the pelletizing operation. 2. Description of the Prior Arts A radioactive waste has been increasingly produced by an atomic power plant concurrently with an increase in the quantity of produced electricity, and therefore, the need for volume-reducing treatment of a radioactive waste has been increased in order to ensure a storage space in a facility. One method of reducing the volume of a radioactive waste has heretofore been proposed in which a concentrated waste liquid (the main component is a soda sulfate) obtained from the concentration of a waste liquid regenerated from ion exchange resins which are produced in large quantities by a boiling water reactor and granular ion exchange resin slurry are dried and milled so as to remove water occupying a large percent of the volume of a radioactive waste, and the thus-treated powder is formed and solidified into a pellet by using a tablet type pelletizer, or alternatively, after inflammable solid wastes have been burnt, the thus-produced ashes are formed and solidified into a pellet by using the tablet type pelletizer. Such method of pelletizing a radioactive waste by the use of the tablet type pelletizer is disclosed in the specifications of Japanese patent unexamined publication No. 100799/1983, Japanese patent unexamined publication No. 100800/1983, and Japanese patent unexamined publication No. 108497/1983. However, these publications only disclose a mixing ratio or a compressive force connected with a radioactive waste powder. According to one of conventional pelletizing methods using the above-mentioned pelletizer, a radioactive waste powder is supplied into a powder receiving cavity formed in a pelletizing section of the pelletizer, and the powder is pelletized within a through bore of a pelletizing die which extends from one end facing the powder receiving cavity to the other end facing the atmosphere, by inserting a first pelletizing rod from the side of the one end of the through bore, through the cavity, into the through bore under condition that a second pelletizing rod is inserted into the through bore by a predetermined length through the other end into the through bore. The waste powder is thus pelletized in a compressed manner within the through bore. However, such prior-art method involves disadvantage in that compressed air is not easily discharged through the through bore and compressing time correspondingly becomes longer. This is because the gap between the first pelletizing rod and the through bore and that between the second pelletizing rod and the through bore constitute minute gaps having substantially the same size or width and the air compressed during the pelletizing or press-molding operation is expelled through the minute gaps out of the through bore. In addition, the above-mentioned method involves a problem in that the compressed air passes through the respective gaps between the through bore and both rods and flows into not only the powder receiving cavity but also the atmosphere, so that part of the waste powder is mixed with the air flowing into the atmosphere, thus raising the problem of environmental pollution. SUMMARY OF THE INVENTION An object of the present invention is to provide method of and an apparatus for pelletizing a radioactive waste powder which is capable of eliminating the above-described disadvantages of the prior art by shortening the compressing time expended during a pelletizing operation and preventing the waste powder from being scattered together with air discharged into the atmosphere. Accordingly, in accordance with one aspect of the present invention, there is provided a method of pelletizing a radioactive waste powder comprising the steps of: supplying the radioactive waste powder in a powder receiving cavity defined in a pelletizing section of a pelletizer; pelletizing the powder within a through bore formed in a pelletizing die by inserting a first pelletizing rod through the receiving cavity into the through bore through one end thereof facing the receiving cavity under condition that a second pelletizing rod is inserted into the through bore by a predetermined length through the other end of said through bore facing the atmosphere, the through bore extending in the pelletizing die from the one end to the other end; and allowing an air compressed in the through bore in the pelletizing step to be discharged into the receiving cavity through the one end without causing the air to leak into the atmosphere through the other end of the through bore. In accordance with another aspect of the present invention, there is provided an apparatus for pelletizing a radioactive waste powder comprising: a pelletizing section; a pelletizing die which has one end facing a cavity defined in the pelletizing section for receiving the radioactive waste powder and the other end exposed to the atmosphere, the pelletizing die being formed therein with a through bore extending from the one end to the other end of the die; a first pelletizing rod arranged to be inserted through the receiving cavity into the through bore from the one end of the die such as to be capable of being drawn out therefrom; a second pelletizing rod arranged to be inserted into the through bore from the other end of the die such as to be capable of being drawn out therefrom; the first and second pelletizing rods being arranged in such a manner that, when the second pelletizing rod is kept stationary in a position inserted in the through bore by a predetermined amount, the first pelletizing rod is inserted though the receiving cavity into the through bore, thereby enabling the pelletizing operation of the powder within the through bore; and an air discharge for allowing air compressed in the through bore to be discharged into the receiving cavity without causing the compressed air to leak into the atmosphere during the pelletizing operation. The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.
054992788	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 3, the preferred embodiment of the present invention comprises a water-filled tank 104 of appropriate shape, containing one or more holes or openings 118 at its lowermost periphery, positioned at an appropriate location within an auxiliary pool chamber 52b. Tank 104 is connected via piping 106 and valving 108 to a high-pressure gas-charged pneumatic tank 110 of appropriate volume, positioned at an appropriate location within reactor building 80. Valve 108 is normally closed, but can be opened at an appropriate time following a LOCA. Preferably, valve 108 is a passive-type valve, such as a squib (i.e., explosive-actuated) valve. Valve 108 opens in response to appropriate control signals from various monitors (not shown) which sense the course of the LOCA, including the drawdown status of the water level in pool chamber 52a and/or auxiliary pool chamber 52b. When valve 108 opens, high-pressure gas, such as nitrogen, inside tank 110 is released to flow passively through piping 106 to pressurize the interior of tank 104. In so doing, the initial water contents 120 of tank 104 are expelled through openings 118. Inasmuch as the expelled contents 120 are discharged to auxiliary pool chamber 52b, the height of this pool chamber will at first tend to increase. However, by the gravity-driven passive leveling of all condenser pool chambers, water will also flow into pool chamber 52a, thereby augmenting the water inventory in pool chamber 52a and allowing credit for further boiloff heat transfer through PCC heat exchanger 54. Gas injected into tank 104 will remain trapped throughout the subsequent course of the LOCA transient, and will thereby essentially displace the initial contents 120 into pool chamber 52a and 52b. This trapping action is facilitated by selection of a gas which does not readily go into solution in water. The preferred such gas is nitrogen. The broad concept of the invention is not limited to any specific design of the volume inside pneumatic tank 110. Any excess gas released into tank 104 will simply escape tank 104 through openings 118 and then be carried upward as bubbles through the water in pool chamber 52b. At the surface of the water in auxiliary pool chamber 52b, the gas blends smoothly with steam passing through moisture separator/dryer 96 and piping/ducting 98 to escape to the environs. This escaping gas has no adverse consequences vis-a-vis the PCC heat exchange process underway in pool chamber 52a. In accordance with one preferred embodiment of the invention, pneumatic tank 110 is instrumented for monitoring its state-of-charge (i.e., pressure) and is connected via piping 112 and valving 114 to a high-pressure nitrogen supply 116. The high-pressure nitrogen supply 116 enables the charge-up of tank 110 to requisite pressure to accomplish the expelling of a design amount of water inventory from tank 104. In accordance with an alternative embodiment, tank 104 may comprise a plurality of partitioned sections and appropriate valving to provide redundancy. Such an arrangement prevents a rupture in one section, or its connected piping, from compromising the water-expelling action of other unaffected sections. In like fashion, pneumatic tank 110 may comprise a plurality of units connected to tank 104 via appropriate valving. In accordance with a further variation, one or more pressure-regulating valves can be incorporated in piping 106 to limit the peak pressure which tank 104 must be designed to withstand. Alternatively, tank 104 could, instead of being a fixed-form tank, comprise an inflatable bladder secured by appropriate means to a selected region of auxiliary pool chamber 52b. Further, wall 81 could be made slidable in a direction perpendicular to wall 84. As wall 81 moved closer to wall 84, the volume inside auxiliary pool chamber 52b would decrease, causing the water level to tend to rise. Thus a movable wall can be used to accomplish the same effect, i.e., a rise in the water level in auxiliary pool chamber 52b, as that achieved by injecting gas into and expelling water from tank 104. In accordance with another design, tank 104 in auxiliary pool chamber 52b can be replaced by one or more smaller tanks located in pool chamber 52a to the extent that available space may exist within the given design arrangement. Alternatively, the smaller tanks in pool chamber 52a can be used in conjunction with, rather than substituted for, tank 104 in auxiliary pool chamber 52b. In accordance with another preferred embodiment of the invention, the pneumatic tank 110 (see FIG. 3) can be combined with the nitrogen accumulator tank 118 (shown in FIG. 4) of a standby liquid control system (SLCS) for shutting down the reactor from full power, without assistance from control rod insertion, by using high-pressure nitrogen to inject a neutron-absorbing solution into the core. Referring to FIG. 4, the accumulator 118 of the SLCS comprises a tank partially filled with a 12.5% solution of isotopically enriched sodium pentaborate and the remaining volume being filled with pressurized nitrogen. The sodium pentaborate solution is neutron-absorbing and is intended to be injected into the fuel core for the purpose of moderating the fission reaction therein under certain conditions. The accumulator 118 is filled with pressurized nitrogen via a pneumatic line 120, which is connected to a tank (not shown) of liquid N.sub.2 via a vaporizer 122 and a compressor 124. Because of continual outleakage of pressurized nitrogen through fittings, pinhole leaks, etc., the gasified liquid nitrogen also fills up one or more gas bottles 126 with nitrogen gas to be used as makeup for leakage. The accumulator 118 outlet is connected to the fuel core 12 via piping and valving 128, 130a, 130b, 132a and 132b. Valve 128 is a quick-closing pneumatic valve which is normally open. Valves 130a and 130b are squib (i.e., explosive-actuated) valves which are connected in parallel and which are normally closed. Valves 132a and 132b are isolation check valves which are connected in series and will open, and close, under suitable differential pressures. In response to certain emergency conditions, the primer fires an explosive charge that blasts open a gate or disk inside squib valves 130a and 130b. As a result, the borate solution is forced out of the accumulator 118 by the pressurized nitrogen and flows into the fuel core 12. When a level transmitter 134 detects that the level of solution in accumulator 118 has reached the bottom, the level transmitter actuates the pneumatic valve 128 to close quickly to prevent the flow of nitrogen into the reactor. In accordance with the proposed embodiment, accumulator 118 in FIG. 4 could, given the addition of suitable piping as shown in FIG. 3, also serve the function of tank 110. The design basis scenario which calls for SLCS accumulator action to discharge the poison solution into the reactor under an "anticipated transients without scram" event, is distinct and separate from any event which calls for tank 110 to function to expel water from tank 104. Because the required pneumatic services are non-coincidental, the existing SLCS accumulator can serve both functions. In so doing, tank 110 in FIG. 3 can be either downsized considerably or eliminated altogether. The foregoing preferred embodiments have been disclosed for the purpose of illustration. Other variations and modifications will be apparent to persons skilled in the design of passive pressure suppression systems for boiling water reactors. All such variations and modifications are intended to be encompassed by the claims set forth hereinafter.
052326560	description	DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a layout scheme of a fast acting nuclear reactor control device 10. The device 10 controls a safety control rod 12 within or without the core 14 of a nuclear reactor. The safety control rod's position is indicated by an encoder system 16. A primary safety control rod drive means, or drive shaft, 18 is operatively connected to the safety control rod 12, for driving and positioning the safety control rod within or without the reactor core 14. More specifically, the control rod 12 is a typical nuclear reactor control rod as described previously that includes a neutron absorber (poison), shown as the shaded portion 13. The position of the control rod 12 shown in FIG. 1 is half withdrawn (or half inserted). Rotation of the shaft 18 to raise the control rod 12 will position the poison portion 13 in the full "out" position for full reactor power. Lowering the assembly will place the poison 13 within the core 14. As shown, the safety control rod 12 is oriented in a substantially vertical position in a reactor of downward coolant flow to allow the safety control rod to fall into the reactor core under the influence of gravity and water pressure during shutdown of the reactor. The drive shaft 18 is also operatively connected to a hydraulic pump 20. The operation of the drive shaft 18 drives and positions the safety control rod 12 within or without the reactor core 14, while simultaneously operating the hydraulic pump 20 such that hydraulic fluid is forced into a pressurized accumulator 22. This fills or charges the accumulator 22 with oil while under pressure of compressed gas which provides storage of potential energy, the us of which will be explained below. A high pressure gas supply 23 supplies gas for pressurizing the accumulator. An electromagnetic clutch 26 is coaxial with the drive shaft 18. The drive shaft 18 is powered by an electric gearmotor 28. The gearmotor has a double worm gear reducer 29 and is self locking. The gear motor 28 driving through the electrically engaged clutch 26 will thus position the safety control rod 12 in the run position. To eliminate constant pressure on the hydraulic pump 20, which would tend to cause the shaft to rotate in the rod-insertion direction, a solenoid operated valve 24 can be interposed between the hydraulic pump 20 and the accumulator 22. This solenoid operated valve is a normally open valve, remaining open except when electrical power is applied to its solenoid. Power is applied to close the valve 24 only when the safety control rod 12 is out of the reactor core 14 for reactor operation. Should electrical power fail or a signal be received from the encoder system 16 calling for rapid insertion of the safety control rod, the solenoid valve 24 will open to release the potential energy in the accumulator to provide primary motive force to drive the safety control rod. The electromagnetic clutch 26 will also release allowing the shaft 18 to rotate. More specifically, the opening of the solenoid valve releases the hydraulic oil, pressurized by compressed gas in the accumulator 22 and forces the hydraulic fluid to flow back through the hydraulic pump, thereby converting the hydraulic pump 20 to a hydraulic motor, rotating the shaft 18, and inserting the safety control rod 12. This hydraulic drive accelerates the safety control rod 12 and maintains a drive force torque via the high pressure gas of the accumulator 22. The insertion of the safety control rod 12 is now powered by the combined effects of high pressure gas, gravity, and differential hydraulic pressure. The compressed gas provides the energy necessary for full length and high speed insertion of the safety control rod 12. The maximum driving force can be easily adjusted by adjusting the gas pressure in the accumulator (up to the maximum pressure that the safety control rod drive motor is able to provide) and can be increased above this level while the reactor is operating in preparation for fast SCRAM. Once the safety control rod is withdrawn the solenoid valve 24 can close and the current to the clutch 26 can automatically drop to a lower level, and thus reduce the clutch release time. With the solenoid valve closed only the safety control rod's torque can pass through the clutch. The safety control rod 12 is also connected to a rack gear 34, and the safety control rod drive shaft 18 has a pinion gear 36 in contact with the rack for allowing the safety control rod to be positioned within or without the reactor core. The novel features of the invention described herein are functional regardless of whether the rack 34 is above the poison 13 and core 14, or below the poison and core. However, for the gravity assisted SCRAM feature, the poison 13 must be above the core 14 as is shown in FIG. 1. Other mechanisms for positioning the safety control rod within or without the reactor core are also possible. In addition, an overrunning clutch 30 can be coaxial with the drive shaft 18, located intermediate the hydraulic motor 20 and the electromagnetic clutch 26. The overrunning clutch 30 is capable of allowing the speed of the drive shaft 18 to rotate at a speed greater than the speed of the hydraulic motor during shutdown of the reactor to provide for rapid insertion of the safety control rod into the reactor core in the event of partial drive system failure. The overrunning clutch 30 will allow the safety control rod 12 to move back down into the reactor core, due to gravity and pressure drop across the safety control rod, caused by coolant flow through the reactor even if the SCRAM system (whether it is the currently utilized cocked-spring system or the disclosed hydraulic system) has failed and locked the SCRAM system. The overrunning clutch also will not allow the SCRAM system to hinder safety control rod insertion speed if the SCRAM shaft is turning slower than the main safety rod shaft. Additionally, a reservoir of hydraulic fluid 32 is connected to the hydraulic pump 20 for pump supply. The electric motor 28, driving through the electrically engaged clutch 26 will position the safety control rod 12 in the run position, while also driving, via the overrunning clutch 30, the hydraulic pump 20, which thus transfers hydraulic fluid from the reservoir 32 to the accumulator 22. The clutch 26 will operate at high current during cocking until the solenoid valve 24 closes. With the hydraulic power now contained, the current may drop to low levels, reducing a release lug in the clutch during a SCRAM. 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 embodiment was chosen and described to best explain the principles of the invention and its practical application and thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as ar suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
051805430	claims	1. A passive injection system for a nuclear power plant including a containment, a reactor vessel having a core, a hot leg in communication with the core, a cold leg, and a borated water supply for injecting into the reactor core during a loss of coolant accident in which the containment is flooded, comprising: a first flow path extending from the hot leg at a point below the flood up level of water in the containment, and providing a passageway from the hot leg to the containment; and a second flow path extending from the reactor vessel and providing a passageway from the containment to the reactor core; the first and second flow paths providing means for inducing a natural circulatory flow of water from within the containment through the reactor core based on differences in water density produced by the reactor core to thereby prevent concentration of boron in the reactor vessel, wherein the first flow path is coupled to a bottom of the hot leg so that steam can vent through an upper portion of the pipe, and wherein the first flow path is coupled to the hot leg at an elevation at the top of the reactor core and below the flood up water level in the containment thus establishing a circulatory flow of water from the containment through the core based on differences in water density. a core makeup tank which is filled with borated water at a predetermined concentration of boric acid and having a drain line for draining the borated water into the reactor vessel and a pressure balance line connecting a top of the core makeup tank to the cold leg; a vent coupling the pressure balance line to the core makeup tank, the vent inducing a natural circulatory flow of borated water from within the core makeup tank to the reactor vessel by means of hot water rising into the pressure balance line and flowing into the core makeup tank through the vent. a reactor vessel having a core; a reactor coolant system in communication with the reactor vessel; at least one in-containment refueling water storage tank in communication with the reactor coolant system; at least one core makeup tank in communication with the reactor coolant system; at least one accumulator in communication with the reactor coolant system, the in-containment refueling water storage tank, the at least one core makeup tank and the at least one accumulator being filled with borated water; and means for filling, draining, and sampling the contents of the in-containment refueling water storage tank, the at least one core makeup tank, and the at least one accumulator to maintain a specified concentration of boric acid in the borated water. a borated water supply flowable substantially by gravity into the reactor core during a loss of coolant accident; and means for filling, draining and sampling the borated water supply to maintain specified concentration of boric acid in the reactor core. 2. A passive safety injection system for a nuclear power plant including a reactor vessel having a core, a reactor hot leg and a cold leg, the system comprising: 3. A passive safety injection system as recited in claim 2, wherein the natural circulatory flow is induced prior to cool down. 4. A passive safety injection system for a nuclear power plant comprising: 5. A passive safety injection system as recited in claim 4, further comprising isolation valves associated with each of the in-containment refueling water storage tank, the at least one core makeup tank, and the at least one accumulator to prevent movement of borated water into the reactor coolant system. 6. A passive injection system for a nuclear power plant including a containment, a reactor vessel having a reactor core, and a reactor coolant system comprising: 7. A passive injection system as recited in claim 6, wherein the borated water supply includes at least one core makeup tank, at least one accumulator tank and an in-core refueling water storage tank. 8. A passive injection system as recited in claim 7, wherein the filling, draining and sampling means includes a fill line associated with each tank, and a drain and sample line associated with each tank. 9. A passive injection system as recited in claim 8, further comprising isolation valves associated with each tank to isolate the borated water from the reactor coolant system.
	claims	1. A method of making a nuclear fuel pellet for a nuclear power reactor, the method comprising the following steps:providing a nuclear fuel material in powder form, wherein the nuclear fuel material is based on UO2;pressing the powder thereby obtaining a green pellet is obtained;providing a liquid that comprises an additive which is to be added to the green pellet, the additive comprises B and/or Cr;contacting the green pellet with the liquid wherein the liquid, with the additive, penetrates into the pellet; andsintering the so treated green pellet,wherein with said additive larger grains in the nuclear fuel material are present in the pellet after the sintering step as compared with the grain size obtained if the additive had not been added but otherwise produced in the same manner. 2. A method according to claim 1, wherein said additive is in the form of particles dispersed in said liquid. 3. A method according to claim 1, comprising a step of controlling the penetration depth of the liquid, and thereby of the additive, into the green pellet. 4. A method according to claim 3, wherein said step of controlling the penetration depth is done by selecting one or both of the following:the viscosity of the liquid with included additive,the amount of the liquid, with the additive, which is added to the green pellet when contacting the green pellet with the liquid, with the additive. 5. A method according to claim 3, wherein the penetration depth of the liquid, with the additive, into the green pellet is controlled to obtain an outer portion of the green pellet containing substantially more liquid, and thereby more additive, than an inner portion of the green pellet, wherein the sintered pellet has a larger grain size in the outer portion than in the inner portion. 6. A method according to claim 1, wherein said liquid with additive is selected and said method is performed wherein the liquid with additive will penetrate into the pores which exist between the grains in the green pellet. 7. A method according to claim 6, wherein said liquid with additive is selected and said method is performed wherein the liquid with additive will not penetrate into the pores which exist in the grains in the green pellet. 8. A method according to claim 6, wherein said liquid with additive is selected and said method is performed wherein the liquid with additive will penetrate also into the pores which exist in the grains in the green pellet. 9. A method according to claim 1, wherein said liquid is selected and said method is performed wherein at least 99% of the liquid will leave the pellet before or during the sintering step. 10. A method according to claim 1, wherein said additive constitutes or includes a substance which causes said larger grains in the sintered pellet, wherein said substance is selected and the method is performed wherein at least 90% of the substance leaves at least an outer portion of the pellet before and/or during the sintering step. 11. A method according to claim 10, wherein at least 95% of the substance leaves at least an outer portion of the pellet before and/or during the sintering step. 12. A method according to claim 11, wherein at least 99% of the substance leaves at least the outer portion of the pellet before and/or during the sintering step. 13. A method according to claim 12, wherein the substance completely leaves at least the outer portion of the pellet before and/or during the sintering step. 14. A method according to claim 1, wherein said additive comprises B and wherein at least 90% of said B is 11B. 15. A method according to claim 1, wherein said liquid is selected so the additive does not dissolve in the liquid, and wherein the nuclear fuel material in the green pellet is not dissolved by the liquid. 16. A method according to claim 1, wherein said liquid is an oil, preferably a mineral oil. 17. A method of making and using nuclear fuel, comprising:making a plurality of nuclear fuel pellets according to the method of claim 1;arranging the nuclear fuel pellets in cladding tubes;arranging the cladding tubes, with the nuclear fuel pellets, in the core of a nuclear power reactor in a nuclear power plant, wherein at least 20% of the nuclear fuel material in said core are made of pellets made in accordance with the aforementioned method of making the plurality of nuclear fuel pellets; andoperating the nuclear reactor to produce energy. 18. A method of making and using nuclear fuel according to claim 17,wherein at least 50% of the nuclear fuel material in said core are made of pellets made in accordance with the aforementioned method of making the plurality of nuclear fuel pellets. 19. A method of making and using nuclear fuel according to claim 18,wherein 100% of the nuclear fuel material in said core are made of pellets made in accordance with the aforementioned method of making the plurality of nuclear fuel pellets.
047675900	summary	BACKGROUND OF THE INVENTION The present invention relates generally to an apparatus and method for maintaining a steady state current in a plasma for magnetically confining the plasma in a toroidal magnetic confinement plasma device such as a tokamak. More particularly, the present invention relates to a method and apparatus for maintaining a steady-state current for magnetically confining the plasma in a toroidal magnetic confinement device using anomalous viscosity current drive. A second aspect of this invention relates to an apparatus and method for the start-up of a magnetically confined toroidal plasma. The apparatus for toroidal magnetic confinement that is most popular in controlled fusion research today is the tokamak device. But, as is widely recognized, the standard tokamak is inherently a pulsed devise. The magnetic-field-aligned, predominantly toroidal, plasma current, essential for tokamak plasma confinement, is, in the standard tokamak, driven by electromagnetic induction. However, a number of means have been proposed to enable steady-state tokamak current drive. To date, the most successful of such means is lower-hybrid radio-frequency current drive, but the efficiency of radio-frequency current drive is projected to be marginal for a fusion reactor. The present invention pertains to a method and apparatus for driving a steady-state current in a magnetically confined plasma, such as a tokamak plasma, that may prove to be of superior efficiency for a fusion reactor. For a classical axisymmetric magnetically confined toroidal plasma, there is no mechanism within resistive magnetohydrodynamic (MHD) theory to balance the electron-ion friction associated with plasma of current flow other than the presence of a toroidal electric field. But the latter can be established inside the tokamak plasma only by magnetic induction, a process inconsistent with steady-state operation. If steady-state current drive is to be created, it must involve forces which do not appear in the usual Ohm's Law, such as injected high-Z ions, or resonant electrons (radiofrequency drive), or mean-field terms that have their origin in non-axisymmetric phenomena. Anomalous viscosity for plasma current flow is just such a non-axisymmetric phenomenon and can be described in mathamatical terms by adding just such a mean field term to Ohm's Law. In more detail, Furth et al., Phys. Fluids 16, 1054 (1973), have demonstrated that a strong current on the edge of a plasma will trigger the double-tearing instablilty, provided the direction of flow of this edge current is parallel to that of the interior plasma current. The process of magnetic reconnection or of magnetic turbulence associated with this instability then facilitates the rapid radial penetration of the properly directed edge current. Rapid current penetration due to the double-tearing instability has been suggested by Furth et al. (op. cit) and by Stix, Phys. Rev. Letters 36, 521 (1976). This penetration can be modeled by adding to Ohm's Law a new term describin,g the meanfield behavior of the instability-driven turbulence. The effective shear viscosity associated with the effect of magnetic turbulance or of magnetic reconnection on magnetic-field-aligned plasma current flow will hereinafter be referred to as anomalous shear viscosity for current flow or more simply, just as anomalous viscosity. For a detailed discussion of this model a reference is made to Stix, Nucl. Fusion 18, 3 (1978). Ono et al., Bull. Am. Phys. Soc. 27,967 (1982), demonstrated in an experiment performed on the ACT-1 plasma facility that an electron beam produced by an electrode system could be used to produce a highly ionized plasma. It should be understood, however that this ACT-1 experiment used the electrode system in a substantially different manner than the electrode system used in the present invention, as discussed below in DETAILED DESCRIPTION OF THE INVENTION. Therefore, in view of the above, it is an object of the present invention to provide an apparatus and method for maintaining a steady-state plasma current in a toroidal magnetically confined plasma. It is another object of the present invention to provide an apparatus and method for maintaining a steady-state current in a toroidal magnetic confinement plasma device, the apparatus and method having a higher efficiency than radiofrequency current drive. It is another object of the present invention to provide an apparatus and method for maintaining a steady-state plasma current in a toroidal magnetic confinement plasma device using anomalous shear viscosity to achieve preferential penetration of properly-directed magnetic-field-aligned plasma current. It is still another object of this invention to provide an apparatus and method for creating a toroidal magnetically confined plasma, ab initio, in a toroidal magnetic confinement device. Additional objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. SUMMARY OF THE INVENTION To achieve the foregoing and other objects in accordance with the purposes of the present invention, as embodied and broadly described herein, the present apparatus and method for maintaining a steady-state plasma current in a toroidal magnetic confinement plasma device may comprise a toroidal vaccuum chamber within which is a magnetically confined toroidal plasma and means for producing and maintaining the flow of electric current in an edge region at or near the outermost good magnetic surface of the toroidal plasma. Theoretical calculations indicate that the density of current flow in the edge region should be greater than the average density of main current flow and that the current flow in the edge region should be maintained in a direction parallel to the main current for a period of one or two current decay times. Current from the edge region will penetrate radially into the plasma due to magnetic reconnection and/or magnetic turbulence and will augment or maintain the main current through the mechanism of anomalous viscosity. In another aspect of the invention, current flow driven between a cathode and an anode is used to establish a start-up plasma current. The start-up current is generated in a magnetic field which has a strong toroidal component and a weak vertical component. The plasma current channel is detached from the electrodes by quickly changing the vertical component of the magnetic field. The detached current channel results in a toroidal plasma which is magnetically insulated from contact with any material obstructions including the cathode and anode.
	claims	1. A design method for a fuel assembly of a light-water reactor, which includes a plurality of fuel rods arranged in parallel separated by a distance in a direction perpendicular to a longitudinal axis of the fuel rods, each of the fuel rods including a fuel clad and a fuel in the fuel clad, the fuel containing material based on uranium dioxide containing enriched uranium 235, some of the fuel rods including a burnable poison in the fuel, the design method comprising:accumulating core feasibility determination data investigated by analyses or experiments, showing whether or not each one of a burnable poison average mass ratio and an average enrichment of the uranium 235 contained in all of the fuel rods in the fuel assembly is within an acceptable range for a core of the fuel assembly;formulating a criterion formula which determines whether the burnable poison average mass ratio and the enrichment value are within acceptable ranges for the core based on the core feasibility determination data;setting a tentative composition of the fuel assembly;determining whether or not the tentative composition of the fuel assembly is acceptable for the core based on the criterion formula, wherein the average enrichment is greater than or equal to 5%; anddesigning the fuel assembly of the light-water reactor based on the tentative composition of the fuel assembly determined to be acceptable for the core. 2. The design method for the fuel assembly of the light-water reactor according to claim 1, wherein the criterion formula is (a1·e)−b<p·n/N<(a2·e)−c, wherein N is an integer equal to or greater than 2 and N is a number of the fuel rods in the fuel assembly, n is a number of the fuel rods containing the burnable poison and an integer equal to or greater than 1 and less than N, p is a ratio wt % of the burnable poison in the fuel, and e is the average enrichment wt % of the uranium 235 contained in all of the fuel rods in the fuel assembly, each of a 1, a2, b and c is a positive constant and a1 is equal to or greater than a2. 3. The design method for the fuel assembly of the light-water reactor according to claim 1, wherein the criterion formula is (a1·e)−b<p·n/N<(a2·e)−c, wherein N is an integer equal to or greater than 2 and N is a number of the fuel rods in the fuel assembly, n is a number of the fuel rods containing the burnable poison and an integer equal to or greater than 1 and less than N, p is a ratio wt % of the burnable poison in the fuel, and e is the average enrichment wt % of the uranium 235 contained in all of the fuel rods in the fuel assembly, each of a1, a2, b and c is a positive constant and a1 is equal to or greater than a2. 4. The design method for the fuel assembly of the light-water reactor according to claim 3, wherein each of a1 and a2 is 0.57, b is 1.8, and c is 0.8. 5. The design method for the fuel assembly of the light-water reactor according to claim 1, wherein the average enrichment of the enriched uranium 235 in the fuel containing the burnable poison is less than the maximum enrichment of the enriched uranium 235 in the fuel in the fuel assembly. 6. The design method for the fuel assembly of the light-water reactor according to claim 1, wherein the fuel rods are arranged into a square lattice array and at least one of the fuel rods containing the burnable poison does not face other fuel rods. 7. The design method for the fuel assembly of the light-water reactor according to claim 1, wherein the fuel rods are arranged into a square lattice array and at least one of the fuel rods containing the burnable poison does face other fuel rods containing the burnable poison with at least one side of the four sides of the fuel rods arranged into the square lattice array. 8. The design method for the fuel assembly of the light-water reactor according to claim 1, wherein the burnable poison contains compounds containing gadolinium, erbium, or boron. 9. The design method for the fuel assembly of the light-water reactor according to claim 1, wherein the burnable poison is gadolinia and maximum concentration of the gadolinia in the fuel is less than 20 wt %. 10. The design method for the fuel assembly of the light-water reactor according to claim 1,wherein the burnable poison is gadolinia wherein gadolinia of odd mass is more concentrated than gadolinia of even mass.
	claims	1. A passive safety system, comprising:a passive containment cooling system;a heat exchangerformed at a space inside a hermetic containment, andallowing heat exchange of internal atmosphere of the containment introduced therein,such that temperature of the internal atmosphere is reduced,when an accident occurs in a reactor system disposed within the containment;a thermoelectric element disposed within the heat exchanger and configured to produce electricitydue to a temperature difference between the internal atmosphere and a cooling fluid, heat-exchanged with the internal atmosphere,when the cooling fluid performs the heat exchange with the internal atmosphere within the heat exchanger; anda fan unitconnected to the thermoelectric element via an electricity path to receive the electricity produced from the thermoelectric element andconfigured to form a flow of fluid inside the containment. 2. The system of claim 1, wherein the fan unit is configured to increase a flow rate of the cooling fluid passing through the heat exchanger, to facilitate the heat exchange between the internal atmosphere and the cooling fluid within the heat exchanger. 3. The system of claim 2, wherein the heat exchanger is arranged within the containment such that the internal atmosphere is introduced directly into the heat exchanger. 4. The system of claim 3, further comprising:an emergency cooling fluid storage section configured to store an emergency cooling fluid introduced into the heat exchanger for the heat exchange with the internal atmosphere upon an occurrence of an accident; andcooling fluid flow paths configured to connect the emergency cooling fluid storage section to the heat exchanger such that the emergency cooling fluid is introduced into the heat exchanger. 5. The system of claim 4, wherein the fan unit is configured to blow the internal atmosphere toward the heat exchanger, to facilitate steam discharged from the reactor system to be introduced into the heat exchanger from a portion above the heat exchanger. 6. The system of claim 1, further comprising:an emergency cooling fluid storage section configured to store an emergency cooling fluid introduced into the heat exchanger for the heat exchange with the internal atmosphere upon an occurrence of an accident; anda circulation flow path configured to allow the emergency cooling fluid within the emergency cooling fluid storage section to be circulated within the heat exchanger and the emergency cooling fluid storage section therethrough,wherein the fan unit is located inside the containment and arranged on an internal atmosphere introduction flow path to introduce the internal atmosphere into the heat exchanger. 7. The system of claim 1, wherein the electricity path is provided with a charging unit disposed on the electricity path to store the electricity produced from the thermoelectric element so as to supply the electricity to the fan unit. 8. The system of claim 1, wherein the heat exchanger is configured as an air-cooling type. 9. The system of claim 8, further comprising:an emergency cooling fluid storage section configured to store the emergency cooling fluid introduced into the heat exchanger for the heat exchange with the internal atmosphere; anda cooling fluid flow path configured to connect the emergency cooling fluid storage section to the heat exchanger such that the emergency cooling fluid is introduced into the heat exchanger. 10. The system of claim 9, wherein a pump unit is disposed on the cooling fluid flow path such that the emergency cooling fluid is efficiently introduced into the heat exchanger,the pump unit allowing the emergency cooling fluid to be supplied from the emergency cooling fluid storage section into the heat exchanger. 11. The system of claim 8, further comprising:a cooling fluid storage section disposed adjacent to the containment to store therein the cooling fluid for reducing the internal temperature of the containment; anda spray device disposed at an upper side within the containment and configured to spray the cooling fluid supplied from the cooling fluid storage section into the containment when an accident occurs within the containment,wherein a pump unit is disposed on a fluid supply flow path for connecting the cooling fluid storage section and the spray device to each other, to supply the cooling fluid into the spray device by using the electricity produced from the thermoelectric element arranged in the heat exchanger. 12. The system of claim 9, further comprising:a cooling fluid storage section disposed adjacent to the containment to store therein the cooling fluid for reducing the internal temperature of the containment; anda safety injection system configured to inject fluid into the reactor system when an accident occurs in the reactor system,wherein a pump unit is disposed on a fluid supply flow path for connecting the safety injection system to the cooling fluid storage section to supply the cooling fluid to the safety injection system by using the electricity produced from the thermoelectric element arranged in the heat exchanger such that the safety injection system injects the cooling fluid into the reactor system. 13. The system of claim 9, further comprising a cooling fluid storage section disposed adjacent to the containment to store therein the cooling fluid for reducing the internal temperature of the containment,wherein a pump unit is configured to introduce the cooling fluid stored in the cooling fluid storage section into the emergency cooling fluid storage section when a water level of the emergency cooling fluid storage section is decreased.
051503921	claims	1. A structure for providing precise alignment in the x,y dimensions and precise gap control in the z dimension between a mask and a wafer in a lithography system comprising: a wafer to be lithographically exposed to radiation having a raised alignment mark on the upper surface thereof, a mask disposed over said wafer, said mask having radiation transparent areas for permitting radiation to strike said wafer in predetermined patterns, said mask having at least one physical opening therein including a cantilever member portion of said mask material projecting from an edge of said mask opening into said opening, said cantilever member being constrained only at one end at said edge of said opening and being free to move in the Z dimension at the end opposite said edge of said opening, a tip affixed to the said opposite end of said projecting cantilever position of said mask material, gap control means, including a tip, disposed vertically in the Z dimension over said opposite end of said projecting cantilever, said gap control means further including means for moving said tip into contact with said projecting cantilever for bending said cantilever down toward said wafer in Z dimension to a predetermined gap spacing distance, means for raising said wafer upward in the Z dimension until substantially proximate said tip on said projecting cantilever, and means for translating said wafer in the X and Y dimensions until said sharp tip on said projecting cantilever is in contact with said alignment mark. 2. A structure according to claim 1 wherein said cantilever member is composed of said mask material and is contiguous with said mask at said constrained end. 3. A structure according to claim 2 wherein said radiation transparent areas are thin membrane areas of said mask having thicknesses significantly less than the thickness of said mask such that radiation passes through said membrane areas and is blocked by said thicker mask. 4. A structure according to claim 2 wherein said radiation is a beam of X-rays. 5. A structure according to claim 2 wherein said gap control means includes a piezoelectric transducer.
046438459	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be described in detail by referring to the embodiments shown in the drawings. FIGS. 1 and 2 show an FCB and a CR respectively cut by the method according to the invention. As described hereinabove, the FCB 200 is an elongated body of a rectangular cross-sectional shape. By cutting the PCB 200 axially through opposing corners 201 and 202, it is possible to obtain two elongated split portions 203 of an L-shape in cross section. As is well known, the CR 300 comprises a blade 301 of a crisscross cross-sectional shape, and a velocity limiter 302. By axially cutting the blade 301 through a central portion after severing the velocity limiter 302 from the blade 301, it is possible to obtain two elongated split portions 303 of the CR 300 of an L-shape in cross section. The two L-shaped elongated split portions 203 and 303 are substantially similar in dimensions and shape. Thus, by stacking them in the same direction or alternately superposing one over another if necessary when they are stored, it is possible to greatly improve storing efficiency. FIGS. 3-5 shows the construction of the cutting apparatus according to the invention, and FIG. 6 shows in a systematic view of the cutting apparatus in its entirety. Referring to FIG. 3, the cutting apparatus is located on a floor of a storage pool 400 and comprises a base 1 extending over the liquid level of the pool 400, and a frame 2 extending downwardly from the base 1 along a wall surface of the pool 400 to be submerged in the water in the pool 400. The frame 2 has an upper cart 3 and a lower cart 4 which move vertically in elevatory movement while being guided by the frame 2. The upper and lower carts 3 and 4 are connected together and supported by a ball screw mechanism 5 connected to a drive motor 12 located on a undersurface of the base 1 for movement as a unit in elevatory movement as the drive motor 12 is actuated. The upper cart 3 has placed thereon a detachable support table 15 suitable for supporting both an FCB and a CR which, as shown in FIG. 5, is formed with an opening 21 for inserting the FCB 200 (CR 300) and has guide rollers 22 which hold, from the side of the lower cart 4, the FCB 200 (CR 300) suspended from an upper portion of the support table 15, to support it in a predetermined position. The lower cart 4 has mounted thereon clamp means 14 operated by an air cylinder for clamping an object to be cut or workpiece by gripping the FCB 200 or CR 300 at its lower end and securing same in position. The clamp means 14 also functions as a contact of a power source to supply power to the workpiece. A portion of the lower cart 4 at which the clamp means 14 is mounted is located at a higher elevation than the rest of the lower cart 4, so that it is possible to ascertain that cutting has been finished because the workpiece slightly moves downwardly when it is cut off. A member 19 is provided for guiding the velocity limiter 302 of the CR 300 toward a velocity limiter housing 18 after it is cut off. For cutting the FCB 200 and CR 300, the water jet cutting technique of the electrode melting type disclosed in Japanese Patent Laid-Open No. 78549/75 is suitable. Torches used in this technique are located as shown in FIG. 5, and two torches 6a and 6b are used when the FCB 200 is cut but only one torch 6a is used when the CR is cut. The torches 6a and 6b which are connected to wire supply means and water supply means on the base 1 through a wire supply line 16 and a water supply line 17 respectively are supported on a cutting torch support table 23 attached to a partition wall 7 for partitioning the pool 400. The cutting torch support table 23 is constructed such that it can be moved to outside in sliding movement to detach the cutting torches 6a and 6b when maintenance and repair are carried out. In order to avoid the dispersion in the pool 400 of drosses, gases and floating solid objects when a cutting operation is performed, the partition 7 serves the useful purpose. Referring to FIG. 3 again, the partition wall 7 has attached to its upper portion a door 13 and a lid 24 that can be moved only in one direction for opening and closing a space defined between the frame 2 and the partition wall 7 to allow the FCB 200 and CR 300 to be moved into or out of the space. The partition wall 7 has the velocity limiter housing 18 attached thereto which is provided with a lid 25 moved to an open position when it is desired to withdraw the velocity limiter 302 from the housing 18. Connected to an upper portion of the partition wall 7 is a gas recovery tube 27 which is connected to a gas recovery box 8 where the gases are mixed with air by means of a blower 28 and diluted before being discharged through an exhaust system. Means for collecting and diluting the gases, such as gas recovery tube 27 and blower 28, are mounted on the partition wall 7. A dross box 9 is located in a lower portion of the partition wall 7 for receiving drosses which freely move downwardly by gravity as they are produced by a cutting operation. A floating object recovery port 26 (see FIG. 4) is formed in the lower portion of the partition wall 7, and floating objects drawn together as a floating object recovery pump 10 is actuated is collected by a filter 11. The filter 11 is provided with a differential manometer 29 enabling the service life of the filter 11 to be checked at all times. Means for clearing the pool 400 of the floating objects, such as pump 10 and filter 11, are also mounted on the partition wall 7. An X-Y table 40 for the CR for cutting off the velocity limiter 302 of the CR 300 will be described by referring to FIGS. 7 and 8. The X-Y table 40 is constructed such that it can be detachably attached to the upper cart 3 after the support table 15 for supporting the FCB or CR is detached therefrom, and is composed of tables 41, 42 and 43 arranged in three stages. The first stage table 41 is movable along guide rails 46 on the second stage table 42 as it is driven by a drive motor 44 through a ball screw 50 for reciprocatory movement. The second stage table 42 is movable along guide rails 47 on the third stage table 43 as it is driven by a drive motor 45 through a ball screw 51 for reciprocatory movement. The guide rails 46 intersect the guide rails 47 at right angles. The first stage table 41 supports thereon clamp means 49 driven by an air cylinder 48. The process steps for cutting the FCB and CR by using the cutting apparatus of the aforesaid construction according to the invention will be described by referring to FIGS. 9-28. The process steps for cutting the FCB will first be described. Referring to FIGS. 9 and 10, a storage rack 101 for holding the FCB 200 is moved to the site of operation. Then, clips and spacers of the FCB 200 are removed by clip removing means 102 and spacer removing means 104 suspended from a jib crane 103 while the FCB 200 is in the FCB storage rack 101. Detailed description of these operations will be omitted because they are no different from those performed in the prior art. Meanwhile, the support table 15 for use with both the FCB and CR is attached to an upper portion of the upper cart 3 of the cutting apparatus. As shown in FIG. 11, the door 13 of the partition wall 7 of the cutting apparatus is brought to an open position, and the FCB 200 is moved downwardly from the upper portion of the upper cart 3 by an FCB handling tool 106 operated from an operation platform 105 as shown in FIG. 12. Thereafter, the door 13 is closed as shown in FIG. 13 and the upper and lower carts 3 and 4 are moved up and down as shown in FIG. 14 to perform cutting. Upon finishing cutting, the elongated split portion 203 of the FCB 200 is taken out by an elongated split portion handling tool 111 as shown in FIG. 15 and placed in an elongated split portion housing 127 as shown in FIG. 16. The process steps for cutting the CR will be described. Referring to FIG. 17, the CR 300 is moved by a CR handling tool 121 to a temporary mount 122 to which the X-Y table 40 for the CR 300 is attached by means of a table hanger 123 as shown in FIG. 18, and the CR 300 is clamped in place by the clamp means 49 (FIGS. 7 and 8) of the X-Y table 40. At this time, the support table 15 for the FCB and CR has been moved from the upper cart 3 of the cutting apparatus. Then, as shown in FIG. 19, the X-Y table 40 for the CR is lifted together with the CR 300 by the table hanger 123 from a CR storage rack 124 and moved into the space defined by the partition wall 7 after the door 13 is opened, to be mounted on the upper cart 3 of the cutting apparatus. At this time, the CR 300 is supported such that its lower end clears the lower cart 4. Thereafter, the upper and lower carts 3 and 4 are moved upwardly until a portion of the CR 300 at which the velocity limiter 302 is severed from the blade 301 is disposed at the same elevation as the cutting torches 6a and 6b. The drive motors 44 and 45 of the X-Y table 40 are suitably actuated to move the CR 300 horizontally to cut off the velocity limiter 302. The velocity limiter 302 severed from the blade 301 in this way is moved, as shown in FIG. 21, by the guiding and moving member 19 (FIG. 3) on the lower cart 4 into the velocity limiter housing 18. Referring to FIG. 22, the blade 301 of the CR 300 from which the velocity limiter section 302 is severed is detached together with the X-Y table 40 for the CR from the cutting apparatus, and moved to the temporary mount 122 for the CR as shown in FIG. 23. Then, the support table 15 for the FCB and CR is mounted on the upper cart 3 of the cutting apparatus by an operation shown in FIG. 24. Thereafter, the CR 300 on the temporary mount 122 for the CR is withdrawn from the X-Y table 40 for the CR as shown in FIG. 25 and inserted through an upper portion of the cutting apparatus and clamped in position by the clamp means 14 (FIG. 3) on the lower cart 3 (FIG. 26). The upper and lower carts 3 and 4 are moved up and down to cut the CR 300 axially through the center of a tie rod by means of the cutting torch 6a. After the cutting operation is finished, the elongated split portion 303 of the CR is withdrawn by the elongated split portion handling tool 111 as shown in FIG. 27, and an inserted in an elongated split portion housing 126 as shown in FIG. 28. The process steps for the cutting operations described hereinabove are shown tables as follows: TABLE 1 __________________________________________________________________________ Process Steps for Cutting FCB No. Item Equipment in Use Operation Site __________________________________________________________________________ 1 FCB moved Operation platform 105 From storage position FCB handling tool 106 to operation position (FCB storage rack 101) 2 Clip removing means 102 -- FCB storage rack 101 mounted 3 Clips removed Exclusive jib crane 103 Clip removing means 102 (FIG. 9) 4 Clips discarded Same as above and discarded containers 5 Clip removing means -- dismounted 6 Spacer removing means -- FCB storage rack 101 104 mounted 7 Spacers removed Exclusive jib crane 103 Spacer removing means 104 (FIG. 10) 8 Spacers discarded Same as above and dicarded vessels 9 Spacer removing means 104 -- dismounted 10 Partition wall door 13 of Cutting apparatus cutting apparatus opened from FCB storage 11 FCB moved Operation platform 105 rack 101 to cutting FCB handling tool 106 apparatus (FIG. 12) 12 Partition wall door 13 Cutting apparatus Cutting apparatus opened 13 FCB cutting commenced Cutting apparatus Cutting apparatus Circulation pump 10 actuated Blower 28 actuated Water supply pump actuated Wire supplied Upper and Lower carts driven 14 FCB cutting terminated (FIG. 14) (equipment deactuated) 15 Partition wall door 13 -- Cutting apparatus opened 16 FCB detached, moved Operation platform 105 From cutting and stored Elongated split portion apparatus to elongat- handling tool 111 ed split portion (FIG. 15) housing 107 17 Partition wall door 13 -- Cutting apparatus closed (FIG. 16) __________________________________________________________________________ (Note) In the operation tabulated hereinabove, the process steps 2-9 and 10-17 can be followed simultaneously. TABLE 2 __________________________________________________________________________ Process Steps for Cutting CR No. Item Equipment in Use Operation Site __________________________________________________________________________ 1 CR300 moved Operation platform 105 From storage position CR handling tool 121 to CR temporary (FIG. 17) mount 122 CR temporary mount 122 2 CR regripped Operation platform 105 CR temporary mount CR handling tool 121 X-Y table 40 for CR 122 switched to table Table hanger 123 (FIG. 18) hanger 123 3 Partition wall door 13 of -- Cutting apparatus apparatus opened 4 CR 300 mounted Operation platform 105 From CR temporary X-Y table 40 for CR mount 122 to cutting Table hanger 123 apparatus Cutting apparatus (FIG. 19) 5 Partition wall door 13 -- Cutting apparatus closed 6 Cutting of CR velocity Cutting apparatus Cutting apparatus limiter 302 commenced Circulation pump 10 actuated Blower 28 actuated Water supply pump actuated Wire supplied X-Y table 40 driven 7 Cutting of CR velocity (FIGS. 20 and 21) limiter 302 terminated (All equipment rendered inoperative) 8 Partition wall door 13 -- Cutting apparatus opened (FIG. 22) 9 CR temporarily removed Operation platform 105 From cutting appa- and moved X-Y table for CR 40 ratus to CR temporary Table hanger 123 mount 122 (FIG. 23) 10 FCB/CR support table 15 Operation platform 105 From temporary mount installed FCB/CR support table 15 122 to cutting Table hanger 123 apparatus Cutting apparatus (FIG. 24) 11 CR regripped Operating platform 105 Cutting apparatus Table hanger 123 CR handling tool 21 switched to CR handling CR temporary mount 122 tool 121 (FIG. 25) 12 CR reinstalled Operation platform 105 From CR temporary CR handling tool 21 mount 122 to Cutting Cutting apparatus apparatus (FIG. 26) 13 Partition wall door 13 -- Cutting apparatus closed 14 Cutting of CR Commenced Cutting apparatus Cutting apparatus Circulation pump 10 actuated Blower 28 actuated Water supply pump actuated Wire supplied Upper and lower carts 3 and 4 driven 15 Cutting of CR terminated (All equipment rendered inoperative) 16 Partition wall door 13 -- Cutting apparatus 17 CR removed, moved and Operation platform 105 From cutting stored Elongated split portion apparatus to elongat- handling tool 111 ed split portion (FIG. 27) housing 126 18 Partition wall door 13 -- Cutting apparatus closed (FIG. 28) __________________________________________________________________________ In the embodiment shown and described hereinabove, the FCB and CR can be cut into elongated split portions of an L shape in cross section. Thus, by storing these elongated split portions in the housing rack as shown in FIG. 28, storing efficiency can be improved from about fourfold to sevenfold as compared with storing the FCB and CR in their original shapes. The cutting operation for cutting the FCB and CR can be performed in the water by remote control by means of the same cutting apparatus. Combined with a shortening of time required for performing the cutting operation made possible by a reduction in the length of the cutting line, this has improved operation efficiency while reducing the risk of exposure of the operator to radiation. In the embodiment shown and described hereinabove, the cutting has been described has being performed by a jet cutting technique. This is because this cutting technique best serves the purpose and suits the condition. However, the invention is not limited to this specific cutting technique when the method according to the invention is carried into practice, and any other suitable cutting technique may be used without departing from the scope of the invention. When the velocity limiter 302 of the CR is severed from the blade 301, the cutting torch 6a can be moved horizontally. When this is the case, the X-Y table 40 for the CR can be eliminated, by means should be provided for moving the cutting torch 6a and lines connected to the cutting torch 6a should be rendered flexible. The cutting apparatus shown and described hereinabove may be simplified as a cutting apparatus exclusively for cutting the CR by doing without the function for cutting the FCB for which a solution has already been found. FIG. 29 shows another embodiment of the cutting apparatus in conformity with the invention which is essentially no different from the embodiment in a condition in which the X-Y table 40 for the CR is attached to the upper cart 3 of the cutting apparatus. Referring to FIG. 30, the CR 300 is formed with a square opening at an upper portion of the velocity limiter 302 which is of a crisscross cross-sectional shape. When cutting is performed, the CR 300 is clamped on to the table 40 by clamp means and moved, as shown in FIG. 31 in an X-Y direction together with the table 40, to thereby cut each of portions of the blade 301 of the crisscross shape. At this time, the two cutting torches 6a and 6b cut two portions each of the blade 301 of the crisscross shape. After the velocity limiter 302 is cut off, the center of the blade 301 of the crisscross shape is moved toward the torch 6a and cutting is effected by feeding a cutting material to the torch 6a. In this embodiment, the need to replace the support table 15 for both the FCB and CR by the X-Y table 40 exclusively for the CR is eliminated, thereby improving the operability of the CR cutting operation. When the cutting method according to the invention is used, the FCB and CR can be cut into split portions of a substantially similar shape that suits storing by effecting cutting along a substantially short cutting line. In the cutting apparatus according to the invention described hereinabove and shown in the drawings, the FCB and CR can be cut in the water by remote control into portions of a substantially similar shape or the CR can be cut at least into portions of an L-shape in cross section.
	abstract	A nuclear fuel assembly having a bottom nozzle with protrusions that extend from the upstream (lower or fluid entry) and downstream (upper or fluid exit) side of a horizontally supported perforated flow plate. The protrusions have a funnel-like shape that gradually decreases the lateral flow area on the upstream side of the perforated flow plate and gradually increases the lateral flow area on the downstream side of the perforated plate. The protrusions on the downstream side are preferably recessed to accommodate the ends of the fuel rods.
048448397	summary	BACKGROUND OF THE INVENTION This invention relates generally to treatment of hazardous wastes, and particularly to the in situ analysis of contaminants and treatment of hazardous waste disposal sites. In various industries it has been common practice to discharge aqueous, dry or semi-solid waste chemicals or radioactive materials into ponds, which waste material after a period of time tends to become pasty or solid due to the evaporation of water therefrom. After the waste material has assumed a substantially solid state, dry particles thereof that are exposed to the ambient atmosphere tend to become airborne and are a health hazard. In addition, the toxic material in such an impoundment tends to leach into the soil adjacent thereto as well as contaminate ground water. In the past, various methods have been proposed to lessen the danger inherent to such hazardous impounded materials, but such methods have not been effective. One such method includes the removal of a portion of the waste material, and erecting a concrete or betonite isolation wall in an attempt to contain the balance of the impounded material. Also it has been proposed to excavate the impounded material and transport the same to existing or newly built disposal sites that may or may not be sealed with a liner. However, when either of the above identified methods is used, the impounded material is subjected to mechanical action that renders a portion of it airborne with consequent health hazards. SUMMARY OF THE INVENTION A major object of the present invention is to provide an insitu method treating impounded toxic and radioactive materials, and one that transforms the impounded material into a solid substantially insoluble mass from which toxic materials will not leach out into adjoining land or water table, nor will any substantial surface particles of the mass become airborne even when the mass is subjected to elements of weather. Another object of the invention is to supply a method of treating hazardous impounded materials in such a manner that the danger of transporting the same over public highways is eliminated. A further object of the invention is to furnish a method of treating hazardous waste material that is more rapid to carry out and less dangerous to the personnel involved than prior art methods that attempted to attain the same results. A further object of the present invention is to treat an impoundment containing radioactive material to minimize the escape of radon gas therefrom and to render radioactive compounds in the impoundment insoluble to the extent that they will not leach out from the treated impoundment. The in situ impoundment treating an assembly of adjacently disposed, power driven, rotating cutter-injectors supported on the lower ends of vertically disposed hollow kelly stems or drill pipe that may move up and down. The assembly is supported by a boom or the like that extends outwardly from a power driven vehicle such as a tractor pipelayer crane or the like. The boom supported assembly may be extended out over the impoundment a substantial distance, while the power driven vehicle remains on solid land adjacent the impoundment. The assembly cutter-injectors are sequentially lowered into adjacent areas or stations of the impoundment while rotating to homogenize the hazardous waste material therein to a desired depth. After the desired depth has been reached, the cutter-injectors are moved upwardly while rotating, and simultaneously treatment chemicals for the hazardous waste material are injected therefrom. The depth to which the cutter-injectors are moved downwardly and then raised upwardly as above described produce different results. If the cutter-injectors are moved downwardly and then upwardly in only the land beneath the impoundment, an impervious liner to contain the hazardous waste may be formed without removing the hazardous material from the impoundment. By lowering the cutter-injectors to the bottom of the impoundment and the raising them upwardly, the entire contents of the impoundment may be transformed to an inert insoluble mass that has substantial strength, and may remain in place. Should the cutter-injectors be moved downwardly below the surface of the impoundment and then upwardly, a rigid cap of a desired thickness may be placed over the hazardous waste in the impoundment that will bear a substantial load and prevent particles of the hazardous waste becoming airborne. Released odors or toxic vapors that escape from the hazardous waste material during the treatment thereof, and that are not destructed by the treatment of chemicals, are reeded to the surface of the impoundment and collected for scrubbing within a confined space defined within a protective collection shroud that extends over the treating area. The multi-head rotating cutter-injectors are so spaced that the circular area through which they rotate overlap to assure complete mixing of the hazardous waste material being treated and the treatment chemicals therewith. Engineering values of the treated material may be predetermined by bench testing representative samples or are taken periodically to determine shear compression, and the load bearing strength of the treated material, and on the basis of these results the rate of injection of the treatment chemicals is varied to obtain treated waste having desired physical characteristics. The specific treatment chemical used will depend on the composition of the hazardous waste material which is determined by an analysis thereof. Waste materials found in impoundments include cyanide waste; toxic metals; metal plating waste; inorganic compounds that may be acid or base solvents and reactive sludges; pestiside compounds; halogenate and nonhalogenate volatile organics, transformed from oil and the like. Impoundments may also contain drilling muds and fluids; oily waste sludges; pasty sludges; pharmaceutical, agricultural and municiple waste water sludges; and low level radioactive waste and uranium mill tailings. The specific treatment chemicals selected for use at a particular impoundment can result in aqueous waste being dewatered and the volume thereof accordingly reduced. Free standing liquids are blended with the solid fraction to eliminate the removal of the liquid phase. Toxic substances in the impoundment are transformed into a stable, inert, insoluble sediment which may be solidified into a nonpermeable matrix. Waste odors or toxic vapors arising during the impoundment treatment are either chemically destroyed, or scrubbed to remove objectionable components prior to being released to the ambient atmosphere. Impounded hazardous waste are not removed from or surfaced on the impoundment during the present treatment method and exposure of workmen to toxic emitions is minimal or completely eliminated. Aqueous waste immediately after treatment are transformed into a dry, earthlike friable material that may be handled safely and transported by use of conventional earth moving equipment. The major chemical use in carrying out the insitu treatment to immobilize, detoxify, destroy or precipitate the toxic substances and transform them into an insoluble state as well as into a highly impermeable and dense matrix, includes limes in form of calcium oxide, calcium hydroxide and milk of lime and suitable clay products. Other chemical additives include a wide range of oxidizing additives of which sodium bisulfate, sodium hydrosulfite, chlorine dioxide, hydrogen peroxide, ozone and acids and alkaline products in various forms are examples. Other chemicals dependent on the composition of the waste material.
043671969	claims	1. A neutronic reactor comprising a core consisting of a plurality of elongated, parallel fuel elements, perpendicular to a midplane of the reactor, containing thermal-neutron-fissionable material and provided with an inlet at one end and an outlet at the other end for coolant, and a plurality of elongated control elements, parallel to each other and to the fuel elements, each consisting of a housing, and a group of control rods which are separately translatable within their housing, each of said groups containing at least one control rod which is substantially shorter than the fuel elements and is located so that its midpoint is downstream, with respect to the flow of coolant through the fuel elements, from the said midplane of the reactor, the remainder of the control rods within a group being of substantially the same length as the fuel elements, said fuel elements and control elements being symmetrically disposed within a body of moderator material. 2. A neutronic reactor according to claim 1 wherein the control elements are arranged in concentric rings about a central control element. 3. A neutronic reactor according to claim 2 wherein at least half the control rods within each control element are constructed of an aluminum-lithium alloy in such a way that they will not absorb all incident neutrons and at least one of the control rods is constructed of cadmium in such a way that it will absorb all incident neutrons. 4. A neutronic reactor according to claim 3 wherein each control element contains a control rod at its center and a plurality of control rods annularly disposed thereabout and the central rod and one of the outer rods are the said substantially shorter control rods. 5. A neutronic reactor according to claim 4 wherein each control element contains two cadmium control rods of the same length as the fuel elements, three lithium-aluminum control rods of the same length as the fuel elements, and two short lithium-aluminum control rods. 6. A neutronic reactor according to claim 5 wherein the fuel elements are vertically disposed and the flow of water past the fuel elements is from top to bottom and the substantially shorter control rods are located with their midplanes located below the midplanes of the fuel elements. 7. A neutronic reactor comprising a core consisting of a plurality of elongated, parallel fuel elements containing thermal-neutron-fissionable material, and a plurality of elongated control elements, parallel to each other and to the fuel elements, each consisting of a housing and a group of control rods separately translatable within their housing, said control elements being symmetrically arranged in concentric rings about a central control element within a body of a moderator material, all control elements within each concentric ring being connected in gangs, means for operating all control rods occupying the same position in each control element within a ring simultaneously and for sequentially withdrawing the said gangs of control rods from the reactor.
047073306	description	DETAILED DISCLOSURE The present invention relates to zirconium metal matrix-silicon carbide compositions and to nuclear reactor components formed from such compositions. Nuclear reactor components comprise, among others, fuel rod cladding, rod guide thimbles, grids and channels, used in nuclear fuel assemblies. Such assemblies are illustrated in FIGS. 1 to 3. In FIG. 1, a fuel assembly 1 for a boiling water reactor comprises a generally square shaped flow channel 3 having a bottom inlet nozzle 5 and upper outlet section 7, usually having a handle 9 for placement in a reactor. Contained within the channel 3 are a plurality of fuel rods 11 and interspersed rod guide thimbles 13, positioned in arrays about a cruciform shaped divider 15. The fuel rods 11 comprise hollow sealed tubular rods that contain the nuclear fuel, and the rod guide thimbles comprise tubular members sized to accept control rods for use in controlling the nuclear reaction as desired. The array of fuel rods 11 and rod guide thimbles 13 are stabilized in a spaced relationship to each other by means of grids 17, which are in the form of thin metal strips interwoven in an egg-crate configuration, the interwoven strips having openings in which separate fuel rods and guide thimbles are located. A useful type of grid structure is illustrated in U.S. Pat. No. 3,920,515, assigned to the assignee of the present invention, the contents of which are incorporated by reference herein. In the type of grid structure illustrated in U.S. Pat. No. 3,920,515, and in FIGS. 2 and 3 of the present application, the grids 17 have springs 19 and dimples 21 on the grid straps 23 which project into each opening to properly support and cool the fuel rods near the grid-fuel rod interface. During operation of the reactor, liquid coolant flows upwardly around the fuel rods and through the openings in the grids and discharge at the upper end of the fuel assembly either in a partially vaporized state in boiling water reactors, or in essentially all-liquid state in pressurized water reactors. The nuclear reactor components of the present invention are produced from a composite that is formed by homogeneous mixing silicon carbide (SiC) whiskers in a zirconium metal matrix and forming the components from said composite. The metal matrix of the composite can comprise zirconium metal or an alloy or zirconium, containing less than about 5 percent by weight of alloying elements, usable in nuclear reactors. Such zirconium alloys contain additional elements which increase the mechanical properties of zirconium metal or the corrosion resistance of zirconium metal. The elements that are used in the formation of such alloys include niobium, oxygen, tin, iron, chromium, nickel, molybdenum, copper, vanadium and the like. Especially useful alloys are those known as Zircaloy-2 and Zircaloy-4. Zircaloy-2 contains, by weight, about 1.2-1.7 percent tin, 0.07-0.20 percent iron, 0.05-0.15 percent chromium, and about 0.03 to 0.08 percent nickel, the balance being zirconium, while Zircaloy-4 contains, by weight about 1.2-1.7 percent tin, 0.12 to 0.18 percent iron, and 0.05 to 0.15 percent chromium, the balance being zirconium. According to the present invention, the matrix of zirconium metal or alloy has silicon carbide whiskers homogeneously distributed throughout the matrix. Such silicon carbide whiskers are known and commercially available. The silicon carbide whiskers are present in the zirconium metal or alloy in an amount of about 10 to 40 volume percent of the composite. Less than about 10 percent by volume of silicon carbide whiskers would probably not be enough to give the structural benefits that are desired, while an amount in excess of about 40 percent by volume would be too high an amount of silicon carbide whiskers and would result in a material that could not be sufficiently thermally or mechanically worked, such as by extrusion or pilgering to produce the nuclear reactor components in the desired shapes and sizes. The silicon carbide whiskers are of a size of about 0.5 microns in diameter and of a length of between about 50 to 100 microns in length, which will enable intimate mixing of the silicon carbide whiskers and powdered zirconium or zirconium alloys and production of a matrix of zirconium or a zirconium alloy with the silicon carbide whiskers homogeneously distributed therethrough. An example of usable whiskers, which are commercially available, are silicon carbide whiskers sold about the trademark SILAR, by Arco Metals Company. In formation of the composite, a zirconium metal or alloy is provided in powdered form, as a finely divided particulate material less than about 325 mesh, U.S. Standard Sieve. To the powdered zirconium metal or alloy, the silicon carbide whiskers of a size previously defined are added and the two components mixed together to give a homogeneous mixture. The mixture is then formed into billets such as by vacuum hot-pressing, or other conventional processing. The hot-pressing is effected on the homogeneous powder mixture to essentially one hundred percent of theoretical density. Conventional vacuum hot-pressing techniques to achieve such a density would be used. Typically, billets of a size of between 500 to 2000 pounds would be formed, which composite billets can then be processed to form the nuclear reactor components. The fabrication of the nuclear reactor components from the present composite material would generally use the conventional fabrication steps for formation of such components from conventional zirconium metal or alloys. In the formation of fuel cladding, the tubular shells used to contain the nuclear fuel, or rod guide thimbles, the billet of composite material would be forged and/or extruded to a rod shape. A central axial bore would then be drilled in the rod and the resultant tube shell extruded and then pilgered to the final desired size. In the fabrication of channels or grid strip material, the billet of composite material would be forged and then rolled to the desired thickness. Since the fabrication steps from the composite billets would be substantially identical to those used in the formation of tubular cladding, thimbles, channels or grid strips used when forming such components from conventional zirconium metal or alloy starting materials, conventional existing metal working and fabricating equipment could be used. It is believed that the present composites of zirconium or zirconium alloy matrix with homogeneously distributed silicon carbide whiskers therein would have an elastic modulus and strength approximately double existing components without such silicon carbide whisker inclusion. Such improved properties would vastly enhance reliability of the nuclear reactor components. Alternatively, components fabricated from the compsites of the present invention, with properties equal to existing components, could be formed having a decreased thickness which would result in a fuel cycle cost savings. The ability to use thinner structural components in boiling water reactors, such as in channels and grids would also increase the flow through the core and reduce the pressure drop across the core which would enable better efficiency and use of smaller reactor unit size. Under certain conditions, it may be desirable to provide a thin layer of zirconium or zirconium alloy (without the silicon carbide whiskers present in said layer) on either one or both surfaces of the zirconium or zirconium alloy composite for enhanced corrosion resistance. The zirconium alloys of such a layer would be selected from those alloys described for use in the composite. Generally, the thickness of such a layer would be about 15 percent or less of the thickness of the composite.
051788217	claims	1. A boiling water nuclear fission reactor having a standby supply of coolant water for submerging the heat producing fissionable fuel core of the reactor during any periods of inadvertent loss of coolant accidents, consisting essentially of the combination of: a nuclear reactor pressure vessel having an inlet for supplying circulating coolant feedwater, and an outlet for steam discharge therefrom; a core of fissionable fuel for producing heat to generate steam from coolant water located centrally in a lower region of the reactor pressure vessel and spaced inward therefrom, said fuel core normally being submerged in circulating coolant water; an open ended cylindrical shroud encircling the fuel core and extending a distance both above and below the fuel core to provide a core upper plenum area above the fuel core and a core lower plenum area below the fuel core, said cylindrical shroud being spaced inward away from the reactor pressure vessel to provide an annular area for a coolant flow path between the inside of the pressure vessel and the outside of the open ended cylindrical core shroud whereby coolant feedwater supplied by the vessel inlet along with recirculating liquid water coolant can flow downward from the upper region of the reactor pressure vessel about the exterior of the fuel core surrounding shroud and then around the shroud bottom and back upward through the heat producing fuel core for submerging same and absorbing heat energy to cool the fuel core and generate steam for discharge from the vessel outlet to perform work; and at least one elongated chamber having an open lower end and closed upper end provided with a bleed vent for venting gaseous contents out from the chamber, positioned generally vertically within the annular area between the reactor pressure vessel and shroud surrounding the fuel core, whereby the chamber can fill from the circulating coolant water and contain liquid coolant water during normal reactor operation and upon the inadvertent occurrence of a reduced level of liquid water coolant for submerging the fuel core due to a loss of coolant accident resulting in a depressurization of the reactor, steam is flashed within the liquid contents in the chamber which forces the contained coolant water from the chamber into the reactor vessel about the fuel core to augment cooling of the same. at least one elongated tubular chamber having an open lower end and closed upper end provided with a bleed vent for venting gaseous contents out from the tubular chamber, positioned generally vertically within the annular area between the reactor pressure vessel and shroud surrounding the fuel core and extending from above to below the position of the fuel core, whereby the chamber can fill and contain liquid water coolant during normal reactor operation and upon the inadvertent occurrence of a reduced level of liquid coolant water for submerging the fuel core due to a lose of coolant accident resulting in a depressurization of the reactor, steam thereby is flashed within the liquid contents in the tubular chamber which forces the contained coolant water from the open lower end of the tubular chamber out into the reactor vessel about the fuel core to augment cooling of the same. a nuclear reactor pressure vessel having an inlet for supplying circulating coolant feedwater into the reactor pressure vessel and to a fuel core therein and an outlet for steam discharge therefrom; a core fissionable fuel for producing heat to generate steam from coolant water located centrally in a low region of the reactor pressure vessel and spaced inward therefrom, said fuel core normally being submerge din circulating coolant water; an open ended cylindrical shroud encircling the fuel core and extending a distance both above and below the fuel core to provide a core upper plenum area above the fuel core and a core lower plenum area below the fuel core, said cylindrical shroud being spaced inward away from the reactor pressure vessel to provide an annular area for a coolant flow path between the inside of the pressure vessel and the outside of the open ended cylindrical core shroud whereby coolant feedwater supplied by the vessel inlet along with recirculating liquid water coolant can flow downward from the upper region of the reactor pressure vessel about the exterior of the fuel core surrounding shroud and then around the shroud bottom and back upward through the heat producing fuel core for submerging same and absorbing heat energy to cool the fuel core and generate steam for discharge from the vessel outlet to perform work; and a generally vertical elongated chamber of annular cross sectional configuration having an open lower end and closed upper end provided with a bleed vent for venting gaseous contents out from the annular chamber, positioned generally vertically within the annular area between the reactor pressure vessel and the shroud encircling around the shroud surrounding the fuel core and extending therein from above to below the position of the fuel core, whereby the chamber can fill and contain liquid coolant water during normal reactor operation and upon the inadvertent occurrence of a reduced level of liquid coolant water for submerging the fuel core due to a loss of coolant accident causing a depressurization of the reactor, steam is flashed within the liquid contents in the annular chamber forcing the contained coolant water from the chamber into the reactor vessel about the fuel core to augment cooling of the 2. The boiling water nuclear reactor of claim 1, wherein a multiplicity of generally vertical elongated chambers are positioned in a spaced apart array around the annular area between the reactor pressure vessel and the shroud surrounding the fuel core. 3. The boiling water nuclear fission reactor of claim 1, where the generally vertical elongated chamber is tubular in configuration. 4. The boiling water nuclear fission reactor of claim 1, wherein the generally vertical elongated chamber is annular in configuration encircling around the shroud surrounding the fuel core within the annular area between the reactor pressure vessel and the shroud. 5. A boiling water nuclear fission reactor having a standby supply of coolant water for submerging the heat producing core of fissionable fuel of the reactor during any periods of inadvertent loss of coolant accidents, consisting essentially of the combination of: a nuclear reactor pressure vessel having an inlet for supplying circulating coolant feedwater into the reactor pressure vessel and to a fuel core therein and an outlet for steam discharge therefrom; a core of fissionable fuel for producing heat to generate steam from coolant water located centrally in a lower region of the reactor pressure vessel and spaced inward therefrom, said fuel core normally being submerged in circulating coolant water; an open ended cylindrical shroud encircling the fuel core and extending a distance both above and below the fuel core to provide a core upper plenum area above the fuel core and a corer lower plenum area below the fuel core, said cylindrical shroud being spaced inward away from the reactor pressure vessel to provide an annular area for a coolant flow path between the inside of the pressure vessel and the outside of the open ended cylindrical core shroud whereby coolant feedwater supplied by the vessel inlet along with recirculating liquid water coolant can flow downward from the upper region of the reactor pressure vessel about the exterior of the fuel core surrounding shroud and then around the shroud bottom and back upward through the heat producing fuel core for submerging same and absorbing heat energy to cool the fuel core and generate steam for discharge from the vessel outlet to perform work; and 6. The boiling water nuclear fission reactor of claim 5, wherein a multiplicity of generally vertical elongated tubular chambers are positioned in a spaced apart array around within the annular area between the reactor pressure vessel and the shroud surrounding the fuel core. 7. The boiling water nuclear fission reactor of claim 5, wherein the bleed vent comprises a capillary tube for the venting of any gases from the interior of the elongated tubular chamber. 8. The boiling water nuclear fission reactor of claim 5, wherein the bleed vent in the closed upper end of the elongated tubular chamber is in fluid communicated through a duct with the core upper plenum area whereby any gases from the interior of the elongated tubular chamber are vented therefrom out into the core upper plenum area. 9. The boiling water nuclear fission reactor of claim 5 wherein the bleed vent in the closed upper end of the elongated tubular chamber is in fluid communication through a duct with a source of fluid pressure external to the reactor pressure vessel for forcing contained coolant water from the open lower end of the tubular chamber out into the reactor vessel about the fuel core to augment cooling the same. 10. A boiling water nuclear fission reactor having a standby supply of coolant water for submerging the heat producing core of fissionable fuel of the reactor during any periods of inadvertent loss of coolant accidents, consisting essentially of the combination of: 11. The boiling water nuclear fission reactor of claim 10, wherein the generally vertical chamber of annular cross sectional configuration is adjoined with the reactor pressure vessel which provides a wall portion of the chamber. 12. The boiling water nuclear fission reactor of claim 10, wherein the bleed vent comprises a capillary tube for the venting of any gases from the interior of the annular chamber. 13. The boiling water nuclear fission reactor of claim 10, wherein the bleed vent in the closed upper end of the annular chamber is in fluid communication through a duct with the core upper plenum area whereby any gases from the interior of the annular chamber are vented therefrom out into the core upper plenum area. 14. The boiling water nuclear fission reactor of claim 10, wherein the bleed vent in the closed upper end of the annular chamber is in fluid communication through a duct with a source of fluid pressure external to the reactor pressure vessel for forcing contained coolant water from the open lower end of the annular chamber out into the reactor vessel about the fuel core to augment cooling of the same.
	claims	1. A method comprising:constructing an index of sensors;clustering sensors together to form groups of sensors in a hierarchal structure, wherein the formation of the groups of sensors is based on at least one or more criteria including: sensor type, sensor location, and sensor schema;responsive to a query requesting sensor data, identifying via the index a random subset of sensors, from the groups of sensors, from which to collect the sensor data, wherein the random subset of sensors exhibits a spatial distribution similar to that of a full set of the sensors, wherein the identifying comprises:ascertaining a target size of a number of sensors to be read;splitting the target size into smaller portions; anddistributing the smaller portions across the index of sensors; andobtaining the sensor data from the subset of sensors, wherein the sensor data includes sensor readings and metadata, the metadata comprising a schema that defines how the sensor readings are formatted. 2. A method as recited in claim 1, wherein the constructing comprises creating a data tree, wherein the structure of the data tree includes a plurality of nodes arranged in a hierarchy of layers, the nodes including leaf nodes that cache sensor data captured from associated sensors and interior nodes that aggregate the sensor data of the leaf nodes dependent therefrom. 3. A method as recited in claim 2, wherein the data tree is configured as a Collection R-tree being a spatial index based on a R-Tree structure. 4. A method as recited in claim 2, wherein the aggregation by the interior nodes comprises dynamically selecting leaf nodes to aggregate using a pixel-based clustering algorithm that groups sensors corresponding with an “n”×“n” block of pixels, wherein “n” is a system parameter. 5. A method as recited in claim 1, wherein the target size is defined by a user. 6. A method as recited in claim 1, wherein the distributing comprises excluding any sensors that would fail to contribute to the sensor data requested in the query and allocating larger portions of the target size to other parts of the index. 7. A method as recited in claim 1, further comprising presenting the sensor data in a user interface in response to one or more of: the query, a region selection, a sensor type selection, a sensor density selection, a format selection, a sensor data newness designation, and a saved view selection. 8. A computer architecture of one or more computing devices, where the one or more computing devices has memory and one or more processors operatively coupled to the memory, the computer architecture comprising:a web portal hosted on at least one computing device, the web portal collecting sensor readings and metadata of sensors, wherein the web portal also indexes the metadata into an index structure, the metadata comprising a schema that defines how the sensor readings are formatted, wherein the web portal clusters sensors together to form groups of sensors in a hierarchal structure, wherein the groups of sensors are formed based on at least one or more criteria including: sensor type, sensor location, and sensor schema;a database to store the index structure and to cache sensor data obtained from the sensors; andthe web portal being configured to receive a query for specified sensor data and to identify, using the index structure, a random subset of sensors, from the groups of sensors, from which to collect the sensor data, wherein the random subset of sensors exhibits a spatial distribution similar to that of a full set of the sensors. 9. A computer architecture as recited in claim 8, wherein the index structure comprises a tree structure with a plurality of nodes arranged in plural layers, the nodes including leaf nodes that cache sensor data captured from associated sensors and interior nodes that aggregate the sensor data of the leaf nodes dependent therefrom. 10. A computer architecture as recited in claim 9, wherein the index structure further comprises:tables associated with the layers in the tree structure, the tables providing associations between nodes in different layers; andone or more data caches to store the sensor data. 11. A computer architecture as recited in claim 8, wherein the web portal comprises:an indexing module to create the index structure as a tree structure with a plurality of nodes arranged in plural layers in a hierarchical manner, the nodes including leaf nodes that cache sensor data captured from associated sensors and interior nodes that aggregate the sensor data of the leaf nodes dependent therefrom;a query processing module to determine, based on the query, the subset of sensors from which to capture sensor data being requested in the query; anda data acquisition module to collect the sensor data from the subset of sensors. 12. One or more computer-readable media comprising computer executable instructions that, when executed on one or more processors, perform acts comprising:generating an index structure comprising a plurality of nodes that are associated with one or more sensors in at least one sensor network, the nodes including leaf nodes that cache sensor data captured from associated sensors and interior nodes that aggregate the sensor data of the leaf nodes dependent therefrom;receiving a query for sensor data;using the index structure to identify a random subset of sensors from which to collect the sensor data in response to the query, wherein the random subset of sensors exhibits a spatial distribution similar to that of a full set of the sensors, wherein identify a random subset of sensors comprises:ascertaining a target size of a number of sensors to be read;splitting the target size into smaller portions; anddistributing the smaller portions across the index of sensors; andacquiring the sensor data from the random subset of sensors, wherein the sensor data includes sensor readings and metadata, the metadata comprising a schema that defines how the sensor readings are formatted. 13. One or more computer-readable media of claim 12, wherein the plurality of nodes are arranged in hierarchical layers generated by clustering the nodes from a bottom layer to an upper layer. 14. One or more computer-readable media of claim 12, wherein the index structure further comprises:tables associated with the layers in the tree structure, the tables providing associations between nodes in different layers; andone or more data caches to store the sensor data. 15. One or more computer-readable media of claim 12, wherein the query includes a target number of sensors from which to capture the sensor data, and the identified subset contains no more than the target number of sensors. 16. One or more computer-readable media of claim 15, wherein the target number of sensors is based on a target size of the sample sensor data defined by a user. 17. One or more computer-readable media of claim 16, further comprising computer executable instructions that, when executed, perform an additional act comprising segregating a target size of the sample sensor data into smaller portions and distributing the smaller portions across the index structure so that groups of sensors in the subset return sensor data that, when combined across the groups, provides sufficient sensor data to satisfy the number of sensors to be read. 18. One or more computer-readable media of claim 17, further comprising computer executable instructions that, when executed, perform additional acts comprising:eliminating sensors from the subset of sensors that do not possess readings that contribute to the sensor data;examining a cache table corresponding to each node to determine whether current data exists that satisfies the query;determining whether additional samples are needed; andredistributing portions of the target size to other sensors. 19. One or more computer-readable media of claim 12, wherein the acquiring comprises retrieving the sensor data from one or more caches of the index structure. 20. One or more computer-readable media of claim 12, wherein the acquiring comprises probing the sensors for updated sensor data. 21. A computer system, comprisingone or more processors; andone or more computer-readable media of claim 12, wherein the computer-executable instructions are executed on the one or more processors.
	description	The present invention refers generally to a cermet matrix composition for nuclear fuel for use in in nuclear reactors, such as water reactors and fast reactors. More specifically, the present invention refers to a nuclear fuel pellet for a nuclear reactor, comprising a metallic matrix and ceramic fuel particles of a fissile material dispersed in the metallic matrix. The invention also refers to a fuel rod, and to a fuel assembly for use in a nuclear reactor. Non-active metallic systems, such as Mo, have been suggested as compounds of the matrix to hold fissile material in nuclear fuel pellets. US 2015/0294747 discloses a method of fabricating a cermet metal fuel matrix fuel pin. The fuel pin may comprise ceramic particles of spent nuclear fuel, thorium oxide, americium oxide, and combinations of these in a metallic matrix from a feedstock. The metallic matrix may include uranium, zirconium, transuranics, molybdenum, reprocessed metal fuel. An object of the present invention is to provide a new matrix material for cermet fuel, and a new ceramic-metallic dual phase fuel. In particular, it is aimed at an improved matrix permitting the nuclear fuel pellet to fulfil the requirements of so called accident tolerant fuels, ATF. This object is achieved by the nuclear fuel pellet initially defined, which is characterized in that that the metallic matrix is an alloy consisting of the principle elements U, Zr, Nb and Ti, and of possible rest elements, wherein the concentration of each of the principle elements in the metallic matrix is at the most 50 molar-%. Such a material of the metallic matrix comprising a four principle elements, and possibly a minor amount of rest elements, i.e. a so called balance, will have the following properties: a high thermal conductivity, low swelling (solid swelling due to fission processes and gaseous swelling due to fission gas bubble formation), similar thermal expansion, good high temperature corrosion behaviour in steam and with cladding materials, high ductility, and suitably low thermal neutron cross-section. These properties of the metallic matrix makes the nuclear fuel pellet suitable as an accident tolerant fuel, ATF. Thanks to the low overall swelling, the nuclear fuel pellet may be contained in any suitable cladding tube to form a fuel rod. The cladding tube may for instance be made of silicon carbide, or of a zirconium based alloy. No additional encapsulation of the nuclear fuel pellet than the cladding tube is needed. Thanks to the presence of uranium, the metallic matrix may be an active fissile matrix. The advantages of an active fissile matrix include lower losses in the uranium content compared to standard sphere packed fuel, and to a non-active matrix. According to an embodiment of the invention, the concentration of each of the principle elements in the metallic matrix is at least 5 molar-%. According to an embodiment of the invention, the alloy is a single phase alloy, or near single phase alloy with precipitates constituting less than 5 volume-% of the alloy. The high ductility of the metallic matrix of a single phase alloy is increased compared to single phase BCC metals. The increased ductility results in an improved Pellet-Cladding Interaction, PCI, of the nuclear fuel pellet in a cladding tube. According to an embodiment of the invention, the alloy is a high entropy alloy, HEA, which has four principle elements, no one of which is dominating. These single phase alloys are named high entropy alloys, HEAs, because their liquid or random solid solution states have significantly higher mixing entropies than those in conventional alloys. Thus, the effect of entropy is much more pronounced in high entropy alloys. According to an embodiment of the invention, the alloy is U5-6Zr3-4NbTi. This single phase alloy forms a possible high entropy alloy for the matrix of the nuclear fuel pellet. U5-6Zr3-4NbTi has a uranium density of approximately 9.7 g/cm3, which is similar to the uranium density of UO2. According to an embodiment of the invention, the alloy has a body centred cubic structure, BCC. According to an embodiment of the invention, the total concentration of the possible rest elements in the metallic matrix is at the most 5 molar-%, preferably at the most 4 molar-%, more preferably at the most 3 molar-%, most preferably at the most 2 molar-%. According to an embodiment of the invention, the ceramic fuel particles are uniformly dispersed in the matrix. According to an embodiment of the invention, the ceramic fuel particles comprise at least one fissile material selected from the group of actinide oxide, actinide nitride, actinide silicide and actinide carbide. According to an embodiment of the invention, the ceramic fuel particles comprise at least one fissile materials selected from the group of UO2, U3Si2, U3Si, USi, UN, PuO2, Pu3Si2, Pu3Si, PuSi, PuN, ThO2, Th3Si2, Th3Si, ThSi and ThN. All of these fissile materials are suitable for being dispersed in the single phase alloy of the nuclear fuel pellet. The single phase alloy of the nuclear fuel pellet will protect the ceramic particles from any detrimental mechanical or chemical effect during operation of the nuclear reactor. Thus no further encapsulation of the ceramic particles would be needed. According to an embodiment of the invention, the ceramic fuel particles comprise at least one of UN, PuN, ThN, wherein the nitrogen of ceramic fuel particles is enriched to contain a higher percentage of the isotope 15N than natural N. The object is also achieved by the fuel rod initially defined, which comprises a cladding tube enclosing a plurality of nuclear fuel pellets as defined above. The object is also achieved by the fuel assembly defined above for use in a nuclear reactor, which comprises a plurality of said fuel rods. FIG. 1 discloses a fuel assembly 1 for use in nuclear reactor, in particular in a water cooled light water reactors, LWR, such as a Boiling Water Reactor, BWR, or a Pressurized Water reactor, PWR. The fuel assembly 1 comprises a bottom member 2, a top member 3 and a plurality of elongated fuel rods 4 extending between the bottom member 2 and the top member 3. The fuel rods 4 are maintained in their positions by means of a plurality of spacers 5. Furthermore, the fuel assembly 1 may, for instance when to be used in a BWR, comprise a flow channel or fuel box indicated by dashed lines 6 and surrounding the fuel rods 4. FIG. 2 discloses one of the fuel rods 4 of the fuel assembly 1 of FIG. 1. The fuel rod 4 comprises a nuclear fuel in the form of a plurality of nuclear fuel pellets 10, and a cladding tube 11 enclosing the nuclear fuel pellets 10. The fuel rod 4 comprises a bottom plug 12 sealing a lower end of the cladding tube 11, and a top plug 13 sealing an upper end of the fuel rod 4. The nuclear fuel pellets 10 are arranged in a pile in the cladding tube 11. The cladding tube 11 thus encloses the fuel pellets 10 and a gas. A spring 14 is arranged in an upper plenum 15 between the pile of nuclear fuel pellets 10 and the top plug 13. The spring 14 presses the pile of nuclear fuel pellets 10 against the bottom plug 12. An embodiment of one of the nuclear fuel pellets 10 is disclosed in FIG. 3. The nuclear fuel pellet 10 comprises, or consists of a metallic matrix 20 and ceramic fuel particles 21 of a fissile material dispersed in the matrix 20. The ceramic fuel particles 21 may be uniformly and randomly dispersed in the matrix 20. The number of ceramic fuel particles 21 in each nuclear fuel pellet 10 may be very high. The volume ratio particles/matrix may be less than 0.01:1 or 0.01:1 up to 1:0.01. The ceramic fuel particles 21 may have a spherical shape, or substantially spherical shape, or may be a form of any shape. The size of the ceramic fuel particles 21 may vary. For instance, the ceramic fuel particles 21 may have an extension, such as the diameter in the spherical example, which lies in the range from 100 to 2000 micrometers. The ceramic fuel particles 21 comprise or consist of at least one fissile material. The fissile material is selected from the group of actinide oxide, actinide nitride, actinide silicide and actinide carbide. In particular, the fissile material selected from the group of UO2, U3Si2, U3Si, USi, UN, PuO2, Pu3Si2, Pu3Si, PuSi, PuN, ThO2, Th3Si2, Th3Si, ThSi and ThN. The ceramic fuel particles 21 may thus comprise or consist of one or more of these materials. The metallic matrix 20 is an alloy consisting of the principle elements U, Zr, Nb and Ti, and possible residual elements. The alloy of the metallic matrix 20 may have a body centered cubic, BCC, structure. The alloy is may be a single phase alloy, or a near single phase alloy with precipitates constituting less than 5 volume-% of the alloy. The concentration of each of the principle elements in the metallic matrix 20 is at the most 50 molar-%, and at least 5 molar-%. The total concentration of the possible rest elements in the metallic matrix 20 is at the most 5 molar-%, preferably at the most 4 molar-%, more preferably at the most 3 molar-%, most preferably at the most 2 molar-%. The single phase alloy, or near single phase alloy, of the metallic matrix 20 is a so called High Entropy Alloy, HEA. More specifically, the single phase alloy, or near single alloy, of the metallic matrix 20 may be U5-6Zr3-4NbTi. The nuclear fuel pellet 10 may also comprise other particles than ceramic fuel particles 21, in particular absorbing particles comprising a neutron absorbing substance. Such a substance with a high neutron absorption cross-section may comprise boron, gadolinium, etc. The nuclear fuel pellet 10 may be a sintered nuclear fuel pellet 10. A powder of the principle elements and the rest elements are mixed with the ceramic fuel particles 21, and possible absorbing particles, to form a mixture. The ceramic fuel particles 21 may have been sintered in advance. The mixture is compressed to a green body, which is then sintered in a suitable oven/furnace or any other suitable method, such as spark-plasma sintering (SPS), to the nuclear fuel pellet 10. The nuclear fuel pellet 10 may also as an alternative be manufactured in other ways, for instance through casting or extrusion. The present invention is not limited to the embodiments disclosed and described herein, but may be varied and modified within the scope of the following claims.
062755684	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of an X-ray examination apparatus. An X-ray source 1 emits an X-ray beam 4 for irradiating an object 3. Differences in the absorption of X-rays in the object 3, for example a patient to be radiologically examined, lead to the formation of an X-ray image on an X-ray-sensitive surface 17 of the X-ray detector 2 which is arranged so as to face the X-ray source 1. The X-ray source 2 is connected to a high voltage and control unit 6. The X-ray detector 2 is provided, for example with an image intensifier pick-up chain which includes an X-ray image intensifier 8 for converting an X-ray image into an optical image on an exit window 9, and a video camera 13 for picking up the optical image. An entrance screen 10 acts as the X-ray-sensitive surface which converts incident X-rays into an electron beam which is imaged on the exit window 9 by way of an electron-optical system 11. The incident electrons generate the optical image by way of a phosphor layer 12 on the exit window. The video camera 13 is optically coupled to the X-ray image intensifier 8 by way of an optical coupling. The optical coupling includes, for example a lens system or an optical fiber coupling 14. The video camera derives an electronic image signal 15 from the optical image and applies the electronic image signal to a monitor 16 in order to visualize the image information contained in the X-ray image. The electronic image signal 15 can also be applied, for example to an image processing unit 17 for further processing. In order to attenuate the X-ray beam 4 locally so as to adjust a two-dimensional intensity profile, an X-ray filter 4 is arranged in the X-ray beam 4 between the X-ray source 1 and the object 3. The X-ray filter includes a large number of filter elements (not shown). Furthermore, a filter element preferably includes a capillary tube. The capillary tubes communicate with a reservoir (not shown in FIG. 1) by way of a first opening, which reservoir contains an X-ray absorbing liquid. The X-ray absorptivity can be adjusted by applying, preferably by means of an adjusting unit 7, electric voltages across the inner side of the capillary tubes and the X-ray absorbing liquid. This is because the adhesion of the X-ray absorbing liquid to the inner side of the capillary tubes is dependent on the electric voltage applied across the inner side of the capillary tubes and the X-ray absorbing liquid. In dependence on the electric voltage applied across the individual capillary tubes (not shown) and the X-ray absorbing liquid, the capillary tubes are filled with a given quantity of X-ray absorbing liquid. The number of capillary tubes of the X-ray filter amounts to, for example 128.times.128. In order to form a projection image of the object 3, the X-ray examination apparatus is preferably provided, as shown in FIG. 2, with adjusting means 22 for keeping the X-ray source 1, the X-ray filter 5 and the X-ray detector 2 oriented along a first axis 23 and for adjusting an orientation of the first axis relative to the horizontal plane. A projection image of the object 3, to be adjusted in advance, is thus obtained on the X-ray detector 2. Means of this kind include, for example a C-arm with control means. FIG. 2 shows such a C-arm with adjusting means 22. The X-ray examination apparatus is also provided with a collimator 25 in which, for example the X-ray filter 5 is mounted so as to be rotatable about the first axis 23. Instead of mounting the X-ray filter 5 so as to be rotatable in the collimator 25, the X-ray filter may also be mounted so as to be fixed in the collimator and the collimator can be mounted so as to be rotatable in the X-ray examination apparatus, so that the collimator and the X-ray filter are capable of rotation together about the first axis 23. The X-ray examination apparatus is also provided with electrically controllable drives, for example an electric motor and a mechanical transmission 26 for rotation of the X-ray filter 5 about the first axis 23. The electrically controllable drive 26 is connected to a control unit 24, for example a microcomputer. According to the invention the supply duct of the X-ray filter 5 includes subducts, each of which connects several filter elements to a reservoir which is preferably integrated in the X-ray filter, the sub-ducts preferably being arranged parallel to one another. The location of such sub-ducts in the X-ray filter 5 will be described in detail hereinafter with reference to FIG. 3 and FIG. 4. In order to provide the X-ray filter 5 with the sub-ducts, an additional step is executed during the manufacture of the X-ray filter. This step will be described in detail with reference to FIG. 3. FIG. 3 is a plan view of a single foil of a stack of foils wherefrom a honeycomb structure is formed. A honeycomb structure of this kind constitutes a bundle of capillary tubes of the X-ray filter 5. The manufacture of such a honeycomb structure is described, for example in the not previously published European patent application 98203986.9. the honeycomb structure is obtained by stretching the stack of foils which are bonded to one another in bonding locations, for example by thermal compression, in order to realize the honeycomb structure in the stretched state. In order to form the sub-ducts, for example the method is extended with a step for forming cut-outs 31 along oppositely situated edges of the foil 30. The cut-outs can be made by locally removing material. To this end, for example a number of foils 30 are stacked and the cut-outs are provided in the oppositely situated edges, for example by means of punching. The cut-outs are then formed in one step and are aligned with respect to one another. The cut-outs 31 may have a rectangular or circular shape. The spacing, the width and the depth of the cut-outs are preferably chosen to be such that they enable an adequate transport flow of liquid and/or air. Preferably, the width of the sub-duct is chosen to be such that the sub-ducts connect three neighboring capillary tubes. For example, if the diameter of a capillary duct amounts to 350 micrometers, the maximum width of the sub-ducts 700 amounts to 700 micrometers and the minimum width of the sub-ducts to 175 micrometers. Subsequently, a stack of such foils 30 is formed and bonded together in the bonding locations. Such a stack constitutes the honeycomb in the stretched state. FIG. 4 shows a first cross-section of an X-ray filter which includes a first plate 41 and a second plate 42. In order to form the tubes, the two plates 41, 42 are provided on the respective sides of the stack of foils in which the cut-outs 30 have been formed. FIG. 4 also shows a co-ordinate system x, y, z. The sub-ducts 53, 54 extend in the x direction and are arranged adjacent one another in the y direction. The capillary tubes, a capillary 55 of which is shown in FIG. 4, are directed in parallel in the z direction and the stack of foils extends in the x direction of the co-ordinate system. The sectional view of the X-ray filter as shown in FIG. 4 has been taken along an y, z plane. Another possibility consists in forming the sub-ducts 53, 54 in the plates 41, 42. To this end, a side of the plates 41, 42 which faces the stack of foils is provided with slots with a spacing which equals the diameter of a capillary tube, said slots following the shape of the stretched foils of the honeycomb structure of the X-ray filter. The depth of such slots amounts to, for example 0.5 mm. The maximum width of such slots amounts to 700 micrometers for a capillary tube having a diameter of, for example 350 micrometers. An advantage of the use of slots in the plates consists in that the direction of the sub-ducts 53, 55 can be chosen at will in a plane perpendicular to the foils. The reservoir containing the X-ray absorbing liquid is preferably integrated in the X-ray filter 5 by providing the X-ray filter with additional capillary tubes 55 which are situated outside the part of the X-ray filter which is traversed by the X-ray beam 4 to be generated. The number of capillary tubes is then increased to, for example 256.times.128. FIG. 5 shows a cross-section of such an X-ray filter with the reservoir which has been taken in the y, z plane. FIG. 5 shows the sub-ducts 50, 51 and the reservoir 52. The sub-duct 50, for example, each time connects three adjacently situated capillary tubes 55 to one another over the entire length of a first side of the X-ray filter. The sub-duct 51 interconnects, for example, each time three adjacently situated capillary tubes 55 over the entire length of a second side of the X-ray filter which lies opposite the first side. FIG. 6 shows a part of a cross-section of the X-ray filter, taken along the x, y plane, and also shows the reservoir 52 which includes chambers 53. In order to counteract an excessively uneven pressure distribution in the sub-ducts 50 of the X-ray filter, the reservoir 52 is preferably subdivided into the chambers 53. The number of chambers in practice amounts to, for example 42. A chamber 53 of this kind contains several capillary tubes 55. The chambers 53 are separated by the walls 56 of the outer capillary tubes 33. FIG. 6 shows the walls 56 whereby the chambers 53 are separated. The sub-duct 50 also connects the chamber 53 to the capillary tubes 55 which are situated in the X-ray beam 4 to be generated, each chamber 53 preferably being connected to a respective sub-duct 50. The X-ray examination apparatus also includes means 25 for generating a signal which represents an angle of inclination between a longitudinal axis of the sub-ducts and the horizontal plane. Means of this kind are provided with, for example an inclinometer which is independent of a rolling motion. Such an inclinometer is insensitive to a rolling motion about the axis with respect to which the inclination relative to the horizontal plane is determined. According to the invention the axis of the inclinometer 23 which is insusceptible to a rolling motion is arranged so as to be parallel to the sub-ducts. Inclinometers of this kind are known per se, for example from the published British patent application GB 2 273 356. When such an inclinometer is inserted in, for example a Wheatstone bridge, a signal 27 representing the angle of inclination can be generated. The signal 27 is applied to the microcomputer 28. The microcomputer, provided with a suitable program, generates the control signals 28 for the electrically controllable drive, for example a second electric motor with a mechanical transmission 26 for rotating the X-ray filter 5 in such a manner that the angle of inclination is adjusted back to zero degrees and the sub-ducts in the X-ray filter 5 are oriented horizontally. Other types of inclinometer may also be used, for example inclinometers of the optical type as known from U.S. Pat. No. 5,425,179, or of the inductive type as known inter alia from U.S. Pat. 5,703,484. In order to compensate the effect of pressure differences in the sub-ducts on the transport from and to the capillary tubes 55, use can also be made of a compensation voltage which is added to the control voltage in order to adjust the quantity of X-ray absorbing liquid in the capillary tubes 55 of the X-ray filter. To this end, the X-ray examination apparatus includes means for generating the compensation voltage. Such a means include, for example a second roll-independent inclinometer 29 which is inserted, for example in a second Wheatstone bridge which generates a second signal 70 which is applied to the microcomputer 28. The microcomputer is also provided with a program for determining the compensation voltage 71 from the second signal 70. This compensation voltage 71 is subsequently applied to the electrical adjusting unit 7 which adds the compensation voltage to the control voltage. In practice it is thus possible to compensate hydrostatic pressure differences due to, for example three capillary tubes which are situated one above the other. A maximum value of such a compensation voltage can be determined experimentally. A value of the compensation voltage 71 to be adjusted is dependent on the orientation of the X-ray filter. The compensation voltage is proportional to sin.THETA., where .THETA. represents an angle between the longitudinal axis of one of the sub-ducts and a vertical plane.
045171521	summary	BRIEF SUMMARY OF THE INVENTION This invention relates to an ultrasonic method for testing fuel element tubes for defects, such tubes being assembled in bundles to form a complete reactor core, using ultrasonic transducers. One transducer, forming the transmit transducer, transmits ultrasonic search pulses into the tube or sheath of the fuel element while an opposite transducer, the receive transducer, receives ultrasonic signals from the tube. The received signals, if falling within a predetermined time range, i.e. a time gate, are evaluated by an evaluation means which includes an amplitude discriminator. A method of this type is known, having been described for example in an article by G. Baro et al entitled "Ortung defekter Brennstabe in bestrahlten Brennelementen", Tagungsbericht der Jahrestagung Kerntechnik 80, Reaktortagung 1980, Berlin, 25-27 March 1980; published by Deutsches Atomforum e.V. Bonn, pp. 827 et seq. The purpose of the time gate, although the latter is not described in detail in that article, is to separate the ultrasonic signals which reach the receive transducer from the tube, known as the revolving or circumferential echo, from the signal transmitted by the transmit transducer and passing directly to the receive transducer, the transmitted signal. Only by this feature is it possible to determine automatically the transit time of the revolving echo signal without obtaining a misreading due to the interference of the transmitted signal. In the methods known heretofore a constant time gate setting has been used. This arrangement, however, has been proven disadvantageous since the distance between the two transducers varies greatly as the transducers pass through the array of tubes. Therefore, it is possible that transmitted signals may also arrive within the gated time interval and, hence, defective fuel tubes may become classified as being defect-free. From German OS No. 24 22 439 it is known to adjust the time gate when the thickness of the workpiece changes. In that described arrangement a change of the workpiece thickness is indicated by a reference signal responsive to the occurrence of the workpiece rear wall echo signal. Utilizing that method, that is, periodically monitoring the thickness of the workpiece and adjusting the time gate accordingly, is possible only with the greatest circuit complexity when testing fuel tubes. Moreover, in such an arrangement changes arising from the spacing between the transducers, i.e. those not caused by a change in thickness of the tubes, are not taken into consideration. The present invention discloses a simplified method for changing the setting of the time gate in response to the spacing between the transmit transducer and receive transducer as both transducers pass through the spaces between the tubes. To this end, the time gate setting is redetermined for each tube to be tested prior to such tube becoming disposed between the transmit transducer and the receive transducer. Accordingly, in the space between the last tested tube and the next to be measured tube the transit time of the echo signal between the transmit transducer and receive transducer is measured. Thereafter, a constant value is subtracted from the transit time, such constant value being selected so that the transmitted signal indication obtained during the transit time measurement no longer falls within the gated time interval. Other particulars and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings.
048440493	claims	1. A water heater device comprising: (a) a water tank; (b) an outer shell concentrically located over the water tank defining an annular space therebetween; (c) a thermal insulating, compressible collar constructed as a pliable material envelope which is filled with loose, discrete insulation material and disposed proximate the bottom end of the water heater device circumscribing the inner water tank, the collar having a radial thickness greater than the radial width of the annular space such that the collar is radially compressed between the inner water tank and outer shell creating a seal at the interface of the inner surface of the outer shell and the collar, and a seal at the interface of the outer surface of the inner water tank and the collar; (d) an insulating disc constructed as a pliable material envelope which is filled with thermal insulation material configured and sized to cover the bottom end of the inner water tank overlaying the bottom end of the water tank; and, (e) expanded insulation foam material filling the annular space between the inner water tank and outer shell above the collar. the insulating disc is disposed within the concavity to substantially fill the concavity. (a) a water tank; (b) an outer shell concentrically located over the water tank defining an annular space therebetween; (c) a thermal insulating collar proximate the bottom end of the water heater device circumscribing the inner water tank, the collar having a radial thickness greater than the radial width of the annular space such that the collar is radially compressed between the inner water tank and outer shell creating a seal at the interface of the inner surface of the outer shell and the collar, and a seal at the interface of the outer surface of the inner water tank and the collar, said insulating collar including an envelope of fluid-impermeable, pliable material which is configured as an elongated tube and which is open at both ends and wherein one open end of said elongated tube is inserted into the other open end of said elongated tube, and further including insulation material disposed within and substantially filling said elongated tube; (d) a disc of insulation material configured and sized to cover the bottom end of the inner water tank overlaying the bottom end of the water tank; and, (e) expanded insulation foam material filling the annular space between the inner water tank and outer shell above the collar. (a) a water tank; (b) an outer shell concentrically located over the water tank defining an annular space therebetween; (c) a thermal insulating collar proximate the bottom end of the water heater device circumscribing the inner water tank, the collar having a radial thickness greater than the radial width of the annular space such that the collar is radially compressed between the inner water tank and outer shell creating a seal at the interface of the inner surface of the outer shell and the collar, and a seal at the interface of the outer surface of the inner water tank and the collar, said insulating collar including an envelope of fluid-impermeable, pliable material which is configured as an elongated tube and which is closed at one end and open at the other end, the closed end of the elongated tube is inserted into the open end of said elongated tube, and further including insulation material disposed within and substantially filling said elongated tube; (d) a disc of insulation material configured and sized to cover the bottom end of the inner water tank overlaying the bottom end of the water tank; and, (e) expanded insulation foam material filling the annular space between the inner water tank and outer shell above the collar. (a) a water tank; (b) an outer shell concentrically located over the water tank defining an annular space therebetween; (c) a thermal insulating collar proximate the bottom end of the water heater device circumscribing the inner water tank, the collar having a radial thickness greater than the radial width of the annular space such that the collar is radially compressed between the inner water tank and outer shell creating a seal at the interface of the inner surface of the outer shell and the collar, and a seal at the interface of the outer surface of the inner water tank and the collar; (d) a thermal insulating disc configured and sized to cover the bottom end of the inner water tank overlaying the bottom end of the water tank, said insulating disc including an envelope of fluid impermeable, pliable material having a peripheral configuration which is generally circular and which corresponds in size and shape to the bottom end of the water tank and the insulating disc further including insulation material which is disposed within and substantially filling said envelope, the envelope further including a central inner circular pocket and a perimeter pocket concentrically surrounding the inner circular pocket; and (e) expanded insulation foam material filling the annular space between the inner water tank and outer shell above the collar. the central inner circular pocket is filled with a fibrous batt of insulation material; and, the perimeter pocket is filled with a discrete, divided insulation material. the central inner circular pocket is filled with a discrete, divided insulation material; and, the perimeter pocket is filled with a fibrous batt of insulation material. (a) a water tank; (b) an outer shell concentrically located over the water tank defining an annular space therebetween; and (c) a thermal insulating member including a pliable material envelope which is filled with loose, discrete insulation material, said envelope being arranged into a first portion which is in the shape of a disc and disposed beneath the bottom end of the water tank and a second portion which is arranged around and connected to said first portion and which has an annular ring shape. 2. The water heater device of claim 1, wherein the insulation material filling the envelope of the collar comprises a fibrous batt of insulation material. 3. The water heater device of claim 1, wherein the insulation material filling the envelope of the collar comprises discrete, divided thermal insulation material. 4. The water heater device of claim 3, wherein the thermal insulation collar further comprises a binder material homogeneously dispersed throughout the divided thermal insulation material enclosed within the collar envelope. 5. The water heater device of claim 1, wherein the envelope of the thermal insulation collar comprises an elongated tube of heat resistant, fluid impermeable material closed at both ends. 6. The water heater device of claim 5, wherein the ends of the envelope abut one another. 7. The water heater device of claim 1, wherein the envelope of the thermal insulation collar comprises a closed toroidal envelope. 8. The water heater device of claim 1, wherein the insulation material filling the envelope of the insulating disc comprises a fibrous batt of insulation material. 9. The water heater device of claim 1, wherein the insulation material filling the envelope of the insulating disc comprises discrete, divided thermal insulation material. 10. The water heater device of claim 9, wherein the thermal insulating disc further comprises a binder material homogeneously dispersed throughout the divided thermal insulation material enclosed within the disc envelope. 11. The water heater device of claim 1, wherein the envelope of the insulating disc has a generally circular periphery. 12. The water heater device of claim 1 wherein the bottom end of the inner water tank is formed with a concavity; and, 13. A water heater device comprising: 14. A water heater device comprising: 15. A water heater device comprising: 16. The water heater device of claim 15, wherein: 17. The water heater device of claim 15, wherein: 18. A water heater device comprising:
043549993	description	DESCRIPTION OF THE PREFERRED EMBODIMENT A power reactor can be built by combining the following: 1. A vacuum tight reaction chamber, in which a low density pure gas of fusible isotopes, such as an equal volume of deuterium and tritium at a density of 5.times.10.sup.14 cm.sup.-3 can be heated to reacting temperature and confined such that, the average temperature, and confinement time are 5 KEV (50,000,000.degree. K.) and one (1) second; PA1 2. A spherical structure consisting of a lithium blanket and shield surrounding the reactor chamber in which neutrons will be thermolized and tritium will be generated; PA1 3. A magnetic Ioffe bar system for generating a confining magnetic field; PA1 4. A thermal cycle in which the heat produced in the blanket is converted to electricity by a conventional power couple; PA1 5. An ignition system consisting of lasers fired through one way apertures and focused to the center of the reaction chamber. PA1 (a) The neutrons (14 MEV) energy are converted to heat and; PA1 (b) Tritium is bred by neutron absorption in the lithium blanket. PA1 (a) In the extraction cycle sea water is pumped in and deuterium extracted from it in the conventional manner. The deuterium is then pumped into the mixing area through the deuterium control valve. Tritium is pumped from the tritium extractor, through the tritium valve and into the D-T mixing area. PA1 (b) In the lithium cycle lithium is heated by nuclear bombardment. The lithium is then pumped through a heat exchanger to heat water and produce steam for the steam cycle. The lithium is then pumped back through the tritium extractor where the tritium is removed from the lithium. PA1 (c) In the steam cycle water is heated to steam in the lithium heat exchanger. This steam runs a conventional steam turbine which drives a conventional generator which produces useful electric energy. The steam is then condensed through a conventional flow through and cascade condensers and the water pumps back through the lithium condenser. The translation of these broad categories, and the numerous subsystems they imply from concept to design are as follows: 1. Reaction Chamber The reaction chamber consists of a stainless steel spherical structure eight (8) meters inside diameter, with a wall thickness of 254 mm. A low density plasma consisting of an equal mixture of deuterium and tritium (plus associated electrons) at an operating temperature of 4.times.10.sup.3 K is introduced into the reactor chamber through the preheat units. The pressure of the low density but high temperature plasma is a few atmospheres and is supported by a magnetic field throughout the entire region of approximately 10 teslas (100,000 guass). The interior walls of the chamber are coated with Beryllium. This coating serves two purposes. First, it acts as a neutron multiplier to make up the neutron deficiency caused by burning tritium (for every triton burned only one neutron is generated and it takes one (1) neutron to breed a triton). Secondly, it serves as a refractory material for the inner surface of the reaction chamber. Covering the inward surface of the Beryllium is a plated coating of copper and nickel. After these coats have been polished a coat of chromium is plated onto the innersurface. This coating of the innersurfaces serves two (2) purposes. First, it reflects the radiant energy back to the focal point of the sphere and secondly, it prevents radiant heat transfer through the walls of the reaction chamber, thus, cooling the walls. 2. Lithium Blanket and Thermocycle Outward from the reaction chamber is a lithium blanket which completely surrounds the reaction chamber. This blanket performs three functions. First, the energy of the 14 MEV neutrons is converted to heat in this region. Secondly, the tritium is bred by neutron absorption in the lithium blanket. Thirdly, the heated lithium at 1250.degree. F. provides the primer mover for the conventional thermo cycle. As the lithium is heated in the reactor it is pumped through a condenser to cool the reactor at the rate of 1600 gallons per minute. The condenser for the reactor is the boiler for the conventional steam cycle. This system would work the same way that a conventional mercury vapor topping unit on a steam cycle works today. 3. Ioffe Bar Magnetic System Outward from the lithium blanket is the Ioffe bar system. The system will be superconductive and therefore be immersed in a cryogenic medium at a temperature of 4.degree. K. The wire consists of V.sub.3 GA which is usable beyond 20 teslas. Its primary purpose is to provide a confining magnetic field for D-T plasma. The general shape of the windings are shown in FIG. 3. The basic idea behind the Ioffe bar system is to provide a magnetic field configuration in which there exists a region where the intensity of the magnetic field increases in every direction outward from the center. In such a field, plasma is stably confined since escape for most particles requires an increase in energy. A cylindrical configuration leaks badly since lines of force leave the volume and although most of the plasma particles are confined, those with velocity vectors parallel to a field line leave the volume and escape directly along the line. The Ioffe bar windings used in this invention have been modified to conform to a spherical configuration to reduce end loses. In accordance with Laplace's law or the Brol-Savart relation the magnetic field intensity at any point P is: ##EQU1## Referring to FIG. 4, current I flows in a circular loop of radius "a" (cm) and point "P", at which the field intensity is desired is distance "b" from center "O" of the loop. Although there are two cases according as "P" is within or without the reaction chamber, for our purposes we will only consider the one within the reactor. The first case may be diagrammed as shown in FIG. 4 of the drawing. If "P" is inside the reactor then b is less than a and .theta. is the angle between the radius vector .nu. from "P" to any point "Q" on the Ioffe bar spherical configuration and a line through "O" and "p". If .DELTA.S=QA is an arc of the circular loop angle APQ will be .DELTA..theta.. With "P" as the center and radius .nu. describes a circle arc cutting PA at B.sub.1 and let .beta. be the angle between QB and S. Since QB is perpendicular to .nu., and .alpha. is the angle between .nu. and .DELTA.S, we have .alpha.=90-.beta.. Therefore, .DELTA.S sin .alpha.=.DELTA.S cos .beta. but .DELTA.S cos .beta. is .apprxeq..nu..DELTA..theta. (approximate expression for field intensity at "P" due to .DELTA.S) ##EQU2## <OPQ we have from the law of cosines-- ##EQU3## solving for: ##EQU4## since .nu. is positive I choose and used .nu. ##EQU5## Multiply numerator and denominator of the integrand by .sqroot.a.sup.2 -b.sup.2 sin .theta.+b cos .theta. to rationalize the denominator. ##EQU6## Since ##EQU7## and since y=.sqroot.a.sup.2 -b.sup.2 sin.sup.2 .theta. has a symmetrical graph we may write: ##EQU8## where ##EQU9## Therefore dividing numerator and denominator of the coefficient of the integral by a.sup.2 : ##EQU10## if K.sub.1 =0 "P" is at the center of the reactor and since E(O)=II/2 the familiar formula: ##EQU11## as K.sub.1 .fwdarw.1, P.fwdarw.conductors; E(K.sub.1).fwdarw.1 H.fwdarw.d; as predicted from Ampere's law. From the above treatise it may be seen that the plasma is stably confined since the intensity of the magnetic field will increase at all points outward from the center of the reactor K=0 to K.sub.1 =1. Furthermore, the semiconducting plasma is thus caused to drop through the magnetic field potential from the walls of the reactor to the center K.sub.1 =1 to K.sub.1 =0 and stably confined there. Although the magnetic fields just described provide a stable confinement of the plasma (increased energy to leave the volume) those particles with velocity vectors parallel to a flux tube still tend to leave the volume through the ends. This is called end loss. To further reduce this loss in the device of the invention, the minimum field intensity axis of the Ioffe bar system is offset from the center of the sphere (see FIG. 3) a distance "P". since the Ioffe bar windings are multipole, the minimum field intensity axis of the Ioffe bar system is offset from the center of the sphere (see FIG. 3) a distance "P". Since the Ioffe bar windings are multipole the axes of minimum field intensity form a family of straight lines of the form EQU (A).function.(x,y,.theta.,)=x cos .theta.+Y sin .theta.-P=0 differentiating with respect to .theta. EQU (B).function..sub..theta. (x,y,.theta.,)=X sin .theta.+y cos .theta.=0 Multiply: (A) by cos .theta. and (B) by sin .theta. and subtract: x=P cos .theta. eliminate X between (A) and (B). The parametric equation of the envelope of the Ioffe bar minimum field intensity axis is as follows: ##EQU12## Squaring these equations we get X.sup.2 +Y.sup.2 =P.sup.2 This is the retangular equation of the cross-section of the reactor ignition point. In other words, end loss will be reduced since as particles with velocity vectors along a flux tube experience additional collisions in the ignition envelope and again become radomized in this area. FIG. 7 illustrates the envelope of minimum field strength axis 1. The equation of these lines is X cos .theta.=+y sin .theta.-P=0. The tangent points of this family of straight lines is described by the equation X.sup.2 +Y.sup.2 =P.sup.2 as shown above. The envelope is shown in FIG. 7 as item 2. Another function of the Ioffe bar system is to continuously pump new fuel to the ignition point from the preheat units and purge the helium by products. This is made possible by the differences in the degree of ionic dissociation between deuterium and tritium and the by product helium. For example, if incoming D-T fuel possesses organized motion it will be randomized by subsequent collisions and reactants will develop a kinetic equilibrium describable by a temperature; that is, they will possess a Maxwellian distribution, and the fuel will be in the form of a hot gas. Since the energy required to produce a reasonable reaction rate is in the Kiloelectron-volt region, well above the ionization energy of the light elements that are of interest, the gas will be a fully ionized plasma. In this state the ion density .eta.i is equal to the electron density .eta.e and the magnetic field of 10 teslas (100,000 guass) induces current into the ionized deuterium and tritium. Under these conditions the Ioffe bar system will force the plasma to the center of the sphere, i.e., to the focal point of the lasser system. This force may be expressed as follows: ##EQU13## Where: F is the magnetic force against the plasma in dynes, I is the induced current in amps. In the plasma and L is the length of the path of the plasma current in centimeters. If the ionic current path is not at right angles with the flux but at an angle .theta. then the length of the ionic current path is L sin .theta.. ##EQU14## Since the ionic current which is induced into the plasma by the magnetic field is proportional to the degree of ionic dissociation, the helium by products of the reaction will induce lower currents than in the deuterium-tritium plasma and thus will not be forced to the center of the sphere by the same force shown above. Since there is a density gradient, this transport process should be governed by a law of diffusion, Fick's law, which states that the current density of the particles, EQU J(cm.sup.-2 S.sup.-1, is given by J=-D.gradient..eta. Where (.gradient..eta.) is the gradiant of particle density, (D) is the diffusion coefficient (cm.sup.-2 S.sup.-1). Therefore, the by product helium, is transported from the center of the reaction chamber to the walls where it can be purged from the system. 4. Laser Ignition and Fuel Injection Neodymium glass lasers are used for the initial ignition of the D-T fuel. The system comprises numerous neodymium laser entry points which are fired in sequence through one-way apertures in the reaction chamber wall (see FIG. 5). Since only one laser is fired at a time the other lasers are pumped in sequence for a subsequent firing order. The energy of the pulse is 10.sup.7 joules with a pulse duration of less than 10.sup.-9 seconds and are introduced into the reactor chamber through the ports at the ends of the Ioffe bar system as shown in FIG. 5 of the drawing. A more detailed drawing of the working parts of the preheat chamber and the laser is shown in FIG. 6. The outward end of the preheat unit is given a negative charge 6 and the inward end a positive charge 4. The container is filled with a deuterium-tritium mixture. The fuel will then conduct an electric current which ionizes it. This will permit a flow of electrons between the positive and negative plates. The plasma current is surrounded by circular lines of magnetic force which tend to pinch inward. As the lines of force push the plasma inward toward the center it is completely ionized and becomes a semiconductor. At this stage the valve is open by moving it inward toward the center and the plasma is allowed to enter the reaction chamber where it is forced to the center of the sphere by the magnetic field of the Ioffe bar system. The same system may be used to remove the helium by products from the walls of the reaction chamber. As may be seen from FIG. 6 the preheat units can also be used to pump the laser system. An additional heating effect of the Ioffe bar confinement system may be realized by providing the proper frequency to cause resonance. If we consider a group of quantum mechanical effects which are related to resonance we find that periodically varying energy to a system close to the natural frequency of the D-T fuel will cause additional heating effects known as cyclotron resonance heating. One of the simplest examples of this is pushing a swing; we are familiar with the large amplitudes that can be achieved by proper timing. The frequency may be calculated as follows: When a particle moves in a curved path, it takes a force directed towards the center--centripetal force--to keep it in this path. ##EQU15## Where R is the radius ##EQU16## The centripetal accelleration would then be: ##EQU17## Where .theta. is the polar angular coordinate of the centipetal force--MV.sup.2 /R If an electron is moving with a velocity V at right angles to a uniform magnetic field .beta. the force exerted on the electron will be: EQU F=.beta.ev If we equate this to the centripetal force to the force exerted by the uniform magnetic field we get: ##EQU18## since ##EQU19## In order to get the cyclotron resonance frequency we must first determine the effective mass as follows: energy (E)=plank's constant (.eta.) X frequency (.upsilon.). Where .eta.=6.6.times.10.sup.-34 joules/sec. also by De Brogle's relation the momentum (P)=.eta..times.k Where K is proagation constant or wave number and is related: ##EQU20## differentiate with respect to K. again ##EQU21## m.sub.e is the effective mass of the electron. Therefore, the cyclotron resonance frequency is as follows: ##EQU22## This is the frequency that should be impressed on the Ioffe bar system to get the maximum absorption of the magnetic field energy in the plasma. In other words, the maximum heating will occur at this frequency. DESCRIPTION OF DRAWINGS The novel features which are believed to be characteristic of my invention both as to structure and to its method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing, in which several of the embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the invention. FIG. 1 is a sectionalized side view of one of the embodiments of the invention. As shown in FIG. 1, a laser system 22 is fired through a one-way mirror 3 into an inner sphere 15 which is evacuated and mirrored on the innersurface 26. The laser beam is focused to the center of the sphere which creates an extremely high temperature point 10. A lithium blanket 24 surrounds the inner sphere producing the tritium required for the reaction. As stated in the equation. A cryogenic jacket 7 surrounds the Ioffe bar system. The superconducting Ioffe bar system 5 is emersed in the cyrogenic jacket and serves as a secondary coil to electromagnetically force the deuterium-tritium plasma to the focal point inner sphere. A preheat chamber 11 supplies fuel to the inner sphere. A primary coil 9 outside of the reactor induces a current into the superconductive Ioffe bar system. An outer shell 8 surrounds the cyrojacket. Suitable insulation material 21 surrounds the cryojacket to prevent heat transfer from the atmosphere. FIG. 2 illustrates the Ioffe bar system 14 modified to fit the sphere 25. FIGS. 1 and 2 are intended to represent identical structures, with FIG. 1 having less wiring detail and being more diagrammatic of the layers of the reactor. The invention has a spherical innermost reaction chamber wall 15, preferably of stainless steel or titanium alloy, the innersurface of which is mirrored to reflect all laser energy to its center. A second concentric, preferably stainless steel, spherical wall is positioned immediately outward of the reaction chamber wall 26 to form a lithium jacket 24 between the inner wall and the second wall. Projecting through the wall of the reactor are the plasma preheat units 11. Spaced outwardly from the lithium blanket is the outer spherical shell 12 which provides a vacuum or other insulation between the lithium and the cryo shells. Outward from the insulating shell is the cryogenic jacket 7. The multiaxis Ioffe bar superconductive windings are contained in this cryogenic jacket and are supercooled by a circulatory supercooled medium such as liquid helium. In this manner the winding are maintained superconductive. The central ignition chamber is evacuated. A meodymium glass laser 22 is fired through a one-way mirrored surface 3. The walls of the ignition chamber do not require a great strength due to the balance of pressure of the lithium outside and the reaction inside the ignition chamber. The lithium blanket absorbs neutrons and provides prime mover for the power generation. Lithium is converted to Tritium in the lithium jacket 24. The laser 22 extends radially through the reactor wall and is focused to the center of the ignition chamber. A one-way mirror protects the fuel source by reflecting radiant energy from the central ignition point. Tritium is separated from the lithium in the blanket by conventional techniques is also introduced into the reaction chamber through the same preheat units. To overcome the end-loss difficulty in the prior art my device employees a number of Ioffe bars, the principle axes of which are offset from the center of the sphere that follow the spherical configuration of the ignition chamber. This produces an area of random collisions of the charged particles which are attempting to leave the volume along a flux line. These collisions occur in the outer shell of the ignition area resulting in a reduction of the end loss. The arrows in FIG. 2 indicates the direction of the current in the windings of the Ioffe bar system which is modified to follow the configuration of a spherical surface. A more detailed view of the Ioffe bar windings may be seen in FIG. 3 where the primary coil 31 induces current into the secondary coil 32. This view also shows the center of the sphere 36, the axis of minimum electromagnetic field intensity 34 and the current carrying elements 35. The arrows again indicate the direction of current flow in the windings. FIG. 4 shows the geometry for calculating the field intensity at any point in the reactor which was mentioned earlier in this specification. FIG. 5 shows the position of the preheat fuel units 2, the laser 51, the secondary coil 56, the off-set of the Ioffe bar system axis 53, and the center of the sphere 54. A more detailed view of the laser and preheat units may be seen in FIG. 6. In this drawing the laser 63 is shown inside the preheat unit 61. A positive plate 4 is provided and a negative plate 6 (bottom of valve) is provided to charge the D-T fuel for preheat. This is done by the thetapinch method. A fused quartz one-way mirror is used for the laser discharge into the reaction chamber. The valve is projected forward through the ignition chamber wall 62 to allow the fuel to enter the ignition chamber. The laser pulse passes through the center of the sphere 67. FIG. 7 shows the axes of the Ioffe bar system 1 and their envelope 2. These calculations are shown earlier in the specification. FIG. 8 shows the isopestic line 83 between the force of the electromagnetic field 1 and the outward force of the plasma 82. ##EQU23## A dimensionless number, is used as an index of the effectiveness of the magnetic confinement: ##EQU24## OPERATION The ionized fuel at a temperature of 4000.degree. R is injected into the chamber continuously from the preheat units and forced to the center of the sphere, which is the focal point of the laser beam, by the electromagnetic field of the multiaxis Ioffe bar system. The laser is fired continuously only until thermonuclear ignition takes place. Since energy cannot be transmitted from the focal point of the ignition chamber by radiation, conduction, or convection the temperature and pressure are increased continuously until the thermonuclear threshold is reached. Once ignition is reached, fusion takes place continuously by continuous introduction of new fuel and by the reflected radiant energy from the mirrored walls of the ignition chamber. This energy is reflected back to the ignition point at the center. At this time the laser can be turned off. The ionized fuel at temperature of 4000.degree. R is injected at the innersurface of the ignition chamber, where reflective surfaces can protect the mechanisms from radiation. Any material such as stainless steel or titanium alloy, having a high reflective index may be suitable as a mirror substance, since the innersurface is cooled by the lithium circulation and the reflection of the radiant energy. The Lawson criteria implies that for 50% D-T and a 33.3% efficiency reaction requires ion temperature of approximately 10 KEV. The ion density times the confinement time should be approximately equal to 10.sup.14 sec/cm.sup.3. The magnetic field strength would be approximately 10 teslas (100,000 guass) in intensity. In this range a suitable Ioffe bar material may be (V.sub.3 GA). The major problem in the existing fusion devices such as Tahomak and Stellarator is primarily that of plasma confinement. However, a recent test on T-3 Tahamak in Moscow indicated improvement in plasma stability with increased temperature. It appears that a diffusion process is operating. In these circumstances the confinement time will vary as follows: ##EQU25## Where "T" is the plasma temperature and "D" is the diffusion coefficient. The multipole Ioffe bar system provides a magnetic field configuration in which exists a region where the intensity of the magnetic field is increasing in every direction outward from the ignition point. Plasma in this magnetic field is stably confined and compressed since, for charged particles, it requires an increase in energy to move outward from the ignition point. The combination of the Ioffe bar windings described employs a number of Ioffe bars, the principle axes of which are made to be off-set from the center of the sphere or the ignition point and follow the spherical configuration of the ignition chamber. One of the problems with the Ioffe bar, open end confinement, art in the past has been that the plasma particles with velocity vectors parallel to the field lines leave the volume and escape along those lines thus resulting in high end loss. This is overcome in the present patent by having the principle axis of the Ioffe bar system intersect as mentioned above, thus producing an area of random collisions in the outer shell of the ignition point. An inverse law of electrohydrodynamics may be acting under these conditions, and may provide a more efficient way of obtaining useful power output. After the plasma reaches the ignition point it will expand outwardly with great force against the electromagnetic fields of the Ioffe bar system. If an inverse law is operating, electrical energy will be induced back into the Ioffe bar windings equal to the force of the plasma times the expanding distance. If this principle holds true, electrical energy can be simply induced into the Ioffe bar system from the expanding plasma. The laser preheating of the ignition chamber will greatly improve the plasma stability, since the latest experiments indicate that the plasma stability condition improves with temperature increase. The laser pulse energy should be between 2.times.10.sup.3 joules and 10.sup.7 joules, as an example 10.sup.6 joules may be used. A low density plasma consisting of equal mixture of deuterium and tritium (plus electrons) at a temperature of 4000.degree. R is fed continuously into the ignition chamber. The pressure of this low density but high temperature plasma is only a few atmospheres. At 4000.degree. R this mixture becomes a semiconductor which can be pushed by an electromagnetic field to the center of the sphere which is the focal point of the laser system. The first wall outward from the ignition chamber is thin, cool by reflection for intercepting the electromagnetic radiation load and reducing the cooling problem. The wall has pressure on both sides and therefore eliminates the need for high structural strength. This wall is mirrored on the innersurface thus isolating the reaction region from the surrounding structure to maintain the purity of the low density plasma. A lithium blanket surrounds the wall which performs two functions: This shield will absorb almost all the neutrons and prevent damage to the Ioffe bar system outside. The equations for this conversion are as follows: EQU h+L.sup.6 i.fwdarw.T+H.sup.4 e EQU h+L.sup.7 i.fwdarw.T+H.sup.4 e+h Outside the lithium blanket is the Ioffe bar system. This system is superconductive, immersed in cryogenic medium such as liquid helium, the by-product of the reaction, at a temperature of 4 to 10 K as stated previously. The Ioffe bar system generating a magnetic field of an average value of 10 teslas. As an example 12 teslas may be used. To do this the maximum field strength adjacent to the conductors may equal or exceed 15 teslas, which is within the practical operating limits for Nb3SN, the most popular superconductor now available. New materials, such as V.sub.3 GA are reported to be usable beyond 20 teslas. Various cryogenic materials may be used in the cryogenic jacket, such as, liquid nitrogen or helium. Because of the very low temperatures in the cryogenic jacket and the heat transfer problem associated with them, the superconducting Ioffe bar system is inductively energized by a primary coil outside the jacket. The deuterium and tritium fuel introduced through the ends of the Ioffe bars undergoes the following reaction: EQU D+T.fwdarw.H.sup.4 e(3.52 MeV)+h(14.06 MEV) It has been shown to be old art to use superconductive solenoids to generate electromagnetic fields, ref. Robert G. Mills, "Super conductive Solenoids with Overheat Protective Structures and Circuits". However, the use of superconductive Ioffe bar systems in spherical configurations for plasma confinement is a new use in combination with laser ignition for steady state fusion. The use of laser ignition of a deuterium-tritium mixture is old art, ref., Authur P. Troos, "Pulsed Laser-ignited Thermonuclear Reactor". This device is primarily a pulse device which requires the system to pass through the threshold temperature on each explosion. The difficulties in this device is that the system goes through the temperature threshold on each fuel injection resulting in an atomic explosion with the associated shock phenomena, containment, and control problems. My invention overcomes these difficulties since the temperature is maintained above the threshold temperature and the deuterium-tritium fuel is introduced continuously, creating a stable, self sustaining, steady state fusion device. The use of laser ignition in a spherical chamber is also old art as shown in "Apparatus Using Lasers To Trigger Thermonuclear Reactors" by J. R. B. Whittlesey. The difficulties in this device, as in the previous devices is one of alternation through the thermonuclear threshold temperatures, which would make it non-applicable as steady state fusion device due to the shock and containment phenomena. Also, no electromagnetic or liquid, such as lithium containment of the plasma is used as it expands from thermonuclear ignition. According to my improvement I overcome these difficulties by providing a system of electromagnetic confinement of the plasma at the point of ignition to produce a self sustaining, steady state, fusion where the nuclear threshold point is only traversed at ignition. After thermonuclear ignition the laser is shut off and the deuterium-tritium mixture is injected continuously into the ignition chamber to sustain the reaction. In FIG. 9 a deuterium extraction unit 91, extractor valve 93, a deuterium pump 96 which pumps deuterium into the reactor. A second valve 95 is provided to control feed into the tritium extractor 94. Lithium is pumped out of the reactor 99 by pump 910 and through the lithium heat exchanger 911. The lithium heat exchanger heats the steam for the turbine 97 which drives the generator 92 and power is coupled out through transformer 913. Steam is then pumped out of the turbine through the condenser 914 and 98 and pumped back into the turbine through a condenser 911. In FIG. 9 the energy conversion system operates as a lithium top unit. Energy would be converted either by this system or by the electrohydrodynamic inversion principle as described previously. The structure of the power couple consists of three main parts, namely; an extraction cycle, a lithium cycle, and a steam cycle. The structures of each of these are as follows: Additional parameters and examples of the operational embodiments are as follows: 1. Laser A neodymium glass laser with an energy of 2.times.10.sup.3 to 10.sup.7 joules is needed for the ignition system. As an example a laser with an energy of 10.sup.6 joules, a power of 10.sup.12 watts, a pulse duration of 10.sup.-9 sec. and a wave length of 5280 A may be employed. 2. Ignition Chamber The temperatures in the ignition chamber could operate at temperatures from 70.times.10.sup.6 .degree. F. to 100.times.10.sup.6 .degree. F. as an example, the above reactor would operate at a temperature of 85.times.10.sup.6 F. The pressures at the inside wall would only be a few atmospheres, a typical pressure would be 30 psi. The thickness of the various layers of the reactor are as follows: As mentioned earlier in the specification the ignition chamber wall thickness would be 254 MM in the lithium in the blanket would be in the liquid state and would be pumped through the system at the rate of 1600 gallons per minute. It would operate at a temperature of 900.degree. to 1880.degree. F. As an example for a steam power couple it would operate at about 1550.degree. F. since the superheat range for the steam cycle would be about 1250.degree. F. The lithium blanket thickness would be 57 cm. Outward from the blanket would be a 58 mm vacuum barrier. The cryojacket for the Ioffe bar system would be 40 cm thick and operate at a temperature of about 4.degree. R A low temperature insulation barrier 52 cm thick would surround the entire reactor. The new fuel would be forced to the ignition point at the center of the reactor and be balanced by the plasma pressure as shown in FIG. 8.
	summary
047626631	summary	FIELD OF THE INVENTION The present invention relates to a self-testing monitoring circuit and more particularly to a self-testing monitoring circuit for a nuclear power plant, the circuit being capable of assuming artificially created fault states for testing both its own operation and the operation of additional monitoring circuitry. BACKGROUND OF THE INVENTION In many applications in control systems for plants, including nuclear power plants, it is desirable or even necessary to sense the status of switch contacts. The switches may be main control board push buttons or selector switches, or they may be limit switches located on motordriven actuators. In either case, it is crucial that the process control system be able to sense the switch status reliably. One measure used to enhance the reliability of such systems involves the use of paired or redundant contacts, in which a switch has at least two pairs of contacts which are always in opposite states. A switch with form "C" contacts or form "D" contacts is such a switch. In the form "C" switch, there are two pairs of switches, one of which is normally open and the other of which is normally closed. Opening one switch automatically closes the other, and vice versa. In a form "C" switch, the contacts are arranged in a "break before make" fashion; in a form "D" switch, they are arranged in a "make before break" fashion. In either case, the switch may be inferred to be malfunctioning if both pairs of contacts have the same state after a short transition time, that is, both are open or both are closed. Therefore, to test the switch reliably, it is necessary only to provide circuitry which is capable of monitoring the condition of each half of the switch, i.e., each pair of contacts, and which produces an error signal if both pairs of contacts are in the same state. In conventional circuitry, this is accomplished by providing a digital indication of the status of the pair of contacts, e.g., a "0" if the pair of contacts is opened, and a "1" is the pair of contacts is closed. The signal indicative of the state of one pair of contacts is then compared logically with that of the other pair of contacts. If the signals have the same logical value (if the parity of a signal which a combination of the two is even) the switch is detected as malfunctioning, and appropriate corrective measures may be instituted. While such circuitry is sufficient to insure reliable operation of an overall system in many instances, it is often necessary to provide an even higher level of reliability of periodically testing the testing circuitry itself. In the past, this higher-level testing has been simply a maintenance procedure carried out on the order of once every six months or so. Again, while this periodic testing is sufficient to insure a sufficient degree of reliably in many systems, there are advantages to be achieved if testing made automatic so that it can easily be carried out more frequently and even on-line. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a switch testing circuit with a self-testing capability. It is a further object of the present invention to provide a switch testing circuit with circuitry which temporarily disconnects the testing circuitry from the switch being tested, and instead, in effect, connects it to relays which controllably mimic operation of the switch. Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. To achieve the foregoing and in accordance with the purposes of the invention, as embodied and broadly described herein, there is provided a self-testing circuit for monitoring operation of a switch, the switch having first and second pairs of contacts, the pairs having a contact in common, with one of the pairs being open and the other being closed unless the switch is malfunctioning. The circuit has first testing means, connected across the first pair and responsive to a first enable signal and a first select signal, for outputting, in the absence of the enable signal, an output signal having a first value if the first pair is open and a second value if the first pair is closed, and for outputting, in the presence of the first enable signal, an output signal having the first value of the second value regardless of whether the first pair is open or closed. The circuit also has second testing means, connected across the second pair and responsive to a second enable signal and a second select signal, for outputting, in the absence of the second enable signal, an output signal having the first value if the second pair is open and the second value if the second pair is closed, and for outputting, in the presence of the second enable signal, an output signal having the first value or the second value regardless of whether the second pair is open or closed. The output signals are applied to logic means, responsive to said first and second testing means, for producing an error signal if the first and second output signals have equal values. The testing means preferably include relays. The relays can then be used to "inject" invalid logic states into the system. If the injection of an invalid logic state fails to prompt an indication of a malfunction, it may then be inferred that the testing circuit itself is malfunctioning, and corrective measures can be taken. The invention provides means and method for self-testing which are sufficiently simple and easy that self-testing can be carried out frequently, thus enhancing reliability.
046510036	summary	BACKGROUND OF THE INVENTION The invention relates to a particle-accelerating electrode designed as a Faraday cage structure and inside of which a blanking system is provided for blanking a particle beam. It is standard in electron beam measuring technology to register high-frequency events at a measuring location with the assistance of stroboscopic measuring methods. Given a stroboscopic measuring method, an electron beam or, in more general terms a particle beam, is gated synchronously with the high-frequency event at a measuring location such that the particle beam senses the measuring location and thus triggers measured signals only during a fraction or during a plurality of fractions of a period duration of the high-frequency event at the measuring location. This occurs during each and every period of the high-frequency event at the measuring location. Stroboscopic measuring methods are preferably executed in scanning electron microscopes. Since the particle beam must be keyed in and blanked out given stroboscopic measuring methods, a particle beam blanking system is required in a stroboscopic measuring apparatus. Such a particle beam blanking system is usually provided as part of a beam generating system. A blanking system for a particle beam is known from U.S. Letters Pat. No. 4,169,229, incorporated herein by reference, wherein the particle beam is shaped after its emission with the assistance of a Wehnelt electrode and then passes an accelerating electrode designed as an apertured disk. After passage through this accelerating electrode, the particle beam impinges a first pin diaphragm, passes through the actual deflection system which comprises two symmetrical deflector plates, passes through a further pin diaphragm, and finally enters a vacuum tube through a third apertured disk secured to the vacuum tube. Since this known apparatus for blanking a particle beam is extended in the direction of the particle beam, the incorporation of such a blanking system in a particle beam apparatus requires a lengthening of the particle-optical column by introducing an additional ring into the particle-optical column. Such an apparatus, moreover, is difficult to manipulate, since many different piece parts must themselves be respectively dismantled when replacing such an arrangement or when merely removing such an arrangement from the particle-optical column. As a consequence of the many different piece parts, involved adjustment systems are required, these making the overall apparatus relatively expensive. The overall arrangement, moreover, requires many individual pin diaphragms or apertured disks in order, on the one hand, to meet particle-optical requirements and, on the other hand, in order to enable a good vacuum seal. Given this known apparatus, the entire blanking system is accommodated in a vacuum-tight housing together with the beam generator. A particle beam generating system is known from German patent application No. P 32 04 897.1, incorporated herein by reference, which comprises a particle-accelerating electrode designed as a Faraday cage and in whose interior a blanking system is attached for blanking a particle beam. This known particle beam generating system is designed such that it permits an optimum beam value or brightness and an optimum centering for a specific accelerating voltage. Since the patent application states nothing with respect to a required vacuum seal of the particle beam generating system, it is assumed that this particle-accelerating electrode is also integrated into the particle-optical beam path together with the blanking system in a fashion that is standard according to the prior art. Since, due to the blanking system, the particle-emitting electrode has a considerable extent in the direction of the particle beam, the particle-optical column must be lengthened in comparison to a particle beam system without the blanking system. This usually occurs by means of an additional introduction of a ring into the particle-optical column. As in the aforementioned apparatus, moreover, additional apertured disks or pin diaphragms are required for the vacuum seal, these resulting in a considerable expenditure for additional adjustment systems. SUMMARY OF THE INVENTION An object of the present invention is to specify a particle-accelerating electrode of the type initially cited which solves the problem of the vacuum seal in a simple way, wherein the particle-optical column need not be lengthened, is easy to manipulate, and can be relatively inexpensively manufactured. This object is achieved by providing a particle-accelerating electrode according to the invention wherein at least one sealing means for vacuum sealing is provided in a beam path as a part of the particle-accelerating electrode. A particle-accelerating electrode of the invention permits a simple adjustment of this electrode in the particle beam optical beam path. A connection piece of a particle-accelerating electrode of the invention can be designed such that it can be fitted in vacuum-tight fashion into an opening of a vacuum wall as a flange. When this opening in the vacuum wall is disposed in defined fashion with respect to the particle-optical axis, then this particle-accelerating electrode is also disposed in defined fashion relative to the particle-optical axis via a defined arrangement of the connecting piece at the particle-accelerating electrode. The connecting piece of the particle-accelerating electrode can be designed such that an additional flange ring can be disposed on it, said flange ring being flexibly adaptable to various openings of vacuum walls of various commercially available particle beam devices. As an apparatus for the vacuum seal, a pin diaphragm or an apertured disk can, in particular, be integrated into the particle-accelerating electrode. Advantageously, the bore of the particle-accelerating electrode at the particle beam input of this particle-accelerating electrode should be designed such that it permits an optimum beam and an optimum centering of the particle beam. It is beneficial for this purpose when the appliance provided for the vacuum seal is not provided until the end of this bore immediately in front of the blanking system. This appliance for the vacuum seal need not be designed as a separate part. The bore at the particle beam input of the particle-accelerating electrode can also be designed such that it is gradually or discontinuously or abruptly tapered to dimensions which are required for the vacuum seal. An appliance for the vacuum seal can also be disposed at the particle beam output of the particle-accelerating electrode. It is fundamentally sufficient when a single appliance for the vacuum seal is integrated into the particle-accelerating electrode. This single appliance for the vacuum seal can be disposed at an arbitrary location of the particle-accelerating electrode insofar as it fulfills the purpose of the vacuum seal. In electron beam measuring technology, an acceleration voltage of 2.5 kV is usually used in the quantitative potential measurement at LSI electronic components. Since the potential resolution is particularly favorable given a high-current source, high-current cathodes such as, for example, lanthanum hexaboride cathodes, are advantageously employed. Such high-current cathodes, however, require a particularly good vacuum in the cathode chamber because the performance capability of these high-current cathodes otherwise suffers. It is beneficial in such a case when a structure for the vacuum seal having a particularly small opening is provided at the particle beam input of the particle-accelerating electrode. In such a case, it is particularly beneficial for the vacuum seal and for the beam shaping when a further structure, for example a pin diaphragm having a small opening, is provided at the particle beam output of the particle-accelerating electrode. Since the vacuum in the particle-optical column need not be particularly good at the level of the imaging structure or deflector structure, the opening of the structure for the vacuum seal and beam shaping at the particle-beam output of the particle-accelerating electrode can be somewhat larger than the opening of the structure for the vacuum seal at the particle beam input of the particle-accelerating electrode. Given an apparatus of the invention, the particle-accelerating electrode together with the blanking system and together with at least one structure for vacuum sealing is compactly replaceable. The invention enables a particle-optical column of a particle beam apparatus to be employed without an extension ring. The invention facilitates the adjustment of the particle-accelerating electrode. The invention solves the vacuum problem better--viewed overall--than is possible with the prior art because not as many parts have to be adjusted in the beam path, and thus tighter tolerances are possible for the applicances for the vacuum seal. When switching between various acceleration voltages, a particle-accelerating electrode of the invention can be interchanged rather comfortably for a different particle-accelerating electrode without a cathode or an anode having to be modified. The electrode is held in position by screws or in some other fashion.
	abstract	A passive cooling system for cooling the in-containment refueling water storage tank and the spent fuel pool of nuclear power plants that can extend the number of days the plants can safely be maintained without operator intervention. The cooling system employs a thermosiphon in a closed loop cycle that circulates a refrigerant around the cooling loop between heat exchangers within the spent fuel and in-containment refueling water and the ambient atmosphere outside the containment, by natural circulation.
062460633	summary	FIELD OF THE INVENTION The present invention relates to a radiation image storage panel employable in the radiation image recording and reproducing method utilizing a stimulable phosphor. BACKGROUND OF THE INVENTION As a method replacing a conventional radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor was proposed and has been practically employed. The method employs a radiation image storage panel comprising a support and a stimulable phosphor layer (stimulable phosphor sheet) provided thereon, and comprises the steps of causing the stimulable phosphor of the panel to absorb radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as "stimulating rays") to release the radiation energy stored in the phosphor as light emission (i.e., stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image from the electric signals. The panel thus treated is subjected to a step for erasing a radiation image remaining therein, and then stored for the next recording and reproducing procedure. Thus, the radiation image storage panel can be repeatedly employed. In the above method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to the object at a considerably smaller dose, as compared with a conventional radiography using a combination of a radiographic film and radiographic intensifying screen. Further, the method is very advantageous from the viewpoints of conservation of resource and economic efficiency because the radiation image storage panel can be repeatedly used while the radiographic film is consumed for each radiographic process in the conventional radiography. The radiation image storage panel employed in the above-described method has a basic structure comprising a support and a stimulable phosphor layer provided on one surface of the support. If the phosphor layer is self-supporting, the support may be omitted. The phosphor layer usually comprises a binder and stimulable phosphor particles dispersed therein, but it may consist of agglomerated phosphor with no binder. The phosphor layer containing no binder can be formed by deposition process or firing process. Further, the layer comprising agglomerated phosphor soaked with a polymer is also known. The stimulable phosphor emits stimulated emission when excited with stimulating rays after having been exposed to a radiation such as X-rays. Accordingly, the radiation having passed through an object or radiated from an object is absorbed by the phosphor layer of the storage panel in proportion to the applied radiation dose, and a radiation image of the object is produced in the panel in the from of a radiation energy-stored image. The radiation energy-stored image can be released as stimulated emission by sequentially irradiating the storage panel with stimulating rays. The stimulated emission is then photoelectrically detected to give electric signals, so as to reproduce a visible image from the electric signals. In general, a transparent film of polymer material is placed on the free surface (surface not facing the support) of the phosphor layer to keep the layer from chemical deterioration or physical shock. This surface protective film can be formed by various method, for example, by applying a solution of resin (e.g., cellulose derivatives, polymethyl methacrylate), by fixing a transparent resin film (e.g., a glass plate, a film of organic polymer such as polyethylene terephthalate) with adhesive, or by depositing inorganic materials on the phosphor layer. In order to improve the quality (e.g., sharpness, graininess) of the resultant visible image, a radiation image storage panel having a protective film of a particular haze is proposed in Japanese Patent Provisional Publication No. 62 (1987)-247298. Further, the inventors proposed a storage panel having a new protective film (U.S. Ser. No. 09/050,953, now allowed). The proposed film has a multi-layered structure comprising a plastic film and a fluorocarbon resin layer containing light-scattering fine particles. The radiation image recording and reproducing method is very useful for obtaining a radiation image as a visible image, and it is desired for the radiation image storage panel employed in the method to have a high sensitivity and give an image of high quality (such as high sharpness and high graininess). The radiation image storage panel is repeatedly used in the cyclic procedure comprising the steps of: exposing to a radiation (for recording of a radiation image), irradiating with stimulating rays (for reading of the recorded image), and exposing to an erasing light (for erasing the remaining image). In this procedure, the storage panel is transferred from one step to another by means of conveying means such as belt and rollers in the radiation image recording and reproducing apparatus, and after a cycle of the steps is conducted, the storage panel is piled up on other storage panels and stored for next cycle. Since the surface of the storage panel is directly brought into contact with the conveying means (e.g., belt and rollers), stains and abrasions are liable to be produced. The stains and abrasions thus produced on the protective film disturb passage of the stimulating ray and/or the stimulated emission, and consequently depress the resultant image quality. For this reason, the surface of the panel has to have enough durability to resist the stains and abrasions. Hitherto, the sharpness of resultant image has been thought to be improved by thinning the protective film. The thin protective film, however, often cannot satisfactorily protect the panel from the stains and abrasions, and hence the storage panel with the thin protective film generally has unsatisfactory durability. In order to solve this problem, various protective films were proposed. For example, a material having both high transparency and enough strength (e.g., polyethylene terephthalate) can be employed, or some kinds of resins can be used in combination. Further, a protective film having a multi-layered structure is also known. Those known protective films have been developed in consideration of protection of the stimulable phosphor layer from chemical and physical deterioration (e.g., scratch resistance, stain resistance and abrasion resistance), as well as sharpness of the resultant image. However, although those protective films are improved to a certain extent, their properties should be more improved. SUMMARY OF THE INVENTION It is an object of the present invention to provide a radiation image storage panel having high surface durability and giving an image of high sharpness with high sensitivity. The inventors studied to achieve the object, and finally have found that the protective film showing light-scattering in a particular degree can improve the sharpness. On the basis of this finding, the inventors have succeeded in preparing a radiation image storage panel which has a protective film having an enough thickness but which can give an image of high sharpness. The present invention resides in a radiation image storage panel having a phosphor layer comprising a stimulable phosphor, and a surface protective film provided thereon, wherein the surface protective film exhibits scattering with a scattering length of 5 to 80 .mu.m observed at a main wavelength of stimulated emission from the stimulable phosphor. The scattering length is used to indicate a mean distance in which light travels straight until it is scattered, and hence a small value of scattering length means that the light is highly scattered. In accordance with Kubeluka-Munk theory, the scattering length can be calculated form the data obtained in the following measurement. First, three film samples are prepared. Each film sample has a different thickness, but consists of the same components as the surface protective film sample. The thickness (.mu.m) and the diffuse transmittance (%) of each sample are measured. The diffuse transmittance (%) can be measured by means of a spectrophotometer equipped with an integrating sphere. In the below-described examples of the present specification, an automatic recording spectrophotometer (U-3210, manufactured by HITACHI, Ltd.) equipped with an integrating sphere of 150 .phi. (150-0901) was used. The diffuse transmittance is measured at a wavelength corresponding to the main peak of the stimulated emission from the phosphor contained in the phosphor layer on which the surface protective film sample is provided. From the thickness (.mu.m) and the diffuse transmittance (%) obtained in the above measurement, the scattering length is calculated in accordance with the following formula (A) derived from Kubeluka-Munk theory. (The following formula (A) can be easily derived, under the boundary condition of the diffuse transmittance (%), from the formulas 5.1.12 to 5.1.15 described in "Keikotai Handbook [in Japanese, Handbook of Phosphor]", published by Ohm-sha, 1987, pp. 403.) Formula (A): EQU T/100=4.beta./[(1+.beta.).sup.2.multidot.exp(.alpha.d)-(1-.beta.).sup. 2.multidot.exp(-.alpha.d)] in which T represents the diffuse transmittance (%), d represents the thickness (.mu.m), and .alpha. and .beta. are defined by the formulas: .alpha.=[K.multidot.(K+2S)].sup.1/2 and .beta.=[K/(K+2S)].sup.1/2, respectively. Into the formula (A) is incorporated the measured T (diffuse transmittance) and d (thickness) of each film sample, and thereby the values of K and S are determined. The scattering length (.mu.m) and the absorption length (.mu.m) described hereinafter are values defined by 1/S and 1/K, respectively. Preferred embodiments of the present invention are as follows. (1) The scattering length is in the range of 10 to 70 .mu.m. (2) The surface protective film comprises light-scattering fine particles dispersed in a resin. (3) The light-scattering fine particles have a refractive index of at least 1.6 and a particle size of 0.1 to 1.0 .mu.m. (4) The light-scattering fine particles have a refractive index of at least 1.9 and a particle size of 0.1 to 0.5 .mu.m. (5) The surface protective film contains light-scattering fine particles in an amount of 0.5 to 10 wt. %. (6) The surface protective film has a thickness of 3.5 to 10 .mu.m. (7) The resin in the protective film is a fluororesin or a fluorocarbon resin. (8) The surface protective film further contains a dispersing agent. DETAILED DESCRIPTION OF THE INVENTION The radiation image storage panel of the invention is now described in detail. The support employed in the invention can be optionally selected from those employed in the conventional radiation image storage panels. On the phosphor layer-side surface of the support, one or more auxiliary layers (e.g., light-reflecting layer containing light-reflecting material such as titanium dioxide, light-absorbing layer containing light-absorbing material such as carbon black, adhesive layer comprising polymer material such as gelatin) may be provided, if desired, for improving sensitivity or image quality (sharpness, graininess) or for enhancing bonding strength between the support and the phosphor layer. Further, for improving the sharpness of the resultant image, fine concaves or convexes may be formed on the phosphor layer-side surface of the support (or on the phosphor layer-side surface of the auxiliary layer, if it is provided). If the phosphor layer is self-supporting, the support may be omitted. On the support, a phosphor layer comprising a stimulable phosphor is provided. As the stimulable phosphor, preferred is a phosphor giving a stimulated emission of a wavelength in the range of 300 to 500 nm when irradiated with stimulating rays of a wavelength in the range of 400 to 900 nm. In Japanese Patent Provisional Publications No. 2(1990)-193100 and No. 4(1992)-310900, examples of the stimulable phosphor are described in more detail. Examples of the preferred phosphors include divalent europium or cerium activated alkaline earth metal halide phosphors (e.g., BaFBr:Eu, BaFBrI:Eu), and cerium activated oxyhalide phosphors. Needless to say, those examples by no means restrict the invention, and other stimulable phosphors can be employed for the invention. A typical stimulable phosphor layer in the invention comprises a binder resin and stimulable phosphor particles dispersed therein, and hence the radiation image storage panel of the invention having that phosphor layer is explained below. The phosphor layer can be formed, for example, in the following known manner. First, the phosphor particles are uniformly dispersed in an organic solution of binder resin to prepare a coating liquid. The ratio between the binder and the phosphor in the solution depends on the characteristics of the phosphor and the desired property of the storage panel, but generally they are employed in the ratio of 1:1 to 1:100 (binder:phosphor, by weight), preferably 1:8 to 1:40. Thus prepared coating liquid is coated on the support by known coating means (such as doctor blade, roll coater, and knife coater), and then dried to form a stimulable phosphor layer. The thickness of the phosphor layer is determined according to the characteristics of the phosphor, the desired property of the radiation image storage panel, and the mixing ratio of binder and phosphor, but generally in the range of 20 .mu.m to 1 mm, preferably 50 .mu.m to 500 .mu.m. The phosphor layer may be formed by other steps, namely, applying the above coating liquid onto a temporary support (e.g., glass plate, metal plate, plastic sheet), drying the applied liquid to form a phosphor layer, peeling off the phosphor layer, and then providing the phosphor sheet with an adhesive or by pressing onto the final support. The stimulable phosphor layer may consist of agglomerated phosphor with no binder. Further, the phosphor layer comprising agglomerated phosphor soaked with a polymer is also employable. On the phosphor layer, the surface protective film having the specific characteristic is formed. The protective film exhibits scattering with the scattering length of 5 to 80 .mu.m (preferably 10 to 70 .mu.m) observed at a main wavelength of stimulated emission from the stimulable phosphor contained in the phosphor layer. Preferably, the protective film contains light-scattering fine particles dispersed in a resin. The particles preferably have a particle size of 0.1 to 1.0 .mu.m (more preferably 0.1 to 0.5 .mu.m) and a refractive index of not less than 1.6 (more preferably not less than 1.9). Examples of the light-scattering fine particles include fine particles of magnesium oxide, zinc oxide, zinc sulfide, titanium dioxide, niobium oxide, barium sulfate, lead carbonate, silicon oxide, polymethyl methacrylate, styrene and melamine. Preferred are zinc oxide, zinc sulfide, titanium dioxide and lead carbonate, and particularly preferred is titanium dioxide. The binder employable for the protective film is not specifically restricted. Examples of the binder materials include polyethylene terephthalate, polyethylene naphthalate, polyamide, aramid, and fluororesin(fluorocarbon resin). Preferred is an organic solvent-soluble fluorocarbon resin, which is a polymer of fluoro-olefin (olefin containing fluorine) or a copolymer comprising fluoro-olefin component. Examples of the fluorocarbon resin include poly (tetrafluoroethylene), poly(chlorotrifluoroethylne), polyvinyl fluoride, polyvinylidene fluoride, copolymer of tetrafluoroethylene and hexafluoropropylene, and copolymer of fluoro-olefin and vinyl ether. The fluorocarbon resin may be used in combination with other resins described above, and may contain an oligomer having polysiloxane structure or perfluoroalkyl group. Further, the fluororesin may be crosslinked with a crosslinking agent. The surface protective film can be formed by the steps of dispersing the light-scattering particles in an organic solution of the binder resin to prepare a coating liquid, applying the liquid onto the phosphor layer directly or via a desired auxiliary layer, and then drying the applied liquid to form the protective film. The surface protective film may be formed by other steps, for instance, applying the coating liquid onto a temporary support, drying the applied liquid to form a protective film, peeling off the protective film from the temporary support, and then providing the protective film with an adhesive onto the phosphor layer directly or via a desired auxiliary layer. The protective film generally contains the light scattering particles in an amount of 0.5 to 10 wt. %, preferably 0.5 to 5 wt. %. For improving dispersibility, the light scattering particles may be beforehand subjected to surface treatment and the film may contain known dispersing agents (e.g., surface active agent type, titanate coupling agent type, aluminate coupling agent type) and/or other various additives such as silicon surface active agent and fluorine surface active agent. The thickness of the protective film generally is in the range of 1 to 20 .mu.m, preferably 3.5 to 10 .mu.m. The absorption length (which indicates a mean distance in which light travels straight until it is absorbed) of the surface protective film is not restricted. From the viewpoint of sensitivity, it is preferred for the protective film not to absorb light. However, in order to make up for light shortage caused by the scattering, the surface protective film may be made to slightly absorb the light. The absorption length preferably is longer than 800 .mu.m, more preferably longer than 1,200 .mu.m. The radiation image storage panel of the invention may have any one of various known structures. For example, at least one of the layers may be colored with a colorant which does not absorb the stimulated emission but the stimulating rays.
053902203	description	DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a pertinent detail of a portion of a reactor core is shown. Control rod drive housing H has fuel support casting C supported thereon. Fuel support casting C includes arm 16 which orients casting C with respect to pin 14 in core plate P. Core plate P divides high pressure lower plenum L from core R, preserving the necessary pressure differential barrier to cause the controlled circulation within the many individual fuel bundles of the reactor. Fuel support casting C includes four apertures 20 onto which four fuel bundles B at their respective lower tie plate assemblies T are placed. Each lower tie plate assembly T is disposed to cause its inlet nozzle N to communicate to one of the apertures 20 of the fuel support casting. Fuel support casting C also includes apertures through which control rods 22 penetrate to the interstices of the four fuel bundles sitting on top of the fuel support casting C. Since the action of the control rods is not important with respect to this invention, further discussion of this aspect of the reactor will not be included. Remembering that only four out of a possible 750 fuel bundles are illustrated, it will be understood that the pressure drop across core plate P is important. Accordingly, a review of the pressure drop within a boiling water nuclear reactor can be instructive. First, and through an orifice (not shown) in the fuel support casting C, an approximate 7 to 8 psi pressure drop occurs at typical 100% power/100% flow operating conditions. This pressure drop is utilized to ensure uniform distribution of bundle coolant flow through the many (up to 750) fuel bundles within a boiling water nuclear reactor. Secondly, at in the lower tie plate of the fuel bundles on each fuel support casting C, approximately 11/2 psi of pressure drop occurs. This pressure drop is a result primarily of the change in flow velocity occurring through this complex geometry structure. Finally, and as the coolant rises and generates steam within the fuel bundle, approximately 10 to 12 psi of pressure drop is incurred. This pressure drop is distributed throughout the length of the fuel bundle - and is important to the operating stability of both the individual fuel bundles and the collective fuel bundles constituting the core of the nuclear reactor. The reader should understand that the summary of pressure drop given above is an over simplification. This is a very complex part of the design and operation of a nuclear reactor. Having said this much, one point must be stressed. Pressure drop within the individual fuel bundles of a boiling water must remain substantially unchanged. Accordingly, if apparatus for preventing debris entrainment into the fuel bundles is going to be utilized, appreciable change in overall fuel bundle pressure drop should be avoided. Having carefully reviewed the requirements for the avoidance of increased pressure drop in debris restricting devices, several further comments can be made. First, any debris catching arrangement should be sufficiently rigid so that the excluding apparatus does not under any circumstance break apart, fail to stop debris, and become the source of further debris itself. For this reason, wire screens are not used. Instead, perforated metal is in all cases utilized in the examples that follow. Second, we have found that it is desirable to restrict pressure drop to a minimum. This can be done by making the velocity of flow through the apertures themselves as low as feasible. A second reason for this limitation is the entrainment of the debris in the flow. Assuming entrainment of debris in the flow, if any possible angle of attack can be realized that will enable debris to pass through an aperture, given sufficient time, passage through the aperture will eventually occur. By maintaining slow velocity at the respective apertures, entrainment of debris is less likely to occur. Further, it has been found that a reorientation of the flow at a rejecting hole to an angle where debris passage is less likely can be achieved. Consequently, flow velocity at restricting apertures is restricted to the minimum possible value. Third, we find that modification of the rod supporting grid--a technique utilized in the prior art--is not satisfactory. Specifically, we prefer to use straining apertures that are as small as possible--down to a dimension of 0.050 of an inch diameter. Unfortunately, the rod supporting grid is a member that must have the required static and dynamic properties to support the fuel rods under all conceivable conditions. Utilizing a matrix of such holes in the rod supporting grid at the pitches required for low pressure drop in the lower tie plate is not practicable. First, since the small apertures would be confined to the plane of the rod supporting grid, a total reduction of flow area will be present that would lead both to unacceptable pressure drop as well as high flow velocities through the individual holes in rod supporting grid. Further, such a matrix of small apertures in the rod supporting grid would reduce the strength of the grid to a level below that required for support of the fuel rods. We have identified the so-called flow volume of the lower tie plate assembly as a primary candidate for the location of debris rejection apparatus--preferably the perforated metal utilized with this construction. In boiling water nuclear reactor fuel bundles at the lower tie plate assembly, there is defined between the nozzle at the lower end and the fuel rod supporting grid at the upper end, a relatively large open flow volume. This flow volume is sufficiently large to accommodate a three dimensional structure--with one side of the three dimension structure communicated to the nozzle inlet and the other side of the three dimensional structure communicated to the rod supporting grid. At the same time, periphery of the three dimensional supporting structure can be attached to the sides of the lower tie plate assembly--so that all fluids passing through the flow volume of the lower tie plate simply must pass through the restricting apertures of the perforated plate. Only small modification to the lower tie plate assembly is required. The flow volume in the lower tie plate assembly has an additional advantage. Specifically, and if the flow restricting grid has to be confined to a plane extending across the lower tie plate flow volume, the apertures in the plate would define a total flow area less than the plane in which the perforated plate was disposed. Where a perforated plate is utilized to manufacture a three dimensional structure, the area of the available apertures can increase beyond that total area possible when the perforated plate is confined to a flat plane. In fact, where sufficient structure is utilized, the total flow area available in the aggregated holes of the three dimensional structure can approach and even exceed the total cross sectional area across the flow volume of the lower tie plate assembly before the insertion of the debris restricting assembly. In addition a properly designed debris catcher assembly could improve the flow distribution at the inlet to the fuel bundle. Having set forth these considerations, attention can be directed to the embodiments of the invention. Referring to FIG. 6, a typical filter insert I for placement of the filter apparatus of this invention to a lower tie plate T within the plenum P is illustrated. FIGS. 2A and 2B contain the respective plan and side elevation views of the disclosed helical spring matrix strainer. Referring to FIG. 2A, a plurality of side-by-side springs 100 are shown fastened between opposite walls 114, 116. Looking at FIG. 3, it can be seen that an additional second layer 102 of side-by-side helical springs has been added. These side-by-side helical springs extend between walls 115, 117 at an approximate 90.degree. angle with respect to springs 100. Referring to FIG. 4, an expanded view of springs 100, 102 is illustrated. It can be seen that these respective spring intersect one another at intersections 101. It is preferred that the springs be attached as by welding at these junctures. This attachment forms a unitary mass from the spring matrix to prevent the individual springs from becoming debris themselves should failure of the individual spring matrix occur. Referring to FIG. 5, it is preferred that four layers of springs 100, 102, 104, and 106 be utilized. As illustrated, layers 100, 104 are at 90.degree. angles with respect to layers 102, 106 with the layers alternating in their angularity. Again--and where the layers cross one another --fastening of the springs one to another occurs at points 101, 103, and 105 so that the springs as finally bound together form a unitary mass. The preferred method of such fastening is presently by welding--although other forms of fastening may be obviously used. Referring further to FIG. 5, just as the springs form a matrix, the filter formed has a series of endlessly interconnected passages. This being the case, local fill with debris will not appreciably interrupt intended flow as alternate channels permitting such flow communicate across the entire filter.
06240153&	summary	SPECIFICATION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to cleaning studs or bolts. More particularly, the invention relates to an apparatus for safely and effectively cleaning the studs used to secure reactor heads on nuclear reactors. 2. Description of the Related Art Nuclear reactor vessels typically have had a reactor head secured to the reactor vessel by large studs or bolts. The reactor studs were very large, typically around 6 feet in length and weighing up to one thousand pounds (1000 lbs.) or more. When the nuclear reactors were shut down at scheduled intervals for maintenance and inspection, the reactor studs had to be removed for cleaning and inspection. The size and weight of the reactor studs made cleaning of the studs a cumbersome and time consuming process. The cleaning process traditionally involved using an A-frame assembly and a manual chain hoist to move the reactor studs into position for cleaning. The reactor studs were then cleaned by hand using brushes or rags to remove any build up of oxides, residues, or dried lubricants. There were several problems with this process for cleaning reactor studs. The cleaning process was very laborious and consumed a significant amount of manual labor. In addition, because of the possibility that the reactor studs were somewhat radioactive, personnel could only be exposed to the studs for a short period of time. Another problem with the traditional reactor stud cleaning process was that it created a large amount of waste such as rags, scrubbing pads, and brushes that had to be treated as radioactive waste. To overcome the problems associated with manual cleaning of the reactor studs, stud cleaning machines were developed such as those disclosed in U.S. Pat. Nos. 4,165,549 and 4,452,753. These machines had housings in which a stud was placed so that the stud's longitudinal axis extended in the horizontal direction. The studs were rotated along the longitudinal axis inside the housings and cleaning was accomplished by the rotating brushes. There were several problems with these machines. First, the stud had to be positioned in a horizontal plane requiring extra handling of the potentially radioactive stud. Additionally, the machines used a mechanical cleaning process and did not have capability to utilize solvents and other cleaning agents. Further, the machines only had the capability of cleaning one reactor stud at a time. U.S. Pat. No., 4,630,410 similarly disclosed an apparatus having horizontal housing for cleaning reactor studs. However, in this apparatus, the rotary brushes were replaced with a high pressure spray nozzle that used water and an abrasive to clean the stud. This apparatus shared many of the same problems including requiring additional handling to put the studs in the horizontal position and being limited to cleaning one reactor stud at a time. SUMMARY OF THE INVENTION Briefly, the present invention provides a reactor stud cleaning apparatus for cleaning connector studs, nuts, and washers used to secure reactor heads on nuclear reactors. The cleaning apparatus is a self-contained unit having a housing that includes at least two independent sealable compartments allowing cleaning of two or more studs at a time. Each sealable compartment has a topside covering with a port that allows the reactor studs to be lowered into the apparatus keeping the longitudinal axis of the reactor stud maintained in a substantially vertical position. Inside the sealable compartments is a turntable for vertically mounting a reactor stud and for rotating the stud about its longitudinal axis. Brushes rotatably mounted inside the compartment are used to clean the reactor stud. The ability to keep the reactor studs in a vertical position decreases the handling required and therefore the safety risk associated with handling of the potentially radioactive studs. Preferably, the apparatus also has a cleaning agent circulation system for circulating solvents or other cleaning agents over the reactor stud during cleaning. The circulation system of the present invention stores cleaning agent in a sump. A pump is used to pump the cleaning agent from the sump to a spray nozzle where the agent is sprayed over the reactor stud during cleaning. The cleaning agent is then drained from the compartment and passed through a filter to remove contaminants before it is returned to the sump for reuse. Spent cleaning agent can be drained from the sump and disposed of according to appropriate hazardous waste regulations. The cleaning agent circulation system enhances the cleaning of the reactor studs, while the amount of waste generated is minimized by filtering and reusing the cleaning agent.
	abstract	Apparatus and methods for measuring radiation in a borehole environment using a YAlO3:Ce (YAP) scintillation crystal. Borehole instruments are disclosed which employ a gamma ray detector comprising a YAP scintillator coupled to a light sensing means such as a photomultiplier tube. One instrument embodiment combines a YAP scintillation detector and a source of pulsed neutrons. Borehole environs are irradiated with neutrons, and induced gamma radiation is measured using a YAP scintillation detector. Response of the detector is used to determine characteristics of the borehole environs. Mechanical and physical properties of YAP are utilized to obtain improved measurements. The relatively short light decay constant of YAP minimized pulse pile-up in the detector when measurements require that the detector be operated during a neutron pulse.
	description	This application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/EP2016/052528, filed Feb. 5, 2016, which claims the benefit of German Application No. 10 2015 102 732.1, filed Feb. 25, 2015. The entire contents of each of the foregoing patent applications are hereby incorporated by reference. 1. Technical Field. The invention relates to a device and a method for checking a fuel rod of a fuel element in a water-filled pool of a nuclear plant. 2. Background and Relevant Art. During operation of nuclear reactors, individual fuel rods may have defects and develop leaks, as the result of which radioactive fission products may escape into the coolant and increase its radioactivity. This in turn results in an undesirable increase in the radiation exposure in the vicinity of the cooling system. Fuel rods are therefore typically checked for defects every time a fuel rod or fuel element is replaced. For this purpose it is known, for example, to transport the fuel rods, which are not in use and are stored in a water-filled storage pool, in so-called hot cells and inspect them at that location, which is very complex. However, checking in the water-filled pool itself is very difficult, since the measuring devices used are often very sensitive to radiation, and their proper functioning can be ensured only in a water-free environment. For example, a device for checking a fuel element in a storage pool of a nuclear plant is known from EP 2 208 206 B1, in which the fuel element is checked underwater with a displaceably mounted image detector, such as a camera, and a scale situated in parallel to a longitudinal axis of the fuel element is provided for locating defects in the fuel element. DE 24 24 431 describes, for example, a device and a method for locating defective fuel rods within a fuel element, in which the fuel element stands in a test container that is stored in a pool of water and covered by a bell, a measuring device being situated in the bell, and the water present in the bell being pressed out by means of a gas stream in order to ensure a water-free space between the measuring device and the fuel rod. However, such a device allows only checking of the upper rod ends or making a distinction between fuel rods that are defective overall and those that are undamaged. The object of the invention, therefore, is to provide a device and a method that allow improved checking of a fuel rod in a water-filled pool of a nuclear plant. The first-mentioned object is achieved with a device for checking a fuel rod of a fuel element in a water-filled pool of a nuclear plant underwater, having the features according to Patent Claim 1. The device comprises a test container having a first chamber and a second chamber, and a first test device situated in the test container. The test container has at least one inlet opening and at least one outlet opening. In addition, the test container has at least one insertion opening for inserting the fuel rod into the second chamber. The first and the second chambers are connected to one another via a connecting channel, and a valve is situated in the connecting channel. The test container is lowerable into the water-filled pool in order to check the fuel rod, so that a check in the water-filled pool, for example a storage pool or a cooling pond, may take place underwater. The fuel rod to be checked is insertable into the second chamber through the insertion opening. The first test device is situated in the test container in the first chamber or in direct contact with the first chamber, in particular in an upper area of the first chamber. In other words, the first test device is situated in the test container in such a way that it is spatially separated by the connecting channel from the second chamber into which the fuel rod is insertable. This has the advantage that if water enters, the first test device may be protected from the water via the valve that is situated in the connecting channel and is movable into the closed position. The first test device and the fuel rod are thus situated in different chambers, which are connected to one another by a connecting channel that is closable by a valve situated therein. A fluid or a gas flows into one of the chambers through the inlet opening, the gas inlet being controllable via a valve, for example. Due to the gas flowing in, the water which is present inside the test container or inside the chambers and/or the connecting channel, and which has entered, for example, due to lowering of the test container into the water-filled pool or the insertion of the fuel rod, may be flushed out through the at least one outlet opening. The inlet opening and the outlet opening are thus fluidically connectable to one another in such a way that the inflowing fluid or gas displaces the water from the chambers or from the interior of the test container and expels it through the outlet opening. The valve, which regulates the flow of the fluid between the first and second chambers and is movable between an open position and a closed position for protection of the first test device, is, for example, a shutoff valve of the known type. By use of the device according to the invention, it is thus also possible to check a fuel rod in a pool of water, since a test device which is water-sensitive or which provides reliable measured values only in a water-free environment is protected from water by the time that the water, which has penetrated upon insertion of the fuel rod, is removed from the interior of the test container. For checking the fuel rod with the first test device, the valve is opened and the check is carried out. The inlet opening as well as the outlet opening may be situated in the second chamber, so that the first chamber is not in contact at all with the water-filled pool. However, without targeted ventilation of the first chamber, there is a risk that after the valve is opened, at least moist air may pass into the first chamber and deposit as condensate on the first test device. To avoid this, the at least one inlet opening preferably leads into the first chamber of the test container, i.e., is situated in a wall of the test container that encloses or forms the first chamber. Supplying the gas after the valve is opened thus expels the water from the entire interior of the test container, i.e., the first chamber, the connecting channel, and the second chamber. Situating the inlet opening in the first chamber has the advantage that the water is always blown out of the interior in the direction of the second chamber, and thus, away from the first test device, so that entry of moisture from the second chamber into the first chamber is largely avoided. In principle, it would be sufficient to provide the at least one outlet opening in the second chamber. However, it is advantageous when the test container has a first outlet opening in the first chamber and a second outlet opening in the second chamber, i.e., an outlet opening in each of the two chambers. When the inlet opening is likewise situated in the first chamber, gas may continuously flow through the first chamber in which the first test device is situated, so that the first chamber always remains free of water and the first test device is protected. The first chamber may thus also be ventilated in a targeted manner when the valve is still closed. In one preferred embodiment, the device has a second inlet opening that leads into the second chamber of the test container. An inlet opening as well as an outlet opening are thus associated in each case with the first chamber and with the second chamber, so that both chambers may be ventilated independently of one another. The inlet openings and the outlet openings are each closable by a valve. In one preferred embodiment, in addition to the insertion opening for inserting the fuel rod into the second chamber, the test container has an exit opening situated behind the insertion opening, relative to an axis. The insertion opening and the exit opening are thus situated in a line, one behind the other. The device and the test container may thus have a more compact design and still carry out a complete check of the fuel rod. The fuel rod is insertable through the insertion opening and removable through the exit opening situated opposite from the insertion opening, so that multiple axial sections of the fuel rod, i.e., areas along its longitudinal axis, may be checked. The fuel rod may thus be moved through the second chamber so that the fuel rod may be checked along its entire length. The insertion opening and/or the exit opening are/is preferably adjoined in each case by a guide channel formed by the wall of the test container. Such a guide device made up of the opening and the channel facilitates linearly inserting the fuel rod into the second chamber and removing it from the second chamber. The guide channel extends from an insertion opening to the upper end (in relation to the pool) of the test container toward the second chamber. A further guide channel extends from an exit opening in the second chamber to a lower end (in relation to the pool) of the test container. The first test device is preferably a spectroscopic measuring device, in particular an infrared measuring device such as an infrared camera, an infrared sensor, or some other spectrometric measuring device that detects the radiation, in particular thermal radiation, emitted from the fuel rod. If layers having different heat conduction or different thicknesses are present on the surface of the fuel rod, for example oxide layers or other deposits, these may be displayed by means of infrared technology. For bright surfaces that have been brushed prior to the check, differences in the heat conduction that occur within the cladding tube of the fuel may be detected. These result, for example, from inhomogeneities in the gap region between the pellets and the inner side of the cladding tube, which may be caused, for example, by pellet separation or by fragments that have chipped off from the pellets. A spectral analysis of the spectrum recorded using the spectroscopic measuring device also allows examination or identification of the composition of the material of the fuel rod. In one preferred refinement of the invention, a second test device is situated in the second chamber of the test container. The second test device is, for example, a conventional camera that is resistant to radiation and insensitive to water. A light source is also preferably situated in the second chamber, so that damage to the fuel rod may first be identified with the second test device prior to a check with the first test device. If the device also has a second inlet opening that leads into the second chamber of the test container, the second chamber may already be vented for the check with the second test device. This has the advantage that the valve may then be opened at any time during the check with the second test device in order to be able to check a position of the fuel rod, to be tested with the first test device, in greater detail without having to ventilate the second chamber beforehand. To protect the test devices from radiation that is emitted from the fuel rod, in particular γ radiation, it is advantageous for the first and/or the second test device to be enclosed by a shielding device. Additional protection of the test devices from radiation is achieved in particular by situating at least one mirror in the first chamber and/or in the second chamber of the test container. A mirror situated in the first chamber in the beam path of the first test device, for example, the infrared camera, reduces the effect of radioactive radiation, emitted from the fuel rod, on the check. The mirror is situated in the beam path in such a way that radiation that is emitted from the fuel rod is directed into an entry window of the first test device. A semitransparent mirror or a folding mirror, for example, is suitable as a mirror. For inserting the fuel rod into the test container and for rotating and moving the fuel rod up and down during the check, the device advantageously includes a handling tool or actuating means such as a gripper, which grips the fuel rod at its upper end and guides it into the second chamber. For this purpose, it is advisable to utilize a handling tool that is already present at the storage pool or cooling pond. To minimize penetration of water into the test container or into the second chamber when the fuel rod is already inserted, in one advantageous embodiment the device has a sealing device that closes off the second chamber from the water-filled pool. Although the second chamber and the insertion opening and optionally the exit opening are already largely sealed off by the fuel rod itself, the sealing device allows the entry of water during the check to be reduced to a minimum. The sealing device includes in particular a flexible sealing element which completely encompasses the insertion opening and optionally the exit opening, and the at least one guide channel. In other words, the sealing device closes off a gap that is present between the wall of the test container that forms the guide channel, and the fuel rod. If an upper guide channel and a lower guide channel, i.e., an insertion opening and an exit opening, are present, for example two ring-shaped elements are provided. These are preferably fillable or inflatable with gas, so that when the fuel rod is inserted they may be activated in order to further seal off the openings. In another preferred embodiment, the test container is designed in such a way that the fuel rod and at least a portion of the handling or actuating means are situated completely within the second chamber, and the interior of the second chamber is sealed off from the water-filled pool via a sealing element. For this purpose, it is possible in principle to design the test container itself in such a way that the fuel rod is completely insertable therein. However, it is advantageous for the test container to have further test housings, having an interior, that are mountable on a top or bottom side of the test container, adjoining the second chamber. In other words, the sealing device includes at least one additional test housing that completely covers the fuel rod and at least a portion of the handling or actuating means outside the test container. The sealing element is situated in the additional test housing, for example in an area of the handling tool, in order to completely seal off the interior, formed by the second chamber and the at least one additional test housing, from the water-filled pool. The sealing element thus closes off a gap that is present between the wall of the additional test housing and the handling tool. The second mentioned object is achieved with a method for checking a fuel rod of a fuel element in a pool of water of a nuclear plant, having the features according to Patent Claim 16. A device that is designed corresponding to the above-described features is used, so that reference is initially made to the previous discussion. The fuel rod is initially inserted into the second chamber of the housing through the insertion opening or the guide channel, with the valve closed. This takes place, for example, using the handling tool or actuating tool, which is able to move the fuel rod in the water-filled pool. During this step the test container is already lowered into the water-flooded pool, so that the second chamber of the test container is flooded with water. A fluid or gas is supplied via the inlet opening of the test container, and flows through the interior of the test container and displaces the water. If the inlet opening is situated in the second chamber, the water that has entered upon insertion of the fuel rod into the second chamber is expelled from the outlet opening, and thus, from the second chamber. If the inlet opening is situated in the first chamber, the fluid flows through the connecting channel into the second chamber as soon as the valve is opened, and displaces the water from the entire interior of the test container. If the inlet opening is situated in the first chamber and the first chamber also has an outlet opening, gas is already supplied during the insertion of the fuel rod into the second chamber in order to preferably keep the first chamber free of water. To check the fuel rod with the first test device, the valve situated in the connecting channel between the first chamber and the second chamber is opened, so that the fuel rod enters into the visual field of the first test device. When the water has been virtually completely removed from the interior of the test container, the checking of the fuel rod with the first test device takes place. The gas flow is preferably maintained during the check of the fuel rod, i.e., fluid is continuously supplied to the interior of the test container, to prevent water from penetrating into the first and/or second chamber through one of the outlet openings, and to keep the interior of the test container free of water. The temperature of the supplied fluid is settable, so that the accuracy of the check, which depends essentially on the temperature ratio of the temperature inside the chambers to the surface temperature of the fuel rod, may be positively influenced. In one advantageous embodiment, the valve is first opened as soon as the sealing device closes off the second chamber from the water-filled pool. When a sealing element corresponding to a ring-shaped, inflatable sealing element that encloses the guide channel is used, it is inflated as soon as the fuel rod is completely inserted in order to further reduce penetration of water through the gap that remains between the wall of the test container and the fuel rod. In one preferred refinement of the method, after it is inserted into the test container the fuel rod is initially checked with the second test device situated in the second chamber, with the valve closed. During the check, the fuel rod is moved up and down along a direction extending parallel to a longitudinal axis of the fuel rod and/or is rotated about the longitudinal axis so that an inspection at multiple axial sections of the fuel rod can take place. The fuel rod is thus initially inspected with the second test device to determine a relevant partial or longitudinal section of the fuel rod. When a measuring device that is insensitive to water is used as the second test device, this may take place without having to displace the water from the second chamber beforehand. A closer inspection of this section of the fuel rod is subsequently carried out with the first test device. During the check with the first test device, the infrared camera, for example, the fuel rod remains stationary. The partial section to be inspected is therefore aligned beforehand in such a way that it is in the field of vision of the first test device. For this purpose, the fuel rod is, for example, rotated until the location to be checked is aligned with the viewing direction toward the infrared camera, for example also with the mirror situated in between. To be able to carry out the check with the infrared camera, the sealing device is activated, i.e., for example the two seals are inflated, the water is blown out of the second chamber, and the valve is opened. As the result of such a pre-inspection using an additional test device, the level of effort for a measurement with the first, water-sensitive test device, for example the infrared measuring device, is greatly reduced. FIG. 1 shows a device 2 for checking a fuel rod 4 of a fuel element (not illustrated) in a water-filled pool 6 of a nuclear plant, with the fuel rod 4 inserted and a valve 24 closed. The device 2 includes a test container 8 that is lowered into the water-flooded pool 6. The test container 8 has an interior that is formed by a first chamber 10, a second chamber 12, and a connecting channel 22. A valve 24, in the present case a shutoff valve, which is movable between an open position (FIG. 2) and a closed position (FIG. 1) for opening and closing the connecting channel 22, and thus, for establishing a fluidic connection between the first chamber 10 and the second chamber 12, is provided in the connecting channel 22. An infrared measuring device or an infrared camera as the test device 14 is situated in the first chamber 10. To protect the radiation-sensitive test device 14 from the radioactive radiation emitted from the fuel rod 4, the test device 14 is enclosed by a shielding device 34. The test device 14 is situated in parallel to the fuel rod 4, so that the exit or entry window 46 of the test device for the infrared radiation points in the direction of the second chamber 12. Gas flows into the first chamber via a first inlet line 44 and a first inlet opening 16 that is present in the wall 26 of the first chamber 10. A second inlet opening 44 and a second inlet opening 16 may be provided in the wall 26 of the second chamber 12, which open into the second chamber 12 and by means of which the second chamber 12 may be separately ventilated. Present in the wall 26 that surrounds the first chamber 10, at the bottom side 52 of the test container 8, is an outlet opening 18a that leads into the water-flooded pool 6 via an outlet channel 48a. An outlet opening 18b, which once again leads into the water-flooded pool 6 via an outlet channel 48b, is also present in the side of the wall 26 surrounding the second chamber 12. The test container 8 has an insertion opening 20a on a top side 50 for inserting the fuel rod 4 into the second chamber 12. An exit opening 20b that is situated behind the insertion opening 20a, relative to the axis Z that extends in parallel to a center longitudinal axis A of the fuel rod, is used for removing the fuel rod 4 from the chamber 12, so that the fuel rod 4 can be moved through the chamber 12 to enable checking of multiple axial sections extending in parallel or along a center longitudinal axis A of the fuel rod 4. The insertion opening 20a and the exit opening 20b are adjoined by a guide channel 28a, b, respectively, that is formed by the wall 26 of the test container 8, the guide channel 28a leading from a top side 50 of the test container 8 into the second chamber 12, and the guide channel 28b leading from the second chamber 12 to a bottom side 52 of the test container 8. The guide channel 28a, b prevents excessive tilting of the fuel rod 4 so that it may be led in and out of the second chamber 12 more easily. The device 2 also includes a second test device 30 that is situated in the second chamber 12 of the test container 8 in such a way that the inserted fuel rod 4 is in the field of vision of the second test device. In the present case, the second test device 30 is a camera that is insensitive to radiation, so that no shielding device 34 is required. A light source 32 is provided in the second chamber 12 for checking the fuel rod 4 with the second test device 30. A mirror 36 is situated in the first chamber 10 for directing the thermal radiation emitted from the fuel rod 4 into the entry window 46 of the first test device 14 or the infrared camera. The radiation exposure for the first test device 14 may be further reduced by the mirror 36, since the first test device is not directly exposed to the radioactive radiation that is emitted from the fuel rod 4. For inserting the fuel rod 4 into the test container 8 and moving it parallel to a direction R and rotating it about a longitudinal axis A of the fuel rod 4 during the check, the device includes a handling tool 38, a gripper, for example, which is already present for transporting the fuel rods 4 in the water-flooded pool 6. The device 2 also includes a sealing device 40 via which the second chamber 12 may be closed off from the water-filled pool 6. The sealing device 40 includes two sealing elements 42, situated in each case in a recess 54 in the wall 26 of the test container 8 adjoining the guide channel 28a, b, and each completely enclosing a guide channel 28a, b. The sealing elements 42, as illustrated in FIG. 2, are fillable with gas or a liquid medium, so that a gap that may be present between the inserted fuel rod 4 and the guide channel 28a, b is completely closable. For checking the fuel rod 4 in the water-flooded pool of the nuclear plant, the fuel rod 4 is inserted into the second chamber 12 of the test container 8 through the insertion opening 20a, with the valve 24 closed (FIG. 1). Gas is supplied via the inlet channel 44 and the inlet opening 16 in order to displace the residual water from the second chamber 10 and to avoid entry of water through the outlet opening 18a and the outlet channel 48a. Supplying of the gas is maintained during the check of the fuel rod 4. When the fuel rod 4 is completely inserted, a check with the second test device 30, situated in the second chamber 12, initially takes place with the valve 24 still closed and the light source 32 switched on. For checking multiple axial sections or the entire surface of the fuel rod 4, during the check with the second test device 30 the fuel rod is moved up and down in parallel to the direction R and rotated about its longitudinal axis A. If a location to be examined in greater detail is detected during the check with the second test device 30, an additional check with the first test device 14 then takes place. In principle, however, it would also be possible to check the entire fuel rod 4 with the first test device 14. For checking the fuel rod with the first test device 14, the fuel rod is rotated by 180° by means of the handling tool 38, so that the surface position to be checked is facing the first test device 14. The two sealing elements 42 are filled with air to avoid entry of water. The valve 24 is subsequently opened (FIG. 2), so that the gas flowing through the first inlet opening passes through the first chamber 10 and the connecting channel 22 and into the second chamber 12, where it displaces the water from the chamber 12. During checking of the fuel rod 4 with the first test device 14, the entire interior of the test container 8, i.e., the first chamber 10, the connecting channel 22, and the second chamber 12, is thus free of water, thereby ensuring the functionality of the infrared measurement. FIG. 3 shows a device 2 in which the sealing device 40 includes two additional test housings 56 which completely cover the fuel rod 4 and at least a portion of the handling or actuating means 38 outside the test container 8. The test housings 56 are mounted on the test container in such a way that an interior of the test housings 56 and the second chamber 12 form a shared interior. The sealing device 40 also includes a sealing element 42 which is fillable with gas or a liquid medium, and which is situated in a recess 54 in the wall 58 of the additional test housing 56 and completely encompassed by the guide channel 28a jointly formed by the wall 58 of the additional test housing 56 and the wall 26 of the test container. For better clarity of the illustration, the sealing element 42, despite the inserted fuel rod 4 and the opened valve 24, is shown in an unfilled state. The device includes a first inlet channel 44a that opens into the first chamber 10 and a first inlet opening 16a in the first chamber 10, as well as a second inlet channel 44b that opens into the second chamber 12 and a second inlet opening 16b in the second chamber 12. Fluid may thus flow through each chamber 10, 12 independently of the other chamber, and the residual water that is present may be removed from the chambers. According to FIG. 3, the second inlet channel 44b is formed by the wall 60 of the additional test housing 56, and the inlet opening 16b opens into the guide channel 28b in an upper area of the additional test housing 56. The test container [sic; test housing] 56 situated on the bottom side 52 has an outlet opening 18b in a lower area. To ensure sufficient fluid flow in the second chamber 12, the guide channel 28b is wider than the diameter of the fuel rod 4. The second chamber 12 may thus be completely vented in the direction of the outlet opening 18b. Directly after the fuel rod is inserted and the additional test housing 56 is mounted, the water may be blown out of the second chamber 12, so that a check or pre-inspection of the fuel rod 4 with the second test device 30 also takes place in a water-free environment. For checking a position of the fuel rod 4 to be examined in greater detail, the valve 24 may then be opened at any time during the check with the second test device to enable a check with the first test device 14 without having to also ventilate the second chamber beforehand, thus saving time. List of reference numerals 2device 4fuel rod 6pool 8test container10first chamber12second chamber14first test device16inlet opening18a, boutlet opening20ainsertion opening20bexit opening22connecting channel24valve26wall of the test container28guide channel30second test device32light source34shielding device36mirror38handling tool40sealing device42sealing element44inlet channel46exit or entry window48a, boutlet channel50top side52bottom side54recess56test housing58wallRdirectionAlongitudinal axisZaxis
	summary
	description	The present application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/FR2019/052847 filed Nov. 29, 2019, which claims priority from French Application No. 1872160 filed Nov. 30, 2018, all of which are incorporated herein by reference. The invention concerns a disposable individual covering worksuit for protection against radioactive particles. The invention is applied in industrial activity in a contaminated environment. Contaminated means an environment in which radioactive particles are dispersed that are likely to come into contact with the operator staff in the facilities. In the following, the disposable individual covering worksuit for protection against radioactive particles is also called covering worksuit. In nuclear power plants, inspections and maintenance of various equipment are scheduled. In some areas, operators are subjected to ionizing radiation. These work areas are called controlled areas. They are classified according to the nature of their hazardousness and conform with very strict rules in order to protect the operator working therein. One of these risks is contamination. It is a question of a radioactive material that can potentially spread in the air and on the ground of a room if a circuit is opened. Every precaution is taken so that the operator cannot ingest or inhale these radioactive particles. Depending on the activity per unit of area measured (contamination rate indicator) in each room, the operator must follow rules for donning and removing clothing. For certain procedures in a so-called controlled area, the operator must cover with a nonwoven paper coverall (the covering worksuit), such as those from the manufacturer Tyvek, on top of their work clothes. Despite these covering worksuits, operators have been observed to contaminate themselves in some phases of work. Some of these contaminations originate from the characteristics of the covering worksuit used. Covering worksuits currently used in a fleet of nuclear power plants in operation of the fleet are universally used for all jobs and environments. These mainly ensure a seal against contamination during activities in contaminated areas. However, these covering worksuits can prove insufficient during the undressing phase, for example. Generally, when the operator has to perform a procedure in a contaminated room or a controlled area, they first cover their usual clothing, called underlying layer (which can be in a first case their personal clothing, so-called “work blues”, or in a second case, a so-called required universal clothing, such as, for example, a T-shirt, a pair of socks, an overall, a pair of cotton gloves, a cap and a helmet), with the covering worksuit, as well as gloves of vinyl or of a thicker material such as rubber or another plasticized material and boot covers. The covering worksuit must be worn when the radioactive activity per unit of area is comprised between 0.4 and 400 Bq/cm2 in the first case and between 4 and 400 Bq/cm2 in the second case. Above 400 Bq/cm2, the operator must wear a ventilated helmet, for example a protection covering the entire head to the base of the neck, or even a sealed ventilated suit over their covering worksuit, for example, a protection covering the entire body. To leave a controlled area, various checks are planned to detect any contamination. However, vigilance at all times is essential in the critical undressing phase. It is all the more important for nuclear power plants, given that said personal clothing of the operators are likely to be worn and washed in the private sphere, unlike universal clothing that does not leave the nuclear power plant. The undressing phase related to the covering worksuit is tricky. For example, in nuclear power plants in France, when in a contaminated area, operators must remove the covering worksuit, gloves and boot covers without contaminating their own clothing—generally “work blues” worn underneath—and operators must then cross a boundary, for example marked by a sawhorse, to pass into a non-contaminated area. Although it has proven itself in radiation protection, this boundary crossing is not always easy for the operator and can lead to disadvantages. Indeed, the operator must put a first leg with the covering worksuit removed behind the sawhorse without touching it and keep the second leg still clothed in the covering worksuit in the contaminated area. Then they must remove the second leg from the covering worksuit in the contaminated area, then cross the boundary to finally reach the uncontaminated area. These crossing conditions can lead to losses of balance and resting the foot of the uncovered leg in the contaminated area. Once the boundary is finally successfully crossed, the operator, who might have been contaminated, goes through control portals as is required in all nuclear power plants in the world, which will signal any actual contamination. The operator then follows the current protocol after detection of contamination, regardless of origin. The risk of so-called accidents on the same level can also be mentioned incidentally. This protection practice of wearing a covering worksuit is a tool for combatting operator contamination but does not solve certain problems that have been identified with covering worksuits bought on the market. The main disadvantages are presented below. A first disadvantage is the risk of contamination in the case of non-standard undressing. In order to overcome constraints related to crossing area boundaries, the operator may find advantageous to first remove their covering worksuit in the contaminated area and then cross the boundary. To do so, they must first open the zip closure from the collar to the crotch, then tear their covering worksuit from the crotch to the bottom of each leg, which will provide ease in the shoulders and prevent them from being in an off-balance position. This practice, not recommended by the plant operator, certainly saves time, but the main disadvantage is that the potential contamination deposited on the covering worksuit during the work can then be suspended in the air following the force of tearing and therefore lead to the contamination of the operator, their coworkers and the premises. A second disadvantage is the risk of contamination by opening the covering worksuit. When working in a controlled area, operators are required to carry documents and portable devices such as, for example, a dosimeter that must be visually accessible according to the regulations. In this case, the operator may have to open the covering worksuit to access the information sought in said documents or displayed by said devices. In doing so, the operator runs a potential risk of direct contamination by their gloves. To resolve this disadvantage, current non-woven covering worksuits comprise at least one transparent plastic window designed to display the underlying clothing in line with the locations of said control devices, badges or documents worn on it. However, said plastic windows can lose transparency quickly, even during a single operation, due to friction, folds, etc. Under these conditions, the information sought by the operator becomes increasingly less clear or visible, so that to access it, the operator must open their covering worksuit, which is in contradiction with the goal of limiting contamination risk. The invention relates to obtaining an individual disposable covering worksuit for protection against radioactive particles that alleviates the disadvantages of covering worksuits mentioned above. To this end, the invention first relates to a disposable and individual covering worksuit for protection against radioactive particles, comprising a trunk part and a trouser part, which is of one piece with the trunk part and which extends down from the trunk part, the trunk part and the trouser part having a flexible and dustproof wall, the covering worksuit comprising a first zip closure, which extends from top to bottom and on the front between two first left and right edges of the wall at least in the trunk part, the first zip closure having a first side attached in a dustproof manner to the left edge of the wall and a second side attached in a dustproof manner to the right edge of the wall, the first and second sides being able to be connected together according to a first prescribed and dustproof meshing line in the closed state of the first zip closure and being able to be separated from each other along the first meshing line in the open state of the first zip closure (FG1), characterized in that the covering worksuit (1) comprises at least one other closure, which extends from top to bottom between two other opposite edges of the wall in at least one of the legs of the trouser part and which comprises two strips respectively attached in a dustproof manner to the two other opposite edges of the wall, the two strips being able to be connected to each other according to at least one other prescribed and dustproof meshing line in the closed state of the other closure and being able to be separated from each other along the other meshing line in the open state of the other closure, at least one connection point connecting together at least two of the strips beyond the other meshing line being present between the first zip closure (FG1) and the other closure in the closed state of the closures, at least one breaking member being provided on at least one of the closures to be able to break the connection point by pulling on the breaking member. According to one embodiment of the invention, the first zip closure further extends from top to bottom between two opposite edges of the wall in the other of the legs of the trouser part. According to one embodiment of the invention, the connection point is located on the first or second side of the first zip closure, the first zip closure comprising a slider making it possible to connect the first and second sides together along the first meshing line by raising the slider along them and making it possible to separate the first and second sides from each other along the first meshing line by lowering the slider along one of the first and second sides, the breaking member being formed by the slider, whose descent along the connection point makes it possible to break the connection point. According to another embodiment of the invention, the following is provided as other closure: at least one second closure, which extends from top to bottom between two second opposite edges of the wall in one of the legs of the trouser part and which comprises two second strips respectively attached in a dustproof manner to the two second opposite edges of the wall, the two second strips being able to be connected to each other according to a second prescribed meshing line, dustproof in the closed state of the second closure, and being able to be separated from one another along the second meshing line in the open state of the second closure, and at least one third closure, which extends from top to bottom between two third opposite edges of the wall in the other of the legs of the trouser part and which comprises two third strips respectively attached in a dustproof manner to the two third opposite edges of the wall, the two third strips being able to be connected to each other according to a third prescribed meshing line, dustproof in the closed state of the third closure, and being able to be separated from one another along the third meshing line in the open state of the third closure. According to one embodiment of the invention, the following are provided as connection point: a first connection point that connects together the upper ends of the two second strips of the second closure, and a second connection point that connects together the upper ends of the two third strips of the third closure, and the breaking member comprising a tab attached to the second strip and to the third strip close to each other and close to the first and second connection points, to allow breaking the first and second connection points by pulling on the tab, separating the two second strips from each other along the second meshing line and separating the two third strips from each other along the third meshing line. According to one embodiment of the invention, the connection point is formed by a connection part, which, in the closed state of the closures, comprises a first connection flank connecting together the lower ends of the first and second sides of the first zip closure, a second connection flank connecting together the upper ends of the two second strips of the second closure and a third connection flank connecting together the upper ends of the two third strips of the third closure, the first zip closure comprising a slider making it possible to connect the first and second sides together along the first meshing line by raising the slider along them and making it possible to separate the first and second sides from each other along the first meshing line by lowering the slider along one of the first and second sides, the breaking member being formed by the slider whose descent along the connection part makes it possible to break the first, second and third connection flanks. According to one embodiment of the invention, the at least one other closure is a zip closure, comprising another slider allowing it to connect the two strips together along the other meshing line by movement of the other slider from bottom to top along these strips and allowing the two strips to be separated from each other along the other meshing line by movement of the other slider from top to bottom along one of the strips. According to another embodiment of the invention, the two strips of the at least one other closure mesh with one another along the other meshing line in the closed state of the at least one other closure, the two strips of the at least one other closure being able to be separated from each other along the other meshing line by pulling on one and/or the other of the two strips. According to one embodiment of the invention, the connection point is located in the crotch or lower abdomen area of the trouser part. According to another embodiment of the invention, the trunk part ends at the top with a dustproof collar, having two left and right front parts connected together by a dustproof front closure strip located beyond the upper end of the first zip closure. According to another embodiment of the invention, two free front and side tags are attached in front of the front closure strip. According to another embodiment of the invention, the covering worksuit comprises stitching lines visible on its wrong side and invisible on its right side. According to another embodiment of the invention, the covering worksuit comprises sleeves to pass the arms therethrough, wherein the sleeves comprise a dustproof second wall, are connected at the top of the trunk part, a free end edge of the sleeves surrounds an end opening allowing the passage of at least the index finger, middle finger, ring finger and little finger of the hand, the sleeves further comprise at least one hole for passing the thumb, distinct from the opening and separated from the end edge by an end part of the second wall. According to another embodiment of the invention, the covering worksuit comprises a tightening elastic situated in a sheath in the waist. According to another embodiment of the invention, the covering worksuit comprises reinforcements at knees of the trouser part. According to another embodiment of the invention, the covering worksuit comprises at least one transparent outer wall, which is located to the right and/or the left of the first closure on the front in the trunk part and which forms at least one pocket with at least one other underlying wall. According to another embodiment of the invention, the covering worksuit comprises a removable stomach pouch having a transparent outer wall, the removable stomach pouch having an upper part comprising a fourth zip closure and fasteners that can be connected and disconnected relative to a front upper part of the trunk part. In the figures, different embodiments of the individual disposable covering worksuit 1 for protection against radioactive particles or of the covering worksuit 1 are shown. Covering worksuit 1 mainly comprises a trunk part 2 joined on the bottom to a trouser part 3 extending from it. Right and left sleeves M for the user's arms are provided in the upper part of trunk 2. A collar C is found in the upper part of trunk 2, that can be extended in the back by a hood, not shown. Trunk part 2, trouser part 3 and sleeves M comprise one or more flexible dustproof walls 4, which are configured to prevent radioactive particles from passing through the covering worksuit from the outside to the inside. Generally, the seal indicated for the various parts of covering worksuit 1, especially for wall 4, is a dustproof seal and may also be waterproof from the outside to the inside and/or water vapor proof from the outside to the inside. Moreover, one or more parts of covering worksuit 1, especially wall 4, can be breathable, i.e., allow water vapor to pass from the inside to the outside. Wall 4 may, for example, be continuous from trunk part 2 to trouser part 3. This flexible wall 4 can be nonwoven, for example, of a paper, as is known. Covering worksuit 1 and/or wall 4 can, for example, have any one or all of the following properties (the standards indicated are those in effect on 22 Dec. 2015): Mass per unit area according to standard NF EN ISO 3801 comprised between 40 and 70 g/m2. Abrasion resistance according to standard NF EN 13034, standard NF EN 1073-2 (test according to standard NF EN 530) and standard NF EN ISO 13982-1: Class 2/6 (>100 abrasive cycles). Resistance to cracking by flexing according to standard NF EN ISO 13982-1 (test according to method B of NF EN ISO 7854): Class 6/6 (>100,000 cycles). Puncture resistance according to standard NF EN ISO 1073-2 (test according to standard EN 863): Class 2/4 (>10 N). Puncture resistance according to standard NF EN 13034 and standard NF EN ISO 13982-1 (test according to standard EN 863): Class 2/6 (>10 N). Trapezoid tearing resistance according to standard NF EN 13034 and standard NF EN ISO 13982-1 (test method: standard EN ISO 9073-4): Class 2/6 (>20 N). Tearing resistance according to standard NF EN 1073-2 (test method according to standard EN ISO 9073-4): Class 3/6 (>20 N). Resistance of seams, joints and assemblies according to standard NF EN 13034 and standard NF EN ISO 13982-1 (test method according to standard EN ISO 13935-2): Class 3/6 (>75 N). Resistance of seams according to standard NF EN 1073 (test method according to standard EN ISO 13935-2): Class 3/5 (>75 N). Tensile strength according to standard NF EN ISO 13034 (test method according to standard EN ISO 13934-1: or standard EN 29073-3): Class 2/6 (>60 N). Property against the penetration of liquid chemical products: Compliance with Type 6 classification according to standard NF EN 13034. The specifications for covering worksuit 1 for protection against liquid radioactive contamination by contact (light and not extended) or by light splashes are assimilated to those of type 6 clothing. Consequently, the requirements of standard NF EN 13034 (type 6) and the associated test methods apply to this product. However, it remains comfortable to wear. Liquid repellency: Class 3/3 (Repellency index>95% at least for standardized products such as H2SO4, NaOH, o-xylene and butane-1-ol). Protection from chemical product penetration: Class 3/3 (Penetration index <1% at least for standardized products such as H2SO4, NaOH, o-xylene and butane-1-ol). Protection against penetration of liquids in the form of a light spray (mist test): compliance with the requirements of standard NF EN 13034. Particle penetration property: The clothing complies with Type 5 classification according to standard NF EN ISO 13982-1 and complies with standard NF EN 1073-2. Inward leaking according to standard NF EN ISO 13982-1 (test according to standard NF EN ISO 13982-2): compliance with the minimum requirement i.e. IL82/90≤30% and TILS8/10≤15%. Total inward leaking according to NF EN 1073-2 (test according to standard NF EN ISO 13982-2): Class 1/3. Anti-electrostatic property: The surface resistivity is evaluated according to the test method described in standard NF EN 1149-1. The homogenous material must have a surface resistivity less than or equal to 5×1010 ohms. Protection against flame: The constituent material (including any hood and translucent windows) must be classified level 1 according to standard NF EN ISO 14116, insofar as this equipment is intended to be worn over base clothing having a higher level of protection. The product is free of toxic chemicals (Pb, B, Ni, Cr, As, Sb, Se, Cd, Hg, Be, CN, asbestos). Covering worksuit 1 comprises a first zip closure FG1 in trunk part 2, as well as one or more other closures FG2, FG3 extending in at least one of the legs 31, 32 of trouser part 3, which will be described below and which can be the zip closures described below with a slider, called first type of closure as for closure FG1, or closures of the second type not bearing the slider on covering worksuit 1 and nevertheless with strips that can be separated along their meshing line LE2 or LE3 of meshing, as described below. Thus, as shown in FIGS. 1 to 10, 15 and 17, first zip closure FG1 is of the first type and extends on the front of wall 4 of trunk part 2 between a first left edge 41 of this wall 4 and a second right edge 42 of this wall 4. First side (or first strip) BA11 of zip closure FG1 is attached in a dustproof manner to left edge 41 of wall 4. Second side (or second strip) BA12 of zip closure FG1 is attached in a dustproof manner to right edge 42 of wall 4 of trunk part 2. The two sides BA11 and BA12 are configured so as to be able to be connected to each other along the first prescribed meshing line LE1, which is dustproof in the closed state of first zip closure FG1. The two sides BA11 and BA12 are also configured to be able to be separated from each other along first meshing line LE1 in the open state of first zip closure FG1. The first zip closure FG1, the two edges 41 and 42, the two sides BA11 and BA12 and the meshing line LE1 extend, for example, from a collar C located at the top of trunk part 2 to at least a crotch area Z of trouser part 3 and can be vertical in the middle of the front part of trunk 2. First zip closure FG1 comprises a slider CU (for example metal or plastic) making it possible to connect first and second sides BA11, BA12 together along first meshing line LE1 by raising (in the closing direction S10 of FIG. 17) slider CU along them and making it possible to separate first and second sides BA11, BA12 from each other along first meshing line LE1 by lowering (in the opening direction S20 of FIG. 17) slider CU along one of the first and second sides BA11, BA12. Slider CU is connected to a manual gripping member OP, for example oblong in shape. In the following, a zip closure has the meaning known to the person skilled in the art and comprises two parallel strips or first and second sides BA11 and BA12 extending in length and each comprising a series of consecutive teeth respectively D1, D2 and Dr, D2′ distributed in the meshing direction LE1, as shown in FIG. 17 for zip closure FG1. Each of teeth D1, D2 of strip BAH collaborates with a space between the teeth of strip BA12 facing it, said collaboration being induced by the movement of slider CU which is moved in the closing direction S10 along strips BA11 and BA12 and which forcibly interweaves teeth D1, D2 of strip BA11 with teeth Dr, D2′ of the other strip BA12, which thus causes the two strips BA11 and BA12 to mesh with each other along meshing line LE1, which has the effect of securing the two strips BA11 and BA12 to each other, zip closure FG1 being in the closed state in this case. To open the zip closure FG1, slider CU is moved in the opening direction S20 reverse to the closing direction S10 along strip BA11 or BA12, which has the effect of separating teeth D1, D2 of strip BA11 relative to teeth D1′, D2′ of the other strip BA12 which are then separated from each other, the zip closure FG1 being in the open state in this case. An opening stop member (separable stop) OA3 located at a lower end BA110 of strip BA11 or at a lower end BA120 of BA12 is provided to stop the course of slider CU in direction S20. Another closing stop member OA1 located at the other end BA111 of strip BA11 and/or another closing stop member OA2 located at the other end BA121 of strip BA12 is provided to stop the course of slider CU in direction S10. The closure strips are, for example, textile braids receiving stitches, for example 5 mm Vislon injected stitches. The other closure FG2 and/or FG3 extends from top to bottom between two other opposite edges respectively 311, 312 and/or 321, 322 of wall 4 located in at least one of the legs 31, 32 of trouser part 3. Leg 31 is, for example the left leg of trouser part 3, and leg 32 is, for example, the right leg of trouser part 3. The other closure FG2 and/or FG3 starts, for example from crotch area Z of covering worksuit 1. This other closure FG2 and/or FG3 comprises two strips, respectively BA21, BA22 and/or BA31, BA32, which are respectively attached in a dustproof manner to the two opposite edges, respectively 311, 312 and/or 321, 322 of wall 4. The two strips BA21, BA22, respectively BA31, BA32 are configured to be able to be connected together along at least one other prescribed meshing line LE2, respectively LE3, which is dustproof in the closed state of closure FG2, respectively FG3 and are configured to be able to be separated from each other along this other meshing line LE2, respectively LE3, in the open state of closure FG2, respectively FG3. As shown in FIGS. 1 to 7, at least one connection point S or S1 or S2 or CO connects together at least two of strips BA21, BA22, BA31, BA32 beyond the other meshing line LE2 and/or LE3. This connection point S or S1 or S2 or CO is present between first zip closure FG1 and the other closure FG2 and/or FG3 in the closed state of closures FG1, FG2, FG3. Connection point S or S1 or S2 or CO is present, for example, in crotch area Z. Connection point S or S1 or S2 or CO prevents the untimely opening of zip closure FG2 and/or FG3 when operators are working. At least one breaking member CU or LA is provided on at least one of closures FG1, FG2 and FG3. This breaking member CU or LA is configured to break connection point S or S1 or S2 or CO when the breaking member CU or LA is pulled. Thus, the embodiment described above of the covering worksuit 1 allows the person wearing it to open the covering worksuit 1 in a prescribed, intuitive and quick way by pulling the breaking member CU or LA, which breaks the connection point S or S1 or S2 or CO, and makes it possible to change from the closed state to the open state the first zip closure FG1 and the other closure(s) FG2 and/or FG3 by separating them along their prescribed meshing line LE1, LE2 and/or LE3. In this way, it is avoided that the individual contaminates himself by the radioactive particles present on the outside of the covering worksuit 1 when he opens this covering worksuit 1 to remove it. Breaking member CU or LA is accessible from the outside of the covering worksuit 1 by the individual who wears the covering worksuit 1. In this way, it is avoided that, when the individual pulls on the breaking member CU or LA, contaminated particles enter the covering worksuit 1 when going to the open state of closures FG1, FG2 and/or FG3. In this way, it is avoided that the operator wearing the covering worksuit 1 contaminates himself or other individuals or the areas when he removes this covering worksuit 1 and comfort is also improved during this undressing phase, in particular to avoid off balance positions when crossing the boundary separating contaminated areas and uncontaminated areas, indicated above. The first closure FG1 and the other closure(s) FG2 and/or FG3 are, for example, arranged in a Y shape, as shown in FIGS. 1, 3 and 5, with connection point(s) S or S1 or S2 or CO located in the center of the Y. This makes it possible to open trunk part 2 along line LE1 then legs 31 and 32 of trouser part 3 along lines LE2 and LE3, so that the individual can be completely free of covering worksuit 1. Covering worksuit 1 is held simply by the top of trunk part 2 on the individual's shoulders, so that no part of covering worksuit 1 comes into contact with the ground. The covering worksuit 1 makes it possible for the person wearing it to avoid having to tear their covering worksuit at the crotch down to the bottom of the trousers, which could potentially resuspend contaminated particles. On the contrary, covering worksuit 1 is opened along the prescribed meshing lines LE1, LE2 and/or LE3 from top to bottom with no abrupt movements accompanying the opening movement and no risk of introducing the hands behind wall 4, down to the bottom of trouser part 3. Below, first, second and third embodiments of the covering worksuit 1 described above will be described. In the first embodiment shown in FIGS. 1 and 2, the first zip closure FG1 extends downward between two opposite edges 311 and 312 of wall 4 in the other 31 of the legs 31, 32 of trouser part 3, while the other closure FG3 described above is present in leg 32 of trouser part 3. First zip closure FG1 extends, for example, to the bottom of leg 31. Closure FG2 extends, for example, from crotch area Z to the bottom of the other leg 32. Of course, this could also be the opposite, i.e., in a variant, first zip closure FG1 extends from top to bottom between two opposite edges 321 and 322 of wall 4 in leg 32 of trouser part 3 and the other closure FG2 is present in leg 31 of trouser part 3. The connection point S initially connects strip BA31 to strip BA32. Connection point S can be located on the first side BA11 of closure FG1 or on the second side BA12 of closure FG1. The breaking member LA is formed by slider CU, whose descent on the connection point S when slider CU descends along the sides BA11 and BA12 to open first meshing line LE1, makes it possible to break the connection point S. FIG. 2 shows that connection point S is located on the second side BA12 of closure FG1. For example, a transverse notch ENT is provided in the second side BA12 of closure FG1, this notch ENT ending between two successive teeth D1 and D2 of the second side BA12. The connection point S is intended to cover at least or partially the notch ENT to connect together the upper part BA121 of the second side BA12 and the lower part BA122 of the second side BA12, which are separated by the notch ENT. The two strips BA31 and BA32 overlap the second side BA12 at their end. The meshing line LE2 is aligned with the connection point S. The meshing line LE2 is, for example, essentially aligned with the notch ENT. In this case, the end of the strip BA31 overlaps the lower part BA122 of the second side BA12 and the strip BA32 overlaps the upper part BA121 of the second side BA12. These ends of the strips BA31 and BA32 are attached, for example sewn, on the two parts BA122 and BA121, respectively. Underneath the notch ENT, a dustproof component SP can be provided, forming a sub-bridge, which is attached, for example by sewing, under the strip BA11 and extends beyond it under the strip BA12. This component SP thus makes it possible to prevent radioactive particles from penetrating to the inside of the covering worksuit 1 by going through notch ENT. During manufacture, notch ENT of strip BA12 is made, then the two teeth D1 and D2 are welded. In case that the closure FG3 is of the first type bearing its other slider, this system does not permit raising this other slider from the bottom of leg 32 to the collar. The covering worksuit 1 can, for example, be supplied with the slider CU of closure FG1 being positioned above the connection point S and closure FG3 being also closed. To put on the covering worksuit 1, the individual lowers the slider CU as far as above the connection point S or S1 or S2 to open the first closure FG1 above this point, puts his head through collar C and its trunk through trunk part 2, its arms in the sleeves M and its legs in the parts 31 and 32 of the trouser part 3. Then the individual raises the slider CU along the meshing line LE1 up to the top to close the closure FG1 again. To open covering worksuit 1, the individual lowers the slider CU of the closure FG1 to pass it on the connection point S, which breaks the connection point S, then continues to lower the slider CU along the leg 31 to the bottom, then the individual opens the closure FG3 along the meshing line LE3 in the leg 32 to the bottom. In the second embodiment shown in FIGS. 3 and 4 and in the third embodiment shown in FIGS. 5 to 9, both the second closure FG2 having the two second strips BA21 and BA22 extending from top to bottom in wall 4 of leg 31 and the third closure FG3 having the two third strips BA31 and BA32 extending from top to bottom in the wall 4 of leg 32 are provided as other closures. In the second embodiment shown in FIGS. 3 and 4, the first connection point S1 connects the upper end BA210 of the second strip BA21 to the upper end BA220 of the second strip BA22 beyond the second meshing LE2 between them. In the second embodiment shown in FIGS. 3 and 4, the second connection point S2 connects the upper end BA310 of the third strip BA31 to the upper end BA320 of the third strip BA32 beyond the second meshing LE3 between them. The breaking member is formed by or comprises a tab LA having a lower side part LA2 fastened, for example by sewing, to the second strip BA22 and another side part LA3 (at a distance from side part LA2) fastened, for example by sewing, to the third strip BA31, the strips BA22 and BA31 being those of the second strips and of the third strips that are the closest to one another. Tab LA is also located near first and second connection point S1 and S2. Tab LA comprises an upper part LA1 for manual gripping that can be formed, for example, by a closed loop of fabric at parts LA2 and LA3 to allow a finger to pass through it. Tab LA is configured to induce, by pulling on tab LA, the breaking of the first and second connection points S1 and S2, the separation of the two seconds strips BA21 and BA22 from one another along the second meshing line LE2 and the separation of the two third strips BA31 and BA32 from one another along the third meshing line LE3. The gripping part LA1 is provided, for example, underneath the lower ends BA110 and BA120 of the sides BA11 and BA12 of the first closure FG1. First closure FG1 extends, for example, from top to bottom from collar C to tab LA at crotch area Z. Second closure FG2 extends, for example, from crotch area Z to the bottom of leg 31 of trouser part 3. Third closure FG3 extends, for example, from crotch area Z to the bottom of leg 32 of trouser part 3. To remove the covering worksuit 1, the individual wearing it lowers the slider CU of the first zip closure FG1 down to tab LA in the crotch area Z. The slider CU then reaches the lower ends BA110 and BA120 above the tab LA to separate the two sides BA11 and BA12 including at their lower end BA110 and BA120 by an interval, which releases an access of the user's hand to the tab LA, for example to its gripping part LA1. The individual then pulls the tab LA downward, i.e., for example, the gripping part LA1, which breaks the connection points S1 and S2 and then opens the closure FG2 from top to bottom along the meshing line LE2 from the upper ends BA210 and BA220 and opens the second closure FG3 from top to bottom along the meshing line LE3 from the upper ends BA310 and BA320. Moreover, the tab LA can comprise an attachment to the wall 4 in the crotch area Z, for example by sewing or gluing. The tab LA can be located higher than the lower ends BA110, BA120 of the zip closure FG1 to constitute a sub-bridge making a barrier to contamination when the operator is working. The first connection point S1 connects, for example, the upper end tooth D21 of the strip BA21 to the upper end tooth D22 of the strip BA22. The first connection point S2 connects, for example, the upper end tooth D31 of the strip BA31 to the upper end tooth D32 of the strip BA32. Due to the fact that, in the closed state of the closures FG1, FG2 and FG3, the tab LA is found inside the covering worksuit 1, the tab LA is not contaminated by radioactives particles. Pulling on the tab LA by the individual who wears the covering worksuit 1 naturally opens the zip closures FG2 and FG3 by simple separation of their respective strips BA21, BA22 and BA31, BA32 along their prescribed meshing line LE2 and LE3. The individual can then pull on the outer edges 311 and 322 of the legs 31 and 32 to finish opening the closures FG2 and FG3 along the meshing lines LE2 and LE3. In a third embodiment shown in FIGS. 5 to 9, the connection point is formed by a connection part CO, for example provided on the outer surface of the covering worksuit 1 when the closures FG1, FG2 and FG3 are in the closed state. The connection part CO comprises a first connection flank J1 connecting the lower end BA110 of the first side BA11 to the lower end BA120 of the second side BA12, a second connection flank J2 connecting the upper end BA210 of the second strip BA21 to the upper end BA220 of the second strip BA22 and a third connection flank J3 connecting the upper end BA310 of the third strip BA31 to the upper end BA320 of the third strip BA32. The breaking member LA is formed by the slider CU of the first zip closure FG1. The breaking member LA is configured so that its descent on the connection part CO makes it possible to break the first, second and third connection flanks J1, J2, J3. The operation is as follows, for example, illustrated in reference to FIGS. 6 to 9. In a first step in FIG. 6, the closures FG1, FG2 and FG3 are in the closed state and the slider CU is located near the upper end thereof. The operator moves the slider CU in the direction of arrow F1 downward to change the closure FG1 to the open state. In a second step in FIG. 7, the zip closure FG1 being open and its sides BA11 and BA12 being separated from each other as shown by arrows F1 and F2, the user continues to lower the slider CU against the first connection flank J1 to start to break the connection part CO connecting the three closures FG1, FG2 and FG3. The connection part CO comprises a prescribed weak point, so that the part CO breaks beyond a force threshold. The connection part CO can comprise, as a non-limiting example, an intrinsic connection in the immediate vicinity of the six strips BA11, BA12, BA21, BA22, BA31, BA32 of the three closures FG1, FG2 and FG3. The connection part CO can also be a fabric component, sewed or glued, that can exhibit tear DE as soon as force threshold is exceeded. In a third step in FIG. 8, the connection part CO is broken into a part CO, which is connected on the one hand to the side BA11 and on the other hand to strip BA21, and into another part CO′, which is connected on the one hand to the side BA12 and on the other hand to the strip BA32, and opens from the connection flanks J2 and J3 the closures FG2 and FG3 along their prescribed meshing line LE2, LE3, as shown by arrows F4, F5, F6 and F7, which represent the separation of the two strips BA21, BA22 and BA31, BA32 of each of closures FG2 and FG3. In a fourth step in FIG. 9, the complete opening of the closures FG1, FG2 and FG3 is accomplished as shown by arrows F8, F9, F10, F11, F12, F13 and the operator can remove the covering worksuit 1. This embodiment is intrinsically hermetically sealed to contamination, since it does not offer any open area requiring arranging a sub-bridge SP like the first embodiment. The other closure FG2 and/or FG3 can also be a zip closure of the first type comprising its own slider (called other slider) separate from the slider CU, to allow strip BA21 to be connected together with strip BA22 or strip BA31 to strip BA32 along the other meshing line LE2 or LE3 by moving this other slider from bottom to top along it and to allow strip BA21 to be separated from strip BA22 or strip BA31 to be separated from strip BA32 along this other meshing line LE2 or LE3 by moving this other slider from top to bottom along one of these strips. However, the two strips BA21 and BA22 can be of the second type not bearing a slider on the covering worksuit 1 as indicated above, to mesh with each other along the other meshing line LE2 in the closed state, these two strips BA21 and BA22 being configured to be able to be separated from each other along the other meshing line LE2 by pulling on one and/or the other of the two strips BA21 and BA22, i.e., without having a slider for them to be separated. The two strips BA31 and BA32 of the other closure FG3 can be of the second type not bearing a slider on the covering worksuit 1 as indicated above, to mesh with each other along the other meshing line LE3 in the closed state, these two strips BA31 and BA32 being configured to be able to be separated from each other along the other meshing line LE3 by pulling on one and/or the other of the two strips BA31 and BA32, i.e., without having a slider for them to be separated. The closure FG2 and/or FG3 of the second type can have been obtained by sectioning a desired length L of a slider zip closure in the closed state, this length L being located behind the slider (for example of plastic) of this zip closure in the closed state in the closing direction S10, as shown in FIG. 17. This length L has the strips BA21 and BA22 or BA31 and BA32 connected to each other by meshing of their teeth along their meshing line LE1 or LE2 and does not bear the slider of this zip closure in the closed state. This length L is kept to make the closure FG2 and/or FG3. According to an embodiment shown in FIG. 10, the trunk part 2 ends at the top in a closed collar C, located beyond the upper end FG10 of first zip closure FG1. The collar C is dustproof and comprises a left front part C1 and a right front part C2, which is connected to the left front part C1 by a front closure strip CF. This front closure strip CF is dustproof and located higher than the upper end FG10 of the first zip closure FG1. This front closure strip CF makes it possible to prevent contaminated particles from crossing collar C and reaching the neck of the individual above closure FG1. Thus zip closure FG1 does not close at the top of collar C but up to the limit of the bottom of collar C. This allows the zip closure FG1 to be easily opened without holding the collar. The collar C is thus of crossover type with the front closure strip CF forming a valve to protect the neck from external contamination and to cover the underlying clothing. Two front and side tags PF1 and PF2, respectively left and right, can be attached in front of the front closure strip CF. The tags PF1 and PF2 serve for manual gripping of collar C without inserting the fingers inside the collar C, which prevents contaminated particles from being introduced therein. According to an embodiment shown in FIG. 10, the gripping member OP of the slider CU of the first zip closure FG1 can be extended by a fabric part, for example of a different color from that of the other parts of the zip closure FG1 and the wall 4. Operators can thus more easily identify and seize the slider CU and avoid searching for it and thus avoid to increase the risk of clothing and/or bodily contamination. This extender PT of slider CU must not be too short, since it must be able to be seized by a hand covered with a cotton glove, nor too long, in order to avoid being caught while working. According to an embodiment show in in FIG. 11, the covering worksuit 1 comprises lines LC1, LC2, LC3 of stitching visible on the wrong side ENV of the wall 4 and invisible on the right side END of the wall 4. These lines of stitching LC1, LC2, LC3 are, for example, of a different color from that of the wall 4 or that of the wrong side ENV of the wall 4. The individual can thus better distinguish the wrong side ENV and the right side END of the covering worksuit 1. Indeed, the covering worksuit 1 is used only once. When undressing, once the covering worksuit 1 is removed, the operator discards it in a dedicated waste bin. During this phase, the operator must not contaminate his hands, particularly when he folds the covering worksuit 1. Indeed, since the wrong side ENV and the right side END of the covering worksuit 1 are most often white in color, the operator can mix up the wrong side ENV free of contamination with the right side END which can be contaminated. These stitching lines guide the operator so as not to contaminate himself. In an embodiment shown in FIG. 12, the covering worksuit 1 comprises two sleeves M for passing the individual's arms. Each sleeve M comprises a second dustproof wall 46 and is connected at the top of the trunk part 2. Each sleeve comprises a free end edge BE, which surrounds the end opening OUV making it possible to pass at least the index, middle, ring and little fingers of the individual's hand. Each sleeve M comprises at least one hole TPP for passage of the thumb of the individual's hand. This thumb hole TPP is distinct from the opening OUV and is separated from the end edge BE by an end part 47 of the second wall 46. The operators can wear cotton gloves, sometimes covered with vinyl or other gloves depending on the type of procedure. Then they put on the covering worksuit 1. Note that under certain working conditions, operators have a tendency to use adhesive tape to connect the covering worksuit of the state of the art to the gloves, so that no part of the arm is found uncovered, which would not be acceptable vis-à-vis the risk of contamination. However, the use of adhesive tape becomes prohibited for some plants. The embodiment described above having the thumb hole TPP integrated into the covering worksuit 1 remedies this issue. This thumb hole TPP can have the form of a vent at the end of the sleeve M. This thumb hole TPP can be indicated on its outline by a different color from the rest of the second wall 46 of the sleeve M, which indicates its position. The positioning of this thumb hole towards the top of the free end edge BE of the sleeve M allows intuitive dressing to pass the thumb therein without hindering the movement of the operator's arms for all work situations. This thumb hole is also called thumb loop. According to an embodiment shown in FIG. 13, the waist T of the covering worksuit 1 comprises a peripheral inner sheath FT in which is positioned an elastic EL for peripheral tightening. In the state of the art, operators habitually choose a size for the covering worksuit 1 greater than their own size, in order to be able to have more room, ease and comfort inside the covering worksuit, especially during sustained physical effort. However, in this case, there is a puffy effect which comes mainly from an elastic sewn into the covering worksuit all around the waist. This puffy effect is conducive to snagging or tearing the covering worksuit, which can then contaminate the operator. This embodiment resolves this problem by making it possible to insert the more flexible elastic EL in the back of the covering worksuit 1 in the sheath FT, this elastic EL not being sown into the covering worksuit 1 in order not to have the puffy effect. According to an embodiment of the invention shown in FIG. 14, the covering worksuit 1 bears reinforcements RG at the knees G of the trouser part 3. This prevents tearing of the covering worksuit 1 and thus prevents contaminations. These reinforcements RG have, for example, a height and width greater than that of the individual's knees, to be able to suit all body shapes. According to an embodiment shown in FIG. 15, the covering worksuit 1 comprises a transparent outer wall 43 located to the left of the first zip closure FG1 on the front in trunk part 2 and/or a transparent outer wall located to the right of the first zip closure FG1 on the front in trunk part 2. This wall 43 and/or 44 forms an outer transparent window. This wall 43 and/or 44 located on the right side END of the covering worksuit 1 respectively forms a left pocket PCH1 and/or a right pocket PCH2 with, respectively, another underlying left wall 43b, located on the wrong side ENV and/or with another underlying right wall 44b, located on the wrong side ENV. The wall 43b and/or 44b can be transparent or opaque. The left pocket PCH1 and/or the right pocket PCH2 has a width greater than or equal to 15 cm and a height greater than or equal to 15 cm. The transparent outer wall 43 and/or 44 allows the individual to see the objects located in the pocket PCH1 and/or PCH2 from the outside and thus to be able to see in real time the numerical value of the dose displayed by a dosimeter present in this pocket. It is imperative for the operator to have continuous access to read the dosimetry on their own dosimeter, so that it does not exceed the predicted dose and, in some cases, the regulatory limits. This prevents the operator from having to open the covering worksuit 1 in order to read this dosimetry and thus prevents that the operator contaminates himself. The wall 43 and/or 44 forms a transparent window at the chest. This wall 43 and/or 44 and/or 43b and/or 44b may be of an acetate type material, or the like, which has the property of remaining transparent when it is folded. The dimension of the window has been designed so that the dosimeter pouch PCH4 is always visible even in cases where it moves during physical exertion, this dosimeter pouch PCH4 itself being formed of transparent walls and having been inserted into pocket PCH1 or PCH2. The pockets PCH1 and/or PCH2 can be of the wallet window type. As a variant, the other wall 43b and/or 44b can be made of the same material as the wall 4, not transparent. The pocket PCH1 and/or PCH2 has an opening located in its upper part between its wall 43 and/or 44 and its wall 43b and/or 44b. The underlying wall 43b and/or 44b is made of a dustproof material. Regulations require that the dosimeters be positioned on the chest. Note that, in the state of the art, it is often tedious to adjust the fasteners of the dosimeter pouch to position it on the chest and it changes position during exertion. The proposed solution resolves this problem and meets regulatory requirements. According to an embodiment shown in FIG. 16, the covering worksuit 1 comprises a removable pouch PCH5 on the stomach with a transparent outer wall 45, This pouch PCH5 is located on the chest and can contain type A4 documents and/or small equipment. The wall 45 can be of acetate, for example. The underlying wall of the pouch PCH5 can also be of a transparent or non-transparent material. The pouch PCH5 has an upper part comprising a fourth zip closure FG4 and fasteners AT configured to be able to be connected and disconnected relative to a corresponding front upper part of the trunk part 2. These fasteners AT are, for example, clip type. The pouch PCH5 can also comprise fasteners in its lower part, these fasteners can be snap buttons, for example. The choice of fastener of different types between the upper part and the lower part of the pouch PCH5 makes it possible to provide a mistake-proofing for the operator and to guide the operator to put the pouch PCH5 on in the right direction. This pouch PCH5 enables the operator to read a document or keep a small equipment (for example a phone or the like) without contaminating it. Of course, the embodiments, features, possibilities and examples above can be combined with one another or selected independently from one another.
	claims	1. A collimator comprising: a guide channel having a longitudinal front end, a longitudinal back end, and an outer wall, wherein the guide channel is adapted to collimate light received at the longitudinal front end and transmit collimated light from the longitudinal back end; a reflector having a generally tapered cylindrical shape wherein the reflector is positioned so that an inner surface of the reflector surrounds a portion of the outer wall of the guide channel and the reflector is coaxial with the guide channel; and an absorber disposed at the back opening of the reflector and adapted to pass light reflected by the reflector at a substantially uniform intensity profile. 2. A collimator in accordance with claim 1 wherein said guide channel comprises a plurality of polycapillary tubes. claim 1 3. A collimator in accordance with claim 1 wherein the guide channel comprises a plurality of microchannel plates. claim 1 4. A collimator in accordance with claim 1 wherein said guide channel comprises at least one polycapillary tube and at least one microchannel plate. claim 1 5. A collimator comprising: a guide channel having a longitudinal front end, a longitudinal back end, and an outer wall, wherein the guide channel is adapted to collimate light received at the longitudinal front end and transmit collimated light from the longitudinal back end; a reflector having a generally tapered cylindrical shape with a front opening and a back opening wherein the reflector is positioned so that an inner surface of the reflector surrounds a portion of the outer wall of the guide channel and the reflector is coaxial with the guide channel, and wherein the reflector is positioned so that light reflected from an inside surface of the reflector is directed to the longitudinal front end of the guide channel. 6. A collimator in accordance with claim 5 , wherein the back opening of the reflector is adjacent to the longitudinal front end of the guide channel. claim 5 7. A collimator in accordance with claim 5 wherein the guide channel comprises a plurality of polycapillary tubes. claim 5 8. A collimator in accordance with claim 5 wherein the guide channel comprises a plurality of microchannel plates. claim 5 9. A collimator in accordance with claim 5 wherein the guide channel comprises at least one polycapillary tube and at least one microchannel plate. claim 5 10. A method of collimating light comprising: providing a guide channel having a longitudinal front end, a longitudinal back end, and an outer wall; providing a reflector having a generally tapered cylindrical shape with a front opening and a back opening wherein the reflector is coaxial with the guide channel; and providing an absorber disposed at the back opening of the reflector providing light to be collimated; collimating a first portion of the light by reflecting the first portion of the light on an inner surface of the reflector; passing the first portion of the light through the absorber so that the first portion of light has a substantially uniform intensity profile; and collimating a second portion of the light with a guide channel. 11. A method in accordance with claim 10 , further comprising: claim 10 applying the first and second portions of collimated light to a photomask so as to define a pattern in a photoactive substance. 12. A method in accordance with claim 10 wherein the collimated light is used in a process selected from a group consisting of lithography, microlithography, tomography, x-ray photoelectron spectroscopy, x-ray diffraction, x-ray microscopy and x-ray fluorescence. claim 10 13. A method of collimating light comprising: providing a guide channel having a longitudinal front end, a longitudinal back end, and an outer wall; A providing a reflector having a generally tapered cylindrical shape with a front opening and a back opening, wherein the reflector is positioned so that an inner surface of the reflector surrounds a portion of the outer wall of the guide channel and the reflector is coaxial with the guide channel; providing light to be collimated; reflecting the portion of the light on an inner surface of the reflector so as to substantially collimate the portion of the light; receiving the substantially collimated portion of the light at the longitudinal front end of the guide channel; and passing a collimated beam of light from the back end of the guide channel. 14. A method in accordance with claim 13 , wherein the collimated beam of light has a substantially uniform intensity profile. claim 13 15. A method in accordance with claim 13 , further comprising: claim 13 applying the collimated beam of light to a photomask so as to define a pattern in a photoactive substance. 16. A method in accordance with claim 13 wherein the collimated beam of light is used in a process selected from a group consisting of lithography, microlithography, tomography, x-ray photoelectron spectroscopy, x-ray diffraction, x-ray microscopy and x-ray fluorescence. claim 13 17. A method of focusing light on a target point comprising: providing a guide channel having a longitudinal front end and a longitudinal back end; providing a reflector having a generally tapered cylindrical shape with a front opening for receiving light and a back opening for transmitting reflected light, wherein the reflector is positioned so that it is coaxial with the guide channel; providing light to be collimated; reflecting a first portion of the light on an inner surface of the reflector so as to focus the first portion of light on a target point outside of the back opening of the reflector; and receiving a second portion of the light at the longitudinal front end of the guide channel and focusing the second portion of light on the target point. 18. A method in accordance with claim 17 wherein the focused light is used in a process selected from a group consisting of lithography, microlithography, tomography, x-ray photoelectron spectroscopy, x-ray diffraction, x-ray microscopy and x-ray fluorescence. claim 17
044505787	description	DETAILED DESCRIPTION OF THE INVENTION Reference is made to FIGS. 1 and 5 showing a variable aperture beam collimator 10 of the invention utilizing four block assemblies defining a constant size beam channel extending through the collimator. An energy beam source 11, for example a neutron beam source, emits an energy beam B for projection through the aligned apertures 12 of the block assemblies of the collimator of the invention. The beam B projects through the channel in a straight line and emerges from the last in-line aperture 12 as a collimated beam (represented by the arrow B). The collimator 10, as best seen by viewing FIG. 1 in connection with FIG. 5, includes separate block assemblies 14, 15, 16 and 17. Assemblies 14 and 16 are in congruent relationship, that is physically oriented in the same way, as are assemblies 15 and 17. In particular, assemblies 15 and 17 are inverted front-to-back about axis A with respect to assemblies 14 and 16. This difference in orientation can also be seen by comparing FIGS. 2A and 3A showing the first two in-line assemblies 14, 15, respectively. Referring to FIGS. 2A and 2B, a plurality of opaque blocks 18, 19, 20 and 21 are illustrated forming assembly 14. The blocks have adjacent edges 22 in interfacial contact. When in the closed position, as shown in FIGS. 2A, the blocks form a completely beam opaque structure. To form the aperture 12, as shown in FIG. 2B, the blocks 18-21 slide relative to one another along the edge interfaces 22. A mechanism is provided for advantageously adjusting the blocks to slid the blocks to create aperture 12. To best explain the adjustment means for sliding the blocks 18-21 to provide the aperture 12, reference is made to the block assembly 14 shown in FIGS. 2A, 2B; it being understood that the adjustment means in the block assemblies 15-17 are substantially the same. In particular, an endless cable 25 is trained around corner pulleys 26, 27, 28 and a drive gear 29. The drive gear meshes with a perforated belt section 30 to insure non-slip driving in response to operation of the hand wheel assembly, generally designated by the reference numeral 31 (see FIG. 2A). The cable is attached in the preferred embodiment to slide brackets 32, 33 attached to the opposite blocks 18, 20. Thus as the drive gear 29 is rotated in the direction of the arrow shown in FIG. 2A, the cable 25 moves and in turn the blocks 18-20 move in the direction of the arrows shown also. The mechanical pressure at the edge interfaces 22 in turn move the blocks 19, 21, also as shown by the arrows. The movement of the blocks 18-21 results in opening of the aperture 12, as shown in FIG. 2B. The configuration of the aperture 12 is assured by the guiding influence of guide rods 35, 36 engaging corresponding apertures in the upstanding legs of slide brackets 32, 33 (compare FIGS. 2A and 2B). Similarly, follower blocks 19, 21 are provided with slide brackets 37, 38, respectively and guided by additional guide rods 39, 40, respectively. The edge interfaces 22 in combination with the guide rods 35, 36 and 39, 40 advantageously insure easy and efficient sliding of the blocks for opening and closing. As will be seen in detail later, the rods are bodily movable toward and away from the center of the array of blocks 18-21 in a unique manner to control the shape of the aperture. It is clear that the drive gear 29 can be actuated in a number of well known ways. Preferably, the assembly 31 includes a worm gear 35 engaging the outer peripheral teeth of the drive gear 29 and a hand wheel 46 for turning shaft 47 of the worm gear. The shaft is suitably rotatably mounted by bearing assembly 48 (see FIG. 2A). The pulleys 26-28 and the drive gear 29 are rotatably mounted on four shafts 50-53, respectively. (See FIG. 1 also). In other words, the pulleys and the gear 29 rotate independently of the corresponding shafts upon which they are rotatably mounted. The ends of the shafts 50-53 are suitably journaled in frame plates F.sub.1, F.sub.2. The operation of a single array of blocks, such as block assembly 14 in order to form the aperture 12 can now be clearly seen. The blocks 18-21 are initially set or closed in FIG. 2A and upon rotation of the hand wheel 46 the cable 25 is moved providing movement to the blocks 18, 20, that is shifting in the direction of the arrows and guided by the rods 35, 36 respectively. Because of the sliding pressure against the two adjacent blocks 19, 21, these blocks are also moved in accordance with the arrows of FIG. 2A and guided along the corresponding rods 39, 40. As a result, the aperture 12 is created. Similarly, in the alternate block assembly 15, wherein like parts are indicated by the same reference numeral but with the suffix a for further identification, the aperture 12a can be generated by moving blocks 18a-21a. Of significance, it will be noted that the entire assembly 15 is inverted front-to-back about axis A with respect to the assembly 14 previously described. Furthermore, the adjustment wheel assembly 31a is positioned not only at 90.degree. from the wheel assembly 31 but also so as to provide movement to the blocks 18a-21a in the opposite direction, as shown by the arrows in FIG. 3A. In other words, the blocks 18a-21a move in a clockwise direction, as viewed in FIG. 3A whereas the blocks 18-21 move in the counter clockwise direction as viewed in FIG. 2A. This is of importance since it assures the relative movement of sliding interfaces 22a in the opposite direction to the sliding interfaces 22. Thus as the aperture 12a is opened (see FIG. 3B) none of the sliding interfaces are congruent. In other words, the sliding interfaces 22, 22a do not overlie each other and accordingly maximum efficiency of sealing against stray neutron beams is assured. This non-congruency is repeated in block assemblies 16, 17, as best shown in FIG. 5 of the drawings. In each position where a sliding interface 22, 22a is provided, on the adjacent block assembly there is a solid block to block any possible leakage of radiation. As mentioned above, the adjustment means of the adjacent block assemblies, such as assemblies 14, 15 are inverted with respect to each other and this is accomplished by simply providing four additional shafts supported by the frame members F.sub.1, F.sub.2. The shafts have been designated 50a-53a (see FIG. 3A) supporting in turn pulleys 26a-28a and drive gear 29a. The relationship of this orientation can be best comprehended viewing the perspective in FIG. 1. The components for the adjustment means in the block assembly 16 are numbered, and are the same as those shown in assembly 14; and likewise the components in assembly 17 are like those shown in assembly 15. While four assemblies 14-17 are shown in the preferred embodiment, it is readily apparent that one assembly 14 could be used as a collimator in accordance with the principles of the present invention. Adding a second block assembly, such as block assembly 15 in back of the block assembly 14, as shown in FIG. 5, provides an additional aperture 12a to regulate the neutron beam B or the like. Furthermore, a third assembly, such as block assembly 16 can be put behind the assembly 15 to provide additional collimation; and the additional assembly 17 can be added if desired. Of course, any additional number of block assemblies may be added as required in order to provide the necessary beam opaque structure desired when utilizing the device as a beam collimator, such as for the neutron source 11. Also, the particular thickness shown for the blocks is for purposes of illustration and it should be understood that the blocks can be wider (indeed up to face-to-face contact) or narrower as desired. As mentioned above, the guide rods 35, 36 and 39, 40 may be simultaneously moved toward and away from the center of the block assemblies. This movement of the rods is generated by moving means including T shaped intermediate actuators 60-63 (see FIG. 2A). As shown, the adjacent ends of the rods are pivotally mounted on the actuators and the actuators are fixedly attached to the shafts supporting the pulleys. For example, the actuators 60-63 for the assembly 14 are mounted on shafts 50a-53a. In FIGS. 1 and 2A, it can be seen that actuator 60 is clamped on to shaft 50a. Similarly, the actuator 60a (see FIG. 3A also) is clamped on shaft 50. In turn, shafts 50, 50a include large drive pinions 70, 70a fixed to the shafts on the outside of frame F.sub.1. A worm gear 71 meshes with the two pinions 70, 70a and is a part of the moving wheel assembly, generally designated by the reference numeral 72 (FIG. 1). Since the pinions 70, 70a engage opposite sides of the worm 71 it will be realized that the shafts 50, 50a may be rotated in opposite directions giving the desired opposite movement described with respect to the blocks in FIGS. 2A and 3A. The advantageous result of movement of all of the guide rods 35, 36, 39, 40 and 35a, 36a, 39a, 40a is that the shape of the apertures 12, 12a can be varied in shape and the variation can be accomplished in unison. For example, in the preferred embodiment the apexes of the blocks 18-21 are offset or skewed, as shown in FIG. 2A. This is accomplished by moving the guide rods as shown by the rotational arrows adjacent the actuators 60-63. In particular, blocks 18, 20 are moved away from each other and blocks 19, 21 are moved toward each other providing the offset or skewing at the apexes. Thus, when the aperture 12 is generated or opened, as shown in FIG. 2B, the sliding movement caused by the cable 25 creates a non-equilateral or in this case a rectangular opening, as desired. When the aperture 12 is closed, the blocks return to the offset or skewed position with the interfaces 22 sealed, as shown in FIG. 2A. The alternate block assemblies, such as block assembly 15 act in the same manner and the offsetting or skewing action is generated concurrently, since as it will be remembered the pinions 70, 70a are simultaneously rotated by the moving wheel assembly 72. Thus in FIG. 3A, the blocks 19a, 21a are moved toward each other by bodily translation of the guide rods 39a, 40a whereas the blocks 18a, 20a are moved away from each other by an equal amount by movement of guide rods 35a, 36a (note movement arrows in FIG. 3A). It will also be noted that the aperture 12a is congruent with the aperture 12 and remains so in all adjusted positions of the blocks. As shown in FIGS. 4A and 4B, the movement of the actuators to shift the guide rods in the direction opposite to that described above allows alignment of the apexes of the blocks 18-21 (FIG. 4A) and then upon actuation of the blocks by the adjustment wheel assembly 31 the aperture 12 formed is square rather than rectangular. It will thus be realized that by a simple adjustment of the rods in unison a desired configuration of each of the apertures 12, 12a can be effected and thus the area for the channel accommodating the beam B is advantageously varied. Also, it will be recognized that where a different number of blocks are used, as indicated above, a different shape of the aperture 12, 12a does result. For example, if three blocks are used, a triangular aperture results; if five blocks are used in an array, then the aperture is a pentagon; and so forth for additional configurations. However, the apparatus of the present invention is such that regardless of the shape of the aperture the apertures of the assemblies remain congruent and thus form a beam channel when set up as shown in FIG. 5. In accordance with another aspect of the present invention, the assemblies 14-17 can be adjusted separately by simply moving the hand wheels of the adjustment wheel assemblies 31, 31a a different amount. Thus in the embodiment of FIG. 6, the adjustment wheel 46 is opened to provide an aperture 12' of a particular size. The aperture 12a' of the blocks in the adjacent assembly 15 is turned a lesser amount providing a smaller aperture 12a'. Similarly, the adjustment assembly of block assembly 16 is opened a lesser amount and the adjustment assembly in the block assembly 17 is opened still less to provide a diverging channel allowing the passage of the beam B'. The beam is thus a diverging beam that can be rectangular as shown, or could be diverging and square if the adjustment of FIGS. 4A, 4B is used. When the diverging channel is to be closed to cut off the beam B' each of the individual adjustment assemblies is simply moved in the reverse direction thus moving the blocks and closing each of the apertures in turn, as described above. In view of the foregoing, it will now be realized that substantial results and advantages over the prior art collimators is provided. The beam opaque blocks 18-21 are capable of efficient opening and closing through the individual adjustment assemblies 14-17. The blocks move along the sliding interface 22 so as to provide a barrier that is tight except for the aperture 12 and with no overlapping surfaces. When closed, the blocks converge at the apexes in the center of the block assembly. The adjustment for creating the variable apertures is provided by a novel cable drive engaging brackets attached to at least one of the sliding blocks. The mechanical pressure on the follower blocks provides the desired opening in a controlled fashion. Guide rods extending through the brackets ensure proper movement of the blocks and the guide rods may be translated toward and away from each other in order to adjust the shape of the apertures. When multiple block assemblies are utilized, a beam channel, including a diverging channel if desired, can be provided in an efficient manner. 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. Obvious modifications or variations are possible in light of the above teachings. The embodiment was chosen and described in order to best illustrate the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to best utilize in the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
062263420	abstract	A fuel assembly (1) comprising a plurality of elongated elements (3) filled with nuclear fuel and at least one component (5, 6, 7) for retaining the elongated elements (3), wherein the retaining component (5, 6, 7) is completely or partly made of a ceramic material.
	claims	1. A nuclear fission reactor system comprising:a core region containing a fuel structure, the fuel structure having a first region and a second region contiguous with the first region, each one of the first and second regions being capable of criticality independent of the other of the first and second regions, the fuel structure being configured to permit propagation of a propagating nuclear fission deflagration wave along a propagation path from the first region to the second region, the propagation path including at least one portion of retracement from the second region to the first region, the fuel structure including a first nuclear fission deflagration wave igniter disposed in the first region and a second nuclear fission deflagration wave igniter disposed in the second region. 2. The nuclear fission reactor system of claim 1, wherein the propagation path includes a first portion along a first direction and wherein the at least one portion of retracement follows the first direction. 3. The nuclear fission reactor system of claim 1, wherein the propagation path includes a first portion along a first direction and wherein the at least one portion of retracement opposes the first direction. 4. The system of claim 1, wherein:the fuel structure includes a first neutron environment ahead of the propagating nuclear fission deflagration wave; anda second neutron environment that is different from the first neutron environment along the at least one portion of retracement. 5. The system of claim 4, wherein:the first neutron environment includes a first amount of fissile isotope; andthe second neutron environment includes a second amount of fissile isotope that is different from the first amount of fissile isotope. 6. The system of claim 4, wherein:the first neutron environment includes a first amount of fission products; andthe second neutron environment includes a second amount of fission products that is different from the first amount of fission products. 7. The system of claim 4, wherein the second neutron environment is different from the first neutron environment due to changes in control of neutron modifying structures. 8. The system of claim 4, wherein the second neutron environment is different from the first neutron environment due to changes in thermal heat extraction levels. 9. The system of claim 1, wherein the propagating nuclear fission deflagration wave and the fuel structure move relative to each other. 10. The system of claim 9, wherein:the fuel structure is stationary; andthe propagating nuclear fission deflagration wave propagates through the fuel structure. 11. The system of claim 9, wherein:the propagating nuclear fission deflagration wave remains substantially spatially fixed; andthe fuel structure is moved relative to the propagating nuclear fission deflagration wave.
	claims	1. A system comprising:a means for defining and identifying a plurality of regions in a facility;a plurality of sensors wherein each sensor produces a load measurement indicating the amount of energy currently consumed in one of the plurality of regions of the facility;a means for determining independent variable values wherein the independent variables comprise outdoor temperature, date, time of day, and regions of the facility;a means for computing a plurality of independent variable measurements indicating the values of the independent variables at different times and for computing a plurality of load measurements indicating values of sensed load measurements at different times;a database storing the load measurements and the plurality of independent variable measurements as historical data;a similar data selector wherein the similar data selector is a Euclidean distance based similar data selector that accepts a recent measurement and produces similar historical data from the historical data, wherein the similar historical data comprises load measurements and independent variable measurements taken when the independent variable measurements were similar to the recent measurement; anda baseline estimation module that accepts the historical load data set and produces at least one baseline estimate for the recent measurement. 2. The system of claim 1 further comprising a periodic trigger that triggers the production of the similar historical data set and the at least one baseline estimate on a set period. 3. The system of claim 1 wherein the independent variables further comprise workday versus non-workday. 4. The system of claim 1 wherein the independent variables further comprise occupancy. 5. The system of claim 1 wherein the baseline estimation module comprises a linear regression model. 6. The system of claim 1 further comprising a graphical user interface wherein the recent measurement is a current independent variable measurement such that the at least one baseline estimate is at least one current baseline estimate; and wherein the graphical user interface presents the plurality of regions with an indication of the difference between the current load measurement and the current baseline estimate for the plurality of regions. 7. A system comprising:a means for defining and identifying a plurality of regions in a facility;a plurality of sensors wherein each sensor produces a sensed load measurement indicating the amount of energy currently consumed in one of the plurality of regions of the facility;a means for determining independent variable values wherein the independent variables comprise outdoor temperature, date, time of day, and regions of the facility;a means for computing a plurality of independent variable measurements indicating the values of the independent variables at different times and for computing a plurality of load measurements indicating values of sensed load measurements at different times;a database storing the load measurements and the independent variable measurements as historical data;a similar data selector that accepts a recent measurement, wherein the similar data selector is a Euclidean distance based similar data selector and a reference period and produces similar reference period data from the historical data;a baseline estimation module that accepts the similar reference period data and produces at least one reference period baseline estimate for the recent measurement;a drift detection means for identifying baseline drift by comparing the reference period baseline estimates to the load measurements, wherein said baseline drift is a difference that slowly changes over a given time period such that said difference will not be recognizable upon short term comparisons of baseline estimates to on-going load measurements. 8. The system of claim 7 further comprising at least one drift detection rule wherein the drift detection means comprises a rule based drift detection means. 9. The system of claim 7 wherein the independent variables further comprise workday versus non-workday. 10. The system of claim 7 wherein the independent variables further comprise occupancy. 11. The system of claim 7 wherein the baseline estimation module comprises a linear regression model. 12. The system of claim 7 further comprising a graphical user interface that presents the at least one region with an indication of the difference between the load measurements and the baseline estimates for the plurality of regions. 13. The system of claim 7 further comprising a graphical user interface that indicates the presence of baseline drift in any of the plurality of regions. 14. The system of claim 7 further comprising:at least one drift detection rule wherein the drift detection means comprises a rule based drift detection means;at least one data selection rule wherein the similar data selector is a rule based similar data selector;a graphical user interface that presents the at least one region with an indication of the difference between the load measurements and the baseline estimates for the at least one region and wherein the graphical user interface also indicates the presence of baseline drift in any of the plurality of regions;wherein the independent variables further comprise workday versus non-workday and building occupancy; andwherein the baseline estimation module comprises a linear regression model. 15. The system of claim 7, further comprising a drift alarm containing a drift amount within an affected region of said facility wherein said drift amount is an average error over an interval of time, such that said drift alarm is triggered when said drift amount is above a preselected value. 16. A system comprising:a means for defining and identifying a plurality of regions in a facility;a means for obtaining a plurality of load measurements for the plurality of regions and covering a plurality of time periods for each region wherein each load measurement is an indication of the amount of energy consumed in one region over a known time period;a means for storing the load measurements;a means for obtaining a plurality of independent variable measurements corresponding to the values of independent variables at known times wherein the independent variables comprise outdoor temperature, date, and time of day, and regions of the facility;a means for storing historical data comprising the load measurements and independent variable measurements;a means for selecting historical data that accepts a recent measurement and produces similar historical data wherein said means for selecting historical data uses a Euclidean distance based selector anda means for producing at least one baseline estimate. 17. The system of claim 16 further comprising a means for determining baseline drift. 18. The system of claim 17 further comprising a means for displaying the baseline drift. 19. The system of claim 16 further comprising a means for displaying the difference between the load measurements and the baseline estimates.
	summary
	abstract	A non-resonance photo-neutralizer for negative ion-based neutral beam injectors. The non-resonance photo-neutralizer utilizes a nonresonant photon accumulation, wherein the path of a photon becomes tangled and trapped in a certain space region, i.e., the photon trap. The trap is preferably formed by two smooth mirror surfaces facing each other with at least one of the mirrors being concave. In its simplest form, the trap is elliptical. A confinement region is a region near a family of normals, which are common to both mirror surfaces. The photons with a sufficiently small angle of deviation from the nearest common normal are confined. Depending on specific conditions, the shape of the mirror surface may be one of spherical, elliptical, cylindrical, or toroidal geometry, or a combination thereof.
	description	The present invention relates to a particle beam therapy system for performing a treatment through irradiation with a particle beam, and in particular, to a range shifter for adjusting a range of the particle beam. A particle beam therapy, which is a treatment of a deceased tissue by irradiating it with a particle beam to thereby damage the tissue, is a part of broad-sense radiation therapy. However, unlike a y-ray, an X-ray or like other ray, the imparted dose of a particle beam such as a proton beam, a heavy ion beam, etc., becomes maximum abruptly in a specific depth range (Bragg peak) in a body according to energy of the particle beam. Thus, in the particle beam therapy, it is possible to control the irradiation region (irradiation field), not only as a planar shape, but also in a depth direction by adjusting the energy. Meanwhile, since the facility of an accelerator that is a beam source for the particle beam therapy is huge, the particle beam emitted from a single beam source is distributed to a plurality of treatment rooms, individually. Although the energy of the particle beam is adjustable by changing the condition of the accelerator, it takes time. Thus, what is generally taken is to provide a device having a transmissive plate of a predetermined thickness, so-called “range shifter”, in each of the treatment rooms, to thereby adjust the energy of the particle beam according to its attenuation amount during transmission in the transmissive plate (see, for example, Patent Documents 1 to 9). Patent Document 1: Japanese Patent Application Laid-open No. H10-314323 (paragraph 0016, FIG. 21(a) to (d)) Patent Document 2: Japanese Patent Application Laid-open No. H11-262538 (paragraphs 0004 to 0005, FIG. 11) Patent Document 3: Japanese Patent Application Laid-open No. 2001-212253 (paragraph 0119, FIG. 7; paragraphs 0141 to 0147, FIG. 9) Patent Document 4: Japanese Patent Application Laid-open No. 2006-034582 (paragraphs 0037 to 0038, FIG. 10) Patent Document 5: Japanese Patent Application Laid-open No. 2007-307223 (paragraph 0017, FIG. 3) Patent Document 6: Japanese Patent Application Laid-open No. 2010-032419 (paragraph 0035, FIG. 1) Patent Document 7: Japanese Patent Application Laid-open No. 2010-148833 (paragraphs 0028 to 0057, FIG. 2 to FIG. 6) Patent Document 8: Japanese Patent Application Laid-open No. 2010-175309 (paragraphs 0019 to 0020, 0024, FIG. 2, FIG. 3) Patent Document 9: Japanese Patent Application Laid-open No. 2010-187900 (paragraphs 0033 to 0037, FIG. 1) However, these technologies disclosed are intended to adjust a water-equivalent thickness, for example, as the attenuation amount equivalent to an in-body depth, by selecting the material or the thickness of the transmissive plate. Nevertheless, the attenuation amount at the time the particle beam transmits through the transmissive plate, i.e. an actual water-equivalent thickness, is not always constant depending on the condition of the transmitting particle beam. Thus, even when a range shifter is used which has, for example, the transmissive plate whose material and thickness have been finished exactly as specified, there is a possibility that a difference in the water-equivalent thickness occurs depending on what the treatment room is, or occurs even in the same treatment room, if its condition has changed by the maintenance or the like. This invention has been made to solve the problem as described above, and an object thereof is to provide a range shifter and a particle beam therapy system which can adjust a range of the particle beam exactly as specified, The range shifter of the invention is a range shifter that outputs a particle beam incident thereto while attenuating energy of the particle beam, characterized by comprising a transmissive plate whose thickness has been adjusted depending on a setup value of an amount of the energy to be attenuated, and a holder portion that holds the transmissive plate, wherein the thickness of the transmissive plate is adjusted to be a thickness equivalent to an attenuation amount lower than the setup value by a predetermined rate thereof, and wherein a superimposing mechanism capable of releasably superimposing an adjustment sheet over the transmissive plate, is provided to at least one of the transmissive plate and the holder portion, said adjustment sheet being adjusted to have a thickness equal to or less than a thickness equivalent to a two-fold attenuation amount of the predetermined rate. According to the range shifter of the invention, even when its attenuation amount of the energy changes due to a change in the condition of the incident particle beam, it is possible to make adjustment to the setup attenuation amount of the energy by superimposing the adjustment sheet whose thickness can be adjusted. Thus, it is possible to achieve a range shifter that adjusts the range of the particle beam accurately, and a particle beam therapy system that can make irradiation with an accurate irradiation field. Embodiment 1 Hereinafter, a configuration of a range shifter according to Embodiment 1 of the invention and a method of adjusting the same, will be described. FIG. 1 to FIG. 4 are for illustrating the range shifter and its adjusting method according to Embodiment 1 of the invention, in which shown at FIG. 1(a) and FIG. 1(b) are a top view (a) showing the configuration of the range shifter, and cross-sectional views (b) taken along line I-I in the top view, individually showing transmissive units of typical three types that are different depending on a thickness of the transmissive plate. Meanwhile, FIG. 2 is a schematic diagram showing a configuration of an irradiation device provided with the range shifter according to Embodiment 1 of the invention. FIG. 3 is a diagram showing a configuration of a particle beam therapy system provided with the aforementioned irradiation device in each treatment room. Further, FIG. 4 is a flowchart for illustrating a method of adjusting the range shifter according to Embodiment 1 of the invention, at the time the irradiation device provided with the range shifter is installed or subjected to its maintenance. As shown in FIG. 1(a), the range shifter 10 includes a plurality of transmissive units 4 in a housing 11, each provided with a transmissive plate 1 in a manner allowing it to enter into or leave from an irradiation region of the particle beam. As shown in FIG. 1(b), the plurality of transmissive units 4 include the transmissive plates 1 having different thicknesses according to their respective setup attenuation amounts of the particle beam energy, and a frame 3 holding the transmissive plate 1 is connected by way of a driving cylinder 12 to the housing 11, so that it is possible to cause the transmissive plate 1 to move between a retracted position and an irradiation position. What is a feature of this invention is that each of the transmissive units 4 is configured in such a manner that an adjustment sheet 2 capable of adjusting thickness can be superimposed releasably over the transmissive plate 1 in order to adjust the attenuation amount. The transmissive plate 1 is formed of a polyethylene plate in which at least a region where the particle beam transmits (for example, a 200-mm diameter area) is adjusted in thickness to have a predetermined thickness depending on a setup value of the attenuation amount set to the corresponding transmissive unit 4. In consideration of variation in attenuation amount as described previously, this region is, however, configured to be thinner than a thickness capable of establishing the setup attenuation amount, in order to ensure its portion of 1 to 2% as a margin for adjustment by the adjustment sheet 2. Actually, in further consideration of material's own variation, when a thickness equivalent to the attenuation amount setup to the corresponding transmissive unit 4 is given as “1”, the transmissive plate is adjusted to have an attenuation amount equivalent to less than “1”, i.e. 0.93 to 0.98 (reduction rate of from 2 to 7%). For example, in the case where the attenuation amount of the energy is set as a water-equivalent thickness corresponding to an in-body mean range and the setup value is 64 mm, when a polyethylene block with a density of from 0.94 to 0.96 g/cm3 is used, by adjusting its actual thickness to 64 mm, it is possible to prepare the transmissive plate 1 whose water-equivalent thickness is less than the water-equivalent thickness of 64 mm, leaving a margin for adjustment. Meanwhile, the adjustment sheet 2 is made to be superimposed, when said transmissive plate 1 is used in the irradiation device, over the transmissive plate 1 so that a predetermined water-equivalent thickness is attained. The thickness of the adjustment sheet 2 can be adjusted in such a manner of laminating a plurality of polyethylene sheets each being pre-adjusted in thickness or polyethylene sheets each being thinner than the margin for adjustment. Note that, as the plurality of the respective transmissive units 4 are represented by 4-1 to 4-n, there are shown, in FIG. 1(a), the transmissive unit 4-1 staying at the retracted position and the unit 4-i staying at the irradiation position. Further, as shown in FIG. 1(b), the respective transmissive units 4 include those of typical three types that are different in structures of the transmissive plate 1 itself and the frame 3 holding the transmissive plate 3, depending on the thickness of each transmissive plate 1, which are indicated as Type-A, Type-B and Type-C, respectively. And, FIG. 1(b) shows cross-sectional views taken along line I-I in FIG. (a) for showing portions of the transmissive units 4 corresponding to the respective Type-A, Type-B and Type-C, in order to illustrate the three types of structures. Note that, in FIG. 1(b), although pan-head screws are shown for clarifying the screw positions, what is actually used are countersunk screws with their heads unprojected. The structures of the transmissive units 4 will be described separately for a commonly-configured portion in the respective types and for a characterizing portion in each type. <Common in Respective Types> Each frame 3 has one end portion fixed to the driving cylinder 12 and the other end portion that serves as a holder portion for holding the transmissive plate 1 and the adjustment sheet 2. The portion that holds the transmissive plate 1 and the adjustment sheet 2 is opened so as not to shut the region where the particle beam goes in or goes out. <Type-A> The transmissive unit 4 of Type-A is to be applied to the transmissive plate 1 with a thickness of 4 mm or less, and its shape in overhead view corresponds to the transmissive unit 4-1 in FIG. 1(a). The frame 3 is configured with a fixed frame 31 in which its one end portion is fixed to the driving cylinder 12 and an opening is formed in the other end portion, and a clamping frame 32 having an opening similar to the above, for clamping in between it and the fixed frame 31, the transmissive plate 1 and the adjustment sheet 2 together. At corner portions of the clamping frame 32, loose holes for passing the screws 6 are formed, and at the positions on the fixed frame 31 corresponding to the holes, thread grooves for fastening the screws 6 are formed. The transmissive plate 1 is flatly shaped, in which holes are formed for passing the screws 6 for fastening the frame 3 and the adjustment sheet 2 together. Namely, although the relatively-thin transmissive plate 1 and the adjustment sheet 2 are held together by the frame 3, the adjustment sheet 2 is made attachable/releasable in the transmissive unit 4. <Type-B> The transmissive unit 4 of Type-B is to be applied to the transmissive plate 1 with a thickness in a range from 4 mm to 16 mm, and, like Type-A, its shape in overhead view corresponds to the transmissive unit 4-1 in FIG. 1(a). Also, the structure of the frame 3 is similar to that of Type-A. Meanwhile, with respect to the transmissive plate 1, in order to reduce its thickness as a whole, its fringe portion is cut down so as to be fitted partially in the opening of the fixed frame 31. Further, like Type-A, the transmissive plate 1 and the adjustment sheet 2 are held together by the frame 3, and the adjustment sheet 2 is made attachable/releasable in the transmissive unit 4. <Type-C> The transmissive unit 4 of Type-C is to be applied to the transmissive plate (block) 1 with a thickness more than 16 mm, and its shape in overhead view corresponds to the transmissive unit 4-i in FIG. 1(a). The frame 3 is configured with a fixed frame 31 in which its one end portion is fixed to the driving cylinder 12 and an opening is formed in the other end portion, an intermediate frame 33 fixed to the fixed frame 31 through a spacer 34 as being apart from the fixed frame 31 according to the thickness of the transmissive plate 1, and a clamping frame 32 for clamping in between it and the intermediate frame 33, the adjustment sheet 2. At corner portions of the clamping frame 32, loose holes for passing the screws 6a are formed, and as corresponding to the positions of the holes, thread grooves for fastening the screws 6a are formed on the intermediate frame 33. At corner portions of the fixed frame 31, screw holes for fastening the screws 6c for fixing the transmissive plate 1 are formed. In addition, at middle portions of the respective sides of the intermediate frame 33, loose holes for passing the screws 6b are also formed; at the positions on the fixed frame 31 corresponding to that holes, thread grooves for fastening the screws 6b are formed; and on the clamping frame 32, incisions are formed so as not to interfere with the heads of the screws 6b. With respect to the transmissive plate 1, in order to reduce the thickness as the transmissive unit 4, its fringe portion is cut down so as to be fitted partially in the opening of the fixed frame 31, and it is formed into a flange-like shape so as to be fixed to the fixed flame 31. Namely, the heavy transmissive plate 1 is solely held by the fixed frame 31, while the adjustment sheet 2 is held by the intermediate frame 33 and the clamping frame 32, independently of the transmissive plate 1. Thus, the adjustment sheet 2 is made attachable/releasable in the transmissive unit 4, independently of the heavy transmissive plate 1. Namely, at least one of the frame 3 and the transmissive plate 1 serves as a superimposing mechanism that releasably superimposes the adjustment sheet 2 over the transmissive plate 1. Note that, shown in this embodiment is a case where the transmissive units 4 are configured with those of three types depending on the thickness of each transmissive plate 1; however, the types are not limited thereto, and may be more than or less than three. Further, the number of the transmissive units 4 (thickness types of the transmissive plate 1) is not required to be limited, and may be singular or plural; however, for example, if the transmissive plates 1 of a binary type each having a thickness t=0.5 to 64 mm are to be arranged, N number of types becomes necessary, where N (=8) satisfies 0.5×2(N-1)=64. Note that, for example, if the thickness of the transmissive plate 1 is adjusted to be a water-equivalent thickness that is less by R % than the setup value of the water-equivalent thickness, by adjusting the thickness of the adjustment sheet 2 within a thickness up to maximum two-fold of R %, it is possible to make adjustment to the setup value. Thus, its suffices that each frame 3 releasably holds the adjustment sheet having a thickness of up to 2R%. Meanwhile, since the frame 3 releasably holds the adjustment sheet 2 by clamping its fringe portion, the number of sheets to be clamped has no limit. Thus, it is not necessary to configure by a single sheet, the adjustment sheet 2 for making adjustment to the required water-equivalent thickness. Therefore, the required water-equivalent thickness may be adjusted by a lamination of sheets each having an appropriate thickness. For that reason, the superimposing mechanism (frame 3 or the transmissive unit 4 including the same) is desired to be configured in such a manner that the adjustment sheet 2 is placed in the upper side of the transmissive plate 1 in a vertical direction of the range shifter 10 in a state of being installed, so as to make easier the replacement or the overlapping of the adjustment sheet 2. Next, the irradiation device and the particle beam therapy system which are provided with the range shifter 10 according to Embodiment 1 of the invention, will be described using FIG. 2 and FIG. 3, As shown in FIG. 2, the irradiation device 100 includes a scanning electromagnet (for example, Wobbler Magnets) 20 that serves as an irradiation nozzle for enlarging the irradiation field by scanning a particle beam B supplied from a beam source; a scatterer 30 that is formed of lead or the like and scatters the particle beam B; a ridge filter 40 that is formed of aluminum or the like and spreads the width of the Bragg peak depending on the thickness of the irradiation target; the range shifter 10 as described above; a multi-leaf collimator 50 that is configured with a leaf portion comprising a plurality of leaf plates and a leaf movement mechanism for moving each of the leaf plates, and serves to make restriction so that the irradiation field (planar shape) matches the shape of the deceased site; and a range monitor 60 used for later-described adjustment of the adjustment sheet 2. Note that, in actual treatment, a bolus 120 is used that is fabricated for every patient K so as to be matched with a shape in depth of the deceased site (irradiation target), and makes restriction on a range distribution of the particle beam B. As shown in FIG. 3, the particle beam therapy system includes, as a source of supplying the particle beam B, a circular accelerator 400 which is a cyclotron (hereinafter, referred to simply as “accelerator”); transport paths 300 for transporting the particle beam supplied from the accelerator 400 to, among a plurality of treatment rooms (200-1 to 200-n; referred to collectively as 200), a selected treatment room 200; and irradiation devices (100-1 to 100-n; referred to collectively as 100) each provided with the range shifter 10 as described above and placed in each treatment room 200, for irradiating the patient K with the particle beam B transported by the transport path 300. The treatment room 200 is a room for performing a treatment by actually irradiating the patient K with the particle beam, and the irradiation device 100 is provided in each treatment room 200. Note that in the figure, there is shown a case where the treatment room 200-1 is a rotating irradiation room (called also as a rotary gantry) in which the irradiation device 100 is rotatable as a whole about the patient K (treatment table) to thereby freely set an irradiation angle of the particle beam to the patient K. Meanwhile, the treatment room 200-2 is shown as a horizontal irradiation room that irradiates the patient K fixed to a treatment table whose angle and position is freely settable, in a horizontal direction with the particle beam from the irradiation device 100-2. In such a manner, generally, to the single accelerator 400, a plurality of treatment rooms 200 including those of different types and/or the similar types, are connected through the transport paths 300. Note that the transport path 300 is formed by joining vacuum ducts 310 each providing a transport cavity for the particle beam B, and is provided with a switching electromagnet 320 that is a switching device for switching the beam trajectory of the particle beam B toward the supply-destination treatment room 200, and with a deflection electromagnet 330 that deflects the particle beam B by a predetermined angle. Connection is established from a main-path 300-0 directly connected to the accelerator 400, to sub-paths 300-1 to 300-n corresponding to the respective treatment rooms 200, through the switching electromagnet 320. Namely, even if there are provided the irradiation devices 100 with specifications similar to each other, the particle beam B is supplied through the different transport path 300 for each of the treatment rooms 200. Next, operations of the particle beam therapy system and the irradiation device will be described, Charged particles entered into the accelerator 400 are accelerated by a high-frequency electric field up to approx. 70 to 80% of the light velocity while being bent by the magnets, and are then emitted as the particle beam B into the transport path 300. In the transport path 300, the emitted particle beam B is led to the irradiation device 100 provided in the designated treatment room 200, by switching, if necessary, the transport path (300-1 to 300-n) by the switching electromagnet 320. Although the particle beam B supplied to the irradiation device 100 is in a state of less than several millimeters in diameter i.e. a so-called pencil beam, it is caused to scan as if it draws, for example, a circle orbit by the scanning electromagnet 20, and then scattered by the scatterer 30, so that its irradiation field is enlarged in an extending direction of a plane (plane direction) perpendicular to the beam axis. The particle beam B with the irradiation field enlarged in the plane direction, passes through the ridge filter 40. The ridge filter 40 is formed, for example, of a number of cone-like objects or cross-sectionally triangle plates, that are arranged in the plane direction, so that there are portions of the particle beam B each passing through different thicknesses in each region divided in the plane direction. In the figure, for ease of understanding, it is illustrated as triangle poles arranged laterally. This makes the Bragg peak to be spread, so that the beam becomes to have an SOBP (Spread-Out Bragg Peak) with a predetermined width. That is, by means of the ridge filter 40, the irradiation field becomes spread also in the beam axis direction (depth direction). Then, the particle beam B whose irradiation field has been spread, passes through the range shifter 10. In the range shifter 10, the energy (range) of the particle beam B is adjusted by placing a given transmissive unit 4 in the entrance region so as to cause the particle beam B to transmit through the transmissive plate 1 and the adjustment sheet 2 that are adjusted to provide an intended water-equivalent thickness (attenuation amount). Because the range is adjusted by the range shifter 10, it is possible to irradiate (to impart dose in) an intended in-body depth with the particle beam B. Then, the particle beam B passes through the multi-leaf collimator 50. The multi-leaf collimator 50 forms an intended opening shape by positioning its plural sets of mutually facing plates at predetermined positions in a direction getting away from or getting close to the beam axis. Thus, the irradiation field of the particle beam B after passing through the multi-leaf collimator 50 is formed into a plane-direction shape matching the shape of the deceased site. Finally, the particle beam B passes through the bolus 120. The bolus 120 is a limiter made of a resin or the like, and is formed into a configuration that compensates for a distal shape, for example, of the deceased site, as the depth-direction shape of the deceased shape. The distal shape means an uneven shape in the deepest side of the deceased site Here, the irradiation field is restricted in energy distribution in an extending direction of the plane (shaped in z-direction), so as to have a shape that is the same as the distal shape. That is, the depth direction shape of the irradiation field of the particle beam B is formed. In the case of performing irradiation by a layer-stacking conformal irradiation method using the irradiation device 100 as described above, the dose injection is made such that spatially-imparted dose is given as being divided in the depth direction. At the initiation of irradiation, the scanning electromagnet 20, the range shifter 10 and the multi-leaf collimator 50 are set in conformity to the dose to be imparted to a layer (slice) including the deepest portion, and then the patient K is irradiated with the particle beam B. After completion of irradiation to the layer (slice) of the deepest portion, the range is adjusted by the range shifter 10 automatically in conformity to a position shallower (a near side viewed from irradiation source) by a depth corresponding to the width of the Bragg peak, and also, the settings of the scanning electromagnet 20 and the multi-leaf collimator 50 are changed, so that irradiation to the next layer is performed. Thereafter, while adjusting the range similarly by the range shifter 10, and changing the settings of the scanning electromagnet 20 and the multi-leaf collimator 50, an optimized dose is imparted as a whole to the shape of the deceased site. In such a particle beam therapy system, the range shifter 10 have an important role in determining the position in each slice. Namely, unless otherwise the water-equivalent thickness (attenuation amount) set in the treatment plan is achieved by the range shifter 10, the irradiation field is shifted relative to the deceased site in the depth direction. Thus, not only a sufficient dose is not imparted to the deceases site, but also a surrounding normal tissue is damaged. Accordingly, for example, even if the setup pitch of the range shifter 10 is 1 mm in the treatment plan, it is required for the range shifter 10 to achieve a water-equivalent thickness accurately with a precision finer than the setup pitch. Meanwhile, as described above, in the particle beam therapy system, a difference in transport path exists for each treatment room 200, in terms of the number of times passing the switching electromagnet 320, the defection electromagnet 330 and the like, and the path length of the vacuum ducts 310. Further, in the irradiation devices 100 in the respective treatment rooms 200, the specifications and the adjusted conditions of the scanning electromagnet 20, the scatterer 30 and the ridge filter 40 are not always the same. Namely, depending on the adjusted condition of the installed treatment room 200 or irradiation device 100, the particle beam B does not always pass through the range shifter 10 in the same condition. Thus, as described in BACKGROUND ART, even if the range shifters 10 can be fabricated in the same specification, the attenuation amount changes depending on what the installed irradiation device 100 is, or changes even in the same irradiation device 100 if its condition has changed by the maintenance or the like. Thus, as described for the range shifter 10 according to Embodiment 1 of the invention, the transmissive plate 1 has been adjusted to have a thickness equivalent to the attenuation amount that is lower than the setup value of the attenuation amount, and the transmissive unit 4 is configured such that the adjustment sheet 2 can be superimposed releasably. This allows to make adjustment to a really-required attenuation amount by adjusting the thickness of the adjustment sheet 2. This method of adjusting the attenuation amount will be described using a flowchart in FIG. 4. Here, description is made to the range shifter 10 having a plurality of transmissive units 4, and a water-equivalent thickness is used as the setup value of the attenuation amount for making its concept easily understandable. First, the range monitor 60 (FIG. 1) is placed at an irradiation position of the particle beam B that is downstream of the range shifter 10 (Step S10). Then, the range shifter 10 is driven so that the transmissive unit 4 subject to adjustment is placed at an irradiation position (Step S20). Subsequently, the range shifter 10 is irradiated with the particle beam B (Step S30), and its range is measured by the range monitor 60 in the downstream side (Step S40). Then, it is determined whether or not the measured range falls within a value acquired from the water-equivalent thickness required for that transmissive unit 4 (Step S50). If not within the value (Step S50, “N”), a thickness adjustment is performed by adjusting the thickness, the number, or its combination, of a sheet(s) used as the adjustment sheet 2 (Step S200), and then the flow moves to Step S30. On the other side, if within the value (Step S50,“Y”), it is determined whether the adjustment is completed or not (Step S60). If there remains another transmissive unit 4 to be adjusted and thus the adjustment is not completed (Step S60,“N”), the flow moves to Step S20. In contrast, if all of the transmissive units 4 have been adjusted and thus the adjustment is completed (Step S60, “Y”), the range monitor 60 is retracted (Step S70) and the adjustment is ended. In the particle beam therapy system after the above adjustment, even if an actual treatment is performed in any treatment room 200 among the treatment rooms 200 and among treatment rooms 200 that are at least subjected to the adjustment, it is possible to make adjustment to a constant and ideal water-equivalent width, so that the treatment can be performed while ensuring compatibility with the treatment plan. For example, if such an adjustment is performed for every maintenance such as a periodic inspection so as to adjust the water-equivalent width of the range shifter 10, even when only a given treatment room 200 is subjected to the maintenance, it is possible to hold a compatibility with another treatment room, and even when the treatment room 200 is changed, it is possible to hold a compatibility with the treatment plan. Note that materials of the transmissive plate 1 and the adjustment sheet 2 are also not limited to the above-described materials so far as they are materials having resistance to radiation and not causing unnecessary scattering, and may be acrylic or polyimide materials, for example. As described above, the range shifter 10 according to Embodiment 1 is a range shifter 10 that outputs the particle beam B incident thereto while attenuating energy of the particle beam B, which comprises: the transmissive plate 1 whose thickness has been adjusted according to a setup value (for example, a water-equivalent thickness) of an amount of the energy to be attenuated; and the frame 3 serving as a holder portion that holds the transmissive plate 1; wherein the thickness of the transmissive plate 1 is adjusted to be a thickness equivalent to an attenuation amount lower than the setup value by a predetermined rate thereof; and wherein the superimposing mechanism capable of releasably superimposing the adjustment sheet 2 over the transmissive plate 1, is provided to at least one of the transmissive plate 1 and the holder portion 3, said adjustment sheet 2 being adjusted to have a thickness equal to or less than a thickness equivalent to a two-fold attenuation amount of the predetermined rate. Thus, even when the attenuation amount of the energy changes due to a change in the condition of the incident particle beam B caused by a difference between the installed irradiation devices 100 or by the maintenance, it is possible to make adjustment to the setup attenuation amount of the energy by superimposing the adjustment sheet 2 whose thickness can be adjusted. Thus, it is possible to output the particle beam B while adjusting its range accurately. In particular, when the predetermined rate used for making lower than the setup value is set to from 2 to 7%, it is possible to make adjustment to the intended water-equivalent thickness by adjusting the thickness of the adjustment sheet 2, even if the condition of the incident particle beam B has changed to the maximum extent. When at least one of the frame 3 and the transmissive plate 1 that constitutes the superimposing mechanism, is configured to superimpose the adjustment sheet 2 over the transmissive plate 1 in the incident side of the particle beam, in a case of irradiation device 100 that makes irradiation with the particle beam in a vertical direction, the adjustment sheet 2 is placed in the upper side of the transmissive plate 1 in a vertical direction of the range shifter 10 in a state of being installed. Thus, it is possible to easily adjust the thickness of the adjustment sheet 2 by its replacement. Meanwhile, the particle beam therapy system according to Embodiment 1 comprises: the accelerator 400 that generates the particle beam B; the plurality of treatment rooms 200; the transport paths 300 that connect between the accelerator 400 and each of the plurality of treatment rooms 200; and the irradiation device 100 provided in each of the plurality of treatment rooms 200, that forms the particle beam B supplied through the transport path 300 into an irradiation field that matches an irradiation target, to thereby irradiate the irradiation target with the particle beam B; wherein the above-described range shifter 10 is provided in the irradiation device 100. Thus, even if any one of the treatment rooms 200 is used, it is possible to make irradiation with an accurate and compatible irradiation field. DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 1: transmissive plate, 2 adjustment sheet, 3: frame, 4: transmissive unit, 10: range shifter, 11: housing, 12: cylinder, 20: scanning electromagnet, 30: scatterer, 40: ridge filter, 50: multi-leaf collimator, 60: range monitor, 100: irradiation device, 200: treatment room, 300: transport path, 400: accelerator.
	description	1. Field The disclosed and claimed concept relates generally to nuclear power generation equipment and, more particularly, to a device usable to detect neutron flux and thus power generation in a nuclear reactor. 2. Background Nuclear power plants and other types of devices that employ controlled nuclear reactions are well known. During operation of a nuclear reactor, it is desirable to understand the rate at which power is being generated at various areas within the reactor. Devices that can sense electric power generation via neutron flux and the like are well known in the relevant art. However, inasmuch as space within a nuclear reactor for instrumentation and the like is limited, it has generally been possible to employ only a limited number of detection devices within the containment of a nuclear reactor. The result has been that the detected values of power generation at various locations within a reactor core have been capable of at most only a coarse approximation. This is due, at least in part, to the fact that known detection devices have each required telemetry wires to extend between the sensing device and an appropriate data logging device. Such wires occupy volume within the reactor core, and available volume for such wires is limited at best. It thus would be desirable to enable more accurate power generation values within the core of a nuclear reactor. An improved discharge apparatus usable in a nuclear reactor includes an emitter apparatus in the form of a plurality of wire segments that emit electrons via beta decay to a collector. The rate at which the electrons are emitted is directly related to the neutron flux in the vicinity of each wire segment. Since the wire segments and the collector are electrically insulated from one another, the continual emission of electrons from the wire segments to the collector results in a charge imbalance between each wire segment and the collector. Eventually, the charge imbalance between the collector and a wire segment overcomes the dielectric properties of the insulation that is interposed between the wire segment and the collector, and an electrostatic discharge event in the form of a spark occurs between the wire segment and the collector. A detection device employs time-of-flight techniques to analyze signals that result from the electrostatic discharge event to determine the position along the discharge apparatus where the electrostatic discharge event occurred. The various occurrences of electrostatic discharge events over the course of time and at various locations along the discharge apparatus where the wire segments are situated are employed in determining the neutron flux and thus the power generation at the locations. Accordingly, an aspect of the disclosed and claimed concept is to provide an improved discharge apparatus that is usable to provide an indication of neutron flux and thus power generation at various locations inside a nuclear containment. Another aspect of the disclosed and claimed concept is to provide such a discharge apparatus that is usable within a limited amount of space within a nuclear containment. Another aspect of the disclosed and claimed concept is to perform various time-of-flight analyses of signals that are detected as a result of electrostatic discharge events to determine the positions of the electrostatic discharge events in order to measure neutron flux and thus power generation rates at various locations within a nuclear reactor containment. Another aspect of the disclosed and claimed concept is to provide a discharge apparatus that employs a plurality of spaced apart emitters in the form of wire segments that emit electrons via beta decay in a neutron bombardment environment and wherein the emitters are electrically insulated from a collector that collects the electrons from the emitters. Accordingly, an aspect of the disclosed and claimed concept is to provide an improved discharge apparatus usable in a nuclear reactor environment for determining neutron flux at a plurality of locations and being structured to be connected with a number of inputs of a detection device. The discharge apparatus can be generally stated as including an elongated emitter apparatus comprising a plurality of emitters spaced apart from one another in a predetermined fashion along the longitudinal extent of the emitter apparatus, the plurality of emitters each being structured to emit a number of electrons via beta decay responsive to its absorption of neutrons, a collector situated in proximity to the emitter apparatus and being structured to collect from the plurality of emitters the number of electrons, an insulator apparatus interposed between the emitter apparatus and the collector, the insulator apparatus electrically insulating from one another at least some of the emitters of the plurality of emitters, the emitter apparatus and the collector being electrically insulated from one another due at least in part to the insulator apparatus, and at least some of the emitters of the plurality of emitters each being structured to undergo an electrostatic discharge event with the collector when an imbalance in electrical charge between the emitter and the collector is sufficient to exceed the dielectric properties of the insulator apparatus. Other aspect of the disclosed and claimed concept are provided by a method of employing the aforementioned discharge apparatus in determining neutron flux at a plurality of locations in a nuclear reactor environment. The method can be generally stated as including connecting the discharge apparatus with a number of inputs of a detection device, detecting an input signal at the number of inputs as being representative of an electrostatic discharge event, determining with the detection device a time differential between a portion of the input signal and another portion of the input signal, employing the time differential to identify a position along the longitudinal extent of the emitter apparatus as being the site where the electrostatic discharge event occurred, and determining a neutron flux at a location that includes the position and that is based at least in part upon the occurrence of the electrostatic discharge event. Similar numerals refer to similar parts throughout the specification. FIG. 1 illustrates a typical pressurized water nuclear reactor 4 having a nuclear containment 6 that encloses a nuclear fuel assembly 10. The fuel assembly 10 has a structural skeleton which, at its lower end includes a bottom nozzle 14. The bottom nozzle 14 supports the fuel assembly 10 on a lower core support plate 18 within the containment 6. In addition to the bottom nozzle 14, the structural skeleton of the fuel assembly 10 also includes a top nozzle 12 at its upper end and a number of guide tubes or thimbles 20, which extend longitudinally between the bottom and top nozzles 14 and 12 at the opposite ends thereof and which are rigidly attached thereto. The structural skeleton of the fuel assembly 10 further includes a plurality of grids 22 that are axially spaced along and are mounted to the guide thimble tubes 20. In the final assembly the grids 22 function to maintain an organized array of elongated fuel rods 24 spaced apart and supported by the grids 22. Also, the structural skeleton of the fuel assembly 10 includes an instrumentation tube 16 located in the center thereof, which extends and is captured between the bottom and top nozzles 14 and 12. With such an arrangement of parts, fuel assembly 20 forms an integral unit capable of being conveniently handled without damaging the assembled parts. The fuel rods 24 are not actually part of the structural skeleton of the fuel assembly 10, but are inserted into the individual cells within the grids 22 before the top nozzle is finally affixed at the end the of fuel assembly 10. As mentioned above, the fuel rods 24, as in the array shown in the fuel assembly 10, are held in a spaced relationship with one another by the grids 22 spaced along the fuel assembly length. Each fuel rod 24 includes a stack of nuclear fuel pellets 26 and is closed at its opposite ends by upper and lower fuel rod end plugs 28 and 30. The pellets 26 are maintained in the stack by plenum spring 32 disposed between the upper end plug 28 and the top of the pellet stack. The fuel pellets 26, composed of fissile material, are responsible for creating the thermal power of the reactor 4. A liquid moderator/coolant such as water or water containing boron, is pumped upwardly through a plurality of flow openings in the lower core support plate 18 to the fuel assembly 10. The bottom nozzle 14 of the fuel assembly 10 passes the coolant upwardly through the guide tubes 20 and along the fuel rods 24 of the assembly 10 in order to extract heat generated therein for the production of useful work. For the purpose of illustration, FIG. 1 shows a 17×17 array of fuel rods 24 in a square configuration. It should be appreciated that other arrays of different designs and geometries are employed in various models of pressurized reactors. For example an alternative fuel assembly may be formed in a hexagonal array with the basic components of the structural skeleton that are illustrated in FIG. 1. To control the fission process, a number of control rods 34 are reciprocally movable in the guide thimbles 20 located at predetermined positions in the fuel assembly 10. A rod cluster control mechanism 36 positioned above the top nozzle 12 supports the control rod 34. The control mechanism has an internally threaded cylindrical member 38 which functions as a drive rod with a plurality of radial extending flukes or arms 40. Each arm 40 is interconnected to a control rod 34 such that the control rod mechanism 36 is operable to move the control rods vertically in the guide thimbles 20 to thereby control the fission process in the fuel assembly 10, all in a well-known manner. The grids 22 are mechanically attached to the control rod guide thimbles 20 and the instrumentation tube 16 by welding or by bulging. Bulging is desirable where welding dissimilar materials is difficult. An improved detection assembly 42 is depicted in FIG. 2 and is usable with the nuclear reactor 4 of FIG. 1. The detection assembly 42 includes a discharge apparatus 44, a detection device 46, and a set of connecting wires 48A and 48B. The connecting wires 48A and 48B are connectable with the ends of the discharge apparatus 44 and are further connectable with a pair of inputs 50A and 50B of the detection device 46. The discharge apparatus 44 is depicted in FIG. 1 as extending through the instrument thimble 16. The discharge apparatus 44 that is depicted in FIGS. 1-3 is a first embodiment thereof, and it is noted that additional embodiments of the discharge apparatus 44 are depicted in FIGS. 5-8. The alternative embodiments of the discharge embodiments 44 are connectable with the connecting wires 48A and 48B for connection with the inputs 50A and 50B of the detection device 46 to form additional embodiments of the detection assembly 42. As will be set forth in greater detail below, the discharge apparatus 44 is advantageously employable to measure the rate at which power is produced within the nuclear reactor at various points along what can be referred to as an “axis of detection” which, in the depicted exemplary embodiment, is generally along the instrument thimble 16. While the exemplary “axis of detection” that is provided by the discharge apparatus 44 is depicted in FIG. 1 as being in the instrument thimble 16, it is noted that the discharge apparatus 44 in particular and the detection assembly 42 as a whole are usable to detect power generation rates at other locations within the nuclear reactor 4 without departing from the present concept. Advantageously, the discharge apparatus 44 is configured to provide an apparatus that enables accurate measurements of power generation at a large number of locations along the “axis of detection” while maintaining a relatively small footprint, i.e., requiring relatively small volume within the nuclear reactor 4. This is at least in part because the discharge apparatus 44 does not rely upon a plurality of sensing elements each having separate wires that are connected with a data logging device. Rather, and in conjunction with the detection device 46, the discharge apparatus 44 relies instead upon time-of-flight analysis of electrostatic discharge events within the discharge apparatus 44 to determine the positions along the discharge apparatus 44 where the electrostatic discharge events have occurred. As will be set forth in greater detail below, such electrostatic discharge events provide an indication of power generation at numerous locations along the length of the discharge apparatus 44. As is depicted in FIG. 4, it understood that the discharge apparatus 44, the connecting wires 48A and 48B, and the inputs 50A and 50B on the detection device 46 can be referred to as together functioning as an input apparatus 52 that provides input signals to a processor apparatus 54. The detection device 46 can be said to include the processor apparatus 54, and the processor apparatus 54 includes a processor 56 and a storage 58 having a number of routines 60 stored therein. As employed herein, the expression “a number of” and variations thereof shall refer broadly to any non-zero quantity, including a quantity of one. The processor 56 can be any of a wide variety of computer processors, including microprocessors and the like that can perform operations based upon instructions that are stored in a memory or other storage. The storage 58 a non-transitory storage medium and can include any one or more of the wide variety of electronic storage devices such as RAM, ROM, EPROM, EEPROM, FLASH, and the like that enable the storage of instructions and data that is used by the processor apparatus 54. The routines 60 are stored in the storage 58 and are executable by the processor 56 and comprise any of a variety of instructions which, when executed on the processor 56, cause the processor apparatus 54 and thus the detection assembly 42 to perform certain operations that will be set forth in greater detail below. The detection device 46 additionally includes an output apparatus 62 that receives output signals from the processor apparatus 54 and which is depicted in FIG. 2 as being a visual display 64 such as in the nature of a computer display or as a CRT of an oscilloscope. The detection device 46 can itself be or include a general purpose computer. The output apparatus 62 can additionally include connections with mainframe computer, servers, and the like, and it is noted that the output apparatus 62 can facilitate distributed processing of certain of the input signals that are provided by the input apparatus 52 to the processor apparatus 54. The discharge apparatus 44 is depicted in a schematic fashion in FIG. 2 and includes an emitter apparatus 66 having a plurality of emitters 68. The discharge apparatus 44 further comprises a collector 70 that is in the form of an elongated tube within which the emitter apparatus 66 is situated. As will be set forth in greater detail below, the discharge apparatus 44 additionally includes an insulator apparatus 78 that is situated within an interior region 76 and which electrically insulates the emitters 68 from one another and further electrically insulates each of the emitters 68 from the collector 70 In the depicted exemplary embodiment, the emitters 68 are short sections of wire, formed of a material such as Vanadium 51 or Rhodium, and may be on the order of one to three inches in length, by way of example. The material from which the emitters 68 are formed is desirably a material that emits high energy electrons via beta decay when bombarded by neutrons, such as is described in U.S. Pat. No. 3,375,370 entitled “Self-Powered Neutron Detector”, the disclosures of which are incorporated herein by reference. As is generally understood in the relevant art, when an emitter 68 is formed of a metal such as is described herein or in the aforementioned patent and is bombarded by neutrons, it periodically emits high energy electrons via beta decay, and such high energy electrons are collected by the collector 70. The collector 70 is typically formed of a material that does not emit large numbers of electrons via beta decay when bombarded by neutrons. In the aforementioned patent, and in contrast to the disclosed and claimed concept, the emitter and the collector are electrically connected together, and the electrons that are emitted by the emitter and that are collected by the collector are then electrically returned via an electrical connection between the emitter and the collector, and the current that results from such transfer of the collected electrons from the collector back to the emitter is measured and the result is communicated to a data logging device. The wires that are required in the aforementioned patent to complete the circuit and to connect with the data logging device occupy a certain amount of space, and is thus impractical to provide a large number of such self-powered neutron detectors along an axis of a nuclear reactor because the wires eventually occupy a large amount of space. The improved discharge apparatus 44 of the disclosed and claimed concept avoids of such numerous connection wires by electrically insulating each of the emitters 68 from the collector 70 during beta decay wherein each emitter 68 is bombarded by neutrons and periodically emits high powered electrons that are collected by the collector 70. As the emitters 68 continue to discharge electrons to the collector 70 without a return of such electrons to the emitters 68, each emitter 68 begins to develop a charge imbalance with respect to the collector 70. The charge imbalance involves the emitter 68 having a relatively positive charge and the collector 70, being grounded, having a neutral charge. Once the charge imbalance reaches a predetermined level, the emitter 68 and the collector 70 will experience an electrostatic discharge event, i.e., a spark between the emitter 68 and the collector 70, wherein electrons are transferred therebetween and the charge imbalance is reduced. As will be set forth in greater detail below, the electrostatic discharge event can be detected and, by employing time-of-flight analysis, the position along the length of the discharge apparatus 44 can be determined. From this, the power generation rate at the position can be determined, as will be set forth in greater detail below. As can be understood from FIG. 2, the collector 70 is elongated and has a pair of ends 72A and 72B, and the discharge apparatus 44 further includes a pair of connectors 74A and 74B that are situated on the ends 72A and 72B, respectively. The exemplary connectors 74A and 74B are coaxial type connectors such as coaxial bayonet connectors or other appropriate types of connectors. Coaxial connectors are contemplated for use in the instant application since the emitters 68 are positioned within the interior region of the tube 76 and are situated in a coaxial fashion with the tube of the collector 70, but it is understood that other types of connectors can be employed as the connectors 74A and 74B without departing from the disclosed and claimed concept. As can be understood from FIGS. 2 and 3, the insulator apparatus 78 is situated within the interior region 76 and electrically insulates the emitters 68 from one another and further electrically insulates each of the emitters 68 from the collector 70. In this regard, it is noted that the emitters 68 are electrically insulated from the collector 70 by virtue of the fact that the insulator apparatus 78 is interposed between the emitters 68 and the collector 70 and because no designated electrically conductive structure such as a wire or other conductor exists to electrically connect together the collector 70 with any of the emitters 68. The emitter apparatus 66 and the collector 70 thus can be said to be electrically insulated from one another. Moreover, the emitter apparatus 66 and the collector 70 can be said to be electrically insulated from one another despite the fact that electrostatic discharge events can occur therebetween across the insulator apparatus 78 when the difference in charge reaches a sufficient level that it overcomes the dielectric properties of the insulator apparatus 78. It thus is understood that the emitter apparatus 68 and the collector 70 are electrically isolated and insulated from one another by the insulator apparatus 78, and it is only when a charge differential exceeds the dielectric properties of the insulator apparatus 78 that a charge-balancing electrostatic discharge event can occur, and it is noted that the occurrence of such electrostatic discharge events does not negate the fact that the emitter apparatus 66 and the collector 70 are electrically insulated from one another. The occurrence of electrostatic discharge events between the emitter apparatus 68 and the collector 70 does not mean that the two are not electrically insulated from one another, and rather it is because the emitter apparatus 68 and the collector 70 are electrically insulated from one another that the charge imbalance that occurs therebetween occasions the electrostatic discharge events therebetween. FIG. 2 depicts the emitter apparatus 66 with the emitters 68 being distributed along the length of the collector 70 at a fixed spacing as is indicated in FIG. 3 at the numeral 79. FIG. 2 also depicts the emitters 68 as each being of the same fixed length, as at the numeral 75 in FIG. 3. It is understood, however, that in other embodiments the particular lengths and spacing of the various emitters may be fixed and/or may vary for any of a variety of reasons. Advantageously, the particular positioning of the various emitters 68 is stored in the storage 58 for use in determining a particular emitter 68 that has undergone an electrostatic discharge event. It thus can be seen that the positioning and spacing of the various emitters potentially can be optimized or refined based upon particular areas of interest, particular known regions of high energy production, or for any of a variety of reasons that such optimization might be appropriate. FIG. 2 depicts purely for purposes of illustration the discharge apparatus 44 being disconnected from the connecting wires 48A and 48B. In operation, the connecting wires 48A and 48B are electrically connected with the connectors 47A and 48B and are likewise electrically connected with the inputs 50A and 50B such that instances of detectable occurrences in the discharge apparatus 44 are electrically communicated to the detection device 46. More specifically, FIG. 2 illustrates in a schematic fashion an electrostatic discharge even 80 in the form of a spark forming between a particular emitter 68A of the plurality of emitters 68 and the collector 70 within the interior region 76. The collector 70 functions in the form of a wave guide to communicate the electromagnetic result of the electrostatic discharge event 80 toward the two ends 72A and 72B. The connector 74A can be said to have a conductor 81A that is situated adjacent or that extends into the interior 76 of the collector 70 and further includes another conductor 82A that is electrically connected with the collector 70. The conductors 81A and 82A are in the exemplary form of a coaxial bayonet connector, as noted above, which is electrically connectable with a cooperative bayonet connector at the end of the connecting wire 48A for connection of the two conductors 81A and 82A with the inputs 50A. Likewise, the connector 74B has a conductor 81B that is situated adjacent or that extends into the interior 76 of the collector 70 and another conductor 82B that is electrically connected with the collector 70, with both conductors 81B and 82B being in the exemplary form of a coaxial bayonet collector that is connectable with a cooperative bayonet connector at the end of the connecting wire 48B for connection of the conductors 81B and 82B with the input 50B. In this regard, while the conductors 82A and 82B are both depicted as being electrically connected with the collector 70, it is understood that this need not necessarily be the case in all circumstances, and situations are envisioned wherein the electrostatic discharge event can be detected in the absence of such an electrically conductive connection between the conductors 82A and 82B with the collector 70. The electrostatic discharge event 80 is indicated in FIG. 2 as occurring at a particular position P that is indicated at the numeral 82 as being a position along the length of the collector 70. As mentioned above, the collector 70 functions in the form of a wave guide that communicates the electromagnetic results of the electrostatic discharge event 80 toward the ends 72A and 72B of the collector 70, and it is understood that a voltage is induced in the conductors 81A and 81B when such electromagnetic energy reaches the ends 72A and 72B of the collector 70. Since such electromagnetic energy travels at the speed of light, which is a fixed velocity, the electromagnetic energy resulting from the electrostatic discharge event 80 will reach the ends 72A and 72B at times that depend upon the distance from the ends 72A and 72B where the electrostatic discharge event 80 occurred. Such electromagnetic energy will reach the ends 72A and 72B at different times unless the electrostatic discharge event 80 has occurred precisely at the middle of the collector 70. In the example depicted in FIG. 2, the position P 82 where the electrostatic discharge event 80 has occurred is offset from the center of the collector 70, thereby occasioning a time delay between the signals detected at the ends 72A and 72B. More specifically, it can be seen that the position P 82 is relatively closer end 72A than it is to the end 72B. Since the electromagnetic energy from the electrostatic discharge event 80 travels at the speed of light in both directions from the position P 82 toward ends 72A and 72B, the electromagnetic energy will be detected at the end 72A prior to its detection at the end 72B in the depicted exemplary electrostatic discharge event 80. Based upon the time lag between the detection at one of the ends 72A and 72B and the detection at the other of the two ends 72A and 72B, the difference in the time of flight from the position P 82 to the two ends 72A and 72B can be relied upon to determine the location of the position P 82 along the length of the collector 70. Advantageously, therefore, the detection device 46 accurately detects the signals communicated by the connecting wires 48A and 48B to the inputs 50A and 50B and determines from the time lag AT the difference between the distance B, which is indicated numeral 88, and which represents the distance between the end 72A of the collector 70 and the position P 82, and the distance D, which represented by the numeral 90, and which is the distance between the opposite end 72B of the collector 70 and the position P. In this regard, it is noted that the length A, indicated at the numeral 86, and which represents the length of the connecting wire 48A, and the length E, which is indicated at the numeral 92, and which represents the length of the connecting wire 48B, may or may not be equal. Regardless of whether the distances A and B 86 and 92 are equal, the positional difference between the distances B and D 88 and 90 can be derived from the following equation: Δ ⁢ ⁢ T = A + B V - D + E V It is reiterated that A and E 86 and 92 are known. One can derive from the previous equation the following equation:D=B=ΔTV+A−E Employing the known values for A and E 86 and 92, the speed of light (which is V), and the ΔT that was detected by the detection device 46 as being the time lag between the detection of the two signals at the inputs 50A and 50B, the value of D−B can readily be determined. If D−B equals 0, the position P 82 is precisely at the center of the collector 70 at equal distances between the ends 72A and 72B. Depending upon whether D−B is positive or negative and its value, the precise position of the occurrence of the electrostatic discharge event 80 can be determined, it being reiterated that the exemplary electrostatic discharge event 80 is depicted in FIG. 2 as occurring at the position P 82. Once the location of the position P 82 has been determined, the routines 60 then employ a lookup feature to determine, based upon a mapping of the emitters 68 along the collector 70, which of the emitters 68 experience the electrostatic discharge event 80. In the depicted exemplary embodiment, the specific emitter 68A experienced the electrostatic discharge event 80. The routines 60 thus will store in the storage 58 a record representative of the fact that emitter 68A has undergone an electrostatic discharge event and, perhaps, the time of such occurrence. In this regard, it is noted that an electrostatic discharge event can occur between the particular emitter 68A and the collector 70 at any of a plurality of positions along the collector 70 that are proximate between the particular emitter 68A and the collector 70. That is, if the particular emitter 68A is, for example, three inches in length, various electrostatic discharge events could occur between the particular emitter 68A and the collector 70 at any of a plurality of positions along an approximately three inch long portion of the collector 70. It thus is desirable to store in the storage or at least be able to obtain from the stored data the fact that the electrostatic discharge event occurred with respect to the emitter 68A rather than merely noting the particular position P 82, and this is because the bombardment of the emitter 68 as a whole is what generates the difference in charge between it and the collector 70. In some instances, a given emitter 68 might be slightly malformed such that all of the electrostatic discharge events that occur on that given emitter 68 occur at one end thereof, by way of example. In such a circumstance, the repeated occurrences of sparks at that end do not represent a high power flux at that precise location, i.e., at the end of the given emitter 68, and rather merely represent that the electrostatic discharge events that were experience by the given emitter 68 have taken place at such location. The occurrences of each electrostatic discharge events on that given emitter 68 indicate that the given emitter 68 as a whole has undergone neutron bombardment. As such, the neutron flux that is determined to have resulted from such electrostatic discharge events occurring at any location on such an emitter 68 would be interpreted as being a part of a power generation value calculated as being situated at the center of such emitter 68. Such a methodology avoids the existence of various formation failures and other issues from erroneously indicating that an accidental concentration of electrostatic discharge events at a particular position along a specific emitter 68 is representative of a concentrated neutron flux at the particular position along the length of the collector 70. Stated otherwise, if one relies solely on the positions of the electrostatic discharge events 80 without relating them back to the specific emitters 68 that underwent such electrostatic discharge events 80, such reliance upon the positions of the sparks could result in data that is less than wholly representative of the neutron flux along the length of each emitter. In this regard, the center of the emitter 68A is designated as being the location L, which is indicated at the numeral 94, and which is situated along the length of the collector 70 and positioned at the longitudinal center of the emitter 68A. The neutron flux experienced by the emitter 68A is thus stored as having its effective location at the location L along the length of the collector 70. The detection assembly 42 could thus be said to operate in the following fashion. First, it would be necessary to connect the discharge apparatus 44 with the inputs 50A and 50B on the detection device 46 by connecting the wires 48A and 48B with the connectors 74A and 74B and with the inputs 50A and 50B. Upon an occurrence of an electrostatic discharge event, the detection device 46 would detect at the inputs 50A and 50B an input signal that is representative of the occurrence of the electrostatic discharge event 80. In this regard, the input signal would likely be in the nature of two electrical signals that are received at the inputs 50A and 50B at different times (or perhaps at the same time). That is, input signal would be comprised of a pair of separate signals that are received at the separate inputs 50A and 50B. The detection device 46 would then determine from the input signal received at the two inputs 50A and 50B a time differential between the portion of the input signal that is received at the input 50A and the portion of the input signal that is received at the input 50B. The detection device 46 would then employ the time differential to identify a position P 82 along the length of the collector 70 as being the site where the electrostatic discharge event 80 occurred. It would then be possible to determine a neutron flux and thus a rate of power generation at a location 94 that is representative of the particular emitter 68A that includes the position P 82 and that is based at least in part upon the occurrence of the electrostatic discharge event 80. In so doing, it may be desirable to employ the position P 82 to identify the particular emitter 68A, for example, that experienced the electrostatic discharge event 80 and to store in the storage 58 a record that is representative of the occurrence of the electrostatic discharge event 80 having occurred at the particular emitter 68A. As mentioned above, the discharge apparatus 44 relies upon electromagnetic energy being received at the connectors 74A and 74B, and, more particularly, at the conductors 81A and 81B to detect the electromagnetic evidence that is indicative of the occurrence of the electrostatic discharge event 80 at the position P 82. It is noted, that in other embodiments, such as those set forth in greater detail, it may be appropriate and desirable to additionally or alternatively detect the occurrence of the electrostatic discharge event by detecting acoustic evidence of the electrostatic discharge event 80. For example, an improved discharge apparatus 144 in accordance with a second embodiment of the disclosed and claimed concept is depicted in FIG. 5 and is usable in conjunction with the detection device 46 and the connecting wires 48A and 48B to form an improved detection assembly in accordance with another embodiment of the disclosed and claimed concept. The discharge apparatus 144 includes an emitter apparatus 166 having a plurality of emitters 168 that are essentially the same as the emitter apparatus 66 and the plurality of emitters 68. The discharge apparatus 144 further includes a collector 170 that is essentially the same as the collector 70 and that includes a pair of opposite ends 172A and 172B. Likewise, an insulator apparatus 178 is provided to electrically insulate the emitters 168 from one another and from the collector 170. It is noted, however, that the discharge apparatus 144 advantageously includes a pair of acoustic energy detectors which are depicted herein in the exemplary form of a pair of microphones 196A and 196B that are situated at the ends 172A and 172B, respectively. The microphone 196A has a pair of leads that are connected with a pair of conductors of a connector 174A, and the microphone 196B has a pair of leads that are electrically connected with the conductors of another connector 174B. When the microphones 196A and 196B detect the acoustic “snap” or other acoustic evidence of the electrostatic discharge event 80, which is not expressly depicted in FIG. 5, the resultant electronic signals are received at the inputs 50A and 50B. These electronic signals that are received at the inputs 50A and 50B make up the input signal, and the time difference in their arrival at the inputs 50A and 50B is employed to determine from the foregoing equations the position along the length of the collector 170 where the electrostatic discharge event occurred. An equation would be employed that would incorporate both a first velocity of acoustic energy within the collector 70 (such as through the insulator apparatus 178 and the emitter apparatus 166) and a second, different velocity of the electronic signals along the connecting wires 48A and 48B themselves. It is noted that the acoustic signals would travel at a given velocity whereas the signals communicated along the connecting wires 48A and 48B would be communicated at the much faster speed of light. The velocity of the acoustic energy within the collector 70 desirably would be measured prior to deployment of the discharge apparatus 144, although it is possible that this velocity could be derived using principles that would be known to those of ordinary skill in the relevant art. Regardless of the fashion in which the velocity of acoustic energy within the collector 170 is determined, it should be apparent that the time of flight of the acoustic energy that results from the electrostatic discharge event and its time-differential detection at the microphones 196A and 196B can be employed as an input to determine the specific position where the electrostatic discharge event occurred. This position can then be employed to determine neutron flux and thus power generation at numerous locations along the length of the collector 170. Depending upon the needs of the particular application, it may be desirable to derive either via experimentation or otherwise velocity curves that represent velocities of sound in the collector 170 according to temperatures, pressures, and the like, as appropriate, which potentially can vary within the interior of the nuclear reactor 4. It may be necessary to make allowances for both the transmission of acoustic energy through the insulator apparatus 178 as well as through the emitters 168. Depending upon the needs of the particular application, however, it may be desirable to provide a more-or-less unobstructed path for the transmission of acoustic energy to the acoustic energy detectors. Accordingly, an improved discharge apparatus 244 in accordance with a third embodiment of the disclosed and claimed concept is depicted in FIG. 6 and can be employed with the detection device 46 and the connecting wires 48A and 48B to provide an improved detection assembly in accordance with another embodiment of the disclosed and claimed concept. The discharge apparatus 244 is similar to the discharge apparatus 144, except that the discharge apparatus 244 and, more particular, an emitter apparatus 266 thereof, includes not only a plurality of emitters 268 but additionally includes a communication tube 284. The communication tube 284 is situated alongside a collector 270 and has a pair of ends 298A and 298B. The discharge apparatus 244 further include a pair of acoustic energy detectors in the form of a pair of microphones 296A and 296B that are situated at the ends 298A and 298B of the communication tube 284 and that are electrically connected with a pair of connectors 274A and 274B. While the discharge apparatus 244 includes an insulator apparatus 278 that electrically insulates the emitters 268 from one another and from the collector 270, any sound that may be communicated through the collector 270 is not necessarily detected at its ends, and rather the detection of sound is instead performed at the ends 298A and 298B of the communication tube 284. The communication tube 284 could communicate acoustic energy in the following fashion, by way of example and without limitation. An electrostatic discharge event 280 might occur at a particular position within the collector 270, and the acoustic energy resultant therefrom would radiate in all directions outwardly from the electrostatic discharge event and be thereby received in the communication tube 284 at a location adjacent the position where the electrostatic discharge event occurred. Such acoustic energy could then be communicated along the communication tube 284 toward its opposite ends 298A and 298B for eventual detection by the microphones 296A and 296B. The sound may be communicated in the communication tube 284 by the material from which the communication tube 284 is itself formed and/or may be communicated through the interior region of the communication tube 284 if some type of medium 285 such as a gas or other material is received in the interior region of the communication tube 284. Moreover, the communication tube 284 may not be hollow at all and may instead be in the form of a solid rod of material, such as a metallic material or other material, which would serve as the medium through which the acoustic energy is communicated to the ends 298A and 298B for detection by the microphones 296A and 296B at the ends 298A and 298B, respectively. It is possible that the acoustic energy that is communicated along the collector 270 could itself further excite the communication tube 284, but such additional transient and secondary acoustic energy in the communication tube 284 could be filtered or ignored, if desirable. Dependent upon the materials from which each of the collector 270, the communication tube 284, the medium 285, and the insulator apparatus 278 are formed, such filtration or the like may be unnecessary if the primary acoustic energy that is initially excited by the occurrence of the electrostatic discharge event 280 in the communication tube 284 is received at the ends 298A and 298B before any such aforementioned transient or secondary acoustic energy is received. Additional microphones potentially could be provided at the ends of the collectors 270 which could provide signals that could be used in performing such filtration of the transitory and/or secondary signals that potentially may be received in the communication tube 284. The position of the electrostatic discharge event 280 could be determined using equations similar to those set forth above, except employing a length F indicated generally at the numeral 289 in place of the dimension B and by employing the dimension G indicated at the numeral 291 in place of the dimension D. Also, the new dimensions F and G 289 and 291 would be divided by the velocity of the acoustic energy through the medium 285 whereas the dimensions A and E 86 and 92 would be divided by the speed of light. Such appropriate equations and others can be employed and would easily be within the capability of a person of ordinary skill in the relevant art. The communication tube 284 is depicted herein in an exemplary fashion as being longer than the collector 270 simply for the purpose of illustrating that the communication tube 284 is different from the collector 270. An improved discharge apparatus 344 in accordance with a fourth. embodiment of the disclosed and claimed concept is depicted in FIG. 7 as including a pair of connectors 374A and 374B situated at a pair of ends 372A and 372B, respectively, and the discharge apparatus 344 is capable of being connected with the detection device 46 and the connecting wires 48A and 48B in order to form another detection assembly that is in accordance with another embodiment of the disclosed and claimed concept. The discharge apparatus 344 includes an emitter apparatus 366 that includes a plurality of emitters 368 in the fashion of the discharge apparatus 44. The discharge apparatus 344 additionally includes a collector 370 that is similar to the collector 70. Furthermore, an insulator apparatus 378 that is employed in the discharge apparatus 344 is similar to the insulator apparatus 78. As can be seen in FIG. 7, however, the discharge apparatus 344 includes a pair of acoustic energy detectors in the form of microphones 396A and 396B that are configured to detect acoustic energy in the discharge apparatus 344 that is communicated via two separate media. In particular, the two separate media in the depicted exemplary embodiments include the material from which the insulator apparatus 378 is formed and the material from which the collector 370 is formed. In this regard, it can be seen that the microphone 396A is situated at the end 372A and is configured to detect acoustic energy traveling through the insulator apparatus 378, and this may include the traveling of the acoustic energy through the emitter apparatus 366. On the other hand, the microphone 396B is depicted in FIG. 7 as being mounted to the collector 370 and as detecting the acoustic energy that travels through it. In this regard, it is understood that the collector 370 and the insulator apparatus 378 are formed of two different materials that serve as transmission media that transmit therethrough acoustic energy at different velocities. That is, an amount of acoustic energy that is of a first wavelength and amplitude would travel through the collector 370 at a velocity that is different than velocity at which the same acoustic energy at the same wavelength and amplitude would travel through the insulator apparatus 378. The insulator apparatus 378 in the depicted exemplary embodiment is an aluminum oxide material, and it is understood that acoustic energy that travels through the insulator apparatus 378 would also, to a certain extent, travel through and be communicated via the emitters 368 that are embedded within the insulator 378. One of ordinary skill in the relevant art could readily derive the equations that could characterize the travel of acoustic energy through the two materials when combined in the fashion described and depicted herein. The time difference in the signal components received at the inputs 50A and 50B would then be employed with such equations to determine the position where the electrostatic discharge event occurred. The microphones 396A and 396B are depicted as being mounted at opposite ends of the discharge apparatus 344 for purposes of illustration. It is understood, however, that in alternative embodiments the microphones 396A and 396B could be mounted at the same end of the discharge apparatus 344, with the acoustic energy traveling through the insulator apparatus 378 being detected by the microphone 396A and with the acoustic energy that travels through the collector 370 being detected by the microphone 396B. The particular materials from which the collector 370 and the insulator apparatus 378 are formed is not necessarily particular, but it is noted that the fourth embodiment of the discharge apparatus 344 relies upon the difference in sound transmission velocity between the two media that make up the collector 370 and the insulator apparatus 378 in order to provide the difference in time of flight that enables the discharge apparatus 344 to be usable to determine a position along its longitudinal extent where an electrostatic discharge event has occurred. An improved discharge apparatus 444 in accordance with a fifth embodiment of the disclosed and claimed concept is depicted generally in FIG. 8 and can be employed in conjunction with the detection device 46 and the connecting wires 48A and 48B to form another improved detection assembly in accordance with another embodiment of the disclosed and claimed concept. The discharge apparatus 444 employs an emitter apparatus 466 having a plurality of emitters 468 and further employs a collector 470, all of which are similar to those of the discharge 44 apparatus. It is noted, however, that the discharge apparatus 444 employs a medium for the transmission of acoustic energy that transmits acoustic energy at different velocities that vary with the wavelength or frequency of the acoustic energy. Nearly every material is capable of communicating acoustic energy at velocities that vary with the wavelength or frequency of the acoustic energy, as is known to those of ordinary skill in the relevant art. While the collector 470 has a pair of opposite ends 472A and 472B, the discharge apparatus 444 includes only a single microphone 496 having leads that are connected with a single connector 474 that is connectable with one of the inputs 50A and 50B, thereby potentially being of less cost to manufacture, i.e., due to the need for only a single microphone, etc. The discharge apparatus employs an insulator apparatus 478 that may be formed from the same aluminum oxide material from which the other insulator apparatus devices mentioned above are formed, although another insulator apparatus may be employed if it provides preferred acoustic energy transmission at the aforementioned velocity that can vary dependent upon the wavelength or frequency of the acoustic energy. Alternatively, the material from which the collector 470 is formed may be selected based upon its properties of communicating acoustic energy at a velocity that varies with the frequency or wavelength of the acoustic energy. Regardless of the material employed for the transmission medium that communicates the acoustic energy therethrough at varying velocities, the improved discharge apparatus 444 can be provided and implemented at a potentially reduced cost and/or with reduced complexity because of the ability of the individual microphone 496 to detect as a first portion of the input signal a first frequency of acoustic energy and to detect at another time another amount of acoustic energy at a second, different frequency or wavelength, with the difference in reception times, i.e., the time lag, being employed to determine the position where an electrostatic discharge event has occurred. Appropriate equations that rely upon a characterization of the medium and its varying-velocity communication of acoustic energy would be employed in making the determination as to where the electrostatic discharge event occurred. It is noted that the speeds of the various frequencies of sound may themselves vary with the materials used for the transmission of such sounds. Signal attenuation will likely be a function of frequency such that the pulse shape will change as different frequencies are attenuated at different rates. Refraction effects will result in fewer than all of the waves traveling the same distance. Diffraction effects possibly may eliminate some frequencies from reaching the microphone 496. Furthermore, it is noted that transverse and longitudinal waves may travel at different velocities. It is expressly noted that the various teachings contained herein can be combined in any of a variety of fashions to achieve improved results. For example, the communication tube 284 may be implemented into the discharge apparatus 444 and it may employ as its medium 285 a specifically selected medium that transmits acoustic energy at different velocities depending upon its frequency and/or wavelength, by way of example. In such a circumstance, the microphone 496 would be mounted to an end of the communication tube 284 rather than being mounted to an end of the collector 470. Other variations would be apparent. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.
044477341	abstract	Radiation-shielding transparent material comprising an aqueous solution of thallium formate with or without thallium malonate, the solution having a density of 2.5 to 4.3 g/cm.sup.3, a radiation length of 3.8 to 1.9 cm, and a transmission of not less than 93% for light of 400 nm wavelength. The material is produced by deoxidizing thallium formate and dissolving the deoxidized thallium formate in deoxidized distilled water.
	description	The invention relates generally to the field of hydrocarbon fuel production from a carbonaceous material, and more specifically to the field of combined production of electricity and hydrocarbon fuel using a nuclear power plant and a hydrocarbon fuel manufacturing plant. Nuclear power plants are usually connected to a power distribution grid, for distributing electric power to final customers. The investment cost for a nuclear power plant is very high. To maximize the return on investment, the power plant should operate at a load as close as possible to 100%, during very long periods. However, electric consumption of the final customers varies along the day, with peak consumption in the morning and in the evening, especially during wintertime. On the other hand, consumption is lower during the night. The electric consumption varies as well with the seasons, and may be higher during winter—heating season—and summer—cooling season—than during spring and autumn. In certain countries, such as France, as a result of their large production share nuclear power plants are operated such that their load follows the power consumption. It is therefore difficult to have the power plant operating continuously at a load close to 100%. Furthermore, a strong and fast modification in power consumption is difficult to accommodate, both at the level of the grid and at the level of the nuclear power plant. WO2006/099573 describes a hydrocarbon fuel manufacturing plant with a nuclear power plant dedicated to feeding electricity only to the fuel manufacturing plant. WO2008/115933 describes a renewable power source, such as a wind power source, dedicated to a hydrocarbon fuel manufacturing plant. US2008/0040975 describes a facility for producing, from a carbonaceous material, fuel, electricity (gas turbine) and urea. WO2008/033812 describes a facility for producing a hydrocarbon fuel from carbonaceous material (biomass) and hydrogen. The hydrogen is produced using electricity from a non carbon emitting dedicated source, such as wind power, solar power or nuclear power. U.S. Pat. No. 6,306,917 describes a facility that can selectively maximize the production of power (gas turbine), hydrocarbons and carbon dioxide. There is a need for a system that helps keep a nuclear power plant close to 100% load, in spite of variations in electric consumption of the final consumers. The Applicant has discovered that coupling the nuclear power plant both to the grid and to a hydrocarbon fuel manufacturing plant permits operation of the nuclear power plant at a near constant power, in spite of the variations of the power consumption of the final consumers connected to the grid, and that the hydrocarbon fuel manufacturing plant can be adapted to take into account changes in the power availability from the power plant, while maintaining a high throughput. One object of the invention is to optimize the operation of a nuclear power plant, to keep the plant at a load close to 100% in spite of the variation of the total consumption of the final consumers. Another alternate or additional object is to propose a system that permits producing both nuclear electrical power and hydrocarbon fuel, while permitting to operate the nuclear power plant and the hydrocarbon fuel manufacturing plant with a high level of efficiency. Another alternate or additional object of the invention is to propose a system in which a major electric power consumer can decrease its electrical power consumption to the grid at will, when the grid regulator requires him to do so. These and other objects of the present invention will become more apparent to those skilled in the art to which the invention pertains, from the following description and appended claims. Reference is now made to the accompanying drawings forming part of this specification. It is to be noted that the embodiments shown herein are for the purpose of description and not limitation. The system on FIG. 1 has a nuclear power plant 1, an hydrocarbon fuel manufacturing plant 3, for manufacturing diesel fuel, and a power distribution grid 5 to which electric power consumers 7 other than said hydrocarbon manufacturing plant 3 are electrically connected. The grid 5 is electrically connected to the nuclear power plant 1 and conveys the electric power from the nuclear power plant to the consumers 7. The power consumers have a variable total power consumption, the power demand of the consumers changing with the time. The total power consumption changes for example in the following way during the course of a day: maximum (100%) from 7:30 a.m. to 9:00 a.m., from 11:30 a.m. to 13:00 p.m., and from 19:00 p.m. to 20:30 p.m.; about 60% between 9 a.m. and 11:30 a.m. and between 13:00 p.m. and 19:00 p.m.; about 20% between 20:30 p.m. and 7:30 a.m. The hydrocarbon fuel manufacturing plant 3 comprises: at least one carbonaceous material conditioning unit 9a, 9b, 9c, 9d, 9e; a gasifier 11, for example a super-critical partial oxidation gasifier; a gas conditioning unit 13; an electrolyzer unit 15, an hydrocarbon fuel synthesis unit 17; a buffer storage 19; a reforming unit 21; a product separation unit 23; a refining unit 25; a water treatment unit 27. The carbonaceous material is one or several of municipal waste, petcoke biomass, polyethylene terephtalate, coal, or other organic material. The plant 3 has to have a conditioning unit 9 dedicated to each type of material, and depending on the type of material, the conditioning unit for example mix the carbonaceous material with water to create a slurry. After conditioning, a stream of conditioned carbonaceous material is fed to the gasifier 11 via line 29. The supercritical partial oxidation gasifier 11 may be of the type described in French patent applications FR 0012929, FR 0451902, FR 0552924, and/or FR 0552926, or the related U.S. Patent Publication Nos. US2008 135496, US2007 201304, US2008 279728 and PCT publication WO2007/036512, which are all incorporated herein by reference. Gasifier 11 receives a stream of super critical water via line 31 and a stream of oxygen coming from the electrolyzer unit via line 33 In the gasifier, the carbonaceous material are partially oxidized to form an oxidized carbonaceous material stream comprising mainly CO, CO2 and H2, plus miscellaneous other gases, such as H2S, argon, N2, C1-C3, butadiene, benzene, toluene and others. The oxidized carbonaceous material stream is fed to the gas conditioning unit 13 via line 35. In the gas conditioning unit, CO2 and the miscellaneous other gases are separated from CO and H2. CO2 and the miscellaneous other gases leave the gas conditioning unit via line 37 and can be subjected to other treatment steps which are out of the scope of the present invention. Said other treatment steps may be pressure swing adsorption for N2 removal, amine or Selexol treatment for H2S removal, or zinc oxide beds for trace H2S removal. H2 and CO form a syngas stream, and are fed via line 39 to the hydrocarbon fuel synthesis unit 17. The gas conditioning unit is of a type known to those skilled in the art and will not be described in detail here. The electrolyzer unit 15 produces hydrogen and oxygen, from water and from electric power provided by the nuclear power plan 1 via line 41. Water comes from outside of the plant via line 43 and/or from the water treatment unit via line 45. A first hydrogen stream is provided from the electrolyzer unit to the hydrocarbon fuel synthesis unit 17 via line 47. Hydrogen is also sent to the refining unit 25 via line 49. Oxygen streams are fed to gasifier 11, and to the reforming unit 21 via line 51. The hydrocarbon fuel synthesis unit 17 comprises one or several reactors 17a and produces a product stream containing a wide range of hydrocarbon compounds. The reactors are fed with the syngas stream from the gas conditioning unit 13, with the first hydrogen stream from the electrolyzer unit 15, and with a second hydrogen stream from the reforming unit 21 (see below). The reactors are for example Fischer-Tropsch reactors, containing adapted catalysts. Such reactors are described for example in PCT Publication No. WO2008/115933, which is hereby incorporated by reference herein. In the reactors, CO and H2 are reacted together to form hydrocarbon compounds. At the exit of the reactors, the product stream contains CO2, unreacted CO and H2, and a wide range of hydrocarbon compounds. The hydrocarbon fuel synthesis unit 17 comprises a preliminary separation unit 17b, fed with the product stream coming from the reactors. In the preliminary separation unit, CO2, CO, H2 and light hydrocarbon compounds are separated from heavier hydrocarbon compounds. Light hydrocarbon compunds comprise mainly hydrocarbon compound with fewer than 4 carbons. CO2, CO, H2 and light hydrocarbons are sent to the reforming unit 21 via line 53 or, alternatively, to a short-term buffer storage (not shown in figures) prior to sending to the reforming unit 21. Heavier hydrocarbon compounds are sent to product separation unit 23 via line 55. In product separation unit 23, the heavier compound stream is separated into a diesel fuel stream, in a heavy hydrocarbon stream and in a naphta stream. Diesel fuel is the final product and exits the plant via line 57. Naphta is fed to the buffer storage 19 via line 59. The heavy hydrocarbon stream comprises for example mostly C16+ compounds and is fed to the refining unit 25 via line 61. For example, the diesel fuel stream can include most of the C10 to C15 hydrocarbons of the product stream, the naptha stream most of the C4 to C9 hydrocarbons of the product stream and the heavy hydrocarbon stream the rest. In the refining unit 25, the heavy hydrocarbon stream is reacted with hydrogen to produce mostly diesel fuel, naphta and a light hydrocarbon stream. The light hydrocarbon stream comprises mainly hydrocarbon compound with fewer than 4 carbons and is sent to the refining unit 21 via line 63. Naphta is sent to the buffer storage 19 via line 64. The hydrocarbon fuel manufacturing plant 3 comprises means to feed naphta from the buffer storage 19 to the reforming unit 21 at a controlled feed flow rate. Such means can be for example a pump 119, controlled by a controller 200. Controller 200 may include, for example, a microprocessor or circuitry such as a ASIC. The reforming unit 21 is fed with the CO2, CO, H2 and light hydrocarbon stream from unit 17 or intermediate short-term buffer storage, with the light hydrocarbon stream from the refining unit 25, with O2 from the electrolyzer unit 15, and with a controlled flow of naphta from buffer storage 19. The reforming unit 21 is for example a combined partial oxidation/steam reforming unit, of a type known to those skilled in the art for reforming low C hydrocarbon and napthas. Reforming unit 21 produces a stream containing H2, CO and CO2. This stream defines the so called second hydrogen stream mentioned above with respect to the inputs to the hydrocarbon fuel synthesis unit 17. The second hydrogen stream is fed to the hydrocarbon fuel synthesis unit 17 via line 65. The reforming unit 21 may be a steam reformer of the type described in US patent publication no US2007212293, which is incorporated herein by reference. The ratio H2/CO in the feed of the synthesis unit 17, calculated taking into account the various streams fed to the hydrocarbon fuel synthesis unit 17 via lines 39, 47 and 65, should be slightly above 2. The system has means to feed the hydrocarbon fuel synthesis unit 17 with the first hydrogen stream at a first controlled flow rate and with the second hydrogen stream at a second controlled flow rate. The means to control the first hydrogen stream at a first controlled rate can include for example a power control unit 141 for the electrolyzer 15, and the means to control the second hydrogen stream at a second controlled rate can include for example the pump 119. The systems also has means to control the first and second controlled flow rate as a function of a current electrical power delivered by the nuclear power plant 1 and the current power consumption of the electric power consumers 7. This control means for the first and second controlled flow rate may include a controller, for example the same controller 200, which may for example include include a microprocessor or circuitry such as an ASIC. A meter or meters 107 for assessing the current power consumption of the electric power consumers 7, and a meter or meters 101 for assessing the current electrical power of the nuclear power plant 1. Said means can be included in the general regulation system of the electric power distribution grid. The means to control the first controlled flow rate thus include means to control the electric power provided by the nuclear power plant 1 to the electrolyzer unit 15. The actual power control can carried out for example manually from the control room of the electrolyzer unit 15 to alter the power control unit 141 or automatically by the controller 200, for example as a function of the data from the power meters. The means to control the second controlled flow rate thus can include the means to control the feed flow rate at which the naphta is fed to the reforming unit 21 from the buffer tank 19, described above. The feed control can carried out for example manually from the control room of the hydrocarbon fuel synthesis unit 17 to alter the pump or automatically by controller 200, for example as a function of the data from from the power meters. The system is operated as follows. When the total electric consumption of the final consumers 7 is low, the electrolyzer unit 15 is operated at a power close to its maximum power, and no naphta is fed from the buffer storage 19 to the reforming unit 21. Naphta is accumulated in the buffer storage 19, for use later when the electric consumption is higher. When sufficient electric power is available for the production of Diesel fuel, the electrolyzer unit is typically operated between 80% and 100% of its maximum power. The second feed rate is maintained at zero. At the periods of peak consumptions by the final customers 7 of the grid, the authority in charge of managing power distribution through the grid can ask the electrolyzer unit 15 to reduce the power received from the nuclear power plant, to avoid shortage at the final customers level. The authority can require the power level to be reduced down to a reduced power level being in a range comprised between 25% and 100% of the maximum power of the electrolyzer unit. Preferably, the reduced power level is between 50% and 100% of the maximum power level. The flow rate of the first hydrogen stream fed to the hydrocarbon fuel synthesis unit 17 is automatically decreased in the same proportion. To compensate and keep the ratio H2/CO above 2 in the feed of the synthesis unit 17, the flow rate of the second hydrogen stream is increased. For that purpose, naphta is fed from the buffer storage 19 to the reforming unit 21 and converted to CO and H2. The changes of the respective flow rates of the first and second hydrogen streams can be carried out quickly, and follow closely the power consumption variations described above. In any case, the nuclear power plant will be operated continuously with a load close to 100%. Said 100% load must be understood as being the maximum available load of the nuclear power plant. The available load may be different from the design load, especially when maintenance operations are under way in the nuclear power plant. The electrolyzer unit requires a high electrical power. For example, the maximum power is between 1000 and 1700 MW for a hydrocarbon fuel manufacturing plant having a capacity of approx 20 000 barrels to 40 000 barrels/day depending on the feedstock. Reducing the power down to 25% of the maximum power releases between 750 and 1275 MW for other customers and is a major practical advantage for the management of the power distribution grid. With CO2 as carbonaceous material and an electrolyzer unit having an electrical power of 1250 MW, the hydrocarbon fuel manufacturing plant can produce about 10 000 barrels/day of hydrocarbon fuel. As illustrated on FIG. 1, the carbonaceous material is not necessarily a solid material but can be gaseous carbon dioxide. CO2 can be used instead a solid carbonaceous material source, or in addition to said source. CO2 can be extracted from the atmosphere or from industrial plant offgases, for example from coal fired power plants. In this case, the hydrocarbon fuel manufacturing plant 3 includes a RWGS unit 67 (Reverse Water Gas Shift), shown in dotted lines on FIG. 1. CO2 is fed to the RWGS unit via line 69, along with hydrogen fed from the electrolyzer unit 15 via line 71. In the RWGS unit, CO2 is reacted with H2 according to the following equation:CO2+H2→CO+H2O The resulting water is separated and fed to the water treatment unit via line 73. The unreacted CO2 can be separated and recycled via line 75. The unreacted H2 and the newly formed CO is fed to the hydrocarbon fuel synthesis unit 17 via line 77. If a solid source of carbonaceous material is used in addition to CO2, the oxidized carbonaceous material stream is separated in the gas conditioning unit 13 in three different streams: a CO2 stream fed to the RWGS via line 79, a miscellaneous other gases stream leaving the gas conditioning unit via line 37, and a syngas stream fed to the hydrocarbon fuel synthesis unit via line 39. FIG. 2 shows a second embodiment of the present invention. Only the features which are different in the first and second embodiments will be described here below. The elements which are identical or which have the same functions will bear the same references in both embodiments. In the first embodiment, the electrolyzer unit 15 is fed electrically by the nuclear power plant 1 via a dedicated power line 41 which is not part of the grid 5. In the second embodiment, the electrolyzer unit 15 is fed electrically by the nuclear power plant 1 via the grid 5. In the first embodiment, the electrolyzer unit 15, and generally the hydrocarbon fuel manufacturing plant 3, are necessarily not too far away from the nuclear power plant, for example in the range of 5 kilometers on less. In the second embodiment, it is possible to take advantage of the grid to build the electrolyzer unit 15 and generally the hydrocarbon fuel manufacturing plant 3 farther away from the nuclear power plant 1. The invention has been described with reference to FIGS. 1 and 2 as including a plant for manufacturing diesel fuel. However, the plant could manufacture any other suitable hydrocarbon fuel, such as kerosene. The hydrocarbon fuel stored in the buffer tank and recycled into the reforming unit has been described as being naphta. It is advantageous to recycle naphta, considering that it has a lower market value than diesel. However, it is possible to store and recycle another hydrocarbon fuel, the final choice being made as a function of the market value of the different fuels produced by the plant. Fischer-Tropsch reactors could be replaced by other types of suitable synthesis reactors, for example methanol-to-gasoline reactors. In the description above, reference is made to the electrical power produced or consumed by various units or plants. Said electrical power must be understood as a peak power (crest power). It includes wherever applicable both active and reactive powers. In the description above, a nuclear power plant is understood as a plant than can include one on several nuclear reactor units. Each nuclear reactor unit usually has an electric power between 1000 MWe and 1700 MWe, depending on the reactor technology.
060350105	claims	1. A monitor for measuring both the gamma spectrum and neutrons emitted by an object, characterized in that said monitor comprises a lead block (1) presenting a front face (8) intended to be brought close to said pin or assembly (7) to be measured and incorporating a gamma detector (2) for gamma spectroscopy located close to a rear face of said block (1) and associated with a collimator (4) extending from said front face to said gamma detector, two neutron detectors (3) which extend parallelly to each other and to said front face (8) and are disposed symmetrically on either side of the axis of said collimator (4) close to said front face (8). 2. A monitor as claimed in claim 1, characterized in that the distance between the center of any of the neutron detectors (3) and the axis of the collimator (4) is between 10 and 50 times larger than the width of the collimator channel. 3. A monitor as claimed in claim 1, characterized in that the collimator (4) is constituted by a removable tube. 4. A monitor as claimed in claim 1, characterized in that the gamma detector (2) comprises a detector crystal operating at room temperature. 5. A monitor as claimed in claim 1, characterized in that at least one of the neutron detectors (3) is provided with mechanical means (9) for inserting a cadmium sheet (6) around its moderator material and for withdrawing the cadmium sheet therefrom. 6. A monitor as claimed in claim 1, characterized in that a moderator material (5') which thermalizes the incident neutrons is provided around each neutron detector (3) only in a sector of substantially 90.degree. beginning in a plane parallel to the collimator axis and extending towards the collimator (FIG. 3). 7. A monitor as claimed in claim 1, characterized in that an arm is fixed to the lead block (1) and intended to hold a neutron source (10) behind a radiating object and in alignment with the collimator axis in such a way that the neutron beam of the source hits the object (7).
	abstract	The present invention relates to methods and systems for 4D ultrafast electron microscopy (UEM)—in situ imaging with ultrafast time resolution in TEM. Single electron imaging is used as a component of the 4D UEM technique to provide high spatial and temporal resolution unavailable using conventional techniques. Other embodiments of the present invention relate to methods and systems for convergent beam UEM, focusing the electron beams onto the specimen to measure structural characteristics in three dimensions as a function of time. Additionally, embodiments provide not only 4D imaging of specimens, but characterization of electron energy, performing time resolved electron energy loss spectroscopy (EELS).
048266507	abstract	In a boiling water reactor, an apparatus and process for ultrasound inspection of the top guide is disclosed. The top guide constitutes a lattice of stainless steel bars overlying the core plate and being assembled at confronting grooves with the lattice mounted at the side edges to the reactor pressure vessel. This lattice braces the upper ends of the vertically supported fuel assemblies in their requisite orientation and spaced apart relation to enable among other things the required spatial interval to be maintained for control rod moderation of the reaction. Because of the proximity of the top guide to the fuel assemblies, the individual bars making up the lattice need to be checked for cracking, especially that cracking produced by irradiation assisted stress crack corrosion. With a defined cell in the lattice emptied of its contained and adjoining fuel assemblies, there is disclosed an ultrasound test for cracking. A sound transducer on a first special frame sweeps horizontally across the top of a bar interrogating the bar with vertical ultrasound waves for detecting horizontal cracks. Similarly, a sound transducer on a second special frame sweeps vertically across the side of a bar interrogating the bar with angularly incident horizontal ultrasound waves for detecting vertical cracks. Nondestructive testing of the lattice assembly occurs without required disassembly.
052727394	claims	1. Heat exchanger of the type having a vessel within which a plurality of parallel heat exchanger tubes are mounted extending through a plurality of support plates with clearance, said support plates extending transversely across the heat exchanger vessel, and means for feeding a fluid, which is to be heated by heat transferred from a heat exchange medium circulating through the heat exchanger tubes, into the vessel in a manner causing the fluid to have a flow path which, at least in part, has a crosswise directional flow component relative to a portion of the heat exchanger tubes extending axially through the vessel; the improvement comprising means for causing alternate ones of said support plates, in a zone containing said part of the flow path having a crosswise directional flow component, to shift in opposite directions transversely relative to said portion of the heat exchanger tubes, as said heat exchanger is brought up to operating temperatures and pressures, in a manner applying a loading on said portion of the heat exchanger tubes which will prevent them from vibrating due to the crosswise directional flow component of said fluid; wherein support plates outside of said zone are free of securement relative to both the central divider plate and the wall of the vessel. 2. Heat exchanger of the type having a vessel within which a plurality of parallel heat exchanger tubes are mounted extending through a plurality of support plates with clearance, said support plates extending transversely across the heat exchanger vessel, and means for feeding a fluid, which is to be heated by heat transferred from a heat exchange medium circulating through the heat exchanger tubes, into the vessel in a manner causing the fluid to have a flow path which, at least in part, has a crosswise directional flow component relative to a portion of the heat exchanger tubes extending axially through the vessel; the improvement comprising means for causing alternate ones of said support plates, in a zone containing said part of the flow path having a crosswise directional flow component, to shift in opposite directions transversely relative to said portion of the heat exchanger tubes, as said heat exchanger is brought up to operating temperatures and pressures, in a manner applying a loading on said portion of the heat exchanger tubes which will prevent them from vibrating due to the crosswise directional flow component of said fluid; wherein the support plates in said zone extend between a central divider plate and a wall of the vessel, said alternate ones of said support plates being alternately connected on one of said central plate and said wall of the vessel and being free of connection to the other of the said central divider plate and said wall of the vessel. 3. Heat exchanger according to claim 2, wherein the connection of the alternate ones of said support plates to one of the central divider and the wall of the vessel comprise a plurality of hook and slot connections, each of which has a hook in pulling contact with a wall of a slot. 4. Heat exchanger according to claim 3, wherein the slot of each hook and slot connection is formed in a respective support plate, and the hook is mounted on the respective one of the central divider plate and the wall of the vessel. 5. Heat exchanger according to claim 4, wherein each slot has a length that is greater than a lateral width of the respective hook received therein for permitting lateral movement of the hook within the respective slot. 6. Heat exchanger according to claim 5, wherein said portion of the heat exchanger tubes is vertically oriented and the support plates are horizontally oriented; and wherein said hooks engage in said slots from above. 7. Heat exchanger according to claim 3, wherein said portion of the heat exchanger tubes is vertically oriented and the support plates are horizontally oriented; and wherein said hooks engage in said slots from above. 8. Nuclear steam generator of the type with a heat exchanger in a secondary side of a vessel having a wrapper within a shell, a plurality of parallel heat exchanger tubes mounted extending through a plurality of support plates with clearance, said support plates extending transversely across the vessel, and means for feeding nonradioactive water, which is to be heated by heat transferred from a radioactive heat exchange medium circulating through the heat exchanger tubes, into the vessel in a manner causing the nonradioactive water to have a flow path which, at least in part, has a crosswise directional flow component relative to a portion of the heat exchanger tubes extending axially through the vessel; the improvement comprising means for causing alternate ones of said support plates, in a zone containing said part of the flow path having a crosswise directional flow component, to shift in opposite directions transversely relative to said portion of the heat exchanger tubes, as said steam generator heat exchanger is brought up to operating temperatures and pressures, in a manner applying a loading on said portion of the heat exchanger tubes which will prevent them from vibrating due to the crosswise directional flow component of said fluid; wherein support plates outside of said zone are free of securement relative to both the central divider plate and the wrapper. 9. Nuclear steam generator of the type with a heat exchanger in a secondary side of a vessel having a wrapper within a shell, a plurality of parallel heat exchanger tubes mounted extending through a plurality of support plates with clearance, said support plates extending transversely across the vessel, and means for feeding nonradioactive water, which is to be heated by heat transferred from a radioactive heat exchange medium circulating through the heat exchanger tubes, into the vessel in a manner causing the nonradioactive water to have a flow path which, at least in part, has a crosswise directional flow component relative to a portion of the heat exchanger tubes extending axially through the vessel; the improvement comprising means for causing alternate ones of said support plates, in a zone containing said part of the flow path having a crosswise directional flow component, to shift in opposite directions transversely relative to said portion of the heat exchanger tubes, as said steam generator heat exchanger is brought up to operating temperatures and pressures, in a manner applying a loading on said portion of the heat exchanger tubes which will prevent them from vibrating due to the crosswise directional flow component of said fluid; wherein the support plates in said zone extend between a central plate and the wrapper of the vessel, said alternate ones of said support plates being alternately connected to one of said central divider plate and said wrapper, and being free of connection to the other of the said central divider plate and said wrapper. 10. Nuclear steam generator according to claim 9, wherein the connection of the alternate ones of said support plates to one of the central divider and the wrapper of the vessel comprise a plurality of hook and slot connections, each of which has a hook in pulling contact with a wall of a slot. 11. Nuclear steam generator according to claim 10, wherein the slot of each hook and slot connection is formed in a respective support plate, and the hook is mounted on the respective one of the central divider plate and the wrapper of the vessel. 12. Nuclear steam generator according to claim 11, wherein each slot has a length that is greater than a lateral width of the respective hook received therein for permitting lateral movement of the hook within the respective slot. 13. Nuclear steam generator according to claim 12, wherein said portion of the heat exchanger tubes is vertically oriented and the support plates are horizontally oriented; and wherein said hooks engage in said slots from above. 14. Nuclear steam generator according to claim 10, wherein said portion of the heat exchanger tubes is vertically oriented and the support plates are horizontally oriented; and wherein said hooks engage in said slots from above. 15. Method of eliminating heat exchanger tube vibration resulting from cross-flows in a heat exchanger of a nuclear steam generator of the type wherein the heat exchanger is located in a secondary side of a vessel having a wrapper within a shell, a plurality of parallel heat exchanger tubes mounted extending through a plurality of support plates with clearance, said support plates extending transversely across the vessel, and nonradioactive water, which is to be heated by heat transferred from a radioactive heat exchange medium circulating through the heat exchanger tubes, is fed into the vessel in a manner causing the nonradioactive water to have a flow path which, at least in part, has a crosswise directional flow component relative to a portion of the heat exchanger tubes extending axially through the vessel; comprising the step of causing alternate ones of said support plates, in a zone containing said part of the flow path having a crosswise directional flow component, to shift in opposite directions transversely relative to said portion of the heat exchanger tubes, as said steam generator heat exchanger is brought up to operating temperatures and pressures, in a manner applying a loading on said portion of the heat exchanger tubes which will prevent them from vibrating due to the crosswise directional flow component of said fluid; wherein said step of causing the alternate ones of said support plates to shift is performed by the support plates in said zone extending between a central divider plate and the wrapper of the vessel, said alternate ones of said support plates being alternately connected to one of said central divider plate and said wrapper, and being free of connection to the other of the said central divider plate and said wrapper, so that a pulling force is exerted on each plate in a direction toward its connection to the respective one of the central divider plate and the wrapper. 16. Method according to claim 15, wherein the pulling force is exerted by a plurality of hook and slot connections, each of which has a hook in pulling contact with a wall of a slot. 17. Method according to claim 15, wherein the loading on said portion of the heat exchanger tubes which will prevent them from vibrating due to the crosswise directional flow component of said fluid is applied by bringing the alternate support plates into engagement with opposite sides of the heat exchanger tubes to provide a passive, positive supporting of the heat exchanger tubes by the supporting plates under operating temperatures and pressures despite the existence of clearance gaps between the heat exchanger tubes and the support plates through which they pass.
052805107	claims	1. A method for coating the inside surface of tubular components of a nuclear fuel assembly, comprising: supporting the component within a vacuum chamber; positioning a source rod having a field emitter tip structure within the component, said structure being formed of material to be coated on said surface; inducing an electrical current flow through the rod sufficient to evaporate at least a portion of the emitter structure; whereby the evaporated material of the emitter structure is deposited on and adheres to said surface as a coating. the vacuum chamber is backfilled with a reactive gas, and the material evaporated from the emitter structure chemically reacts with the gas before adhering to said surface. supporting the component within a vacuum chamber; positioning a source rod having a gated field emitter structure within the component, said structure being formed of material to be coated on said surface; inducing an electrical current flow through the rod sufficient to evaporate at least a portion of the emitter structure; whereby the evaporated material of the emitter structure is deposited on and adheres to said surface as a coating. the vacuum chamber is backfilled with a reactive gas, and the material evaporated from the emitter structure chemically reacts with the gas before adhering to said surface. 2. The method of claim 1, wherein 3. The method of claim 2, wherein the reactive gas is one of nitrogen, oxygen, or carbon plasma and the coating adhered to the component is one of a nitride, oxide, or carbide, respectively. 4. The method of claim 1, wherein the material is a neutron burnable poison metal. 5. The method of claim 4, wherein the material is one of gadolinium, erbium, or boron. 6. The method of claim 1, wherein the coating is a neutron burnable poison metal compound. 7. The method of claim 6, wherein the coating is one of ZrB.sub.2, or TiB.sub.2. 8. The method of claim I, wherein the coating is a neutron burnable poison ceramic. 9. The method of claim 8, wherein the coating is B.sub.4 C. 10. The method of claim 1, wherein the material is a neutron burnable poison glass. 11. The method of claim 10, wherein the material is one of 20Li.sub.1 080B.sub.3 or 15 Na.sub.2 085B 20. 12. The method of claim 1, wherein the material is a hydrogen getter. 13. The method of claim 12, wherein the material is one of yttrium, a zirconium nickel alloy, or a zirconium-titanium-nickel alloy. 14. The method of claim 2, wherein the reactive gas is nitrogen, the source material is boron, and the coating is BN. 15. The method of claim 2, wherein the reactive gas nitrogen and the coating is a wear resistant nitride. 16. The method of claim 15, wherein the material is a metal and the coating is one of ZrN, TiN, CrN, HfN, TaAlVN, or TaN. 17. The method of claim 1, wherein the coating is a corrosion resistant ceramic or glass. 18. The method of claim 1, wherein the coating is one of Zr.sub.2 0.sub.3, Al.sub.2 O.sub.3, TiCN, TiC, CrC, ZrC, WC, calcium magnesium aluminosilicate, sodium borosilicate, or calcium zinc borate. 19. A method for coating the inside surface of a tubular component for a nuclear fuel assembly, comprising: 20. The method of claim 19, wherein
	claims	1. A containment enclosure for shielding a nuclear waste cask comprising:a lower base portion at least partially embedded in a concrete pad, the base portion comprising a baseplate supporting a plurality of coaxially aligned shells defining a lower cavity;an upper radiation shielding portion coupled to and supported by the lower base portion, the shielding portion defining an upper cavity;the shielding portion comprising a radiation shielding material configured to block gamma and neutron radiation;the lower and upper cavities collectively defining a contiguous containment space configured for holding the cask;wherein the base and shielding portions enclose the cask. 2. The system according to claim 1, wherein the radiation shielding material comprises boron. 3. The system according to claim 2, wherein the shielding portion has a composite wall construction comprising an outer wall, an inner wall, and an intermediate layer sandwiched therebetween which comprises the boron. 4. The system according to claim 3, wherein the outer and inner walls are formed of steel. 5. The system according to claim 3, wherein the shielding portion comprises a straight cylindrical sidewall section and a frustoconical top wall section terminating in a top opening. 6. The system according to claim 1, wherein the shielding portion is separated from and sealed to the lower base portion at a horizontal joint by an annular gasket compressed between an annular upper seal plate of the lower base portion and an annular lower seal plate of the shielding portion. 7. The system according to claim 6, wherein the annular gasket is spaced radially inwards from an exterior surface of the cask containment enclosure. 8. The system according to claim 1, further comprising an ambient cooling air ventilation system comprising an annular downcomer formed in the lower base portion, and an annular riser collectively formed in the lower base and shielding portions between the cask and the base and shielding portions. 9. The system according to claim 8, wherein the ventilation system further comprises:a plurality of upper air inlets circumferentially spaced apart at a circumferential joint between the base portion and the shielding portion;an annular upper air inlet plenum in fluid communication with the upper air inlets and the downcomer;a plurality of air exchange passageways circumferentially spaced apart at a bottom of the base portion, the passageways in fluid communication with the downcomer and riser; anda top discharge opening formed in the shielding portion in fluid communication with the riser. 10. The system according to claim 9, wherein the ventilation system defines a natural convection-driven ventilation air pathway in which air enters the upper air inlets in a laterally inward direction, flows downwards in the downcomer to the air exchange passageways, reverses direction and flows upwards in the riser to the top discharge opening. 11. The system according to claim 9, wherein a bottom end of the shielding portion has a castellated configuration which defines the upper air inlets. 12. The system according to claim 11, further comprising a castellated annular air inlet skirt welded to a bottom end of shielding portion which comprises a plurality of circumferentially spaced castellations. 13. The system according to claim 12, wherein bottom ends of the castellations are welded to a top end of the base portion. 14. The system according to claim 9, wherein the annular upper air inlet plenum is located at the circumferential joint and recessed inside the shielding portion. 15. The system according to claim 14, wherein the circumferential joint comprises an annular gasket located inboard of the annular air inlet plenum. 16. The system according to claim 9, further comprising a frustoconical shaped discharge plenum located in the upper shielding portion above the cask. 17. The system according to claim 9, wherein no straight line of sight exists through the upper air inlets to outside to prevent straight line radiation streaming. 18. The system according to claim 1, wherein the containment space is configured for holding no more than a single one of the cask. 19. The system according to claim 1, wherein the cask contains a spent nuclear fuel canister therein which contains the nuclear waste. 20. The system according to claim 3, wherein the shells of the base portion comprises an outer shell, and a pair of conjugate shells spaced radially inwards therefrom by a distance greater than a radial gap formed between the conjugate shells. 21. The system according to claim 20, wherein a bottom end of the shielding portion comprises an inwardly recessed stepped portion including a pair of conjugate walls spaced radially apart by a radial gap the same as the radial gap between the conjugate shells of the base portion. 22. The system according to claim 21, further comprising a first annular seal plate attached to the conjugate walls and a second annular seal plate attached to the conjugate shells, and an annular gasket compressed between the first and second annular seal plates. 23. A nuclear waste storage facility comprising a plurality of the containment enclosures according to claim 1. 24. A nuclear waste storage system comprising:a concrete pad;a plurality of cask containment enclosures arranged on the concrete pad, each containment enclosure housing a storage cask containing a canister holding radioactive nuclear waste;each containment enclosure comprising:a cylindrical lower base portion at least partially embedded in the concrete pad, the lower base portion comprising a baseplate supporting a plurality of coaxially aligned shells defining a lower cavity;a separate upper shield jacket coupled to and supported by the lower base portion, the shield jacket having a wall construction comprising boron-containing radiation shielding materials, the upper shield jacket defining an upper cavity;a plurality of ambient cooling air inlets formed in the shield jacket, the air inlets circumferentially spaced apart at a circumferential joint between the base portion and the shield jacket;an annular air inlet plenum formed at a bottom of the shield jacket by an inwardly recessed stepped portion of the shield jacket, air inlet plenum located at the circumferential joint and in direct fluid communication with the air inlets and a downcomer formed in the lower base portion;a plurality of air exchange passageways circumferentially spaced apart at a bottom of the base portion, the passageways in fluid communication with the downcomer and a riser which extends vertically between the cask and innermost surfaces of the lower base portion and shield jacket; anda top discharge opening formed in the shield jacket in fluid communication with the riser and ambient air;wherein the storage cask containing nuclear waste is positioned partially in both the upper and lower cavities of the lower base portion and shield jacket. 25. The system according to claim 24, further comprising a cap attached to a top of the shield jacket, the cap defining a plurality of laterally open air discharge openings for venting air heated in the riser by the cask to atmosphere. 26. The system according to claim 24, wherein the cooling air inlets are formed by an annular castellated skirt attached to a bottom end of the shield jacket. 27. The system according to claim 24, wherein the circumferential joint is located radially inboard of the cooling air inlets, the circumferential joint including an annular gasket compressed between the lower base portion and the shield jacket. 28. The system according to claim 24, wherein the upper and lower cavities are collectively configured to hold no more than a single storage cask. 29. The system according to claim 24, wherein ambient cooling air flow is driven by natural convection circulation, the cooling air flowing through the cooling air inlets into the inlet plenum, downward through the downcomer, inwards through the air exchange passageways into a bottom of the riser, and upwards through the riser to the discharge opening in the shield jacket. 30. The system according to claim 24, wherein the shield jacket comprises an upper frustoconical section, a lower cylindrical section, and an annular air inlet skirt attached to the lower cylindrical section which defines openings for the cooling air inlets.
042736137	summary	BACKGROUND OF THE INVENTION The present invention relates to a method of operating a nuclear reactor, and also to a nuclear reactor construction enabling it to be operated in accordance with the novel method. The invention is particularly applicable to heavy-water moderated power reactors, and is therefore described below with respect to such application. Nuclear reactors moderated by heavy water provide a number of advantages as compared to those using ordinary water as a moderator. One advantage is that it is possible to use natural uranium as well as slightly enriched uranium as the fuel. Another advantage is that the burn-up is high. Such reactors, however, are subject to a number of disadvantages, besides the high price of heavy water. Thus, they exhibit a "positive void coefficient," which means that if heavy water is lost, the reactivity rises thereby increasing the danger of a "run-away." In addition, even though the burn-up rate is high, such reactors still require large amounts of natural uranium, the present supplies of which are extremely limited. OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to provide a nuclear reactor, and a method of operating a reactor, providing advantages in the above respects. More particularly, an object of the present invention is to provide a method of operating a nuclear reactor, and a reactor construction enabling such operation, in which a significant portion of the total core power is derived from burning natural thorium, rather than uranium. Thorium-232 (which constitutes nearly 100% of natural thorium) is converted into fissile uranium-233 by the capture of neutrons, the conversion being effected after the lapse of a few days to permit decay of the protactinium produced upon the exposure of the thorium. Because of the relatively high thermal absorption and low resonance capture of irradiated thorium, as compared to natural uranium, applying the invention to heavy-water moderated reactors would remove the present "positive void coefficient" of such reactors, which would thereby reduce the danger of a "run-away" by loss of moderator. In addition, such a reactor construction and operation would have the further important advantage of producing substantial savings in the requirements for uranium. The invention is applicable to reactors, particularly of the heavy-water moderated type, having an active core comprising a pressure tube including a cluster of fuel rods of fissile-material (particularly natural uranium) rod segments, some of which rods occupy exterior positions in the cluster and the remainder of which rods occupy interior positions in the cluster. According to a broad aspect of the present invention, there is provided a method of operating a nuclear reactor of the above type, comprising the Phases: (A) providing interior rod positions at one end of the cluster with thorium-containing rod segments to irradiate the thorium until its multiplication factor is built up to about that of natural uranium; and (B) utilizing the thorium-containing rod segments irradiated in the interior rod positions of the cluster to refuel exterior rod positions at the charge end of the cluster. In the preferred embodiment of the invention described below, the method includes, after Phase B, the further Phase C of removing depleted thorium-containing rod segments from the discharge end of exterior rod positions of the cluster and utilizing them to refuel interior rod positions at the charge end of the cluster. After all the interior and exterior rod positions have been refueled with thorium-containing segments during Phase C, fresh thorium-containing rod segments are periodically introduced into the interior rod positions of the cluster to replace rod segments whose thorium has reached its irradiation limit. The method may include the further step of providing, in Phase A, booster rods of enriched uranium in the moderator in order to increase the reactivity of the core, thereby permitting an increase in the number of thorium-containing rod segments irradiated in Phase A to shorten the transition to Phase B. According to another aspect of the present invention, there is provided a nuclear reactor adapted to be operated in accordance with the above described method, the nuclear reactor having an active core comprising a pressure tube including a cluster of fuel rods some of which occupy exterior positions and the remainder of which occupy interior positions in the cluster. The cluster of rods is constituted of a plurality of cluster segments each including a pair of end plates and a plurality of rod segments attached thereto to extend therebetween. The rod segments and the end plates include cooperable mechanical fastener devices permitting the quick attachment and detachment of the rod segments to the end plates to enable refueling the reactor as set forth. In the preferred embodiment described below, the cooperable mechanical fastener devices include bayonet pins carried by the rod segments receivable in bayonet slots formed in the end plates.
	summary
046631291	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, one embodiment of the radionuclide generator system is indicated generally at 10. The generator system 10 is divisible into a radiologically contained portion 12 and an accessible generator portion 14. In general the production of the desired product radionuclides in the system 10 involves beginning the process with thorium-228 starting material in the contained portion 12, radium-224 is then separated from the thorium-228, the radium-224 is transferred to the accessible generator portion 14 and natural radioactive decay enables the production of bismuth-212 and lead-212 which is withdrawn for therapeutic medical use. This division of the generator system 10 into the two portions 12 and 14 is preferable because highly active starting material, such as thorium-228, has a rather long half life (for example, 1.9 years for thorium-228) and the daughter materials exhibit high levels of .gamma. radioactivity. Consequently, these radioactivity characteristics require the use of expensive, inconvenient preparation facilities and of safety measures which are usually unavailable or impractical to implement for the end users of the product radionuclides. The system 10 has an advantage of allowing preparation of the desired radionuclides in the accessible generator portion 14 and shipment to the end user in a form which is safe for use without having to exercise extreme safety measures for long periods of time. In the illustrated embodiment the contained portion 12 of the generator system 10 includes a supply means, such as a vial 16, which contains thorium-228 as a starting material 18 in the form of thorium nitrate complex in an eight molar solution of nitric acid as a carrier solution. There are also present in the solution equilibrium concentrations of nitrate ions of daughter materials, such as radium-224. The starting material 18 in the vial 16 is accessible by needle connections 20. New thorium-228 material is taken from the vial 16 whenever the recycled material from a previous production cycle is insufficient to produce the desired end product. Flexible hose 22, such as 1/8 inch o.d. Teflon tubing, is coupled to the needle connections 20, and air pressure 21 is supplied from an external supply (not shown) to the starting material 18. The air pressure 21 forces the starting material 18 through the line 22 (in the illustrated embodiment the abovementioned 1/8 inch o.d. Teflon tubing is used for all line connections in the system 10). The starting material 18 then passes through a bulkhead fitting 26, along a line 27 and through a valve 28 positioned to deliver the starting material 18 through a line 29 to a supply container 30. The bulkhead fittings, such as the fitting 26, allow convenient, safe coupling to the Teflon tubing and ready access to the system components without having to disturb the connections intimately associated with the process components. Typically the various process components are mounted on a rigid sheet of aluminum or steel. In the illustrated embodiment, the bulkhead fitting 26 is a quick-disconnect, Luer taper plastic fitting (see, for example, the 1983-84 catalog of Rainan Instrument Co., Mack Road, Woburn, Mass. 01801, which is incorporated by reference herein). The valves 28 used throughout the system 10 are low pressure switching valves, such as a Hamilton Miniature HPV valve, (see, for example, p. 116 of the Rainan Instrument Company catalog described hereinbefore and incorporated by reference herein) having either three or four ports with single direction flow arrangeable between each of the pair of ports. The fittings to the valves 28 and the line 22 are preferably swivel connectors, such as H2461 detailed on page 103 of the Rainan catalog, described hereinbefore and incorporated by reference herein. In the illustrated embodiment these fittings are also used throughout the system 10. In FIG. 3 the supply container 30 is a sealed quartz vessel coupled from quartz tubing 32 to the flexible Teflon tubing by universal two way connectors 34 which are used throughout for all quartz to Teflon seals. Preferably the connectors 34 have a Tefzel type coupling for connecting to the flexible Teflon tubing, such as a line 36, and have a large bore end for coupling to the glass tubing 32 (see, for example, p. 109 of the Rainan catalog cited hereinbefore and incorporated by reference herein). Referring to FIG. 1, in response to the air pressure 21, the starting material 18 from the vial 16 and/or any material recycled from a previous production cycle collects as supply material 33 in a platinum crucible 35 disposed within the supply container 30. Gas exhaust (substantially air and some radon) is output along the line 36, through a valve 38 and along a line 39 through a bulkhead fitting 41 to a gas trap or repository (not shown). Typically, a five gallon polyethylene bottle acts as a repository for both the gas and any waste material output from the various steps in preparing the radionuclides. The repository, or gas trap, allows the radon gas to decay to a nonvolatile species, such as lead-212 and bismuth-212. After accumulating the desired amount of the supply material 33 in the platinum crucible 35, air pressure is applied through another bulkhead fitting 40, through a line 42, a valve 44 and output along line 46 into a quartz tubing inlet 48. Responsive to the input air pressure the supply material 33 is transferred from the platinum crucible 35, through a quartz tubing outlet 50, along the line 29, through the valve 28 and along a line 56 into an anion exchange column 58. To equilibrate gas pressure and allow for fluid displacement, some exhaust gas (air and radon) is output from the column 58 along a line 60, through the valve 38 and along a line 39 through the bulkhead fitting 41 to the repository described hereinbefore. Preferably, the column 58 contains a strongly basic anion exchange media, such as, for example an AG 1, AG 2 or AG MP-1 exchange media having a chemical makeup of quaternary ammonium functional groups attached to a styrene divinylbenzene copolymer lattice (see pp. 7 and 8 of the January, 1984, catalog of Bio-Rad Chemical Division, 2200 Wright Avenue, Richmond, Calif. 94804, which is incorporated by reference herein). For purposes of this application the term exchange column is meant to include a container and its ion exchange media therein. The ion exchange media in the column 58 acts as separating means by retaining thorium-228, and allowing radium-224 and various daughter materials (see FIG. 2) to pass through in the nitric acid carrier solution. Documentation of the selectivity of strongly basic anion exchangers is set forth in FIG. 70 in Buchanan et al., International Atomic Energy Agency, Copenhagen Conference on the Use of Radioisotopes in the Physical Sciences and Industry, Sept. 6-17, 1960, which is incorporated by reference herein. In the illustrated embodiment the components of the system 10 are arranged to allow a gravity feed of the radium nitrate/nitric acid solution output from the exchange column 58, through a valve 62 and a line 64 to an evaporation unit 66. The gas exhaust from the unit 66 traverses a line 60, the valve 38, the line 39 and the bulkhead fitting 41 before terminating at the previously described repository (not shown). Similarly, the gas exhaust from the evaporation unit 66 is output through a line 68, a valve 70, a line 72 and through a bulkhead fitting 74 to the repository. The radium nitrate/nitric acid solution in the evaporation unit 66 has no detectable thorium-228 present. The exchange column 58 is then washed with about 10 milliliters of eight molar nitric solution to remove any residual radium-224. This nitric acid solution originates from an external source (not shown), and passes through a bulkhead fitting 76, a line 78, the valve 28, the line 56, the column 58, the valve 62 and the line 64 before emptying into the evaporation unit 66. The gas exhaust from the column 58 and the unit 66 follows the same paths as in the previously described step of gravity transfer from the exchange column 58 to the evaporation unit 66. In order to prepare the radium-224 for generation of the bismuth-212 and lead-212 end products in the accessible portion 14, the nitric acid solution is removed from the evaporation unit 66 by evaporating the solution, leaving a dried compound of radium-224. In this embodiment the compound is radium-nitrate because HNO.sub.3 was used to separate the thorium-228 from the radium-224 in the anion exchange column 58. A nichrome wire resistance heater 80 is wound around the evaporation unit 66, and approximately 50 to 80 watts of power are utilized to raise the temperature of the solution to increase the vapor pressure and evaporate all the water and concentrated nitric acid. Since the preferred solution is approximately an eight molar nitric acid solution, the water with a higher vapor pressure is driven off first, followed by sixteen molar concentrated nitric acid. In order to assist the elevated temperature evaporation process, air is input through a bulkhead fitting 82, passing through a line 84, the valve 62 and through the line 64 into the evaporation unit 66. The vapor exhaust from the evaporation unit 66 follows the gas exhaust path from the unit 66 discussed hereinbefore for the nitric acid wash step which removed residual radium-224 from the exchange column 58. After the evaporation step has been completed, a liquid, such as water or 0.1M HCl, for dissolving the dried radium nitrate is input from an external source (not shown) to form a radium compound solution. The resulting radium-224 compound solution is transferred to the evaporation unit 66 through a bulkhead fitting 86, along a line 88, through the valve 28 and along a line 90 coupled to the unit 66. The water dissolves the dried radium nitrate, and exhaust gases from the unit 66 follow the same path discussed in the immediately previous paragraph. The radium nitrate solution is then ready for transfer from the evaporation unit 66 to a calibrated dispenser 92, such as a pipette or a burette. This dispenser 92 enables a predetermined number of aliquots to be output to the accessible generator portion 14, wherein the associated desired quantity of bismuth-212 and lead-212 can be produced. To carry out the dispensing operation, air is input to the unit 66 from the external air supply (not shown) via the fitting 82, through the line 84, the valve 62 and the line 64. Responsive to the air pressure the radium nitrate solution is output from the unit 66 along the line 90, through the valve 28 and the line 94 before input to the calibrated dispenser 92. The gas exhaust from the dispenser 92 passes through a line 96 through the valve 38, the line 39 and the fitting 41 to the repository described hereinbefore. Each of the desired predetermined aliquots of radium nitrate solution is dispensed to the accessible portion 14 by a means for transferring, which includes various parts of the system 10, such as, for example, those elements of the system 10 defined by the following procedure: applying air pressure through a fitting 98, a line 100, the valve 28 and the line 94 coupled to the upstream side of the dispenser 92. The radium nitrate solution is output from the dispenser 92, through a coupled valve 102 and along a line 104 which joins the closed portion 12 with the accessible generator portion 14. The solution is then transferred through a valve 106 to retaining means, such as an ion exchange media, which retains the radium-224. The ion exchange media is held in container means, such as a cation exchange column 108. In the illustrated embodiment the predetermined aliquot of radium-224 cations undergoes ion exchange in the selected ion exchange media, such as, for example, a macroporous cation exchange AG MP-50 or another strongly acidic cation exchange media composed of, for example, sulfonic acid functional groups attached to a styrene divinylbenzene copolymer lattice (see, for example, pp. 7 and 8 of the January, 1984, catalog of Bio-Rad Chemical Division, cited hereinbefore and which is incorporated by reference herein). Effluent is output from the column 108 through a line 110 and a fitting 112 to the previously discussed repository. Preparatory to removing the cation exchange column 108 from the system 10, various coupled supply lines must be decontaminated. Decontamination is effectuated by inputting air from an external source (not shown) via a fitting 114, along a line 116, through the valve 112, output through the line 104 and into the column 108 through the valve 106. The effluent from the column 108 passes through the line 110 and the fitting 112 to the repository for those radioactive species which are removed from the supply lines and are not retained by the column 108. As discussed hereinbefore, the repository functions generally as the waste container. The line 110 is then purged of radioactivity in preparation for removal of the column 108 by applying air pressure 111 to the valve 106, and the solution is output along the line 110 through the bulkhead fitting 112 to the repository. Once sufficient radium-224 is present in the cation exchange column 108 it can be disconnected and utilized as a completely separate isotopic generator system. In this case the radium-224 becomes a starting material provided by radium supply means, such as the contained portion 12. The user can collect selectively the end products of lead-212 and/or bismuth-212 radionuclides for medical applications such as, cancer treatment and suppression of immune response. Referring to FIG. 2, the radium-224 has a 3.6 day half life, and the desired end product radionuclide of lead-212 has approximately a 10.6 hour half life and the bismuth-212 has about a one hour half life. The 3.6 day half life of the radium-224 provides an adequate supply of lead-212 and bismuth-212 over a period of about two weeks time, and after about thirty-five to forty-five days the level of radiation is diminished sufficiently to enable disposal without extraordinary safety procedures. Medical therapy applications, such as cancer treatment and immune response suppression, are particularly desirable applications for the lead-212 and bismuth-212 radionuclides because the bismuth-212 decays with emission of high energy .alpha. particles of various energies having an average of about 7.8 MeV energy. The sharp localization of radiation, high radiation density and high radiation level for each particle make bismuth-212 attractive for the above-mentioned medical treatments. Selective withdrawal of the bismuth-212 and lead-212 radionuclides from the column 108 is accomplished by passing one or more acids of appropriate molarity through the cation exchange column 108. Useful acids include, for example, HCl, HI, HBr, HNO.sub.3 and ascorbic acid. Each of these acids has appropriate ranges of molar concentration for selective removal of the bismuth-212 and/or lead-212. In the case of HCl the bismuth-212 is first removed by a solution of lower appropriate molarity of about 0.25 to 1.0 and requires about one column volume (a standard known measure in the art of chromatography). If a molarity less than 0.25 is used, an increased number of column volumes is required. In order to remove lead-212, after withdrawal of bismuth-212, the exchange column 108 is charged with three column volumes of appropriate higher molarity HCl acid, about 1 to 6. In the case of HI the bismuth-212 is first removed by a solution of appropriate molarity of about 0.05 to 0.20 HI for about one column volume. Subsequently, lead-212 is removed by using three column volumes of appropriate higher molarity of about 0.2 to 1.0 molar HI. In the case of HBr the bismuth-212 can be removed by using about one column volume of appropriate molarity, or about 0.1 to 0.8 molar HBr. Subsequently, lead-212 is removed by using three column volumes of appropriate higher molarity of about 0.4 to 2.5. In the case of HNO.sub.3 the bismuth-212 can be removed by using about one column volume of appropriate molarity, or about 3 to 5 molar nitric acid, but HNO.sub.3 alone cannot be used to remove lead-212. Similarly, in the case of absorbic acid alone, lead-212 cannot be removed; however, about one column volume of appropriate molarity of about 1 to 2 molar absorbic acid removes most of the bismuth-212. Various combinations of these acids with appropriate molarity and column values can also be used to effectuate bismuth-212 and lead-212 removal from the exchange column 108. After removal of the cation exchange column 108 for conveyance to the end user, a new one of the exchange columns 108 can be installed in the system 10, and the calibrated dispenser 92 can output to the column 108 another predetermined aliquot of the radium-224 nitrate solution. This procedure can be repeated by recycling a predetermined number of times until the predetermined aliquots are dispensed to each of the exchange columns 108. Referring again to FIG. 1, after dispensing of the radium-224 solution by the calibrated dispenser 92, the contained portion 12 can undergo a recycling operation to prepare a completely new batch of the radium-224. This is accomplished by chemically stripping the thorium-228 from the anion exchange column 58. Water and then six molar hydrochloric acid is input to the column 58 through the fitting 76, along the line 78, through the valve 28, along the line 56 into the column 58, thereby washing the nitric acid from the column 58 through the valve 62 and through a line 116 into a thorium evaporation unit 118. Responsive to the input of water, HCl and residual HNO.sub.3, exhaust gas is output from the evaporation unit 118 along a line 120, through the valve 70, along the line 72 and through the fitting 74 to the previously described repository. Gas exhaust is also output from the ion exchange column 58 along the line 60, through the valve 38, and output along the line 39 and through the fitting 41 to the repository. To carry out evaporation of the solution in the evaporation unit 118, about 50 to 80 watts of heat are applied by a nichrome wire heater 122. In order to assist the elevated temperature evaporation process, air is input through the fitting 82, the line 84, through the valve 62 and output along the line 116 into the unit 118. Elevated temperature evaporation proceeds in the order of water, hydrochloric acid and nitric acid with vapors of these chemical compounds output along the line 120, through the valve 70, the line 72 and output through the fitting 74 to the repository. Upon completion of the evaporation process, residual thorium-228 material remains in the unit 118. This residual thorium-228 is dissolved in additional eight molar nitric acid which is transferred into the evaporation unit 118 through a fitting 124, a line 126, the valve 44 and output through the line 128 into the unit 118. Exhaust air and radon gas are output along the same path as the evaporated water and acids described at the beginning of this paragraph. In the final step of the illustrated embodiment, the thorium-228, nitric acid solution is returned to the supply material 33 in the platinum crucible 35 disposed within the supply container 30. This step is accomplished by applying air pressure to the evaporation unit 118. Air from the external source (not shown) is input through the fitting 82, the line 84, the valve 62, and output through the line 116 into the unit 118. The thorium-228, nitric acid solution is output along the line 128, through the valve 44 and the line 46 into the platinum crucible 35 wherein the supply material 33 is contained. Air and radon are output from the supply container 30 along the line 36, through the valve 38 and output through the line 39, through the fitting 41 to the repository described hereinbefore. Once the thorium-228 has been returned to the platinum crucible 35, the system 10 is ready to operate again provided a sufficient quantity of radium-224 has been generated in the supply material 33. This procedure helps to minimize radiation damage to the anion column 58 and the various quartz containers, such as the thorium evaporation unit 118. The present invention provides improved methods and apparati which use thorium-228 supply material disposed in a radiologically contained portion for producing bismuth-212 and lead-212. The bismuth-212 and lead-212 are generated in an accessible generator portion which can be removed and safely utilized apart from the radiologically contained portion 12 which encloses the relatively hazardous part of the generator system 10. Radium-224 is retained on a cation exchange column of the accessible generator portion 14, and the relatively long (3.6 day) half life of radium-224 provides a long term beneficial output of the short half life lead-212 and bismuth-212, about ten hours and one hour half life, respectively. The following example is included for illustrative purposes only and is not intended to limit the scope of the invention. EXAMPLE The generator system is located in a .gamma. shielded facility (a cave) in the Chemistry Division of Argonne National Laboratory, Argonne, Ill. Shielding is required because some of the short lived daughter activities include high energy .gamma. radiation, as well as .alpha. and .beta. radiation. The cave is at a negative pressure relative to atmospheric pressure for control of potentially hazardous gas emission. Manipulation of valves and changing of ion exchange columns is done by master slave manipulators. All exhaust of air and liquids is through tubing which terminates in a five gallon polyethylene container. This radiologically controlled generator system permits entrapped radon with a half life of about one minute to decay to a nonvolatile species, such as lead-212 or bismuth-212. The apparatus remains free of external contamination to facilitate any emergency repairs. Reagent solutions and air for liquid transfer and drying purposes are supplied from outside the cave through the cave walls by means of 1/16 inch i.d. silicone rubber tubing. Reagents are measured and dispensed through these tubes by glass hypodermic syringes. Air flow is controlled by a commercial pressure regulator and an adjustable flowmeter. The apparatus for generation of bismuth-212 and lead-212 is constructed primarily of quartz and Teflon for maximum resistance to chemical and radiological damage. Only those parts which are not subject to such conditions (air lines and reagent water lines) are made of less resistant silicone rubber. Disposable items which need only survive one cycle also are constructed of less resistant material. Except for the platinum crucible which holds the thorium-228 supply material, the rest of apparatus is in intimate contact with the acids and thorium-228 material for less than three hours in a two week cycle. All acid solutions are prepared from chemically pure reagent grade acids diluted with deionized and distilled water. The ion-exchange resins used are from a commercial supplier, Bio-Rad Chemical Division, Richmond, Calif. One of the preferable anion resins, Dowex-1, is supplied in a chloride form and must be converted to the nitrate form by repeated alternate washing with 6 molar HNO.sub.3 and water. The cation resin, such as AG MP50, 100-200 mesh, must be conditioned by alternate acid/water washes to insure the resin is in the hydrogen form and free of extraneous cations. The resins are treated in a relatively large batch to insure an ample supply of uniform quality and are stored in water until needed. A cycle or production batch run begins by packing a Bio-Rad Econo disposable ion exchange column with 3/4 milliliter of conditioned anion resin. A glass wool plug is inserted on top of the resin bed to minimize disruption of the bed by subsequent operations. The resin is preconditioned with 5 milliliters of 8 molar HNO.sub.3. The cation exchange column is filled with 0.4 milliliters of cation resin, and water is used to condition this column. The anion column is mounted in the separation apparatus by inserting the male Luer connection on the discharge end of the column into the mating fitting on the top of the coupled valve. The input end of the column is similarly coupled into the system with Luer fittings. A 5 milliliter charge of 8 molar HNO.sub.3 is injected into the thorium-228 supply container using an external hypodermic syringe. The nitric acid carrier solution dissolves the thorium-228 and daughter material (such as radium-224) nitrates and complexes the nitrates for adsorption on the anion resin. About 5 psi of air pressure is used to move the nitrate solution to the anion column. The solution moves through the anion resin bed into the radium evaporation unit under the force of gravity. Thorium-228 is adsorbed on the anion resin and radium-224 passes into the evaporation unit. To insure complete recovery of the radium-224, an additional 10 milliliters of 8 molar HNO.sub.3 acid is washed through the resin using an external syringe. The combined 15 milliliters of nitric acid containing the radium-224 and daughter activities is evaporated using a nichrome wire-wound electric resistance heater at 50-80 watts of power. To speed the evaporation process, air at 5 psi and 0.2 liters/minutes is passed through the evaporation unit which is heated to dryness. Five milliliters of water is injected into the evaporation unit to dissolve the radium-224 nitrate. Five psi of air pressure transports the radium-224 nitrate solution from the evaporation unit into the calibrated dispenser. The dispenser is used to aliquot the requisite predetermined quantity of radium-224 to the cation exchange column in which is generated the radionuclides of bismuth-212 and lead-212. This is accomplished by applying 0.1 psi of air pressure to the dispenser transferring the solution to the cation exchange column. After an air purge of the cation exchange column and its associated tubing, the cation exchange column is manually disconnected from the closed portion of the system, and its mating Luer fittings at each end are secured together to minimize radon leakage. It is then inserted into a shielded shipping pot for distribution to the user. The next cation exchange column is mounted and the cycle of dispensing radium-224 is repeated for the desired predetermined number of times. The operational range of the above-described accessible portion 14 is capable of providing output radionuclide quantities in the range of twenty to fifty millicuries for each batch, and the apparatus can be enlarged to provide greater quantities if desirable. The thorium-228 adsorbed on the anion exchange column should also be desorbed and returned to the supply container to minimize radiation damage effects and to recycle material to begin production again. This process can be carried out concurrently with the loading of the cation exchange column described above. A 10 milliliter water wash will remove about 85-90% of the thorium-228 from the cation exchange column. An additional 10 milliliter wash of 6 molar HCl will desorb most of the remainder. The washings flow by gravity into the thorium-228 evaporation unit, and the thorium-228 solution is evaporated to dryness in the same manner as the radium-224 solution. The dried salt of thorium-228 is dissolved in 5 milliliters of 8 molar HNO.sub.3, and five psi of air pressure moves the thorium-228 solution back to the supply container. The used anion exchange column is normally discarded, and before commencing the next production cycle the system is left in an "idle" state to replenish the radium-224 removed in the production process. In this idle condition the radiation heating of the thorium-228 and daughter material in the supply container will evaporate the HNO.sub.3 solution. Although the present invention is described in terms of specific process steps, components and materials, it will be clear that various modifications within the skill of the art may be made within the scope of the following claims. Various features of the invention are set forth in the following claims.
051456354	summary	FIELD OF THE INVENTION This invention relates to nuclear fuel assemblies and nuclear reactors. In particular, it is concerned with light water cooled, light water moderated reactors, having a high conversion ratio of fertile to fissile substances with uranium-plutonium mixed fuel. BACKGROUND OF THE INVENTION In a nuclear reactor, fissile substances such as uranium-235 are consumed by a fission reaction, new fissile substances such as plutonium-239 being yielded as uranium-238 undergoes neutron absorption. The conversion ratio of the reactor is the ratio, at the time of unloading a spent fuel assembly, of the amount of fissile substance yielded to the amount of fissile substance consumed. In a conventional light water cooled and moderated reactor the conversion ratio is about 0.5. With the general aim of conserving uranium resources, recently there has been interest in increasing the conversion ratio of reactors. In particular, recently published JP-A-1/227993 discloses a fuel assembly construction designed to achieve a conversion ratio approaching unity. The fuel assembly comprises an array of fuel rods arranged in a particularly dense configuration so that the effective volume ratio of water to fuel, as an average over the assembly, is not more than 0.4. The reactor is a boiling water reactor. So, this densely-packed fuel assembly construction will provide for recovery of nearly as much plutonium-239 etc. as the amount of fissile substance (uranium-235, plutonium-239) consumed. The recovered plutonium can be used to enrich uranium from any suitable source, and this can be burned in a nuclear reactor. In a reactor, however, there are many factors other than conversion ratio which are important. In particular, reactors must be safe not only during normal operation but also should some abnormal transient condition arise. In a conventional boiling water reactor, the effective volume ratio of water to fuel is usually about 2.0; much higher than in JP-A-1/227993. With a soft neutron spectrum, the void coefficient of uranium-plutonium mixed fuel (void coefficient=change of reactivity with change of void fraction of coolant) is much less (more negative) than the corresponding void coefficient for an enriched uranium fuel. When the fuel rod configuration is made more dense to raise the conversion ratio, as disclosed in JP-A-1/227993, we observe that the void coefficient of uranium-plutonium mixed fuel tends to increase and approach positive values. Indeed, the prior art core having effective water to fuel volume ratio of 0.4 has a positive void coefficient. This has important implications as regards safety. The safety of a reactor in the event of some abnormal transient or accident can be assessed with reference to a power coefficient. The power coefficient is the rate of reactivity change with unit power change, and is expressed as a sum of the void coefficient and a Doppler coefficient which is a component indicating reactivity change with temperature. In fact, the particular construction described in JP-A-1/227993 does have a negative power coefficient and hence is safe in principle, because the Doppler coefficient is sufficiently negative to compensate for the positive value of the void coefficient. For increased control of safety, however, it would be desirable not to have to rely on the Doppler coefficient, but to be able to reduce (i.e. make less positive or more negative) the void coefficient contribution to the power coefficient. It is known that void coefficient of a reactor core can be kept down by constructing the core so that electrons can leak easily, since void coefficient in a core depends on a sum of the changes of neutron infinite multiplication factor and neutron leakage value. Leakage of neutrons can suppress neutron infinite multiplication factor since although increased void fraction increases the number of neutrons in the core, it also increases the amount of leakage. However, a core which allows neutrons to leak easily has serious disadvantages, namely a lowering of reactivity with the leakage of neutrons at steady state. SUMMARY OF THE INVENTION In view of the above, it is a primary object herein to enable a high conversion water reactor using uranium-plutonium mixed oxide fuel to have a power coefficient commensurate with safety, and preferably improved safety, without a disadvantageous loss in reactivity. This is a new object which we have perceived in relation to these new, high conversion reactors. To achieve this object would contribute to the practical usefulness of a high conversion reactor. According to the invention, surprisingly we can reduce the void coefficient by using a fuel assembly comprising a plurality of uranium-plutonium mixed oxide fuel rods extending axially between a water coolant intake end (upstream) and a water coolant discharge end (downstream), the rods being densely packed to give a high conversion ratio, and in which the plutonium enrichment is axially non-uniform in an effective fuel region of the assembly, such that an upstream half of the effective fuel region has a higher average plutonium enrichment than the corresponding enrichment in the downstream half. In other aspects, the invention provides a reactor core consisting of a plurality of such fuel assemblies, a nuclear reactor loaded with the assemblies, and a method of operating such a reactor at a high conversion ratio. It should be noted that the invention applies only to high conversion reactors, in particular to those which operate with an effective water to fuel volume ratio which is usually less than 1.5 and most preferably 0.4 or less. Operating such a reactor is desirably so as to achieve a conversion ratio of at least 0.6, more preferably greater than 0.8 and most preferably about 1.0. The difference in average plutonium enrichment between the upstream and downstream halves of the effective fuel region should be at least 0.05% but usually less than 1.5%; a larger void coefficient reduction may be obtained in the range of 0.1 to 1.1% enrichment difference. The overall average plutonium enrichment in the effective fuel region is not usually more than about 10% by weight. The fuel region should preferably contain uranium-plutonium mixed oxide fuel for substantially its entire axial extent so that a good output is achieved. The effect achieved by the invention is a surprising one. In the prior art, a fuel assembly having a non-uniformity of plutonium enrichment has already been disclosed in JP-A-60/66187. This is a conventional, low-conversion reactor in which the fuel rods of the assembly are not densely packed. These fuel rods have a downstream portion of uranium fuel, and an upstream portion--which may be as much as two-thirds of the fuel region--of plutonium-uranium mixed oxide fuel. Consequently, the average enrichment of plutonium is greater upstream. However, in JP-A-60/66187 the higher upstream plutonium enrichment is disclosed as increasing the void coefficient of the reactor which, though perfectly safe, has a void coefficient so low as to be inadequate. The effective volume ratio of water to fuel in this prior art document is the conventional value; about 2.0. The present inventors have discovered that in a high conversion reactor, where the fuel rods are relatively densely packed, quite the opposite effect can be achieved. That is, by having a higher plutonium enrichment at the upstream half a void coefficient which otherwise might be dangerously high can be reduced. This is based on the appreciation that, when fuel rods are densely packed and the reactor is operated at a low effective water:fuel volume ratio e.g. less than 0.4, the fuel gives a positive void coefficient all over the range of voids fraction; fuel of lower plutonium enrichment gives a smaller void coefficient than a highly enriched fuel at the same degree of burn-up and, for a given plutonium enrichment, a larger void coefficient is achieved for a fuel operating at a higher burning average void fraction. By reducing the relative enrichment in the upper region where the void fraction is high, the contribution of this upper region to void coefficient can be reduced. Relatively high enrichment in the lower region, however, contributes less seriously to void coefficient while maintaining good reactivity. These effects will be described below in more detail. The fuel assembly may have portions of relatively low enrichment at both ends of the effective fuel region. These can increase the overall reactivity by limiting the large neutron infinite multiplication factor towards the central part of the effective fuel region, where the contribution to reactivity is large. Preferred aspects of the invention provide particular distribution patterns for regions of uniform enrichment in the axial dimension, which provide variously for different effects on the void coefficient, ease of construction, good reactivity etc. according to choice. Fuel assemblies embodying the invention are constructed so as to operate at high conversion ratios. To achieve the necessary low effective water:fuel volume ratio in operation, the geometrical coolant space:fuel volume ratio will also generally be substantially smaller than conventional. For example, it may be less than 1.5, more particularly less than 1.0.
043222684	claims	1. In a gas-cooled nuclear reactor having a reactor vessel defining a reactor core, at least one primary cooling loop including a primary flow conduit communicating with said core and having primary circulator means adapted to effect flow of coolant through said core, and at least one auxiliary cooling loop including an auxiliary flow conduit communicating with said core and having auxiliary circulator means selectively operable to effect flow of coolant through said core, the improvement wherein said primary and auxiliary flow conduits are axially aligned and defined by a common penetration in said reactor vessel, and including a common flow return duct communicating with said core and intersecting said common penetration to form a common junction with said primary and auxiliary flow conduits so that coolant flow through either of said primary and auxiliary flow conduits is returned to said core through said common flow return duct, said primary and auxiliary circulator means being mounted within said common penetration so as to facilitate selective circulation of flow through said primary and auxiliary cooling loops, and flow diverter means located within said common junction and adapted for selective operation between a first mode operative to effect coolant circulation through only said primary cooling loop and a second mode operative to effect coolant circulation through only said auxiliary cooling loop. 2. The combination as defined in claim 1 wherein said flow diverter means includes a diverter plate moveable between first and second positions to establish said first and second modes of operation. 3. The combination as defined in claim 1 wherein said flow diverter means comprises a flow diverter valve mounted within the reactor at said common junction, said diverter valve including a diverter valve plate rotatably mounted within said common junction for movement between a first position facilitating flow of coolant from said core through said primary cooling loop while isolating said auxiliary cooling loop to prevent flow therethrough, and a second position facilitating flow of coolant from said core through said auxiliary cooling loop while isolating said primary coolant loop to prevent flow therethrough. 4. The combination as defined in claim 3 wherein said diverter valve plate is mounted for rotation about an axis coincident with the axis of said common flow return duct. 5. The combination as defined in claim 4 including linear actuator means operatively associated with said diverter valve plate for effecting selective movement thereof between its said first and second positions. 6. The combination as defined in claim 4 including an actuating shaft secured to said diverter valve plate coaxially with its axis of rotation, and actuator means operatively associated with said actuating shaft for effecting selective rotation of said diverter valve plate through approximately 180 degrees rotation between said first and second positions. 7. The combination of claim 6 wherein said diverter valve plate has a configuration approximating one-half a quarter segment of a sphere.
	abstract	A system for storing high level radioactive waste. In one embodiment, the invention can be a system comprising an overpack body extending along a vertical axis and having a cavity for storing high level radioactive waste, the cavity having an open top end and a floor; an overpack lid positioned atop the overpack body to enclose the open top end of the cavity; an air inlet vent for introducing cool air into the cavity, the air inlet vent extending from an opening in an outer surface of the overpack body to an opening in the floor; and an air outlet vent in the overpack lid for removing warmed air from the cavity.
	description	FIG. 1 is a sectional view, with parts cut away, of a boiling water nuclear reactor pressure vessel (RPV) 10. RPV 10 has a generally cylindrical shape and is closed at one end by a bottom head 12 and at its other end by a removable top head 14. A side wall 16 extends from bottom head 12 to top head 14. A cylindrically shaped core shroud 20 surrounds a reactor core 22. Shroud 20 is supported at one end by a shroud support 24 and includes a removable shroud head 26 at the other end. An annulus 28 is formed between shroud 20 and side wall 16. Heat is generated within core 22, which includes fuel bundles 36 of fissionable material. Water circulated up through core 22 is at least partially converted to steam. Steam separators 38 separates steam from water, which is recirculated. Residual water is removed from the steam by steam dryers 40. The steam exits RPV 10 through a steam outlet 42 near vessel top head 14. The amount of heat generated in core 22 is regulated by inserting and withdrawing control rods 44 of neutron absorbing material, such as for example, hafnium. To the extent that control rod 44 is inserted into fuel bundle 36, it absorbs neutrons that would otherwise be available to promote the chain reaction which generates heat in core 22. Control rod guide tubes 46 maintain the vertical motion of control rods 44 during insertion and withdrawal. Control rod drives 48 effect the insertion and withdrawal of control rods 44. Control rod drives 48 extend through bottom head 12. Fuel bundles 36 are aligned by a core plate assembly 50 located at the base of core 22. A top guide 52 aligns fuel bundles 36 as they are lowered into core 22. Core plate 50 and top guide 52 are supported by core shroud 20. Fuel bundles 36 have a substantially square cross section. In alternative embodiments, fuel bundles can have a rectangular or other polygon cross section. FIG. 2 is a top schematic view of an F-lattice configuration of core 22 of reactor pressure vessel 10. Substantially standard size fuel bundles 36 and large control rods 44 are utilized in core 22. Each large control rod 44 is sized to provide poison control for sixteen conventional size fuel bundles 36. Conventional size fuel assemblies 36 and large control rods 44 are arranged in an F-lattice configuration 54 to facilitate minimizing the number of control rod drives and control rods. F-lattice configuration 54 has large control rods 44 in staggered rows 56 with sixteen conventional fuel bundles 36 surrounding each large control rod 44. FIG. 3 is a top schematic view of core plate assembly 50 for F-lattice core configuration 54, and FIG. 4 is a top sectional schematic view of core plate assembly 50. Referring to FIGS. 3 and 4, core plate assembly 50 includes a flat plate 58 supported by a plurality of support beams 60. Flat plate 58 includes a plurality of control rod guide tube openings 62 sized to receive cruciform shaped control rod guide tubes 46. Each guide tube opening 62 has a cruciform shape and includes slots 64, 66, 68, and 70 extending radially from a central portion 72 at right angles to each other. Slots 64, 66, 68, and 70 define four fuel bundle receiving areas 74. Core plate assembly 50 also includes four fuel bundle supports 76 located in each fuel bundle receiving area 74. Each fuel bundle support 76 extends through flat plate 58 and includes a coolant flow outlet 78. FIG. 5 is a sectional side view of a known fuel bundle support 80 extending through a core plate 82. Fuel support 80 includes a coolant flow inlet 84 and a coolant flow outlet 86. A bore 88 extends from inlet 84 to outlet 86. An orifice plate 90 is located inside bore 88. Coolant flows into flow inlet 84, through bore 88 and flow outlet 86 and into fuel bundle 36. Coolant flow inlet 84 and coolant flow outlet 86 are coaxial and centerline 92 passes through the center of both inlet 84 and outlet 86. Coolant flow outlet 86 is configured to receive a lower tie plate 94 of a fuel bundle 36. Because of the geometry of F-lattice core configuration 54, a core plate support beam 96 obstructs coolant flow inlet 84 of about 50% of fuel bundle supports 80 located on core plate 82. The obstruction of flow inlet 84 caused by support beam 96 can create flow separation and bi-stable flow which can influence the coolant flow pattern at both coolant flow inlet 84 and within fuel bundle 36. FIG. 6 is a sectional side view of a fuel bundle support 98, in accordance with an embodiment of the present invention, extending through flat plate 58 of core plate assembly 50. Fuel support 98 includes a coolant flow inlet 100, a coolant flow outlet 102 sized to receive lower tie plate 94 of a fuel bundle 36. A coolant flow bore 104 extends between coolant flow inlet 100 and coolant flow outlet 102. Coolant flow inlet 100 is offset from coolant flow outlet 102 so that a centerline 106 of coolant flow inlet 100 is parallel to a centerline 108 of coolant flow outlet 102. Coolant flow inlet 100 includes an orifice plate 110. Coolant flow inlet 100 is positioned adjacent to a support beam 60 of core plate assembly 50. FIG. 7 is a top schematic view of core plate assembly 50. Core plate assembly 50 includes a plurality of fuel bundle supports 98 and a plurality of cruciform shaped control rod guide tube openings 62 arranged in an F-lattice core configuration 54. Four fuel bundle supports 98 are located in each fuel bundle receiving area 74. Because of the offset configuration of coolant flow inlet 100 and coolant flow outlet 102 in fuel bundle supports 98, each coolant flow inlet 100 is positioned adjacent a core plate support beam 60, and therefore, there are no obstructions of coolant flow inlets 100. FIG. 8 is a top schematic view of a core plate assembly 112 that includes a plurality fuel bundle supports 114 in accordance with another embodiment of the present invention. FIG. 9 is an enlarged top view of fuel bundle support 114, and FIG. 10 is a cross sectional view of fuel bundle support 114 through line Axe2x80x94A. Core plate assembly 112, similar to core plate assembly 50 described above, includes a flat plate 116 supported by a plurality of support beams 118, a plurality of control rod guide tube openings 120, and a plurality of fuel bundle receiving areas 122. Each fuel bundle support 114 supports four fuel bundles 36 (see FIG. 6) and includes four coolant flow inlets 124 and four coolant flow outlets 126. Each fuel bundle receiving area 122 contains one fuel bundle support 114. Each coolant flow inlet 124 has a corresponding coolant flow outlet 126 and a bore 128 extending from coolant flow inlet 124 to corresponding coolant flow outlet 126. Coolant flow inlet 124 is offset from corresponding coolant flow outlet 126 so that a centerline 130 of coolant flow inlet 124 is parallel to a centerline 132 of corresponding coolant flow outlet 128. An orifice plate 134 is located in each coolant flow inlet 124. Additionally, coolant flow inlets 124 are located in fuel bundle support 114 so that each coolant flow inlet 124 is the same distance from a support beam 118. Particularly, a distance xe2x80x9cBxe2x80x9d from coolant flow inlet 124 is the same for all coolant flow inlets 124 in fuel bundle support 114. The above described core plate assembly 50 with fuel bundle supports 98 and core plate assembly 112 with fuel supports 114 provide unobstructed coolant flow inlets and therefore identical flow entrance conditions for all fuel assemblies 36. FIG. 11 is a top schematic view of a core plate assembly 136 that includes a plurality fuel bundle supports 138 in accordance with another embodiment of the present invention. Core plate assembly 136, similar to core plate assembly 112 described above, includes a flat plate 140 supported by a plurality of support beams 142, a plurality of control rod guide tube openings 144, and a plurality of fuel bundle receiving areas 146. Each fuel bundle receiving area 146 includes one fuel bundle support 138, and each fuel bundle support is configured to support one large fuel bundle (not shown). Each large fuel bundle is approximately 1.5 times the size of a standard fuel bundle 36. Fuel support 138 includes a coolant flow inlet 148 and a coolant flow outlet 150. A coolant flow bore (not shown) extends between coolant flow inlet 148 and coolant flow outlet 150. Coolant flow inlet 148 is offset from coolant flow outlet 150. Coolant flow inlet 148 is positioned adjacent to a support beam 142 of core plate assembly 136. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
	abstract	A multilayer mirror having a cap with a multilayer structure including a top layer and a series of bilayers each having an absorber layer and a spacer layer, where the materials for the top layer, absorber layers, and spacer layers are chosen to resist blistering.
	description	This application relates to U.S. patent application Ser. No. 15/147,565, filed on May 5, 2016, the disclosure of which is incorporated by reference herein in its entirety. The present disclosure generally relates to design and making method of a neutron generating target which can be used in boron neutron capture therapy. Neutron sources have many potential applications, including medical treatments, isotope production, explosive/fissile materials detection, assaying of precious metal ores, imaging, and others. A particular area of interest is boron neutron capture therapy (BNCT), which is a cancer treatment technique in which boron is preferentially concentrated in a patient's malignant tumor and a neutron beam is aimed through the patient at the boron-containing tumor. When the boron atoms capture a neutron, particles are produced having sufficient energy to cause severe damage to the tissue in which it is present. The effect is highly localized, and, as a result, this technique can be used as a highly selective cancer treatment method, effecting only specifically targeted cells. Many activities employing neutron sources are presently carried out at nuclear research reactors where neutrons are plentiful. However, many practical issues such as safety, nuclear materials handling, and the approach of end-of life and decommissioning of many research reactors make this approach challenging. Accelerator-based neutron sources can be used as a relatively low-cost, compact alternative. For example, a small, relatively inexpensive linear accelerator can be used to accelerate ions, such as protons, which can then be focused on a target capable of generating neutrons. The present disclosure relates to a method for making a neutron generating target. The method can include modifying a surface of a target substrate to form one or more surface features. The method can also include disposing a neutron source layer on the surface of the target substrate. In some embodiments, the method can include a material removal process or a material addition process. The material removal process can include abrasive blasting, etching, or polishing. The material addition process can include vacuum deposition, plating, or printing. In some embodiments, the target substrate can include at least one of copper, aluminum, titanium, molybdenum, and stainless steel. The neutron source layer can include at least one of lithium, beryllium, and carbon. In some embodiments, the neutron source layer can be pressed on the surface of the target substrate. In some embodiments, the neutron source layer can be deposited on the surface of the target substrate by evaporation. In some embodiments, the method can include heating the neutron source layer and the target substrate to an elevated temperature for a duration of time for form a bond between the neutron source layer and the target substrate. In some embodiments, the elevated temperature can be between about 100 degrees Celsius and about 500 degrees Celsius. In some embodiments, the duration of time can be between about 0.1 hours and 10 hours. In some embodiments, the method can also include modifying a top surface of the neutron source layer to form one or more surface features. The present disclosure also relates to a neutron generating target. The target can include a target substrate having an uneven surface. The uneven surface can include one or more surface features. The target can also include a neutron source layer disposed on the surface of the target substrate and bonded to the target substrate. In some embodiments, the one or more surface features can be recessed into the target substrate. The one or more surface features can have a depth of between about 1 micron and about 50 microns. In some embodiments, the one or more surface features can protrude from the target substrate. The one or more surface features can have a height of between about 1 micron and about 50 microns. In some embodiments, the one or more surface features can include a plurality of surface features with an average pitch of between about 1 micron and about 50 microns. In some embodiments, the target substrate can include at least one of copper, aluminum, titanium, molybdenum, and stainless steel. The neutron source layer can include at least one of lithium, beryllium, and carbon. In some embodiments, the neutron source layer can have a thickness of between about 10 microns and about 500 microns. The present disclosure relates to design and manufacture method of a neutron generating target which can be used in boron neutron capture therapy (BNCT). BNCT is a targeted radiation therapy for cancer treatment during which a patient is infused with a boron rich solution such as fructose-BPA. The boron is then selectively absorbed by the cancer cells, e.g., at a tumor site. Neutrons, for example, generated by a lithium neutron source, interact with the boron by the nuclear reaction: 10B+nth→[11B]*α+Li+2.31 MeV. By irradiating the patient's tumor site with a flux of epithermal neutrons, which thermalize near the tumor site, the cancer cells are killed by the alpha particles and lithium ions. The alpha particles and lithium ions released have very short ranges, for example about 5-9 microns, and thus are similar in size to a cancer cell. BNCT treatment requires a high flux of epithermal neutrons, typically between 1 eV and 10 keV. Fluxes required for clinical treatments are on the order of 1×109 n/cm2/s. Historically, BNCT treatments have been performed at nuclear research reactor facilities, however accelerator-based neutron sources are preferred for widespread implementation of the treatment in hospital environments. To produce the appropriate level of neutron flux using an accelerator, several nuclear reactions have been proposed. One of the most promising reactions is the 7Li(p,n)→7Be reaction. This reaction has a high neutron yield and produces neutrons of modest energy, both conditions being desirable for many applications. The neutron flux produced by this reaction is desirable for BNCT, for example because the flux can be easily moderated to epithermal neutrons without many high energy neutrons. To accomplish this reaction with an accelerator-based neutron source, a target bearing a source material (e.g., lithium) is presented to a proton beam generated by the proton accelerator. Neutrons are emitted from the source material and may be moderated and collimated by a beam shaping assembly into the desired neutron “beam” for treatment. The proton beam size can be of comparable size or smaller size than the neutron beam at the exit of the beam shaping assembly. For example, the proton beam size can be between about 20 mm and about 150 mm. There are two general approaches to the lithium P,N reaction for BNCT: “near threshold,” where the proton beam energy is about 1.9 MeV, and “above threshold,” where the proton beam energy is about 2.5 MeV. The “near threshold” approach has the advantage that the neutron energy distribution from the target is close to the epithermal energy distribution for treatment, thus only minimal moderation can be used. The “above threshold” approach produces a higher energy distribution of neutrons, and therefore can use more moderation, but takes advantage of a large peak in the reaction cross section at about 2.3 MeV resulting in a much higher initial yield of neutrons. Embodiments of the present disclosure overcome the neutron generation system issues described above using a direct-cooled, modularized rotating target architecture approach. For example, in some embodiments, a rotatable structure such as a disk or a drum includes a plurality of segmented target “petals” (also referred to herein as “segments”) attached to a central hub (also referred to herein as a “rotary fixture”), where each petal is directly cooled via its own dedicated micro-channels. The plurality of target petals, collectively, may be said to constitute a target. Each petal can include a substrate and a solid neutron source layer disposed on a surface of the substrate. An exemplary system includes 16 petals on a planar rotatable structure, each petal occupying 22.5 degrees of a circumference of the rotatable structure, with the rotatable structure having an outer diameter (OD) of about 1 meter, and a semi-continuous strip of lithium deposited on the petals 0.14 meters in the radial direction centered on a 0.84 meter diameter. FIG. 1A is a block diagram of an apparatus suitable for use in BNCT, in accordance with some embodiments of the present disclosure. As shown in FIG. 1A, a rotatable structure 102 includes a plurality of target petals or segments 104A-104D, and each segment of the plurality of segments 104A-104D has a corresponding substrate 106A-106D coupled to a corresponding neutron source layer 108A-108D. The neutron source layer(s) 108A-108D can include solid lithium. One or more of the substrates 106A-106D includes a corresponding coolant channel (110A-110D), such as a micro-channel, for actively cooling the associated substrate and/or neutron source layer (e.g., to maintain the neutron source layer 108A-108D in solid form). The segments 104A-104D are optionally coupled to a rotary fixture 112 having an inlet 112A and an outlet 112B for conducting a coolant fluid. The segments 104A-104D can be coupled to the rotary fixture 112 via one or more of: screws, bolts, quick-disconnect fittings, clamps, and/or the like. The coolant fluid can include one or more of: water (e.g., deionized water, which provides higher heat capacity and thermal conductivity than oils, and lower corrosive activity as compared with city water), glycol, a glycol/water mixture, heat transfer oils (e.g., to avoid possible water/lithium interaction during a failure), “Galinstan” (a commercial liquid gallium/indium/tin mixture), liquid nitrogen, and/or other coolants. The rotary fixture 112 can be configured to couple to an external spindle assembly and/or drive motor via a coupling such as a rotary water seal and/or a rotary vacuum seal. When the segments 104A-104D are connected to the rotary fixture 112, the coolant channels 110A-110D may be in sealed fluid communication with the inlet 112A and outlet 112B of the rotary fixture 112. FIG. 1A also depicts a proton beam generator 113 and a proton beam 113A. Each segment of the segments 104A-104D can have a shape that is one of: a portion of an annulus, a pie-shape or “sector” (defined as the plane figure enclosed by two radii of a circle or ellipse and the arc between them), a truncated sector (i.e., a portion of a sector), a square, and a rectangle. The neutron source layer 108A-108D can include lithium, beryllium, or another suitable neutron source in solid form and at a thickness that is sufficient to produce the desired neutron flux, for example for lithium at least about 10 μm, or at least about 90 μm (e.g., about 400 μm), or between about 10 μm and about 200 μm, or between about 90 μm and about 150 μm. The neutron source layer 108A-108D can be adhered to the substrates 106A-106D of the segments 104A-104D via a thermal bond. For example, in some embodiments, one or more of the substrates 106A-106D include copper, and a lithium neutron source layer 108A-108D is bonded to the one or more copper substrates 106A-106D via a pressure and temperature method. As lithium is a reactive metal, it can form an amalgam with the copper. When properly bonded, a low thermal resistance between the copper and the lithium is formed. At such thicknesses of the neutron source layer(s) 108A-108D, the protons are deposited in the lithium during use, as opposed to the copper that underlies the lithium. In some cases, there is no drop in neutron yield up to doses of 1×1019 ions/cm2, and it can be expected that doses of 1×1020 ions/cm2 and beyond are possible. The neutron source layer 108A-108D can change during irradiation, for example becoming more brittle and/or different in color, however as long as it remains intact and produces the same or nearly the same neutron yield, it is suitable for use. Alternatively or in addition, the neutron source layer 108A-108D can be evaporated onto the substrates 106A-106D in a thin layer, for example of about 100 microns. A very thin, blister-resistant middle layer can be included in such designs as well (as has done in the stationary targets, described above). The base petal or substrate can be made of copper or aluminum. Even materials such as stainless steel, titanium, and molybdenum are possible since the distributed heat power is so much lower than in the stationary case. FIG. 1B is a diagram of a plan view of a disk-shaped rotatable structure, in accordance with some embodiments. As shown, the rotatable structure 102 has a central hub portion “H” with a plurality of segments 104 attached thereto and emanating therefrom. The segments 104 each include a corresponding neutron source layer with a major surface that can be, for example, substantially normal to an axis of rotation of the rotatable structure 102. The axis of rotation may be defined as an axis that passes through the center of the hub “H” and is substantially normal thereto. FIG. 1C is a diagram showing a cross-sectional view of the rotatable structure of FIG. 1B, corresponding to line A-A′ of FIG. 1B. As shown in FIG. 1C, a neutron source layer 108 is disposed on a substrate 106 with an embedded coolant channel 110. FIG. 1D is a diagram of the rotatable structure of FIG. 1B during use as part of boron neutron capture therapy (BNCT), in accordance with some embodiments. As shown, the rotatable structure 102 is rotating about its axis of rotation, and a proton beam generator 113 emits a proton beam 113 toward the rotatable structure 102 such that the proton beam 113A contacts a surface of the rotatable structure 102, e.g., at a neutron source layer of a segment 104. The proton beam 113A can be stationary (e.g., at a predetermined position) or rastering over a predetermined region of the rotatable structure 102, where the predetermined region may be fixed or may change over time. The proton beam 113A can form an angle with the contacting surface of the rotatable structure 102, for example of about 90.degree. Since the rotatable structure 102 is rotating, segments 104 of the rotatable structure 102 can be sequentially contacted by the proton beam 113A. As a result of the interaction of the proton beam 113A with the neutron source layer of segment(s) 104, a neutron beam 113B is generated and directed (e.g., via a collimator or other beam-shaping structure) towards a treatment area of a patient P. One major failure mode of the neutron generating target in the art is hydrogen impregnation within the target. The hydrogen deposited in the target may damage the target materials, cause blistering of the target, limit the lifetime of the target, and necessitate servicing of the target prior to failure. Blistering is material damage (e.g., delamination, exfoliation, bubble, etc.) in the target due to internal hydrogen pressure exceeding the strength of the target material. When the proton beam hits the target, the depth where the protons stop depends on the energy of the proton and the neutron source material. For example, in a target with a thick lithium neutron source layer (about 400 μm) bonded to a copper substrate, a 2.6 MeV proton beam may be stopped in the lithium layer. Instead, if a thinner lithium neutron source layer (between about 100 μm and about 200 μm) is used, the proton beam may be stopped in the copper layer. When the hydrogen concentration reached a point where internal pressure exceeds the strength of the material, a blistering might happen. The blistering can happen in the lithium layer or in the copper layer. The present disclosure provides a target design which significantly reduces target blistering failure. In the target used in the art, the surface of the target substrate is substantially flat and neutron source materials are bonded on the top surface of the target substrate. Protons with similar energies will stop in the target at a same depth. As a result, hydrogen concentration may become high at this depth and lead to target damage. The present disclosure shows a different target design where the surface of the target substrate is modified. In some embodiment, the target substrate can be copper, aluminum, titanium, stainless steel, or other metals. The goal of the surface modification is to increase the roughness of the target substrate. In some embodiments, the target substrate can be modified with a material removal process. For example, the substrate can be modified with abrasive blasting. Different blasting media can be used in accordance with roughness requirements and substrate materials. In some embodiments, the blasting media can be sand, silicon dioxide, metal shot, etc. The substrate can also be modified by etching or polishing. In some embodiments, the target substrate can also be modified with a material addition process. For example, a thin layer of material can be added to the target substrate surface by vacuum deposition, plating, printing, or other techniques. In some embodiments, the material to be added can be copper, aluminum, titanium, stainless steel, or other metals. The roughness or features created on the substrate surface can be periodic or non-periodic. In some embodiments, the average pitch of the features can be between about 1 μm and about 10 μm. The depth/height of the features can be between about 5 μm and about 20 μm. FIGS. 2A-2B shows cross-section views of targets according to some embodiments of the present disclosure. As shown in FIG. 2A, target substrate 202 can be modified to have periodic surface features with a fixed pitch. As shown in FIG. 2B, target substrate 205 can be modified to have non-periodic surface features. The average pitch of the surface features can be between 1 μm and 10 μm. The height of the surface features can be between 5 μm and 20 μm. After the surface is modified, the target substrate can be cleaned thoroughly to remove any debris. Then a neutron source layer can be disposed on the target substrate. The neutron source layer can be lithium, beryllium, graphite (carbon), or other materials, depending on different neutron producing reactions. The neutron source layer can be disposed onto the target substrate surface by pressing, evaporation, or other methods, to make sure the neutron source layer has a close contact with the target substrate surface. For example, lithium can be pressed onto the substrate. In some embodiments, the thickness of the lithium layer can be about 100 μm to about 200 μm for a neutron producing reaction with a proton energy of between about 2 MeV and about 3 MeV. Next the assembly of target substrate and neutron source layer can be heated to an elevated temperature. The heating can be performed with a hot-plate, a thermal chamber, or other equipment which can provide heating power. To maintain the purity of the neutron source layer and prevent any unwanted reactions, the heating can be performed in an inert environment, such as in an argon filled glove-box. The heating temperature and time duration can differ depending on the substrate material and the neutron source material. For example, for a target with lithium on a copper substrate, heating for 4 hours at 200° C. can form a good thermal and mechanical bond between the lithium and the copper. The lithium can form an amalgam with the copper, resulting in a low thermal resistance. In some embodiments, the heating procedure may not be necessary. For example, if the lithium neutron source layer is deposited on the target substrate by evaporation, the heating can be skipped because there can be a good bond between the lithium and the target substrate formed during the deposition. Referring to FIG. 2A, a neutron source layer 203 can be disposed on the surface of target substrate 202. The whole target assembly 201 can be heated to an elevated temperature to form a good bond between the neutron source layer 203 and target substrate 202. As shown in FIG. 2B, Then a neutron source layer 206 can be disposed on the surface of target substrate 205 and the whole target assembly 204 can be heated to an elevated temperature to form a good bond between the neutron source layer 206 and target substrate 205. An advantage of the target design with substrate surface modification described herein over the existing design in the art is that protons will not stop in the target uniformly because of the roughness of the substrate. As a result, the hydrogen will not be concentrated at a same depth. This design can reduce blistering and material exfoliation in the target. FIG. 3 shows a flow chart describing a neutron generating target making method 300 according to some embodiments of the present disclosure. The method 300 starts with step 301 where a surface of a target substrate can be modified, either by a material removal process or a material addition process. In some embodiments, the material removal process can include abrasive blasting, etching, or polishing. In some embodiments, the material addition process can include vacuum deposition, plating, or printing. In step 302, a neutron source layer can be disposed on the surface of the target substrate by pressing, evaporation, or other techniques. Then in step 303, the whole assembly of the neutron source layer and the target substrate can be heated to an elevated temperature for a duration of time to form a good thermal and mechanical bond. FIG. 4 shows a flow chart describing a neutron generating target making method 400 according to some embodiments of the present disclosure. The method 400 starts with step 401 where a neutron source layer can be disposed on a target substrate. In some embodiments, the neutron source layer can be pressed onto the target substrate. In some embodiments, the neutron source layer can be deposited on the target substrate by evaporation. In step 402, the neutron source layer can be bonded to the target substrate. For example, if the neutron source layer is pressed onto the target substrate, the neutron source layer and the target substrate can be heated to an elevated temperature for a duration of time to form a bond. If the neutron source layer is deposited by evaporation, the heating procedure can be skipped. In step 403, a top surface of the neutron source layer can be modified to form one or more surface features. In some embodiment, the modification can be a material removal process which can include abrasive blasting, etching, or polishing. In some embodiment, the modification can be a material addition process which can include vacuum deposition, plating, or printing. The method 400 can create roughness on the neutron source layer surface, which can lead to variations in stopping depth of the protons so that the hydrogen concentration can be reduced. As a result, target blistering can be prevented. The method and system described above for the 7Li(p,n)→7Be can be extended to other neutron producing reactions with other neutron producing materials. In addition to the “near threshold” approach using a 1.9 MeV proton beam and the “above threshold” approach using a 2.5 MeV proton beam on lithium, other reactions that have been proposed for BNCT include: 9Be(p,n) using a 4 MeV proton beam, 9Be(d,n) using a 1.5 MeV deuterium beam, and 13C(d,n) using a 1.5 MeV deuterium beam. To utilize these reactions, a solid sheet of beryllium could be thermally bonded to the petals in place of the lithium and bombarded with either 4 MeV protons or 1.5 MeV deuterons. In addition, the lithium could be replaced with thin sheets of graphite or carbon to produce neutrons using the 13C(d,n) reaction. A general schematic of an embodiment of the present BNCT system and method is shown in FIG. 5. For example, referring to FIG. 5, which is not drawn to scale, BNCT system 500 includes neutron generating system 550 and patient positioning and treatment system 580. Neutron generating system 550 includes proton beam generator 510 and neutron source target 520, which is provided on a rotatable structure (not shown). Any of the rotatable structures of the present disclosure and described above can be used. Proton beam generator 510 can be provided in a variety of different positions relative to neutron source target 520, depending upon, for example, the size and design of the facility in which they are placed. Various known bending or focusing magnets can be used to direct the generated proton beam to the target. Proton beam 590, produced by proton beam generator 510, passes through beam transport system 515, which may include, for example, various types of focusing magnets, and reacts with neutron source target 520, thereby generating neutrons, which are generally produced in multiple directions around the source depending on their energy—higher energy neutrons moving forward from the target and lower energy neutrons scattering perpendicular to or back from the source. To generate neutron beam 570 having the desired energy and direction for BNCT treatment, neutron generating system 550 further includes reflector 526, beam moderator 591, and beam collimator 592. Any neutron beam reflector, moderator, or beam collimator/delimiter known in the art can be used, and each can be positioned around the target as desired in order to capture neutrons having the desired energy range. For example, reflector 526 can be positioned around the sides and behind the target, as shown in FIG. 5, and can comprise any material known in the art that is relatively non-absorbent to neutrons, such as high atomic number material (including lead, bismuth, or alumina), or carbonaceous materials (including graphite). In this way, low energy back-scattered neutrons are reflected back into the system, thereby protecting or shielding surrounding components as well as patient 599. The forward-directed, relatively higher energy neutrons can be captured by moderator 591 (also comprising materials that are relatively non-absorbent to neutrons), in order to reduce their energy to a desired epithermal range. In this way, for example, neutrons having an initial energy of approximately 500 keV can be reduced to a final energy of from about 1 eV to about 10 keV, which is a range desirable for BNCT treatment. Suitable moderator materials are known in the art and include, for example, D2O, MgF, LiF, AlF3, Al, Teflon, and mixtures thereof. Finally, as shown, beam collimator 592 can be positioned after moderator 591 to produce and focus the desired neutron beam onto target 598 in patient 599. As shown in FIG. 5, BNCT system 500 further includes patient positioning and treatment system 580 which includes equipment and controls for delivering the neutron beam to the patient. For example, a boron delivery system and protocol are used in which the chosen boron-containing treating agent is delivered to patient 599 at the prescribed dose in order to produce target 598. Control systems are used to accurately position the target to coincide with expected neutron beam path, and such control systems would be known to one skilled in the art. Additional equipment and components can also be used as needed and would also be well known in the field. As used herein, the terms “about” and “approximately” generally mean plus or minus 10% of the value stated, e.g., a value of about 250 would include 225 to 275, and about 1,000 would include 900 to 1,100. The foregoing description of preferred embodiments of the present disclosure has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Modifications and variations are possible in light of the above teachings, or may be acquired from practice of the invention. The embodiments presented herein were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.
	abstract	An irradiation field limiting device includes a plurality of aperture leaves arranged in a thickness direction, a flexible linear member secured to a thick portion of the aperture leaf, a driver section which drives the linear member a specific amount, and the like. One end of the linear member is secured to an aperture leaf through a connection section tangentially to the outer arc of the aperture leaf, and the other end is connected with a slider provided in a driver section. The slider is connected with a driving source through a connection portion and moves along an axial direction of a drive shaft inserted into a base accompanying rotation of the drive shaft. A load accompanying the movement of the slider is directly transmitted to the linear member, and the aperture leaf is driven a specific amount due to the load.
044406738	abstract	A method of and an apparatus for the treatment of radioactive waste water from a nuclear electricity-generating power plant. The radioactive waste water containing soluble solids, usually boric acid, is concentrated by evaporation according to the invention to a solids concentration above that which will form a saturated solution at room temperature, whereupon the resulting concentrate is introduced into a storage vessel and cooled therein to room temperature. Solids precipitate and sediment in this vessel and water is decanted from the sediment and recycled to the evaporator where the process is repeated. The process allows the amount of waste in terms of the original material treated which must be stored for a given prolonged period, say between one half and three quarters of a year, for radioactive decay prior to packaging of the waste to be significantly reduced by comparison with earlier systems.
	description	The invention relates to gratings for X-ray differential phase-contrast imaging, a detector arrangement and X-ray system for generating phase-contrast images of an object and a method of phase-contrast imaging for examining an object of interest. Phase-contrast imaging with X-rays is used for example to enhance the contrast of low absorbing specimen compared to conventional amplitude contrast images. This allows to use less radiation applied to the object such as a patient. In order to be able to use the phase of a wave in relation with phase-contrast imaging the waves need to have a well-defined phase relation both in time and space. The temporal coherence can be provided by applying monochromatic X-ray radiation. Further, it is known to obtain X-rays with sufficient coherence from synchrotron sources. Since these methods are related to the disadvantage of higher costs and complexity, it is proposed in WO 2004/071298 A1 to provide an apparatus for generating a phase-contrast X-ray image comprising in an optical path an incoherent X-ray source, a first beam splitter grating, a second beam recombiner grating, an optical analyzer grating and an image detector. It has further recently been proposed to use higher X-ray energies in differential phase-contrast imaging (DPC). A severe obstacle in this translation is the production of phase gratings and absorption grating with high aspect ratios. If the Talbot distance of the first grating and thus the distance of the two gratings is kept constant, the aspect ratio R of the phase grating increases like E3/2, where E is the X-ray energy. The term Talbot refers to that in case of a laterally periodic wave distribution due to a diffraction grating, an image is repeated at regular distances away from the grating plane which regular distance is called the Talbot Length. The limit in aspect ratio R of state-of-the-art fabrication of gratings, for example made from silicon, is currently in the range of 15 to 20, depending on many factors like pitch (in a region of a few microns), surface roughness etc. It has shown that the range of usable energies for differential phase-contrast imaging currently ends about 30-40 keV. Hence, there may be a need to provide gratings with a high aspect ratio. According to an exemplary embodiment of the invention, a grating for X-ray differential phase-contrast imaging is provided, which grating comprises a first sub-grating and at least a second sub-grating. The sub-gratings each comprise a body structure with bars and gaps being arranged periodically with a pitch. The sub-gratings are arranged consecutively in the direction of the X-ray beam. Further, the sub-gratings are positioned displaced to each other perpendicularly to the X-ray beam. One of the advantages is that a grating is provided where the function is a combination of the sub-gratings. By distributing the function to a number of sub-gratings, the manufacture of the sub-gratings is facilitated. In an exemplary embodiment the projections of the sub-gratings result in an effective grating with a smaller effective pitch than the pitches of the sub-gratings. For example, in order to provide a grating with a determined effective pitch it is possible to provide two sub-gratings each sub-grating having a pitch with the double amount of the predetermined effective pitch of the grating. In other words, an equivalent grating consisting of only one grating would require much smaller gaps to provide the same aspect ratio as a grating according to the invention with a number of sub-gratings. The aspect ratio is defined by the height/width ratio of the gaps. The combination of the sub-gratings results in a grating with an aspect ratio being an effective combination of the aspect ratios of the sub-gratings. In an exemplary embodiment the sub-gratings have the same pitch. Thereby it is possible to provide one type of sub-grating, in other words it is only necessary to produce or manufacture a single type of sub-grating which is then added in form of a first and at least a second sub-grating to form the inventive grating. In a further exemplary embodiment, the pitch of one of the sub-gratings is a multiple of the pitch of another one of the sub-gratings. This provides the possibility to manufacture different sub-gratings according to, for example, constructional or otherwise aspects. For example, a first sub-grating with a medium pitch can be combined with a second and a third sub-grating having a larger pitch. The second and third gratings can have a pitch which is twice as large as the pitch of the first grating. In an example the first grating is arranged between the second and third grating formed a sort of sandwich. The effective grating has then an effective pitch which is for example half the amount of the pitch of the medium pitch of the first grating. Of course the second and third gratings are offset in relation both to each other and in relation to the pitch of the first grating. In another exemplary embodiment, the sub-gratings have an equal bars/gap ratio. In other words, the width of the gaps is the same as the width of the bars arranged in a row. For example, the bars/gap ratio (s/t) is about 1/1. This allows for an easy manufacturing process and provides for a positioning and displacement of the sub-gratings in relation to each other forming the inventive grating. In a further exemplary embodiment the offset of the displacement is a fraction of the pitch. In a further exemplary embodiment the offset of the displacement is half the pitch. In a further exemplary embodiment the offset of the displacement is a fraction of half the pitch. For example, a first and a second sub-grating having the same pitch and having a bars/gap ratio of 1/1 can be combined to form an effective grating with an effective pitch which is much smaller than the pitch of the sub-gratings. In a further exemplary embodiment, the effective grating is defined by the sidewalls in direction of the X-ray beam. That means, the pitch is defined by the edges of the bar in form of the sidewalls defining the gap. This results in an effective pitch which is for example, starting with sub-gratings having an equal pitch with a gap/bar ratio of 1/1, the effective pitch being a quarter of the pitch of the first or second sub-grating. For example, for sub-gratings with a bars/gap ratio (s/t) of about 1/1 the following results are given. In case the number of sub-gratings (n) is defined and the effective pitch, referenced by z, is also predetermined, the pitch of the sub-grating results from the following equation: a=2nz. Having thus prepared sub-gratings with calculated pitch, the two sub-gratings have to be positioned displaced to each other with the following offset: d=1/2 1/na = z. In a further exemplary embodiment, in cases where the bars/gap ratio (s/t) is smaller than 1, the following condition arises. In cases where the number of sub-gratings (n) and the effective pitch (z) is known and the width of the bars (s) equals the effective pitch (s=z), the pitch is as follows: a=2nz. Further, the sub-gratings have to be positioned displaced to each other with the following offset: d=1/na=2z. Further, it is noted that having calculated the pitch and knowing the bar width being the same size as the effective pitch, it is possible to determine the width of the gap. In case the width of the gap is still meaning an obstacle for manufacturing the sub-gratings, the number of sub-gratings can be increased thereby increasing the pitch which also results in a larger gap width suitable for manufacturing. In a further exemplary embodiment the height of each sub-grating creates a π phase shift at the design wavelength. This provides the advantage to ensure the correct phase shift of the wavelength suitable for phase-contrast images. In a further exemplary embodiment, the design wavelength is predetermined according to the purpose of the apparatus where the gratings are applied. In a further exemplary embodiment, the sub-gratings are arranged on a single wafer. This allows an easy handling for further manufacturing and assembling steps. Another advantage is that the alignment takes place during manufacturing where a correct positioning is facilitated. In an alternative exemplary embodiment, each sub-grating is arranged on an individual wafer. This provides an easier manufacturing process and allows providing different types of gratings that can be combined according to individual needs. In a further exemplary embodiment, the sub-gratings are made from silicon with an additional gold layer covering the bars and gaps. For example, such sub-gratings can be used for an absorption grating. In a further exemplary embodiment, the gold layer is not applied in order to provide a phase grating. According to an exemplary embodiment of the invention, a detector arrangement of an X-ray system for generating phase-contrast images of an object is provided comprising an X-ray source, a source grating, a phase grating, an analyzer grating and a detector, wherein the X-ray source is adapted to generate polychromatic spectrum of X-rays and wherein at least one of the gratings is a grating according to one of the preceding embodiments. This provides a detector arrangement with gratings having small effective pitches but which gratings due to the fact that they are formed by a combination of at least two sub-gratings, wherein these sub-gratings can be manufactured with larger pitch gratings. In an exemplary embodiment the detector arranegement is a focus detector arrangement. Further, in an exemplary embodiment an X-ray system for generating phase-contrast data of an object is provided, which X-ray system comprises a detector arrangement of the preceding exemplary embodiment. Still further, in an exemplary embodiment, a method of phase-contrast imaging for examining an object of interest is provided, the method comprising the following steps: Applying X-ray radiation beams of a conventional X-ray source to a source grating splitting the beams; applying the split beams to a phase grating recombining the split beams in an analyzer plane; applying the recombined beams to an analyzer grating; recording raw image data with a sensor while stepping the analyzer grating transversally over one period of the analyzer grating; and wherein at least one of the gratings is a grating of one of the preceding embodiments. In an exemplary embodiment of the method, the source grating, the phase grating and the analyzer grating consist of a grating according to one of the preceding exemplary embodiments with a first sub-grating and at least a second sub-grating. An advantage lies in the possibility to provide gratings with a small effective pitch but which gratings comprise sub-grating with larger pitches. In other words, gratings can be provided suitable for higher X-ray energies but which gratings are easier to manufacture because the gratings have pitches larger than the effective pitch. According to another exemplary embodiment of the invention, a computer-readable medium is provided, in which a computer program for examination of an object of interest is stored which, when executed by a processor of an X-ray system, causes the system to carry out the above-mentioned method steps. According to another exemplary embodiment of the invention, a program element for examination of an object of interest is provied which, when being executed by a processor of an X-ray system, causes the system to carry out the above-mentioned method steps. FIG. 1 schematically shows an X-ray imaging system 10 with an examination apparatus for generating phase-contrast images of an object. The examination apparatus comprises an X-ray image acquisition device with a source of X-ray radiation 12 provided to generate X-ray radiation beams with a conventional X-ray source. A table 14 is provided to receive a subject to be examined. Further, an X-ray image detection module 16 is located opposite the source of X-ray radiation 12, i.e. during the radiation procedure the subject is located between the source of X-ray radiation 12 and the detection module 16. The latter is sending data to a data processing unit or calculation unit 18, which is connected to both the detection module 16 and the radiation source 12. The calculation unit 18 is located underneath the table 14 to save space within the examination room. Of course, it could also be located at a different place, such as a different laboratory. Furthermore, a display device 20 is arranged in the vicinity of a table 14 to display information to the person operating the X-ray imaging system, which can be a clinician for example. Preferably, the display device is movably mounted to allow for an individual adjustment depending on the examination situation. Also, an interface unit 22 is arranged to input information by the user. Basically, the image detection module 16 generates image data by exposing the subject to X-ray radiation, wherein said image data is further processed in the data processing unit 18. It is noted that the example shown is of a so-called C-type X-ray image acquisition device. The X-ray image acquisition device comprises an arm in form of a C where the image detection module 16 is arranged at one end of the C-arm and the source of X-ray radiation 12 is located at the opposite end of the C-arm. The C-arm is movably mounted and can be rotated around the object of interest located on the table 14. In other words, it is possible to acquire images with different directions of view. FIG. 2 schematically shows a focus detector arrangement 24 of an X-ray system for generating phase-contrast images of an object 26. A conventional X-ray source 28 is provided applying X-ray radiation beams 30 to a source grating 32 splitting the beams 30. The splitted beams are then further applied to a phase grating 34 recombining the split beams in an analyzer plane. The object 26, for example a patient or a sample shown in FIG. 2, is arranged between the source grating 32 and the phase grating 34. After recombining the split beams behind the phase grating 34 the recombined beam 30 is applied to an analyzer grating 36. Finally a detector 38 is provided recording raw image data with a sensor while the analyzer grating 36 is stepped transversally over one period of the analyzer grating 36. The arrangement of at least one of the gratings 34, 36 comprising inventive sub-gratings is described in the following. It is noted that the sub-gratings according to the invention can also be applied to the source grating 32. In FIGS. 3 to 9 different exemplary embodiments of a grating according to the invention are shown comprising at least two sub-gratings. In FIG. 3 a first sub-grating 112a and a second sub-grating 114a are shown. The sub-gratings 112a, 114a each comprise a body structure 120a with bars 122a and gaps 124a being arranged periodically with a pitch aa. The sub-grating 112a, 114a are arranged consecutively in the direction of the X-ray beam (not shown in FIGS. 3 to 9). For an easier understanding the sub-gratings are shown horizontally, whereas the sub-gratings in FIG. 2 are arranged vertically. Simply said, in FIGS. 3 to 17 the direction of the X-ray beam is from top of the page to the bottom of the page. The sub-gratings 112a, 114a are positioned with a displacement da in relation to each other in a perpendicularly direction to the X-ray beam. In other words, the sub-grating 114a is arranged in relation to the sub-grating 112a with the offset da such that the sub-grating 114a is shifted towards the right in relation to sub-grating 112a. The sub-gratings 112a, 114a of FIG. 3 have the same pitch aa. Further, the sub-gratings 112a, 114a have an equal bars/gap ratio (sa/ta). Hence, the width sa of a bar 122a is equal to the width ta of a gap 124a. The displacement da is a fraction of half the pitch aa. The projections of the sub-gratings 112a, 114a result in an effective grating 130a (depicted by lines 131a) with a smaller effective pitch za than the pitch aa of the sub-gratings 112a, 114a. In FIG. 3 the displacement da is equal to the effective pitch za. In a further exemplary embodiment the grating comprises three sub-gratings 112b, 114b, 116b. It is noted that similar features of the different exemplary embodiments have the same reference numeral added by a letter to indicate the different embodiments. For easier reading of the claims, the reference numbers in the claims are shown without the letter indizes. The sub-gratings of FIG. 4 have the same pitch ab. Here too, the bars/gap ratio (sb/tb) is 1/1. The sub-gratings 112b, 114b, 116b also comprise a body structure 120b with bars 122b and gaps 124b. Although the gaps and the bars 124b, 122b have a larger width compared to the respective width of FIG. 3, an effective grating 130b is achieved with an effective pitch zb which is the same as the effective pitch za of FIG. 3. In FIG. 5 the grating comprises two sub-gratings 112c and 114c. The sub-gratings also comprise a body structure 120c with bars 122c and gaps 124c. The width of the gaps 124c is larger than the width of the bar 122c, hence the bars/gap ratio (sc/tc) is smaller than 1. The two sub-gratings 112c and 114c are arranged such that the effective grating 130c and the effective pitch zc is the same as in the figures discussed above. In FIG. 5 the width of the bars sc is equal to the effective pitch zc. The width of the gap tc is 3 times the width of the bars sc. The pitch zc of the sub-gratings which is the same for both sub-gratings can be calculated by the equation: a=2nz where n is the number of sub-gratings and z is the effective pitch. In a further exemplary embodiment, shown in. FIG. 6, three sub-gratings 112d, 114d, 116d are provided in a similar way as discussed above. The width of the gap 124d can be larger compared to the sub-gratings of FIG. 5, although the same effective grating 130d is provided due to the larger number of sub-gratings. This is also shown in FIG. 7 where four sub-gratings 112e, 114e, 116e and 118e are shown. Here the sub-gratings have the same pitch ze and are arranged with an offset of: de=2*ze; ze being the effective pitch illustrated for a better understanding beneath each schematic description of the sub-gratings in relation with the effective grating 130e. In a further exemplary embodiment in FIG. 8, three sub-gratings 112f, 114f, 116f are provided where one of the sub-gratings, in FIG. 8 the middle sub-grating 114f, is having a different pitch af2 compared to the pitch af1 of the other sub-gratings 112f and 116f. In fact, the pitch af1 of the first and third sub-gratings 112f, 116f is a multiple of the pitch af2 of the middle sub-grating 114f. In fact the ratio of the pitches of the sub-gratings is 1/2. Hence, the pitch af1 of the upper sub-grating 112f is twice the pitch af1 of the second sub-grating 114f. Here too, an effective 130f grating with an effective pitch similar to the embodiment discussed above is achieved. Whereas in FIG. 8 the width of the bars of all three sub-gratings is having the same size, in a further exemplary embodiment shown in FIG. 9 the width of the bars of the sub-gratings is different. In FIG. 9 three sub-gratings 112g, 114g and 116g are arranged such that the middle sub-grating 114g is having a pitch ag2 which is half the amount of a pitch ag1 of the upper and lower sub-gratings 112g, 116g. The three sub-gratings are offset to each other such that the effective grating 130g with an effective pitch, shown underneath by lines, is the same as the effective pitches of the embodiments discussed above. Providing sub-gratings which are arranged with an offset to each other allows an easier manufacturing of the sub-gratings because the gaps that are, for example, etched into the body structure's substance are wider and thus easier to apply during manufacture. However, the projections of the sub-gratings result in an effective grating with an effective pitch which is smaller than the pitches of the sub-gratings. In a further exemplary embodiment the sub-gratings 112h, 114h are arranged on a single wafer 111h, shown in FIG. 10. Here two sub-gratings are provided with offset pitches ah by offset dh and effective pitch zh, shown in FIG.10 on the effective grating 130h. In a further exemplary embodiment, two sub-gratings 112j, 114j having a pitch aj are configured such that they are arrangeable with their closed sides or flat sides 116j, 118j adjacent to each other (FIG. 11). This provides the advantage that two individual sub-gratings 112j, 114j can be manufactured which are then attached to each other so that no further positioning or alignment steps of the two sub-gratings in relation to each other are necessary. An effective grating 130j of smaller pitch zj results. In FIG. 12 a grating for a phase grating is shown comprising two sub-gratings 112k and 114k. The sub-gratings 112k, 114k each have the same pitch and the bars/gap ratio, i.e. s/t=1/1. FIG. 14 shows the equivalent grating 132 when providing only a single grating in order to achieve the same pitch as the effective pitch of the two sub-gratings 112k, 114k. It can be seen that the pitch ak of the sub-gratings is larger than the pitch ze of the equivalent grating 132. The same effective grating with the same effective pitch can also be achieved by providing two sub-gratings 1121, 1141 for a phase grating having the same pitch a1 but in contrary to the sub-gratings of FIG. 12, the bars/gap ratio (s/t) is smaller 1, in the exemplary embodiment in FIG. 13 the bars/gap ratio is 1/3. The equivalent is the same as for FIG. 12 (see FIG. 14). In FIGS. 15 and 16 a similar arrangement is provided for an absorption grating with high aspect ratio. In FIG. 15 two sub-gratings 112m, 114m having the same pitch are shown with a bars/gap ratio of 1/1; whereas, in FIG. 16 two sub-gratings 112n, 114n have a bars/gap ratio that is smaller than 1. The sub-gratings 112m, 114m, 112n, 114n respectively comprise silicon body structures 134m and 134n with an additional corresponding gold layer 136m, 136n. The results in an effective gold granting 138 shown underneath each pair of the sub-grantings 112m, 114m, 112n, 114n for illustrative purposes. FIG. 17 shows the equivalent grating 140 when providing only a single grating and the resulting pitch 142 due to the gold layer. It can be seen that in order to provide a grating with a high aspect ratio, a grating has to be provided with smaller gaps to provide the same effective grating as the combination of two sub-gratings shown in FIGS. 12, 13, 15 and 16. Hence, compared to the equivalent single gratings shown in FIGS. 14 and 17, the sub-gratings according to the invention can be manufactured in an easier and thus cheaper and more economic way. The sub-gratings can be used instead of single gratings, for example in phase-contrast X-ray imaging. The steps of an exemplary embodiment of a method are shown in FIG. 18. In a first step X-ray radiation beams of a conventional X-ray source 28 are applied 52 to a source-grating 32 where the beams are splitted 54. The source grating 32 comprises two sub-gratings (not shown in FIG. 18) arranged consecutively in the direction of the X-ray beam and positioned displaced to each other perpendicularly to the X-ray beam. The splitted beams are then transmitted 56 towards an object of interest 26, wherein the beams are passing through the object 26 where adsorption and refraction 58 occurs. The beams are further applied to a phase grating 34 where the splitted beams are recombined 60 in an analyser plane 62. Also, the phase grating 34 comprises two sub-gratings (not shown in FIG. 18). Then, the recombined beams are applied 64 to an analyzer grating 36 also comprising two sub-gratings (not shown in FIG. 18). Further, a sensor 38 is recording 66 raw image data 68 while the analyzer grating 36 is stepped transversely 70 over one period of the analyzer grating. Finally, the raw data 68 is transmitted 72 to a control unit 18 where the data is computed 74 into display data 76 to show 78 images on a display 20. While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. It should be noted that the term “comprising” does not exclude elements or steps and the “a” or “an” does not exclude a plurality. Also, elements described in association with different embodiments may be combined.
	summary
055816053	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with the preferred embodiments thereof with reference to the accompanying drawings. Embodiment I FIG. 4 shows an optical element according to the present invention. The optical element 1 has a number of fine convex surfaces 7 two-dimensionally and regularly arranged on a substrate 6. Multilayer films 9 for reflecting X-rays are formed on each convex surface 7, by which the X-rays are reflected. FIG. 6 shows a cross section of the element. As shown in FIG. 6, the convex surfaces 7 have a same shape and a substantially same curvature. Also, the optical element 1 can be constructed of concave surfaces 8 as shown in FIG. 7. It is preferred that the size of these convex surfaces 7 or concave surfaces 8 is considerably smaller than the size of element itself. The convex surfaces 7 or the concave surfaces 8 may be constructed such that they are formed each in a circular shape in the region of X-ray-reflecting surface as shown in FIG. 4 or that they are continuously formed in the entire X-ray-reflecting surface as shown in FIG. 5. FIG. 8 shows a state of spread of reflected X-rays when X-rays (represented by A, B and C) are incident into a convex surface 10 of a spherical portion of multilayer films which reflect X-rays. Let r be a radius of curvature of the spherical surface, d be a diameter thereof, .theta. be an angle of incidence of an X-ray at the vertex of the convex surface 10, and 2.PHI. be an angle spanned by a circular arc with a radius being r and a length of chord being d. Since the distance from the light source (X-ray source) to the convex surface 10 is set as very long as compared with d and r, incident light may be considered as a beam of parallel rays in this case. In this arrangement, an X-ray B incident into the vertex of the convex surface 10 is reflected at an angle of .theta. with respect to the normal line n at the vertex, while an X-ray incident into another point is reflected at an angle different from that of the reflected light at the vertex, because the reflection (plane for reflecting X-rays) thereof is inclined. For example, as shown in FIG. 8, an X-ray A incident into one edge of the convex surface 10 is reflected at angle of (.theta.-2.PHI.) with respect to the normal line n and another X-ray C incident into the other edge at angle of (.theta.+2.PHI.). Consequently, a beam of parallel rays incident at angle .theta. into the convex surface 10 is reflected as diverging in a shape of circular cone with an angle of divergence of 2.PHI. and with the center thereof in the direction of specular reflection of angle .theta.. Also, as shown in FIG. 9, the condition is the same in case a beam of parallel rays is incident into a convex surface 11 of spherical shape. In this case, the reflected light is converged once and then diverges. As described above, the surface of optical element 1 for X-ray reflection, in which a lot of sufficiently small convex surfaces or concave surfaces are arranged, functions as secondary light sources with a diverging angle of 2.PHI.. If .PHI. is expressed by r and d, the relation of 2r.multidot.sin.PHI.=d holds. If .PHI. is sufficiently small then 2.PHI.=d/r. The illumination optical system focuses real-size images or several-times-magnified images of the secondary X-ray sources on the entrance pupil of reduction projection optical system, on the mask, or at a position between them. At this time, the X-ray beam illuminating the mask must have an angle of divergence enough to fill the entrance numerical aperture of reduction projection optical system. Suppose a beam with a diverging angle of 2.PHI. is incident into the illumination optical system. Then the entrance numerical aperture is defined as sin2.PHI..about.2.PHI.. Also, the exit numerical aperture is defined as follows with the magnification m of optical system: (sin2.PHI.)/m.about.2.PHI./m=d/(r.multidot.m). In order to use the entire numerical aperture of reduction projection optical system for the purpose of obtaining the desired resolving power of the diffraction limit, the exit numerical aperture of the illumination optical system should be set to a value equal to or larger than the entrance numerical aperture of reduction projection optical system. However, when the exit numerical aperture of illumination system is set larger than the entrance numerical aperture of projection system, the exposure time must be lengthened because of an increase in ratio of rays not entering the reduction projection optical system, which lowers the throughput of exposure apparatus. Accordingly, it is preferred that the exit numerical aperture of illumination optical system is set equal to the value of entrance numerical aperture of reduction projection optical system. The optical element for X-ray reflection used as the secondary X-ray sources is composed of a substrate with fine convex and concave surfaces formed thereon and multilayer films formed on the substrate to reflect X-rays. The incident angle of X-rays into the multilayer films changes in the range of (.theta..+-..PHI.) as shown in FIG. 8 or FIG. 9. Accordingly, the half width of reflection peak of the multilayer films is preferably about 2.PHI. or more. Generally, the peak half width of the multilayer films is sufficiently larger than 2.PHI.. If .PHI. is desired to be further greater in particular, the peak half width may be enlarged by decreasing the number of layers in the multilayer films. Another embodiment of optical element according to the present invention is next described with FIGS. 10 to 17. A surface of each convex portion or concave portion, that is, a convex surface 10 or concave surface 11, is formed such that a radius of curvature in a curve defined by crossing a first plane and the concave surfaces 10 or convex surfaces is different from a radius of curvature in a curve defined by crossing a second plane and the concave surfaces 10 or convex surfaces 11. The first plane is a plane of incidence with respect to X-rays, and passes through a vertex of the concave surfaces 10 or convex surfaces 11. The second plane is a plane passing through the vertex and being perpendicular to the first plane. Now described is what angle of divergence a reflected beam has when parallel rays are incident into a convex portion or concave portion having such a shape. Consider a coordinate system as shown in FIG. 13, in which the origin is at the vertex of a convex portion and the xy plane is parallel to the reflecting surface of X-ray optical element (more precisely to a plane of substrate). A concave portion will have slight differences in intermediate equations from those for a convex portion, but a finally obtained angle of divergence of reflected light is the same between them. Therefore, the following description concerns only the case of convex portion. First investigated is a case in which the surface of convex portion is a spherical surface. Let R.sub.0 be a radius of curvature of the spherical surface and R be a radius of convex portion. It is assumed that R.sub.0 is sufficiently larger than R. Namely, taking x, y and r as -R<x<R, -R<y<R and r=(x.sup.2 +y.sup.2).sup.1/2, terms of second and higher orders of x/R.sub.0, y/R.sub.0 and r/R.sub.0 can be negligible. In other words, following approximations stand: c(x/R.sub.0).sup.2 .apprxeq.0 (c is an arbitrary constant), . . . . A projecting amount of convex portion in the z direction is an amount proportional to (r/R.sub.0).sup.2, which can be thus negligible herein. Let us now consider a normal vector n(x,y) to the convex portion at an arbitrary point (x,y) on the surface of convex portion (i.e., the spherical surface) as shown in FIG. 14. FIG. 14 shows a state in a plane including the Z axis and the normal vector n(x,y). The following vector representation is used to discriminate a vector from ordinary scalar quantities: In drawings and equations alphabets are italicized for vectors and in the specification a word "vector" is simply given as prefix. As apparent from FIGS. 14 and 15, the vector n(x,y) is given by the following equation. EQU n(x,y)=(sin.alpha..multidot.cos.beta.,sin.alpha..multidot.sin.beta.,con.alp ha.) (1) Here, .alpha. is an angle between the vector n(x,y) and the z axis as defined in FIG. 14, and .beta. is an angle between the x axis and a straight line connecting the origin O and the point (x,y) (as projected onto the xy plane) as defined in FIG. 15. Using sin.alpha.=r/R.sub.0, cos.alpha.=(1-(r.sup.2 /R.sub.0.sup.2)).sup.1/2, sin.beta.=y/r and cos.beta.=x/r, the vector n(x,y) may be expressed as follows. EQU n(x,y)=(x/R.sub.0,y/R.sub.0,1) (2) Suppose a parallel beam is incident in a direction at .theta..sub.0 to the z axis in the xz plane as shown in FIG. 16. Then a direction vector n.sub.in of the beam is given by the following equation. EQU n.sub.in =(sin.theta..sub.0,0,-cos.theta..sub.0) (3) Further, let n.sub.out (x,y) be a direction vector representing a direction in which a ray reflected a surface near the point (x,y) on the convex portion proceeds. As apparent from FIG. 17, the vector n.sub.out (x,y) is given by the following equation. EQU n.sub.out (x,y)=n.sub.in -2(n,n.sub.in).multidot.n=(sin.theta..sub.0 +(2x/R.sub.0)cos.theta..sub.0,(2y/R.sub.0)cos.theta..sub.0, cos.theta..sub.0 -(2x/R.sub.0)sin.theta..sub.0) (4) The following facts are derived from this equation. (1) When the incident ray impinges on the surface at a position shifted in the x direction, the direction of reflected ray changes in proportion with x in the xz plane (plane of incidence); when it is shifted in the y direction, the direction of reflected ray changes in proportion with y in the direction perpendicular to the xz plane (plane of incidence). (2) When the incident-ray-impinging position is shifted within the range of the divergence angle of reflected beam in the plane of incidence (xz plane), that is, in the range of -R<x<R and -R<y<R, an angular range in which the reflected beam spreads in the plane of incidence is .+-.2R/R.sub.0 [rad], which is independent of the incident angle .theta..sub.0. (3) Also, the divergence angle of reflected beam is .+-.2R/R.sub.0 .multidot.cos.theta..sub.0 [rad] in the direction perpendicular to the plane of incidence (xz plane), which is dependent on the incident angle .theta..sub.0. The range of divergence is coincident with the divergence angle in the plane of incidence upon normal incidence (.theta..sub.0 =0), and the divergence angle decreases as the incident angle .theta..sub.0 increases. From the above facts, it is found that the divergence angle of reflected light differs depending upon the direction if the surface of convex portion or concave portion is spherical. Next investigated is a case in which the surface of convex portion is a toroidal surface. Let us consider a toroidal surface two axes of rotation center of which are parallel to the x axis and the y axis, respectively, as shown in FIG. 10. Let R.sub.0x be a radius of curvature in the direction parallel to the x axis, 2R.sub.x be a length of the toroidal surface in the direction of x axis, R.sub.0y be a radius of curvature in the direction parallel to the y axis and 2R.sub.y be a length of the toroidal surface in the direction of y axis. It is assumed herein that R.sub.0x and R.sub.0y are sufficiently larger than R.sub.x and R.sub.y. Taking x and y as -R.sub.x <x<R.sub.x and -R.sub.y <y<R.sub.y, terms of second and higher orders of x/R.sub.0x and y/R.sub.0y can be negligible. A projecting amount of the convex portion in the z direction is an amount proportional to these quantities, which can be also negligible. Now let us consider a normal vector n(x,y) at point (x,y) on the convex portion as shown in FIG. 10. As apparent from FIG. 10, EQU n(x,0)=(x/R.sub.0x,0,1) (5) EQU n(0,y)=(0,y/R.sub.0y, 1) (6). The vector n(x,y) is obtained by rotating the vector n(x,0) about the straight line 1 by the same angle of rotation as the angle of rotation when the vector n(0,0) is rotated about the straight line 1 up to the vector n(0,y). Thus, the vector n(x,y) is given by the following equation. EQU n(x,y)=(x/R.sub.0x,y/.sub.0y,1) (7) When a parallel beam having the direction vector n.sub.in given by Equation (3) is incident in the xz plane into the convex portion of such toroidal surface shape, a direction vector n.sub.out (x,y) representing the direction in which a ray reflected on a surface near the point (x,y) on the convex portion proceeds is given by the following equation. EQU n.sub.out (x,y)=n.sub.in -2(n,n.sub.in).multidot.n=(sin.theta..sub.0 +(2x/R.sub.0x)cos.theta..sub.0,(2y/R.sub.oy)cos.theta..sub.0,cos.theta..su b.0 -(2x/R.sub.0x)sin.theta..sub.0 (8) The following facts are derived from this equation. (1) When the incident ray impinges on the surface at a position shifted in the x direction, the direction of reflected ray changes in proportion with x in the xz plane (plane of incidence); when it is shifted in the y direction, the direction of reflected ray changes in proportion with y in the direction perpendicular to the xz plane (plane of incidence). (2) The divergence angle of reflected beam is .+-.2R.sub.X /R.sub.0x [rad] in the plane of incidence (xz plane), which is independent of the incident angle .theta..sub.0. (3) The divergence angle of reflected beam is .+-.2R.sub.y /R.sub.0y .multidot.cos.theta..sub.0 [rad] in the direction perpendicular to the plane of incidence (xz plane), which is dependent on the incident angle .theta..sub.0. The divergence angle reduces as the incident angle .theta..sub.0 increases. The divergence angle upon normal incidence (.theta..sub.0 =0) is not always coincident with the divergence angle in the plane of incidence in this case. As described, in case the shape of the convex portion is toroidal, the divergence angle of reflected light in the direction parallel to the plane of incidence is determined by R.sub.0x, R.sub.x, while the divergence angle of reflected light in the direction perpendicular to the plane of incidence by R.sub.0y and R.sub.y. Therefore, the divergence angles of reflected light can be independently determined in the respective directions. The following three equations can be used to determine the shape of toroidal surface as to just fit the entrance numerical aperture of illumination optical system. EQU R.sub.x /R.sub.0x =(entrance numerical aperture of illumination optical system)/2 (9) EQU (R.sub.y)/(R.sub.0y)cos.theta..sub.0 =(entrance numerical aperture of illumination optical system)/2 (10) EQU (R.sub.y /R.sub.x).sup.2 =R.sub.0y /R.sub.0x (11) Equations (9) and (10) are derived from the conditions to make the divergence angle of reflected beam coincident with the entrance numerical aperture of illumination optical system. Also, Equation (11) is obtained by approximating and expanding an equation which defines the height of convex portion (height from the bottom of convex portion to the vertex) using R.sub.0x, R.sub.0y, R.sub.x and R.sub.y. The four parameters of R.sub.0x, R.sub.0y, R.sub.x and R.sub.y are not independent of each other. Equation (11) indicates the relation to be satisfied by the parameters. To determine each parameter from the above equations, the following steps should be taken for example. (1) First, R.sub.0x and R.sub.x (a ratio thereof) is determined by Equation (9) from the entrance numerical aperture required for the illumination optical system. (2) R.sub.y is determined by R.sub.y =R.sub.x .multidot.cos.theta..sub.0 from the incident angle .theta..sub.0. (3) R.sub.0y is then determined by R.sub.0y =R.sub.0x .multidot.cos.sup.2 .theta..sub.2. These steps determine a ratio of the parameters but provide no absolute value of each parameter. The absolute values can be determined by the conditions of processing method for forming such fine convex portions or concave portions. As described above, the surface of X-ray-reflecting optical element according to the present invention functions as the secondary light sources having a conic diverging angle without bias when each convex or concave portion is formed as a toroidal surface and a lot of sufficiently small convex or concave portions are arranged in the surface of optical element. The illumination optical system focuses real-size images or several-times-magnified images of the secondary light sources on the entrance pupil of reduction projection optical system, on the mask or at an arbitrary position between them. At this occasion, the X-ray beam illuminating the mask must have an angle of divergence enough to match the entrance numerical aperture of reduction projection optical system. Suppose a beam having a diverging angle of .psi. is incident into the illumination optical system. Then the entrance numerical aperture is sin.psi..apprxeq..psi.. Also, the exit numerical aperture is sin.psi./m.apprxeq..psi./m, where m is the magnification of illumination optical system. In order to use the entire numerical aperture of reduction projection optical system for the purpose of obtaining a desired resolving power of the diffraction limit, the exit numerical aperture of illumination optical system should be set to a value equal to or larger than the entrance numerical aperture of reduction projection optical system. However, if the exit numerical aperture of illumination optical system is set larger than the entrance numerical aperture of reduction projection optical system, exposure time must be lengthened because of an increase in ratio of rays not entering the reduction projection optical system, which lowers the throughput of exposure apparatus. Accordingly, it is preferred that the exit numerical aperture of illumination optical system is set to the same value as the entrance numerical aperture of reduction projection optical system. In other words, using Equations (9) and (10), the parameters defining the shape of the toroidal surface forming the surface of convex portion or concave portion in the X-ray-reflecting optical element according to the present invention may be determined to satisfy the following relations of Equations (12) and (13). EQU (entrance numerical aperture of reduction projection optical system)=.psi./m=2R.sub.x /mR.sub.0x =d.sub.x /mR.sub.0x (12) EQU (entrance numerical aperture of reduction projection optical system)=.psi./m=(2R.sub.y /mR.sub.0y)cos.theta..sub.0 =(d.sub.y /mR.sub.0y)cos.theta..sub.0 (13) In the above equations, d.sub.x =2R.sub.x and d.sub.y =2R.sub.y correspond to x-directional and y-directional lengths of the toroidal surface, respectively. The X-ray incident angle .omega. into the multilayer films 9 in the X-ray optical element 1 is given by the following equation as apparent from FIG. 16. EQU cos.omega.=-(n.sub.in,n)=cos.theta..sub.0 -(x/R.sub.0x)sin.theta..sub.0 ( 14) As the X-ray incident position is changed within the range of -R<x<R, the incident angle .omega. changes in the range of .theta..sub.0 .+-.cos.sup.-1 (R.sub.x /R.sub.0x sin.theta..sub.0). Accordingly, it is desired that the half width of reflection peak of the multilayer films is at least about 2.multidot.cos.sup.-1 (R.sub.x /R.sub.0x sin.theta..sub.0). Generally, the peak half width of multilayer films is sufficiently larger than that. In case the change of incident angle is specifically large, the peak half width may be widened by decreasing the number of layers in the multilayer films. Namely, since the peak half width of multilayer films becomes smaller in proportion to the inverse of the number of layers in the multilayer films, decreasing the number of layers lowers the peak value of reflectivity but widens the peak half width as to match the change of incident angle .omega.. The multilayer films 9 reflecting the X-rays are now described referring to FIG. 18. The multilayer films in the present embodiment constitute a multilayer film reflecting mirror in which two types of materials having mutually different indices of refraction are alternately laminated at a constant period. The multilayer film reflecting mirror strongly reflects X-rays when the Bragg condition given by 2d cos.theta.=n.lambda. (where n is a positive integer) is satisfied, where d is the period, .lambda. the wavelength of the X-rays and .theta. an incident angle (to the normal line). The equation is the same as the equation of Bragg diffraction for crystal (where d is a surface separation in case of crystal). Since the Bragg condition gives only the condition among d, .theta. and .lambda. providing a peak of reflectivity, the reflectivity should be calculated using the Fresnel's formulas. Fresnel's formulas: p-polarized light: EQU r.sub.j (n.sub.j+1)=(n.sub.j cos.PHI..sub.i+1 -n.sub.j+1 cos.PHI..sub.i)/(n.sub.j cos.PHI..sub.j+1 +n.sub.j+1 cos.PHI..sub.j) s-polarized light: EQU r.sub.j (n.sub.j+1)=(n.sub.j+1 cos.PHI..sub.j+1 -n.sub.j cos.PHI..sub.j)/(n.sub.j+1 cos.PHI..sub.j+1 +n.sub.j cos.PHI..sub.j) Recurrence formula of amplitude reflectance: EQU R.sub.j (n.sub.j+1)={r.sub.j (n.sub.j+1)+R.sub.j-1 (n.sub.j)exp(-i.delta..sub.j)}/{1+r.sub.j (n.sub.j+1)R.sub.j-1 (n.sub.j)exp(-i.delta..sub.j)} Phase difference at j-th layer: EQU .delta..sub.j =(4.pi./.lambda..sub.0)n.sub.j d.sub.j cos.PHI..sub.j Snell's formula: EQU n.sub.j sin.PHI..sub.j =n.sub.j+1 sin.PHI..sub.j+1 Actually produced multilayer films generally have reflectivities lower than the calculated values. Main factors to cause the difference are scattering losses due to roughness of substrate surface or interfaces in the multilayer films, and diffusion layers formed in the interfaces. A method for taking in these factors into calculation is exemplified. If a scattering loss occurs, the reflectivity lowers exp{-(4.pi..sigma.cos.theta./.lambda.).sup.2 } times using the Debye-Waller factor .sigma.. The factor .sigma. indicates a quantity representing a degree of roughness. In case diffusion layers exist in the interfaces, the reflectivities can be calculated by the Fresnel's formulas not as the alternate layers of two types of materials but as layers including third material layers in the interfaces. There are many specific materials for the multilayer films, among which W/C and Mo/Si are most popular. Other combinations often used are W/Si, W/B.sub.4 C, Mo/C, Mo/B.sub.4 C, Mo/SiC, Ru/Si, Rh/Si, Ni/C, etc., among which a most suitable combination is selected depending upon the operating wavelength. FIG. 19 was obtained by the simple calculation method by Vinogradov (A. V. Vinogradov and B. Ya. Zeldovich, Appl. Opt. 16 (1977) 89). FIG. 19 shows a graph of maximum reflectivity against wavelength. Mo/Si shows a high reflectivity near 130 .ANG. (=13 nm). Ru/Si, Rh/Si or Mo/SiC also has a reflectivity close to that of Mo/Si. Particularly, it is noted that Mo/SiC shows higher thermal resistance than Mo/Si. As the number of layers in the multilayer films increases, the reflectivity first increases in proportion to the number of layers and then is saturated at a certain point (see FIG. 20A). FIG. 20A shows calculated values for Mo/Si multilayer films for use with light of wavelength 13 nm under normal incidence. Since the reflectivity is saturated at about 50 layers, the multilayer films preferably include 50 layers (50 layers for each of Mo and Si). This calculation was made taking the diffusion layers in the interfaces into consideration. (Proc. SPIE Vol. 1742 (1992) 614) The wavelength half width of reflectivity peak decreases with an increase in number of layers and is saturated at a nearly same number of layers as the reflectivity. When 50 layers are laminated, the half width is about 5 .ANG. (see FIG. 20B). Strictly speaking, the period of layers must be changed according to the Bragg's formula in case of the multilayer films being formed over the convex portions or concave portions, because the incident angle changes depending upon the location. However, the multilayer films may be formed at a constant period as long as the change in reflectivity is small with a change in incident angle. FIGS. 21A and 21B are drawings for Mo/Si multilayer films to show changes in reflectivity obtained when the incident angle is changed from the normal incidence. The layers can be laminated at a constant thickness if the change in incident angle is in the range of about 0.degree. to 8.degree.. If the change in incident angle exceeds the range, the layers in the multilayer films must be formed at different periods. Specifically, such multilayer films can be formed by the method using a film thickness distribution correction slit while rocking a substrate (for example as described in Japanese Patent Application No. 5-237590). In the present embodiment, the X-rays preferably have the wavelength of not more than 50 nm in case they are used as a light source for an illumination optical apparatus as described later. More preferably, the wavelength is in the range of 5 nm to 20 nm. Accordingly, the film thickness of multilayer films may be suitably selected according to the wavelength of X-rays employed. Here, other embodiments of optical element are shown in FIGS. 22 and 23. An optical element 1a is so arranged that concave surfaces are formed in a shape of groove on the surface thereof and each groove concave surface is arranged one-dimensionally. Also, an optical element 1b is so arranged that convex surfaces are one-dimensionally arranged, contrary to the optical element 1a. These optical elements 1a, 1b are used in combination of two optical elements. An example in FIG. 24 employs two optical elements 1a and another example in FIG. 25 two optical elements 1a, 1b. In either case, the two optical elements are arranged such that the concave surfaces are perpendicular to the convex or concave surfaces and radii of curvature thereof are determined as parallel beams are focused at a same position (I) (i.e., as multiple images of a light source at the infinity are formed at this position). Next, FIG. 26 schematically shows an example of structure of an X-ray optical system arranged with such an optical element. The X-ray optical system shown in FIG. 26 is composed mainly of an X-ray source 2 emitting X-rays, an optical element 1, an illumination optical system 3 and a mask 4 on which a predetermined mask pattern is formed. Reference numeral 50 designates the position of entrance pupil of an imaging optical system (not shown). In such an optical system, X-rays emitted from the X-ray source 2 are irradiated onto convex surfaces (or concave surfaces) in the optical element 1. The X-rays irradiated onto the convex surfaces are not simply reflected by specular reflection, but reflected as diffusing with a certain spread around the direction of specular reflection. Thus, the surface (reflecting surface) of the optical element 1 becomes secondary X-ray sources having a wide area and a wide diverging angle. X-rays uniformly emerging from the numerous secondary X-ray sources are focused at the entrance pupil position 50 through the illumination optical system 3. FIG. 27 is a scheme to show another X-ray optical system, which is used in X-ray reduction projection exposure apparatus. The X-ray optical system is provided with an X-ray-reflecting optical element 1 functioning as secondary X-ray sources, an elliptic mirror 13 on which multilayer films are formed of a combination of Mo (molybdenum)/Si (silicon), a mask 4 and a reduction projection optical system 14, by which a demagnified image of a pattern formed on a mask 4 is focused on a wafer 5. X-rays 12 entering the X-ray optical system are supplied after such a process that an X-ray source (synchrotrom radiation source employed in the present embodiment) emits X-rays, a front-end optical system composed mainly of an oblique incidence mirror and a filter (both not shown) selects X-rays with wavelength near 130 .ANG., and then a slit (not shown) shapes a beam of X-rays in a square of about 30 mm side. Then, the beam of nearly parallel rays with a diverging angle of at most about 0.1.degree. enters the X-ray optical system. The X-ray-reflecting optical element 1 has a reflecting surface (a surface into which the X-rays 12 are incident) formed by multilayer films in combination of Mo (molybdenum)/Si (silicon). Further, the reflecting surface is formed such that a plurality of semispherical convex portions with a diameter d of each portion being about 10 .mu.m and a radius of curvature r of each spherical surface being about 170 .mu.m are formed at pitch of about 10 .mu.m in a square region of 30 mm side. The elliptic mirror 13 is located such that one of two foci is at the setting position of optical element 1. FIG. 27 omits the detail of the structure of reduction projection optical system 14, which is composed of three mirrors in total, i.e., a mirror having a parabolic surface and two mirrors each having an ellipsoidal surface. Each of the three mirrors has a reflecting surface of multilayer films in combination of Mo/Si. The reduction projection optical system 14 in the present embodiment is set to have a demagnification ratio of 1/5 and an image-side numerical aperture of 0.06 in order to obtain the resolving power of not more than 0.1 .mu.m and the depth of focus of at least 1.8 .mu.m, in which the mask-side numerical aperture becomes 0.012. In the X-ray optical system as so arranged, the reflecting surface of optical element 1 first reflects the X-rays 12 incident thereinto as the beam of nearly parallel rays with diverging angle of at most about 0.1.degree. as described above. The optical element 1 functions as secondary light sources with diverging angle of 2.PHI.. The value of .PHI. is determined as follows. Since 2.PHI.=d/r where d is the diameter of each convex portion in the reflecting surface and r is the radius of curvature of spherical surface, the diverging angle of reflected X-rays is d/r=10/170=0.06(rad)=3.4.degree.. Namely, the optical element 1 functions as secondary X-ray sources having the size of 30 mm square and the diverging angle of 3.4.degree.. The X-rays reflected by the optical element 1 are again reflected by the elliptic mirror 13, which forms five times larger images of the secondary X-ray sources at the entrance pupil of reduction projection optical system 14. Accordingly, the mask 4 is illuminated in a wide region of at least 150 mm square. The diverging angle of X-rays on this occasion decreases according to the magnification ratio of the elliptic mirror 13, which will be about 0.012(rad)=0.69.degree. coinciding with the mask-side numerical aperture of reduction projection optical system 14. The X-rays illuminating and passing through the mask 4 then pass through the reduction projection optical system 14 to form a demagnified image of a pattern formed on the mask 4, on the wafer 5. Reduction projection exposure experiments were conducted using the X-ray optical system in the present embodiment. The experiments assured that lines and spaces of 0.1 .mu.m were resolved all over an arc-shaped region in length of 30 mm, width of 0.2 mm and radius of 17.5 mm. Another exposure experiment was conducted under the same conditions except that the optical element 1 was replaced by a plane multilayer film mirror, which showed that only lines and spaces of up to 0.2 .mu.m could be resolved. FIG. 28 is a schematic constitutional drawing to show another X-ray optical system, which is used in X-ray reduction projection exposure apparatus. In FIG. 28, constituents having the same structure and function as those in FIG. 27 are denoted by the same reference numerals and will be properly omitted to explain. The X-ray optical system in the present embodiment is provided with a laser plasma X-ray source 15 as the X-ray source, a parabolic surface mirror 16 reflecting X-rays emitted from the X-ray source 15 to supply a beam of nearly parallel rays, an X-ray-reflecting optical element 1 functioning as secondary X-ray sources, a Schwarzschild mirror 17, a mask 4 and a reduction projection optical system 14, by which a demagnified image of a pattern formed on the mask 4 is formed on a wafer 5. The parabolic surface mirror 16 has coatings of multilayer films in combination of Mo/Si on a reflecting surface thereof. The shape of the reflecting surface (parabolic surface) is determined as the reflected X-rays 12 become nearly parallel. The optical element 1 has a reflecting surface (surface which the X-rays 12 enter) formed by multilayer films in combination of Mo (molybdenum)/Si (silicon). Further, the reflecting surface is so arranged that a plurality of semispherical convex portions each with diameter d of about 10 .mu.m and radius of curvature r of spherical surface being about 80 .mu.m are formed at pitch of about 10 .mu.m in a circular region of diameter 15 mm. The Schwarzschild mirror 17 is an optical system composed of two spherical mirrors 17a, 17b having a common central axis. Multilayer films in combination of Mo/Si are formed on a reflecting surface of each spherical mirror. In order to avoid interference between the incident X-rays and the spherical mirror (convex mirror) 17a disposed near the optical axis of the Schwarzschild mirror 17, the optical element 1 is so arranged that the direction of principal rays of reflected light is inclined at about 10.degree. relative to the optical axis of Schwarzschild mirror 17. The magnification of Schwarzschild mirror 17 is set to 10. The reduction projection optical system 14 has the same structure as that in the previous embodiment, which is set to the demagnification ratio of 1/5 and the image-side numerical aperture of 0.06 and in which the mask-side numerical aperture is 0.012. In the X-ray optical system as so arranged, the reflecting surface of optical element 1 first reflects the X-rays 12 incident thereinto as a beam of nearly parallel rays with diverging angle of at most about 0.1.degree. as described above. The optical element 1 functions as secondary X-ray sources with diverging angle of 2.PHI.. The value of .PHI. is determined as follows. Since 2.PHI.=d/r where d is the diameter of each convex portion in the reflecting surface and r a radius of curvature of spherical surface, the diverging angle of reflected X-rays is d/r=10/80=0.12(rad)=6.9.degree.. Namely, the optical element 1 functions as secondary light sources with diameter 15 mm and diverging angle 6.9.degree.. The X-rays reflected by the optical element 1 are again reflected by the Schwarzschild mirror 17 to form 10 times larger images of the secondary X-ray sources at the entrance pupil of reduction projection optical system 14. Accordingly, the mask 4 is illuminated in a wide region of about 150 mm. The diverging angle of X-rays on this occasion decreases according to the magnification ratio of Schwarzschild mirror 17, which is 0.012(rad)=0.69.degree. coinciding with the mask-side numerical aperture of reduction projection optical system 14. The X-rays illuminating and passing through the mask 4 pass through the reduction projection optical system 14 to form a demagnified image of a pattern formed on the mask 4, on the wafer 5. Reduction projection exposure experiments were conducted using the X-ray optical system in the present embodiment. The experiments assured that lines and spaces of 0.1 .mu.m were resolved over an entire arc-shaped region in length of 30 mm, width of 0.2 mm and radius of 17.5 mm. Another exposure experiment was conducted under the same conditions except that the optical element 1 was replaced by a plane multilayer film mirror, which showed that only lines and spaces of up to 0.2 .mu.m could be resolved. Another X-ray optical system is next described. The structure of optical system is the same as that shown in FIG. 27 and therefore omitted to depict. X-rays 12 to enter the X-ray optical system are emitted from an X-ray source (photon radiation source employed in the present embodiment). A front-end optical system composed mainly of an oblique incidence mirror and a filter (both not shown) selects X-rays with wavelength near 130 .ANG.. After that, a slit (not shown) shapes the X-rays into a beam of about 30 mm square. The thus shaped beam of parallel rays with diverging angle of at most about 0.1.degree. then enters the X-ray optical system. Multilayer films in combination of Mo (molybdenum)/Si (silicon) are formed on the surface of X-ray optical element 1. Further, the surface is so arranged that a plurality of convex portions (not shown) having external surface of toroidal surface are formed as filling up a square region of 30 mm side. The toroidal surface is constructed in such dimensions that the radius of curvature is R.sub.0x =160 .mu.m and the length is 2R.sub.x =10 .mu.m in the direction parallel to a line connecting intersection points between the plane of incidence of X-rays (in the plane of FIG. 27) and the surface of a convex portion and that the radius of curvature is R.sub.0y =40 .mu.m and the length is 2R.sub.y =5 .mu.m in the direction perpendicular to the line connecting the above intersection points (in the direction normally crossing the plane of FIG. 27). The incident angle of X-rays 12 into the optical element 1 is set to .theta..sub.0 =60.degree.. The elliptic mirror 13 is set such that one of two foci is located at the setting position of optical element 1. The figure omits the detail of the reduction projection optical system 14, which is composed of three mirrors in total, i.e., a mirror having a parabolic surface and two mirrors each having an ellipsoidal surface. Each of the three mirrors has a reflecting surface on which multilayer films are formed in combination of Mo/Si. The reduction projection optical system 14 in the present embodiment is arranged to have the demagnification ratio of 1/5 and the image-side (exit-side) numerical aperture of 0.0625 to obtain the resolving power of not more than 0.1 .mu.m and the depth of focus of at least 1.8 .mu.m, in which the mask-side (entrance-side) numerical aperture is 0.0125. In the X-ray optical system as so arranged, the surface (reflecting surface) of optical element 1 first reflects the X-rays 12 incident thereinto as a beam of nearly parallel rays with diverging angle of at most about 0.1.degree. as described above. The optical element 1 functions as secondary light sources with diverging angle of .psi.. The value of .psi. is determined by the shape of convex portions formed on the surface of optical element 1, which is 2R.sub.x /R.sub.0x =10/160=0.0625(rad)=3.6.degree. in the direction parallel to the plane of incidence while 2R.sub.y /R.sub.0y .multidot.cos.theta..sub.0 =5/40.multidot.0.5=0.0625(rad)=3.6.degree. in the direction normal to the plane of incidence. Namely, the optical element 1 functions as secondary X-ray sources having the size of 30 mm square and the diverging angle of 3.6.degree. in either direction. The X-rays reflected by the optical element 1 are again reflected by the elliptic mirror 13 to form five times larger images of the secondary X-ray sources at the entrance pupil of reduction projection optical system 14. Accordingly, the mask 4 is illuminated in a wide region of over 150 mm square. A diverging angle of X-rays on this occasion decreases according to the magnification ratio of elliptic mirror 13, which is about 0.0125(rad)=0.72.degree. coinciding with the mask-side numerical aperture of reduction projection optical system 14. The X-rays illuminating and passing through the mask 4 then pass through the reduction projection optical system 14 to form a demagnified image of a pattern formed on the mask 4, on the wafer 5. Reduction projection exposure experiments were conducted using the X-ray optical system in the present embodiment. The experiments assured that lines and spaces of 0.1 .mu.m were resolved over an entire arc-shaped region in length of 30 mm, width of 0.2 mm and radius of 17.5 mm. Also, no difference was observed in resolving power depending on the direction in the pattern. Another exposure experiment was conducted under the same conditions except that the optical element 1 was replaced by a simple plane multilayer film mirror, which showed that only lines and spaces of up to 0.2 .mu.m could be resolved. Another X-ray optical system is next described. The structure of optical system is the same as that in FIG. 28 and omitted to show. The X-ray optical system in the present embodiment is provided with a laser plasma X-ray source 15 as X-ray source, a parabolic surface mirror 16 for reflecting X-rays emitted from the X-ray source 15 to supply a beam of nearly parallel rays, an optical element 1 functioning as secondary X-ray sources, a Schwarzschild mirror 17 acting as an illumination optical system, a mask 4 and a reduction projection optical system 14, by which a demagnified image of a pattern formed on a mask 4 is focused on a wafer 5. The parabolic surface mirror 16 has a reflecting surface having coatings of multilayer films in combination of Mo/Si, which covers X-rays in a wide solid angle range out of the X-rays isotropically emitted from the laser plasma X-ray source 15 and in which the reflecting surface (parabolic surface) is so shaped that the reflected X-rays 12 become a beam of nearly parallel rays. Multilayer films in combination of Mo/Si are formed on the surface of optical element 1. Further, the surface is so arranged that a plurality of convex portions each having an external surface of toroidal surface are formed as filling up a circular region of diameter 15 mm. The toroidal surface has such dimensions that the radius of curvature is R.sub.0x =80 .mu.m and the length is 2R.sub.x =10 .mu.m in the direction parallel to a line connecting intersection points between the plane of incidence of the X-rays (in the plane of FIG. 28) and the surface of each convex portion and that the radius of curvature is R.sub.0y =65 .mu.m and the length is 2R.sub.y =9 .mu.m in the direction perpendicular to the line connecting the above intersection points (in the direction normally passing through the plane of FIG. 28). The incident angle of X-rays 12 into the optical element 1 is set to .theta..sub.0 =26.degree.. The Schwarzschild mirror 17 is an optical system composed of two spherical mirrors 17a, 17b having a common center. Multilayer films in combination of Mo/Si are formed on a reflecting surface of each spherical mirror 17a, 17b. In order to avoid interference between the incident X-rays and the spherical mirror (convex mirror) 17a disposed near the optical axis of Schwarzschild mirror 17, the direction of principal rays of reflected light by the X-ray optical element 1 is inclined at about 10.degree. relative to the optical axis of Schwarzschild mirror 17. The reduction projection optical system 14 has the same structure as that in the previous embodiment, which is set to have the reduction ratio of 1/5 and the image-side (exit-side) numerical aperture of 0.0625 and in which the mask-side (entrance-side) numerical aperture is 0.0125. In the X-ray optical system as so arranged, the surface (reflecting surface) of X-ray optical element 1 first reflects the X-rays 12 incident thereinto as a beam of nearly parallel rays with diverging angle of at most about 0.1.degree. as described above. The optical element 1 functions as secondary X-ray sources with diverging angle of .psi.. The value of .psi. is determined by the shape of convex portions in the surface, which is 2R.sub.x /R.sub.0x =10/80=0.125(rad)=7.2.degree. in the direction parallel to the plane of incidence while 2R.sub.y /R.sub.0y .multidot.cos.theta..sub.0 =9/65.multidot.0.9=0.125(rad)=7.2.degree. in the direction perpendicular to the plane of incidence. Namely, the X-ray optical element 1 functions as secondary light sources with diameter 15 mm and diverging angle 7.2.degree.. The X-rays reflected by the optical element 1 are again reflected by the Schwarzschild mirror 17 to form 10-times larger images of the secondary X-ray sources at the entrance pupil of reduction projection optical system 14. Accordingly, the mask 4 is illuminated in a wide region of about 150 mm. A diverging angle of X-rays on this occasion decreases according to the magnification ratio of Schwarzschild mirror, which is 0.0125(rad)=0.72.degree. coinciding with the mask-side numerical aperture of reduction projection optical system 14. The X-rays illuminating and passing through the mask 4 then pass through the reduction projection optical system 14 to form a demagnified image of the pattern formed on the mask 4, on the wafer 5. Reduction projection exposure experiments were conducted using the X-ray optical system in the present embodiment. The experiments assured that lines and spaces of 0.1 .mu.m were resolved over an entire arc-shaped region in length of 30 mm, width of 0.2 mm and radius of 17.5 mm. Also, no difference was observed in resolving power in either direction in pattern. Another exposure experiment was conducted under the same conditions except that the optical element 1 was replaced by a plane multilayer film mirror, which showed that only lines and spaces of up to 0.2 .mu.m could be resolved. Incidentally, the optical elements in the present embodiment are not limited to the applications in the X-ray reduction projection exposure apparatus, but can be widely applied to other X-ray optical instruments utilizing image formation with X-rays. For example, the present embodiment may also be applied to a 1:1 projection exposure apparatus using the Offner optical system, whereby a resolving power of the diffraction limit can be attained in a wide exposure region similarly as in the case of reduction projection exposure. Also, applying the present invention to an illumination optical system in X-ray microscope, the field of microscope can be greatly increased. Embodiment II Next described are preferred embodiments of production method of the optical elements as described above. Embodiment a FIGS. 29A to 29C are drawings to illustrate the scheme of an embodiment of an optical element for X-ray reflection in the present invention and steps for producing it. As shown in FIG. 29C, an X-ray-reflecting optical element 1 is composed of a substrate 20 made of silicon, a photoresist layer 21 formed on the substrate 20 and having a plurality of nearly semispherical convex portions, and multilayer films 23 formed on the resist layer 21. In producing the optical element 1, as shown in FIG. 29A, a mirror-polished silicon substrate 20 in diameter of 3 inches and thickness of 5 mm was first prepared and a photoresist was uniformly deposited in thickness of 0.2 .mu.m on the polished surface to form a photoresist layer 21. Then, ultraviolet rays 81 were irradiated through a mask 22 with a predetermined pattern formed thereon to effect exposure on the resist layer 21. The mask 22 had a pattern of circles each in diameter of 5 .mu.m as arranged at pitch of 10 .mu.m. Employed as the exposure method was the proximity exposure method in which the photoresist layer 21 and the mask 22 were set with a separation s between them without contact with each other. The value of s was about 100 .mu.m in the present embodiment. Diffraction of light in the exposure caused an unfocused image of the pattern on the mask 22 to be transferred onto the photoresist layer 21, and therefore the cross section of photoresist layer 21 after development was smooth as shown in FIG. 29B, whereby almost semispherical convex portions were formed. Further, molybdenum and silicon were alternately deposited by the sputtering method on the photoresist layer 21 to form multilayer films 23 thereon, thus obtaining the optical element 1 for X-ray reflection as shown in FIG. 29C. Although the convex portions were formed using the photoresist in the present embodiment, another photosensitive material such as photoreactive polyimide may be employed. Also, changing the pattern of mask 22 can change the shape of convex portions formed in the photoresist layer 21. For example, in case the convex portions are desired to be formed in a shape of toroidal surface, the pattern on the mask 22 may be formed in an elliptic shape having different pitches in the vertical and horizontal directions. As an example, ellipses with 5 .mu.m (major axis diameter).times.3 .mu.m (minor axis diameter) are preferably formed at pitch of 10 .mu.m in the direction of major axis and at pitch of 6 .mu.m in the direction of minor axis on the mask 22. A multilayer film reflecting surface can be formed in the shape of toroidal surface by similarly forming multilayer films 23 on the thus formed photoresist layer 21. Embodiment b FIGS. 30A to 30C are drawings to illustrate the scheme of an embodiment of optical element and steps for producing it. As shown in FIG. 30C, an optical element 1 is composed, similarly as in Embodiment a, of a substrate 20 made of silicon, a photoresist layer 21 formed on the substrate and having a plurality of nearly semispherical convex portions, and multilayer films 23 formed on the resist layer 21. In producing the optical element 1, a mirror-polished silicon substrate 20 with diameter of 3 inches and thickness of 5 mm was first prepared and a photoresist was uniformly deposited in thickness of 0.2 .mu.m on the polished surface. Then, the photoresist was patterned by the ordinary photolithography process. The patterning was set such that the photoresist layer 21 after development had a pattern of circular cylinders of photoresist each with diameter of 6 .mu.m and height of 0.2 .mu.m aligned at pitch of 10 .mu.m as shown in FIG. 30A. After the patterning, post-bake of photoresist layer 21 was carried out at a temperature (200.degree. C. in the present embodiment) higher than the glass transition point of the photoresist. The post-bake softened the photoresist layer 21 to make the shape smooth as shown in FIG. 30B, forming nearly semispherical convex portions. Further, molybdenum and silicon were alternately deposited by the sputtering method on the photoresist layer 21 to form the multilayer films 23, thus obtaining the optical element 1 as shown in FIG. 30C. Also, changing the shape of photoresist columns (reference numeral 21) shown in FIG. 30A can change the shape of the convex portions (reference numeral 21) in FIG. 30B. For example, if the patterning is effected with photoresist columns shaped in the form of elliptic cylinder, the convex portions in FIG. 30B may be formed in the shape of toroidal surface. In this case, it is preferred that elliptic cylinders with 6 .mu.m (major axis diameter).times.4.5 .mu.m (minor axis diameter) are arranged at pitch of 10 .mu.m in the direction of major axis and at pitch of 7.5 .mu.m in the direction of minor axis. A multilayer reflecting surface having the toroidal surface shape can also be formed by similarly forming multilayer films 23 on the convex portions. Embodiment c FIGS. 31A to 31C are drawings to illustrate the scheme of an embodiment of optical element and steps for producing it. As shown in FIG. 31C, an optical element 1 is composed of a substrate 20 made of silicon, a polyimide layer 24 formed on the substrate 20 and having a plurality of nearly semispherical convex portions, and multilayer films 23 formed on the polyimide layer 24. In producing the optical element 1, a mirror-polished silicon substrate 20 with diameter of 3 inches and thickness of 5 mm was first prepared and a photoreactive polyimide resin was deposited in thickness of 1 .mu.m on the polished surface. Then the polyimide resin was subjected to exposure, development and baking to obtain a first polyimide layer 24a in which cylinders of the polyimide resin each with diameter of 5 .mu.m and height of 1 .mu.m as shown in FIG. 31A were arranged in pitch of 10 .mu.m. Then, the polyimide resin was again deposited (in thickness of about 0.5 .mu.m) on the first polyimide layer 24a to cover the pattern portions. A second polyimide layer 24b was formed by baking it with performing neither exposure nor development. The viscosity of polyimide resin caused the second polyimide layer 24b to have ups and downs according to the shape of first polyimide layer 24a as the underlayer, forming nearly semispherical convex portions. Further, molybdenum and silicon were alternately deposited by the sputtering method on the second polyimide layer 24b to form multilayer films 23, thus obtaining the optical element 1 as shown in FIG. 31C. The second polyimide layer 24b does not always have to be the same photoreactive polyimide resin as the first polyimide layer 24a, but may be a polyimide resin which is not photosensitive. The production method in the present embodiment can be also effective in case either one or the both of the first polyimide layer 24a and the second polyimide layer 24b are replaced by a layer or layers of photoresist. Changing the shape of photoresist columns (reference numeral 24a) as shown in FIG. 31A can change the shape of convex portions (reference numeral 24b) in FIG. 31B into the shape of toroidal surface. In this case, the photoresist columns 24a in FIG. 31A are preferably formed for example as elliptic cylinders each with 5 .mu.m (major axis diameter).times.4 .mu.m (minor axis diameter) arranged at pitch of 10 .mu.m in the direction of major axis and at pitch of about 8 .mu.m in the direction of minor axis. Embodiment d FIGS. 32A to 32C are drawings to illustrate the scheme of an embodiment of optical element and steps for producing it. As shown in FIG. 32C, an optical element 1 is composed of a substrate 20 made of silicon, a polyimide layer 24 formed on the substrate 20 and having a plurality of nearly semispherical convex portions, and multilayer films 23 formed on the polyimide layer 24. In producing the optical element 1, a mirror-polished silicon substrate 20 with diameter of 3 inches and thickness of 5 mm was first prepared and a polyimide resin was screen-printed onto the polished surface to form a polyimide layer 24 in a pattern of cylinders each with diameter of 5 .mu.m and height of 1 .mu.m as shown in FIG. 32A. Then, the pattern was left to stand in a clean atmosphere for thirty minutes. As a result, the polyimide layer 24 after the patterning spread over the substrate 20 by its own weight to become nearly semispherical in shape because of the surface tension. Then the polyimide layer 24 was baked to form semispherical convex portions. Further, molybdenum and silicon were alternately deposited by the sputtering method on the polyimide layer 24 to form multilayer films 23, thus obtaining the optical element 1 as shown in FIG. 32C. Although the convex portions in the optical element were formed using the polyimide resin in the present embodiment, the convex portions may be formed by screen-printing a glass paste on a substrate 20 made of a ceramic such as alumina (Al.sub.2 O.sub.3) or silicon carbide (SIC) and baking it. Also in this case, if the photoresist columns (reference numeral 24) in FIG. 32A are formed in elliptic shape, the convex portions in the polyimide layer 24 can be formed in the shape of toroidal surface. A preferable shape and arrangement pitches of the elliptic cylinders in this case are the same as those in Embodiment c. Embodiment e FIGS. 33A to 33D are drawings to illustrate the scheme of an embodiment of optical element and steps for producing it. As shown in FIG. 33D, an optical element 1 is composed of a substrate 20 made of silicon and having a plurality of convex portions, and multilayer films 23 formed on the substrate 20. In producing the optical element 1, a mirror-polished silicon substrate 20 with diameter of 3 inches and thickness of 5 mm was first prepared and a photoresist was uniformly deposited in thickness of 1 .mu.m on the polished surface. Then, the patterning of photoresist was carried out by the ordinary photolithography process similarly as in Embodiment b. The patterning was set such that cylinders of photoresist each with diameter of 6 .mu.m and height of 0.2 .mu.m were formed in a pattern arranged at pitch of 10 .mu.m after development. After the patterning, post-bake of the photoresist layer 21 was carried out at a temperature (200.degree. C. in the present embodiment) higher than the glass transition point of the photoresist. The post-bake caused the photoresist to soften to form nearly semispherical convex portions, whereby the photoresist layer 21 was shaped in a pattern as shown in FIG. 33A. Then, reactive ion etching was carried out with a mask of the thus patterned photoresist layer 21 under the condition that a selection ratio of resist and silicon was approximately 1. Mixture gas of CF.sub.4 and H.sub.2 was used as reactive gas in the etching. FIG. 33B shows a midway state of the etching. Since the etching speed for resist layer 21 was equal to that for silicon substrate 20, the silicon substrate 20 was etched deeper in thinner portions in the patterned resist. As a result, the shape of resist layer 21 is transferred onto the silicon substrate 20. Accordingly, the reactive ion etching forms nearly semispherical convex portions as shown in FIG. 33C on the silicon substrate 20. After the etching was completed, molybdenum and silicon were alternately deposited by the sputtering method on the silicon substrate 20 to form multilayer films 23, thus obtaining the optical element 1 as shown in FIG. 33D. Although the present embodiment employed silicon as a material for substrate, the substrate material may be a ceramic such as silicon carbide (SIC) or glass. Also, the patterning of resist layer 21 can be performed using either one of the methods used in Embodiments a, c and d, as well as the method used in Embodiment b. Further, the resist may be replaced by a resin such as polyimide. Also in this method, the convex portions in the silicon substrate 20 can be formed in the shape of toroidal surface. In this case, the convex portions (reference numeral 21) in FIG. 33A are formed in the shape of semi-elliptic sphere. This example of formation is the same as that in Embodiment b. For example, a preferable shape of the elliptic cylinders formed by the photolithography process is elliptic of 6 .mu.m (major axis diameter).times.4.5 .mu.m (minor axis diameter) and they are preferably arranged at pitch of 10 .mu.m in the direction of major axis and at pitch of about 7.5 .mu.m in the direction of minor axis. Embodiment f FIGS. 34A to 34D are drawings to illustrate the scheme of an embodiment of optical element and steps for producing it. As shown in FIG. 34D, an optical element 1 is composed of a substrate 20 made of silicon and having a plurality of concave portions, and multilayer films 23 formed on the substrate 20. In producing the optical element 1, a mirror-polished silicon substrate 20 with diameter of 3 inches and thickness of 5 mm was first prepared and the polished surface was thermally oxidized to form a SiO.sub.2 layer 25 of thickness 0.5 .mu.m as shown in FIG. 34A. Then, a resist (not shown) was deposited on the layer 25, and the deposited resist was subjected to patterning by the ordinary photolithography process. Further, reactive ion etching was carried out with mixture gas of CHF.sub.3, H.sub.2 and O.sub.2 using the mask of thus patterned resist, whereby holes were formed in diameter of 2 .mu.m and at pitch of 10 .mu.m in the SiO.sub.2 layer 25 (FIG. 34B shows a state after the resist was removed). After that, the silicon substrate 20 was etched while dipped in an etching solution which was a mixture solution of hydrogen fluoride (HF), nitric acid (HNO.sub.3) and acetic acid (CH.sub.3 COOH). In the etching, the etching solution isotropically etched the silicon substrate 20 through the holes formed in the SiO.sub.2 layer 25. Thus, when the silicon substrate 20 was lifted up from the etching solution after a predetermined time elapsed, semispherical concave portions as shown in FIG. 34C were formed in the silicon substrate 20. After the etching was completed, the SiO.sub.2 layer 25 was dissolved with hydrogen fluoride (HF) to be removed. Then, molybdenum and silicon were alternately deposited by the sputtering method on the silicon substrate 20 to form multilayer films 23, thus obtaining the optical element 1 as shown in FIG. 34D. Using this method, the concave portions formed in the silicon substrate 20 may be formed in the shape of toroidal surface by forming the holes in the SiO.sub.2 layer 25 in the shape of predetermined ellipse. A preferable shape of ellipse is of 4 .mu.m (major axis diameter).times.2 .mu.m (minor axis diameter). The ellipses are preferably arranged at pitch of 12 .mu.m in the direction of major axis and at pitch of about 10 .mu.m in the direction of minor axis. Embodiment g Next described are other embodiments for forming concave surfaces on a substrate. If the optical element of the type shown in FIG. 22 is desired to be formed, the concave portions may be made by a die body 100 having a convex portion 101 corresponding to a concave portion of groove to be formed, at the lower distal end thereof, as shown in FIG. 35. The concave portions each corresponding to the convex portion 101 are formed on the surface of substrate 102 by pressing the die body 100 against the surface of substrate 102. Although FIG. 35 shows a die body 100 having a single convex portion 101, the die body 100 may have a plurality of columns of convex portions 101. In this case, a plurality of concave portions 101 can be formed at a time on the surface of substrate 102 by pressing the die body 100 against the substrate 102. In another embodiment, the concave portions may be formed by grinding the surface of substrate 102 by a rotary disk grinder 105 as shown in FIG. 36, or by polishing the surface of substrate 102 utilizing a polishing arm 106 as shown in FIG. 37. These methods permit spherical surfaces or toroidal surfaces to be formed as well as the concave portions of grooves. Although the above embodiments showed examples in which the concave portions are formed, convex portions may also be formed on the substrate by a replica of the concave portions with a glass or plastic material. The optical elements as described in the above embodiments are exposed to relatively strong X-rays, because they are set at a position close to the X-ray source as a light source. Most of X-rays which were not reflected are absorbed by the optical element and the energy of absorbed X-rays increases the temperature of optical element. Therefore, the thermal resistance is an important factor for the optical element for X-ray reflection. Although the optical elements in the present invention can be produced by the various methods as described in Embodiments a to g, the methods for forming the convex portions on the reflecting surface using a photoresist (as in Embodiments a and b) are relatively easy but provide optical elements low in thermal resistance, for example about 100.degree. C., because the thermal resistance of optical element depends upon the thermal resistance of the resist. In contrast, when the polyimide, which is a heat resistant resin, is used (as in Embodiments c and d), the thermal resistance is more than 300.degree. C. Further, the thermal resistance is about 800.degree. C. in the method of printing and baking a glass paste on a ceramic substrate or in the method of making concave portions on a silicon substrate by etching. Yet further, higher thermal resistance of over 1000.degree. C. is possible by the method in which the concave portions are formed by etching a ceramic substrate. The issue of thermal resistance should be considered also for the multilayer films for reflecting the X-rays. The above embodiments employed the multilayer films in combination of Mo/Si, which has the thermal resistance only of about 300.degree. C. Accordingly, in case further higher thermal resistance is necessary, the multilayer films should be made of materials themselves having higher thermal resistance (for example, a combination of Mo/SiC). As described, the optical elements of the present invention can be used for an X-ray source emitting X-rays with very high intensity and produced with necessary thermal resistance matching the intensity of operating X-rays. Also, the optical elements do not have to be formed too strict as to the accuracy of shape of fine convex portions or concave portions provided on the substrate. However, it is preferable that the roughness of the surface is too low to lower the reflectivity of multilayer films formed on the substrate. For example, it is preferable that the surface is smooth in roughness of below several angstroms in square mean. Embodiment III Next described is an exposure apparatus using either one of the optical elements as described above. Conventional optical apparatus have an optical system for irradiating a certain region with light emitted from a light source, for example as disclosed in U.S. Pat. No. 4,668,077. The optical apparatus, however, has such a drawback that an X-ray-irradiated region cannot be wide enough in case of the X-rays being used as light source. In contrast, an exposure apparatus according to the present invention utilizes the optical element(s) as described above to enable irradiation of X-rays in a wide region. Preferred embodiments of exposure apparatus will be described in the following. As shown in FIG. 38, an exposure apparatus is constituted by an illumination optical apparatus for irradiating X-rays onto a mask M and a stepper composed mainly of a mask stage MS and a wafer stage WS. The illumination optical apparatus is composed of a light source portion 110 for radiating X-rays, a plane mirror 111, an integrator mirror 120 and a parabolic surface mirror 130. Also, the stepper is composed of a mask stage MS for successively moving the mask M, a projection optical system 140 provided below the mask stage MS, and a wafer stage WS for successively moving the wafer W. The structure of each device will be described in detail. The light source portion 110 has an X-ray source for supplying SOR radiation, a front-end optical system having an oblique incidence mirror and a filter, and a slit. The radiation from the X-ray source passes through the front-end optical system where X-rays only with wavelengths near 130 .ANG. are selected. Then the selected X-rays pass through a slit to be shaped in a desired beam shape and then the shaped X-rays are emitted from the light source portion 110. The light source portion 110 may be so constructed as to have a laser plasma X-ray source and a parabolic surface mirror for converting X-rays from the X-ray source into a beam of parallel rays. FIG. 39 shows an optical system set in the illumination optical apparatus. Subsequently, the thus collimated X-rays from the light source portion 110 reach the plane mirror 111 inclined at 45.degree. relative to the X-ray outgoing direction, whereby the optical paths of the rays are deflected by 90.degree.. Then the rays reach the integrator mirror 120 inclined at a predetermined angle relative to the X-ray proceeding direction. Here, multilayer films in combination of Mo (molybdenum)/Si (silicon) are formed on the surface of each of the above-described oblique incidence mirror, parabolic surface mirror, plane mirror 111 and integrator mirror 120. The integrator mirror 120 has such a structure that there are a plurality of fine convex portions 7 provided on a substrate 6 and multilayer films 9 for reflecting X-rays formed on the convex surfaces 7, as shown in FIG. 6. Here, a portion of multilayer films 9 on each convex surfaces 7 will be called as a mirror element 7a. An enough condition is that the size of the mirror elements 7a is sufficiently smaller than the size of integrator mirror 120 itself. In the present embodiment, each mirror element 7a is formed in a spherical shape. The mirror elements 7a are preferably arranged such that the convex surfaces 7 are continuously formed as shown in FIG. 5, which is a perspective view of the integrator mirror 120. If there are flat portions between convex portions, X-rays reflected by the flat portions could be condensed by the parabolic surface mirror 130 on the mask M, which is not preferable. Returning to FIG. 39, the X-rays entering the integrator mirror 120 are reflected by a plurality of mirror elements 7a to form a plurality of secondary X-ray sources LS.sub.1 to LS.sub.3. It should be noted here that FIG. 39 shows only three secondary X-ray sources LS.sub.1 to LS.sub.3 out of numerous secondary light sources actually formed. Since each mirror element 7a is constructed with the convex surface thereof being on the X-ray incidence side, the collimated X-rays are reflected with a certain diverging angle according to the curvature of each mirror element 7a. Virtual images of the X-rays with the diverging angle become the secondary X-ray sources LS.sub.1 to LS.sub.3. Namely, a plurality of secondary X-ray sources LS.sub.1 to LS.sub.3 are formed on a plane parallel to the surface of integrator mirror 120 below the integrator mirror 120 (on the opposite side to the entrance side). Here, the number of secondary X-ray sources LS.sub.1 to LS.sub.3 corresponds to the number of mirror elements 7a in the integrator mirror 120. The X-rays outgoing from the integrator mirror 120 reach the parabolic surface mirror 130 with the certain diverging angle. The parabolic surface mirror 130 is constructed such that multilayer films in combination of Mo (molybdenum)/Si (silicon) are formed on a paraboloid of revolution having the center of axis Ax.sub.30 inclined with respect to the normal line to the mask M. The parabolic surface mirror 130 is so set that the focus of parabolic surface is located on the mask M and the front focus of the parabolic surface mirror 130 is located on the secondary X-ray sources LS.sub.1 to LS.sub.3. The front focus of parabolic surface mirror 130 in the present embodiment means a point where a beam of parallel rays emitted from the focus of parabolic surface is focused via the parabolic surface mirror 130. In other words, the front focus of parabolic surface mirror is a Fourier transform plane for the focus of parabolic surface. Accordingly, the diverging X-rays from the secondary X-ray source LS.sub.2 become parallel rays via the parabolic surface mirror 130 and the parallel rays proceed along the normal line to the mask M. Also, the diverging X-rays from the secondary X-ray sources LS.sub.1 and LS.sub.3 become parallel rays via the parabolic surface mirror 130 and the parallel rays proceed at respective certain angles relative to the normal line to the mask M. Namely, the X-rays from the plurality of secondary X-ray sources LS.sub.1 to LS.sub.3 via the parabolic surface mirror 130 illuminate the mask M in a superimposed manner to form a lighting field LF. Since the rays emerging from the secondary X-ray source LS.sub.2 are principal rays, telecentric illumination can be achieved on the mask M. In the illumination optical apparatus in the present embodiment, an unrepresented supporting member supports the integrator mirror 120 and the parabolic surface mirror 130 in a united manner, and the supporting member is arranged as rotatable about a rotation axis Ax.sub.20 passing through the integrator mirror 120 and being parallel to the principal rays from the parabolic surface mirror 130. The supporting member is driven by a motor 112 to rotate about the rotation axis Ax.sub.20. FIG. 40 shows a positional relation between the illumination area and the mask. In case the focus of parabolic surface in the parabolic surface mirror 130 is at the left edge of mask M, the X-rays from the light source portion 110 via the integrator mirror 120 and the parabolic surface mirror 130 form a nearly circular light field LF.sub.L at the left edge of mask M. Also, in case the focus of parabolic surface in the parabolic surface mirror 130 is at the right edge of mask M, the X-rays from the light source portion 110 via the integrator mirror 120 and the parabolic surface mirror 130 form a nearly circular light field LF.sub.R at the right edge of mask M. An arc-shaped illumination area LA is formed around the rotation axis Ax.sub.20 on the mask M by irradiating the X-rays onto the mask M while pivoting the integrator mirror 120 and the parabolic surface mirror 130 in a united manner. An annular illumination area can be formed by fully rotating the integrating mirror 120 and the parabolic surface mirror 130 instead of pivoting the integrator mirror 120 and the parabolic surface mirror 130 in a certain range as described. If the integrator mirror 120 and the parabolic surface mirror 130 are located at respective positions where the X-rays are irradiated onto a portion different from a position on the mask M (i.e., onto a position different from the illumination area LA in FIG. 40), it is preferable that the X-rays from the light source portion 110 are arranged to be interrupted. It is preferred that the rotation axis Ax.sub.20 is arranged to pass through the position of barycenter in the effective reflection area in the integrator mirror 120. If the rotation axis Ax.sub.20 is greatly offset from the barycenter position of effective reflection area in the integrator mirror 120, a loss occurs in reflecting the X-rays from the plane mirror 111, which is not preferable. The effective reflection area in the integrator mirror 120 means an area where the multilayer films 9 are provided. Next described with FIG. 41 is the structure of the stepper for successively moving the mask stage MS and the wafer stage WS. The stepper has the general structure for example as disclosed in Japanese Laid-open Patent Application No. 61-251025. The mask stage MS is constructed as movable in the Y direction, in the Z direction (in the direction normal to the plane of FIG. 41) and in a direction oblique to the YZ plane while carrying the mask M thereon. Also, the wafer stage WS set below the mask stage MS is constructed as movable in the Y direction, in the Z direction and in a direction oblique to the YZ plane as described while carrying the wafer W thereon. The mask stage MS and the wafer stage WS are intermittently driven along the Y direction by pulse motors 61 and 62, respectively. The moving positions of the stages MS and WS are detected by laser interferometers 63 and 64, respectively. The detection results are supplied to a drive control unit 65. The drive control unit 65 performs a synchronous control of moving amounts of the mask stage MS and the wafer stage WS, based on the detection results. In more detail, the drive control unit 65 outputs pulse signals as control signals to the pulse motors 61, 62. The drive control unit 65 also controls the rotation of motor 112 for rotation-driving the rotation axis Ax.sub.20. Accordingly, the X-rays can be irradiated over the entire surface of mask M by conveying the mask M in the X direction while rotating (pivoting) the integrator mirror 120 and the parabolic surface mirror 130 under the control of drive control unit 65. The exposure operation on the mask M is next described with reference to FIGS. 42A to 42C. FIGS. 42A to 42C are plan views to show the relation between the mask M and the illumination area. The following description concerns a case in which the integrator mirror 120 and the parabolic surface mirror 130 are reciprocated as pivoted about the rotation axis Ax.sub.20. In FIG. 42A, when the integrator mirror 120 and the parabolic surface mirror 130 are pivoted rightward (in the direction of arrow in the figure) about the rotation axis Ax.sub.20, an arc-shaped illumination are LA.sub.1 is formed on the mask M. On this occasion, the mask M is also moved along the X direction in the figure. It is preferable that the speed of pivotal movement for forming the illumination area LA.sub.1 is sufficiently faster than the conveying speed of mask M. If a difference of speed is little between the conveying speed and the pivoting speed of mask M, dispersion of exposure could occur in the direction perpendicular to the conveying direction (in the direction of Y axis) on the mask M. After the rightward pivoting operation of integrator mirror 120 and parabolic surface mirror 130 is completed (or when the right edge of illumination area LA.sub.1 is formed), the integrator mirror 120 and the parabolic surface mirror 130 start pivoting leftward (in the direction of arrow in the figure) about the rotation axis Ax.sub.20, as shown in FIG. 42B. The leftward pivotal operation forms an illumination area LA.sub.2 on the mask M. Taking the reference on the mask M, the illumination area LA.sub.1 and the illumination area LA.sub.2 are formed as partly overlapping. After the leftward pivoting operation of integrator mirror 120 and the parabolic surface mirror 130 is completed (when the left edge of illumination area LA.sub.2 is formed), the integrator mirror 120 and the parabolic surface mirror 130 then start pivoting again rightward (in the direction of arrow in the figure) about the rotation axis Ax.sub.20, as shown in FIG. 42C. This operation forms an illumination area LA.sub.3 on the mask M. With reference on the mask M, the illumination area LA.sub.2 and the illumination area LA.sub.3 are formed as partly overlapping with each other. As described above, the X-rays can be irradiated over the entire surface of mask M by scanning the lighting field LF in an arc shape while conveying the mask M. It is recommended that the pivoting (rotating) operation of integrator mirror 120 and the parabolic surface mirror 130 be started from the point where the mask M is located outside the illumination area LA. There are shielding patterns formed on the mask M. X-rays through the mask M pass through the projection optical system 140 disposed below the mask M and then form an image of a pattern on mask M, on the wafer W the surface of which is coated with a resist. The projection optical system 140 is at a magnification ratio of 1:1 and bitelecentric. The projection optical system 140 is a so-called Offner optical system having the basic structure including a concave mirror 42 and a convex mirror 43 (see FIG. 38). Reflecting mirrors 41 and 44 are provided in an optical path between the mask M and the concave mirror 42 and in an optical path between the concave mirror 42 and the wafer W, respectively, to deflect the respective optical paths by about 90.degree.. The concave mirror 42 and the convex mirror 43 are arranged such that their centers of curvature approximately coincide with each other. The radius of curvature of the convex mirror 43 is a half of the radius of curvature of the concave mirror 42. Multilayer films in combination of Mo (molybdenum)/Si (silicon) are formed on the surface of each of the concave mirror 42, convex mirror 43 and plane mirrors 41, 44 constituting the projection optical system 140. In the present embodiment, images of the secondary X-ray sources LS.sub.1 to LS.sub.3 formed by the integrator mirror 120 are formed on the pupil plane of projection optical system 140. The images of the plural secondary X-ray sources LS.sub.1 to LS.sub.3 formed on the pupil plane of projection optical system 140 have the size approximately equal to the pupil of projection optical system 140. In other words, the numerical aperture on the mask M side by the integrator mirror 120 and the parabolic surface mirror 130 is almost equal to the numerical aperture of projection optical system 140 on the mask M side. This can permit an image of mask M to be formed on the wafer W under the resolving power of the diffraction limit of projection optical system 140. The numerical aperture of illumination apparatus can be made variable of course by changing the area of the effective reflection region in the integrator mirror 120. The present embodiment employs the Offner optical system for forming a real size image of mask M, as the projection optical system 140, but a reduction projection optical system for forming a demagnified image of mask M can be employed instead thereof. For example, a Schwarzschild optical system may be applied as such a reduction projection optical system. The wafer W is mounted on the wafer stage WS movable along the X axis in FIG. 38. Since the present embodiment employs the 1:1 projection optical system, the wafer stage WS is arranged to move at the same speed as that of mask stage MS. In case the projection optical system is a reduction projection optical system, a moving amount of wafer stage WS may be set a demagnification ratio smaller than that of mask stage MS. When the mask M and the wafer W are moved while pivoting (rotating) the integrator mirror 120 and the parabolic surface mirror 130, an image of mask M is successively formed on the wafer W with the movement of mask M and wafer W. This can enlarge the illumination region in the direction perpendicular to the conveying direction (in the direction of Y axis) by rotation (pivotal movement) of the integrator mirror 120 and the parabolic surface mirror 130 even if the size of parabolic surface mirror 130 is small (even if the lighting field LF is small). Namely, the present embodiment permits a large illumination area (exposure area) to be obtained without increasing the size of parabolic surface mirror 130. In the present embodiment, the integrator mirror 120 is inclined at the predetermined angle relative to the direction of incidence of X-rays. This can spatially separate the X-ray beams (incident beams) entering the integrator mirror 120 from the X-ray beams (outgoing beams) outgoing from the integrator mirror 120. The incident angle of X-rays into the integrator mirror 120 (an angle which the X-rays entering the integrator mirror 120 make with the normal line to the integrator mirror 120) is preferably as small as possible. The incident angle must be determined as an angle by which the incident beams and the outgoing beams can at least be spatially separated from each other. Especially, if the SOR radiation is used as the light source portion 110, the radiation is nearly linearly polarized. Then, with an increase in incident angle into the integrator mirror 120, the polarization state of X-rays incident into the integrator mirror 120 changes upon rotation of integrator mirror 120, which could unpreferably change the intensity of reflected X-rays. Another embodiment is next described referring to FIG. 43. FIG. 43 is a drawing to show the main part of illumination apparatus. FIG. 43 employs the same coordinate system as in FIG. 39 and the same reference numerals for elements or members having the same functions as those in the embodiment shown in FIG. 39 for brevity of illustration. The embodiment in FIG. 43 is different from the embodiment in FIG. 39 in that an integrator mirror 125 having concave portions on the surface thereof replaces the integrator mirror 120 having the convex portions on the surface thereof. The integrator mirror 125 is constructed such that a plurality of fine concave portions 8 are formed on a substrate 6 and multilayer films 9 for reflecting X-rays are formed over the concave portions 8, as shown in the cross section of FIG. 7. A portion of multilayer films 9 on each concave portion 8 will be called as a mirror element 8a. A sufficient condition is that the size of the mirror elements 8a is sufficiently smaller than the size of integrator mirror 125 itself. In the present embodiment, each mirror element 8a is formed in a spherical shape. It is preferable for the mirror elements 8a that the concave portions 8 are continuously formed similarly as in the previous embodiment. Now returning to FIG. 43, X-rays of predetermined wavelength (for example 130 .ANG.) from an unrepresented light source portion reach the plane mirror 111, which deflects the optical path thereof by about 90.degree., similarly as in the previous embodiment. The deflected X-rays then reach the integrator mirror 125 inclined relative to the deflected optical path. The X-rays entering the integrator mirror 125 are parallel. Accordingly, the parallel rays (X-rays) are condensed by a plurality of mirror elements 8a in the integrator mirror 125 to form a plurality of secondary X-ray sources LS.sub.1 to LS.sub.3 at a distant position on the other side of integrator mirror 125. It should be noted that FIG. 43 shows only three secondary X-ray sources LS.sub.1 to LS.sub.3 out of numerous secondary X-ray sources actually formed. Here, the plurality of secondary X-ray sources LS.sub.1 to LS.sub.3 are formed nearly in parallel with the surface of integrator mirror 125. X-rays from the plurality of secondary X-ray sources LS.sub.1 to LS.sub.3 proceed toward the parabolic surface mirror 130 with a certain diverging angle according to the curvature of each mirror element 8a in the integrator mirror 125. The parabolic surface mirror 30 is constituted by a paraboloid of revolution about the axis Ax.sub.30 inclined with respect to the normal line to the mask M. The focus of parabolic surface is arranged to be located on the mask M and the front focus of parabolic surface mirror 130 is located on the plurality of secondary X-ray sources LS.sub.1 to LS.sub.3. Thus, the diverging X-rays from the secondary X-ray source LS.sub.2 pass via the parabolic surface mirror 130 to become a beam of parallel rays. Then the parallel beam proceeds along the normal line to the mask M. Namely, since the X-rays from the secondary X-ray source LS.sub.2 are principal rays, telecentric illumination is achieved on the mask M. Also, the diverging X-rays from the secondary X-ray sources LS.sub.1 and LS.sub.3 become parallel via the parabolic surface mirror 130, and the parallel rays proceed at respective angles to the normal line to the mask M. In other words, the X-rays from the plurality of secondary X-ray sources LS.sub.1 to LS.sub.3 via the parabolic surface mirror 130 illuminate the mask M in a superimposed manner to form a lighting field LF. In the present embodiment, the integrator mirror 125 and the parabolic surface mirror 130 are also arranged as rotatable about the rotation axis Ax.sub.25. The rotation axis Ax.sub.25 passes through the integrator mirror 125 and is parallel to the principal rays of X-rays from the parabolic surface mirror 130. From the same reason as in the previous embodiment, the rotation axis Ax.sub.25 is preferably set to pass through the position of barycenter of the effective reflection region in the integrator mirror 125. When the lighting field LF is formed on the mask M by the X-rays from the unrepresented light source portion while rotating the integrator mirror 125 and the parabolic surface mirror 130 about the rotation axis Ax.sub.25, an arc-shaped illumination area is formed about the rotation axis Ax.sub.25 on the mask M. Then, the X-rays can be irradiated over the entire surface of mask M by conveying the mask M along the X axis. As described above, the present embodiment also permits enlargement of illumination area in the direction perpendicular to the conveying direction of mask M (in the direction of Y axis) by rotating (pivoting) the integrator mirror 125 and the parabolic surface mirror 130. This permits a wide illumination area to be obtained without increasing the size of parabolic surface mirror 130. An exposure apparatus which can achieve a resolving power of the diffraction limit over a wide exposure area can be provided by combining the illumination optical apparatus in the present embodiment with the projection optical system in FIG. 41. From the above embodiments, it is seen that the integrator mirror for forming a plurality of secondary X-ray sources may have the surface constructed of either convex surfaces or concave surfaces. Also, the above embodiments employed the transmitting mask with an illuminated surface transmitting X-rays, but a reflecting mask with an illuminated surface reflecting X-rays may also be employed. In case of the reflecting mask being employed, the mask is arranged as inclined such that a certain angle is made between the normal line to the reflecting mask and the principal rays of X-rays from the parabolic surface mirror. This arrangement can spatially separate the X-rays irradiated from the illumination apparatus onto the mask, from the X-rays reflected by the mask and then proceeding toward the projection optical system, and can avoid mechanical interference between the illumination apparatus and the projection optical system. The conveying direction of mask is a direction along and in the mask surface, which is perpendicular to a chord to the arc-shaped illumination area formed on the mask. Although the previous embodiments used X-rays of predetermined wavelength as electromagnetic waves, the present invention is not limited to them. Next described is an embodiment using ultraviolet light as electromagnetic waves, referring to FIG. 44. FIG. 44 employs the same coordinate system as in FIGS. 38, 39 and 43 and the same reference numerals for elements or members having the same functions as those in FIG. 38 and FIG. 39 for brevity of illustration. In FIG. 44, a light source portion 115 is composed of a laser beam source for supplying an excimer laser beam for example of ArF (193 nm), KrF (249 nm), etc. and a beam expander for expanding the beam size of excimer laser beam. Alternatively, the light source portion may be constructed of a light source such as a mercury lamp, an elliptic mirror with first focus located at the position of light source, and a collimator lens for collecting light from the light source via the elliptic mirror and converting it into a beam of parallel rays. The illumination light from the light source portion 115 reaches a plane mirror 116 inclined at 45.degree. relative to the optical path of illumination light. The optical path is deflected about 90.degree. by the plane mirror 116 and the thus deflected light enters a fly's eye lens 150. The fly's eye lens 150 has a plurality of lens elements 150a.sub.1 to 150a.sub.3 and forms a plurality of secondary light source images LS.sub.1 to LS.sub.3 on the exit side of fly's eye lens 150, based on the parallel rays from the light source portion 115 via the plane mirror 116. FIG. 44 shows only three lens elements 150a.sub.1 to 150a.sub.3 out of numerous lens elements actually provided and only three secondary light source images LS.sub.1 to LS.sub.3 out of numerous secondary light source images actually formed. The number of secondary light source images LS.sub.1 to LS.sub.3 corresponds to the number of plural lens elements 150a.sub.1 to 150a.sub.3. A satisfactory condition is that the size of each element is sufficiently smaller than the size of fly's eye lens 150. The plurality of secondary light source images are formed at a distant position from the exit plane of fly's eye lens 150 in the present embodiment, but the plurality of secondary light source images may be formed on the exit plane of fly's eye lens 150 if the light source portion 115 supplies illumination light with low intensity. Then, the illumination light from the plurality of secondary light source images LS.sub.1 to LS.sub.3 proceeds to a deflecting mirror 151 in the form of rays with predetermined diverging angle according to the focal length of each lens element 150a.sub.1 to 150a.sub.3. The deflecting mirror 151 is inclined at a certain angle relative to the optical path of the illumination light. The deflecting mirror 151 reflects the rays of illumination light toward a parabolic surface mirror 135. The deflecting mirror 151 is inclined at such an angle that the incident rays into the deflecting mirror 151 can be spatially separated from the outgoing rays from the deflecting mirror 151. The parabolic surface mirror 135 is constructed by a paraboloid of revolution about the axis Ax.sub.35 inclined with respect to the normal line to the mask M. The parabolic surface mirror 135 is so arranged that the focus of parabolic surface is located on the mask M and that the front focus of parabolic surface mirror 135 is located on the plurality of secondary light source images LS.sub.1 to LS.sub.3. This arrangement causes a diverging beam from the secondary light source image LS.sub.2 to become a beam of parallel rays via the parabolic surface mirror 135 and to proceed along the normal line to the mask M. Namely, since the rays from the secondary light source image LS.sub.2 are principal rays, telecentric illumination is achieved on the mask M. Also, diverging beams from the secondary light source images LS.sub.1 and LS.sub.3 become parallel beams via the parabolic surface mirror 135 and the parallel beams proceed at respective angles to the normal line to the mask M. In other words, the illumination light from the plurality of secondary light source images LS.sub.1 to LS.sub.3 via the parabolic surface mirror 135 illuminates the mask M in a superimposed manner to form a lighting field LF. In the present embodiment, a reflection enhancing film is formed on the surface of each of the plane mirror 116, deflecting mirror 151 and parabolic surface mirror 135. Also in the present embodiment, the deflecting mirror 151 and the parabolic surface mirror 135 are arranged as rotatable about the rotation axis Ax.sub.51. The rotation axis Ax.sub.51 passes through the reflecting mirror 151 and is parallel to the principal rays of illumination light from the parabolic surface mirror 135. It is also preferable in the present embodiment that the rotation axis Ax.sub.51 passes through the position of barycenter of the effective reflection region in the deflecting mirror 151. When the lighting field LF is formed on the mask M by the illumination light from the light source portion 115 while rotating the deflecting mirror 151 and the parabolic surface mirror 135 about the rotation axis Ax.sub.51, an arc-shaped illumination area is formed about the rotation axis Ax.sub.51 on the mask M. The illumination light can be irradiated over the entire surface of mask M by conveying the mask M along the X axis. In the present embodiment, it is conceivable that the fly's eye lens 150, the deflecting mirror 151 and the parabolic surface mirror 135 are arranged to be rotated (pivoted) in a united manner. As described above, the present embodiment also permits enlargement of illumination area in the direction perpendicular to the conveying direction of mask M (in the direction of Y axis) by rotating (pivoting) the deflecting mirror 151 and the parabolic surface mirror 135. This permits a wide illumination area to be obtained without increasing the size of parabolic surface mirror 135. Although the present embodiment was described as the illumination apparatus for illuminating the mask M, an exposure apparatus which can achieve the resolving power of diffraction limit over a wide exposure area can be provided by adding a mask stage for carrying the mask M, a projection optical system for forming an image of mask M on a wafer, and a wafer stage for moving the wafer in synchronism with the mask. Another embodiment is next described referring to FIG. 45. FIG. 45 is a drawing to show the structure of the another embodiment and employs the same coordinate system as in FIG. 44. Members or elements having the same functions as those in the previous embodiment shown in FIG. 44 are denoted by the same reference numerals for brevity of illustration. In FIG. 45, illumination light from an unrepresented light source portion is reflected by a plane mirror 116 inclined at 45.degree. with respect to the optical path of illumination light, so that the optical path of illumination light may be deflected about 90.degree. to enter a fly's eye lens 150. The fly's eye lens 150 forms a plurality of secondary light source images LS.sub.1 to LS.sub.3 at a position distant from the exit plane thereof. The illumination light from the plurality of secondary light source images LS.sub.1 to LS.sub.3 becomes diverging beams with a predetermined diverging angle and the optical paths thereof are deflected about 90.degree. by a deflecting mirror 152 inclined at 45.degree. relative to the optical path of illumination light. The deflected beams then reach a parabolic surface mirror 136. If the illumination light supplied from the unrepresented light source portion has no polarization, the illumination light entering the deflecting mirror 152 can be set to a large incident angle of about 45.degree. as in the present embodiment. The parabolic surface mirror 136 is constructed by a paraboloid of revolution about the axis Ax.sub.36 in the plane of mask M. The parabolic surface mirror 136 is so arranged that the focus of parabolic surface is located on the mask M and that the front focus of parabolic surface mirror 136 is located on the plurality of secondary light source images LS.sub.1 to LS.sub.3. This causes a diverging beam from the secondary light source image LS.sub.2 to become a beam of parallel rays via the parabolic surface mirror 136 and then to proceed along the normal line to the mask M. Namely, since the rays from the secondary light source image LS.sub.2 are principal rays, telecentric illumination is achieved on the mask M. Also, diverging beams from the secondary light source images LS.sub.1 and LS.sub.3 become parallel beams via the parabolic surface mirror 136 and the parallel beams proceed at respective certain angles to the normal line to the mask M. In other words, the illumination light from the plurality of secondary light source images LS.sub.1 to LS.sub.3 via the parabolic surface mirror 136 illuminates the mask M in a superimposed manner to form a lighting field LF. Also in the present embodiment, a reflection enhancing film is formed on the surface of each of the plane mirror 116, deflecting mirror 151 and parabolic surface mirror 136 similarly as in the previous embodiment in FIG. 44. In the present embodiment, the deflecting mirror 152 and the parabolic surface mirror 136 are supported in a united manner by an unrepresented supporting member, which is arranged as rotatable (pivotable) about the rotation axis Ax.sub.52. Here, the rotation axis Ax.sub.52 passes through the deflecting mirror 152 and is parallel to the principal rays of illumination light from the parabolic surface mirror 136. It is preferable that the rotation axis Ax.sub.52 is arranged to pass through the position of barycenter of the effective reflection region in the deflecting mirror 152. When the lighting field LF is formed on the mask M by the illumination light from the unrepresented light source portion while rotating (pivoting) the deflecting mirror 152 and the parabolic surface mirror 136 about the rotation axis Ax.sub.52, an arc-shaped illumination area is formed about the rotation axis Ax.sub.52 on the mask M. The illumination light can be irradiated over the entire surface of mask M by conveying the mask M along the X-axis. The present embodiment may be modified such that the fly's eye lens 150 is also supported by the supporting member supporting the deflecting mirror 152 and the parabolic surface mirror 136 and that the fly's eye lens 150, the deflecting mirror 152 and the parabolic surface mirror 136 are rotated (or pivoted) in a united manner upon illumination. As described above, the present embodiment also permits enlargement of illumination area in the direction perpendicular to the conveying direction of mask M (in the direction of Y axis) by rotating (pivoting) the deflecting mirror 152 and the parabolic surface mirror 136. This can permit a wide illumination area to be obtained without increasing the size of parabolic surface mirror 136. In the above-described embodiments, a blind may be placed as a field stop near the mask to define the illumination area. Also, a relay system may be provided on the mask side of parabolic surface mirror. In this case, a field stop may be set on a plane conjugate with the mask. Also, each of the embodiments as described above is so arranged that after the electromagnetic waves (X-rays or illumination light) from the light source portion is deflected by 90.degree., the waves are guided to enter the integrator mirror or the fly's eye lens, but such an alternative arrangement may be employed that the electromagnetic waves from the light source portion are guided along the rotation axis directly into the integrator mirror or the fly's eye lens. As described, the present invention is not limited to the embodiments as described above and may include various arrangements within the essence of the invention. As described above, the present invention can provide illumination apparatus and exposure apparatus which can achieve a wide exposure area without increasing the size of condenser optical system. Embodiment IV An embodiment of an optical apparatus is next described. FIG. 46 and FIG. 47 show an optical reflector 203 constituting a part of the illumination optical apparatus. FIG. 46 is a cross sectional view of the optical reflector 203 in the meridional direction, and FIG. 47 is a perspective view of the optical reflector 203. In FIG. 46, the origin is at the vertex O of an arbitrary parabola PA, the Y axis on the symmetry axis Ax.sub.0 of the parabola PA passing the vertex O, and the X axis on the axis passing the vertex O and being perpendicular to the symmetry axis Ax.sub.0 (as will be denoted by Y). As shown in FIG. 46, the cross section of the optical reflector 203 in the meridional direction constitutes a part of the parabola PA. Letting D be the directrix of the parabola PA, a reflective surface 203a of the optical reflector 203 is formed in the shape of a curved surface forming a part of parabolic toric surface obtained by rotating the parabola PA about a reference axis Ax.sub.1 being parallel to the directrix D and passing a point Y.sub.0 on the symmetry axis Y on the opposite side to the directrix D of the parabola PA with respect to the focus position of the parabola PA. Namely, the optical reflector 203 has the shape of belt-like arc between two latitudes 231 and 232 on the parabolic toric surface, as shown in FIG. 47. Returning to FIG. 46, the function of optical reflector 203 is now described as to beams in the meridional direction. Meridional beams mean beams in a plane including the reference axis Ax.sub.1 of the optical reflector 203 while sagittal beams mean beams in a plane perpendicular to the meridional plane. When a light source image I of predetermined size (or light source with predetermined size) is formed at a certain position on the reference axis Ax.sub.1 by an unrepresented optical system, emergent beams from an arbitrary point on the light source image I (or light source) are reflected by the optical reflector 203 and the reflected beams are converted into parallel beams by the converging function thereof. For example, beams from the center "a" of the light source image I (or light source) are converted into parallel beams by the optical reflector 203 to illuminate an area BA.sub.0 on the illuminated surface normally thereto, and beams from the lower edge b of the light source image I (or light source) are converted into parallel beams by the optical reflector 203 to illuminate the area BA.sub.0 on the illuminated surface obliquely from right upper. Also, beams from the upper edge c of the light source image I (or light source) are converted into parallel beams by the optical reflector 203 to illuminate the area BA.sub.0 on the illuminated surface obliquely from left upper. As described, beams from each position of light source image I (or light source) are converted into parallel beams by the optical reflector 203 to uniformly illuminate the area BA.sub.0 on the illuminated surface in a superposed manner. Observing the numerical aperture in the meridional direction by the optical reflector 203 in this arrangement, parallel beams (beams shown by solid lines) from light source image I (or light source) parallel to the optical axis Ax.sub.20 are converged at the center of the area BA.sub.0 on the illuminated surface under a numerical aperture NA.sub.M (=sin.theta..sub.M) by the optical reflector 203. Also, parallel beams (beams shown by dotted lines) outgoing from the light source image I (or light source) at an angle of divergence .epsilon..sub.1 to the optical axis Ax.sub.20 are converged at the left edge of the area BA.sub.0 on the illuminated surface under the numerical aperture NA.sub.M by the optical reflector 203. Further, parallel beams (beams shown by dotted lines) outgoing from the light source image I (or light source) at an angle of divergence .epsilon..sub.2 (=.epsilon..sub.1) equal in amplitude to the angle of divergence .epsilon..sub.1 but different in divergent direction from the angle of divergence .epsilon..sub.1 are converged at the right edge of the area BA.sub.0 on the illuminated surface under the numerical aperture NA.sub.M by the optical reflector 203. The optical axis Ax.sub.20 is bent at 90 degrees by the optical reflector 203. Accordingly, parallel beams having an arbitrary angle of divergence in the range of from .epsilon..sub.1 to .epsilon..sub.2 from the light source image I (or light source) are converged under the constant numerical aperture NA.sub.M at any position in the meridional direction on the area BA.sub.0 of the illuminated surface. In addition, it is seen that principal beams (P.sub.a, P.sub.b, P.sub.c) of the parallel beams from the light source image I (or light source) are always parallel to the optical axis Ax.sub.20, maintaining the telecentricity. Next described referring to FIG. 47 is the function of the optical reflector 203 in the sagittal direction. Parallel beams L.sub.0 from the light source image I (or light source) formed on the reference axis Ax.sub.1 are converged on the area BA.sub.0 of the illuminated surface by the optical reflector 203, and parallel beams L.sub.1 from the light source image I (or light source) outgoing at an angle of divergence inclined at angle .psi. to the parallel beams L.sub.0 are converged on an area BA.sub.1 of the illuminated surface by the optical reflector 203. Here, let us look at beams in the meridional direction among the beams from the light source image I forming the area BA.sub.1 on the illuminated surface. Then, similarly as in FIG. 46, parallel beams having an arbitrary angle of divergence from the light source image I (or light source) are converged under a constant numerical aperture .theta..sub.M at any position in the meridional direction on the area BA.sub.1 of the illuminated surface, and in addition the principal beams in the parallel beams from the light source image I (or light source) are always parallel to the optical axis Ax.sub.20, maintaining the telecentricity. Accordingly, when parallel beams from the light source image I (or light source) formed on the reference axis Ax.sub.1 are radially outgoing as spread in the arc direction of optical reflector 203 (in the direction along the latitudes 231, 232 of the parabolic toric surface), an arcuate illumination region BF is formed while maintaining the telecentricity. The arcuate illumination region BF corresponds to the illuminated surface, and the light source image or light source is present at infinity to the illuminated surface. The stepper as shown in FIG. 41 is set below the illuminated surface. The stepper is provided with a projection optical system that is telecentric on the entrance side. The light source image is formed at the position of entrance pupil of the projection optical system or at infinity. It is therefore understood that the illuminated surface can be illuminated under so-called Kohler illumination. Next studied referring to FIGS. 48A to 48F are the analysis of the above description using equations, a suitable shape of the optical reflector, a suitable position of the light source image I (or light source), and a suitable position of the illumination region BF. As shown in FIG. 48A, let us assume that the reflective surface of the optical reflector 203 has a surface which can be expressed in the meridional direction by a quadratic function with the origin of XY coordinate system at the vertex O of a parabola PA, that is, by y=.alpha.x.sup.2 (where .alpha. is a constant). First studied are rays parallel to the Y axis in the meridional direction. I) Rays parallel to the Y axis in the meridional direction A normal vector T can be expressed by Equation (21) at an arbitrary point on a parabola PA (y=.alpha.x.sup.2). ##EQU1## Let a unit vector S.sub.1 parallel to the Y axis in the plane of FIG. 48A be S.sub.1 =(0, 1), an intersection between the unit vector S.sub.1 and the parabola PA (y=.alpha.x.sup.2) be (u, .alpha.u.sup.2), and a unit vector S.sub.1 ' of a beam reflected by the parabola PA be S.sub.1 '=(S.sub.X1, S.sub.Y1). Then following Equation (22) holds. EQU S.sub.1 '=S.sub.1 -2T(T.multidot.S.sub.1) (22) Thus, the unit vector S.sub.1 ' after reflection is obtained as in Equation (23) from Equations (21) and (22). ##EQU2## A straight line being parallel to the unit vector S.sub.1 ' after reflection and passing through the point (u, .alpha.u.sup.2) on the parabola PA is expressed by following Equations (24) and (25). EQU x=S.sub.X1 t+u (24) EQU y=S.sub.Y1 t+.alpha.u.sup.2 (25) In the equations t is a variable. As shown in FIG. 48A, a ray reflected at the point (u, .alpha.u.sup.2) on the parabola PA intersects with the y axis at x=0. The intersecting position is obtained as follows. From Equation (24), x=S.sub.X1 t+u=0. Then t=-u/S.sub.X1. Substituting this value into t in above Equation (25) and using the relation of Equation (23), following Equation (26) is obtained after arranged. ##EQU3## Therefore, it is seen from Equation (26) that any ray in the meridional plane parallel to the unit vector S.sub.1, that is, parallel to the Y axis is converged irrespective of the value of u at the point (0, (4.alpha.).sup.-1) on the Y axis, which is the focus position of the parabola, and that the position of convergence is the illuminated surface. As shown in FIG. 46, the ray traveling on the optical axis Ax.sub.20 is reflected at the point ((2.alpha.).sup.-1, (4.alpha.).sup.-1) on the parabola PA and turns by 90 degrees. The distance (2.alpha.).sup.-1 from the reflection point to the illuminated surface is the focal length of the optical reflector 203. II) Rays parallel to the X axis in the meridional direction Next described referring to FIG. 48B are rays parallel to the X axis in the meridional direction. When a ray emergent from the point (0, (4.alpha.).sup.-1) on the Y axis is reflected at the point c ((2.alpha.).sup.-1, (4.alpha.).sup.-1) on the parabola PA, the emergent ray becomes parallel to the Y axis, as described above. Then, let us obtain a position F where a ray reflected at a position p.sub.0 ((2.alpha.).sup.-1 +.DELTA.x, (4.alpha.).sup.-1 +.DELTA.y) apart by .DELTA.x and .DELTA.y on the parabola PA from the point c intersects with a straight line x=(2.alpha.).sup.-1 becoming the optical axis Ax.sub.20 shown in FIG. 46. Let a unit vector S.sub.2 parallel to the X axis in the plane of FIG. 48B be S.sub.2 =(1, 0) and a unit vector S.sub.2 ' after reflected by the parabola PA be S.sub.2 '=(S.sub.X2, S.sub.Y2). Then following Equation (27) holds. EQU S.sub.2 '=S.sub.2 -2T(T.multidot.S.sub.2) (27) Thus, the unit vector S.sub.2 ' after reflection is given by Equation (28) from Equations (21) and (27). ##EQU4## Further, let a position vector P.sub.0 be a vector between the origin O (0, 0) and the point p.sub.0 ((2.alpha.).sup.-1 +.DELTA.x, (4.alpha.).sup.-1 +.DELTA.y), P be a vector between the origin O (0, 0) and the position F, and r be a distance between the point p.sub.0 and the position F. Then the following relation of Equation (29) stands. EQU P=P.sub.0 +rS.sub.2 ' (29) Defining the vector P as P=(P.sub.X, P.sub.Y) where P.sub.X =(2.alpha.).sup.-1, Equation (30) is obtained. ##EQU5## Reforming Equation (30), following Equation (31) is obtained. ##EQU6## If .DELTA.x unlimitedly approaches zero, the limit of Equation (31) is expressed by following Equation (32). ##EQU7## As apparent from Equation (32), rays parallel to the unit vector S.sub.2, that is, rays parallel to the X axis are converged at a focal position of the position F ((2.alpha.).sup.-1, (4.alpha.).sup.-1 +(2.alpha.).sup.-1) by the parabola PA. It is seen that this relation holds in the paraxial region. It is thus understood that if a light source or light source image is formed at the position F then beams diverging from this position F can be converted into parallel beams by the reflective surface of the optical reflector 203 to illuminate the point (0, (4.alpha.).sup.-1) on the illuminated surface and a region on the Y axis near the point. In addition, the rays diverging from the center (0, (4.alpha.).sup.-1) of the light source or light source image are always parallel to the X axis after reflected by the optical reflector 203. In other words, the exit pupil of the optical reflector 203 appears at infinity when the optical reflector 203 is seen from the illuminated surface side. Therefore, it is understood that the telecentricity is maintained. III) Beams parallel to the Y axis and passing x=(2.alpha.).sup.-1 in the sagittal direction Rays in the sagittal direction are next studied referring to FIG. 48C and FIG. 48D. FIG. 48C shows a state in the XY plane (meridional plane), and FIG. 48D is a drawing to show a section along AA' in FIG. 48C as seen in the direction of arrows A, A', which shows a state in a plane parallel to the YZ plane at a height of x=(2.alpha.).sup.-1. Consider a ray passing x=(2.alpha.).sup.-1 in parallel with the Y axis, as shown in FIG. 48C and in FIG. 48D. Let p.sub.3 =((2.alpha.).sup.-1, P.sub.y3, P.sub.z3) be a point p.sub.3 where the ray is reflected at the reflective surface 203a on the optical reflector 203, q be a distance between the reference axis Ax.sub.1 and the reflection point p.sub.3, and .psi. be an angle expanded by a straight line connecting the reference axis Ax.sub.1 with the reflection point p.sub.3 with respect to the YZ plane including the origin O. Then P.sub.y3 and P.sub.z3 may be expressed by Equations (33) and (34), respectively. ##EQU8## A normal vector T at the reflection point p.sub.3 may be expressed by following Equation (35). ##EQU9## Now let a unit vector S.sub.3 of a ray parallel to the Y axis and passing x=(2.alpha.).sup.-1 be S.sub.3 =(0, -1, 0) and a unit vector S.sub.3 ' of a ray reflected at the point p.sub.3 on the reflective surface 203a be S.sub.3 '=(S.sub.X3, S.sub.Y3, S.sub.Z3). Then the following relation of Equation (36) holds. EQU S.sub.3 '=S.sub.3 -2T(T.multidot.S.sub.3) (36) Thus, the unit vector S.sub.3 ' after reflection is given by Equation (37) from Equations (35) and (36). ##EQU10## Let us consider a straight line passing through the reflection point p.sub.3 and being parallel to the unit vector S.sub.3 ' after reflection. The line may be expressed by Equations (38), (39) and (40). ##EQU11## In the equations t is a variable. Now let us calculate a position where the line parallel to the unit vector S.sub.3 ' after reflection and passing through the reflection point p.sub.3 intersects with the YZ plane including the origin O, as shown in FIG. 48D. Since x=0 in this case, putting x=0 into Equation (38) yields t=-1/(2.alpha.S.sub.X3). Substituting this value of t into Equation (39) and using the relation of Equation (37), Equation (41) is obtained after arranged. ##EQU12## As seen from Equation (41), cos.psi..apprxeq.1. Namely, y=(4.alpha.).sup.-1 in the paraxial region on the YZ plane at P.sub.z3 .apprxeq.0 as shown in FIG. 48D. Also, substituting t=-1/(2.alpha.S.sub.X3) into Equation (40), Equation (42) is obtained after arranged. ##EQU13## From this Equation (42), z=0 irrespective of the value of P.sub.z3, when the radius of the arcuate reflective surface 203a with the center at the reference axis Ax.sub.1 is q=(2.alpha.).sup.-1, that is, when a rotation radius of the reference axis Ax.sub.1 with respect to the origin O is 3(4.alpha.).sup.-1 (=(2.alpha.).sup.-1 +(4.alpha.).sup.-1). It is thus understood that if the rotation radius of the reference axis Ax.sub.1 to the origin O is 3(4.alpha.).sup.-1 then the rays parallel to the Y axis in the sagittal direction in the plane parallel to the YZ plane at height of x=(2.alpha.).sup.-1 as shown in FIG. 48D are converged at the position (0, (4.alpha.).sup.-1, 0) in the paraxial region where the rays in the meridional direction are converged as described above. IV) Beams parallel to the X axis in the sagittal direction Finally studied referring to FIG. 48E and FIG. 48F are beams parallel to the X axis in the sagittal direction which are reflected at the reflection point p.sub.3 shown in FIG. 48C and FIG. 48D. FIG. 48E shows the state in the XY plane (meridional plane), and FIG. 48F is a cross section along AA' as seen in the direction of arrows A, A' in FIG. 48E, which shows the state in the plane parallel to the YZ plane at a height of x=(2.alpha.).sup.-1. Let P.sub.4 =(1, 0, 0) be a unit vector P.sub.4 of a beam going to the reflection point p.sub.3 in parallel with the X axis, and S.sub.4 '=(S.sub.X4, S.sub.Y4, S.sub.Z4) be a unit vector S.sub.4 ' of a beam reflected at the point p.sub.3 on the reflective surface 203a, as shown in FIGS. 48E and 48F. Then the following relation of Equation (43) holds. EQU S.sub.4 '=S.sub.4 -2T(T.multidot.S.sub.4) (43) Thus, the unit vector S.sub.4 ' after reflection is expressed by Equation (44), from Equations (35) and (43). EQU S.sub.4 '=(S.sub.X4, S.sub.Y4, S.sub.Z4)=(0, cos.psi., -sin.psi.) (44) Here, consider a straight line passing through the reflection point p.sub.3 and being parallel to the unit vector S.sub.4 ' after reflection. Then the line is expressed by Equations (45), (46) and (47). ##EQU14## Now let us obtain a point where the beam reflected at the reflection point p.sub.3 intersects with the XY plane (the plane of FIG. 48E) including the origin O, as shown in FIG. 48E and FIG. 48F. Then, since z=0, t=-q sin.psi./S.sub.Z4 by putting z=0 into Equation (47). Substituting this value of t into above Equation (46) and using the relations of Equations (44) and (42), Equation (48) is obtained after arranged. ##EQU15## Accordingly, the beam passing through the reflection point p.sub.3 in parallel with the X axis in the sagittal direction is converged at the point F ((2.alpha.).sup.-1, 3(4.alpha.).sup.-1, 0), which coincides with the converging point of the beams parallel to the X axis in the meridional direction as described in section II. It is thus understood that this relation holds outside the paraxial region without aberrations. Thus, diverging beams from the point F ((2.alpha.).sup.-1, 3(4.alpha.).sup.-1, 0) at the center of light source image or light source are always parallel to the XZ plane so that the parallel beams illuminate the illuminated plane in the shape of arc. It is thus understood that the telecentricity is maintained over the illuminated surface of arc. The result of the above analysis finds the fact that the optical reflector 203 is preferably formed by a part of a parabolic toric body of rotation satisfying following Equations (49) and (50) when the origin is at the vertex O of parabola (y=.alpha.x.sup.2), the Y axis is defined along the direction parallel to the symmetry axis of the parabola while passing through the origin O, the reference axis Ax.sub.0 is normal to the symmetry axis Y at the position apart by a certain distance along the symmetry axis from the vertex O of the parabola, the X axis extends along the direction in parallel with the reference axis Ax.sub.0 while passing through the vertex O, the Z axis is normal to the reference axis Ax.sub.0 and to the symmetry axis Y while passing through the vertex O, and R is a distance from the vertex O to the intersection between the reference axis Ax.sub.0 and the symmetry axis Y. ##EQU16## If the entrance to the optical reflector 203 is located at the position of the light source side focus ((2.alpha.).sup.-1) of the optical reflector 203 on the reference axis Ax.sub.1, as shown in FIG. 46, while satisfying the relations of Equations (49) and (50) and if a generally circular light source image or light source is formed thereat, beams from the light source or light source image are converted by the optical reflector 203 into parallel beams having an arcuate cross section of beam to form an arc illumination area, in which the telecentricity and Kohler illumination state is maintained. The center of light source image I (or light source) is at coordinates ((2.alpha.).sup.-1, 3(4.alpha.).sup.-1, 0) and the center C.sub.BF of the illuminated surface BF shown in FIG. 47 is a part of a circle in the YZ plane satisfying following Equation (51). ##EQU17## As described above, the conditions for Kohler illumination are satisfied at each point in the arc illumination area. Incidentally, the above description concerns an example in which the center of light source image I (or light source) is formed at the coordinates ((2.alpha.).sup.-1, 3(4.alpha.).sup.-1, 0) on the reference axis Ax.sub.1 of the optical reflector 203. However, as far as a generally circle light source image (or light source) is formed on the reference axis Ax.sub.1 of the optical reflector 203, as shown in FIG. 49 and FIG. 47, the beams therefrom are converted by the optical reflector 203 into parallel beams having an arcuate cross section of beam to form an arc illumination area under Kohler illumination. In this case, the center of illumination area is formed on the symmetry axis Ax.sub.0 and the coordinates thereof is ((2.alpha.).sup.-1, 3(4.alpha.).sup.-1, 0). Accordingly, the center C.sub.BF of the illuminated surface in the YZ plane is a part of a circle satisfying above Equation (51). Next described is an embodiment of the illumination optical apparatus using the optical reflector 203 as described above. As shown in FIG. 50, the illumination optical apparatus is constructed of an excimer laser 201 as a light source, a reflection-type concave fly's eye 202a as a reflective element, and the optical reflector 203 as described above. First, the excimer laser 201 supplies collimated beams or nearly collimated beams. The beams are let to enter the reflection-type concave fly's eye 202a at a predetermined angle. The reflection-type concave fly's eye 202a is composed of a plurality of mirror elements 220a each having a concave reflective surface, which are arranged in a matrix for example as shown in FIGS. 51A and 51C. The fly's eye 202a has a function to reflect the collimated beams entering the respective mirror elements 220a and to converge them. Here, FIG. 51A shows a cross section in the meridional direction, of the reflection-type concave fly's eye 202a in the present embodiment, and FIG. 51C a front view of the reflection-type concave fly's eye 202a in the present embodiment. In FIG. 51C, the vertical direction in the plane is the meridional direction and the horizontal direction in the plane is the sagittal direction. The reflective surface of each mirror element 220a shown in FIG. 51A and FIG. 51C is so arranged that the focal length in the meridional direction is equal to that in the sagittal direction. Further, as shown in FIG. 51C, each mirror element 220a is formed in a rectangular shape longer in the sagittal direction than in the meridional direction. The reason why each mirror element 220a is rectangular will be described hereinafter. Returning to FIG. 50, real images I of the light source, which are an assembly of point light sources in a number corresponding to a number of mirror elements, are formed at the focus position where the beams are converged after reflected by the reflection-type concave fly's eye 202a. The real images I are substantially a surface illuminant (secondary light source). Beams from the secondary light source formed by the reflection-type concave fly's eye 202a are reflected and converged by the optical reflector 203. FIG. 50 shows a state in the meridional direction, of the optical reflector 203, wherein with the origin at the vertex O of parabola PA, letting Y be the symmetry axis Ax.sub.0 passing the origin O and X be a direction passing the origin O and being perpendicular to the symmetry axis Ax.sub.0 (Y axis), the optical reflector 203 is constructed of a part of the parabola PA (y=.alpha.x.sup.2) in the meridional direction. Three-dimensionally, the optical reflector 203 is constructed, as shown in FIG. 47, of a part of a parabolic toric body of revolution obtained by rotating the parabola about the reference axis Ax.sub.1 being perpendicular to the symmetry axis Ax.sub.0 (Y axis) and passing the position Y.sub.0 apart by a predetermined distance (3(4.alpha.).sup.-1) from the vertex O on the symmetry axis Ax.sub.0 (Y axis). More specifically, it has an arcuate belt shape of the parabolic toric body of revolution between two latitudes (231, 232). In this case, the reference axis (axis of revolution) Ax.sub.1 is arranged to pass the position of the plurality of light source images I (secondary light source) formed by the reflection-type concave fly's eye 202a, and these light source images I are formed at the light-source-side focus position of the optical reflector 203 (where the light-source-side focal length f is given by f=(2.alpha.).sup.-1). Accordingly, the beams from the reflection-type concave fly's eye 202a are converted into parallel beams by the optical reflector 203 as shown by the dotted lines in the drawing, and an arcuate illumination area BF under the Kohler illumination is formed with telecentricity at the illuminated-surface-side focus position of the optical reflector 203 (where the illuminated-surface-side focal length f is given by f=(2.alpha.).sup.-1). Now, the reason why each mirror element 220a as a constituent in the reflection-type concave fly's eye 202a is rectangular as shown in FIG. 51C is described. As shown in FIG. 47, because an angle of divergence .PHI. in the sagittal direction, of the beams traveling from the light source images I to the optical reflector 203 becomes larger than that in the meridional direction, a problem that the light is not supplied to the edges of the optical reflector 203 in the sagittal direction will arise if the angle of divergence in the meridional direction, of the beams from the reflection-type concave fly's eye 202a is equal to that in the sagittal direction. Thus, each of the mirror elements 220a constituting the reflection-type concave fly's eye 202a is formed in a rectangular shape longer in the sagittal direction than in the meridional direction, whereby the angle of divergence in the sagittal direction, of the beams reflected from the each mirror element 220a becomes larger than that in the meridional direction. If the angle of divergence .PHI. in the sagittal direction is nearly equal to that in the meridional direction, the length in the meridional direction, of each mirror element 220a may be set as equal to the length in the sagittal direction. In the present embodiment, as shown in FIG. 51C, the number of mirror elements 220a arranged along the meridional direction is larger than the number of mirror elements 220a arranged along the sagittal direction in order to form the reflection-type concave fly's eye 202a in a square shape with the length in the meridional direction nearly equal to the length in the sagittal direction. The light source unit for supplying the parallel beams or nearly parallel beams is not limited to the lasers, but may be one composed, for example, of an ellipsoidal mirror, a mercury arc lamp set at the first focus position of the ellipsoidal mirror, and an optical element for converting beams of light from the mercury arc lamp as collected by the ellipsoidal mirror into parallel beams. Further, the light source unit may be constructed, for example, of an X-ray source for supplying synchrotron radiation (SOR), an oblique incident mirror, and a slit or of a laser plasma X-ray source and a paraboloidal mirror for converting X-rays from the X-ray source into parallel beams. As described, the light source unit according to the present invention is by no means limited to those for supplying parallel beams in the ultraviolet wavelength region, but may be those for supplying light in the visible region or in the infrared region, or X-rays. Also, in FIG. 50, a beam expander (for expanding the beam size or for changing a cross section of beam) for shaping the beams from the excimer laser 201 may be provided in the optical path between the excimer laser 201 as the light source unit and the reflection-type concave fly's eye 202a. In the present embodiment, the images I of the light source are arranged to be formed on the reference axis Ax.sub.1 of the optical reflector 203. However, as seen from the derivation of Equation (32), some errors are permissible without a need to locate the position of the images I of the light source precisely on the reference axis Ax.sub.1 of the optical reflector 203 as long as the position of the images I of the light source and the reference axis Ax.sub.1 of the optical reflector 203 approximately coincide with each other. In order to form the real images I of the light source precisely on the reference axis Ax.sub.1 of the optical reflector 203, a possible arrangement is such that a beam splitter is set on the exit side of the light source 201 and the reflection-type concave fly's eye 202a is set on the opposite side of the beam splitter so that the light from the light source 201 through the beam splitter is incident normally to the reflection-type concave fly's eye 202a. In this case, a half mirror may replace the beam splitter. As shown in FIG. 50, where the rays from the light source 201 are incident at a predetermined angle to the reflection-type concave fly's eye 202a, curvatures of the reflective surfaces of the respective mirror elements 220a constituting the reflection-type concave fly's eye 202a should be determined as different from each other so that a focus of each mirror element 220a is located on the reference axis Ax.sub.1 of the optical reflector 203. Next described referring to the drawings is another embodiment where a reflection-type convex fly's eye 202b composed of a plurality of convex mirrors is used as an optical integrator element. As shown in FIG. 52, the illumination optical apparatus is composed of the excimer laser 201 as a light source unit, a reflection-type convex fly's eye 202b, and the optical reflector 203. First, the excimer laser 201 supplies collimated beams or nearly collimated beams. The beams are let to enter the reflection-type convex fly's eye 202b at a predetermined angle. The reflection-type convex fly's eye 202b is composed of a plurality of mirror elements 220b each having a convex reflective surface, which are arranged in a matrix for example as shown in FIGS. 51B and 51D. The fly's eye 202b has a function to reflect the collimated beams entering the respective mirror elements 220b and to diverge them. Here, FIG. 51B shows a cross section in the meridional direction, of the reflection-type convex fly's eye 202b, and FIG. 51D a front view of the reflection-type convex fly's eye 202b. In FIG. 51D, the vertical direction in the plane is the meridional direction and the horizontal direction in the plane is the sagittal direction. The reflective surface of each mirror element 220b shown in FIG. 51B and FIG. 51D is so arranged that the focal length in the meridional direction is equal to that in the sagittal direction. Further, as shown in FIG. 51D, each mirror element 220b is formed in a rectangular shape longer in the sagittal direction than in the meridional direction. The reason why each mirror element 220b is rectangular is the same as that why each mirror element 220a is rectangular as shown in FIG. 51C in the previous embodiment, and thus is omitted to explain herein. Returning to FIG. 52, virtual images I of the light source, which are an assembly of point light sources in a number corresponding to a number of mirror elements, are formed at the focus position where the beams are diverged after reflected by the reflection-type convex fly's eye 202b. The virtual images I are substantially a surface illuminant (secondary light source). Beams from the secondary light source formed by the reflection-type convex fly's eye 202b are reflected and converged by the optical reflector 203. FIG. 52 shows a state in the meridional direction, of the optical reflector 203, wherein with the origin at the vertex O of parabola PA, letting Y be the symmetry axis Ax.sub.0 passing the origin O and X be a direction passing the origin O and being perpendicular to the symmetry axis Ax.sub.0 (Y axis), the optical reflector 203 is constructed of a part of the parabola PA (y=.alpha.x.sup.2) in the meridional direction. Three-dimensionally, the optical reflector 203 is constructed, as shown in FIG. 47, of a part of a parabolic toric body of revolution obtained by rotating the parabola about the reference axis Ax.sub.1 being perpendicular to the symmetry axis Ax.sub.0 (Y axis) and passing the position Y.sub.0 apart by a predetermined distance (3(4.alpha.).sup.-1) from the vertex O on the symmetry axis Ax.sub.0 (Y axis). More specifically, it has an arcuate belt shape of the parabolic toric body of revolution between two latitudes (231, 232). In this case, the reference axis (axis of revolution) Ax.sub.1 is arranged to pass the position of the plurality of light source images I (secondary light source) formed by the reflection-type convex fly's eye 202b, and these light source images I are formed at the light-source-side focus position of the optical reflector 203 (where the light-source-side focal length f is given by f=(2.alpha.).sup.-1). Accordingly, the beams from the reflection-type convex fly's eye 202b are converted into parallel beams by the optical reflector 203 as shown by the dotted lines in the drawing, and an arcuate illumination area BF under the Kohler illumination is formed with telecentricity at the illuminated-surface-side focus position of the optical reflector 203 (where the illuminated-surface-side focal length f is given by f=(2.alpha.).sup.-1). If the angle of divergence .PHI. in the sagittal direction is nearly equal to that in the meridional direction, the length in the meridional direction, of each mirror element 220b may be set as equal to the length in the sagittal direction. In the present embodiment, as shown in FIG. 51D, the number of mirror elements 220b arranged along the meridional direction is larger than the number of mirror elements 220b arranged along the sagittal direction in order to form the reflection-type convex fly's eye 202b in a square shape with the length in the meridional direction nearly equal to the length in the sagittal direction. The light source unit for supplying the parallel beams or nearly parallel beams is not limited to the lasers, but may be one composed, for example, of an ellipsoidal mirror, a mercury arc lamp set at the first focus position of the ellipsoidal mirror, and an optical element for converting beams of light from the mercury arc lamp as collected by the ellipsoidal mirror into parallel beams. Further, the light source unit may be constructed, for example, of an X-ray source for supplying synchrotron radiation (SOR), an oblique incident mirror, and a slit or of a laser plasma X-ray source and a paraboloidal mirror for converting X-rays from the X-ray source into parallel beams. As described, the light source unit according to the present invention is by no means limited to those for supplying parallel beams in the ultraviolet wavelength region, but may be those for supplying light in the visible region or in the infrared region, or X-rays. Also, in FIG. 52, a beam expander (for expanding the beam size or for changing a cross section of beam) for shaping the beams from the excimer laser 201 may be provided in the optical path between the excimer laser 201 as the light source unit and the reflection-type convex fly's eye 202b. In the present embodiment, the images I of the light source are arranged to be formed on the reference axis Ax.sub.1 of the optical reflector 203. However, as seen from the derivation of Equation (32), some errors are permissible without a need to locate the position of the images I of the light source precisely on the reference axis Ax.sub.1 of the optical reflector 203 as long as the position of the images I of the light source and the reference axis Ax.sub.1 of the optical reflector 203 approximately coincide with each other. In order to form the virtual images I of the light source precisely on the reference axis Ax.sub.1 of the optical reflector 203, a possible arrangement is such that a beam splitter is set on the exit side of the light source 201 and the reflection-type convex fly's eye 202b is set on the opposite side of the beam splitter so that the light from the light source 201 through the beam splitter is incident normally to the reflection-type convex fly's eye 202b. In this case, a half mirror may replace the beam splitter. As shown in FIG. 52, where the rays from the light source 201 are incident at a predetermined angle to the reflection-type convex fly's eye 202b, curvatures of the reflective surfaces of the respective mirror elements 220b constituting the reflection-type convex fly's eye 202b should be determined as different from each other so that a focus of each mirror element 220b is located on the reference axis Ax.sub.1 of the optical reflector 203. FIG. 53A shows another embodiment using two reflection-type optical integrators 204a and 204b. As shown in the drawing, the illumination optical apparatus is composed of the laser light source 201, first and second reflection-type optical integrators 204a, 204b, and the optical reflector 203. The first reflection-type optical integrator 204a is composed of a plurality of concave cylindrical mirrors 240a having a same curvature, as shown in FIG. 54A. The second reflection-type optical integrator 204b is composed of concave cylindrical mirrors 240b having a different curvature from that of the first reflection-type optical integrator 204a. These cylindrical mirrors 240a and 240b are provided in a same number and generators of the respective mirrors are arranged in parallel with each other. Returning to FIG. 53A, the first and second reflection-type optical integrators 204a, 204b are arranged so that the generators thereof are perpendicular to each other. Here, "the generators are perpendicular to each other" stated herein means that the generators of the concave cylindrical mirrors 240a in the first reflection-type optical integrator 204a are substantially perpendicular to the generators of the concave cylindrical mirrors 240b in the second reflection-type optical integrators 204b even via an optical element such as a reflective member in an optical path between the first and second reflection-type optical integrators 204a, 204b. In the present embodiment, a direction of the generators of the plurality of concave cylindrical mirrors 240a constituting the first reflection-type optical integrator 204a (hereinafter referred to as an axis of the first reflection-type optical integrator 204a) is set normal to the plane of the drawing, while a direction of the generators of the plurality of concave cylindrical mirrors 240b constituting the second reflection-type optical integrator 204b (hereinafter referred to as an axis of the second reflection-type optical integrator 204b) within the plane of the drawing. Rays emitted from the laser light source I travel in respective optical paths bent by the first reflection-type optical integrator 204a to be focused at the focus position (the position of light source images) I in the in-plane direction by the respective concave cylindrical mirrors 240a. The rays in the in-plane direction are the rays in the meridional plane in the optical reflector 203. The second reflection-type optical integrator 204b is placed between the first reflection-type optical integrator 204a and the focus position I, so that the rays from the first reflection-type optical integrator 204a take respective optical paths bent by the second reflection-type optical integrator 204b. Beams from the respective cylindrical mirrors 240b in the second reflection-type optical integrator 204b are focused only in the direction perpendicular to the plane of the drawing. The focus position of the second reflection-type optical integrator 204b coincides with the focus position of the first reflection-type optical integrator 204a. Here, the rays in the direction perpendicular to the plane of the drawing are the rays on the sagittal plane in the optical reflector 203. Thus, the first reflection-type optical integrator 204a becomes a secondary light source in the meridional plane of the optical reflector 203, while the second reflection-type optical integrator 204b a secondary light source in the sagittal plane of the optical reflector 203. The rays having passed via the first and second reflection-type optical integrators 204a, 204b then pass the focus position I to be incident to the optical reflector 203. In this arrangement, the angles of divergence in the meridional direction and in the sagittal direction can be changed by changing the curvatures of the cylindrical mirrors in the respective reflection-type optical integrators. As a result, illumination areas can be changed independently of each other. The plane of the secondary light sources as represented by I is formed by selecting a distance between the first and second reflection-type optical integrators 204a, 204b so that image points thereof coincide with each other. Providing the integrators with a same number of cylindrical mirrors, the number of images in the secondary light source in the meridional direction can be the same as that in the sagittal direction. The present embodiment is so arranged that the images I of the light source are formed on the reference axis Ax.sub.1 of the optical reflector 203. However, as seen from the derivation of Equation (32), some errors are permissible without a need to locate the position of the images I of the light source precisely on the reference axis Ax.sub.1 of the optical reflector 203 as long as the position of the images I of the light source and the reference axis Ax.sub.1 of the optical reflector 203 approximately coincide with each other. FIG. 53A shows a state in the meridional direction, of the optical reflector 203, wherein with the origin at the vertex O of parabola PA, letting Y be the symmetry axis Ax.sub.0 passing the origin O and X be a direction passing the origin O and being perpendicular to the symmetry axis Ax.sub.0 (Y axis), the optical reflector 203 is constructed of a part of the parabola PA (y=.alpha.x.sup.2) in the meridional direction. Three-dimensionally, the optical reflector 203 is constructed, as shown in FIG. 47, of a part of a parabolic toric body of revolution obtained by rotating the parabola about the reference axis Ax.sub.1 perpendicular to the symmetry axis Ax.sub.0 (Y axis) passing the position Y.sub.0 apart by a predetermined distance (3(4.alpha.).sup.-1) from the vertex O on the symmetry axis Ax.sub.0 (Y axis). More specifically, it has an arcuate belt shape of the parabolic toric body of revolution between two latitudes (231, 232). In this case, the reference axis Ax.sub.1 is arranged to pass the position of the plurality of light source images I (secondary light source) formed by the reflection-type optical integrators 204a and 204b, and these light source images I are formed at the light-source side focus position of the optical reflector 203. Accordingly, the beams from the reflection-type optical integrators 204a and 204b are converted into parallel beams by the optical reflector 203 as shown by the dotted lines in the drawing, and an arcuate illumination area BF under the Kohler illumination is formed with telecentricity at the illuminated-surface-side focus position of the optical reflector 203 (where the illuminated-surface-side focal length f is given by f=(2.alpha.).sup.-1). FIG. 53B shows an optical system where each cylindrical mirror in the second reflection-type optical integrator is convex as shown in FIG. 54B. The optical system shown in FIG. 53A presents the real images as a secondary light source, whereas the optical system shown in FIG. 53B virtual images as a secondary light source from rays in the direction perpendicular to the plane of the drawing. Where the second reflection-type optical integrator is composed of convex cylindrical mirrors 240c, the second reflection-type optical integrator 204c is located at a position after the rays in the in-plane direction are once focused. As described, the number of images in the secondary light source in the meridional direction can also be made the same as that in the sagittal direction where each cylindrical mirror in the second reflection-type optical integrator is convex. FIG. 55 shows an embodiment where the illumination optical apparatus is constructed using a reflection-type concave fly's eye 205 and a plane rotating mirror 206. FIG. 55 shows a state in the sagittal plane. The illumination optical apparatus is composed of the laser light source 201, the reflection-type concave fly's eye 205 as a reflection-type optical integrator, the plane rotating mirror 206 arranged as rotatable about the reference axis Ax.sub.1, and the optical reflector 203. The light emitted from the light source is incident at a predetermined angle into the reflection-type concave fly's eye 205. As shown in FIG. 56, the reflection-type concave fly's eye 205 is an assembly of a plurality of concave mirror elements 250a, wherein a number of mirror elements 250a in the meridional direction is equal to that in the sagittal direction. Each mirror element 250a has same lengths and same focal lengths in the meridional direction and in the sagittal direction. The plane rotating mirror 206 is set at a rear focus position of each mirror element 250a, so that beams from the reflection-type concave fly's eye 205 form images as a secondary light source in a same number in the meridional direction and in the sagittal direction on the plane rotating mirror 206, as shown by the dotted lines in the drawing. The light from the secondary light source is reflected and converged by the optical reflector 203 to form a nearly circular illumination area BF.sub.2 under Kohler illumination with the telecentricity maintained, at the illuminated-surface-side focus position of the optical reflector 203 (where the illuminated-surface-side focal length f is given by f=(2.alpha.).sup.-1). Rotating the plane rotating mirror 206 about the rotation axis Ax.sub.1 of plane rotating mirror, the illumination area BF.sub.2 scan along the rotational direction about the reference axis Ax.sub.1, thereby forming an annular illumination area BF on the optical reflector 203. In this case, because a sufficient numerical aperture of each mirror element 250a in the reflection-type concave fly's eye 205 is one to fill the meridional width of the optical reflector 203, the number of images in the secondary light source in the meridional direction can be set as same as that in the sagittal direction without a need to make the shape of aperture elongated as in the previous embodiment. The present embodiment is so arranged that the images I of the light source are formed on the reference axis Ax.sub.1 of the optical reflector 203. However, as seen from the derivation of Equation (32), some errors are permissible without a need to locate the position of the images I of the light source precisely on the reference axis Ax.sub.1 of the optical reflector 203 as long as the position of the images I of the light source and the reference axis Ax.sub.1 of the optical reflector 203 approximately coincide with each other. Using the optical apparatus as described above, the illuminated surface can be uniformly illuminated in an arcuate shape with a much higher illumination efficiency than with the conventional apparatus, while maintaining the telecentricity and Kohler illumination state. Further, because the members in the optical system except for the light-emitting unit are the reflective members, absorption of the light passing the optical system can be considerably low. The optical apparatus as illustrated in EMBODIMENT IV can also be applied to exposure apparatus in combination with the stepper as illustrated in FIG. 41 in EMBODIMENT III. In this case, the optical system illuminates an arcuate area in the mask M on the mask stage MS and the stepper successively moves the mask stage MS and the wafer stage WS on which the wafer W is mounted. By this, the pattern on the reticle can be faithfully transferred onto the wafer with a high throughput. Reference should be made to EMBODIMENT III as to the details of the stepper. From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. The basic Japanese Application Nos. 5-21577 (21577/1993) filed on Feb. 10, 1993; 5-229173 (229173/1993) filed on Sep. 14, 1993; 5-237654 (237654/1993) filed on Sep. 24, 1993; and 6-38799 (38799/1994) filed on Mar. 9, 1994 are hereby incorporated by reference.
	claims	1. A combination of a guide thimble and a top nozzle for a nuclear fuel assembly, the combination comprising:a guide thimble, anda top nozzle coupled to the guide thimble, the top nozzle comprising:a flow plate located above the guide thimble, with a coupling through hole formed through the flow plate;an outer guide post coupled at a lower end thereof to the coupling through hole of the flow plate;an inner-extension tube disposed in the outer guide post in such a way that a lower end of the inner-extension tube passes through the coupling through hole of the flow plate; andan inner-extension tube head coupled to an upper end of the inner-extension tube and to an upper end of the outer guide post,wherein:the inner-extension tube includes at least one rotation-preventing protrusion provided on a circumferential outer surface of the inner-extension tube such that the rotation-preventing protrusion is disposed within the coupling through hole of the flow plate;a circumferential inner surface of the coupling through hole of the flow plate includes a first part disposed at a position corresponding to the rotation-preventing protrusion of the inner-extension tube and a second part; andthe rotation-preventing protrusion and the first part, collectively, prevent the inner-extension tube from rotating when the inner-extension tube head is rotated. 2. The combination as set forth in claim 1, wherein the rotation-preventing protrusion has a planar surface, and the first part is formed as a planar surface. 3. The combination as set forth in claim 1 further comprising:a first coupling protrusion provided on a circumferential outer surface of the inner-extension tube head;a first coupling groove formed in a circumferential inner surface of the inner-extension tube so that the first coupling protrusion is inserted into the first coupling groove;a second coupling protrusion provided on the circumferential outer surface of the inner-extension tube; anda second coupling groove formed in a circumferential inner surface of the outer guide post so that the second coupling protrusion is inserted into the second coupling groove. 4. The combination as set forth in claim 3, wherein the inner-extension tube has at least one longitudinal slit extending a predetermined length from an upper end of the inner-extension tube.
	abstract	A radiation shield device (100) and method, the apparatus comprising either an absorbing shield (130), a scattering shield (200) or an absorbing and scattering shield (300) arranged in a processing tool (50) that irradiates a workpiece (70) with high-irradiance radiation (80) from a light source (78). The processing tool has a tool portion (66) having an irradiance damage threshold (IDT). The radiation shield device is designed to intercept a portion of the high-irradiance radiation that would otherwise be incident the tool portion, and to ensure that radiation exiting the particular shield comprising the radiation shield device and incident the tool portion has an irradiance below the tool portion irradiance damage threshold. The method includes using the radiation shield device in processing a workpiece using a processing tool.
	abstract	A method including providing an internal control rod drive mechanism (CRDM) including an electric motor and a support surface including sealed electrical connectors electrically connected with the electric motor to deliver electrical power to the electrical motor, installing the internal CRDM inside a nuclear reactor, the installing including placing the support surface of the internal CRDM onto a support element inside the nuclear reactor, the placing causing sealed electrical connectors disposed on the support element to mate with the sealed electrical connectors on the support surface of the internal CRDM, wherein the nuclear reactor contains coolant water and the installing is performed with the internal CRDM submerged in the coolant water and the seals of the sealed electrical connectors of the internal CRDM and the support element are effective to prevent coolant water ingress into the sealed electrical connectors.
	claims	1. An X-ray optical element for reflection of a cross-sectionally reflected X-ray radiation in two dimensions, comprising:a first reflective, curved surface;a second reflective, curved surface adjacent to the first element at a joint angle; andan X-ray beam source producing the X-ray radiation directed onto the first and second reflective surfaces, the X-ray radiation being reflected from one of the first and second surfaces onto the other surface, the first surface curved at a first angle different than a second angle at which the second surface is curved, the first surface exhibiting a first focal length different than a second focal length that the second surface exhibits. 2. The X-ray optical element according to claim 1, wherein the joint angle is 90°. 3. The X-ray optical element according to claim 1, wherein the joint angle is less than 90°. 4. The X-ray optical element according to claim 1, wherein the first and second reflective surfaces are curved one of parabolically, elliptically, and a combination thereof. 5. The X-ray optical element according to claim 1, wherein the first and second reflective surfaces are formed with multilayer systems having graded layer thicknesses. 6. The X-ray optical element according claim 5, wherein the layer depths of one of the multilayer systems is graded. 7. The X-ray optical element according to claim 1, wherein the X-ray radiation is directed and reflected onto the first and second surfaces in compliance with a Bragg condition. 8. The X-ray optical element according to claim 1, wherein the first and second focal lengths have respective focal points are arranged within a focal point volume. 9. The X-ray optical element according to claim 1, wherein the X-ray beam source is located prior to the first and second reflective surfaces so that the X-ray radiation forms a tetraeder. 10. A method for at least one of local and temporal influencing of at least one of a homogeneity, an energy/photon density over a cross section, a form of the cross section, an area of the cross section, a divergence for an X-ray radiation, comprising:directing the X-ray radiation to a first and second reflective, curved surfaces, the first and second surfaces adjacent to one another at a joint angle; andreflecting the X-ray radiation from one of the first and second surfaces onto the other surface, the first surface curved at a first angle different than a second angle at which the second surface is curved, the first surface exhibiting a first focal length different than a second focal length that the second surface exhibits.
	claims	1. Radiation resistant clothing, comprising:a first radiation resistant layer for reflecting electromagnetic radiation (EMR); anda second radiation resistant layer comprising radiation absorbing material for absorbing EMR, the second radiation resistant layer positioned on an inside of the first radiation resistant layer. 2. The radiation resistant clothing of claim 1, wherein the radiation absorbing material comprises silicon carbide fiber material. 3. The radiation resistant clothing of claim 1, wherein the radiation absorbing material comprises multi-ion fabric material. 4. The radiation resistant clothing of claim 3, wherein the multi-ion fabric material is multi-ion acrylic fiber material. 5. The radiation resistant clothing of claim 1, wherein the first radiation resistant layer comprises metal fiber material. 6. The radiation resistant clothing of claim 5, wherein the metal fiber material is material selected from the group consisting of steel fiber material and silver fiber material. 7. The radiation resistant clothing of claim 5, wherein the first radiation resistant layer comprises nanometer metal fiber material. 8. The radiation resistant clothing of claim 7, wherein the nanometer metal fiber material is nanometer sliver fiber material. 9. The radiation resistant clothing of claim 1, further comprising an outer cloth layer positioned on an outside of the first radiation resistant layer away from the second radiation resistant layer. 10. The radiation resistant clothing of claim 1, further comprising an inner cloth layer positioned on an inside of the second radiation resistant layer away from the first radiation resistant layer. 11. The radiation resistant clothing of claim 1, wherein the second radiation resistant layer comprises mixed material made of the radiation absorbing material and common clothing fiber material, and the common clothing fiber material comprises material selected from the group consisting of bamboo rayon fiber material, bamboo carbon fiber material, cotton fiber material, polyester fiber material, and polyamide fiber material. 12. The radiation resistant clothing of claim 11, wherein the radiation absorbing material comprises silicon carbide fiber material. 13. The radiation resistant clothing of claim 1, wherein the first radiation resistant layer comprises mixed material made of radiation shielding material and common clothing fiber material, and the common clothing fiber material comprises material selected from the group consisting of bamboo rayon fiber material, bamboo carbon fiber material, cotton fiber material, polyester fiber material, and polyamide fiber material. 14. The radiation resistant clothing of claim 13, wherein the radiation shielding material comprises material selected from the group consisting of metal fiber material and nanometer metal fiber material.
	summary
	description	This application claims the benefit of the U.S. Provisional Application No. 60/494,699 filed Aug. 12, 2003 and U.S. Provisional Application No. 60/579,095 filed Jun. 10, 2004 both entitled “Precision Patient Alignment and Beam Therapy System”. This invention was made with United States Government support under the DAMD17-99-1-9477 and DAMD17-02-1-0205 grants awarded by the Department of Defense. The Government has certain rights in the invention. 1. Field of the Invention The invention relates to the field of radiation therapy systems. One embodiment includes an alignment system with an external measurement system and local feedback to improve accuracy of patient registration and positioning and to compensate for misalignment caused by factors such as mechanical movement tolerances and non-strictly rigid structures. 2. Description of the Related Art Radiation therapy systems are known and used to provide treatment to patients suffering a wide variety of conditions. Radiation therapy is typically used to kill or inhibit the growth of undesired tissue, such as cancerous tissue. A determined quantity of high-energy electromagnetic radiation and/or high-energy particles is directed into the undesired tissue with the goal of damaging the undesired tissue while reducing unintentional damage to desired or healthy tissue through which the radiation passes on its path to the undesired tissue. Proton therapy has emerged as a particularly efficacious treatment for a variety of conditions. In proton therapy, positively charged proton subatomic particles are accelerated, collimated into a tightly focused beam, and directed towards a designated target region within the patient. Protons exhibit less lateral dispersion upon impact with patient tissue than electromagnetic radiation or low mass electron charged particles and can thus be more precisely aimed and delivered along a beam axis. Also, upon impact with patient tissue, the accelerated protons pass through the proximal tissue with relatively low energy transfer and then exhibit a characteristic Bragg peak wherein a significant portion of the kinetic energy of the accelerated mass is deposited within a relatively narrow penetration depth range within the patient. This offers the significant advantage of reducing delivery of energy from the accelerated proton particles to healthy tissue interposed between the target region and the delivery nozzle of a proton therapy machine as well as to “downrange” tissue lying beyond the designated target region. Depending on the indications for a particular patient and their condition, delivery of the therapeutic proton beam may preferably take place from a plurality of directions in multiple treatment fractions to achieve a total dose delivered to the target region while reducing collateral exposure of interposed desired/healthy tissue. Thus, a radiation therapy system, such as a proton beam therapy system, typically has provision for positioning and aligning a patient with respect to a proton beam in multiple orientations. In order to determine a preferred aiming point for the proton beam within the patient, the typical procedure has been to perform a computed tomography (CT) scan in an initial planning or prescription stage from which multiple digitally reconstructed radiographs (DRRs) can be determined. The DRRs synthetically represent the three dimensional data representative of the internal physiological structure of the patient obtained from the CT scan in two dimensional views considered from multiple orientations and thus can function as a target image of the tissue to be irradiated. A desired target isocenter corresponding to the tissue to which therapy is to be provided is designated. The spatial location of the target isocenter can be referenced with respect to physiological structure of the patient (monuments) as indicated in the target image. Upon subsequent setup for delivery of the radiation therapy, a radiographic image is taken of the patient, such as a known x-ray image, and this radiographic image is compared or registered with the target image with respect to the designated target isocenter. The patient's position is adjusted to, as closely as possible or within a given tolerance, align the target isocenter in a desired pose with respect to the radiation beam as indicated by the physician's prescription. The desired pose is frequently chosen as that of the initial planning or prescription scan. In order to reduce misalignment of the radiation beam with respect to the desired target isocenter to achieve the desired therapeutic benefit and reduce undesired irradiation of other tissue, it will be appreciated that accuracy of placement of the patient with respect to the beam nozzle is important to achieve these goals. In particular, the target isocenter is to be positioned translationally to coincide with the delivered beam axis as well as in the correct angular position to place the patient in the desired pose in a rotational aspect. In particular, as the spatial location of the Bragg peak is dependent both upon the energy of the delivered proton beam as well as the depth and constitution of tissue through which the beam passes, it will be appreciated that a rotation of the patient about the target isocenter even though translationally aligned can present a varying depth and constituency of tissue between the initial impact point and the target isocenter located within the patient's body, thus varying the penetration depth. A further difficulty with registration and positioning is that a radiation therapy regimen typically is implemented via a plurality of separate treatment sessions administered over a period of time, such as daily treatments administered over a several week period. Thus, the alignment of the patient and the target isocenter as well as positioning of the patient in the desired pose with respect to the beam is typically repeatedly determined and executed multiple times over a period of days or weeks. There are several difficulties with accurately performing this patient positioning with respect to the radiation treatment apparatus. As previously mentioned, patient registration is performed by obtaining radiographic images of the patient at a current treatment session at the radiation therapy delivery site and comparing this obtained image with the previously obtained DRR or target image which is used to indicate the particular treatment prescription for the patient. As the patient will have removed and repositioned themselves within the radiation therapy apparatus, the exact position and pose of a patient will not be exactly repeated from treatment session to treatment session nor to the exact position and pose with which the target image was generated, e.g., the orientation from which the original CT scan generated the DRRs. Thus, each treatment session/fraction typically involves precisely matching a subsequently obtained radiographic image with an appropriate corresponding DRR to facilitate the determination of a corrective translational and/or rotational vector to position the patient in the desired location and pose. In addition to the measurement and computational difficulties presented by such an operation, is the desire for speed in execution as well as accuracy. In particular, a radiation therapy apparatus is an expensive piece of medical equipment to construct and maintain both because of the materials and equipment needed in construction and the indication for relatively highly trained personnel to operate and maintain the apparatus. In addition, radiation therapy, such as proton therapy, is increasingly being found an effective treatment for a variety of patient conditions and thus it is desirable to increase patient throughput both to expand the availability of this beneficial treatment to more patients in need of the same as well as reducing the end costs to the patients or insurance companies paying for the treatment and increase the profitability for the therapy delivery providers. As the actual delivery of the radiation dose, once the patient is properly positioned, is a relatively quick process, any additional latency in patient ingress and egress from the therapy apparatus, imaging, and patient positioning and registration detracts from the overall patient throughput and thus the availability, costs, and profitability of the system. A further difficulty with accurately positioning the patient and the corresponding target isocenter in the desired position and pose with respect to the beam nozzle are the multiple and additive uncertainties in the exact position and relative angle of the various components of a radiation therapy system. For example, the beam nozzle can be fitted to a relatively rigid gantry structure to allow the beam nozzle to revolve about a gantry center to facilitate presentation of the radiation beam from a variety of angles with respect to the patient without requiring uncomfortable or inconvenient positioning of the patient themselves. However, as the gantry structure is relatively large (on the order of several meters), massive, and made out of non-strictly rigid materials, there is inevitably some degree of structural flex/distortion and non-repeatable mechanical tolerance as the nozzle revolves about the gantry. Further, the nozzle may be configured as an elongate distributed mass that is also not strictly rigid such that the distal emissions end of the nozzle can flex to some degree, for example as the nozzle moves from an overhead vertical position to a horizontal, sideways presentation of the beam. Accurate identification of the precise nozzle position can also be complicated by a cork screwing with the gantry. Similarly, the patient may be placed on a supportive pod or table and it may be connected to a patient positioning apparatus, both of which are subject to some degree of mechanical flex under gravity load, as well as mechanical tolerances at moving joints that are not necessarily consistent throughout the range of possible patient postures. While it is possible to estimate and measure certain of these variations, as they are typically variable and non-repeatable, it remains a significant challenge to repeatedly position a patient consistently over multiple treatment sessions in both location and pose to tight accuracy limits, such as to millimeter or less accuracy on a predictive basis. Thus, the known way to address gantry and patient table misalignment is to re-register the patient before treatment. This is undesirable as the patient is exposed to additional x-ray radiation for the imaging and overall patient throughput is reduced by the added latency of the re-registration. From the foregoing it will be understood that there is a need for increasing the accuracy and speed of the patient registration process. There is also a need for reducing iteratively imaging and reorienting the patient to achieve a desired pose. There is also a need for a system that accounts for variable and unpredictable position errors to increase the accuracy of patient registration and alignment with a radiation therapy delivery system. Embodiments of the invention provide a patient alignment system that externally measures and provides corrective feedback for variations or deviations from nominal position and orientation between the patient and a delivered therapeutic radiation beam. The alignment system can readily accommodate variable and unpredictable mechanical tolerances and structural flex of both fixed and movable components of the radiation therapy system. The patient alignment system reduces the need for imaging the patient between treatment fractions and decreases the latency of the registration process, thus increasing patient throughput. Other embodiments comprise a radiation therapy delivery system comprising a gantry, a patient fixation device configured to secure a patient with respect to the patient fixation device, a patient positioner interconnected to the patient fixation device so as to position the patient fixation device along translational and rotational axes within the gantry, a radiation therapy nozzle interconnected to the gantry and selectively delivering radiation therapy along a beam axis, a plurality of external measurement devices which obtain position measurements of at least the patient fixation device and the nozzle, and a controller which receives the position measurements of at least the patient fixation device and the nozzle and provides control signals to the patient positioner to position the patient in a desired orientation with respect to the beam axis. Another embodiment comprises a patient positioning system for a radiation therapy system having a plurality of components that are subject to movement, the positioning system comprising a plurality of external measurement devices arranged to obtain position measurements of the plurality of components so as to provide location information, a movable patient support configured to support a patient substantially fixed in position with respect to the patient support and controllably position the patient in multiple translational and rotational axes, and a controller receiving information from the plurality of external measurement devices and providing movement commands to the movable patient support to align the patient in a desired pose such that the positioning system compensates for movement of the plurality of components. Further embodiments include a method of registering and positioning a patient for delivery of therapy with a system having a plurality of components subject to movement, the method comprising the steps of positioning a patient in an initial treatment pose with a controllable patient positioner, externally measuring the location of selected points of the plurality of components, determining a difference vector between the observed initial patient pose and a desired patient pose, and providing movement commands to the patient positioner to bring the patient to the desired patient pose. Yet another embodiment comprises a positioning system for use with a radiation treatment facility wherein the radiation treatment facility has a plurality of components that includes a source of particles and a nozzle from which the particles are emitted, wherein the nozzle is movable with respect to the patient to facilitate delivery of the particles to a selected region of the patient via a plurality of different paths, the positioning system comprising a patient positioner that receives the patient wherein the patient positioner is movable so as to orient the patient with respect to the nozzle to facilitate delivery of the particles in the selected region of the patient, a monitoring system that images at least one component of the radiation treatment facility in proximity to the patient positioner, wherein the monitoring system develops a treatment image indicative of the orientation of the at least one component with respect to the patient prior to treatment, and a control system that controls delivery of particles to the patient wherein the control system receives signals indicative of the treatment to be performed, the signals including a desired orientation of the at least one component when the particles are to be delivered to the patient, wherein the control system further receives the treatment image and the control system evaluates the treatment image to determine an actual orientation of the at least one component prior to treatment and wherein the control system compares the actual orientation of the at least one component prior to treatment to the desired orientation of the at least one component and, if the actual orientation does not meet a predetermined criteria for correspondence with the desired orientation, the control system sends signals to the patient positioner to move the patient positioner such that the actual orientation more closely corresponds to the desired orientation during delivery of the particles. These and other objects and advantages of the invention will become more apparent from the following description taken in conjunction with the accompanying drawings. Reference will now be made to the drawings wherein like reference designators refer to like parts throughout. FIGS. 1A and 1B illustrate schematically first and second orientations of one embodiment of a radiation therapy system 100, such as based on the proton therapy system currently in use at Loma Linda University Medical Center in Loma Linda, Calif. and as described in U.S. Pat. No. 4,870,287 of Sep. 26, 1989 which is incorporated herein in its entirety by reference. The radiation therapy system 100 is designed to deliver therapeutic radiation doses to a target region within a patient for treatment of malignancies or other conditions from one or more angles or orientations with respect to the patient. The system 100 includes a gantry 102 which includes a generally hemispherical or frustoconical support frame for attachment and support of other components of the radiation therapy system 100. Additional details on the structure and operation of embodiments of the gantry 102 may be found in U.S. Pat. No. 4,917,344 and U.S. Pat. No. 5,039,057, both of which are incorporated herein in their entirety by reference. The system 100 also comprises a nozzle 104 which is attached and supported by the gantry 102 such that the gantry 102 and nozzle 104 may revolve relatively precisely about a gantry isocenter 120, but subject to corkscrew, sag, and other distortions from nominal. The system 100 also comprises a radiation source 106 delivering a radiation beam along a radiation beam axis 140, such as a beam of accelerated protons. The radiation beam passes through and is shaped by an aperture 110 to define a therapeutic beam delivered along a delivery axis 142. The aperture 110 is positioned on the distal end of the nozzle 104 and the aperture 110 may preferably be specifically configured for a patient's particular prescription of therapeutic radiation therapy. In certain applications, multiple apertures 110 are provided for different treatment fractions. The system 100 also comprises one or more imagers 112 which, in this embodiment, are retractable with respect to the gantry 102 between an extended position as illustrated in FIG. 2A and a retracted position as illustrated in FIG. 2B. The imager 112 in one implementation comprises a commercially available solid-state amorphous silicon x-ray imager which can develop image information such as from incident x-ray radiation that has passed through a patient's body. The retractable aspect of the imager 112 provides the advantage of withdrawing the imager screen from the delivery axis 142 of the radiation source 106 when the imager 112 is not needed thereby providing additional clearance within the gantry 102 enclosure as well as placing the imager 112 out of the path of potentially harmful emissions from the radiation source 106 thereby reducing the need for shielding to be provided to the imager 112. The system 100 also comprises corresponding one or more x-ray sources 130 which selectively emit appropriate x-ray radiation along one or more x-ray source axes 144 so as to pass through interposed patient tissue to generate a radiographic image of the interposed materials via the imager 112. The particular energy, dose, duration, and other exposure parameters preferably employed by the x-ray source(s) 130 for imaging and the radiation source 106 for therapy will vary in different applications and will be readily understood and determined by one of ordinary skill in the art. In this embodiment, at least one of the x-ray sources 130 is positionable such that the x-ray source axis 144 can be positioned so as to be nominally coincident with the delivery axis 142. This embodiment provides the advantage of developing a patient image for registration from a perspective which is nominally identical to a treatment perspective. This embodiment also includes the aspect that a first imager 112 and x-ray source 130 pair and a second imager 112 and x-ray source 130 pair are arranged substantially orthogonal to each other. This embodiment provides the advantage of being able to obtain patient images in two orthogonal perspectives to increase registration accuracy as will be described in greater detail below. The imaging system can be similar to the systems described in U.S. Pat. Nos. 5,825,845 and 5,117,829 which are hereby incorporated by reference. The system 100 also comprises a patient positioner 114 (FIG. 3) and a patient pod 116 which is attached to a distal or working end of the patient positioner 114. The patient positioner 114 is adapted to, upon receipt of appropriate movement commands, position the patient pod 116 in multiple translational and rotational axes and preferably is capable of positioning the patient pod 116 in three orthogonal translational axes as well as three orthogonal rotational axes so as to provide a full six degree freedom of motion to placement of the patient pod 116. The patient pod 116 is configured to hold a patient securely in place in the patient pod 116 so to as substantially inhibit any relative movement of the patient with respect to the patient pod 116. In various embodiments, the patient pod 116 comprises expandable foam, bite blocks, and/or fitted facemasks as immobilizing devices and/or materials. The patient pod 116 is also preferably configured to reduce difficulties encountered when a treatment fraction indicates delivery at an edge or transition region of the patient pod 116. Additional details of preferred embodiments of the patient positioner 114 and patient pod 116 can be found in the commonly assigned application (Ser. No. 10/917,022, filed Aug. 12, 2004) entitled “Modular Patient Support System” filed concurrently herewith and which is incorporated herein in its entirety by reference. As previously mentioned, in certain applications of the system 100, accurate relative positioning and orientation of the therapeutic beam delivery axis 142 provided by the radiation source 106 with target tissue within the patient as supported by the patient pod 116 and patient positioner 114 is an important goal of the system 100, such as when comprising a proton beam therapy system. However, as previously mentioned, the various components of the system 100, such as the gantry 102, the nozzle 104, radiation source 106, the imager(s) 112, the patient positioner 114, the patient pod 116, and x-ray source(s) 130 are subject to certain amounts of structural flex and movement tolerances from a nominal position and orientation which can affect accurate delivery of the beam to that patient. FIGS. 1A and 1B illustrate different arrangements of certain components of the system 100 and indicate by the broken arrows both translational and rotational deviations from nominal that can occur in the system 100. For example, in the embodiment shown in FIG. 1A, the nozzle 104 and first imager 112 extend substantially horizontally and are subject to bending due to gravity, particularly at their respective distal ends. The second imager 112 is arranged substantially vertically and is not subject to the horizontal bending of the first imager 112. FIG. 1B illustrates the system 100 in a different arrangement rotated approximately 45° counterclockwise from the orientation of FIG. 1A. In this orientation, both of the imagers 112 as well as the nozzle 104 are subject to bending under gravity, but to a different degree than in the orientation illustrated in FIG. 1A. The movement of the gantry 102 between different orientations, such as is illustrated in FIGS. 1A and 1B also subjects components of the system 100 to mechanical tolerances at the moving surfaces. As these deviations from nominal are at least partially unpredictable, non-repeatable, and additive, correcting for the deviations on a predictive basis is extremely challenging and limits overall alignment accuracy. It will be appreciated that these deviations from the nominal orientation of the system are simply exemplary and that any of a number of sources of error can be addressed by the system disclosed herein without departing from the spirit of the present invention. FIGS. 4A–4E illustrate in greater detail embodiments of potential uncertainties or errors which can present themselves upon procedures for alignment of, for example, the nozzle 104 and the target tissue of the patient at an isocenter 120. FIGS. 4A–4E illustrate these sources of uncertainty or error with reference to certain distances and positions. It will be appreciated that the sources of error described are simply illustrative of the types of errors addressed by the system 100 of the illustrated embodiments and that the system 100 described is capable of addressing additional errors. In this embodiment, a distance SAD is defined as a source to axis distance from the radiation source 106 to the rotation axis of the gantry, which ideally passes through the isocenter 120. For purposes of explanation and appreciation of relative scale and distances, in this embodiment, SAD is approximately equal to 2.3 meters. FIG. 4A illustrates that one of the potential sources of error is a source error where the true location of the radiation source 106 is subject to offset from a presumed or nominal location. In this embodiment, the therapeutic radiation beam as provided by the radiation source 106 passes through two transmission ion chambers (TIC) which serve to center the beam. These are indicated as TIC 1 and TIC 3 and these are also affixed to the nozzle 104. The source error can arise from numerous sources including movement of the beam as observed on TIC 1 and/or TIC 3, error in the true gantry 102 rotational angle, and error due to “egging” or distortion from round of the gantry 102 as it rotates. FIG. 4A illustrates source error comprising an offset of the true position of the radiation source 106 from a presumed or nominal location and the propagation of the radiation beam across the SAD distance through the aperture 110 providing a corresponding error at isocenter 120. FIG. 4B illustrates possible error caused by TIC location error, where TIC 1, the radiation source 106, and TIC 3 are offset from an ideal beam axis passing through the nominal gantry isocenter 120. As the errors illustrated by FIGS. 4A and 4B are assumed random and uncorrelated, they can be combined in quadrature and projected through an assumed nominal center of the aperture 110 to establish a total error contribution due to radiation source 106 error projected to the isocenter 120. In this embodiment, before corrective measures are taken (as described in greater detail below), the radiation source error can range from approximately ±0.6 mm to ±0.4 mm. FIG. 4C illustrates error or uncertainty due to position of the aperture 110. The location of the radiation source 106 is assumed nominal; however, error or uncertainty is introduced both by tolerance stack-up, skew, and flex of the nozzle 104 as well as manufacturing tolerances of the aperture 110 itself. Again, as projected from the radiation source 106 across the distance SAD to the nominal isocenter 120, a beam delivery aiming point (BDAP) error is possible between a presumed nominal BDAP and an actual BDAP. In this embodiment, this BDAP error arising from error in the aperture 110 location ranges from approximately ±1.1 mm to ±1.5 mm. The system 100 is also subject to error due to positioning of the imager(s) 112 as well as the x-ray source(s) 130 as illustrated in FIGS. 4D and 4E. FIG. 4D illustrates the error due to uncertainty in the imager(s) 112 position with the position of the corresponding x-ray source(s) 130 assumed nominal. As the emissions from the x-ray source 130 pass through the patient assumed located substantially at isocenter 120 and onward to the imager 112, this distance may be different than the SAD distance and in this embodiment is approximately equal to 2.2 meters. Error or uncertainty in the true position of an imager 112 can arise from lateral shifts in the true position of the imager 112, errors due to axial shifting of the imager 112 with respect to the corresponding x-ray source 130, as well as errors in registration of images obtained by imager 112 to the DRRs. In this embodiment, before correction, the errors due to each imager 112 are approximately ±0.7 mm. Similarly, FIG. 4E illustrates errors due to uncertainty in positioning of the x-ray source(s) 130 with the position of the corresponding imager(s) 112 assumed nominal. Possible sources of error due to the x-ray source 130 include errors due to initial alignment of the x-ray source 130, errors arising from movement of the x-ray source 130 into and out of the beam line, and errors due to interpretation of sags and relative distances of TIC 1 and TIC 3. These errors are also assumed random and uncorrelated or independent and are thus added in quadrature resulting, in this embodiment, in error due to each x-ray source 130 of approximately ±0.7 mm. As these errors are random and independent and uncorrelated and thus potentially additive, in this embodiment the system 100 also comprises a plurality of external measurement devices 124 to evaluate and facilitate compensating for these errors. In one embodiment, the system 100 also comprises monuments, such as markers 122, cooperating with the external measurement devices 124 as shown in FIGS. 2A, 2B, 6 and 7. The external measurement devices 124 each obtain measurement information about the three-dimensional position in space of one or more components of the system 100 as indicated by the monuments as well as one or more fixed landmarks 132 also referred to herein as the “world” 132. In this embodiment, the external measurement devices 124 comprise commercially available cameras, such as CMOS digital cameras with megapixel resolution and frame rates of 200–1000 Hz, which independently obtain optical images of objects within a field of view 126, which in this embodiment is approximately 85° horizontally and 70° vertically. The external measurement devices 124 comprising digital cameras are commercially available, for example as components of the Vicon Tracker system from Vicon Motion Systems Inc. of Lake Forrest, Calif. However, in other embodiments, the external measurement devices 124 can comprise laser measurement devices and/or radio location devices in addition to or as an alternative to the optical cameras of this embodiment. In this embodiment, the markers 122 comprise spherical, highly reflective landmarks which are fixed to various components of the system 100. In this embodiment, at least three markers 122 are fixed to each component of the system 100 of interest and are preferably placed asymmetrically, e.g. not equidistant from a centerline nor evenly on corners, about the object. The external measurement devices 124 are arranged such that at least two external measurement devices 124 have a given component of the system 100 and the corresponding markers 122 in their field of view and in one embodiment a total of ten external measurement devices 124 are provided. This aspect provides the ability to provide binocular vision to the system 100 to enable the system 100 to more accurately determine the location and orientation of components of the system 100. The markers 122 are provided to facilitate recognition and precise determination of the position and orientation of the objects to which the markers 122 are affixed, however in other embodiments, the system 100 employs the external measurement devices 124 to obtain position information based on monuments comprising characteristic outer contours of objects, such as edges or corners, comprising the system 100 without use of the external markers 122. FIG. 5 illustrates one embodiment of determining the spatial position and angular orientation of a component of the system 100. As the component(s) of interest can be the gantry 102, nozzle 104, aperture 110, imager 112, world 132 or other components, reference will be made to a generic “object”. It will be appreciated that the process described for the object can proceed in parallel or in a series manner for multiple objects. Following a start state, in state 150 the system 100 calibrates the multiple external measurement devices 124 with respect to each other and the world 132. In the calibration state, the system 100 determines the spatial position and angular orientation of each external measurement device 124. The system 100 also determines the location of the world 132 which can be defined by a dedicated L-frame and can define a spatial origin or frame-of-reference of the system 100. The world 132 can, of course, comprise any component or structure that is substantially fixed within the field of view of the external measurement devices 124. Hence, structures that are not likely to move or deflect as a result of the system 100 can comprise the world 132 or point of reference for the external measurement devices 124. A wand, which can include one or more markers 122 is moved within the fields of view 126 of the external measurement devices 124. As the external measurement devices 124 are arranged such that multiple external measurement devices 124 (in this embodiment at least two) have an object in the active area of the system 100 in their field of view 126 at any given time, the system 100 correlates the independently provided location and orientation information from each external measurement device 124 and determines corrective factors such that the multiple external measurement devices 124 provide independent location and orientation information that is in agreement following calibration. The particular mathematical steps to calibrate the external measurement devices 124 are dependent on their number, relative spacing, geometrical orientations to each other and the world 132, as well as the coordinate system used and can vary among particular applications, however will be understood by one of ordinary skill in the art. It will also be appreciated that in certain applications, the calibration state 150 would need to be repeated if one or more of the external measurement devices 124 or world 132 is moved following calibration. Following the calibration state 150, in state 152 multiple external measurement devices 124 obtain an image of the object(s) of interest. From the images obtained in state 152, the system 100 determines a corresponding direction vector 155 to the object from each corresponding external measurement device 124 which images the object in state 154. This is illustrated in FIG. 6 as vectors 155a–d corresponding to the external measurement devices 124a–d which have the object in their respective fields of view 126. Then, in state 156, the system 100 calculates the point in space where the vectors 155 (FIG. 6) determined in state 154 intersect. State 156 thus returns a three-dimensional location in space, with reference to the world 132, for the object corresponding to multiple vectors intersecting at the location. As the object has been provided with three or more movements or markers 122, the system 100 can also determine the three-dimensional angular orientation of the object by evaluating the relative locations of the individual markers 122 associated with the object. In this implementation, the external measurement devices 124 comprise cameras, however, any of a number of different devices can be used to image, e.g., determine the location, of the monuments without departing from the spirit of the present invention. In particular, devices that emit or receive electromagnetic or audio energy including visible and non-visible wavelength energy and ultra-sound can be used to image or determine the location of the monuments. The location and orientation information determined for the object is provided in state 160 for use in the system 100 as described in greater detail below. In one embodiment, the calibration state 150 can be performed within approximately one minute and allows the system 100 to determine the object's location in states 152, 154, 156, and 160 to within 0.1 min and orientation to within 0.15° with a latency of no more than 10 ms. As previously mentioned, in other embodiments, the external measurement devices 124 can comprise laser measurement devices, radio-location devices or other devices that can determine direction to or distance from the external measurement devices 124 in addition to or as an alternative to the external measurement devices 124 described above. Thus, in certain embodiments a single external measurement device 124 can determine both range and direction to the object to determine the object location and orientation. In other embodiments, the external measurement devices 124 provide only distance information to the object and the object's location in space is determined by determining the intersection of multiple virtual spheres centered on the corresponding external measurement devices 124. In certain embodiments, the system 100 also comprises one or more local position feedback devices or resolvers 134 (See, e.g., FIG. 1). The local feedback devices or resolvers 134 are embodied within or in communication with one or more components of the system 100, such as the gantry 102, the nozzle 104, the radiation source 106, the aperture 110, the imager(s) 112, patient positioner 114, patient pod 116, and/or world 132. The local feedback devices 134 provide independent position information relating to the associated component of the system 100. In various embodiments, the local feedback devices 134 comprise rotary encoders, linear encoders, servos, or other position indicators that are commercially available and whose operation is well understood by one of ordinary skill in the art. The local feedback devices 134 provide independent position information that can be utilized by the system 100 in addition to the information provided by the external measurement devices 124 to more accurately position the patient. The system 100 also comprises, in this embodiment, a precision patient alignment system 200 which employs the location information provided in state 160 for the object(s). As illustrated in FIG. 8, the patient alignment system 200 comprises a command and control module 202 communicating with a 6D system 204, a patient registration module 206, data files 210, a motion control module 212, a safety module 214, and a user interface 216. The patient alignment system 200 employs location information provided by the 6D system 204 to more accurately register the patient and move the nozzle 104 and the patient positioner 114 to achieve a desired treatment pose as indicated by the prescription for the patient provided by the data files 210. In this embodiment, the 6D system 204 receives position data from the external measurement devices 124 and from the resolvers 134 relating to the current location of the nozzle 104, the aperture 110, the imager 112, the patient positioner 114, and patient pod 116, as well as the location of one or more fixed landmarks 132 indicated in FIG. 9 as the world 132. The fixed landmarks, or world, 132 provide a non-moving origin or frame of reference to facilitate determination of the position of the moving components of the radiation therapy system 100. This location information is provided to a primary 6D position measurement system 220 which then uses the observed data from the external measurement devices 124 and resolvers 134 to calculate position and orientation coordinates of these five components and origin in a first reference frame. This position information is provided to a 6D coordination module 222 which comprises a coordinate transform module 224 and an arbitration module 226. The coordinate transform module 224 communicates with other modules of the patient alignment system 200, such as the command and control module 202 and the motion control with path planning and collision avoidance module 212. Depending on the stage of the patient registration and therapy delivery process, other modules of the patient alignment system 200 can submit calls to the 6D system 204 for a position request of the current configuration of the radiation therapy system 100. Other modules of the patient alignment system 200 can also provide calls to the 6D system 204 such as a coordinate transform request. Such a request typically will include submission of location data in a given reference frame, an indication of the reference frame in which the data is submitted and a desired frame of reference which the calling module wishes to have the position data transformed into. This coordinate transform request is submitted to the coordinate transform module 224 which performs the appropriate calculations upon the submitted data in the given reference frame and transforms the data into the desired frame of reference and returns this to the calling module of the patient alignment system 200. For example, the radiation therapy system 100 may determine that movement of the patient positioner 114 is indicated to correctly register the patient. For example, a translation of plus 2 mm along an x-axis, minus 1.5 mm along a y-axis, no change along a z-axis, and a positive 1° rotation about a vertical axis is indicated. This data would be submitted to the coordinate transform module 224 which would then operate upon the data to return corresponding movement commands to the patient positioner 114. The exact coordinate transformations will vary in specific implementations of the system 100 depending, for example, on the exact configuration and dimensions of the patient positioner 114 and the relative position of the patient positioner 114 with respect to other components of the system 100. However, such coordinate transforms can be readily determined by one of ordinary skill in the art for a particular application. The arbitration module 226 assists in operation of the motion control module 212 by providing specific object position information upon receipt of a position request. A secondary position measurement system 230 provides an alternative or backup position measurement function for the various components of the radiation therapy system 100. In one embodiment, the secondary position measurement system 230 comprises a conventional positioning functionality employing predicted position information based on an initial position and commanded moves. In one embodiment, the primary position measurement system 220 receives information from the external measurement devices 124 and the secondary position measurement system 230 receives independent position information from the resolvers 134. It will generally be preferred that the 6D measurement system 220 operate as the primary positioning system for the previously described advantages of positioning accuracy and speed. FIG. 10 illustrates in greater detail the patient registration module 206 of the patient alignment system 200. As previously described, the 6D system 204 obtains location measurements of various components of the radiation therapy system 100, including the table or patient pod 116 and the nozzle 104 and determines position coordinates of these various components and presents them in a desired frame of reference. The data files 210 provide information relating to the patient's treatment prescription, including the treatment plan and CT data previously obtained at a planning or prescription session. This patient's data can be configured by a data converter 232 to present the data in a preferred format. The imager 112 also provides location information to the 6D system 204 as well as to an image capture module 236. The image capture module 236 receives raw image data from the imager 112 and processes this data, such as with filtering, exposure correction, scaling, and cropping to provide corrected image data to a registration algorithm 241. In this embodiment, the CT data undergoes an intermediate processing step via a transgraph creation module 234 to transform the CT data into transgraphs which are provided to the registration algorithm 241. The transgraphs are an intermediate data representation and increase the speed of generation of DRRs. The registration algorithm 241 uses the transgraphs, the treatment plan, the current object position data provided by the 6D system 204 and the corrected image data from the imager(s) 112 to determine a registered pose which information is provided to the command and control module 202. The registration algorithm 241 attempts to match either as closely as possible or to within a designated tolerance the corrected image data from the imager 112 with an appropriate DRR to establish a desired pose or to register the patient. The command and control module 202 can evaluate the current registered pose and provide commands or requests to induce movement of one or more of the components of the radiation therapy system 100 to achieve this desired pose. Additional details for a suitable registration algorithm may be found in the published doctoral dissertation of David A. LaRose of May 2001 submitted to Carnegie Mellon University entitled “Iterative X-ray/CT Registration Using Accelerated Volume Rendering” which is incorporated herein in its entirety by reference. FIGS. 11–13 illustrate embodiments with which the system 100 performs this movement. FIG. 11 illustrates that the command and control module 202 has provided a call for movement of one or more of the components of the radiation therapy system 100. In state 238, the motion control module 212 retrieves a current position configuration from the 6D system 204 and provides this with the newly requested position configuration to a path planning module 240. The path planning module 240 comprises a library of three-dimensional model data which represent position envelopes defined by possible movement of the various components of the radiation therapy system 100. For example, as previously described, the imager 112 is retractable and a 3D model data module 242 indicates the envelope or volume in space through which the imager 112 can move depending on its present and end locations. The path planning module 240 also comprises an object movement simulator 244 which receives data from the 3D model data module 242 and can calculate movement simulations for the various components of the radiation therapy system 100 based upon this data. This object movement simulation module 244 preferably works in concert with a collision avoidance module 270 as illustrated in FIG. 12. FIG. 12 again illustrates one embodiment of the operation of the 6D system 204 which in this embodiment obtains location measurements of the aperture 110, imager 112, nozzle 104, patient positioner and patient pod 114 and 116 as well as the fixed landmarks or world 132. FIG. 12 also illustrates that, in this embodiment, local feedback is gathered from resolvers 134 corresponding to the patient positioner 114, the nozzle 104, the imager 112, and the angle of the gantry 102. This position information is provided to the collision avoidance module 270 which gathers the object information in an object position data library 272. This object data is provided to a decision module 274 which evaluates whether the data is verifiable. In certain embodiments, the evaluation of the module 274 can investigate possible inconsistencies or conflicts with the object position data from the library 272 such as out-of-range data or data which indicates, for example, that multiple objects are occupying the same location. If a conflict or out-of-range condition is determined, e.g., the result of the termination module 274 is negative, a system halt is indicated in state 284 to inhibit further movement of components of the radiation therapy system 100 and further proceeds to a fault recovery state 286 where appropriate measures are taken to recover or correct the fault or faults. Upon completion of the fault recovery state 286, a reset state 290 is performed followed by a return to the data retrieval of the object position data library in module 272. If the evaluation of state 274 is affirmative, a state 276 follows where the collision avoidance module 270 calculates relative distances along current and projected trajectories and provides this calculated information to an evaluation state 280 which determines whether one or more of the objects or components of the radiation therapy system 100 are too close. If the evaluation of stage 280 is negative, e.g., that the current locations and projected trajectories do not present a collision hazard, a sleep or pause state 282 follows during which movement of the one or more components of the radiation therapy system 100 is allowed to continue as indicated and proceeds to a recursive sequence through modules 272, 274, 276, 280, and 282 as indicated. However, if the results of the evaluation state 280 are affirmative, e.g., that either one or more of the objects are too close or that their projected trajectories would bring them into collision, the system halt of state 284 is implemented with the fault recovery and reset states 286 and 290, following as previously described. Thus, the collision avoidance module 270 allows the radiation therapy system 100 to proactively evaluate both current and projected locations and movement trajectories of movable components of the system 100 to mitigate possible collisions before they occur or are even initiated. This is advantageous over systems employing motion stops triggered, for example, by contact switches which halt motion upon activation of stop or contact switches, which by themselves may be inadequate to prevent damage to the moving components which can be relatively large and massive having significant inertia, or to prevent injury to a user or patient of the system. Assuming that the object movement simulation module 244 as cooperating with the collision avoidance module 270 indicates that the indicated movements will not pose a collision risk, the actual movement commands are forwarded to a motion sequence coordinator module 246 which evaluates the indicated movement vectors of the one or more components of the radiation therapy system 100 and sequences these movements via, in this embodiment, five translation modules. In particular, the translation modules 250, 252, 254, 260, and 262 translate indicated movement vectors from a provided reference frame to a command reference frame appropriate to the patient positioner 114, the gantry 102, the x-ray source 130, the imager 112, and the nozzle 104, respectively. As previously mentioned, the various moveable components of the radiation therapy system 100 can assume different dimensions and be subject to different control parameters and the translation modules 250, 252, 254, 260, and 262 interrelate or translate a motion vector in a first frame of reference into the appropriate reference frame for the corresponding component of the radiation therapy system 100. For example, in this embodiment the gantry 102 is capable of clockwise and counterclockwise rotation about an axis whereas the patient positioner 114 is positionable in six degrees of translational and rotational movement freedom and thus operates under a different frame of reference for movement commands as compared to the gantry 102. By having the availability of externally measured location information for the various components of the radiation therapy system 100, the motion sequence coordinator module 246 can efficiently plan the movement of these components in a straightforward, efficient and safe manner. FIG. 14 illustrates a workflow or method 300 of one embodiment of operation of the radiation therapy system 100 as provided with the patient alignment system 200. From a start state 302, follows an identification state 304 wherein the particular patient and treatment portal to be provided is identified. This is followed by a treatment prescription retrieval state 306 and the identification and treatment prescription retrieval of states 304 and 306 can be performed via the user interface 216 and accessing the data files of module 210. The patient is then moved to an imaging position in state 310 by entering into the patient pod 116 and actuation of the patient positioner 114 to position the patient pod 116 securing the patient in the approximate position for imaging. The gantry 102, imager(s) 112, and radiation source(s) 130 are also moved to an imaging position in state 312 and in state 314 the x-ray imaging axis parameters are determined as previously described via the 6D system 204 employing the external measurement devices 124, cooperating markers 122, and resolvers 134. In state 316, a radiographic image of the patient is captured by the imager 112 and corrections can be applied as needed as previously described by the module 236. In this embodiment, two imagers 112 and corresponding x-ray sources 130 are arranged substantially perpendicularly to each other. Thus, two independent radiographic images are obtained from orthogonal perspectives. This aspect provides more complete radiographic image information than from a single perspective. It will also be appreciated that in certain embodiments, multiple imaging of states 316 can be performed for additional data. An evaluation is performed in state 320 to determine whether the radiographic image acquisition process is complete and the determination of this decision results either in the negative case with continuation of the movement of state 312, the determination of state 314 and the capture of state 316 as indicated or, when affirmative, followed by state 322. In state 322, external measurements are performed by the 6D system 204 as previously described to determine the relative positions and orientations of the various components of the radiation therapy system 100 via the patient registration module 206 as previously described. In state 324, motion computations are made as indicated to properly align the patient in the desired pose. While not necessarily required in each instance of treatment delivery, this embodiment illustrates that in state 326 some degree of gantry 102 movement is indicated to position the gantry 102 in a treatment position as well as movement of the patient, such as via the patient positioner 114 in state 330 to position the patient in the indicated pose. Following these movements, state 332 again employs the 6D system 204 to externally measure and in state 334 to compute and analyze the measured position to determine in state 336 whether the desired patient pose has been achieved within the desired tolerance. If adequately accurate registration and positioning of the patient has not yet been achieved, state 340 follows where a correction vector is computed and transformed into the appropriate frame of reference for further movement of the gantry 102 and/or patient positioner 114. If the decision of state 336 is affirmative, e.g., that the patient has been satisfactorily positioned in the desired pose, the radiation therapy fraction is enabled in state 342 in accordance with the patient's prescription. For certain patient prescriptions, it will be understood that the treatment session may indicate multiple treatment fractions, such as treatment from a plurality of orientations and that appropriate portions of the method 300 may be iteratively repeated for multiple prescribed treatment fractions. However, for simplicity of illustration, a single iteration is illustrated in FIG. 14. Thus, following the treatment delivery of state 342, a finished state 344 follows which may comprise the completion of treatment for that patient for the day or for a given series of treatments. Thus, the radiation therapy system 100 with the patient alignment system 200, by directly measuring movable components of the system 100, employs a measured feedback to more accurately determine and control the positioning of these various components. A particular advantage of the system 100 is that the patient can be more accurately registered at a treatment delivery session than is possible with known systems and without an iterative sequence of radiographic imaging, repositioning of the patient, and subsequent radiographic imaging and data analysis. This offers the significant advantage both of more accurately delivering the therapeutic radiation, significantly decreasing the latency of the registration, imaging and positioning processes and thus increasing the possible patient throughput as well as reducing the exposure of the patient to x-ray radiation during radiographic imaging by reducing the need for multiple x-ray exposures during a treatment session. Although the preferred embodiments of the present invention have shown, described and pointed out the fundamental novel features of the invention as applied to those embodiments, it will be understood that various omissions, substitutions and changes in the form of the detail of the device illustrated may be made by those skilled in the art without departing from the spirit of the present invention. Consequently, the scope of the invention should not be limited to the foregoing description but is to be defined by the appended claims.
	claims	1. An apparatus adapted to induce fluorescence in an explosive detection system, comprising:an electromagnetic source configured to generate pulses of radiation with a selected profile, the selected profile having a center wavelength at about 236.2 nm and having a bandwidth between about 0.2 nm and about 2 nm. 2. The apparatus of claim 1, wherein the electromagnetic source comprises:an optical source for producing an electromagnetic output, the electromagnetic output characterized by a wavelength center being an integer multiple of 236.2 nm, the electromagnetic output having a bandwidth consistent with the generation of a bandwidth between about 0.2 nm and about 2 nm at a center wavelength of about 236.2 nm; andat least one harmonic converter to convert the electromagnetic output of the optical source into the electromagnetic radiation centered at about 236.2 nm. 3. The apparatus of claim 2, wherein the optical source is configured to produce a pulsed electromagnetic output. 4. The apparatus of claim 3, wherein the pulsed electromagnetic output is characterized by a repetition rate greater than about 1 kHz. 5. The apparatus of claim 3, wherein the pulsed electromagnetic output is characterized by a pulse length less than about 10 nsec. 6. The apparatus of claim 3, wherein the pulsed electromagnetic output is characterized by a pulse length less than about 2 nsec. 7. The apparatus of claim 1 further comprising:a spectral filter optically coupled to the apparatus and configured to filter at least one wavelength outside the selected profile. 8. The apparatus of claim 2 wherein the optical source comprises at least one of an amplified time-gated superluminescent diode and another type of amplified spontaneous emission source. 9. An apparatus for generating electromagnetic radiation, comprising:an electromagnetic source configured to generate radiation with a selected profile, the profile having at a center wavelength of about 236.2 nm and having a bandwidth between about 0.2 nm and about 2 nm; wherein the source comprises:a pulsed laser; andan optical parametric generator configured to be pumped by at least one of the pulsed laser and a harmonic of the pulsed laser to produce the electromagnetic output, andat least one harmonic converter to convert the electromagnetic output of the source into the electromagnetic radiation centered at about 236.2 nm. 10. The apparatus of claim 9, wherein the pulsed laser comprises at least one of a Q-switched laser, a cavity-dumped laser, a gain-switched laser, an amplified time-gated continuous wave laser, and a gated long-pulse laser. 11. The apparatus of claim 9, wherein the pulsed laser comprises a passively Q-switched Nd:YAG laser. 12. The apparatus of claim 9, wherein the optical parametric generator comprises periodically poled lithium niobate or periodically poled lithium tantalate, and is configured to produce the electromagnetic output with the wavelength center at about 1889 nm. 13. The apparatus of claim 9, wherein at least one harmonic converter comprises at least one of a lithium-based crystal and a barium-based crystal. 14. The apparatus of claim 1 wherein the electromagnetic source further comprises:at least one amplifier for increasing power of the electromagnetic radiation to provide at least a selected target energy density. 15. An apparatus for generating electromagnetic radiation, comprising:an electromagnetic source configured to generate radiation with a selected profile, the selected profile having a center wavelength at about 236.2 nm and having a bandwidth between about 0.2 nm and about 2 nm, wherein the electromagnetic source further comprises:at least one amplifier for increasing power of the electromagnetic radiation to provide at least a selected target energy density, andwherein the at least one amplifier comprises a Nd-doped mixed garnet configured to increase the power of electromagnetic radiation having a wavelength of about 944.8 nm. 16. A system for remotely detecting a presence of an explosive, comprising:the electromagnetic source of claim 9; anda detector configured to receive electromagnetic radiation from a fluorescing NO molecule. 17. The system of claim 16, wherein the system is configured to detect the presence of the explosive at a distance of at least about 10 meters. 18. The system of claim 16, wherein the detector is configured to detect electromagnetic radiation comprising a wavelength of about 226 nm. 19. The apparatus of claim 9, wherein the pulsed laser has a repetition rate greater than about 1 kHz. 20. The apparatus of claim 9, wherein the pulsed laser is configured to generate pulses having a pulse length less than about 10 nsec. 21. The apparatus of claim 9, wherein the pulsed laser is configured to generate pulses having a pulse length less than about 2 nsec. 22. The apparatus of claim 9 further comprising:a spectral filter optically coupled to the apparatus and configured to filter at least one wavelength outside the selected profile. 23. The apparatus of claim 9 wherein the optical source comprises at least one of an amplified time-gated superluminescent diode and another type of amplified spontaneous emission source. 24. The apparatus of claim 9 wherein the electromagnetic source further comprises:at least one amplifier for increasing power of the electromagnetic radiation to provide at least a selected target energy density.
	description	This application is related to and claims the priority benefit of U.S. Provisional Application 60/581,854, filed Jun. 21, 2004, incorporated herein by reference. This invention relates to a charged particle system and a method for focusing a charged particle beam. Modem inspection, defect review and metrology tools use one or more charged particle beams in order to inspect, analyze and measure features or defects. The resolution of these systems is responsive to various parameters including the focus error, astigmatism and the like. Modem systems are also required to inspect, review or measure samples with an increased throughput. High throughput systems requires fast focal error detection methods. As the size of features and defects gets smaller there is a need to provide an efficient method for determining focal errors. A method for focusing a charged particle beam, the method including: (a) altering a focal point of a charged particle beam according to a first focal pattern while scanning a first area of a sample and collecting a first set of detection signals; (b) altering a focal point of a charged particle beam according to a second focal pattern while scanning a second area that is ideally identical to the first area and collecting a second set of detection signals; and (c) processing the first and second set of detection signals to determine a focal characteristic; wherein the first focal pattern and the second focal pattern differ by the location of an optimal focal point. Conveniently, the method can include applying the first and or second focal patterns during inspection sessions or between inspection sessions. A system that includes: (i) illumination optics, adapted to alter a focal point of a charged particle beam according to a first focal pattern while scanning a first area of a sample; and adapted to alter a focal point of a charged particle beam according to a second focal pattern while scanning a second area that is ideally identical to the first area; (ii) at least one detector adapted to provide a first set of detection signals resulting from the scanning of the first area and adapted to provide a second set of detection signals resulting from the scanning of the second area; and (iii) a processor, adapted to process the first and second set of detection signals to determine a focal characteristic; whereas the first focal pattern and the second focal pattern differ by the location of an optimal focal point. In the following detailed description of the preferred embodiments and other embodiments of the invention, reference is made to the accompanying drawings. It is to be understood that those of skill in the art will readily see other embodiments and changes may be made without departing from the scope of the invention. According to various embodiments of the invention, focal characteristics can be determined by applying one, two or more focal patterns. Some figures refer to a first and second focal pattern but the amount of focal patterns can vary. The two focal patterns can be a part of the same focal pattern. According to an embodiment of the invention, the focus can be changed according to a focal pattern to enable the detection of focal errors. The focal pattern can include small deviations from proper focus but this is not necessarily so. The focal pattern can include large or moderate deviations from proper focus. According to an embodiment of the invention, the focal pattern can be applied in a manner that allows one to inspect areas that are imaged while focus changes occur, but this is not necessarily so. The focal changes can occur during an inspection stage of a sample, but this is not necessarily so. According to an embodiment of the invention, the focus can be fixed during a scan of a certain sub-area or strip, while the focal point changes between different sub-areas or strips. The focal pattern is applied while a certain region is scanned. The size of that region can change from sample to sample, from scan to scan, from area to area. According to an embodiment of the invention, one or more characteristic of the focal pattern can be determined in response to focal errors that were previously detected, to the pattern or shape of the scanned sample, and the like. Conveniently, the focus is changed along an imaginary first axis while the sample is translated along an traverse (conveniently perpendicular) axis. This is not necessarily so. The method can be applied in systems where the sample is stationary and a part of the inspection system moves. According to another embodiment of the invention, the method can be applied while a rotational displacement is introduced between the sample and the inspection system. Conveniently, the method includes collecting scattered charged particle beams from a sample, but this is not necessarily so. The following figures refer to an inspection system. It is noted that the invention can be applied in other systems such as but not limited to metrology systems, review systems and the like. The inventors inspected a wafer, but other samples, such as but not limited to reticles can be scanned. It is further noted that the invention can be applied to transmissive inspection systems. FIG. 1 illustrates portion 10 of an inspection system, according to an embodiment of the invention. It is noted that various prior art charged particle beam devices, including devices that utilize one or more charged particle beams, can be used for applying the invention. It is noted that such a prior art system has to be able to perform fast alteration of the focus point, and to be able to process the detections signals according to various embodiments of the invention. A fast focus alteration can be applied at various times during a single scan of a slice of a sample. Conveniently, fast scan changes should not exceed a rate of 1 cm/sec. Portion 10 includes many components. Some components are optional. The portion includes illumination optics and inspection optics. The illumination optics generate and direct a charged particle beam towards the sample. The focal point of the charged particle beam can be altered by various components of the illumination optics. The term “optics” includes components such as objective lenses, magnetic coils, polepieces, electrostatic lenses, apertures, scanners, and the like. These components affect various characteristics of the charged particle beam. The optics can also include the components such as power suppliers, current supply sources, components that control these components and the like. The illumination path includes a charged particle beam source 11. The source 11 usually includes an electron gun, a filament, a suppressor, an extractor and an anode. The charged particle beam source 11 is followed by a upper octupole 12, aperture alignment coils 13, beam defining aperture 14, blanker 15, differential vacuum aperture 16, an upper group of coils 17, a blanking aperture 19, a lower group of coils 20, a lower octupole 21 and a magnetic objective lens 22. The charged particle beam can also be diverted to a Farady cup 18. The inspection path includes the magnetic objective lens 22, the lower octupole 21, the lower group of coils 20, beam bending electrodes 24, an electrostatic quadrupole 26, an electrostatic focus lens 28, a grounded aperture 30, an electrostatic filter 32 and a detector 34. Various components of portion 10 receive high voltage supply from a high voltage module 40. Various components, and especially magnetic components receive current from a current supply module 42. The focal points of the charged particle beam can be changed (modulated) by various components of the illumination path such as the upper and lower group of coils 17 and 20, the upper and lower octupoles 12 and 21. Fine focal point changes are usually achieved by the octupoles. Typically, the inspection system also includes a stage, image processors, a vacuum chamber, optical components, a human machine interface and the like. The charged particle beam propagates through vacuum. FIG. 2 illustrates a first focal pattern 110 and a second focal pattern 120 according to an embodiment of the invention. FIG. 2 illustrates ideal focal patterns that ignore various inaccuracies in the sample or in the scanning process. It is noted that the distance between the sample and the optics of the charged particle beam can change during the scanning of the sample due to various results such as curvatures in the sample surface, stage inaccuracies and the like. Conveniently, a focal pattern that is applied during a scanning process is also responsive to the various sample and inspection system inaccuracies and deviations. Due to various reasons, including sample manufacturing inaccuracies, inspection system mechanical inaccuracies (such as stage curvature) the distance between the sample and the inspecting system optics changes. When using high-resolution inspection, even sub-micron height changes can affect the focus. Typically, in order to adjust the focus, a preliminary mapping of the sample (as being conveyed by the stage of the inspection system) takes place. Although this map reflects both sample and inspection system deviations, this map is referred to as a sample map. This preliminary mapping is relatively accurate and time consuming. A set of mapping locations of the sample is selected. In each mapping location a charged particle beam is directed towards the sample and is inspected while altering the focal point, in order to locate the optimal focal point. After the focal point is found, the focal point of the various mapping locations are processed (for example by extrapolation) in order to provide a map of focal changes. It is noted that various prior art methods for performing mapping can be applied, including fringe base methods and the like. Conveniently, one or more “general” focal patterns, such as focal patterns 110 and 120, are determined. These “general” focal patterns are adjusted according to the mapping of each sample, to provide a unique focal pattern that can be applied while a certain sample is scanned. Once such a mapping is achieved, the focal pattern that is applied during the focus correction sequence is responsive to the mapping and to the above mentioned focal patterns. FIG. 2 illustrates the change of focal point (represented by a control signal that controls the focal point of the system) while the charged particle beam is scanned along an imaginary Y axis. It is noted that during this scan, the sample is usually moved along an imaginary X axis. It is noted that more than a single control signal can be used in order to provide the desired focal pattern. Both focal patterns 110 and 120 are sloped lines that differ from each other by the optimal focal point. The optimal focal point is theoretically located at the crossing between a curve and the horizontal axis. FIG. 3 illustrates the relationship between focal grades associated with the first and second curves 110 and 120 of FIG. 1. The focal grade reflects deviations from an optimal focal point, assuming that a focal pattern such as focal pattern 110 and focal pattern 120 are applied. Curve 130 illustrates the focal grade achieved from applying the first focal pattern 110 and curve 140 illustrates the focal grade achieved from applying the second focal pattern. It is noted that the focal grade differs as a result of the known difference between the focal pattern and also as a result of the unknown focus difference between the scanning of the first and second area. This unknown focal difference has to be found. Conveniently, two focus grades are generated from each focal pattern. The focal grade is responsive to the square of the focal error and is symmetrical in relation to the optimal focal point. Accordingly, curve 130 and curve 140 have a parabolic shape. The horizontal displacement between the two parabolas is responsive to the shift between the first and second focal patterns and to the unknown focus difference between the scans. The horizontal displacement is measured and used to determine the focus correction signal. Assuming that: (a) the optimal focal point is located at point where these two parabolas cross each other and, (b) an optimal focal point of each curve is located at the parabola center (or minimum), then the optimal focal point can be found by: (i) finding the minimal point of one parabola and storing the corresponding height value (Z min1), (ii) determining the horizontal displacement between the parabolas (ΔZ), and (iii) either adding (from the minimum of curve 130) or subtracting (from the minimum of curve 140) half of the horizontal displacement to or from the minimal point respectively. Typical illumination path components introduce aberrations, thus the location of the focal point differs along the Y axis and along the X axis. In order to determine the proper focal points, the method generates two gradient images—one along the X axis and another along the Y axis. FIG. 4 illustrates a focal pattern 160 that is responsive to a mapping of a sample, according to an embodiment of the invention. As previously mentioned, focal patterns are adjusted according to the mapping of a sample. First focal pattern 160 is a superposition of a linear mapping curve 150 that represent a linear portion of the sample mapping and of first linear curve 130. The first focal pattern includes large deviations from the optimal focus. In order to prevent large gaps in the coverage of a scanned sample, the first focal pattern is relatively short and steep. Thus, only a small area of the sample is scanned out of focus. According to another embodiment of the invention, the focal pattern includes minor height changes. These minor changes do not prevent the acquisition of images from the sample, thus then can be implemented during the inspection phase, without forming gaps in the image. Conveniently, these changes can be applied over large areas of the sample, but this is not necessarily so. The inventors use a sinusoidal focal pattern that includes relatively small focus deviations. This sinusoidal pattern is added to a map of the sample. FIG. 5 illustrates a sinusoidal focal pattern 170 and a linear mapping pattern 180, according to an embodiment of the invention. The actual focal pattern 190 is a superposition of both patterns. FIG. 6 includes a timing diagram 200 which illustrates the timing of inspection periods and short focus correction periods according to an embodiment of the invention. For convenience of explanation, timing diagram 200 illustrates four inspection periods (IP1-IP4 211-214) and three focus correction periods (FC1-FC3 221-223), but the number of periods can change. It is also noted that the length of each period can differ from the other. Conveniently, the inspection periods are longer and even much longer than the focus correction periods. The inspection periods and the focus correction period are interlaced. Each focus correction period is timed between two inspection periods. The first, second and third inspection periods IP1-IP3 211-214 are followed by the first, second and third focus correction periods FC1-FC3 221-223 accordingly. IP1, FC1, IP2, FC2, IP3, FC3 and IP4 start at times T1, T2, T3, T4, T5, T6 and T7 respectively. IP4 ends at T8. It is assumed that at T1 mapping of the sample is completed. During the first inspection period IP1 211, the focus is altered according to the sample mapping and a first portion of the sample is imaged. The focus alterations can also be responsive to previous focus correction periods, for example of focus correction periods that were applied during previous scans of the sample, scans of other stripes of the sample and the like. During each focus correction period (FC1-FC3), the focus is changed according to a focal pattern that can be responsive to the mapping of the sample and also allows to correct focus. Conveniently, each focal pattern includes under-focused points as well as under-focused points. The focus during each of inspection periods IP2-IP4 is responsive to the mapping of the sample, but is also responsive to the results of the preceding focus correction period. Conveniently, before such an inspection period starts (or immediately after such a period begins), the focus is corrected in response to the results of the previous focus correction period. FIG. 7 is a flow chart illustrating a method 300 for focusing a charged particle beam, according to an embodiment of the invention. Method 300 starts by stage 310 of mapping an upper surface of the sample. Stage 310 is followed by stage 320 of altering a focal point of a charged particle beam according to a first focal pattern while scanning a first area of a sample and collecting a first set of detection signals. The first set of detection signals can form an image of and/or be representative of an image of the scanned first area. Conveniently, the image of the first area is denoted I1(i,j). Conveniently, the first focal pattern includes under-focused points and over-focused points. Stage 320 is followed by stage 330 of altering a focal point of a charged particle beam according to a second focal pattern while scanning a second area that is ideally identical to the first area and collecting a second set of detection signals. The second set of detection signals can form an image of and/or be representative of an image of the scanned second area. Conveniently, the image of the second area is denoted I2(i,j). According to an embodiment of the invention, the altering includes a mechanical translation. Conveniently, the alteration can include an alteration of a characteristic of an illumination path through which the charged particle beam propagates. Conveniently, the altering is responsive to an estimated distance between at least one element of a charged beam device and between the surface of the sample. Conveniently, stages 320 and 330 are repeated various times, during the imaging of the sample. It is noted that during each repetition a new image is acquired. Conveniently, stages 320 and 330 are also repeated such as to collect a third set of detection signals from a third area that is ideally identical to the first area; and wherein the processing further includes processing the third set of detection signals. Conveniently, method 300 also includes scanning a reference area that is ideally identical to the first area while maintaining a substantial constant focal point to collect a reference set of detection signals; and wherein the processing further includes processing the reference set of detection signals. Conveniently, the first area includes multiple non-continuous segments. Conveniently, the area includes multiple segments and the focal point is maintained substantially fixed in relation to a surface of the sample while scanning a single segment. According to various embodiments of the invention, the focal pattern can have many shapes. It can be continuous or non-continuous. Conveniently, the shape of the focal pattern is determined in response to the inspection system characteristics and especially to the response time of the focal changing elements. The inventors use ramp shaped focal patterns and sinusoidal shaped focal patterns but other shapes as well as combination of various shapes can be used. Conveniently, stages 320 and 330 are executed during an inspection session of the wafer. According an embodiment of the invention, the first focal pattern is applied during an inspection session of the sample. Conveniently, the first focal pattern is applied during focal correction sessions between inspection sessions of the sample. According to an embodiment of the invention, the first area includes a first group of sub-areas and wherein the second area includes a second group of sub-areas. Conveniently, the processing includes processing detection signals from each sub-area to provide a sub-area grade and determining the focal characteristic in response to the grades of each sub-area. Stage 330 is followed by stage 340 of processing the first and second set of detection signals to determine a focal characteristic; wherein the first focal pattern and the second focal pattern differ by the location of an optimal focal point. According to an embodiment of the invention, stage 340 includes estimating a focal change along a first axis (such as an imaginary Y axis) and along a second traverse axis (such as an imaginary X axis). Conveniently, the focal characteristic is determined in response to the focal change along a first axis and in response to a focal change along the second axis. Conveniently, stage 340 involves generating two gradient images of the first area and two gradient images of the second area. Conveniently, stage 340 includes: (i) generating a first axis gradient image of the first area; (ii) generating a second axis gradient image of the first area; (iii) calculating a focal grade of the first axis gradient image of the first area; and (iv) calculating a focal grade of the second axis gradient image of the first area. Conveniently, stage 340 includes: (i) generating a first axis gradient image of the second area; (ii) generating a second axis gradient image of the second area; (iii) calculating a focal grade of the first axis gradient image of the second area; (iv) calculating a focal grade of the second axis gradient image of the second area; (v) comparing between the focal grade of the first axis gradient image of the first area and between focal grade of the first axis gradient image of the second area; and (vi) comparing between the focal grade of the second axis gradient image of the first area and between focal grade of the second axis gradient image of the second area. Assuming that the gradient images are denoted Gx1, Gx2, Gy1 and Gy2, that the focus grades are calculated per line and are denoted FocusGradex1(line_j), FocusGradex2(line_j), FocusGradey1(line_j) and FocusGradey2(line_j) then the following mathematical terms represent the first stages of the mentioned above processes: G x1 ⁡ ( i , j ) = ϑ ⁢ ⁢ I 1 ⁡ ( i , j ) ϑ ⁢ ⁢ x , G y1 ⁡ ( i , j ) = ϑ ⁢ ⁢ I 1 ⁡ ( i , j ) ϑ ⁢ ⁢ y G x2 ⁡ ( i , j ) = ϑ ⁢ ⁢ I 2 ⁡ ( i , j ) ϑ ⁢ ⁢ x , G y2 ⁡ ( i , j ) = ϑ ⁢ ⁢ I 2 ⁡ ( i , j ) ϑ ⁢ ⁢ y FocusGrade x1 ⁡ ( line_j ) = ∑ j ⁢  G x1 ⁡ ( i , j )  2 FocusGrade y1 ⁡ ( line_j ) = ∑ j ⁢  G y1 ⁡ ( i , j )  2 FocusGrade x2 ⁡ ( line_j ) = ∑ j ⁢  G x2 ⁡ ( i , j )  2 FocusGrade y2 ⁡ ( line_j ) = ∑ j ⁢  G y2 ⁡ ( i , j )  2 The focus grade of a certain line is proportional to the focus grade at the best focus point and to the square of the height deviation from that. According to an embodiment of the invention, the method can be applied on a sample that includes multiple repetitive patterns (cells). A first focal pattern can be applied while scanning a first group of repetitive patterns (cells) and a second focal pattern can be applied while scanning a second group of repetitive patterns (cells). In such a case the previously stages can be applied, but according to another embodiment of the invention instead of selecting the best line in a image the method can select the best cell. The focus error can be calculated by comparing the location of the best cells. The present invention can be practiced by employing conventional tools, methodology and components. Accordingly, the details of such tools, component and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, such as shapes of test structures and materials that are electro-optically active, in order to provide a thorough understanding of the present invention. However, it should be recognized that the present invention might be practiced without resorting to the details specifically set forth. Only exemplary embodiments of the present invention and a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.
039502716	summary	BACKGROUND OF THE INVENTION I. Field of the Invention Superior nuclear shields may be constructed from gadolinium filled chloro-fluoro substituted ethylene polymers, particularly filled ethylene-chlorotrifluoroethylene or filled polychlorotrifluoroethylene. The fillers used in conjunction with these polymers comprise gadolinium compounds, preferably compounds such as gadolinium boride, gadolinium oxide, gadolinium aluminate and gadolinium aluminum borate. II. Brief Description of the Prior Art Nuclear shields which are intended to absorb neutrons are usually made from boron compounds such as elemental boron, boron oxide, boron carbide, etc. These compounds are usually refractory in nature, brittle and difficult or expensive to produce in precise or odd shapes. Recent attempts to use these boron compounds as fillers in plastics or glass have met with mixed results. In the case of glass artifacts, particularly borosilicate glass Raschig rings, the fragile nature of the glass as well as difficulty in processing tends to reduce any inherent advantages. The use of fluorine substituted polymers has been proposed since plastics are easier to process than glass; however, some of these fluorine substituted compounds, particularly polytetrafluoroethylene (PTFE), cannot be melt processed using conventional techniques and instead require special molding and extrusion methods consisting of formulating the granular plastic powder into the desired part under pressure and then sintering below the melt temperature to coalesce the particles. Moreover, the resulting fluorine-substituted polymeric compositions exhibit poorer properties when filled and degrade when exposed to radiation. Additionally, for many applications where the artifacts are to be exposed to high radiation dosages, it is necessary to employ a large amount, i.e., greater than 10% filler in the plastic materials. Such materials containing these large amounts of boron are extremely difficult to extrude and/or mold and cause significant wear on the processing equipment. Moreover, the conditions under which the neutron absorbers function must be considered. Since such artifacts, e.g. Raschig rings, are subjected to high amounts of degrading radiation and are often required to operate in acidic or other highly corrosive environments, the lifetime of most such fluorine substituted plastic or glass filled artifacts will be substantially reduced due to degrading of the glass or plastic and leaching of the filler. In addition to the problems caused by leaching of filler or plastic, many of the proposed plastics, such as polyvinylidine fluoride and polyvinyl chloride, absorb undue amounts of acid causing swelling and subsequent reduction in performance of the resulting product. Furthermore, in the case of glass Raschig rings, the relatively large amount of breakage, compounded by the leaching of filler material, results in a relatively short life for the ring. Subsequently, it is necessary to periodically dispose of large quantities of broken or otherwise unserviceable radioactive Raschig rings. There is also a need in the art for materials suitable for use in pipes, blow molded or roto-molded vessels, etc. to be used for transporting or containing radioactive material. The materials required for such applications would have to exhibit the same properties as previously described, i.e. they would have to possess high neutron absorbing properties, be easily processable and not subject to degradation in radioactive or acidic enviornments. Moreover, although many applications deal with only thermal neutrons, i.e. neutrons which are of relatively low energy such as are given off as a consequence of natural radioactive decay, there are an increasing number of cases, such as in breeder reactors or nuclear weapons, where it may be desirable to eliminate certain atoms, particularly hydrogen, from the plastic polymer in order to prevent their participation in a nuclear reaction. There is thus a need for easily processable, corrosion resistant effective nuclear shielding materials which can be highly filled without brittleness or loss in mechanical properties and which will maintain their superior properties even after exposure to intense radiation and/or highly acidic environments. SUMMARY OF THE INVENTION This invention discloses novel melt processable compositions having a shielding effect against neutron radiation comprising a chloro-fluoro substituted ethylene polymer having distrubuted therethrough and intimately admixed therewith from about 1 to about 75% by weight of a gadolinium compound. Accordingly, we have found that such compositions possessing a unique combination of properties heretofore unattainable in compositions suitable for use in nuclear shielding applications, may be prepared by incorporating up to about 75% by weight gadolinium compounds in chloro-fluoro substituted ethylene polymer compositions, particularly in ethylenechlorotrifluoroethylene (E-CTFE) polymers and polychlorotrifluoroethylene PCTFE polymers. The resulting compositions of matter are easily processable, chemically inert to acidic environment, mechanically strong and shock resistant. An additional feature of these novel compositions is that not only are the shielding properties of these polymers highly resistant to the degrative effects of radiation, but that the radiation induces cross-linking and thus enhances the mechanical properties of the polymers. This invention also discloses shaped articles of manufacture having a shielding effect against neutron radiation comprising a melt-processed chloro-fluoro substituted ethylene polymer having distributed therethrough and intimately admixed therewith from about 1 to about 75% by weight of a gadolinium compound. The articles are useful in a large number of applications such as for Raschig rings or similar packing devices for criticality control; pipes, blow-molded or roto-molded containers for plutonium or uranium solutions; as intricate molded parts for reactors or other nuclear devices; or as lightweight portable neutron absorbing structures or shields, etc. The compositions of the present invention can also be spun into filaments or a melt thereof coated onto filaments and loomed into fabric for neutron absorbing clothing or the like. These materials, it is thus seen, may be tailored in accordance with the desired end-use. For example, in cases where they will be exposed to fast moving neutrons, the gadolinium filled E-CTFE composition provides a high hydrogen content for attenuating these neutrons. However, in cases such as in breeder reactors, wherein the presence of hydrogen is detrimental, the gadolinium filled PCTFE composition is appropriate. DESCRIPTION OF THE PREFERRED EMBODIMENT The thermoplastic chloro-fluoro substituted ethylene polymers containing the gadolinium compounds which may be used in these applications include particularly ethylene chlorofluoroethylene and polychlorotrifluoroethylene and blends containing more than 50% of such polymers. Polychlorotrifluoroethylene (PCTFE) polymer is flexible, moldable, and radiation resistant. It is non-flammable in air, has good abrasion resistance and good mechanical properties. Additionally, the polymer is chemically resistant to organic solvents and oxidizing mineral acids. Moreover, its resistance to permeability of water vapor and other molecules is better than other known polymers. The preferred polymer ethylene chlorotrifluoroethylene, is useful wherever high concentrations of hydrogen are acceptable. The E-CTFE polymer possesses the mechanical strength, chemical resistance, and non-flammability of the PCTFE polymer. In addition to these characteristics, it has been found that the E-CTFE composition is easily melt processed and moreover the mechanical properties thereof may be improved by cross-linking upon exposure to radiation, thus making this polymer a composition valuable for nuclear shielding operations. The particular gadolinium compound used as filler in the novel nuclear shielding compositions of the present invention to some extent may depend upon the polymer which is to be filled and the environment in which the shield is to be used. In the invention, any of a variety of available gadolinium compounds may be used. Preferred gadolinium compounds include gadolinium boride, gadolinium oxide, gadolinium aluminate, and gadolinium aluminum borate. These compounds exhibit excellent nuclear absorption as indicated in Table I which lists the nuclear absorption per gram relative to boron. Table I ______________________________________ Compound Nuclear Absorption/gm. ______________________________________ Boron 1.0 Gadolinium boride 3.26 Gadolinium oxide 3.63 Gadolinium aluminate 2.71 Gadolinium aluminum borate 1.47 ______________________________________ It is obvious from Table I that great weight-cost savings or increased shielding can be obtained by using the gadolinium compounds. Moreover, since gadolinium has a much higher density than boron, the neutron absorption per unit volume will be much higher than if boron compounds were used. The amount of the gadolinium compound employed is dependent upon the particular gadolinium compound, the particular polymer, and the amount of radiation to which it will be subjected. In general, amounts of about 1 to 75 weight % preferably about 7.5 to about 60% are employed. Specifically, in the case of E-CTFE polymer filled with gadolinium oxide, amounts of 7.5 to about 25% of the gadolinium filler are preferred. For similar gadolinium oxide filled PCTFE polymer, the preferred amount of filler ranges from about 25 to about 60%. The particular size of the gadolinium fillers used to produce the novel shielding composition should preferably be within the range of about 0.1.mu. to 70.mu., preferably from about 3.mu. to about 40.mu.. An additional advantage to the use of these gadolinium filled chloro-fluoro substituted ethylene polymers in nuclear shielding artifacts is that not only does the neutron absorbing capacity of the resulting composition increase, but the flexural strength and modulus also increase as the amount of filler is increased. Moreover, due to the unique properties of the chlorofluoro compounds, it is possible to load these compositions to an extremely high degree, i.e. in some cases up to about 45% by volume, and still be able to process the composition in conventional extrusion or injection molding equipment. The gadolinium compounds may be incorporated into the chloro-fluoro substituted ethylene compositions using any conventional mechanical blending techniques. The resulting filled compositions can be easily fabricated into the desired nuclear shielding devices. By way of illustration, the filled polymer could be extruded into tubing and cut and shaped into Raschig rings. Similarly, the filled composition could be extruded to form piping. Alternatively, the inner or outer surfaces of metal pipes or tubes could be readily coated with the molten filled composition which upon quenching would provide superior radiation shielding. The filled composition could also be blow-molded or rotomolded to produce containers or vessels for radioactive materials or could be compressed and injection molded into intricate parts for reactors or other nuclear devices. Additionally, the filled composition could be melt processed to produce fibers and then fabricated into protective clothing. The PCTFE polymers used herein are commercially known and available materials which may be prepared by a variety of methods such as by the polymerization of chlorotrifluoroethylene in the presence of an initiator. The ethylene chlorotrifluoroethylene copolymers are also known, commercially available materials. These E-CTFE thermoplastic polymers are normally solid, contain between 40 and 60 mol percent, preferably 45 to 55 mol percent, ethylene units and have a melting point above about 200.degree.C. preferably between about 220.degree. and 265.degree.C. These copolymers may be prepared by processes well known to those skilled in the art, as described, for example, in Hanford U.S. Pat. Nos. 3,371,076 and 3,501,446 in Nucleonics, Sept., 1964, pp. 72-74 and in British Pat. No. 949,422. Moreover, it has been found that these E-CTFE copolymer systems may be stabilized and rendered melt processable by the addition of anti-oxidants which function to prevent rapid increase in viscosity. It is also desirable to add 0.1 to 30% of an acid scavenger which acts to neutralize any acidic gases which may be liberated during radiation or other processing operations and which cause odor emission and bubble formation. Useful acid scavengers include the oxides of any metal in Group II of the Periodic Table. Depending upon the desired application, it may also be desirable to add 0.1 to 5% of a radiation cross-linking promoter triallylisocyonate, triallycyanurate, triallylphosphate, diallylfumatates, diallyisophthalate, diallylterephthalate, and the like. According to the method of the present invention, these and any other additives can be added separately or be mixed prior to addition and may be added in solution or be dry blended with the chloro-fluoro substituted ethylene copolymer and gadolinium compound. Liquid or soluble additives containing no hydroxyl groups, such as ketones and ethers, as well as with non-polar aliphatic or aromatic solvents, such as hexane, heptane or toluene, and be sprayed onto the polymer if in finely divided form in conventional tumbling or blending devices. For molding operations, such as extrusion or injection molding, the blended mixture may be passed through an extruder and the extruded rod chopped into pellets of desired size. Alternatively, the additives and gadolinium compounds may be admixed with the copolymer by tumbling pellets of the copolymer, adding liquid additives, tumbling again to distribute the liquid additives, then adding the dry additives and gadolinium compound continuing tumbling to distribute the dry components evenly over the surface of the pellets, and then extruding the resultant mixture to intimately blend the reactants. Alternatively, the PCTFE or E-CTFE copolymer system may be prepared and the gadolinium compounds incorporated under pressure thereto.
043366147	summary	BACKGROUND OF THE INVENTION This invention relates to tube-in-shell heat exchangers and is directed towards intermediate heat exchangers for use in liquid metal cooled fast breeder nuclear reactor constructions. A tube-in-shell heat exchanger comprises a closed shell housing a bundle of heat exchange tubes which pass through the shell by way of a transverse tube sheet or sheets. In use a first fluid flows through the shell in heat exchange with a second fluid flowing through the tubes. In one kind of tube-in-shell heat exchanger used as an intermediate heat exchanger in a liquid metal cooled fast breeder nuclear reactor constructions, the tubes being elongate and extending between opposed tubes sheets incorporate expansion bends and therefore are subject to severe vibration due to fluid flow through the shell. One expedient to prevent vibrational movement is to support the tubes transversely by a series of longitudinally spaced grids of which successive grids radially displace the tubes from their nominal in-line positions in opposed directions in order to strain the tubes. However, tube support provided by this expedient can be too rigid, and the differential movement of the tubes relative to the other parts of the structure thereby induces severe stress. SUMMARY OF THE INVENTION According to the invention in a tube-in-shell heat exchanger wherein the heat exchange tubes are arranged in a bundle and braced transversely by a longitudinal series of spaced grids, the grids are resiliently supported from a central spine of the tube bundle. The resilient supports provide flexibility in the mountings of the tube bundle on the central spine so that groups of heat exchange tubes can be longitudinally displaced relative to the spine and to adjoining groups of tubes to accommodate differential linear thermal expansion. In a preferred construction of heat exchanger the spine has an annular series of radially outwardly extending forked brackets and each grid has an annular series of radially inwardly extending forked brackets, each bracket of one annular series being interposed between two neighbouring brackets of the other annular series, and there is a resilient annular member disposed to interengage each forked bracket. In a liquid metal cooled fast breeder nuclear reactor construction of the kind comprising a nuclear fuel assembly submerged in a pool of coolant in a primary vessel, and a tube-in-shell intermediate heat exchanger according to the invention, the intermediate heat exchanger comprises a bundle of heat exchange tubes having a central spine extending longitudinally through the shell and a series of longitudinally spaced transverse grids resiliently mounted on the central spine within the shell and disposed to provide transverse support for bracing the tubes apart, successive grids displacing the tubes from their nominal in-line positions in opposed directions, resilient mountings for the grids on the central spine each comprising an annular series of brackets rigidly secured to the spine, the brackets each having a pair of radially outwardly extending forked arms, a complementary annular series of forked brackets having radially inwardly extending arms rigidly secured to a grid, each bracket of one series being interposed between two neighbouring brackets of the complementary series, and a resilient annular member disposed transversely to the spine in engagement with the forked arms of both complementary series of brackets.
	summary
	description	This application is a divisional of U.S. patent application Ser. No. 13/832,443, filed Mar. 15, 2013, now U.S. Pat. No. 10,102,932, which claims the benefit of U.S. Provisional Patent Application No. 61/625,200, filed Apr. 17, 2012, which applications are hereby incorporated by reference in their entireties. The following relates to the nuclear reactor arts, nuclear power generation arts, nuclear reactor control arts, nuclear reactor electrical power distribution arts, and related arts. In nuclear reactor designs of the integral pressurized water reactor (integral PWR) type, a nuclear reactor core is immersed in primary coolant water at or near the bottom of a pressure vessel. In a typical design, the primary coolant is maintained in a subcooled liquid phase in a cylindrical pressure vessel that is mounted generally upright (that is, with its cylinder axis oriented vertically). A hollow cylindrical central riser is disposed concentrically inside the pressure vessel. Primary coolant flows upward through the reactor core where it is heated, rises through the central riser, discharges from the top of the central riser, and reverses direction to flow downward back toward the reactor core through a downcomer annulus. The nuclear reactor core is built up from multiple fuel assemblies. Each fuel assembly includes a number of fuel rods. Control rods comprising neutron absorbing material are inserted into and lifted out of the reactor core to control core reactivity. The control rods are supported and guided through control rod guide tubes inside the reactor core and by guide tube frames outside the core. In the integral PWR design, at least one steam generator is located inside the pressure vessel (i.e. “integral with” the reactor), typically in the downcomer annulus, and the pressurizer is located at the top of the pressure vessel, with a steam space as the top most point of the reactor. Alternatively an external pressurizer can be used to control reactor pressure. A set of control rods is arranged as a control rod assembly that includes the control rods connected at their upper ends with a yoke or spider, and a connecting rod extending upward from the spider. The control rod assembly is raised or lowered to move the control rods out of or into the reactor core using a control rod drive mechanism (CRDM). In a typical CRDM configuration, an electrically driven motor or magnetic assembly selectively rotates a roller nut assembly or other threaded element that engages a lead screw that in turn connects with the connecting rod of the control rod assembly. The control rods are typically also configured to “SCRAM”, by which it is meant that the control rods can be quickly released in an emergency so as to fall into the reactor core under force of gravity and quickly terminate the power-generating nuclear chain reaction. Toward this end, the roller nut assembly may be configured to be separable so as to release the control rod assembly and lead screw which then fall toward the core as a translating unit. In another configuration, the connection of the lead screw with the connecting rod is latched and SCRAM is performed by releasing the latch so that the control rod assembly falls toward the core while the lead screw remains engaged with the roller nut. See Stambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”, U.S. Pub. No. 2010/0316177 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety; and DeSantis, “Control Rod Drive Mechanism for Nuclear Reactor”, U.S. Pub. No. 2011/0222640 A1 published Sep. 15, 2011 which is incorporated herein by reference in its entirety. The CRDMs are complex precision devices which typically include an electric motor requiring electrical power, and may also require hydraulic, pneumatic, or another source of power to overcome the passive SCRAM release mechanism (e.g., to hold the separable roller nut in the engaged position, or to maintain latching of the connecting rod latch) unless this is also electrically operated (e.g., an electromagnetic clamp that releases upon removal of electrical power). In existing commercial nuclear power reactors, the CRDMs are located externally, i.e. outside of the pressure vessel, typically above the vessel in PWR designs, or below the reactor in boiling water reactor (BWR) designs. An external CRDM has the advantage of accessibility for maintenance and can be powered through external electrical and hydraulic connectors. However, the requisite mechanical penetrations into the pressure vessel present safety concerns. Additionally, in compact integral PWR designs, especially those employing an integral pressurizer, it may be difficult to configure the reactor design to allow for overhead external placement of the CRDMs. Accordingly, internal CRDM designs have been developed. See U.S. Pub. No. 2010/0316177 A1 and U.S. Pub. No. 2011/0222640 A1 which are both incorporated herein by reference in their entireties. However, a difficulty with this approach is that it entails extensive electrical (and possibly hydraulic and/or pneumatic) cabling inside the reactor pressure vessel. For example, if there are sixty nine CRDM units with three electrical cables per CRDM unit (e.g., power, position indicator, and ground), then 207 electrical cables are required for the sixty nine units. The locations of the CRDM units are substantially constrained, e.g. all CRDM units are above the reactor core in the case of a PWR, and at a distance from the core effective to allow the CRDM units to move the control rod assemblies into or out of the core. An approach for relaxing the positioning constraint is to stagger neighboring CRDM units vertically, as disclosed in U.S. Pub. No. 2011/0222640 A1. However, the space for the electrical cabling is still tight. Electrical cabling in a nuclear reactor is typically in the form of mineral insulated (MI) cables, which have limited bend radius specifications. Cabling operations such as splicing or joining cables is complex for MI cables, because the mineral insulation can be damaged by water exposure. The SCRAM function is safety-related, and so nuclear safety regulations may require shutdown of the reactor if even one CRDM unit becomes non-operative, making reliability of this extensive MI cabling of especial importance. Disclosed herein are improvements that provide various benefits that will become apparent to the skilled artisan upon reading the following. In one illustrative embodiment, a nuclear reactor comprises a pressure vessel containing primary coolant water and further containing: a nuclear reactor core comprising fissile material; a mounting plate; a set of electric devices mounted on the mounting plate wherein the set of electric devices is one of (1) a set of control rod drive mechanism (CRDM) units and (2) a set of reactor coolant pumps (RCPs); a distribution plate; and a plurality of cable modules mounted in receptacles of the distribution plate. Each cable module includes mineral insulated (MI) cables connected with one or more of the electric devices, the cable module including its MI cables being removable as a unit from the receptacle of the distribution plate. In another illustrative embodiment, a nuclear reactor comprises a pressure vessel containing primary coolant water and further containing: a nuclear reactor core comprising fissile material; a mounting plate; a distribution plate mounted on the mounting plate; and a set of electric devices mounted on the distribution plate. The distribution plate includes mineral insulated (MI) cables disposed in or on the distribution plate and connected with the set of electric devices. The set of electric devices is one of (1) a set of control rod drive mechanism (CRDM) units and (2) a set of reactor coolant pumps (RCPs). The distribution plate is incapable of supporting the weight of the set of electric devices, the distribution plate transferring weight of the set of electric devices to the mounting plate which supports the combined weight of both the set of electric devices and the distribution plate. The distribution plate in some embodiments comprises a plate having a plurality of grooves, and cable modules disposed in the grooves of the plate, each cable module including a portion of the MI cables disposed on or in the distribution plate, each cable module including its portion of the MI cables being removable from the plate as a unit. In another illustrative embodiment, an electrical distribution plate comprises a plate having a plurality of receptacles, and cable modules disposed in the receptacles of the plate. Each cable module includes mineral insulated (MI) cables, and each cable module including its MI cables is removable from the plate as a unit. Each cable module when mounted in its receptacle of the plate defines a conduit or raceway through which its MI cables run. In some embodiments, each cable module includes electrical connectors that are externally accessible when the cable module is mounted in its receptacle of the plate. In another illustrative embodiment, a nuclear reactor comprises: a pressure vessel; a nuclear reactor core comprising fissile material disposed in the pressure vessel; an electrical distribution plate as set forth in the immediately preceding paragraph disposed in the pressure vessel; and a set of electrical devices electrically connected with the MI cables of the cable modules of the electrical distribution plate. In some embodiments the set of electrical devices is a set of control rod drive mechanism (CRDM) units. FIG. 1 illustrates an integral pressurized water reactor (integral PWR) generally designated by the numeral 10. A reactor vessel 11 is generally cylindrical and contains primary coolant water, a reactor core 1, one or more steam generators 2, and a pressurizer 3. A central riser 4 separates a hot leg of the primary coolant circuit flowing upward through the central riser 4 from a cold leg of the primary coolant circuit flowing downward through a downcomer annulus defined between the central riser 4 and the pressure vessel 11. The one or more steam generators are suitably disposed in the downcomer annulus. Although a pressurized water reactor (PWR) is depicted, a boiling water reactor (BWR) or other type of nuclear reactor is also contemplated. The reactor 10 is an illustrative example, and numerous variants are contemplated, such as replacing the pressurizer 3 with an external pressurizer, employing external steam generators, and so forth. Moreover, while the disclosed rapid installation and servicing techniques are described with reference to illustrative internal CRDM units, these techniques are readily adapted for use with other internal nuclear reactor components such as internal reactor coolant pumps. In the illustrative PWR, above the core 1 are the reactor upper internals 12 of integral PWR 10, shown in inset. In the illustrative PWR 10, the upper internals 12 are supported laterally by a mid-flange 14, which in the illustrative embodiment also supports internal canned reactor coolant pumps (RCPs) 16. More generally, the RCPs may be external pumps or have other configurations (or, RCPs may be omitted entirely and the reactor may rely upon natural circulation of primary coolant), and the upper internals may be supported otherwise than by the illustrative mid flange 14. The upper internals include control rod guide frames 18 to guide the control rod assemblies for controlling the nuclear chain reaction in the core 1. Control rod drive mechanisms (CRDMs) 20 raise and lower the control rods to control the reactor. In accordance with one embodiment, a CRDM distribution plate 22 supports the CRDMs and provides power and/or hydraulics to the CRDMs. The CRDM distribution plate may be combined with or include separate “mid-hanger plate.” A riser transition 24 connects the lower end of the central riser 4 with a core shroud or the like to separate the hot and cold legs of the primary coolant circuit in the lower vessel region. Control rods are withdrawn from the core 1 by the CRDMs 20 to provide enough positive reactivity to achieve criticality. Control rod guide tubes passing through the reactor core 1 and the guide frames 18 above the core provide space for the rods and interconnecting spider to be raised upward away from the reactor core. The CRDMs 20 include electric motors which move the rods via a suitable mechanism such as a nut/screw mechanism, rack-and-pinion mechanism, or so forth. In illustrative examples, a nut-screw mechanism is assumed. For any motor driven mechanism, electrical cables are needed to power the motor, and electric cables may also be needed for auxiliary electrical components such as rod position indicators and/or rod bottom sensors. In some designs, the force to latch the connecting rod to the lead screw, or to maintain engagement of the separable roller nut, is hydraulic, necessitating a hydraulic connection to the CRDM. Alternatively, electric mechanisms can be employed for these purposes, thus calling for additional electric cabling. To ensure passive safety, a positive force is usually required to prevent SCRAM, such that removal of the positive force initiates a SCRAM. The illustrative CRDM 20 is an internal CRDM, that is, is located inside the reactor vessel, and so the electrical connections to the CRDMs 20 are difficult to access. The distribution plate 22 provides a structural support for this electrical cabling. Servicing of a CRDM during a plant shutdown should preferably be rapid in order to minimize the length of the shutdown. To facilitate replacing a CRDM, the CRDM assembly (possibly including a standoff) is connected to the distribution plate 22 to provide electrical power and hydraulics to the CRDM 20 via connectors that require no action to effectuate the connection other than placement of the standoff assembly onto the distribution plate 22. After placement, the CRDM assembly is secured to the distribution plate by bolts or other fasteners. Additionally or alternatively, it is contemplated to rely upon the weight of the CRDM to hold the assembly in place, or to use welds to secure the assembly. FIG. 2 illustrates one embodiment of a distribution plate 22 which is a single plate that contains the electrical and hydraulic lines and also is strong enough to provide support to the CRDMs and upper internals without reinforcement. The motor/roller nut assembly of the CRDM is generally located in the middle of the lead screw's travel path. When the control rod is fully inserted into the core, the roller nut is holding the top of the lead screw, and, when the control rod is at the top of the core, the roller nut is holding the bottom of the lead screw and most of the length of the lead screw extends upward above the motor/roller nut assembly. Hence the distribution plate 22 that supports the CRDM is positioned “below” the CRDM units and a relatively short distance above the reactor core. FIG. 2 shows the distribution plate 22 with a single standoff assembly 24 mounted for illustration, though it should be understood that all openings 26 would have a standoff assembly (and accompanying CRDM) mounted in place during operation of the reactor. Each opening 26 allows a lead screw of a control rod to pass through and the periphery of the opening provides a connection site for a standoff assembly that supports the CRDM. The lead screw passes down through the CRDM, through the standoff assembly, and then through the opening 26. The distribution plate 22 has, either internally embedded within the plate or mounted to it, electrical power lines (e.g., electrical conductors) and hydraulic power lines (if needed) to supply the CRDM with power and hydraulics. The illustrative openings 26 are asymmetric or keyed so that the CRDM can only be mounted in one orientation. As illustrated, there are 69 openings arranged in nine rows to form a grid, but more or fewer could be used depending on the number of connecting rod/CRDM units in the reactor. The distribution plate 22 is circular to fit the interior of the reactor, with openings 28 to allow for flow through the plate. Flow may also be designed through the CRDMs 20, i.e. through the flow passages 26 around or through components of the CRDMs 20. In some designs, not all openings 26 may have CRDMs mounted to them. Each internal control rod drive mechanism (CRDM) unit 20 is powered by electrical power and/or hydraulic power. In the design of FIG. 1, the CRDM units are packed closely together, which creates a high density of electrical and/or hydraulic cabling. The distribution plate 22 facilitates efficient deployment of this extensive cabling. However, it is recognized herein that such rapid deployment preferably should be augmented by an efficient mechanism for repair or replacement of the MI cabling and/or hydraulic cabling. Although MI cabling is robust, which is why it is typically selected for use in a nuclear reactor environment, it is still susceptible to damage due to the challenging reactor environment that exposes the cabling to high temperature, high pressure and pressure cycling, radioactivity, and possibly caustic chemicals (e.g., soluble boron-based chemical shim). In the event of a failure of a cable of the distribution plate 22, the failed component would need to be accessed and repaired in-place (which is difficult due to the special handling required for MI cables in order to avoid degradation due to water exposure) or the entire distribution plate 22 would need to be removed (which would involve removal of all 69 CRDM units 20 in the case of the illustrative embodiment of FIGS. 1 and 2). With reference to FIGS. 3-11, an improved distribution plate design is disclosed, which is constructed as a multi-component assembly. A power distribution plate (PDP) 40 shown in FIG. 3 provides the structural frame for power distribution to the CRDMs 20. The illustrative embodiment is a two-plate design in which the PDP 40 sits on top of a support plate, for example a mid-hanger plate 50 shown in FIG. 4) and transfers the weight of the CRDMs 20 to the support plate 50. In this two-plate design, the PDP 40 of FIG. 3 is not strong enough to support the weight of the CRDMs and instead transfers the load to the support plate 50 shown in FIG. 4, which carries the weight of both the CRDMs 20 and the PDP 40 and its installed cable modules (see FIGS. 7-10). The two-plate design advantageously facilitates fabrication of the PDP 40 with its relatively intricate features using machining. In one embodiment, the PDP 40 is machined from plate stock or a forging of 304L, although other materials and/or manufacturing methods are contemplated. In a variant two-plate design (not shown), the power distribution plate is contemplated to be mounted underneath the support plate, in which case the power distribution plate would not perform a load transfer function respective to the CRDMs. As yet another contemplated variant, in a single-plate design (not shown) the PDP also provides structural support for the CRDMs, in which case the PDP would be a substantially thicker plate, formed for example by casting and/or forging. The PDP 40 of FIG. 3 is shown without installed cable modules, so as to show receptacles 42 into which the power cable modules 60 (FIGS. 7 and 8) and sensor cable modules 70 (FIGS. 9 and 10, e.g. cables for sensors such as position indicators and rod bottom, i.e. PI, indicators) are inserted. The receptacles 42 are generally formed as grooves so that the cable modules 60, 70 of relatively narrow aspect-ratio can deliver cabling to the interior of the PDP 40. The cable modules 60, 70 route the electrical cables. Hydraulic lines 78 are mounted to the PDP 40 (see FIG. 11), although it is alternatively contemplated to include the hydraulic lines in the modules as well. FIG. 5 shows the PDP 40 with the cable modules 60, 70 installed, while FIG. 6 shows an enlarged portion of the PDP 40 with the cable modules 60, 70 installed, and with the footprints of four CRDM standoffs indicated by four dashed squares. In FIG. 5, power MI cables 61 of the power cable modules 60 and signal MI cables 71 of the signal cable modules 70 are diagrammatically shown. (Note that FIG. 5 is diagrammatic in that it shows the MI cables 61, 71 which are actually mostly or completely occluded by the tops of the installed modules 60, 70; compare with FIGS. 7-10). The MI cables of each module run from a pigtail, input connector, or other electrical input located (when the module is installed on the PDP 40) at the periphery of the PDP 40 and run to connectors arranged to connect with the CRDMs 20. External power input cables run from electrical feedthroughs of the pressure vessel 11 to the pigtails or other peripheral electrical inputs of the cable module 60, 70. As seen in FIG. 6, the CRDMs 20 are mounted overlapping the cable modules, receiving power, hydraulics, and providing signal cable connections via the cable modules 60, 70. It will be noted that the power cable modules 60 and the sensor cable modules 70 alternate across the PDP 40, and each CRDM standoff is arranged to overlap a portion of one power cable module 60 and a portion of one sensor cable module 70 (see FIG. 6) in order to connect with both power lines and signal lines. With reference back to FIG. 3, the PDP 40 has an opening (four of which are labeled 46 in FIG. 3) for each CRDM, which allows the lead screw, connecting rod, or other connecting element to pass through to the control rods (or to the spider or yoke holding the control rods). In the illustrative embodiment shown, there are 69 such openings for the 69 CRDMs 20. These openings 46 of the PDP 40 are aligned with openings 54 through the support plate 50 to allow the lead screw, connecting rod, or other connecting element to pass through both the PDP 40 (via openings 46) and the support plate 50 (via openings 54). Attachment points 52 (see FIG. 4) connect the mid-hanger support plate 50 to the upper internals 12. The PDP 40 of FIG. 3 also has flow slots (four of which are labeled 44) to reduce head loss due to the PDP (that is, to reduce pressure drop over the PDP 40). Aligned flow holes may be provided in the support plate 50 as well, but are not shown. With continuing reference to FIG. 6 and with further reference to FIGS. 7 and 8, the MI cables 61 of the power cable module 60 run from the peripheral pigtail, input connector, or other electrical input at an input station 67 to one or more connection blocks 69 of the cable module 60. At each connection block 69, one or (typically) more of the MI cables terminate at electric power connections 64 that feed one of the CRDM units. The illustrative power cable module 60 has two connection blocks 69 and six MI cables 61: three of the cables terminate at the connection block 69 that is more proximate to the input station 67, while the remaining three MI cables continue on and terminate at the connection block 69 that is more distal from the input station 67. Other configurations are possible—for example, the uppermost and lowermost power cable modules 60 of the distribution plate of FIG. 5 has a different configuration since those power cable modules are roughly parallel with the periphery of the PDP 40: those power cable blocks have two outer stations with both inputs and CRDM outputs and a middle station that has only CRDM outputs. With continuing reference to FIG. 6 and with further reference to FIGS. 9 and 10, a signal cable module 70 is shown having a similar configuration to the power module 60 of FIGS. 7 and 8. The signal cable module 70 of FIGS. 9 and 10 again includes an end input block 77 and two connection blocks 79, one in the middle and the other at the opposite end from the input block. As with the power cable modules, various configurations are possible for the signal cable modules: for example, in the distribution plate of FIG. 5 the upper rightmost signal cable module 70 has only an input block and a single connection block. With particular reference to FIG. 11, in the embodiment shown, hydraulic lines 78 run in the receptacles/grooves 42 of the PDP 40 that receive the power cable modules 60, and are overlaid by the installed power cable modules 60. (Note that FIG. 11 is diagrammatic in that it shows the hydraulic lines 78 which are actually mostly or completely occluded by the overlaid installed power cable modules 60). The power cable modules 60 also have openings 65 (labeled in FIGS. 7 and 8) through which hydraulic connections that connect with the hydraulic lines 78 are accessed. This arrangement of power and signal cable modules 60, 70 allows the disclosed distribution plate to be more modular during construction and servicing. The power cable modules 60 (shown in FIGS. 7 and 8) allow the removal of a failed MI cable or electrical connector (along with those neighboring MI cables and connectors that are part of the same power cable module) while removing only a few CRDMs in the neighborhood of the failed power MI cable. Similar considerations apply to a failed signal MI cable or connector. When the PDP 40 assembly is broken down, all of the MI cables and electrical connectors come out with the cable modules 60, 70, leaving the hydraulic lines 78 and their connectors behind. This exposes the hydraulics to allow for service within the PDP. If only one hydraulic line or connector needs servicing, then only the power cable module overlying that hydraulic line needs to be removed. These features allow for modularity and serviceability of the distribution plate, simplifying manufacturing and servicing, reducing outage times. The PDP 40 with its installed cable modules 60, 70 is the interface to the CRDMs 20, and supports or houses all electrical cabling and hydraulics, and provides all connector receptacles. This allows a CRDM 20 to be removed and replaced relatively routinely. The interface points could be at any location along the length of the CRDM 20, but placing the interface point (the point at which the CRDM is broken from the upper internals) at the bottom of the CRDM allows the PDP to have a relatively flat face which simplifies installation and removal of the CRDMs. Optionally, a CRDM standoff connects the CRDM and the power distribution plate 40; alternatively, the CRDM can connect directly to the plate. Enclosing the electrical cabling and hydraulic lines in the PDP 40, as in the illustrative embodiment, provides protection from flow induced vibrations (FIV). It also provides a direct load transfer of the weight of the CRDMs 20 to the mid hanger plate 50 (see FIG. 4). The mid hanger plate 50 also provides structural support for the PDP 40. In other embodiments, the PDP is of sufficient thickness to structurally support the CRDMs directly. In other words, the PDP and the mid-hanger plate are integrated together in these embodiments. In yet other embodiments, the PDP is not associated with the CRDM structural support at all, and provides only power distribution functionality. This is the case, for example, if the PDP is located below the mid-hanger plate, or if the CRDM units are supported from above (i.e. suspended from an upper hanger plate) rather than bottom-supported. As yet another variant, the PDP may be integrated with or connected with an upper hanger plate located above the CRDMs (and the PDP may or may not bear the suspension load of the CRDMs in such embodiments). The electrical connection of the CRDM 20 to the PDP 40 (with its installed cable modules 60, 70) can be by various techniques. In some embodiments, conventional MI cable junctions and hydraulic connections are employed. In such embodiments, the servicing entails making/breaking MI cable junctions at the reactor, which can be labor-intensive and raises the potential for detrimental water ingress to the mineral insulation of the MI cables. In an alternative approach, “quick connect” connections may be employed, in which the MI cables of the CRDM terminate in male plugs that connect with mating female receptacles of the cable modules 60, 70 (or vice versa), with the weight of the CRDM 20 being sufficient (optionally along with suitable fasteners) to ensure an electrically conductive connection between the male plugs and female mating receptacles. Similarly, “quick connect” hydraulic connections may be employed, in which the hydraulic lines of the CRDM terminate in male nozzles that connect with mating female receptacles of the hydraulic lines 78 (or vice versa), with the weight of the CRDM 20 being sufficient (optionally along with suitable fasteners) to form a (possibly leaky) hydraulic connection. (The working fluid is assumed to be purified primary coolant water, for example from a reactor coolant inventory and purification system, RCIPS). Such “plug-and-play” connection designs are further described in U.S. Ser. No. 13/405,405 filed Feb. 27, 2012 entitled “Control Rod Drive Mechanism (CRDM) Mounting System For Pressurized Water Reactors”, first named inventor Scott J. Shargots, which is incorporated herein by reference in its entirety. When plug-and-play connections are employed, in-service replacement of a failed CRDM is further simplified. The CRDM is pulled by removing the hold-down bolts and then lifted from its position. The plug-and-play connectors easily break between the CRDM and the power distribution plate. A new CRDM is then lowered into the vacated position. The connectors again function to connect the new CRDM to the power source and hydraulic supply of the upper internals. Another advantage to the CRDM plug and play method involves the manufacturing flexibility, since the male plugs and female receptacles can be installed at the factory where suitably dry conditions can be maintained to avoid water ingress into the mineral insulation. With returning reference to FIG. 6, an overhead view is shown of a portion of the PDP 40 with power and signal cable modules 60, 62 installed. The power cable module 60 has electrical power connections 64 and openings 65 (labeled in FIGS. 7 and 8) to accept hydraulic connections 66. The signal cable module 70 has sensor connections 68 for rod position indication and rod bottom indication. Other sensors, such as CRDM temperature or current, may also have connectors (not shown). The sensors may all use identical connectors and one connector may serve multiple sensors, although different types of connectors may also be used to prevent the CRDM from being installed in an incorrect orientation. Alternatively, the connection site of the CRDM may be keyed to prevent improper installation of the CRDM. FIGS. 7 and 8 show alternative perspective views of one power cable module 60, with FIG. 7 tilted to show the top of the module and FIG. 8 tilted to show the bottom of the module. FIG. 7 shows the top of the module 60 and the electrical power connections 64. The electrical power connection provides power to the CRDM motor and may provide latching power if the latching mechanism is electrical. Openings 65 accept the hydraulic connectors 66 (see FIG. 5) when the module 60 is installed in the receptacle 42 (see FIG. 3) of the PDP 40. The hydraulics provide the latching power if a hydraulic latching mechanism is employed. FIG. 8 shows the bottom of the power cable module 60 with installed power MI cabling 61. FIGS. 9 and 10 show alternative perspective views of one signal cable module 70, with FIG. 9 tilted to show the top of the module and FIG. 10 tilted to show the bottom of the module. The PI connectors (several of which are labeled 74) connect to the position indicator cables of the CRDMs 20. The signal MI cables 71 are visible in FIG. 10, and connect to the PI connectors 74. With general reference to FIGS. 7-10, the undersides of the cable modules 60, 70 are constructed so that when the cable modules 60, 70 are installed in the receptacles 42 of the PDP 40 (see FIG. 3), a cable conduit or raceway is defined between the module and the PDP. In the illustrative cable modules 60, 70, this is achieved by having peripheral (i.e. side) standoffs 80, 82 at the periphery of the modules that raise the tops of the modules to define the cable conduit or raceway. The hydraulic lines 78 shown in FIG. 11 are mounted to the PDP 40 inside the receptacles 42 for the power cable modules 60, and the aforementioned conduit or raceway also houses the hydraulic lines 78. The hydraulic lines are attached to the PDP 40 in the illustrative embodiment, but alternatively may be attached to the modules (or omitted entirely if the CRDMs do not employ hydraulic power). While the disclosed PDP with installable cable modules is described in conjunction with powering CRDM units, it is also suitable for powering internal electrically driven reactor coolant pump (RCP) units. For example, if internal RCP's are disposed on (or in) an annular pump plate in the downcomer annulus, then the PDP could suitably be an annular plate mounted on the pump plate (a two-plate design) or, if thick enough, serving as the pump plate (a one-plate design). The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
	summary
046363360	claims	1. A process for reducing the volume of a low-level radioactive liquid waste containing an organic amine chelating agent comprising: burning a fuel and an oxygen-containing gas to produce a hot gas stream having a temperature in excess of the thermal decomposition temperature of the chelating agent; introducing the hot gas stream into a spray drying zone; introducing a finely atomized spray of said liquid waste into said spray drying zone and into intimate contact with said hot gas stream; controlling the proportions of said hot gas stream and said liquid waste to rapidly evaporate water from said liquid waste and cool said hot gas to a temperature below the decomposition temperature of said chelating agent in a time of less than six seconds to produce (a) a dry, flowable powder product including said chelating agent, and (b) a product gas substantially free of any gaseous products of said chelating agent and volatile fission products of the radioactive constituents of said liquid waste; and separating said powder product from said product gas. 2. The process of claim 1 wherein said chelating agent is an organic amine acid compound. 3. The process of claim 2 wherein said chelating agent is selected from the group consisting of EDTA, DTPA, HEDTA and NTA. 4. The process of claim 3 wherein said hot gas stream has a temperature within the range of 250.degree. to 400.degree. C. 5. The process of claim 4 wherein said hot gas is cooled to a temperature of from about 150.degree. to 200.degree. C. in a time within the range of from about 1 to 6 seconds. 6. The process of claim 5 wherein said time is within the range of from about 1.5 to 3 seconds. 7. The process of claim 6 wherein said chelating agent is EDTA. 8. The process of claim 5 wherein the gas is further cooled to a temperature of less than about 90.degree. C. prior to separating said powder product from said product gas.
	summary
047175338	abstract	A grid for supporting and spacing nuclear fuel rods, particularly at the nodes of a triangular array, has a peripheral frame of regular polygonal, typically hexagonal, shape and at least two beds of wires spaced in the longitudinal direction of the fuel assembly. Each bed has at least two series of mutually parallel wires secured to said frame at the end thereof, the wires of a same one of said series being parallel to two opposed side of said frame and all said wires defining passages for said fuel elements.
055641059	abstract	A borated aqueous solution from a nuclear reactor coolant system dilute chemical-decontamination process or from an equipment washing process which has been contaminated with radioactive metals or heavy metals including cobalt, nickel, chromium, iron, manganese, lead or mercury and with a chelating agent, detergent or soap is treated with an oxidizing agent to oxidize the chelating agent, detergent or soap and to precipitate the contaminant metals. The contaminant metals are then separated from the solution by centrifugal filtration, micromembrane belt filtration or magnetic separation. Advantageously, a very small volume of precipitate may then be buried and the decontaminated solution may be recycled or further treated and released for other uses.
	claims	1. A device for repairing a damaged area of an underwater wall region of a container or tank, comprising:a guide system to be mounted along a side wall, at a spacing distance from, and secured to, said side wall;at least one first carriage guided on said guide system, and movable in a longitudinal direction of said guide system;a receptacle displaceably mounted on said at least one first carriage, said receptacle being configured for holding a repair overlay to be applied with an adhesive surface to the wall region having the damaged area; andat least one suction mount disposed on said first carriage and configured for placement against the side wall and connected to a suction line, said at least one suction mount being disposed and configured for fixing said first carriage on the side wall for absorbing forces generated by applying the repair overlay to the side wall. 2. The device according to claim 1, wherein said at least one first carriage is one of at least two first carriages and comprising at least one second carriage movably mounted along said guide system and arranged in a working position between two adjacent first carriages as a space keeper. 3. The device according to claim 2, wherein a distance between said repair overlays, as defined by said second carriage, corresponds substantially to an extent of a repair overlay in the longitudinal direction. 4. The device according to claim 2, wherein said first and second carriages are driveless carriages configured to be moved exclusively by the force of gravity. 5. The device according to claim 1, wherein said at least one first carriage is a driveless carriage configured to be moved exclusively by the force of gravity. 6. The device according to claim 1, wherein said guide system is composed of sections that are detachably connected to one another. 7. The device according to claim 1, which comprises a multiplicity of suction mounts disposed on said guide system and connected to a suction line for securing said guide system to the side wall. 8. The device according to claim 1, configured for repairing a wall region of a tank in a nuclear reactor installation.
043326404	summary	The invention relates to refueling mechanisms for reactors, particularly to a fuel grapple for removing spent fuel assemblies from a reactor core, and more particularly to a vibrating fuel grapple for enabling additional withdrawal capability. Reactor refueling operations remove fuel assemblies at refueling by applying an axial force greater than the assembly weight. With significant friction forces due to the design, environment and material behavior, the axial force will have to be large enough to overcome these friction forces also. The refueling approach to these concerns has been to limit allowable withdrawal loads to an assumed safe level. In liquid metal fast breeder reactor (LMFBR) core restraint systems, the current design trend is for a restrained system which utilizes above-core and top load pads and formers along with a nozzle/receptacle restraint at the bottom of the core assemblies. The operating environment of an LMFBR exposes core structural materials to temperature and fast-flux irradiation gradients. Core structural materials exposed to fast-flux irradiation exhibit swelling and creep behavior as a function of irradiation and time. The combined effects of the restrained components, the environment and the material behavior, result in core assemblies with permanently bowed shapes which interact within the core restraint system. This condition results in load interactions, on the cores fuel assemblies, which, as a result of friction, produce retraining loads on the assemblies. This tends to prevent easy removal of assemblies for refueling at end of life (with the design trend to larger cores for commercial reactors, these loads could be significantly large). In addition, the existence of these friction loads can cause damage to remaining adjacent assemblies. Significant changes to remaining fuel assembly surfaces can cause undesirable operational stick-slip behavior and create difficulties for future refueling operations. It is thus seen that it is extremely difficult to predict accurately the load pad normal forces and ultimately the force required to withdraw or insert an LMFBR core fuel assembly at refueling, since the accuracy of such load predictions is subject to the uncertainties in the operational environment, creep and swelling correlations, and the uncertainties of pad-to-pad and nozzle-to-receptacle friction coefficients. Thus, it is possible that actual withdrawal loads will exceed core fuel assembly withdrawal force design limits. Various mechanisms exist in the prior art for removing assemblies, fuel and control, from the core of nuclear reactors. These prior efforts are exemplified by U.S. Pat. No. 3,151,033 issued Sept. 29, 1964; No. 3,175,854 issued Mar. 30, 1965; No. 3,801,148 issued Apr. 2, 1974; No. 3,856,621 issued Nov. 24, 1974; and No. 3,950,020 issued Apr. 13, 1976. Apparatus is known for dislodging stuck elements, such as well pipe, drilling bits, etc. where accoustic energy or vibration is utilized. These prior approaches for removing stuck items are exemplified by U.S. Pat. No. 3,132,707 issued May 13, 1964; No. 3,399,724 issued Sept. 3, 1968; and No. 4,058,163 issued Nov. 15, 1977. The latter patent, for example, uses an eccentric weight which is rotated by means of a pressurized fluid, wherein the rotation of the eccentric weight results in vibration of the apparatus and the well bore member. Thus, while the use of apparatus for dislodging stuck components by vibration, for example, is known in the field of well drilling, there is no known apparatus, as pointed out above, which utilizes a technique such as vibration, to loosen a stuck fuel assembly in the core of a reactor, such that the axial force applied to the fuel assembly does not increase beyond a safe limit. SUMMARY OF THE INVENTION The present invention provides an improved reactor refueling method utilizing a fuel grapple mechanism that incorporates therein a pneumatic vibrator which enables additional withdrawal capability without exceeding the allowable axial force limit. Thus, the present invention provides increased capability for removing spent fuel assemblies wherein the friction loads thereof have increased due to the environment and the material behavior resulting from the fuel assemblies being irradiated in the reactor core. Vibration has been shown to be an effective means to reduce the effective coefficient of friction. By incorporating a pneumatic vibrator into the fuel grapple head, the withdrawal capability is increased. The only moving part in the vibrator is a steel ball, pneumatically driven by a gas around a track. Centrifugal force created by the ball is transmitted through the grapple to the fuel assembly handling socket, causing vibration of the fuel assembly and a reduction in the friction load involved in removable of the fuel assembly. Therefore, it is an object of this invention to provide a reactor refueling method which utilizes vibration of the fuel assemblies being removed from a reactor core for reducing functional loads thereon. A further object of the invention is to provide an improved refueling fuel grapple mechanism. Another object of the invention is to provide a fuel grapple mechanism utilizing vibration techniques for reducing friction loading of the fuel assemblies during withdrawal from a reactor core. Another object of the invention is to provide a refueling grapple mechanism utilizing a pneumatic vibrator in the grapple head enabling additional withdrawal capability without exceeding the allowable axial force limit. Another object of the invention is to provide a vibrating fuel grapple for reducing the effective coefficient of friction resulting from the removal of fuel assemblies from a reactor core. Another object of the invention is to provide a vibrating fuel assembly grapple wherein the only moving part in the vibrator is a steel ball pneumatically driven by gas, such as argon, around a track, such that centrifugal force created by the ball is transmitted through the grapple to the fuel assembly handling socket. Other objects of the invention will become readily apparent to those skilled in the art from the following description and accompanying drawings.
039878600	summary	BACKGROUND AND SUMMARY OF THE INVENTION This invention relates in general to nuclear reactor core construction and more particularly to a nuclear reactor core stabilizing arrangement whereby fuel elements making up the core are pressed together and thereby stabilized against vibration induced by coolant flow through the core or by externally applied forces, such as seismic or other vibration induced forces. In reactor cores having a plurality of elongated fuel assemblies positioned together in adjacent, laterally spaced-apart relation to one another to form a compact group, there generally exist clearance gaps of somewhat differing dimensions between adjacent fuel assemblies. This presents a problem under seismic and dynamic loading conditions, since the assemblies, with their high long column slenderness ratio can be easily set vibrating and such vibration can cause them to slam together with high impact loads, and the consequent hazard of breakage. To withstand such impact, canned fuel assemblies were used in the prior art. The invention provides a core stabilizing arrangement whereby the fuel assemblies within the core are passed together at the mid-point of their span by actuators arranged in a pattern laterally surrounding the core. These actuators have platens positioned for contact with respective assemblies positioned about the periphery of the core. Consequently, the clearance between adjacent assemblies is reduced and the core assembly is firmly compacted to resist vibration, and to minimize the amplitude of any vibration that does occur. With the invention, it is therefore permissible to use less expensive canless fuel assemblies without sacrificing core integrity. According to a preferred embodiment of the invention, the actuators are operated by input forces induced and applied by the emplacement of an upper grid structure that serves, together with a lower grid structure, to hold and retain the fuel assemblies in their intended parallel alignment. These input forces are directed substantially parallel to the longitudinal axis of the fuel assemblies, whereas the output forces exerted by the actuator platens against the fuel assemblies are directed in a substantially common plane perpendicular to these same axes. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention .
	claims	1. A depth diaphragm for an x-ray device, comprising a plurality of adjustable diaphragm blades for fading in an examination area, wherein the diaphragm blades are shaped as disks and include at least two pairs of diaphragm blades individually moveable in a common direction, the pairs arranged in two layers, the layers arranged one upon the other, so that the examination area is faded in asymmetrically. 2. The depth diaphragm according to claim 1, wherein each diaphragm blade is individually moveable by a drive. 3. The depth diaphragm according to claim 1, wherein the diaphragm blades are made of lead and are embedded in or coated with a plastic material. 4. The depth diaphragm according to claim 1, wherein the depth diaphragm is operatively connected to a diaphragm operating device, the diaphragm operating device arranged and constructed such tat each diaphragm blade is actuated individually. 5. An X-ray device, comprising a depth diaphragm, the depth diaphragm comprising a plurality of adjustable diaphragm blades for fading in an examination area, wherein the diaphragm blades are shaped as disks and include at least two pairs of diaphragm blades individually moveable in a common direction, the pairs arranged in two layers, the layers arranged one upon the other, so that the examination area is faded in asymmetrically.
	abstract	A scintillation based imaging system. The device utilizes a single-crystal inorganic scintillator to convert ionizing radiation to light in a spectral range or ranges within the visible or ultraviolet spectral ranges. The conversion takes place inside the single crystal material, preserving special resolution. The single crystal scintillator is sandwiched between a first plate that is substantially transparent to the ionization radiation and a second plate that is transparent to the visible or ultraviolet light. The ionization radiation is directed from the submicron source through a target to create a shadow image of the target inside the scintillator crystal. Several submicron sources of radiation are described. These include submicron x-ray and high-energy ultraviolet sources, submicron electron beam sources, submicron alpha particle sources, submicron proton sources, submicron positron sources and sub-micron neutron sources. Also, Applicants describe submicron spot size x-ray sources produced using electron beams alpha particles, protons and positrons. In preferred embodiments larger size sources are converted to submicron sources by focusing the radiation to a submicron neck, by blocking all but a submicron portion using a pinhole arrangement or by channeling the radiation with a pinhole funnel.
	summary
	claims	1. A system for vertically-stacked storage of nuclear waste canisters comprising:an elongated outer shell defining a vertical axis and an internal cavity;an elongated inner shell disposed in the cavity and concentrically aligned with the outer shell;a first canister positioned in the cavity in a lower position;a second canister vertically stacked above the first canister in an upper position, the first and second canisters being concentrically aligned with the vertical axis;a centering and spacing ring assembly interspersed between the first and second canisters; anda removable top lid mounted on top of the outer shell covering the cavity;wherein the centering and spacing ring assembly includes a plurality of radially extending centering lugs spaced circumferentially apart around the ring;wherein the inner shell has a vertical height coextensive with a vertical height of the outer shell;wherein the lugs of the centering and spacing ring assembly are engageable with the inner shell;wherein the centering and spacing ring assembly has a castellated surface. 2. The system of claim 1, wherein the centering and spacing ring assembly is arranged and operable to transfer weight of the second canister to the first canister. 3. The system of claim 1, wherein the castellated surface includes a plurality of alternating arcuate raised segments and arcuate recessed segments. 4. The system according to claim 1, further comprising a top centering and spacing ring assembly engaged with a top of the second canister. 5. The system according to claim 1, further comprising a bottom centering and spacing ring assembly engaged with a bottom of the first canister. 6. The system of claim 1, further comprising a bottom plate hermetically sealed to the outer shell forming an impermeable moisture barrier. 7. The system of claim 6, further comprising a concrete top pad surrounding a top of the outer shell and a concrete base pad engaging the bottom plate on outer shell. 8. The system according to claim 1, wherein the outer and inner shells are formed of steel. 9. A system for vertically-stacked storage of nuclear waste canisters comprising:an elongated outer shell defining a vertical axis and an internal cavity;a first canister positioned in the cavity in a lower position;a second canister vertically stacked above the first canister in an upper position, the first and second canisters being concentrically aligned with the vertical axis;a centering and spacing ring assembly interspersed between the first and second canisters;a removable top lid mounted on top of the outer shell covering the cavity;a concrete top pad surrounding a top of the outer shell and a concrete base pad engaging the bottom plate on outer shell;a bottom plate hermetically sealed to the outer shell forming an impermeable moisture barrier; andsoil filled adjacent to the outer shell and extending between the top pad and the base pad. 10. A storage module for vertically-stacked storage of nuclear waste canisters comprising:an elongated outer shell defining a vertical axis and an internal cavity;an elongated inner shell disposed in the internal cavity;a first annular space formed between the inner and outer shells, the first annular spacing defining a vertical downcomer ventilation shaft operable to convey ambient cooling air downwards to the cavity;a first canister positioned in the cavity in a lower position;a second canister vertically stacked above the first canister in an upper position, the first and second canisters being concentrically aligned with the vertical axis;a middle centering and spacing ring assembly interspersed between the first and second canisters, the middle centering and spacing ring assembly operable to transfer weight of the second canister to the first canister;a second annular space formed between the first and second canisters and the inner shell, the second annular space defining a vertical riser ventilation shaft operable to convey cooling air upwards across outer surfaces of the canisters; anda removable top lid mounted on top of the outer shell covering the cavity, the top lid being in fluid communication with the riser ventilation shaft and configured to form an airflow pathway to atmosphere through the lid;wherein the middle centering and spacing ring assembly has a castellated surface including a plurality of alternating arcuate raised segments and arcuate recessed segments. 11. The storage module of claim 10, wherein the outer and inner shells are formed of steel. 12. The storage module of claim 10, wherein the middle centering and spacing ring assembly is arranged and operable to transfer weight of the second canister to the first canister. 13. The storage module of claim 10, wherein the middle centering and spacing ring assembly includes a plurality of radially extending centering lugs spaced circumferentially apart around the ring, the lugs engaging the inner shell. 14. The storage module of claim 10, further comprising a top centering and spacing ring assembly engaged with a top of the second canister and a bottom centering and spacing ring assembly engaged with a bottom of the first canister. 15. A storage module for vertically-stacked storage of nuclear waste canisters comprising:an elongated outer shell defining a vertical axis and an internal cavity;an elongated inner shell disposed in the internal cavity;a first annular space formed between the inner and outer shells, the first annular spacing defining a vertical downcomer ventilation shaft operable to convey ambient cooling air downwards to the cavity;a first canister positioned in the cavity in a lower position;a second canister vertically stacked above the first canister in an upper position, the first and second canisters being concentrically aligned with the vertical axis;a middle centering and spacing ring assembly interspersed between the first and second canisters, the middle centering and spacing ring assembly operable to transfer weight of the second canister to the first canister;a second annular space formed between the first and second canisters and the inner shell, the second annular space defining a vertical riser ventilation shaft operable to convey cooling air upwards across outer surfaces of the canisters; anda removable top lid mounted on top of the outer shell covering the cavity, the top lid being in fluid communication with the riser ventilation shaft and configured to form an airflow pathway to atmosphere through the lid;wherein the middle centering and spacing ring assembly includes a plurality of radially extending centering lugs spaced circumferentially apart around the ring, the lugs engaging the inner shell;wherein the lugs are configured and dimensioned to simultaneously engage both the first and second canisters.
048572624	summary	BACKGROUND OF THE INVENTION The present invention concerns a method, in the wider concept of claim 1, an apparatus, for singularizing the fuel rods of a fuel element. It is well known that a fuel element consists of a larger number of individual fuel rods. Such fuel rods comprise closed tubular cans containing nuclear fuel as well as a smaller number of control or absorber rods. With the help of spacers, which are arranged in the form of a grid cage, of a head piece, and of a foot piece, the fuel rods and the control rod guide tubes are arranged in a square matrix. Spent fuel elements are stored in the storage pool of the reactor or in storage containers, before reprocessing or final disposal. The spent fuel rods require a great deal of storage space in the matrix arrangements. Thus, it is desirable that the storage facility be as compact as possible. However, the fuel rods have to be singularizer for compact storage. An apparatus is known from document EP-A No. 0066695 for consolidating spent fuel rods of fuel elements, which is provided with a fuel element head. The fuel element head is connected to control rod guide tubes. The fuel rods are maintained at a distance from one another by means of spacers. The foot of the fuel element can be firmly clamped in this arrangement. With the help of an arrangement of internal cutters, comprising a cutting tool, the head parts of the control guide tubes can be severed and removed together with the head itself. With the help of a grappler arrangement, the fuel rods can then be extracted and transferred to a consolidating stage. The consolidating stage is provided with guide tubes, one end of which is arranged in a first rack in exactly the same way as the fuel rods in the fuel element. The fuel rods themselves are inserted in the guide tubes. At their other end, the guide rods extend through a second rack in which they are arranged in a more compact way. The fuel rods are then advanced out of the guide tubes into a horizontal arrangement in which they are further consolidated and they are finally inserted in an arrangement in which they are consolidated vertically. After horizontal and vertical consolidation, the fuel rods are then placed in storage containers. This known arrangement is relatively complex. Moreover, the arrangement requires a great deal of space, since extra space has to be found corresponding to, the extended length of the rods. Since the guide tubes are positioned at an angle between the two parts of the rack and are bent along part of their length, there is always the danger of fracturing the fuel rods while they are being inserted into or extracted from these guide tubes. An arrangement is shown in document U.S. Pat. No. 2,853,625 for unloading a number of spent uranium fuel rods from a reactor. The reactor is provided with a charging and a discharging side, whereby the rods are arranged in cladding tubes. This arrangement consists of a trolley which can travel both vertically and horizontally. The trolley is provided with a storage chamber partially filled with water. The trolley is also provided with a pick-up nose which can be aligned with a cladding tube. To expel the spent uranium rods, fresh fuel rods are inserted in the cladding tube on the charging side of the reactor. The spent uranium fuel rods are then pushed into a channel in the charging stage of the trolley on the discharge side of the reactor. The free end of the expelled spent rods is taken up by a piston which travels through the chamber under hydraulic power. The channel ends in this storage chamber. As soon as the end of the spent rod reaches the end of the channel, it will fall into the storage chamber. This process is repeated until the required number of uranium rods has dropped into the storage chamber. The increased space and complexity of this design are disadvantageous features of this arrangement. In particular, an extra chamber is required for the extraction of the fuel rods, and the chamber has to be at least twice the length of the rods. Furthermore, in this known singularizer process, there is always the risk of fracturing the rods as they are pushed out of the cladding tube or the channel of the pick-up nose as well as when they fall into the storage chamber. In document DE-OS No. 27 30 723, an apparatus and a process are described for space saving disposal of channels for radioactive fuel material. With the help of a cutting arrangement, the square-sectioned empty metal tubular channels are cut open in a water bath. This produces four individual side plates, which can be placed on top of one another in a storage container to save space. This document, however, provides no indication of how the fuel is removed from the channels. Document DE-PS No. 17 64 523 provides a description of an arrangement for severing the inert end zones of a fuel element in order to remove the nuclear fuel from the casing enclosed by the inert end zones. This cutting arrangement is provided with a holder to maintain the fuel element horizontally. The cutting arrangement takes the form of a band saw at each end zone. This holder can be moved towards the band saws so that both end zones can be pushed toward the band saws and can be cut off at the same time. However, this document does not contain any indication of how the fuel is removed from the casings, either. SUMMARY OF THE INVENTION The purpose of the present invention is to provide an improved version of the method or means and of the apparatus or arrangement of the type referred to above. With the present invention, the fuel rods can be more simply removed from a fuel element with less risk of breakage and with less space. Furthermore, this apparatus may be capable of operating in any position. This requirement is met in the method according to the present invention, as set out in claim 1. An apparatus which meets this requirement is also described in claim 5. With the solution provided by the present invention, it is no longer necessary to withdraw or expel the fuel rods from a fuel element. This invention makes it possible to decompose or break down a fuel element in an extremely limited space. No extra space is required to allow for the length of the fuel rod when it is withdrawn or expelled. The risk of fuel rod fracture has been almost entirely eliminated. Apart from some very fine shavings, when the bird cage is cut open, there are no large pieces of waste which have to be picked up separately and which might provide an obstacle to a remote controlled process. The process defined by the present invention is safer and more reliable and can be easily performed under remote control. The apparatus according to the present invention can be employed in a horizontal or a vertical configuration. Both the method and the apparatus are suitable for use in reactor plants as well as in shielded cells. That is, both the method and apparatus are suitable for use in either wet or dry environments. Further useful and advantageous embodiments of the solution according to the present invention are characterized in the subclaims.
051014220	abstract	The ends of a tapered glass capillary are secured in relatively movable mounting blocks for application of axial tension to the capillary. This mounting enables the capillary to be pulled taut so that its axis is straight to facilitate propagation of X-rays. The capillary is coated to provide flexibility and strength. The ends of the capillary extend into their respective mounting blocks, with at least a portion of each end being stripped of the coating material. A bonding material contacts the glass and the coating material and secures both to their corresponding mounting blocks to hold the capillary in place when tension is applied and to provide shear strength for the capillary wall.
	claims	1. A method of producing a Fresnel zone plate, virtually without limitation of an aspect ratio, comprising:making available a substrate of glass which is rotationally symmetrical with respect to its centre axis;applying layers following in succession by means of an atomic layer deposition (ALD) method to faces of the substrate without rotation of the substrate at a thickness, wherein the thickness of each individual layer, as applied, is identical to a thickness of a corresponding zone of the zone pate in order to form a coated substrate; andsevering at least one slice from the coated substrate, by the coated substrate being divided at least once at a right angle to the centre axis. 2. A method according to claim 1, characterized in that an elongate substrate, the longitudinal centre axis of which represents the centre axis, is used as the substrate, wherein the faces constitute longitudinal sides of the elongate substrate. 3. A method according to claim 2, characterized in that a cylindrical element is used as an elongate substrate. 4. A method according to claim 3, characterized in that the cylindrical element has a centrally arranged through opening in the direction of its longitudinal centre axis. 5. A method according to claim 4, characterized in that the layers following in succession are applied to the cylindrical element with the through opening on the inside along walls of the through opening. 6. A method according to claim 3, characterized in that the layers following in succession are applied to the cylindrical element or a tapered or frustoconical element on the outside. 7. A method according to claim 2, characterized in that a tapered or frustoconical element is used as the elongate substrate. 8. A method according to claim 2, characterized in that a wire is used as an elongate substrate. 9. A method according to claim 1, characterized in that a sphere or a portion thereof is used as the substrate. 10. A method according to claim 1, characterized in that the severed slice is reduced in its slice thickness by grinding and/or polishing procedures. 11. A method according to claim 1, characterized in that the severed slice is applied to a further substrate. 12. A method according to claim 1, characterized in that the layers with the greatest radius with a layer thickness from a range of 1-150 nm are applied. 13. A method according to claim 1, characterized in that the layers are formed alternately from Ta2O5 and Al2O3. 14. A method according to claim 1, characterized in that the slice with a slice thickness from a range of from 100 nm to 10 μm is severed. 15. A method according to claim 1, characterized in that the layers with the greatest radius are applied by atomic layer deposition with a layer thickness from a range of 1-15 nm. 16. A method according to claim 1, characterized in that the actual number and thickness of the individual layers is pre-set by a zone plate formula. 17. A method according to claim 1, characterized in that the substrate has a roundness with respect to the longitudinal centre axis with a deviation of 25-50 nm. 18. A method according to claim 1, characterized in that the layers display sharp and smooth boundary faces over the entire coating width. 19. A method according to claim 1, characterized in that the substrate has a roundness with respect to the longitudinal centre axis with a deviation of less than 50 nm.
	summary
053902181	abstract	A process of preparing a fuel pellet for a nuclear reactor, comprising washing the gel particle using an organic solvent miscible with water to substitute the organic solvent for the water, removing the organic solvent, moistening again the dry gel particle, followed by press molding and sintering.
043839533	summary	This invention relates to manufacturing techniques and procedures comprising compressing particulate ceramic materials into compacted, coherent and handleable bodies for subsequent sintering to produce integrated units or products, and it particularly relates to a method of forming green or presintered pellets of particulate fissionable nuclear fuel material having increased physical strength and integrity for enduring subsequent handling or processing, such as sintering and grinding to dimensions, and their final utilization. Various materials are used as fissionable nuclear fuels for nuclear reactors including ceramic compounds of uranium, plutonium and thorium with particularly preferred compounds being uranium oxide, plutonium oxide, thorium oxide and mixtures thereof. An especially preferred fissionable nuclear fuel for use in nuclear reactors is uranium dioxide. Uranium dioxide is produced commercially as a fine, fairly porous powder which cannot be used directly as nuclear fuel. It is not a free-flowing powder but clumps and agglomerates, making it difficult to pack in reactor tubes to the desired density. The specific composition of a given commercial uranium dioxide powder may also prevent it from being used directly as a nuclear fuel. Uranium dioxide is an exception to the law of definite proportions since "UO.sub.2 " actually denotes a single, stable phase that may vary in composition from UO.sub.1.7 to UO.sub.2.25. Because thermal conductivity decreases with increasing O/U ratios, uranium dioxide having as low an O/U ratio as possible is preferred. However, since uranium dioxide powder oxidizes easily in air and absorbs moisture readily, the O/U ratio of this powder is significantly in excess of that acceptable for fuel. Although uranium dioxide suitable as a fissionable nuclear fuel can have an O/U ratio ranging from 1.7 to 2.015, as a practical matter, a ratio of 2.00 and suitably as high as 2.015 has been used since it can be consistently produced in commercial sintering operations. In some instances, it may be desirable to maintain the O/U ratio of the uranium dioxide at a level higher than 2.00 at sintering temperature. For example, it may be more suitable under the particular manufacturing process to produce a nuclear fuel having an O/U ratio as high as 2.195, and then later treat the sintered product in a reducing atmosphere to obtain the desired O/U ratio. A number of methods have been used to make uranium dioxide powder suitable as a fissionable nuclear fuel. Formerly, the most common method was to die press the powder into cylindrically-shaped green bodies of specific size without the assistance of binders since the complete removal of binders and their decomposition products was difficult to achieve prior to sintering. The entrainment of binder residues is considered unacceptable in sintered nuclear fuels. In the sintering process, it is desirable to develop strong diffusion bonds between the individual particles without significantly reducing the interconnecting porosity of the body. The use of organic binders inhibits the formation of strong bonds unless a presintering treatment is applied to remove the binder. The higher compacting pressures and sintering temperatures required to develop such bonds sharply reduce the desired porosity. Sintering atmospheres may range from about 1000.degree. C. to about 2400.degree. C. with the particular sintering temperature depending largely on the sintering atmosphere. For example, when wet hydrogen gas is used as the sintering atmosphere, its water vapor accelerates the sintering rate thereby allowing the use of correspondingly lower sintering temperatures such as a temperature of about 1700.degree. C. The sintering operation is designed to densify the bodies and bring them down to the desired O/U ratio or close to the desired O/U ratio. Conventional organic or plastic binders are unsuitable for use in powder fabrication of nuclear fuel since they tend to contaminate the interior of the sintered body with impurities such as carbon, and their removal requires a separate binder removal treatment or operation. In addition, upon decomposition, these binder materials often leave deposits of organic materials in the equipment utlized to sinter the article, thereby complicating the maintenance procedures for the equipment. U.S. Pat. No. 4,061,700, issued Dec. 6, 1977 to Gallivan, and assigned to the same assignee as this application, discloses a group of new fugitive binders that produce improved sintered bodies of nuclear fuel materials for nuclear reactors by powder ceramic techniques without contaminating the resultant fuel or manufacturing systems, and which permit, through sintering, the formation of strong bonds between the sintered particles without deleteriously affecting porosity. The improved fugitive binders of said U.S. Pat. No. 4,061,700 comprise 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, preferably a binder selected from the group consisting of ammonium bicarbonate, ammonium carbonate, ammonium bicarbonate carbamate, ammonium sesquicarbonate, ammonium carbamate and mixtures thereof. The binders disclosed in this patent are efficient binders for use in nuclear fuels, and further the binders enable the realization of defect free, pressed bodies of nuclear fuel materials and tensile strength in the bodies comparable to strengths achieved with long chain hydrocarbon binders. Further, the binders in this patent leave substantially no impurities in the nuclear fuel material since these binders decompose upon heating into ammonia (NH.sub.3), carbon dioxide (CO.sub.2) and water (H.sub.2 O) (or water vapor) at temperatures as low as 30.degree. C. The disclosure of the aforesaid U.S. Pat. No. 4,061,700, and U.S. Pat. Nos. 3,803,273; 3,923,933; and 3,927,154, also assigned to the same assignee as the subject application, each relating to significant aspects in the subject field of producing nuclear fuel pellets or bodies from particulate fissionable ceramic material, are all incorporated herein by reference. Notwithstanding the significant contributions of the inventions of above patents to this field and their specific advances in that technology, there remains a need to further increase the green or unfired strength and durability of consolidated bodies or pellets of such particulate ceramic nuclear fuel materials prior to their sintering and thereafter, to thereby reduce the high number of rejects and production costs incurred during manufacture resulting from imperfections or flaws attributable to marginal green or unfired strength or physical integrity. SUMMARY OF THE INVENTION This invention comprises a method for producing green or unfired compressed bodies or pellets of particulate fissionable ceramic fuel materials with fugitive binders of the type and materials set forth in the above cited patents, having significantly greater strength and physical integrity prior to firing or in the green stage, and thereafter, and the improved products derived therefrom. In addition to the specific components or ingredients given, this invention comprises a combination of sequenced manufacturing steps or operations including an essential aging period effected or carried out intermediate to certain of such sequenced steps or operations of the overall procedure. The method of this invention enables the practice of a process with an exceptionally low level of rejects or physical imperfections for the formation and subsequent sintering of bodies of fissionable nuclear fuel, comprising the steps of admixing the nuclear fuel material in particulate form with the binder, forming the resulting mixture into a green body having a density ranging from about 30% to about 70% of theoretical density of the nuclear fuel material, heating said green body to decompose substantially all the binder into gases, further heating the body to produce a sintered body and cooling the sintered body in a controlled atmosphere. This invention also provides a composition of matter that is suitable for sintering in the form of a compacted, coherent handleable structure 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 and preferably a binder selected from the group consisting of ammonium bicarbonate, ammonium carbonate and mixtures thereof. OBJECTS OF THE INVENTION It is an object of this invention to provide an improved method of manufacturing compacted, coherent and handleable bodies or pellets of nuclear fuel from particulate fissionable ceramic material, and the compressed products of such method. It is also an object of this invention to provide a method of improving the strength and physical integrity of green or unfired compressed and integrated bodies or pellets of nuclear fuel comprising particulate fissionable material and a fugitive binder, and the physically enhanced products thereof. It is a further object of this invention to provide a method for forming and sintering a body of nuclear fuel comprising the steps of admixing the nuclear fuel material in fine particulate form with a binder, forming the resulting mixture into a coherent and handleable green body, heating said green body to dispel any binder ingredients and to produce a durable sintered body wherein the number of rejects due to inadequate strength or physical durability of the green or as yet unsintered bodies, and in turn production costs, are significantly reduced. It is another object of this invention to provide a method for preparing particulate admixtures for producing green or unfired compressed bodies or pellets of particulate fissionable nuclear fuel materials admixed with a fugitive binder that are resistant to pressing flaws or deformities whereby the compressed bodies or pellets formed therefrom are substantially uniform throughout in configuration and physical integrity, and substantially free of physical imperfections or irregularities such as end flakes, radial cracks, fractures, chips and the like debilitating defects that impair the physical integrity of the units and cause their inability to meet specifications for nuclear fuel or simply their ultimate failure in physical structure. A still further object of this invention is to provide a method for preparing particulate admixtures of fissionable nuclear fuel material with a binder for producing compressed and sintered bodies or pellets wherein the density of the sintered product is controlled by the inclusion of a pore forming substance such as ammonium oxalate.

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