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claims | 1. An electron microscope, comprising:an illuminating lens system that illuminates an electron beam that is emitted from an electron source onto a specimen as a planar illuminating electron beam having a two-dimensional spread;an imaging lens system that projects and magnifies the reflecting electron beam emitted from the specimen to project and form a specimen image;a beam separator that separates the illuminating electron beam from reflecting electron beam;control means for controlling the reflecting electron beam so as to go straight through the beam separator, and the illuminating electron beam so as to keep a deflection angle of the illuminating electron beam which is made by the beam separator substantially constant;wherein the beam separator is formed of an E×B deflector that makes an electric field and a magnetic field orthogonal to each other and superimposed on one another, and the control means controls a voltage and a current which are supplied to the E×B deflector so that a Wien condition by which the deflections caused by the electric field and the magnetic field cancel each other is met with respect to the reflecting electron beam while keeping the deflection angle with respect to the illuminating electron beam substantially constant;a mirror electron microscope mode that magnifies and projects the mirror electron beam, and a low energy electron microscope mode that magnifies and projects the secondary electron beam or the backscattered electron beam; andmeans for changing over the mirror electron microscope mode and the low energy electron microscope mode;wherein the changeover from the mirror electron microscope mode to the low energy electron microscope mode is conducted by supplying a deflection voltage and a supply current which are obtained by multiplying a deflection voltage and a supply current of the E×B deflector by a value of γ that is represented by the following expression γ = V 0 V 1 2 1 + V 1 V 0 at the same time as the changeover of the specimen supply voltage when it is assumed that an energy of the electron beam that is supplied to the E×B deflector is eV0, and an energy of the outgoing electron beam that is supplied to the E×B deflector in the low energy electron microscope mode is eV1. 2. An electron microscope, comprising:electron source voltage applying means for applying an accelerating voltage to an electron source;specimen voltage applying means for applying a specimen supply voltage to a stage that supports a specimen;an illuminating lens system that illuminates an electron beam that is emitted from the electron source onto a specimen as a planar illuminating electron beam having a two-dimensional spread;an imaging lens system that projects and magnifies the reflecting electron beam emitted from the specimen to project and form a specimen image;a beam separator that separates the illuminating electron beam from the reflecting electron beam;means for changing over the reflecting electron beam to mirror electrons that is returned back in the vicinity of the surface of the specimen without colliding with the specimen, and secondary electrons that are generated from the specimen or backscattered electrons;control means for controlling the reflecting electron beam so as to go straight through the beam separator, and the illuminating electron beam so as to keep a deflection angle of the illuminating electron beam which is made by the beam separator substantially constant;wherein the beam separator is formed of an E×B deflector that makes an electric field and a magnetic field orthogonal to each other and superimposed on one another, and the control means controls a voltage and a current which are supplied to the E×B deflector so that a Wien condition by which the deflections caused by the electric field and the magnetic field cancel each other is met with respect to the reflecting electron beam while keeping the deflection angle with respect to the illuminating electron beam substantially constant;a mirror electron microscope mode that magnifies and projects the mirror electron beam, and a low energy electron microscope mode that magnifies and projects the secondary electron beam or the backscattered electron beam; andmeans for changing over the mirror electron microscope mode and the low energy electron microscope mode;wherein the changeover from the mirror electron microscope mode to the low energy electron microscope mode is conducted by supplying a deflection voltage and a supply current which are obtained by multiplying a deflection voltage and a supply current of the E×B deflector by a value of γ that is represented by the following expression γ = V 0 V 1 2 1 + V 1 V 0 at the same time as the changeover of the specimen supply voltage when it is assumed that an energy of the electron beam that is supplied to the E×B deflector is eV0, and an energy of the outgoing electron beam that is supplied to the E×B deflector in the low energy electron microscope mode is eV1. 3. The electron microscope according to claim 1 or 2, wherein the changeover from the mirror electron microscope mode to the low energy electron microscope mode is conducted by setting the specimen supply voltage to a positive potential side of the electron source supply voltage. 4. An electron beam inspection system, comprising:electron source voltage applying means for applying an accelerating voltage to an electron source;specimen voltage applying means for applying a specimen supply voltage to a stage that supports a specimen;an illuminating lens system that images the illuminating electron beam emitted from the electron source onto a focal plane of an objective lens by an illuminating lens to make a planar illuminating electron beam having a two-dimensional spread illuminate the specimen;an imaging lens system that projects and magnifies the reflecting electron beam emitted from the specimen to project and form a specimen image;a beam separator that separates the illuminating electron beam from the reflecting electron beam;control means for controlling the reflecting electron beam so as to go straight through the beam separator, and the illuminating electron beam so as to keep a deflection angle of the illuminating electron beam which is made by the beam separator substantially constant;image detecting means for sequentially illuminating the planar illuminating electron beam to a plurality of illuminating areas of a specimen surface to which a negative potential is applied, imaging the reflecting electron beam generated from the specimen, sequentially forming an magnified electron image of all or a part of the plurality of illuminating areas, and converting the magnified electron image into an electric image signal;image processing means for detecting a pattern defect formed on the specimen on the basis of the image signals;means for changing over the reflecting electron beam to mirror electrons that are returned back in the vicinity of the surface of the specimen without colliding with the specimen, and the secondary electrons or the backscattered electrons which are generated from the specimen with colliding the primary electron beam with the specimen by controlling the accelerating voltage and the specimen supply voltage;a mirror electron microscope mode that magnifies and projects the mirror electrons, and a low energy electron microscope mode that detects, enlarges and projects the secondary electrons or the backscattered electrons; andmeans for changing over the mirror electron microscope mode and the low energy electron microscope mode to detect a pattern defect formed in the specimen;wherein the changeover from the mirror electron microscope mode to the low energy electron microscope mode is conducted by supplying a deflection voltage and a supply current which are obtained by multiplying a deflection voltage and a supply current of the E×B deflector by a value of γ that is represented by the following expression γ = V 0 V 1 2 1 + V 1 V 0 at the same time as the changeover of the specimen supply voltage when it is assumed that an energy of the electron beam that is supplied to the E×B deflector is eV0, and an energy of the outgoing electron beam that is supplied to the E×B deflector in the low energy electron microscope mode is eV1. 5. The electron beam inspection system according to claim 4, wherein the beam separator is formed of an E×B deflector that makes an electric field and a magnetic field orthogonal to each other and superimposed on one another, and the control means controls a voltage and a current which are supplied to the deflector so that a Wien condition by which the deflections caused by the electric field and the magnetic field cancel each other is met with respect to the reflecting electron beam while keeping the deflection angle with respect to the illuminating electron beam substantially constant. 6. The electron beam inspection system according to claim 4, wherein the image processing means compares the image signals related to the plurality of illuminating areas with each other, or compares the image signals with an image signal related to a desired inspection area of a specimen that is standard, which is stored in advance, to detect a pattern defect formed in the specimen and display the defect as an image. |
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claims | 1. An X-ray CT scanner for reconstructing a CT image of a subject, comprising:an X-ray source configured to emit an X-ray beam;an X-ray detector having a plurality of detecting elements and configured to detect X-rays transmitted through the subject;a reconstructing unit configured to reconstruct the CT image based on an output of the X-ray detector;a determining unit configured to allow a user to set a thickness of the X-ray beam to an arbitrary integral multiple of a pitch of the detecting elements, as measured in a body axis direction of the subject, by graphically manipulating a frame representing the ends of the X-ray beam;a control unit configured to generate a calibration data file used to correct projection data obtained using the set X-ray beam thickness, from stored calibration data corresponding to predetermined X-ray beam thicknesses other than the set X-ray beam thickness; anda display unit configured to display a scanogram based on the reconstructed CT image, and to graphically display on the scanogram, the frame representing the ends of the X-ray beam set by the determining unit. 2. The scanner according to claim 1, wherein the display unit is configured to display, on the scanogram, information regarding a scanning range covered by a helical scan. 3. The scanner according to claim 1, wherein the display unit is configured to display a cursor indicating a center of an X-ray beam and a cursor indicating ends of an X-ray beam. 4. The X-ray CT scanner of claim 1, wherein the control unit is configured to generate the calibration data file by interpolation using the stored calibration data and the set X-ray beam thickness. 5. The X-ray CT scanner of claim 1, wherein the control unit is configured to generate the calibration data file by extrapolation using the stored calibration data and the set X-ray beam thickness. 6. An X-ray CT scanner, comprising:an X-ray tube configured to emit X-rays;an X-ray detector having a plurality of detecting elements and configured to detect X-rays transmitted through a subject;a scanogram generating unit configured to generate scanogram data based on an output of the X-ray detector;an image reconstructing unit configured to reconstruct tomographic data based on an output of the X-ray detector;a display unit;a screen generating unit configured to generate data of an X-ray beam thickness setting support screen, which is to be displayed on the display unit, the X-ray beam thickness setting support screen including the scanogram and a frame including both ends of an X-ray beam obtained in accordance with a thickness of the X-ray beam arranged on the scanogram;a manipulating unit configured to allow a user to graphically manipulate a size of the frame so as to set the thickness of the X-ray beam to an arbitrary integral multiple of a pitch of the detecting elements; anda control unit configured to generate a calibration data file used to correct projection data obtained using the set X-ray beam thickness, from stored calibration data corresponding to predetermined X-ray beam thicknesses other than the set X-ray beam thickness. 7. The X-ray CT scanner of claim 6, wherein the display unit is configured to display, on the scanogram, information regarding a scanning range covered by a helical scan. 8. The X-ray CT scanner of claim 6, wherein the display unit is configured to display a cursor indicating a center of an X-ray beam and a cursor indicating ends of an X-ray beam. |
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040509869 | summary | CROSS REFERENCE TO RELATED APPLICATIONS This application relates to, and incorporates by reference, each of the following applications, all asigned to Westinghouse Electric Corporation: 1. Application Ser. No. 503,148 filed Sept. 4, 1974 to W. E. Pennell and W. J. Rowan (herein called Pennell application) for Nuclear Reactor. 2. Application Ser. No. 503,149 filed Sept. 4, 1974 to John A. Rylat (herein called Rylatt application) for Nuclear Reactor. 3. Application Ser. No. 505,891 filed Sept. 13, 1974 to H. W. Yant, K. Stincher and G. C. Anzar (herein called Yant application) for Nuclear Reactor. BACKGROUND OF THE INVENTION This invention relates to the art of nuclear reactors and has particular relationship to the upper-internals structure of nuclear reactors. A nuclear reactor includes a pressure vessel into which a heat-transfer fluid, typically liquid sodium for fast breeder reactors, or pressurized or boiling water for more conventional commercial reactors, is pumped under pressure. The fluid flows through the core and is heated; the hot fluid emerges from the vessel and the heat flows via mechanically separated primary and secondary loops to electrical-power generating equipment. Within the vessel there is supporting structure for the core components. Typically, for a liquid-metal-cooled fast breeder nuclear reactor which generates more fissile fule than it burns up, these components include fuel-rod bundles or assemblies, control-rod assemblies, blanket fertile-material or fertile-rod assemblies and removable radial shielding assemblies. The expression "core assemblies" or "core component assemblies" or the word "assembly", when used in this application with reference to components of the core, means one or more types of these assemblies. The core-support structure serves the purposes of locating, supporting, distributing coolant to, and providing axial and radial restraint for, these assemblies. The core component assemblies, which in the illustrated embodiment include fuel assemblies, both fissile and fertile fuel containing types, control-rod assemblies and shielding assemblies, which form the core of a liquid metal cooled fast breeder nuclear reactor, are separately supported in inlet-support modules or modular units. Each inlet-support modular unit is removably mounted, held only by gravity, in liners in the lower core-support structure with fluid seals interposed between the aligned fluid inlet openings in the module and liner and the upper and lower parts of the module and liner. Each module directs flow of the heat-transfer or coolant fluid to a plurality (typically 7) of reactor component assemblies which are removably mounted, held only by gravity, in receptacles of the corresponding modular unit. Below the seal each module is subjected to low pressure which balances the low pressure in the region where the fluid emerges from the core components. The low pressure in the volume below the module lower seal is generated and maintained by venting this volume to the low pressure regions of the vessel of the reactor. Gravity is adequate to hold the modules in the liner. Typically, this invention applies to a 975 Megawatts -thermal, 400 Mwt-electrical (Mwt.) liquid-metal cooled fast breeder reactor which has 198 hexagonal-core fuel assemblies surrounded by 150 radial blanket assemblies and 324 radial shield assemblies. In this typical reactor the assemblies are received in 61 inlet modules each having 7 receptacles. The velocity of the heat-transfer or cooling fluid, which is sodium, and its distribution varies with the character of the component or assembly which it cools. The velociyt is about 30 feet per second in non-replaceable components while in replaceable components it may be as high as 50 feet per second at the inlet-lower-temperatures end and 40 feet per second at the outlet-higher-temperature end. In the fuel rod bundles it is 25 feet per second. Eighty percent of the fluid is allocated to the core, 12% to the radial blanket, 1.6% to control assemblies, and the remainder to shielding, bypass and leakage. Typically a reactor of the type to which to which this invention relates, for example, a sodium-cooled breeder reactor, operates at a bulk coolant temperature differential of 300F.degree. or greater between the core inlet and core outlet. This temperature gradient is not uniform across the core; it fluctuates widely and has peaks in temperature throughout the core caused by core geometry, fuel "Burnup," and deliberate variations in fuel enrichment. Localized temperature variations may also occur by reason of local anomalies in the core such as control assemblies. Also typically, a sodium-cooled breeder reactor undergoes rapid and severe changes in the core outlet temperature because of rapid changes in power load-level during postulated `upset` events such as reactor trips, rapid unloading, etc. The structure within the reactor vessel above the core, variously called instrument trees, upper core support structures, or upper-internals structure, or upper internals as it is called in this application, provide primary or secondary `holddown` of the reactor core for the contingency that the gravity holddown fails during emergencies such as scram, and support control-rod drivelines and instrumentation. These upper internals are exposed to the core effluent flow, thermal gradients, thermal transient conditions and periodic "stripping" of hot and cold coolant streams. The word "stripping" means the overlap in temperature which occurs between adjacent parts of a reactor, for example adjacent core-component assemblies, which operate at widely different temperatures. The resulting thermal stress and thermal fatigue may reduce the design lifetime of upper-internals structures, which are normally designed for a lifetime equal to that of the reactor itself. To assure a reasonable or long lifetime for a reactor, the core-outlet liquid-metal flow streams are mixed as they are delivered at the core outlet. This mixing reduces thermal gradients between flow streams at widely different temperatures and isolates the remaining structure of the upper internals from direct impingement by the flow streams, reducing the rate of change for thermal transient events. The mixing is effected by outlet modules, each outlet module serving a plurality of core-component assemblies. These outlet modules collect effluent coolant from the core assemblies and duct it through the above core structure to the reactor outlet plenum. Each outlet module includes a support or `holddown` grid, a flow collector, a chimney, and thermal liners or stubs isolating each chimney from the other upper internals. The support grid is designed to avoid direct impingement of core effluent streams on neighboring parts of the upper internals and it limits the axial travel of the core assemblies below it, thus serving as "holddown" grid. Core effluent is ducted from the flow collector of each outlet module through the upper internals by the chimneys. Each chimney and its thermal liners protect the upper core support structure from high cycle thermal transients. Flow mixing within the collector and chimney mix hot and cold streams entering the module, providing more even radial gradients between chimneys. The thermal isolation between chimney and `structure` reduces the severity in rate of change for thermal transients due to core power-level changes. It has been found that the mixing of high and low temperature jets of the liquid from the core starts immediately above the core and continues for some distance downstream towards the outlet plenum. Temperatures in these flow streams differ substantially and the mixing of these streams near the inner portion of the outlet modules results in a number of thermal stripping transients. The material selected for the modules must therefore have an endurance limit stress in excess of the maximum anticipated stress amplitude produced by fluid mixing. The part of the outlet module assembly which is subjected to these sharp temperature fluctuations is fabricated from alloys with superior cyclic thermal stress characteristics, while the remainder of the structure is made of relatively inexpensive material. Typically the part of the assembly which is subject to sharp temperature variations is fabricated from the refractory corrosion-resistant nickel-chromium-iron alloy,, INCONEL-718, and the other parts are fabricated from AISI-304 or 316 stainless steel. INCONEL-718 has the following typical composition: ______________________________________ Nickel 50.00 - 55.00 Chromium 17.00 - 21.00 Columbium (plus Tantalum) 4.75 - 5.50 Molybdenum 2.80 - 3.30 Titanium 0.65 - 1.15 Aluminum 0.20 - 0.80 Cobalt 1.00 Max. Carbon 0.08 Max. Manganese 0.35 Max. Silicon 0.35 Max. Phosphorus 0.015 Max. Sulfur 0.015 Max. Boron 0.006 Max. Copper 0.30 Max. Iron Balance ______________________________________ The 304 stainless steel has the following composition: ______________________________________ Carbon 0.08% Max. Manganese 2.00% Max. Phosphorus 0.040% Max. Sulphur 0.030% Max. Silicon 1.00% Max. Nickel 8.00 - 11.00% Chromium 18.00 - 20.00% Iron Balance ______________________________________ The 316 stainless steel has the following composition: ______________________________________ Carbon 0.08% Max. Manganese 2.00% Max. Phosphorus 0.040% Max. Sulphur 0.030% Max. Silicon 1.00% Max. Nickel 10.00 - 14.00 Chromium 16.00 - 18.00 Molybdenum 2.00 - 3.00 Iron Balance ______________________________________ The cobalt in these alloys and the cobalt and tantalum in the 718 are restricted for use within a reactor vessel. The cobalt and/or tantalum limit is a function of the neutron flux at the location of the material, surface area exposed to primary coolant, velocity of coolant past the exposed area, and the residence time of the material within the reactor vessel. The 718 is not weld compatible with either stainless steel. Even with the chimneys localized temperature variations occur. Sodium streams, exiting from the chimneys at significantly differing temperatures, mix in the outlet plenum imposing fluctuating temperatures on the surface material of the upper internals. During the scram transient, the section of the upper internals immersed in the sodium or other liquid pool is subjected to a very rapid drop in surface temperature because the control rods are fully inserted in the core. Jet impingement forces from the core outlet flow, and upper plenum cross flow forces are both unsteady, and tend to produce flow induced vibration of the upper internals structure. It has been found that this structure must have adequate structural stiffness. In providing the required stiffness the problem is confronted that only structural configurations which will perform satisfactorily in an ill defined thermal environment can be used. It has been proposed that the necessary stiffness be achieved by providing a cross-braced frame configuration between the columns in the area below the head plate and the tops of the chimneys. This proposal has proved unsatisfactory because of its sensitivity to thermal inertia matching of the structural members. The expression "thermal inertia" means the facility of a structure to resist temperature change produced by thermal gradients. Structures having higher moments of inertia transmit thermal strains more readily than structures having lower moments of inertia. For example, a corrugated plate transmits thermal strains more readily than an equivalent flat plate. It is essential that any structural member take up the strain arising from the stresses by its flexibility rather than transmitting the strain. Effective utilization of the reactor vessel outlet plenum mixing volume is essential for mitigation of the transients experienced by the reactor vessel and all the hot leg components. The natural flow characteristics in the outlet plenum assures this to an extent but difficulties are encountered in the case of a scram transient. Stratification of the cool core effluent following a scram have led to concerns that adequate outlet plenum mixing may not occur unless forced. The upper-internals structure outlet-module chimneys provide a means for forcing the required mixing by ensuring that a major portion of the core effluent exits into the plenum at a high elevation. However, a serious problem is presented in fabrication of the complete structure including the chimneys because the highly refractory, high corrosive resistant nickel-chromium alloy of which the chimneys are composed, to be able to withstand the stresses, cannot be joined to the remainder of the structure by welding. It is an object of this invention to overcome the above-described disadvantages of the prior art and to provide a nuclear reactor in which the upper internals including the chimneys shall have the necessary stiffness without being sensitive to thermal inertia matching. It is also an object of this invention to provide an unwelded assembly including the chimneys and their associated structure which shall maintain its integrity in the face of the violent wide temperature fluctuations to which it is subject in use. It is a further object of this invention to suppress the effects of the temperature changes in the coolant during emergencies and particularly during scram. SUMMARY OF THE INVENTION It has been realized in arriving at this invention that the main load-bearing structure, which, in the interest of economy, is composed of stainless steel, must be stiff to suppress flow-induced vibrations and must be light to minimize thermal stress in the non-isothermal environment. It has also been realized that the thermal inertia of the individual structural members must be low to maintain within permissible limits cumulative creep-fatigue damage with appropriate modification for carbon and nitrogen depletion. Typically uniform plate thicknesses should not exceed one inch and this thickness is reduced at the junction between members. In accordance with this invention, the main load bearing structure for the assembly including the chimneys is a welded sandwich plate assembly. This assembly includes a plurality of pairs of plates, typically of 316 stainless steel. The shear web for each pair of plates is made by welded stub tubes which surround each of the outlet module chimney penetrations. The shear web so made is not continuous, but the unsupported span between shear webs is sufficiently short that the secondary bending moments induced in the top and bottom plates of each pair are small. The sandwich plate assembly including the grids and the chimneys is supported from the columns which are secured to the head plate at the top and are keyed to the core barrel at the bottom. This double-portal (there are two pairs of columns) frame configuration derives its stiffness through bending of the frame members; i.e., the columns, and is structurally insensitive to differences in bulk temperature of the various major structural members. Core seismic or loss of hydraulic holddown loads are transmitted directly to the upper plate of the pairs via the outlet module chimneys. The plates are of sufficient strength to provide the required strength for the upper internals to survive undamaged an operational basis earthquake with the locating keys in the core barrel disengaged. The upper internals are movable to different positions within the reactor vessel by the rotatable plugs in the head. When the upper internals are to be moved the key is with the upper internals raised to disengage from the keyway. To suppress flow-induced vibration, a close tolerance fit at operating temperature is required at the connection between each nickel-chromium-iron chimney and the stainless steel structure. To accomplish this object an extension of another nickel-chromium-iron alloy which is weld compatible with the stainless steel (typically 316) and has about the same thermal coefficient of expansion as the highly refractory nickel-chromium-iron alloy is welded to the stainless steel. Typically this other nickel-chromium-iron alloy is INCONEL-600 which has the following composition: ______________________________________ Nickel plus Cobalt 72.0 Min Chromium 14.0 - 17.0 Iron 6.0 - 10.0 Carbon 0.15 Max. Manganese 1.00 Max. Sulphur 0.015 Max. Silicon 0.50 Max. Copper 0.50 Max. ______________________________________ In the above alloy the cobalt should be limited to 0.10% where, as here, the alloy is to be used within a reactor. The weld of the extension to the plates is made at a sufficient distance from the plate to reduce local bending moments at operating temperature to an acceptable level. The extension at the top end of the chimney carries the lateral and vertical load from the top end of the chimney. A lateral load pad is provided at the upper one of the lower pair of plates. Up load on the chimney is carried to the stainless steel structure by a ledge and down load is carried by the split key. Both the ledge and the key are at the upper plate of the upper pair. A locking band holds the key in place. A thermal liner is held in place by the locking band. The unique feature of this structure is that the joint can carry lateral and vertical (up and down) loads from the chimney to the stainless steel structure (materials with different rates of thermal expansion and materials that cannot be welded) without creating large gaps at operating temperature. To suppress lateral flow of the coolant to the vessel walls and through the outlet nozzles a peripheral seal is provided at the upper end of the core over the shielding assemblies of the core. This seal consists of highly-refractory alloy members (typically INCONEL-718). This seal is positioned over the removable shielding assemblies. To fit over these assemblies the seal is formed of parts with matching edges which are in engagement like a jig-saw puzzle. Because the seal is made in this form rather than a cylinder adjacent the core barrel the radius over which the upper internals, including the seal, must be swung is reduced and the diameter of the pressure vessel may be correspondingly reduced. |
abstract | In a pattern definition device for use in a particle-beam exposure apparatus a plurality of blanking openings (910) are arranged within a pattern definition field (bf) composed of a plurality of staggered lines (bl) of blanking openings, each provided with a deflection means controllable by a blanking signal (911); for the lines of blanking openings, according to a partition of the blanking openings of a line into several groups (g4,g5,g6), the deflection means of the blanking openings of each group are fed a common group blanking signal (911), and the group blanking signal of each group of a line is fed to the blanking means and connected to the respective blanking openings independently of the group blanking signals of the other groups of the same line. |
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claims | 1. A pattern definition device (102) for use in a particle-beam processing apparatus (100), said device being adapted to be irradiated with a beam (lp,bp) of electrically charged particles and allow passage of the beam only through a plurality of apertures, said apertures (21,230) of identical shape defining the shape of beamlets (bm) permeating said apertures, wherein the apertures (21) are arranged within a pattern definition field (pf), wherein with said apertures are associated corresponding blanking openings (220) located such that each of the beamlets (bm) traverses that blanking opening which corresponds to the aperture defining the beamlet respectively, each blanking opening (220) being provided with a deflection means (221) controllable by a blanking signal (911) between two deflection states, namely, a first state (‘switched on’) when the deflection means has assumed a state in which particles radiated through the opening are allowed to travel along a desired path (pl), and a second state (‘switched off’) when the deflection means is deflecting particles radiated through the opening off said path (pl), wherein the positions of the apertures (21) in the pattern definition field (pf) taken with respect to a direction (Y) perpendicular to a scanning direction and/or a direction (X) taken with respect to a direction parallel to said scanning direction are offset to each other by not only multiple integers of the effective width (w) of an aperture taken along said direction, but also additional multiple integers of an integer fraction of said effective width (‘fractional offsets’), said scanning direction (sd) denoting a direction along which an image of the apertures formed by said beam on a target surface is moved over the target surface during an irradiation process. 2. The device of claim 1, comprising an aperture array means (203) for forming a number of beamlets and a blanking means (202) for controlling the passage of selected beamlets, said aperture array means (203) having a plurality of apertures (21,230) of identical shape defining the shape of beamlets (bm) permeating said apertures, wherein the apertures (21) are arranged within a pattern definition field (pf) in which the positions of the apertures (21) taken with respect to a direction (Y) perpendicular to the scanning direction and/or a direction (X) taken with respect to a direction parallel to the scanning direction are offset to each other by not only multiple integers of the effective width of an aperture taken along said direction, but also by additional multiple integers of an integer fraction of said effective width (‘fractional offsets’), and said blanking means (202) having a plurality of blanking openings (220) arranged in an arrangement corresponding to the apertures (230) of the aperture array means (203). 3. The device of claim 1, wherein the fractional offsets are integer multiples of ½N times the effective width of an aperture, where N is a positive integer, preferably greater than 1. 4. The device of claim 1, wherein the pattern definition field (pf) is segmented into several domains (D), each domain being composed of a plurality of staggered lines (pl) of apertures running along the scanning direction, wherein the apertures are spaced apart within said lines by an integer multiple of the effective width (w) of an aperture and are offset between neighboring lines by a fraction (mw) of said integer multiple width,wherein along the direction perpendicular to the scanning direction, the apertures of a domain are offset to each other by multiple integers of the effective width (w) of an aperture, whereas the offsets of apertures of different domains are fractional offsets. 5. The device of claim 4, wherein the domains have arrangements of apertures which are corresponding as regards the relative position of aperture within each domain. 6. The device of claim 5, wherein the domains have the same number of apertures. 7. The device of claim 4, wherein the fractional offsets are integer multiples of ½N times the effective width of an aperture, where N is a positive integer greater than 1, and the number of domains with different fractional offsets is 22N−1. 8. The device of claim 4, wherein the fractional offsets are integer multiples of ½N times the effective width of an aperture, where N is a positive integer greater than 1, and the number of domains with different fractional offsets is 2N, the fractional offsets running along a diagonal of an aperture's base shape. 9. The device of claim 1, wherein the blanking signals are fed to the pattern definition field (pf) partly at a side running parallel to the scanning direction, partly at a side running perpendicular. 10. The device of claim 1, wherein the shape of the apertures is substantially equivalent to a two-dimensional geometrical base shape of a contiguous covering of the plane. 11. The device of claim 10, wherein the base shape is a square. 12. The device of claim 1, comprising blanking openings whose line feeding the respective blanking signal comprises a component which is accessible on a surface of the device by a structural modification and which is adapted to change its transmissivity for the respective blanking signal between a electrical connecting state and a blocking state upon treatment by said structural modification. 13. The device of claim 12, wherein the component is realized as a conductor segment adapted to be irreversibly modified between an electrical well-conducting and a non-conducting state. 14. The device of claim 1, wherein the blanking signals are derived from feeding lines, each feeding line serving blanking signals for a number of blanking openings, which are propagated through a series of shift registers into a sequence of intermediate buffer means, one buffer means for each blanking opening, and the data contained in the buffer means are activated by a common trigger signal. 15. The device of claim 14, wherein the blanking signal for each blanking opening is a multi-bit signal, said signal coding a duration of how long within one exposure time the respective aperture is switched on. 16. The device of claim 1, wherein the deflection means are adapted to deflect, in the switched off state, the particles to an absorbing surface (204) of said exposure apparatus (100) mounted after the device as seen in the direction of the particle beam. 17. The device of claim 10, wherein the shape of the apertures is equivalent to a two-dimensional polygonal base shape of a contiguous covering of the plane, with rounded and/or beveled edges. 18. The device of claim 17, wherein the area of the shape of the apertures is the same as that of the original polygonal base shape. 19. The device of claim 17, wherein the shape of the apertures is a corner-rounded square. |
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claims | 1. A method, comprising:receiving at least one first reactor core parameter distribution associated with a state of a first core of a reference nuclear reactor;generating an initial fuel loading distribution for a simulated beginning-of-cycle (BOC) core of a nuclear reactor, wherein the BOC core of the nuclear reactor includes a plurality of simulated fuel assemblies;selecting an initial set of positions associated with a set of regions within the simulated BOC core;generating an initial set of fuel design parameter values utilizing at least one design variable of at least one of the set of regions;calculating at least one second reactor core parameter distribution of the simulated BOC core utilizing the initial set of fuel design parameter values associated with the set of regions located at the initial set of positions; andgenerating, by a controller, a loading distribution by performing at least one perturbation process on the set of regions located at the initial set of positions in order to determine a subsequent set of positions for the set of regions of the simulated BOC core; andarranging, by a fuel handler communicatively coupled to the controller, at least one fuel assembly of a second core of the nuclear reactor according to the subsequent set of positions. 2. The method of claim 1, wherein the state of the first core of the reference nuclear reactor includes an equilibrium state of the first core of the reference nuclear reactor. 3. The method of claim 1, wherein the reference nuclear reactor includes at least one of a reference thermal nuclear reactor, a reference fast nuclear reactor, a reference breed-and-burn nuclear reactor, or a reference traveling wave reactor. 4. The method of claim 1, wherein the at least one first reactor core parameter distributionincludes at least one of a power density distribution, a rate of change of the power density distribution, a reactivity distribution, or a rate of change of the reactivity distribution. 5. The method of claim 1, wherein the first core of the reference nuclear reactor includes at least one reference fuel assembly. 6. The method of claim 1, wherein at least a portion of the BOC core includes at least one of simulated recycled nuclear fuel, simulated unburned nuclear fuel, or simulated enriched nuclear fuel. 7. The method of claim 1, wherein the simulated BOC core includes a simulated beginning-of-life (BOL) core of the nuclear reactor. 8. The method of claim 1, wherein at least one of the initial set of positions corresponds to one of the set of regions. 9. The method of claim 8, wherein at least one of the set of regions encompasses at least one simulated fuel assembly. 10. The method of claim 8, wherein the at least one of the set of regions is a three-dimensional region corresponding to at least one of a selected volume, a selected shape, or a selected number of the set of regions. 11. The method of claim 1, wherein at least one of the initial set of fuel design parameter values is associated with one of the set of regions, andwherein generating the initial set of fuel design parameter values includes utilizing a thermodynamic variable of the at least one of the set of regions. 12. The method of claim 1, wherein at least one of the fuel design parameter values is associated with one of the set of regions, andwherein generating the initial set of fuel design parameter values includes utilizing a neutronic parameter of the at least one of the set of regions. 13. The method of claim 12, wherein generating the initial set of fuel design parameter values utilizing the neutronic parameter of the at least one of the set of regions includes utilizing a k-infinity value of the at least one of the set of regions. 14. The method of claim 1, wherein generating the initial set of fuel design parameter valuesincludes generating an initial set of enrichment values utilizing the at least one design variable. 15. The method of claim 1, wherein generating the initial set of fuel design parameter valuesincludes generating an initial set of pin dimension values associated with a set of pins of a simulated fuel assembly of the simulated BOC core utilizing the at least one design variable. 16. The method of claim 15, wherein generating the initial set of pin dimension valuesincludes generating at least one of an initial set of pin configuration values, an initial set of pin geometry values, or an initial set of pin composition values associated with the set of pins of the simulated fuel assembly utilizing the at least one design variable. 17. The method of claim 1, wherein the at least one design variable corresponds to at least one of a set of pins of the set of regions, wherein at least one of the initial set of fuel design parameter values is associated with one of the set of regions. 18. The method of claim 17, wherein the at least one of the initial set of fuel design parameter values is associated with one of the set of pins. 19. The method of claim 1, wherein calculating the at least one second reactor core parameter distributionincludes calculating at least one of a power density distribution, a rate of change of the power density distribution, a reactivity distribution, or a rate of change of the reactivity distribution of the simulated BOC core by utilizing the initial set of fuel design parameter values. 20. The method of claim 1, wherein the subsequent set of positions define the loading distribution for the simulated BOC core. 21. The method of claim 1, wherein the subsequent set of positions reduce a deviation metric between the at least one second reactor core parameter distribution and the at least one first reactor core parameter distribution below a selected tolerance level. 22. The method of claim 1, wherein arranging the at least one fuel assembly is performed in response to generating the loading distribution. 23. The method of claim 1, wherein the nuclear reactor includes at least one of a thermal nuclear reactor, a fast nuclear reactor, a breed-and-burn nuclear reactor, or a traveling wave nuclear reactor. 24. The method of claim 1, wherein arranging the at least one fuel assemblyincludes translating, by the fuel handler, the at least one fuel assembly from an initial location to a subsequent location according to the subsequent set of positions. 25. The method of claim 1, wherein arranging the at least one fuel assemblyincludes replacing, by the fuel handler, the at least one fuel assembly according to the subsequent set of positions. 26. A non-transitory computer-readable medium comprising program instructions, wherein the program instructions are executable to:receive at least one first reactor core parameter distribution associated with a state of a first core of a reference nuclear reactor;generate an initial fuel loading distribution for a simulated beginning-of-cycle (BOC) core of a nuclear reactor, the simulated BOC core of the nuclear reactor containing a plurality of simulated fuel assemblies:select an initial set of positions associated with a set of regions within the simulated BOC core;generate an initial set of fuel design parameter values utilizing at least one design variable of at least one of the set of regions;calculate at least one second reactor core parameter distribution of the simulated BOC core utilizing the initial set of fuel design parameter values associated with the set of regions located at the initial set of positions of the simulated BOC core;generate a subsequent loading distribution by performing at least one perturbation process on the set of regions located at the initial set of positions in order to determine a subsequent set of positions for the set of regions; andcontrol a fuel handler to arrange at least one fuel assembly of a second core of the nuclear reactor according to the subsequent set of positions. 27. The non-transitory computer-readable medium of claim 26, wherein the at least one first reactor core parameter distribution is associated with an equilibrium state of the first core of the reference nuclear reactor. 28. The non-transitory computer-readable medium of claim 26, wherein the reference nuclear reactor includes at least one of a reference thermal nuclear reactor, a reference fast nuclear reactor, a reference breed-and-burn nuclear reactor, or a reference traveling wave reactor. 29. The non-transitory computer-readable medium of claim 26, wherein the at least one first reactor core parameter distributionincludes at least one of a power density distribution, a rate of change of the power density distribution, a reactivity distribution, or a rate of change of the reactivity distribution. 30. The non-transitory computer-readable medium of claim 26, wherein at least a portion of the simulated BOC core includes at least one of simulated recycled nuclear fuel, simulated unburned nuclear fuel, or simulated enriched nuclear fuel. 31. The non-transitory computer-readable medium of claim 26, wherein causing the fuel handler to arrange the at least one fuel assembly is in response to generating the loading distribution determination. 32. The non-transitory computer-readable medium of claim 26, wherein the simulated BOC core includes a simulated beginning-of-life (BOL) core of the nuclear reactor. 33. The non-transitory computer-readable medium of claim 26, wherein at least one of the set of regions encompasses at least one simulated fuel assembly. 34. A nuclear reactor system comprising:a controller configured to:receive at least one first reactor core parameter distribution associated with a state of a core of a reference nuclear reactor;generate an initial fuel loading distribution for a simulated beginning-of-cycle (BOC) core of a nuclear reactor;select an initial set of positions associated with a set of regions within the simulated BOC core, at least one of the initial set of positions corresponding to one of the set of regions;generate an initial set of fuel design parameter values utilizing at least one design variable of at least one of the set of regions, wherein the at least one of the initial set of fuel design parameter values is associated with one of the set of regions of the simulated BOC core;calculate at least one second reactor core parameter distribution of the simulated BOC core utilizing the initial set of fuel design parameter values associated with the set of regions located at the initial set of positions; andgenerate a subsequent loading distribution by performing at least one perturbation process on the set of regions located at the initial set of positions in order to determine a subsequent set of positions for the set of regions, the subsequent set of positions defining the loading distribution for the simulated BOC core, wherein the subsequent set of positions reduce the difference between the at least one first reactor core parameter distribution and the at least one second reactor core parameter distribution below a selected tolerance level;the nuclear reactor, the nuclear reactor including a nuclear reactor core including a plurality of fuel assemblies; anda fuel handler configured to arrange at least one of the plurality of fuel assemblies according to the subsequent loading distribution determined by the controller. 35. The nuclear reactor system of claim 34, wherein the at least one first reactor core parameter distribution is associated with an equilibrium state of the core of the reference nuclear reactor. 36. The nuclear reactor system of claim 34, wherein the reference nuclear reactor includes at least one of a reference thermal nuclear reactor, a reference fast nuclear reactor, a reference breed-and-burn nuclear reactor, or a reference traveling wave reactor. 37. The nuclear reactor system of claim 34, wherein the at least one first reactor core parameter distributionincludes at least one of a power density distribution, a rate of change of the power density distribution, a reactivity distribution, or a rate of change of the reactivity distribution. 38. The nuclear reactor system of claim 34, wherein at least a portion of the simulated BOC core includes at least one of simulated recycled nuclear fuel, simulated unburned nuclear fuel, or simulated enriched nuclear fuel. 39. The nuclear reactor system of claim 34, wherein the simulated BOC core includes a plurality of simulated fuel assemblies. 40. The nuclear reactor system of claim 34, wherein the at least one of the initial set of positions corresponds to one of the set of regions. 41. The nuclear reactor system of claim 34, wherein generating the initial set of fuel design parameter valuesincludes utilizing a thermodynamic variable of the at least one of the set of regions. 42. The nuclear reactor system of claim 34, wherein generating the initial set of fuel design parameter valuesincludes utilizing a neutronic parameter of the at least one of the set of regions. 43. The nuclear reactor system of claim 34, wherein calculating the at least one second reactor core parameter distributionincludes calculating at least one of a power density distribution, a rate of change of the power density distribution, a reactivity distribution, or a rate of change of the reactivity distribution of the simulated BOC core. 44. The nuclear reactor system of claim 34, wherein the subsequent set of positions define the loading distribution for the simulated BOC core. 45. The nuclear reactor system of claim 34, wherein the fuel handler is communicatively coupled to the controller and is configured to arrange the at least one of the plurality of fuel assemblies in response to the controller generating the subsequent loading distribution. 46. The nuclear reactor system of claim 34, wherein the fuel handler is communicatively coupled to the controller and is configured to arrange the at least one of the plurality of fuel assemblies in response to a signal from a user input device. 47. The nuclear reactor system of claim 34, wherein the nuclear reactor includes at least one of a thermal nuclear reactor, a fast nuclear reactor, a breed-and-burn nuclear reactor, or a traveling waver nuclear reactor. 48. The nuclear reactor system of claim 34, wherein the fuel handler is configured to translate the at least one of the plurality of fuel assemblies from an initial location to a subsequent location according to the subsequent set of positions. 49. The nuclear reactor system of claim 34, wherein the fuel handler is configured to replace the at least one of the plurality of fuel assemblies according to the subsequent set of positions. |
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abstract | The present disclosure, in an embodiment, is a facility that includes a device configured to generate a beam having an energy range of 5 MeV to 500 MeV, a first radiation shielding wall surrounding the device, a second radiation shielding wall surrounding the first radiation shielding wall, radiation shielding fill material positioned between the first radiation shielding wall and the second radiation shielding wall forming a first barrier. In embodiments, the radiation shielding fill material includes at least fifty percent by weight of an element having an atomic number from 12 to 83, and a thickness of the first barrier is 0.5 meter to 6 meters. |
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050154346 | summary | BACKGROUND OF THE INVENTION This invention relates to the monitoring of thermal neutron flux within a nuclear reactor. More particularly, a new monitoring string having paired or grouped conventional local power range detectors and gamma thermometers is utilized, the disclosed utility including relating gamma thermometer output to a heat balance used for in-service life local power range detector calibration. In the nuclear reaction interior of conventional boiling water reactors (BWR), it is possible to monitor the state of the reaction by either the measurement of thermal neutron flux or alternatively gamma ray flux. Thermal neutron flux is the preferred measurement. As it is directly proportional to power and provides for a prompt (instantaneous) signal from a fission chamber. The alternative measurement of gamma radiation does not have the required prompt response necessary for reactor safety requirements. Consequently, gamma radiation as measured by gamma thermometers is not used to measure and immediately control the state of a reaction in boiling water nuclear reactors. Boiling water reactors have their thermal neutron flux monitored by local power range detectors. These local power range detectors include a cathode having fissionable material coated thereon. The fissionable material is usually a mixture of U235 and U234. The U235 is to provide a signal proportional to neutron flux and the U234 to lengthen the life of the detector. The thermal neutrons interact with the U235 and cause fission fragments to ionize an inert gas environment, typically argon, interior of the conventional local power range detector. There results an electric charge flow between the anode and cathode with the resultant DC current. The amperage of the DC current indicates on a substantial real time basis the thermal neutron flux within the reactor core. The boiling water reactor local power range detectors are inserted to the core of the reactor in strings. Each string extends vertically and typically has four spaced apart local power range detectors. Each detector is electrically connected for reading the thermal neutron flux in real time and for outputting the state of the reaction within the reactor. It is to be understood that a large reactor can have on the order of 30 to 50 such vertical strings with a total of about 120 to 200 local power range detectors. Such local power range detectors use finite amounts of U235 during their in-service life. Consequently the sensitivity changes with exposure. They must be periodically calibrated. Calibration is presently accomplished by using traversing in-core probes or (TIPs). These traversing in-core probes are typically withdrawn from the reactor, as the traversing in-core probes are of the same basic construction as the local power range detectors and thus change their sensitivity with in-service life due to uranium 235 burnup. In operation, the traversing in-core probes are typically calibrated. Such calibration includes inserting about five such probes separately to a common portion of a boiling water reactor. The boiling water reactor is operated at steady state and made the subject of an energy balance. The insertion of the traversing in-core probes occurs by placing the probes at an end of a semirigid cable and effecting the insertion within a tube system. Once a full core scan has occurred, during steady state operation, a heat balance is utilized in combination with the readings of the traversing in-core probes to calibrate the local power range detectors. Thereafter, the newly calibrated traversing in-core probes travel through the reactor in a specially designed tube system. This tube system constitutes through containment conduits into the interior of the reactor vessel. Into these conduits are placed semirigid cables which cables have the TIPs on the distal end thereof. The TIPs are driven into the drive tube system from large drive mechanisms and the entire system is controlled from an electronic drive control unit. The cables pass through so-called "shear valves" which valves can shear the cable and seal the conduit to prevent through the tube system leaks, which leaks may well be substantial before the cable and probes could be withdrawn. The cables further pass through stop valves admitting the traversing in-core probes to the interior of the vessel containment. Finally, the cables reach so-called indexers, and then to the interior of the reactor vessel. These indexers are a mechanical system for routing each of the TIPs to pass adjacent the site of an assigned segment of the 170 some odd local power range detectors in a large boiling water nuclear reactor. It is normal for an indexer to include 10 alternative paths for a single traversing in-core probe to follow during a calibration procedure. Needless to say, this system is elaborate and complex. Calibration of each local power range monitor is a function of the probe measurement of the local thermal neutron flux as well as a function of the position of the end of the inserting semirigid cable. Naturally, this position of the end of the semirigid cable has to be referenced to the proper alternative path for the necessary calibration to occur. Further, the necessary tube system includes a matrix of tubes below the reactor vessel. Normally these tubes must be removed for required below vessel service and replaced thereafter. Despite the presence of both stop valves and shear valves, the system remains as a possible escape route for water containing radioactive particles from the reactor. Further, the withdrawn cable can have mechanical complications as well as being radioactive. Gamma thermometers are known. These thermometers measure the gamma ray output from a reactor reaction. Unfortunately, gamma ray output as measured by gamma thermometers does not provide a prompt response to power transients as required for safe operation of the reactor. Consequently, gamma thermometers have not been heretofore used for monitoring core reactive state in boiling water reactors. SUMMARY OF THE INVENTION In the core of a boiling water nuclear reactor, local power range monitor strings typically including four vertically spaced monitoring sites are modified. Each monitoring site includes a conventional local power range detector in which fissionable material exposed to thermal neutron radiation produces fission fragments, ionizes a gas and produces a current between the anode and cathode. In the improvement herein, each conventional local power range detector is provided with one or two adjacent gamma thermometers each including an interior mass to be heated by gamma radiation, a thermocouple for measuring the heated mass and a reference thermocouple connected in series. Both the conventional local power range detector and the gamma thermometer(s) are distributed along the length of the string each being provided with a cable and connector for external connection. When the string is inserted into the core and the reactor operated at a steady state, the gamma thermometers can be utilized to calibrate the local power range monitors in conjunction with a conventional reactor heat balance. By the expedient of referencing the gamma flux to the output of the heat balance, calibration of the local power range monitors occurs over their useful in-service life. OTHER OBJECTS, FEATURES AND ADVANTAGES An object to this invention is to vastly simplify the local power range monitor calibration system. Accordingly, a new so-called "monitor" string is disclosed in which conventional local power range detectors for the measurement of thermal neutron flux are placed immediately adjacent to gamma thermometers. An advantage of the disclosed construction is that the gamma thermometers are not appreciably sensitive with prolonged in-service life. Accordingly, and during the steady state operation of the reactor, the gamma thermometers can be used with supplemental heat balances for the required calibration of their adjacent local power range monitors. A further object to this invention is to disclose a process for the calibration of local power range monitors within a boiling water nuclear reactor. According to this aspect, the reactor is operated at a steady state and a heat balance taken to determine overall reactor output. Thereafter, the gamma thermometers are read for gamma flux and the gamma flux related to reactor power. Corresponding readings are taken from the local power range detectors. These readings, which readings vary with in-service life, are calibrated to the gamma thermometer results. A reliable periodic calibration of the local power range detectors by their adjacent gamma thermometers can occur. An advantage is that the need for the traversing in-core probe of the prior art is obviated. Accordingly, the system of drive mechanisms, drive control units, tubes, stop valves, shear valves, indexers, and cables utilized in the prior art for periodic calibration can be removed. |
description | This is a continuation, under 35 U.S.C. §120, of copending international application No. PCT/EP2007/001052, filed Feb. 8, 2007, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2006 007 591.9, filed Feb. 18, 2006; the prior applications are herewith incorporated by reference in their entirety. The invention relates to a fuel assembly for a pressurized-water nuclear reactor, as is known, for example, from German patent No. DE 103 34 580 B3. The basic design of a fuel assembly for a pressurized-water nuclear reactor is illustrated by way of example in FIG. 6. In the fuel assembly of this type, a large number of fuel rods 2 are guided parallel to one another in the rod direction (axially) by a plurality of spacers 4 which are axially spaced apart from one another and in each case form a two-dimensional grid with a plurality of cells 6 arranged in columns 8 and rows 10. As well as the fuel rods 2, at selected positions support tubes, which do not contain any fuel and are intended to receive and guide control rods (known as control rod guide tubes 12), are also guided through the cells 6 of this grid. Moreover, there may also be support tubes, which likewise do not contain any fuel and serve only to increase the stability (instrumentation thimbles or structure tubes; in the fuel assembly 2 illustrated by way of example neither instrumentation thimbles nor structure tubes are provided). These support tubes, unlike the fuel rods, are welded to the spacers 4 in the cells 6, so that their stabilizing action is ensured throughout the entire life span of the fuel assembly 2. In the event of hypothetical external accidents, for example in the event of an earthquake or a loss of coolant accident (LOCA) with a major leak, the spacers may be subject to a considerable impact load from the adjacent fuel assemblies. The permanent deformations which then occur and are usually noticed as formationing of individual rows or columns must not exceed maximum permissible values, in order to ensure that the control rods can still be introduced into the control rod guide tubes in order in this way to allow operation to continue safely or to allow the plant to be shut down safely. Whereas plastic deformations to a limited extent are in principle permitted, accordingly relatively extensive buckling, which leads to a significant offset of the control rod guide tubes arranged in the fuel assembly, must be avoided. Accordingly, the spacers are configured in such a way that the expected impact loads do not lead to relatively extensive buckling or formationing of the spacer. In practice, the development aim is a buckling resistance for fresh, unirradiated spacers (BOL (=beginning of life) spacers) of approximately 20 kN. Therefore BOL spacers can withstand the impact load (areally active transverse force) which occurs in the event of an accident (earthquake, LOCA) provided that this impact load is lower than 20 kN. In particular spacers which have been in use for a relatively long period of time and have reached the end of their service life (EOL=end of life) can still experience, in unfavorable situations, forces which are greater than their buckling resistance, since the latter can be significantly reduced compared to new spacers. This reduction in the buckling resistance is in this case dependent on the particular type of spacer and may amount to more than 50 to 60%. German patent DE 103 34 580 B3, corresponding to U.S. Patent Application Publication No. US 2006/0285629 A1, therefore proposes, in order to improve the accident safety, to configure the spacer such that, when a limit force acting laterally on the spacer is exceeded, only a region of the spacer whose cells are located outside an internal region which contains the control rod guide tubes begins to deform. This deformation behavior can be achieved in that the spacer outside the internal region is configured to be mechanically weaker. It is accordingly an object of the invention to provide a fuel assembly for a pressurized-water nuclear reactor which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which has a high accident safety and good thermohydraulic characteristics. With the foregoing and other objects in view there is provided, in accordance with the invention, a fuel assembly for a pressurized-water nuclear reactor. The fuel assembly contains a plurality of axially spaced spacers in each case forming a square grid. The spacers have grid webs defining a plurality of cells disposed in rows and columns. A plurality of fuel rods are guided in the axially spaced spacers and control rod guide tubes are provided. In each case one of the control rod guide tubes is guided through a number of the cells. At least one of the spacers has a first partial region configured mechanically stronger than a second partial region and has in the second partial region at least one resistance body projecting into a flow subpassage, formed between the fuel rods. The resistance body increases a flow resistance and counteracts a reduction in the flow resistance in the second partial region caused by the second partial region being mechanically weaker. According to these features, and starting from the fuel assembly known from German patent DE 103 34 580 B3 in which at least one spacer is configured with a first partial region being mechanically stronger than a second partial region, at least one resistance body is provided in the second partial region. The resistance body projects into a flow subpassage that is formed between the fuel rods, and increases the flow resistance which counteracts a reduction of the flow resistance in the second partial region, which reduction accompanies the mechanically weaker configuration. The invention is now based on the findings that the weaker configuration of the spacer in the edge region, which can be achieved by way of example by reducing the wall thickness of the grid webs in the edge region or by reducing the number or extent of the weld spots where the grid webs are welded together, results in the flow resistance of the spacer in the weakened external regions being smaller than in the internal region. In other words, the mechanical inhomogeneity of the spacer, introduced in order to improve the EOL behavior, can bring about a hydraulic inhomogeneity, i.e. a heterogeneous distribution of the loss of pressure occurring from the flow of the coolant through the spacer in the axial direction of the fuel rods. Increasing the flow resistance in the second partial region which is configured to be mechanically weaker according to the invention in a targeted manner, locally increases the pressure loss there such that the hydraulic inhomogeneities, which occur on account of the differing mechanical configurations in the first and second partial regions, are reduced. In other words, despite an inhomogeneity of the mechanical configuration of the spacers, the measures according to the invention achieve a large degree of homogeneity in the pressure loss produced via the spacers. It is preferably desired here to configure the resistance body or bodies such that the reduction, accompanying the mechanically weaker configuration, in the flow resistance in the second partial region is at least approximately compensated for. The resistance bodies are preferably disposed at a point of intersection of the grid webs, i.e. in the center of a flow subpassage formed by four neighboring fuel rods. Such a central arrangement, in particular one in the region of the edge of a grid web, of the resistance bodies can be used to produce local flow profiles in a particularly simple manner, which flow profiles run rotation-symmetrically around the center of the flow subpassage such that the resistance bodies do not produce flow patterns which bring about forces which act transversely to the flow direction of the coolant on the fuel assembly. The resistance bodies can be a separate component which is welded together with at least one of the grid webs. Alternatively to this, the resistance bodies can also, in a particularly simple manner in terms of manufacturing technology, be in the form of a shaped section introduced into the grid webs. The cells of the spacer are preferably formed by grid edge webs disposed on the edge and by internal grid webs which are located inside, wherein the term grid web can refer to both grid edge webs and internal grid webs below in the following text. The edge zone or the second partial region in which such mechanical weakening is carried out is then formed from the internal grid webs located outside the internal region, from the ends, which project outwardly beyond the internal region, of the internal grid webs passing through the internal region and from the grid edge webs. The grid webs are preferably connected to one another by way of weld connections, wherein at least some of the weld connections of the internal grid webs outside the first partial region have a lower stability than the weld connections of the internal grid webs inside the first partial region. In an advantageous embodiment of the invention, at least some of the internal grid webs have a material weakening in a web region located outside the first partial region with respect to the web regions arranged inside the internal region, wherein the material weakening is brought about in particular by a smaller wall thickness (web width) of the internal grid webs. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a fuel assembly for a pressurized-water nuclear reactor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a spacer 4 constructed from grid webs 141-1417 and 161-1617 which are welded together at points of intersection. The grid webs 141, 1417, 161 and 1617 form an edge of the grid and are denoted as grid edge webs below. The grid webs 142-1416 and 162-1616 extend inside the grid and are denoted as internal grid webs below. The intersecting grid webs 141-1417 and 161-1617 form a square grid with a large number of (in the example 16×16) cells 6, by way of which webs the fuel rods 2 are guided in the cells 6 through which support tubes do not pass, only a few of the fuel rods being illustrated in FIG. 1 for clarity reasons. In each case four neighboring fuel rods 2 determine a flow subpassage 17 through which the coolant flows parallel to the fuel rods 2 (axially) and thus perpendicular to the drawing plane. In the exemplary embodiment, all the support tubes are control rod guide tubes 12. Further structure tubes are not present in this exemplary embodiment. The control rod guide tubes 12 determine a first partial region 18 (highlighted by hatching) which is formed in the exemplary embodiment by a square internal region which is limited by the internal grid webs 143, 1415, 163 and 1615 and contains the internal grid webs 143, 1415, 163 and 1615. The first partial region 18 is surrounded by a second partial region 19, which in FIG. 1 is an edge region containing two columns 8 and rows 10. The spacer 4 is now of a mechanically stronger configuration, according to German patent DE 103 34 580 B3, in its first partial region 18 than in the second partial region 19. The technical measures which are necessary for such a stronger configuration of the first partial region 18 or, if viewed from the opposite point of view, a weaker configuration of the second partial region 19—variation in thickness or number of weld points, increase or decrease of the wall thickness of the grid webs, introduction of instances of material weakening, for example in the form of cutouts in the web regions of the second partial region 19—would now result in the flow resistance of the spacer 4 in the first partial region 18 being larger than in the second partial region 19, so that the pressure loss produced by the spacer 4 in the coolant which flows parallel to the axial direction of the fuel rods 2, i.e. perpendicular to the grid plane, would become inhomogeneous. In this manner, pressure gradients in the grid plane which extends perpendicular to the axial direction of the fuel rods would be produced and would lead to undesired transverse flows. In order to avoid this inhomogeneity, the invention therefore provides measures in the second partial region 19 with which the reduction of the flow resistance is largely compensated for. This is illustrated FIG. 1 with the aid of the points which are characterized by a black circle and which indicate that flow subpassages 17, which are located outside the first partial region 18, are provided, in the region of the internal grid webs 162-1616 and 142-1416 which intersect there, with a resistance body 20 which increases the flow resistance in these flow subpassages 17 without canceling out the mechanical weakening which was introduced deliberately, according to German patent DE 103 34 580 B3, in the internal grid webs 142-16 and 162-16 which extend in the second partial region 19. In the exemplary embodiment according to FIG. 2, such an increase in the flow resistance at a point of intersection which is located in the second partial region 19 is achieved in the spacer 4 which is made of double-walled grid webs 14i, 16i in that each metal-sheet strip of an internal grid web 16i exhibits at its upper edge (in the fuel assembly which is inserted vertically in the core) in the region of the point of intersection a buckling or a formation 20a which is inclined into the flow subpassage 17 associated with this point of intersection or into the inside of the respectively adjoining cell 6. These formations 20a have an approximately triangular shape. The internal grid web 142 or 1416, which intersects the internal grid web 16i, has in this region an approximately V-shaped cutout 24 and is welded, at its base, to the internal grid web 16i. The weld connection is configured, according to the procedure proposed in German patent DE 103 34 580 B3, to be weaker than the weld connections present in the first partial region 18. This is illustrated in FIG. 2 by way of a weld node 26 which has a smaller diameter than the weld nodes 27 (drawn in FIG. 2 at a neighboring point of intersection in an exaggerated and schematic manner) which are present in the first partial region 18 in order to in this manner produce a targeted weakening of the mechanical stability in the second partial region 19. Formations 20a, of which only one formation 20a can be seen in FIG. 2, are also attached on the lower edge, which lies opposite the upper edge, to the internal grid web 142 or 1416. The small weld node 26, by way of which the intersecting grid webs 16i and 142,16 are welded together, is also located here on the base of the V-shaped cutout 24. A coolant K flowing (axially) in the direction of arrow 30 is deflected at the formations 20a such that a flow component is formed which is directed parallel to the grid plane, as is illustrated in FIG. 2 by arrows 32. The deflection is oriented here in pairs in opposite directions such that the transverse force which is produced by the deflection of the flow onto the spacer and thus onto the fuel assembly disappears. In the exemplary embodiment according to FIG. 3, triangular formations 20b, which cause a swirl around the central axis of the flow subpassage 17 in the flowing coolant on the remote flow side, are likewise provided in the region of the point of intersection both at the upper edge and on the lower edge of the grid webs 142(16), 16i in a spacer 4 which is made of single-wall grid webs 142(16), 16i. The internal grid webs 142(16) and 16i are welded together by weld nodes 27 in the region of the upper edge, the extent of the weld nodes and the associated mechanical stability of the weld connection being comparable with the weld nodes used in the first partial region. In this exemplary embodiment, the targeted mechanical weakening in the second partial region is achieved by reducing the number of weld nodes 27 and thus the stability of the weld connection. This is illustrated by the absence of a weld node—illustrated in FIG. 3 by dashes—on the lower edge. In the exemplary embodiments according to FIGS. 4 and 5, the resistance bodies are formed by plate-type components 20c and 20d which are separately welded together with the internal grid webs 142(16) and 16i with in each case four weld nodes 26, which components have, in the exemplary embodiment according to FIG. 4, an approximately cross-type shape and in the exemplary embodiment according to FIG. 5 have a circular disk-type shape. The internal grid webs 142(16) and 16i are in this case provided at the points of intersection with cutouts into which the components 20c, 20d are inserted such that their flat side, which faces away from the support face, lies in the same plane as the upper edge or lower edge of the grid webs 142,16 and 16i. In the exemplary embodiment according to FIG. 4, the targeted weakening of the second partial region is effected by a material weakening caused by cutouts 36, whereas in the exemplary embodiment according to FIG. 5, the internal grid webs 142 and 1416 which extend completely in the second partial region (and, analogously, the internal grid webs 162 and 1616) have a smaller wall thickness than the other grid webs. The invention is not limited to fuel assemblies with the square 16×16 spacer illustrated in the exemplary embodiment, but can also be used in fuel assemblies with other spacer geometries. |
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claims | 1. A system, comprising:a nuclear reactor chamber comprising an inlet portion;wherein the chamber is part of a nuclear power plant,at least one container,wherein each respective container of the at least one container contains liquid nitrogen and boron powder,wherein each respective container comprises an outlet portion in fluid communication with said inlet portion; andat least one valve associated with the at least one container,wherein each respective container is associated with a respective valve of the at least one valve,wherein opening of the at least one valve causes both liquid nitrogen and boron powder to flow from at least one respective container of the at least one container into the chamber. 2. The system of claim 1 wherein a first container has a first volume; and the system further comprising a second container containing liquid nitrogen, the second container having a second volume greater than the first volume, the second container in fluid communication with the at least one container. 3. The system of claim 2, further comprising an apparatus configured to produce liquid nitrogen, the apparatus configured to produce liquid nitrogen is in fluid communication with the first container. 4. The system of claim 2, wherein the boron powder is added into the first container, the boron powder is ejected into the nuclear reactor chamber along with the flow of liquid nitrogen from the first container to the nuclear reactor chamber. |
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039322165 | abstract | A typical embodiment of the invention provides an efficient aid in positioning fuel elements in a nuclear reactor core. The corner edges of the peripheral band that binds the fuel element grid structure together, as well as the ends of the individual grid plates that protrude beyond the last marginal rows of fuel rods in each of the fuel elements are chamfered or bevelled. Thus, when fuel elements are being inserted, relocated or withdrawn from a reactor core the sloping edges of the grid structures in adjacent elements slide past without locking together or otherwise undesirably engaging each other. |
054147468 | abstract | An X-ray exposure mask comprises an X-ray transmission layer and an X-ray absorption layer formed on the X-ray transmission layer and being patterned. The X-ray absorption layer has a first region having a first thickness and a second region having a second thickness less than the first thickness. |
claims | 1. A method of stabilizing a fuel containing a reactive sodium metal, comprising:puncturing a cladding of a fuel pin enclosing the fuel containing the reactive sodium metal to form an injection passage and an extraction passage;injecting a reaction gas into the fuel pin through the injection passage to react with the reactive sodium metal to form a stable sodium compound;measuring a ratio of a product gas and a remaining quantity of the reaction gas exiting the fuel pin through the extraction passage, the product gas being a reaction product of the reaction gas and the reactive sodium metal within the fuel pin; andsealing the injection passage and the extraction passage so as to confine the stable sodium compound within the fuel pin once the ratio indicates that a reaction between the reaction gas and the reactive sodium metal is complete. 2. The method of claim 1, wherein the puncturing includes orienting the fuel pin in a vertical position such that the injection passage and the extraction passage are formed on a planar end of the fuel pin. 3. The method of claim 1, wherein the puncturing includes orienting the fuel pin in a horizontal or vertical position such that the injection passage and the extraction passage are formed on a curved surface of the fuel pin. 4. The method of claim 1, wherein the injecting a reaction gas includes introducing at least one of an oxygen-containing gas and a halogen gas. 5. The method of claim 1, wherein the injecting a reaction gas includes introducing at least one of carbon dioxide (CO2), oxygen (O2), methane (CH4), and chlorine (Cl2). 6. The method of claim 1, wherein the injecting involves forming at least one of Na2O and NaCl from the reactive sodium metal. 7. The method of claim 1, wherein the sealing includes closing the injection passage and the extraction passage by welding. 8. The method of claim 1, further comprising:venting an existing gas from the fuel pin after the puncturing a cladding and prior to the injecting a reaction gas. 9. The method of claim 8, wherein the venting an existing gas includes extracting a radioactive gas from the fuel pin. 10. The method of claim 8, wherein the venting an existing gas includes removing fission product gases from the fuel pin. 11. The method of claim 1, further comprising:purging the fuel pin with an inert gas after the measuring a ratio and prior to the sealing the injection passage and the extraction passage. 12. The method of claim 11, wherein the purging includes introducing at least one of argon, nitrogen, and helium. |
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051714833 | abstract | A method for the long term storage of radioactive hazardous waste in a hollowed out chamber of salt bed in which sealed, relatively incompressible containers of hazardous materials are immobilized in a regular spaced array with the remaining space in the chamber filled with a granular compressive load equalization medium. |
abstract | A method for the production of a mirror element (10) that has a reflective coating (10a) for the EUV wavelength range and a substrate (10b). The substrate (10b) is pre-compacted by hot isostatic pressing, and the reflective coating (10a) is applied to the pre-compacted substrate (10b). In the method, either the pre-compacting of the substrate (10b) is performed until a saturation value of the compaction of the substrate (10b) by long-term EUV irradiation is reached, or, for further compaction, the pre-compacted substrate (10b) is irradiated, preferably homogeneously, with ions (16) and/or with electrons in a surface region (15) in which the coating (10a) has been or will be applied. A mirror element (10) for the EUV wavelength range associated with the method has a substrate (10b) pre-compacted by hot isostatic pressing. Such a mirror element (10) is suitable to be provided in an EUV projection exposure system. |
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053717740 | summary | BACKGROUND AND SUMMARY The invention relates to X-ray systems and X-ray lithography utilizing synchrotron radiation, and more particularly to an X-ray lithography beamline imaging system. The invention also relates to commonly owned U.S. Pat. No. 5,031,199, incorporated herein by reference. In the manufacture of microelectronic devices, photolithographic techniques are commonly utilized. To obtain greater resolution in the formation of microstructures than can be obtained with visible light wavelengths, efforts have been made to use shorter wavelength radiation, particularly X-rays. To achieve adequate resolution, for example, 0.25 micron lithography, the beam of X-rays must display high spectral and spatial uniformity at the plane of the wafer being exposed. Synchrotrons are particularly promising X-ray sources for lithography because they provide a very stable and defined source of X-rays. The electrons orbiting inside the vacuum enclosure of the synchrotron emit electromagnetic radiation as they are bent by the magnetic fields used to define the path of travel. This electromagnetic radiation is an unavoidable consequence of changing the direction of travel of the electrons and is typically referred to as synchrotron radiation. The energy that the electrons lose in the form of synchrotron radiation must be regained at some point in their orbit around the ring, or they will spiral in from the desired path and be lost. Orbiting electrons can also be lost through collisions with residual gas atoms and ions within the vacuum chamber. Thus, ultra-high quality vacuums are necessary to obtain satisfactory lifetimes of the stored beam. Synchrotron radiation is emitted in a continuous spectrum of "light", ranging from radio and infrared wavelengths upwards through the spectrum, without the intense, narrow peaks associated with other sources. The shape of a spectral curve of a representative synchrotron storage ring, the Aladdin ring, is shown in FIG. 1. FIGS. 1-4 and a portion of FIG. 5 of incorporated U.S. Pat. No. 5,031,199 are reproduced herein as FIGS. 1-5, respectively, and use like reference numerals where appropriate to facilitate understanding. All synchrotrons have similar curves as in FIG. 1 that define their spectra, which vary from one another in intensity and the critical photon energy. The critical photon energy E.sub.c is determined by the radius of curvature of the path of the electrons and their kinetic energy and is given by the relationship: ##EQU1## where R.sub.m is the bending radius, m.sub.e is the electron's rest mass, h is Plank's constant, E.sub.e is the energy of the electron beam and c is the speed of light. Half of the total power is radiated above the critical energy and half below. The higher the kinetic energy of the electrons, or the steeper the bend of the orbit, the higher the critical photon energy. By knowing this information, the synchrotron can be designed to match the spectral requirements of the user. Parameters describing the size of the source of synchrotron radiation and the rate at which it is diverging from the source are also of importance. Since the electrons are the source of synchrotron radiation, the cross section of the electron beam defines the cross section of the source. Within the plane of the orbit the light is emitted in a broad, continuous fan, which is tangent to the path of the electrons, as illustrated in FIG. 2--which shows a section of a synchrotron 20 having an orbiting electron beam 21 and a fan of synchrotron radiation indicated by the arrows 22. FIG. 3 shows the distribution of the flux of the synchrotron radiation at a plane perpendicular to the plane of the ring, with the distribution of flux indicated by the density of the dots shown within the box 25 in FIG. 3. The flux is substantially uniform horizontally, as shown in the graph at 26, and exhibits a Gaussian distribution profile vertically as shown by the graph 27 in FIG. 3. Because of the relatively small height and width of the electron beam, it acts as a point source of radiation, providing crisp images at an exposure plane which is typically 8 meters or more away from the ring. However, at a distance of 8 meters a 1 inch wide exposure field typically collects only 3.2 milli-radians of the available radiation. There are two ways to improve the power incident at a photo-resist: either shorten the beamline or install focusing elements. The use of focusing elements has the potential advantage of collecting X-rays from a very wide aperture and providing a wide image with a very small vertical height. However, the use of focusing elements results in a loss of power at each element because of low reflectivity of the X-rays and introduces aberrations. To operate within acceptable values of reflectivity and maximize the delivered power, it is necessary to work at grazing angles (i.e., at angles of incidence e from a normal to the surface such that 86.degree. .ltoreq..THETA..ltoreq.89.5.degree. ). Furthermore, because synchrotron radiation is emitted in a horizontal fan, the use of grazing incidence optics is particularly suitable. The small vertical divergence of the synchrotron radiation implies that a wide horizontal mirror can accept a large fan of light at a small grazing angle without being unacceptably long. The optical system (beamline) must deliver uniform power over the exposure area, typically 2 inches horizontally by 1 inch vertically. This can be achieved by (a) expanding the X-ray beam or (b) scanning the X-ray beam across the image. The first approach is not compatible with vacuum isolation. The present invention is well suited to the second approach, both in the form of mask-wafer scanning and beam rastering. An X-ray lithography beamline suitable for production purposes should deliver a stable and well characterized flux of X-rays to the exposure field. Desirable characteristics for an X-ray lithography beamline for production purposes include uniform power density over the entire scan region, large collection angle near the source, minimal losses of useful X-rays, a modular optical package with stable, inexpensive recoatable optical elements, and an exposure field measuring at least 1 inch by 1 inch and preferably 2 inches by 2 inches. Various beamline designs have been proposed for use in X-ray lithography. These include straight-through transmission systems, for example as in B. Lai et al, "University of Wisconsin X-Ray Lithography Beamline: First Results" Nucl. Instrum. Methods A 246, pp. 681 et seq., (1986); H. Oertel et al, "Exposure Instrumentation For the Application of X-Ray Lithography Using Synchrotron Radiation", Rev. Sci. Instrum. 60(7), pp. 2140 et seq., 1989. Other systems have utilized planar optics to provide scanning and filtering capabilities. See, H. Betz, "High Resolution Lithography Using Synchrotron Radiation", Nucl. Instrum. Methods A 246, pp. 659 et seq., 1986; P. Pianetta et al, "X-Ray Lithography and the Stanford Synchrotron Radiation Laboratory", Nucl. Instrum. Methods A 246, pp. 641 et seq., 1986; S. Qian et al, "Lithography Beamline Design and Exposure Uniformity Controlling and Measuring", Rev. Sci. Instrum. 60(7) pp. 2148 et seq., 1989; E. Bernieri et al, "Optimization of a Synchrotron Based X-Ray Lithographic System", Rev. Sci. Instrum. 60(7), pp. 2137 et seq., 1989; U.S. Pat. No. 4,803,713 to K. Fujii entitled "X-Ray Lithography System Using Synchrotron Radiation"; E. Burattini et al, "The Adone Wiggler X-Ray Lithography Beamline", Rev. Sci. Instrum. 60(7), pp. 2133 et seq., 1989. The use of single figured mirrors is proposed in the article by J. Warlaumont, "X-Ray Lithography in Storage Rings", Nucl. Instrum. Methods A 246, pp. 687 et seq., 1986. Other proposed systems include the use of Bragg reflections from crystalline surfaces as described in U.S. Pat. No. 4,028,547 entitled "X-Ray Photolithography" and microfabricated structures as described by R. J. Rosser, "Saddle Toroid Arrays: Novel Grazing Incidences Optics for Synchrotron X-Ray Lithography", Blackett Laboratory, Imperial College, London, England. In an X-ray lithography system, the X-rays are directed through an X-ray mask and onto the photo-resist in those areas which are not shadowed by the non-transmissive pattern formed on the X-ray mask. Generally, the mask will consist of a thin substrate layer which is overlaid by an X-ray absorbing material in the desired pattern. The transmission of the X-ray mask substrate and the absorption of the photo-resist can be used to define the efficiency of the mask/resist system. Low energy X-rays striking the mask substrate are readily absorbed by the substrate material and never make it to the photo-resist. The energy of these absorbed photons goes into heating the mask, which can lead to undesirable side effects as expansion and distortion of the mask. Very high energy X-rays pass through the mask substrate, the absorber, and the photo-resist with few of the interactions that lead to image formation, reducing the usefulness of these photons. On the other hand, those high energy photons that do interact with the photo-resist may have passed through the absorber or "dark" areas of the pattern on the mask, thus reducing the contrast of the image produced in the resist. The product of the mask transmission and the photoresist absorption defines the system response. Thus, it is preferable that the X-ray flux which reaches the X-ray mask be mainly composed of photons which have an energy which lies in an optimal energy region referred to as the "Process Window". The Process Window will vary depending on the mask substrate and the photo-resist chosen, but in general the Process Window will be in the range of 600 eV to 2000 eV, as illustrated in FIG. 4 for the case of the 2 micron thick polycrystalline silicon mask substrate and a 1 micron thick Novolack photo-resist. Various beamline designs have been implemented in the prior art, including two and three mirror systems, and a single cylindrical mirror system. The X-ray optics involve simple surfaces such as spherical, cylindrical, elliptical or toroidal. Such surfaces are all symmetrical about an axis. When the requisite imaging does not have a symmetrical property, however, single and symmetric surfaces cannot meet the imaging requirement. Thus, multiple surfaces have been used to correct each others'aberration and deliver required uniformity. In incorporated U.S. Pat. No. 5,031,199, an X-ray beamline apparatus receives synchrotron radiation X-rays and collects and focuses the beam utilizing two grazing incidence X-ray mirrors which sequentially deflect the beam. The first or entrance mirror is a toroidal mirror which is concave along its length and width. It acts to collect the diverging fan of synchrotron radiation and to collimate partially the X-rays horizontally. The second or refocusing mirror is a concave-convex mirror which is concave in length but convex along its width. The refocusing mirror acts to collimate the light horizontally and to focus the light vertically. The curves of the reflecting surfaces of the two mirrors act in concert to provide a substantially uniform image with uniform power distribution. The two radii of curvatures of the two mirrors, the distance of separation between them, and the inclination angle of the refocusing mirror provide 6 degrees of freedom that can be used to optimize the shape of the image at the exposure field. Parameters of the two mirrors work in concert to produce a better shaped image than either mirror alone. In addition to focusing and collimating the beam, the two mirrors serve to attenuate the high energy photons, e.g., those above approximately 2,200 electron volts (eV). Low energy photons (below 600 eV) are attenuated by a window closing the end of the beamline, preferably formed of beryllium, although a variety of other materials may be used for the window, such as silicon, silicon nitride, silicon carbide and diamond. The beamline system effectively acts as a bandpass filter of photon energies to provide a spectral through-put that closely matches the desired Process Window, resulting in excellent carrier/absorber contrast and good photo-resist response, while simultaneously reducing the heat load on the mask. To obtain scanning of the beam across the image field, a third flat mirror may be interposed in the beamline. This mirror is mounted to pivot slightly about an axis perpendicular to the beam at a low grazing angle of incidence to deflect the beam across the image field as desired. Each of the mirrors is preferably housed within its own self-contained vacuum chamber, with sectioning dual gate valves between these chambers providing the capability of isolating an individual component. Each element of the system can be removed for modification, maintenance or repair without affecting the other elements. Very slight changes in the location and tilt of the two toroidal mirrors can be used to alter the distance to the final image without compromising either the power or the uniformity of the image shape. The resulting beam at the image plane is very sharply defined and substantially uniform in flux across the horizontal width of the beam. Variations in flux across the beam can be compensated, if desired, in various ways, including, but not limited to, profiling the thickness of the exit window to achieve greater attenuation at some areas of the beam than in others, by using variable thickness filters and by using shaped beam apertures. The present invention provides an X-ray lithography beamline imaging system utilizing a single mirror, and satisfies the imaging requirement with an aspherical reflecting surface. The reflecting surface has symmetry only about a plane, and does not have axial symmetry. The surface function is described by polynomials. |
052710467 | abstract | A nuclear power plant includes a primary loop having a vessel with a connection piece. A manipulator for working in the vicinity of the connection piece, especially for non-destructive testing, includes two trolleys being moveable circumferentially of the connection piece. A jointed-shank arm disposed on the trolleys has two shanks each having first and second ends. Hinged supports are each disposed on a respective one of the trolleys and each support the first end of a respective one of the shanks. A crown hinge joins the second ends of the shanks together. A support for a tool or a test head is mounted on the crown hinge. A process for carrying out work in the connection-piece region with a maneuvering unit includes adjusting a position of each of the trolleys with a respective drive motor, pressing the tool or test head against a wall of the vessel with spring means acting upon the shanks, such as pneumatic or hydraulic cylinders, and maneuvering the crown hinge into a predetermined position and/or over a predetermined path by varying the position of at least one of the trolleys with a control device acting upon the drive motors. |
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claims | 1. An electron beam irradiation apparatus comprising an electron beam system for directing electrons into an irradiation zone, the electron beam system and the irradiation zone being configured for irradiating outwardly exposed surfaces of a 3-dimensional article passing through the irradiation zone from different directions with electrons from the electron beam system, the electron beam system comprising multiple electron beam emitters having at least one opposed pair of electron beam emitters which are positioned to irradiate the irradiation zone with electrons; and an adjustment system capable of moving the electron beam emitters for changing the position of the electron beam emitters relative to the article. 2. The apparatus of claim 1 in which the adjustment system is capable of moving the electron beam emitters towards or away from the irradiation zone. claim 1 3. The apparatus of claim 2 in which the adjustment system is capable of rotating the electron beam emitters about the irradiation zone. claim 2 4. The apparatus of claim 3 in which the adjustment system includes an adjustable rotating mechanism capable of rotating the electron beam emitters about the irradiation zone. claim 3 5. The apparatus of claim 3 in which the electron beam system comprises four electron beam emitters. claim 3 6. The apparatus of claim 5 in which the electron beam emitters are positioned in first and second opposed pairs. claim 5 7. The apparatus of claim 6 in which the second opposed pair is downstream from the first opposed pair. claim 6 8. The apparatus of claim 2 in which the adjustment system includes an adjustable linear mechanism capable of moving the electron beam emitters towards or away from the irradiation zone. claim 2 9. The apparatus of claim 1 further comprising a conveyance system for conveying the article through the irradiation zone, the conveyance system being configured to allow the article to be irradiated with electrons on the outwardly exposed surfaces. claim 1 10. The apparatus of claim 9 in which the article is a continuous profile, the conveyance system including at least one roller positioned beyond the irradiation zone for conveying the profile through the irradiation zone. claim 9 11. The apparatus of claim 1 in which the apparatus cures coatings on said surfaces of the article. claim 1 12. The apparatus of claim 1 in which the apparatus sterilizes said surfaces of the article. claim 1 13. The apparatus of claim 1 in which the apparatus provides surface modification of said surfaces of the article. claim 1 14. The apparatus of claim 1 in which the electron beam system provides electrons from opposing directions. claim 1 15. The apparatus of claim 14 in which the electron beam system comprises two opposed electron beam emitters separated from each other by a gap. claim 14 16. The apparatus of claim 15 in which the conveyance system comprises two conveyor belts for conveying the article between the opposed electron beam emitters through the gap therebetween, the conveyor belts being spaced apart from each other in tho region of the gap so that the article passing between the electron beam emitters can be frilly irradiated by the electrons. claim 15 17. An electron beam irradiation apparatus for curing coatings on a continuously moving 3-dimensional profile comprising: an electron beam system for directing electrons into an irradiation zone, the electron beam system and the irradiation zone being configured for irradiating outwardly exposed surfaces of the profile passing through the irradiation zone with electrons from the electron beam system for curing coatings thereon, the electron beam system including multiple electron beam emitters having at least one opposed pair of electron beam emitters which are positioned to irradiate the irradiation zone with electrons each from a different direction; and an adjustment system capable of moving the electron beam emitters for changing the position of the electron beam emitters relative to the article. 18. An electron beam irradiation apparatus for sterilizing a 3-dimensional article comprising an electron beam system for directing electrons into an irradiation zone, the electron beam system and the irradiation zone being configured for irradiating outwardly exposed surfaces of the 3-dimensional article passing through the irradiation zone from different directions with electrons from the electron beam system to sterilize said surfaces, the electron beam system comprising multiple electron beam emitters having at least one opposed pair of electron beam emitters which are positioned to irradiate the irradiation zone with electrons; and an adjustment system capable of moving the electron beam emitters for changing the position of the electron beam emitters relative to the article. 19. An electron beam irradiation apparatus comprising: an electron beam system comprising multiple electron beam emitters having at least one opposed pair of electron beam emitters for directing electrons into an irradiation zone, the electron beam system and the irradiation zone being configured for irradiating an article passing through the irradiation zone with electrons from the electron beam system; and an adjustment system capable of moving the electron beam emitters for changing the position of the electron beam emitters relative to the article. 20. The apparatus of claim 19 in which the adjustment system is capable of moving the electron beam emitters towards or away from the irradiation zone. claim 19 21. The apparatus of claim 20 in which the adjustment system is capable of rotating the electron beam emitters about the irradiation zone. claim 20 22. A method of forming an electron beam apparatus comprising: providing an electron beam system for directing electrons into an irradiation zone; configuring the electron beam system and the irradiation zone for irradiating outwardly exposed surfaces of a 3-dimensional article passing through the irradiation zone from different directions with electrons from the electron beam system, the electron beam system comprising multiple electron beam emitters having at least one opposed pair of electron beam emitters which are positioned to irradiate the irradiation zone with electrons; and providing an adjustment system capable of moving the electron beam emitters for changing the position of the electron beam emitters relative to the article. 23. The method of claim 22 further comprising providing the adjustment system with the capability of moving the electron beam emitters towards or away from the irradiation zone. claim 22 24. The method of claim 23 further comprising providing the adjustment system with the capability of rotating the electron beam emitters about the irradiation zone. claim 23 25. The method of claim 24 further comprising providing the adjustment system with an adjustable rotating mechanism capable of rotating the electron beam emitters about the irradiation zone. claim 24 26. The method of claim 23 further comprising providing the adjustment system with cm adjustable linear mechanism capable of moving the electron beam emitters towards or away from the irradiation zone. claim 23 27. The method of claim 23 further comprising providing the electron beam system with four electron beam emitters. claim 23 28. The method of claim 27 further comprising positioning the electron beam emitters in first and second opposed pairs. claim 27 29. The method of claim 28 further comprising positioning the second opposed pair downstream from the first opposed pair. claim 28 30. The method of claim 22 further comprising providing a conveyance system for conveying the article through the irradiation zone, the conveyance system being configured to allow the article to be irradiated with electrons on the outwardly exposed surfaces. claim 22 31. The method of claim 30 in which the article is a continuous profile, the method further comprising providing the conveyance system with at least one roller positioned beyond the irradiation zone for conveying the profile through the irradiation zone. claim 30 32. The method of claim 22 further comprising configuring the apparatus for curing coatings on said surfaces of the article. claim 22 33. The method of claim 22 further comprising configuring the apparatus for sterilizing said surfaces of the article. claim 22 34. The method of claim 22 further comprising configuring the apparatus for providing surface modification of said surfaces of the article. claim 22 35. The method of claim 22 further comprising providing electrons from opposing directions. claim 22 36. The method of claim 35 further providing the electron beam system with two opposed electron beam emitters separated from each other by a gap. claim 35 37. The method of claim 36 further comprising providing the conveyance system with the two conveyor belts for conveying the article between the opposed electron beam emitters through the gap therebetween, the conveyor belts being spaced apart from each other in the region of the gap so that the article passing between the electron beam emitters can be fully irradiated by the electrons. claim 36 38. A method of forming an electron beam apparatus comprising: providing an electron beam system comprising multiple electron beam emitters having at least one opposed pair of electron beam emitters for directing electrons into an irradiation zone; configuring the electron beam system and the irradiation zone for irradiating an article passing through the irradiation zone with electrons from the electron beam system and providing an adjustment system capable of moving the electron beam emitters for changing the position of the electron beam emitters relative to the article. 39. The method of claim 38 further comprising providing the adjustment system with the capability of moving the electron beam emitters towards or away from the irradiation zone. claim 38 40. The method of claim 39 further comprising providing the adjustment system with the capability of rotating the electron beam emitters about the irradiation zone. claim 39 41. A method of curing coatings on a continuously moving 3-dimensional profile comprising: directing electrons from an electron beam system into an irradiation zone; passing the profile through the irradiation zone, the electron beam system and the irradiation zone being configured for irradiating outwardly exposed surfaces of the profile with electrons from the electron beam system for curing coatings thereon, the electron beam system including multiple electron beam emitters having at least one opposed pair of electron beam emitters which are positioned to irradiate the irradiation zone with electrons each from a different direction; and moving the electron beam emitters for positioning the electron beam emitters in the proper position relative to the article with an adjustment system. 42. A method of sterilizing a moving 3-dimensional article comprising: directing electrons from an electron beam system into an irradiation zone; passing the 3-dimensional article through the irradiation zone, the electron beam system and the irradiation zone being configured for irradiating outwardly exposed surfaces of the 3-dimensional article from different directions with electrons from the electron beam system to sterilize said surfaces, the electron beam system comprising multiple electron beam emitters having at least one opposed pair of electron beam emitters which are positioned to irradiate the irradiation zone with electrons; and providing an adjustment system capable of moving the electron beam emitters for changing the position of the electron beam emitters relative to the article. 43. A method of irradiating an article comprising: directing electrons from an electron beam system into an irradiation zone, the electron beam system comprising multiple electron beam emitters having at least one opposed pair of electron beam emitters; introducing the article into the irradiation zone, the electron beam system and the irradiation zone being configured for irradiating the article with electrons from the electron beam system; and moving the electron beam emitters for positioning the electron beam emitters in the proper position relative to the article with an adjustment system. 44. A method of irradiating a moving 3-dimensional article comprising: directing electrons from an electron beam system into an irradiation zone; and passing the 3-dimensional article through the irradiation zones the electron beam system and the irradiation zone being configured for irradiating outwardly exposed surfaces of the 3-dimensional article from different directions with electrons from the electron beam system, the electron beam system comprising multiple electron beam emitters having at least one opposed pair of electron beam emitters which are positioned to irradiate the irradiation zone with electrons; and providing an adjustment system capable of moving the electron beam emitters for changing the position of the electron beam emitters relative to the article. 45. An electron beam irradiation apparatus comprising: an electron beam system comprising a plurality of electron beam emitters generally surrounding an irradiation zone for directing electrons into the irradiation zone, the electron beam system and the irradiation zone being configured for irradiating an article passing through the irradiation zone with electrons from the electron beam system; and an adjustment system capable of moving the electron beam emitters for changing the position of the electron beam emitters relative to the article. 46. The apparatus of claim 45 in which the electron beam system includes three electron beam emitters positioned around the irradiation zone. claim 45 |
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055127592 | summary | II. BACKGROUND OF THE INVENTION A. Field of the Invention The present invention relates in general to the field of condensers (a.k.a., illuminators) for collecting and condensing light and directing the light into a projection camera designed for projection lithography. More specifically, the present invention relates to condensers that collect and condense synchrotron emission light from a synchrotron radiation source using a plurality of mirrors and couple the light to the ringfield of a camera operating in a ringfield scanning mode. B. Discussion of Related Art In general, lithography refers to processes for pattern transfer between various media. A lithographic coating is generally a radiation-sensitized coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive of the subject pattern. Typically, a "transparency" of the subject pattern is made having areas which are selectively transparent, opaque, reflective, or non-reflective to the "projecting" radiation. Exposure of the coating through the transparency causes the image area to become selectively crosslinked and consequently either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble (i.e., uncrosslinked) areas are removed in the developing process to leave the pattern image in the coating as less soluble crosslinked polymer. Projection lithography is a powerful and essential tool for microelectronics processing. As feature sizes are driven smaller and smaller, optical systems are approaching their limits caused by the wavelengths of the optical radiation. "Long" or "soft" x-rays (wavelength range of .lambda.=100 to 200 .ANG. ("Angstrom")) are now at the forefront of research in efforts to achieve the smaller desired feature sizes. Soft x-ray radiation, however, has its own problems. The complicated and precise optical lens systems used in conventional projection lithography do not work well for a variety of reasons. Chief among them is the fact that most x-ray reflectors have efficiencies of only about 60%, which in itself dictates very simple beam guiding optics with very few surfaces. One approach has been to develop cameras that use only a few surfaces and can image with acuity (i.e., sharpness of sense perception) only along a narrow arc or ringfield. Such cameras then use the ringfield to scan a reflective mask and translate the image onto a wafer for processing. Although cameras have been designed for ringfield scanning (e.g., Jewell et al., U.S. Pat. No. 5,315,629 and Offner, U.S. Pat. No. 3,748,015), available condensers that can efficiently couple the light from a synchrotron source to the ringfield required by this type of camera have not been fully explored. Furthermore, full field imaging, as opposed to ringfield imaging, requires severely aspheric mirrors. Such mirrors cannot be manufactured to the necessary tolerances with present technology for use at the required wavelengths. The present state-of-the-art for Very Large Scale Integration ("VLSF") is a 16 megabit chip with circuitry built to design rules of 0.5 .mu.m. Effort directed to further miniaturization takes the initial form of more fully utilizing the resolution capability of presently-used ultraviolet ("UV") delineating radiation. "Deep UV" (wavelength range of .lambda.=0.3 .mu.m to 0.1 .mu.m), with techniques such as phase masking, off-axis illumination, and step-and-repeat may permit design rules (minimum feature or space dimension) of 0.25 .mu.m or slightly smaller. To achieve still smaller design rules, a different form of delineating radiation is required to avoid wavelength-related resolution limits. One research path is to utilize electron or other charged-particle radiation. Use of electromagnetic radiation for this purpose will require x-ray wavelengths. Two x-ray radiation sources are under consideration. One source, a plasma x-ray source, depends upon a high power, pulsed laser (e.g., a yttrium aluminum garnet ("YAG") laser), or an excimer laser, delivering 500 to 1,000 watts of power to a 50 .mu.m to 250 .mu.m spot, thereby heating a source material to, for example, 250,000.degree. C., to emit x-ray radiation from the resulting plasma. Plasma sources are compact, and may be dedicated to a single production line (so that malfunction does not close down the entire plant). Another source, the electron storage ring synchrotron, has been used for many years and is at an advanced stage of development. Synchrotrons are particularly promising sources of x-rays for lithography because they provide very stable and defined sources of x-rays. Electrons, accelerated to relativistic velocity, follow their magnetic-field-constrained orbit inside a vacuum enclosure of the synchrotron and emit electromagnetic radiation as they are bent by a magnetic field used to define their path of travel. Radiation, in the wavelength range of consequence for lithography, is reliably produced. The synchrotron produces precisely defined radiation to meet the demands of extremely sophisticated experimentation. The electromagnetic radiation emitted by the electrons is an unavoidable consequence of changing the direction of travel of the electrons and is typically referred to as synchrotron radiation. Synchrotron radiation is comprised of electromagnetic waves of very strong directivity emitted when electron or positron particles, which are emitted from a synchrotron source, travel at velocities approximate to the velocity of light and are deflected from their orbits by a magnetic field. Synchrotron radiation is emitted in a continuous spectrum or fan of "light", referred to as synchrotron emission light, ranging from radio and infrared wavelengths upwards through the spectrum, without the intense, narrow peaks associated with other sources. Synchrotron emission light has characteristics such that the beam intensity is high, the linearity is strong, and the divergence is small so that it becomes possible to accurately and deeply sensitize a photolithographic mask pattern into a thickly applied resist. Generally, all synchrotrons have spectral curves similar to the shape shown in FIG. 1 of Cerrina et al. (U.S. Pat. No. 5,371,774) that define their spectra, which vary from one another in intensity and the critical photon energy. Parameters describing the size of the source of synchrotron radiation and the rate at which it is diverging from the source are of importance. Because the electrons are the source of synchrotron radiation, the cross section of the electron beam defines the cross section of the source. Within the plane of the orbit, the light is emitted in a broad, continuous fan, which is tangent to the path of the electrons, as illustrated in FIG. 1. FIG. 1 shows a section of a synchrotron having an orbiting electron beam (10) and a fan of synchrotron radiation indicated by the arrow (12). Because of the relatively small height and width of the electron beam, any point along its length acts as a point source of radiation, providing crisp images at an exposure plane which is typically 8 meters or more away from the ring. At a distance of 8 meters, however, a 1 inch wide exposure field typically collects only 3.2 milli-radians ("mrad") of the available radiation. There are two ways to improve the power incident at a photo-resist: either shorten the beamline or install focusing elements. The use of focusing elements has the potential advantage of collecting x-rays from a very wide aperture and providing a wide image with a very small vertical height. However, the use of focusing elements results in a loss of power at each element because of low reflectivity of the x-rays and introduces aberrations. Synchrotron radiation is emitted in a horizontal fan. The small vertical divergence of the synchrotron radiation implies that a wide horizontal mirror, or a plurality of smaller parallel systems, can accept a large fan of light, whose outputs are added together at the mask plane. A variety of x-ray patterning approaches are under study. Probably the most developed form of x-ray lithography is proximity printing. In proximity printing, object:image size ratio is necessarily limited to a 1:1 ratio and is produced much in the manner of photographic contact printing. A fine-membrane mask is maintained at one or a few microns spacing from the wafer (i.e., out of contact with the wafer, thus, the term "proximity"), which lessens the likelihood of mask damage but does not eliminate it. Making perfect masks on a fragile membrane continues to be a major problem. Necessary absence of optics in-between the mask and the wafer necessitates a high level of parallelicity in the incident radiation. X-ray radiation of wavelength .lambda..ltoreq.16 .ANG. is required for 0.25 .mu.m or smaller patterning to limit diffraction at feature edges on the mask. Use has been made of the synchrotron source in proximity printing. (Consistent with traditional, highly demanding, scientific usage, proximity printing has been based on the usual small collection arc. Relatively small power resulting from the 10 mrad to 20 mrad arc of collection, together with the high-aspect ratio of the synchrotron emission light, has led to use of a scanning high-aspect ratio illumination field (rather than the use of a full-field imaging field). Projection lithography has natural advantages over proximity printing. One advantage is that the likelihood of mask damage is reduced, which reduces the cost of the now larger-feature mask. Imaging or camera optics in-between the mask and the wafer compensate for edge scattering and, so, permit use of longer wavelength radiation. Use of extreme ultra-violet radiation (a.k.a., soft x-rays) increases the permitted angle of incidence for glancing-angle optics. The resulting system is known as extreme UV ("EUVL") lithography (a.k.a., soft x-ray projection lithography ("SXPL")). A favored form of EUVL is ringfield scanning. All ringfield optical forms are based on radial dependence of aberration and use the technique of balancing low order aberrations, i.e., third order aberrations, with higher order aberrations to create long, narrow illumination fields or annular regions of correction away from the optical axis of the system (regions of constant radius, rotationally symmetric with respect to the axis). Consequently, the shape of the corrected region is an arcuate or curved strip rather than a straight strip. The arcuate strip is a segment of the circular ring with its center of revolution at the optic axis of the camera. See FIG. 4 of U.S. Pat. No. 5,315,629 for an exemplary schematic representation of an arcuate slit defined by width, W, and length, L, and depicted as a portion of a ringfield defined by radial dimension, R, spanning the distance from an optic axis and the center of the arcuate slit. The strip width is a function of the smallest feature to be printed with increasing residual astigmatism at distances greater or smaller than the design radius being of greater consequence for greater resolution. Use of such an arcuate field avoids radially-dependent image aberrations in the image. Use of object:image size reduction of, for example, 5:1 reduction, results in significant cost reduction of the, now, enlarged-feature mask. It is expected that effort toward adaptation of electron storage ring synchrotron sources for EUVL will continue. Economical high-throughput fabrication of 0.25 .mu.m or smaller design-rule devices is made possible by use of synchrotron-derived x-ray delineating radiation. Large angle collection over at least 100 mrad will be important for device fabrication. Design of collection and processing optics design of the condenser is complicated by the severe mismatch between the synchrotron light emission pattern and that of the ringfield scan line. The present invention discloses a condenser for collecting and processing illumination from a synchrotron source and directing the illumination into a ringfield camera designed for photolithography. The condenser employs a relatively simple and inexpensive design, which utilizes spherical and flat mirrors that are easily manufactured. The condenser employs a plurality of optical mirrors and lenses, which form collecting, processing, and imaging optics to accomplish this objective. III. SUMMARY OF THE INVENTION The principal object of the present invention is to permit very high quality illumination of a narrow ringfield of a lithography camera using synchrotron radiation as the source. It is also an object of the present invention to ensure that the ringfield of a lithography camera is illuminated with a synchrotron source that has uniform, intensity and partial coherence properties along the ting. It is another object of the present invention to ensure that the ringfield of a lithography camera is illuminated with a synchrotron source that has uniform, partial coherence properties in all orientations (angles measured in the r-.THETA. plane). It is still another object of the present invention to collect over at least 100 mrad to a full radian, or greater, of synchrotron emission light and efficiently illuminate the ringfield of a lithography camera. It is yet another object of the present invention to ensure that the condenser has a very small Etendu or Lagrange Optical Invariant. Additional objects, advantages, and novel features will become apparent to those of ordinary skill in the art upon examination of the following detailed description of the invention or may be learned by practice of the present invention. The objects and advantages of the present invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. Accordingly, the present invention accomplishes the foregoing objects by providing a condenser system to collect and condense large amounts of synchrotron emission light emitted from a synchrotron radiation source, direct it into the ringfield of a camera designed for photolithography, which delivers it to a mask. The light beams emitted from the condenser system produce arc-shaped light beams that correspond directly with the arc-shaped ringfield of the camera, thus providing a high quality, uniformly illuminated image. Because the synchrotron emission light takes the shape of a fan with several legs, the present invention positions sets of collecting and processing optics on each leg of the fan, and positions imaging optics on the respective legs of the fan that are common to the collecting and processing optics. The condenser system comprises a collecting means, positioned about the periphery of a synchrotron source, for collecting a plurality of synchrotron light beams emitted from the fan of synchrotron emission light and for transforming the plurality of synchrotron light beams into a plurality of arc-shaped light beams, each one of the plurality of arc-shaped light beams having an arc-shaped cross-section; processing means, succeeding the collecting means, for rotating and directing the plurality of arc-shaped light beams toward the plane (hereinafter referred to as the real entrance pupil, which is an image of the actual pupil in the camera), of a camera and for positioning a plurality of substantially parallel arc-shaped light beams at the real entrance pupil of the camera; and imaging means, succeeding the processing means, for converging the substantially parallel arc-shaped light beams, for transmitting the plurality of the substantially parallel arc-shaped light beams through a resistive mask and into the virtual entrance pupil of the camera, and for illuminating the ringfield of the camera. The collecting, processing, and imaging optics combine to produce an image quality to adequately illuminate any ringfield with a width of W.gtoreq.100 .mu.m. The collecting optics comprise a plurality of spherical mirrors, each plurality of spherical mirrors comprising a concave mirror and a convex mirror, for collecting and converting the light beams into arc-shaped light beams. In an alternative embodiment, the first mirror may be convex, and the second mirror may be concave. The processing optics comprise a plurality of flat mirrors, each one of the flat mirrors being common to a respective pair of the spherical mirrors, for rotating and directing the arc-shaped light beams into a real entrance pupil of the camera in a symmetrical, circular pattern where flat mirrors are positioned to direct the beams towards the ringfield of a camera. The light beams collected at the real entrance pupil are imaged into a virtual entrance pupil of the camera by the use of imaging optics. The condenser system provides uniform coherence properties for features on the mask oriented at any angle. Further scope of applicability of the present invention will become apparent from the detailed description of the invention provided hereinafter. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating preferred embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the spirit and scope of the present invention will become apparent to those of ordinary skill in the art from the detailed description of the invention that follows. |
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06041099& | abstract | An x-ray reflecting system comprising a Kirkpatrick-Baez side-by-side optic in a single corner configuration having multi-layer Bragg x-ray reflective surfaces. |
050892142 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now to FIGS. 1 and 2, the principal purpose of the pressure monitoring apparatus 1 of the invention is to monitor the pressure of the helium gas contained within the interior 3 of a cask 5 used to either store or to transport radioactive materials. Such helium is typically pressurized to approximately 1.5 atmospheres, and serves the two-fold purpose of enhancing the expulsion of heat out of the cask 5 generated by the decay-down of the radioactive materials contained therein, and further retarding the occurrence of corrosion within the cask interior 3. Such casks 5 generally comprise a cylindrical wall 7 whose lower portion 9 includes a floor plate 11 welded therearound, and whose upper portion 13 includes a stepped rim 14 for receiving a lid assembly 15. The stepped rim 14 includes a plurality of uniformly-spaced bolt holes 16 for receiving bolts (not shown) that secure the lid assembly 15 into sealing engagement with the stepped rim 14 of the cask 5. While the pressure monitoring apparatus 1 of the invention may be used in conjunction with any transportation and storage cask, the cask illustrated in this example of the invention is a peripheral-finned transportation and storage cask of the type disclosed and claimed in U.S. Pat. No. 4,997,618, and assigned to the Westinghouse Electric Corporation. With reference now to FIGS. 2, 3A and 3B, the pressure monitoring apparatus includes an annular housing 20 whose inner edge is disposed within an annular recess 22 in the upper portion 13 of the wall 7 of cask 5. The housing 20 includes an lower annular member 24 whose inner edge 25 is welded around the recess 22 to form a gas-tight seal. The housing 20 further includes an upper annular member 26 disposed over the outer edge of the lower annular member 24 as shown. A removable inner cover 28 is disposed between the outer edges of the lower annular member 24, and the inner edges of the upper annular member 26. A gasket 29 is disposed between the inner edge of the inner cover 28 and the outer edge of the lower annular member 24, and a plurality of bolts 30 compresses the inner edge of the inner cover 28 in gas-tight relationship with this gasket 29. These bolts 30 are screwed into threaded bores 32 present around the circumference of the lower annular member 24. Together, the recess 22, the lower annular member 24 and the removable cover 28 define an evacuated sensor chamber 35 within the housing 20 of the pressure monitoring apparatus 1. As will be described in more detail presently, this evacuated sensor chamber 35 contains most of the sensor assembly 50 (illustrated in phantom 3A) of the apparatus 1, and further provides a second barrier between the pressurized helium gas disposed within the interior 3 of the cask 5, and the ambient atmosphere. With reference again to FIGS. 2, 3A and 3B, the housing 20 further includes a removable outer cover 36 that is secured to the outer edges of the upper annular member 26 by means of bolts 37. Together, the upper annular member 26, the removable inner cover 28, and the removable outer cover 36 define an access chamber 38 which contains the electrical terminals leading to the sensor assembly 50 disposed within the evacuated sensor chamber 35, as well as a test conduit that is connected to a test port which allows a direct pressure measurement to be made of the pressure within the evacuated sensor chamber 35. With specific reference now to FIG. 3A, the evacuated sensor chamber 35 surrounds the outer end 40 of a bore 41 that penetrates completely through the cylindrical wall 7 of the cask 5. A shielding insert 43 is disposed within the bore 41 to prevent "streaming" of any radiation which may be emitted by radioactive materials disposed within the interior 3 of the cask 5. The principal purpose of the shielding insert 43 is to define tortuous path 44 which may be easily traversed by the compressed helium within the interior 3 of the cask 5, but which does not provide a straight path for any radiation emanating from the interior 3 of the cask 5. This tortuous path 44 is defined by a combination of intercommunicating radially disposed bores 45 and longitudinally disposed bores 47 as shown. While it is within the scope of the instant invention that the through-wall bore 41 might be placed in positions other than the upper portion 13 of the cylindrical wall 7 of the cask 5, the upper portion 13 is preferred due to the fact that the density of radiation emanating out of the cask interior 3 is considerably less at the upper portion 13 of the cask than it is in the middle portion, since the uppermost height of the radioactive material in the cask is always below the stepped rim 14. While such a low density of radiation is also present near the lower portion 9 of the cask 5, this location is not preferred to two reasons. First, a lower location of the housing 20 of the pressure monitoring apparatus 1 on the cask wall 7 renders it more exposed to mechanical shock from fork lifts, etc., when the cask 5 is being handled. Secondly, if any significant amount of liquid should accumulate within the cask interior 3, these liquids might flow up through the bore 41, and damage the components of the sensor assembly 50 disposed therein. With reference now to FIGS. 4A and 4B, the sensor assembly 50 of the apparatus generally includes a mounting plate 52 having three bolt holes 54a,b,c for receiving bolts (not shown) when the assembly 50 is mounted within the evacuated sensor chamber 35 of the housing 20. The two key components of the sensor assembly 50 are a differential pressure sensor 55, and an absolute pressure sensor 56, each of which are secured (either directly or indirectly) to the mounting plate 52. In the preferred embodiment, the differential pressure sensor is an Aschcroft.RTM. Model No. B427S XG9 differential pressure sensor manufactured by Dresser Industries located in Milford, Conn., having a stainless steel diaphragm and a setpoint of up to 30 psi (differential). The absolute pressure sensor 6 is preferably a model no. 211-75-700 pressure sensor Corporation located in Seattle, Wash. A conduit 57 connects both the differential pressure sensor 55 and the absolute pressure sensor 56 in parallel to the outer end 40 of the through-wall bore 41. The conduit 57 includes an intake tube 58 whose upstream end 59 is brazed or welded to the outer end 40 of the through-wall bore 41, and whose downstream end is connected to two-serially connected isolation valves 60 and 62. In the preferred embodiment, isolation valves 60 and 62 (as well as all of the other isolation valves 83 and 91 discussed later) are preferably model no. SS-4H-TW "H" Series, bellows-type valves manufactured by the Nupro Company located in Willoughby, Ohio. The purpose of the isolation valves 60 and 62 is to completely isolate both the differential pressure sensor 55 and the absolute pressure sensor 56 from the outer end 40 of the through-wall bore 41 in the event that either of these two components requires replacement or maintenance. While one such isolation valve would be adequate for this purpose, two serially-connected valves 60 and 62 are preferred due to the extra measure of safety that the use of two valves provides against leakage during a replacement operation. The outlet of the second isolation valve 62 is connected to the inlet 63 of a T fitting 64 by way of a tube elbow 66 as shown. The first outlet 67 of the T fitting 65 is connected to another T coupling 69 which fluidly connects the differential pressure sensor 55 to the gas conduit 57. For this purpose, a conduit segment 71 is disposed between the first outlet 67 of the T fitting 64, and the T coupling 69. On its downstream side, the T coupling 69 is connected to an elbow coupling 73 which in turn leads to the absolute pressure sensor 56, thereby connecting absolute pressure sensor 56 to the gas conducting conduit 57. A conduit segment 75 interconnects the downstream side of the T coupling 69 and the elbow coupling 73 in the manner shown. The second outlet 77 of the T fitting 64 ultimately leads to a vent plug 79 by way of a conduit segment 81. Conduit segment 81 further includes a vent valve 83 which, in the preferred embodiment, is the same type of isolation valve as described with respect to valve 60 and 62. The purpose of the vent plug 79, conduit segment 81 and vent valve 83 is to provide a controlled venting of any gas trapped between the isolation valve 62 and the differential and absolute pressure sensors 55 and 56 in the event that either of these two components requires maintenance or replacement. More specifically, the provision of these vent components allows any helium that contains radioactive particulate material to be sucked out of the segment of the gas conducting conduit 57 disposed between the isolation valve 62 and the pressure sensors 55 and 56 prior to the de-coupling of these sensors 55 and 56 from their respective fittings 69 and 73. The balance of the components that form the sensor assembly 50 are mounted on the outer surface of the removal inner cover 28, and are illustrated in FIG. 3B. These components include a chamber pressure test port 85 (indicated partially in phantom) which in turn is welded or brazed in a gas-tight relationship to a testing conduit 87 that terminates in a test cap 89. The testing conduit 87 preferably includes an isolation valve 91 of the same type as previously described with respect to the isolation valve 60 and 62. The purpose of the test port 85, testing conduit 87, test cap 89 and isolation valve 91 is to allow the system operator to make a direct measurement of the pressure of the evacuated sensor chamber 35 for the purpose of confirming whether or not a chamber leakage signal generated by the pressure sensors 55 and 56 is the result of a true leakage condition within the chamber 35, or is merely the result of a defective sensor 55, 56. The removable inner cover further includes a sealed electrical penetration 93 which conducts the output signal-carrying cables from the pressure sensors 55 and 56 to a terminal block 95 which in turn is connected to an electrical socket assembly 97 through connecting wires 98. The electric socket assembly 97 receives the plug 98.5 of a monitor cable 99 as shown. This monitor cable 99 is connected to commercially-available read-out circuitry (not shown) which converts the electrical signals generated by the differential and absolute pressure sensors 55, 56 into pressure readings. The final component of the sensor assembly 50 is an auxiliary pressure sensor 100 (indicated in phantom) which is detachably connectable to the testing conduit 87 after the test cap 89 has been removed. The provision of the auxiliary absolute pressure sensor 100 allows the operator of the apparatus to make a direct measurement of the pressure within the evacuated sensor chamber 35 when such a measurement becomes desirable. In operation, the differential pressure sensor 55 continuously generates an electrical signal indicative of the absolute pressure of the helium disposed within the cask interior 3, since the chamber 35 that surrounds the differential pressure sensor 55 is evacuated. As the helium disposed within the interior 3 of such cask 5 is typically pressurized to about 1.5 atmospheres, the output of this sensor 55 will generally read 1.5 atmospheres. Because the absolute pressure sensor 56 is in fact only a differential pressure sensor that uses it own, self-contained evacuated chamber as a reference point for making pressure measurements, the absolute pressure sensor 56 should likewise continuously generate a signal indicative of a pressure reading of 1.5 atmospheres. However, in the event that a leakage condition should occur in either the cask 5, or in the evacuated sensor chamber 35 that surrounds the differential pressure sensor 55, the sensor 55 will begin to generate a signal indicative of the presence of a lower pressure. In the preferred method of the invention, the circuitry (not shown) connected to the output of the differential pressure sensor 55 is programmed to generate an alarm signal when the differential pressure measured falls to about 1.2 atmospheres or lower. When this occurs, the operator of the apparatus immediately checks the pressure read-out generated by the absolute pressure sensor 56. If this pressure sensor 56 likewise indicates a pressure read-out of 1.2 atmospheres or lower, then the system operator concludes that a leakage condition has occurred with respect to the cask 3. If, however, the pressure read-out of the absolute pressure sensor 56 has not fallen and is still substantially at a level of approximately 1.5 atmospheres, then the operator of the apparatus tentatively concludes that a leakage condition has occurred with respect to the evacuated sensor chamber 35. The next step of the method of the invention, the operator of the apparatus confirms whether or not a leakage condition has occurred with respect to the evacuated sensor chamber 35 by removing the outer cover 36, and the test cap 89, and connecting the auxiliary pressure sensor 100 to the testing conduit 87. Once this has been accomplished, the isolation valve 91 is opened. If the resulting pressure reading is 0.30 atmospheres or higher, then the system operator concludes that a leakage condition with respect to the evacuated sensor chamber 35 has, indeed, occurred. If on the other hand the auxiliary pressure sensor 100 indicates that the evacuated sensor chamber 35 is still substantially evacuated, then the operator of the apparatus 1 concludes that the output of the differential pressure sensor 55 is in error, either as the result of drift in its set point, or some other type of mechanical failure. In either case, the operator of the apparatus 1 proceeds to either repair or replace the differential pressure sensor 55 by first removing removable inner cover 28, and then closing the isolation valves 60 and 62, and then effecting a controlled venting of any helium gas disposed within the section of the gas-conducting conduit 57 by removing the vent plug 79, connecting a suction hose to the vent port, and then opening the vent valve 83. After the venting operation has been accomplished, not only is the differential pressure sensor 55 removed and repaired, but the absolute pressure sensor 56 is tested to make sure that the read-out generated thereby is accurate and correct. After the foregoing maintenance operations have been accomplished, the apparatus 1 is reassembled, and placed back into operation. |
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description | The present invention relates to a contamination barrier and a lithographic apparatus comprising same. A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive metal compound (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. Radiation sources used in EUV lithography typically generate contaminant material that is harmful to the optics and the working environment wherein the lithographic process is carried out. Such is especially the case for EUV sources operating via a laser induced plasma or discharge plasma. Hence, in EUV lithography, a desire exists to limit the contamination of the optical system arranged to condition the beam of radiation coming from an EUV source. To this end, a foil trap, for instance, as disclosed in European patent application publication EP1491963, has been proposed. A foil trap uses a high number of closely packed foils or blades. Contaminant debris, such as micro-particles, nano-particles and ions can be trapped in the walls provided by the blades. Thus, the foil trap functions as a contamination barrier trapping contaminant material from the source. In an embodiment, a rotatable foil trap may be oriented with an axis of rotation oriented along an optical axis of the system, in particular in front of an extreme ultraviolet radiation source configured to provide extreme ultraviolet radiation. The blades configured to trap contaminant material thus may be radially-oriented relative to a central rotating shaft of the contamination barrier and may be aligned substantially parallel to the direction of radiation. By rotating the foil trap at a sufficiently high speed, traveling contaminant debris may be captured by the blades of the contaminant barrier. Due to design limitations, the rotation speed of the contaminant barrier may be quite high, since otherwise the length of the blades along the direction of travel of the debris would be unacceptably large. Typical revolution speeds are 15000-30000 RPM. Furthermore, the foil trap is operated in (near) vacuum conditions, which gives special constraints to the type of bearing that can be used for the rotating foil trap. In particular, one type of bearing that may be used is a gas bearing, wherein the rotating shaft of the foil trap is borne by gas (e.g., air) pressure. To not compromise the vacuum conditions, the gap present between the shaft and such a bearing should be kept very small, typically only several microns. A consequence of such an arrangement is that there may be imbalance of the foil trap. Such imbalance may be detrimental to the vacuum and/or to the operation of the machine. It is desirable, for example, to provide a rotatable contamination barrier that has improved balancing properties. According to an aspect of the invention, there is provided a rotatable contamination barrier for use with an EUV radiation system, the barrier comprising: a blade structure configured to trap contaminant material coming from a radiation source; a bearing structure, coupled to a static frame, configured to rotatably bear the blade structure; and an eccentric mass element displaced relative to a central axis of rotation to balance the blade structure in the bearing structure. According to an aspect of the invention, there is provided a balancing unit to balance a rotatable contamination barrier, the unit comprising: a bearing structure configured to bear a blade structure of the rotatable contamination barrier; a imbalance sensor unit configured to provide a signal of a sensed imbalance of the blade structure in the bearing structure during rotation of the blade structure; and a calculating unit configured to calculate a location to provide one or more eccentric mass elements on or to the blade structure and the amount of such mass, the calculating unit communicatively coupled to the imbalance sensor. According to an aspect of the invention, there is provided a method of balancing a rotatable contamination barrier for use in an EUV radiation system, comprising: bearing a blade structure in a bearing structure provided in a vacuum environment; sensing an imbalance of the blade structure in the bearing structure during rotation of the blade structure; and calculating, based on the sensed imbalance, a location to provide an eccentric mass element on or to the blade structure and an amount of such mass. According to an aspect of the invention, there is provided a method of cleaning a rotatable contamination barrier for use with an EUV radiation system, comprising: adjusting an eccentric mass element of a blade structure of the contamination barrier to provide an imbalance; and rotating the blade structure with the imbalance to shake clean the contamination barrier. According to an aspect of the invention, there is provided a lithographic apparatus, comprising: a rotatable contamination barrier configured to receive a beam of radiation, the contamination barrier comprising a blade structure configured to trap contaminant material coming from a radiation source, a bearing structure, coupled to a static frame, configured to rotatably bear the blade structure, and an eccentric mass element displaced relative to a central axis of rotation to balance the blade structure in the bearing structure; an illumination system configured to condition the radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate. FIG. 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or EUV radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. The support structure holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix. The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”. As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask). Alternatively, the apparatus may be of a transmissive type (e.g. employing a transmissive mask). The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more support structures). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure. Referring to FIG. 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system. The illuminator IL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may comprise various other components, such as an integrator and a condenser. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies. The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. 2. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. 3. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed. Although the principles of one or more embodiments of the invention may be applied to a rotatable contamination barrier having any rotatable blade structure, FIG. 2 schematically shows an exemplary embodiment of a rotatable contamination barrier or foil trap 1 wherein the blade structure 2 is comprised of a central rotation shaft 3 with blades or foils 4 mounted thereon. The barrier 1 is typically used in or with a radiation system 5 to provide a projection beam of radiation. In an embodiment, the radiation system 1 comprises an extreme ultraviolet radiation source 6 configured to provide extreme ultraviolet radiation. In FIG. 2, the dashed lines represent EUV radiation 7 coming from EUV source 6, typically a laser induced plasma source or a plasma discharge source such as a tin, lithium or xenon source, however, other sources are possible, in particular, any other source that produces EUV radiation in combination with fast particles that escape from the source 6 and that should be trapped in order to prevent damage to the downstream optics of the lithographic apparatus (not shown). To this end, the blade structure 2 is provided with a plurality of closely packed blades 4 configured to trap contaminant material coming from the radiation source 6. In the exemplary embodiment, the blades 4 are radially oriented relative to a central rotation shaft 3 of the contamination barrier 1. By rotation of the blades 4, fast moving particles, in particular, tin particles and gaseous and ion like particles traveling away from the source 6 can be trapped while EUV radiation, due to the speed of light, can travel generally unhindered by the blades 4. The foil trap 1 thus functions as a contamination barrier to trap contaminant material coming from the radiation source 6. Typically, the blades 4 are arranged at a distance of 0.3-5 mm apart and have a generally rectangular form. Advantageously, the source 6 is positioned at an intersection of extended planes through the plurality of blades 4 which define an optical center of the contamination barrier 5, which in FIG. 2 coincides with the rotation shaft 3 of the foil trap 1. For an ideal point like EUV source 6 at this center, radiation would pass in a direction generally parallel to an orientation of the blades 4. Thus, shielding of EUV radiation is low and only takes place over a thickness of the blade (which, in an embodiment, is accordingly kept small without compromising mechanical integrity). A typical value of the thickness of the blade can be about 100 microns, which may result in a shielding of about 10 percent of the radiation. FIG. 3 shows a schematic view of an axial cross-sectional view of a rotating foil trap such as illustrated in FIG. 2. In particular, FIG. 3 shows a central rotating shaft 3 which is mounted in a bearing structure 8, which comprises, in the context of this embodiment, two gas bearings 9 enclosing the shaft 3. The gas bearings 9 are operated in a vacuum environment, which poses special constraints on the gap 10 between the shaft 3 and the bearings 9. For example, the gap 10 should be very small in order not to pose problems for the vacuum environment. Thus, reducing or minimizing eccentric movements of the shaft 3 should allow for a smaller gap 10, which would be beneficial to operation in a vacuum environment. In FIG. 3, a modeled representation of an axis of inertia 11 is schematically indicated. FIG. 4 shows a schematic lateral cross-sectional view of the rotating foil trap according to FIG. 3 along line I-I, showing the axis of inertia viewed along an axial direction. The axis of inertia, for a rigid elongate body, can be represented by two off-centered masses 12 at the respective ends of the axis, which are schematically illustrated as not coincident with a central (geometrical) axis of rotation 13. To reduce or eliminate the eccentricity of the axis of inertia, one or more eccentric mass elements (see FIG. 6) may be provided in at least two planes 14 lateral the central axis of rotation 13. In an embodiment, the one or more corrective masses are provided in the same planes 14 as is measured (as discussed below), but other lateral planes are possible when taking into account the specific geometry of the blade structure 2. In an embodiment, the imbalance of the blade structure 2 is measured by two force sensors 15 which sense a force in a single dimension, in two planes 14 spaced apart from each other along the central axis of rotation 13. The blade structure 2 is mounted rigidly in another direction than the measuring direction (see FIG. 5). The force sensors 15 thus measure an eccentric displacement of the blade structure 2 in a lateral plane. In an embodiment, also in this plane, one or more eccentric mass elements (see FIG. 6) are provided relative to the central axis of rotation 13 in order to avoid recalculation necessary for geometric deviations. The shaft 3 further comprises a coupling element 16 connecting the shaft part that is borne by the gas bearings 9 to the shaft part 17 to which the blades 4 are mounted. The coupling element 16 is formed of a material having a relatively low thermal conductivity compared to the material of the shaft 3, which, due to the relevant operating temperature range of 800-1200° C., may be a molybdenum alloy. A suitable material for the coupling element 16 to provide the thermal isolation is tantalum, because, for example, the coefficients of thermal expansion of the shaft 3 and the coupling element 16 would then almost match (5 μ/m-K for molybdenum while 6 μ/m-K for tantalum). FIG. 5 shows schematically an exploded view of a balancing unit 18 according to an embodiment of the invention. The balancing unit can be used as a test setup to test the balancing properties of the foil trap, in particular, of the blade structure 2. The blade structure 2 (including the gas bearing structure 8) may be taken out of the operative environment of the foil trap and inserted in the setup 18 as illustrated in FIG. 5. Due to the fragility of the blade structure 2, the balancing procedure should be carried out in vacuum conditions, therefore the balancing unit would be operated in a vacuum chamber (not shown). Furthermore, the (initial) test rotation frequency is usually much lower, typically about 20-50 Hz, than the operating rotation frequency of the foil trap. In a balanced condition, the rotation frequency of the blade structure 2 may be typically a factor ten higher. As discussed with reference to FIG. 2, force sensors 15 are present to sense a force variation in one direction in order to provide a direct measurement of the imbalance of the blade structure 2. Alternatively, other imbalance sensing methods may be used, in particular, a displacement sensor which can be contactless or the like. The gas bearing structure 8 is stabilized by leaf springs 19 mounted in a rigid frame 20, which effectively limit the freedom of movement to a single direction. In addition, a rotation sensor is present (not shown) to sense a rotation angle of the blade structure 2. Based on the sensed force variations from the force sensors 15 and the rotation angle from the rotation sensor, a calculating unit (not shown) calculates a location to add one or more eccentric mass element to the blade structure as well as the amount of mass that should be added. FIG. 6 shows a practical embodiment that may be used for automatic adjustment of the imbalance that is measured. This embodiment allows for a continuous operation in an operative environment of the foil trap 1. In particular, when a blade is accidentally lost or deformed in the blade structure 2, or if an imbalance is caused by an uneven spread of colliding debris from the radiation source 6, balance may be restored by adjustment of the balance weights. In addition to the imbalance measurement sensors 15 detailed with respect to FIGS. 2 and 5, an adjustment unit 21 may be provided to provide automatic adjustment of one or more eccentric mass elements in response to an imbalance signal caused by an eccentricity schematically illustrated by item 22. Typically, along the central axis of rotation 13, at least two of these adjustment units 21 may be used to balance the elongated geometrical form of the foil trap 1. The adjustment unit 21, in an embodiment, comprises a pair of rotatable mass elements 23, which may be positioned freely relative to the shaft 3 and provide an effective eccentric mass that is adjustable relative to the central axis of rotation 13. Additionally or alternatively, other types of providing one or more (effective) eccentric mass elements are feasible, including adding, shifting and/or removing mass from or attached to the rotatable shaft 3. For non-automatic adjustment, such as using the balancing unit detailed in FIG. 5, a way of balancing is to provide eccentric bore holes in the rotatable shaft. In na embodiment, an aspect of the automatic balancing unit or other balancing mechanism is that it may allow for creation of a temporary imbalance, the temporary imbalance causing vibrations that may be effective in cleaning cycles when cleaning the barrier 1. Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers. Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured. The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams. The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components. While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below. |
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047479930 | claims | 1. A nuclear reactor containment arrangement including: a. a reactor vessel which thermally expands and contracts during cyclic operation of the reactor and which has a peripheral wall; b. a containment wall spaced apart from and surrounding the peripheral wall of the reactor vessel and defining an annular thermal expansion gap therebetween for accommodating thermal expansion; and c. an annular ring seal which sealingly engages and is affixed to and extends between the peripheral wall of the reactor vessel and the containment wall, and comprises: a. a reactor vessel which thermally expands and contracts during cyclic operation of the reactor and which has a peripheral wall; b. a containment wall spaced apart from and surrounding the peripheral wall of the reactor vessel and defining an annular thermal expansion gap therebetween for accommodating thermal expansion; and c. an annular ring seal which sealingly engages and is affixed to and extends between the peripheral wall of the reactor vessel and the containment wall, and comprises: a. a reactor vessel which thermally expands and contracts during cyclic operation of the reactor and which has a peripheral wall; b. a containment wall spaced apart from and surrounding the peripheral wall of the reactor vessel and defining an annular thermal expansion gap therebetween for accommodating thermal expansion; and c. an annular ring seal which sealingly engages and is affixed to and extends between the peripheral wall of the reactor vessel and the containment wall, and comprises: 2. The containment arrangement according to claim 1, wherein the containment wall further comprises a shelf, which shelf is provided with a mating plate which sealingly engages and is affixed thereto, the mating plate overlappingly and sealingly engaging and being affixed to the outer peripheral surface of the first annular portion of the annular ring plate. 3. The containment arrangement according to claim 1, further comprising a plurality of support arms, each support arm extending from the cylindrical portion of the annular ring seal toward the reactor vessel and being adapted to rest on the reactor vessel to thereby provide auxiliary support for the annular ring seal. 4. The containment arrangement according to claim 3, wherein the reactor vessel comprises an annular ledge extending outwardly from the reactor vessel toward the containment wall, the annular ledge having a first surface which overlappingly and sealingly engages the leg of the flexure member and wherein each support arm overlappingly engages the annular ledge of the reactor vessel and is provided with alignment means. 5. The containment arrangement according to claim 1, wherein the annular ring plate of the annular ring seal comprises a plurality of arc sections. 6. The containment arrangement according to claim 5, wherein each arc section has a pair of flanges for interconnection thereof with adajacent arc sections, and flange connection means. 7. The containment arrangement according to claim 2, wherein a recess is defined along the outer peripheral surface of the first annular portion of the annular ring plate such that the thickness thereof in the area of the recess is less than the thickness of the remainder thereof to permit plastic deformation of the first annular portion and facilitate overlapping and sealing engagement thereof with the mating plate. 8. A nuclear reactor containment arrangement including: 9. The containment arrangement according to claim 8, wherein the backup member further comprises a flashing which extends from the second perimeter and is biased to engage the peripheral wall of the reactor vessel. 10. The containment arrangement according to claim 8, wherein the reactor vessel further comprises an annular ledge extending outwardly from the peripheral wall thereof, the annular ledge having a first surface which overlapping and sealingly engages the leg of the flexure member. 11. The containment arrangement according to claim 10, wherein the annular ledge has a second surface toward which the second perimeter of the backup member extends. 12. The containment arrangement according to claim 11, wherein the backup member further comprises a flashing which extends from the second perimeter thereof and is biased to engage the second surface of the annular ledge. 13. The containment arrangement according to claim 8, wherein the containment wall further comprises a shelf, which shelf is provided with a mating plate which sealingly engages and is affixed thereto, the mating plate overlappingly and sealingly engaging and being affixed to the outer peripheral surface of the first annular portion of the annular ring plate. 14. The containment arrangement according to claim 13, wherein a recess is defined along the outer peripheral surface of the first annular portion of the annular ring plate such that the thickness thereof in the area of the recess is less than the thickness of the remainder thereof to permit plastic deformation of the first annular portion and facilitate overlapping and sealing engagement thereof with the mating plate. 15. The containment arrangement according to claim 8, further comprising a plurality of support arms, each support arm extending from the cylindrical portion of the annular ring seal toward the reactor vessel and being adapted to rest on the reactor vessel to thereby provide auxiliary support for the annular ring seal. 16. The containment arrangement according to claim 15, wherein the reactor vessel comprises an annular ledge extending outwardly from the reactor vessel toward the containment wall, the annular ledge having a first surface which overlappingly and sealingly engages the leg of the flexure member and wherein each support arm overlappingly engages the annular ledge of the reactor vessel and is provided with alignment means. 17. The containment arrangement according to claim 8, wherein the annular ring plate of the annular ring seal comprises a plurality of arc sections. 18. The containment arrangement according to claim 17, wherein each arc section has a pair of flanges for interconnection thereof with adjacent arc sections, and flange connection means. 19. The containment arrangement according to claim 1, wherein the flexure member, in a longitudinal plane containing the longitudinal axis, has an L-shaped cross-section and the leg thereof is linear in cross-section. 20. The containment arrangement according to claim 1, wherein the reactor vessel comprises an annular ledge extending outwardly from the reactor vessel toward the containment wall and wherein the flexure member is nested under the annular ledge whereby the flexure member is substantially protected from vertically dropped objects. 21. A nuclear reactor containment arrangement including: 22. The containment arrangement according to claim 21, wherein the leg of the flexure member extends downwardly from the annular base plate. 23. The containment arrangement according to claim 21, wherein the reactor vessel has a flange provided on the peripheral wall thereof and an annular ledge provided on the flange, wherein the containment wall has an annular shelf which lies substantially in the same plane as the annular ledge of the reactor vessel, wherein the annular base plate is offset from the plane occupied by the annular ledge and the annular shelf, and wherein the leg of the flexure member sealingly engages and is affixed to the annular ledge of the reactor vessel. 24. The containment arrangement according to claim 23, wherein the annular base plate is offset and positioned above the plane occupied by the annular ledge and the annular shelf, and wherein the leg of the flexure member extends downwardly from the annular base plate. |
047568747 | description | DETAILED DESCRIPTION OF THE INVENTION Naturally occurring zinc has an approximate isotopic composition as follows: ______________________________________ Isotope Concentration (%) ______________________________________ .sup.64 Zn 48.6 .sup.66 Zn 27.9 .sup.67 Zn 4.1 .sup.68 Zn 18.8 .sup.70 Zn 0.6 ______________________________________ The zinc used in accordance with the present invention has a composition in which the .sup.64 Zn is present in a substantially lower proportion than that indicated above, the term "substantially lower" referring to any amount which results in a significant lessening of the amount of radiation that arises from the zinc itself due to its exposure to neutron irradiation inside the reactor. In more specific terms, it is preferred that the proportoin of .sup.64 Zn be lowered to less than about 10%, particularly less than about 1%. It is most preferred that the zinc be substantially devoid of the isotope. Treatment of the zinc to reduce the .sup.64 Zn content or to remove the latter entirely may be done according to conventional techniques for isotope separation of metals. Application of these techniques to zinc is within the routine skill of those skilled in the art. One such separation process is the gaseous-diffusion process. According to this process, zinc is first highly purified and converted to the vapor state, generally by reaction to form volatile compounds such as fluorinated zinc alkyls. The vaporized compound is then pumped through a series of diffusion aggregates arrayed in cells in a cascade pattern. The various isotopes diffuse through the cells at slightly different rates, permitting separation. High degrees of separation may be achieved by the use of multiple stages. Another example is centrifugal isotope separation, again using zinc in the vapor state. Dimethyl fluorinated zinc is one example of a volatile zinc compound which renders zinc susceptible to this kind of separation. Other methods of separation include electromagnetic separation, liquid thermal diffusion, and laser excitation. In the laser excitation process, zinc vapor is ionized by means of a tunable lazer specific to a wavelength which selectively excites .sup.64 Zn atoms to form positive ions, which are then collected on a negative electrode. The remaining vapor is accordingly comprised of zinc depleted of this isotope. Still further methods will be known to those skilled in the art. Once the zinc has been treated to reduce or eliminate its .sup.64 Zn content, it is added to the reactor water in any form which will result in zinc ion in solution. The zinc may thus be added in the form of a salt such as, for example, zinc chromate, or as zinc oxide. With zinc oxide, no extraneous anions are added. The use of zinc oxide is preferred. The major component of radioactive deposition on the walls of water-bearing vessels in nuclear reactors is radioactive cobalt. While inhibition of the radioactive cobalt deposition may be achieved with very small amounts of zinc, the actual amount used is not critical and may vary over a wide range. For most applications, a concentration from about 1 to about 1,000 ppb (parts per billion by weight). preferably from about 3 to about 100 ppb, maintained in the reactor water during operation of the reactor will provide the best results. The invention may be applied to any waterbearing vessel in a nuclear reactor in which radioactive depositions tend to occur. Such vessels may include tubes, shells, feed and recirculation piping, and transfer and storage vessels in general. Recirculation piping is of particular concern, since it is a major source of exposure to plant workers during maintenance shutdowns. The zinc oxide may be added through feedlines to such vessels or, where appropriate, to recirculation lines branching off of such vessels. The zinc oxide may be added in any form which permits it to be dissolved in the reactor water. Examples include slurries, pastes, and preformed solutions. When pastes or slurries are used, the zinc oxide is preferably in the form of a finely divided powder, fumed zinc oxide being most preferred. The zinc oxide contents in these pastes and slurries are not critical, since the concentration in the reactor vessels where the zinc oxide is needed may be controlled by the rate of addition of the paste or slurry to the incoming water. In most cases, pastes will have zinc oxide contents ranging from about 25% to about 95% by weight, preferably from about 40% to 80%. Slurries will generally contain from about 0.1% to about 20% by weight, preferably from about 1% to about 5%. A convenient way of adding the zinc oxide as an aqueous solution is to pass a stream of the water entering the vessel over solid zinc oxide in a receptacle located either in the feed line or in a recirculation loop. A bed of zinc oxide pellets or particles, preferably sintered, will provide effective results. Examples of ways in which the zinc oxide may be added are described in commonly assigned copending application Ser. No. 900,927, filed Aug. 27, 1986, which is incorporated herein by reference. The present invention is applicable to water-cooled nuclear reactors in general, including light water reactors and heavy water reactors. The invention finds particular utility in boiling water reactors. The foregoing is offered primarily for purposes of illustration. It will be readily apparent to those skilled in the art that numerous modifications and variations of the features of construction and operation disclosed herein may be made without departing from the spirit and scope of the invention. |
claims | 1. An extended lifetime system for generating neutrons comprising:an external enclosure;an insulating dielectric contained within the external enclosure;a high voltage power supply;a target at a target location capable of being loaded with hydrogen isotopes selected from the group consisting of: deuterium and tritium;an ion source assembly configured to supply a beam of ions, the ion source assembly comprising:a vessel comprising a wall made from an insulator material and having a plasma source cavity containing a plasma source from which a plasma is generated;an anode electrode, connected to the high voltage power supply, the anode electrode being configured to bias the plasma;an external applicator that is:electrically connected to an excitation signal source, andconfigured to deposit electromagnetic energy into the plasma source cavity through electromagnetic fields passing through the wall made from an insulator material,wherein the external applicator is selected from the group consisting of an RF antenna and a microwave launcher,wherein an insulating gap comprising the insulating dielectric separates the external applicator and the plasma source cavity; anda target electrode electrically coupled to the targetwherein the high voltage power supply is configured to deliver a voltage between the anode electrode and the target electrode between 10 kV and 500 kV. 2. The system according to claim 1, wherein the target electrode is electrically grounded to the external enclosure. 3. The system according to claim 1, wherein the target is physically located outside of the external enclosure. 4. The system according to claim 1, further comprising a gas-filling port, a sealing mechanism, and a gas reservoir containing hydrogen isotopes. 5. The system according to claim 1, further comprising a plurality of sensors and diagnostic instruments selected from the group consisting of: a charged-particle detector, a neutron detector, a photon detector, a beam sensor, a current detector, a voltage detector, a resistivity monitor, a temperature sensor, a pressure gauge and a sputtering meter. 6. The system according to claim 1, wherein the target is located near an extreme end of the system to place maximum neutron flux on objects under test. 7. The system according to claim 1, further comprising a magnetic field producing structure, the magnetic field producing structure having at least one magnet configured to produce a magnetic field having a peak magnetic induction between 0.001 to 1 Tesla near one or more ion beam extraction locations. 8. The system according to claim 1, further comprising a suppression electrode connected to a voltage supply configured to bias the suppression electrode between 0 and −10 kV relative to the target electrode. 9. The system according to claim 8, wherein the target location is beyond the suppressor electrode in a path of the ion beam. 10. The system according to claim 1, further comprising a surface material of the target that can be deposited and/or refreshed in situ. 11. The system according to claim 1, further comprising an extraction electrode and/or beam-bunching electrodes. 12. The system according to claim 1, wherein the insulating dielectric is a solid material. 13. The system according to claim 1, wherein the microwave launcher is selected from the group containing a waveguide, dielectric window or antenna launching structure. 14. The system according to claim 1, wherein the external applicator is configured to supply electromagnetic energy having a frequency of between 0.1 MHz and 20 GHz to the plasma source cavity. 15. The system according to claim 1, wherein the target electrode is thermally-connected to one or more of a thermal management system and a vacuum vessel that encloses the plasma source cavity. 16. The system according to claim 1, wherein the target electrode is one or more of thermally-connected to the external enclosure and electrically-connected to the external enclosure. 17. The system according to claim 1, wherein the high-voltage power supply is contained within the external enclosure. 18. The system according to claim 1 wherein in operation the external applicator is maintained near ground electric potential. 19. The system according to claim 1, wherein the target material comprises lithium. 20. A method for generating neutrons using a neutron generator comprisingan external enclosure;an insulating fluid contained within the external enclosure;a high voltage power supply;a target at a target location supporting a layer of target material capable of being loaded with hydrogen isotopes selected from the group consisting of: deuterium and tritium;an ion source assembly configured to supply a beam of ions, the ion source assembly comprising:a vessel comprising a wall made from an insulator material and having a plasma source cavity containing a plasma source from which a plasma is generated;an anode electrode, connected to the high voltage power supply, the anode electrode being configured to bias the plasma;an external applicator that is:electrically connected to an excitation signal source, andconfigured to deposit electromagnetic energy into the plasma source cavity through electromagnetic fields passing through the wall made from an insulator material,wherein the external applicator is selected from the group consisting of an RF antenna and a microwave launcher,wherein an insulating gap comprising the insulating fluid separates the external applicator and the plasma source cavity; anda target electrode electrically coupled to the targetwherein the high voltage power supply is configured to maintain a voltage between the anode electrode and the target electrode between 10 kV and 500 kV,the method comprising:feeding an excitation signal to the external applicator;coupling, through electromagnetic fields, electromagnetic energy produced by the external applicator into a gas within the plasma source cavity;extracting, from the plasma source cavity, an ion beam, andcausing the ions in the ion beam to collide with target material in the target material layer to generate neutrons. 21. The method according to claim 20, further comprising one or more of the group consisting of:applying an extraction electrode or electrostatic field shaping element to improve beam quality such that a substantial fraction of ions exiting the ion source are on trajectories to impinge on the target;substantially occluding metallic electrodes from contacting the plasma contained within the ion source to reduce sputtering and erosion; andoperating a plasma source at or near a resonance condition to generate a majority fraction of monatomic ions that improve the effective energy per ion accelerated to a target location,wherein the plasma ion source is generated in a cavity having one or more reduced atomic-recombination surfaces resulting from material selection and surface treatment and one or more constrictions that decrease the flow of neutral atomic species out of the ion source. |
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description | 1. Field of the Invention The present invention relates generally to nuclear reactors, and more particularly, to nuclear reactors having fuel assemblies that employ grids. 2. Description of the Related Art In most water cooled nuclear reactors, the reactor core is comprised of a large number of elongated fuel assemblies. In pressurized water nuclear reactors, these fuel assemblies typically include a plurality of fuel rods held in an organized array by a plurality of grids spaced axially along the fuel assembly length and attached to a plurality of elongated thimble tubes. The thimble tubes typically receive control rods or instrumentation therein. Top and bottom nozzles are on opposite ends of the fuel assembly and are secured to the ends of the thimble tubes that extend slightly above and below the ends of the fuel rods. During manufacture, subsequent installation and repair of components of the nuclear reactor coolant circulation system, a diligent effort is made to help assure the removal of all debris from the reactor vessel and its associated systems, which circulate coolant throughout the primary reactor coolant loop under various operating conditions. Although elaborate procedures are carried out to help assure debris removal, experience shows that in spite of the safeguards used to effect such removal, some chips and metal particles still remain hidden in the system. Most of the debris consists of metal turnings, which were probably left in the primary system after steam generator repair or replacement. Fuel assembly damage due to debris trapped at the lower most grid has been noted in several reactors. Debris enters through the fuel assembly bottom nozzle flow holes from the coolant flow openings in the lower core support plate when the plant is started up. The debris tends to be engaged in the lower most support grid of the fuel assembly within the spaces between the fuel rod support cell walls of the grid and the lower end portions of the fuel rod tubes. The damage consists of fuel rod tube perforations caused by fretting of the debris in contact with the exterior of the cladding tubes which sealably enclose the fissile material in the fuel rod. Debris also becomes entangled in the lower nozzle plate holes. The flowing coolant causes the debris to gyrate, which tends to cut through the cladding of the fuel rods. Due to the potential for debris to damage components of the fuel assembly, it is known to additionally provide a protective grid that is disposed between the bottom support grid and the lower nozzle. The protective grid functions as a filter to protect the fuel rods from debris. It is also known to securely dispose the protective grid against the lower nozzle and to space the protective grid from the lower nozzle in order to avoid undesirable contact between the lower nozzle and irregularities on the edges of the assembled straps of the grid. All of the grids of the fuel assemblies of the nuclear reactor, including the protective grids, are typically made up of a plurality of straps that are arranged in a lattice pattern and are fastened to one another to define a plurality of cells. The cells include control rod guide thimble cells and fuel rod cells. The top support grid, bottom support grid and middle support grids are mechanically or otherwise fastened to the thimble tubes which are disposed in the thimble cells. The fuel rods typically are held within the fuel rod cells of the grids, including the protective grid, by a plurality of springs and/or dimples within each fuel rod cell that are formed in the straps of the grids. The protective grid typically has spacers that are welded or otherwise attached to the underside of the grid and are securely captured between the protective grid and the fuel assembly bottom nozzle. Cracking has recently been experienced in the protective grid features which has led to fuel rod failures. These failures have been determined to be caused by intergranular cracking, consistent with stress corrosion cracking. One of the sources of stress is the differential thermal expansion between the bottom nozzle and the protective grid, since the bottom nozzle is made of stainless steel and the protective grid is made of alloy-718. These parts are rigidly connected via a thimble screw which is screwed through the underside of the bottom nozzle and into the end plug on the control rod guide thimble. The stainless steel expands more during heat up than does the alloy-718, thus causing stresses in the protective grid, particularly near the attachment point. Accordingly, a new means of attaching the protective grid is desired that will avoid the build-up of stresses during heat-up of the reactor. This invention achieves the foregoing objective by providing an improved fuel assembly for a nuclear reactor. The fuel assembly has a plurality of elongated nuclear fuel rods having an extended axial length. A lower most grid supports the fuel rods in an organized array having unoccupied spacers to allow a flow of fluid coolant therethrough and past the fuel rods when the fuel assembly is installed in the nuclear reactor. A plurality of guide thimbles extend along the fuel rods and through the lower most grid. A bottom nozzle is disposed below the grid, below the lower ends of the fuel rods and supports the guide thimbles and permits the flow of fluid coolant into the fuel assembly. The bottom nozzle includes a substantially horizontal plate that extends transverse to the axis of the fuel rods and has an upper face directed toward the lower most grid. The upper face of the nozzle plate has defined therethrough a plurality of flow through holes that extend completely through the nozzle plate for the passage of the fluid coolant from a lower face of the nozzle plate to an upper face, with each of the coolant flow through holes in fluid communication with the unoccupied spaces. The lower most grid includes a plurality of straps that are interconnected with one another to define at least a first thimble cell through which one of the guide thimbles is supported. The straps each include a lower edge. A spacer in the form of a spacer plate is situated between the lower edge of the straps and the upper face of the bottom nozzle. The spacer plate has a substantially planar engagement surface and a substantially planar retention surface opposite one another, and is fixedly mounted on the underside of the lower most grid with the engagement surface protruding outwardly from the lower most grid. The engagement surface is structured to be disposed on the upper face of the bottom nozzle between the edge of the straps defining the first thimble cell and the upper face of the nozzle to space the grid from the nozzle. A hole in the spacer plate is structured to receive at least a portion of a fastener therethrough and the retention surface is structured to receive the end of the thimble tube when the fastener is received through the hole and is connected with the thimble tube. A portion of the end of the thimble tube protrudes through the hole to directly contact the upper face of the bottom nozzle and the portion of the end of the thimble tube that protrudes through the hole is sized to create a space in both the axial and radial directions between the end of the thimble tube and the spacer, so that in a cold condition the spacer does not substantially contact the end of the thimble tube. Preferably, the space between the end of the thimble tube and the spacer is large enough to accommodate any differential in thermal expansion between the spacer material, the nozzle material and the end of the thimble tube. Desirably, the lateral space between the end of the thimble tube and the spacer is approximately between 0.001 and 0.002 inches (0.003 and 0.005 cms.). The lateral clearance takes up the differential thermal expansion. In addition, a small axial clearance provides for a non-rigid connection so that the grid, spacer and bottom nozzle can move independently. Referring now to the drawings and particularly to FIG. 1, there is shown an elevational view of a fuel assembly, represented in vertically shortened form and being generally designated by reference character 10. The fuel assembly 10 is of the type used in a pressurized water reactor and has a structural skeleton which, at its lower end includes a bottom nozzle 12. The bottom nozzle 12 supports the fuel assembly 10 on a lower core support plate 14 in the core region of the nuclear reactor (not shown). In addition to the bottom nozzle 12, the structural skeleton of the fuel assembly 10 also includes a top nozzle 16 at its upper end and a number of guide tubes or thimbles 18, which extend longitudinally between the bottom and top nozzles 12 and 16 and at opposite ends are rigidly attached thereto. The fuel assembly 10 further includes a plurality of transverse grids 20 axially spaced along and mounted to the guide thimbles 18 and an organized array of elongated fuel rods 22 transversely spaced and supported by the grids 20. Also, the fuel assembly 10 has an instrumentation tube 24 located in the center thereof that extends between and is either captured by or mounted to the bottom and top nozzles 12 and 16. With such an arrangement of parts, fuel assembly 10 forms an integral unit capable of being conveniently handled without damaging the assembly of parts. As mentioned above, the fuel rods 22 in the array thereof in fuel assembly 10 are held in spaced relationship with one another by the grids 20 spaced along the fuel assembly length. Each fuel rod 22 includes nuclear fuel pellets 26 and is closed at opposite ends by upper and lower end plugs 28 and 30. The pellets 26 are maintained in a stack by a 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 reactive power of the reactor. A liquid moderator/coolant such as water or water-containing boron, is pumped upwardly through a plurality of flow openings in the lower core plate 14 to the fuel assembly. The bottom nozzle 12 of the fuel assembly 10 passes the coolant upwardly through the guide tubes 18 and along the fuel rods 22 of the assembly in order to extract heat generated therein for the production of useful work. To control the fission process, a number of control rods 34 are reciprocably movable in the guide thimbles 18 located at predetermined positions in the fuel assembly 10. Specifically, a rod cluster control mechanism 36 positioned above the top nozzle 16 supports the control rods 34. The control mechanism has an internally threaded cylindrical hub 37 with a plurality of radially extending flukes or arms 38. Each arm 38 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 18 to thereby control the fission process in the fuel assembly 10, all in a well known manner. A protective grid 40 is the lower most grid in the fuel assembly and functions to restrain debris entering the fuel assembly in the coolant flowing through the bottom nozzle. The protective grids 40 are similar to the other grids 20 in that they are made up of a plurality of straps that are arranged in a lattice pattern and are fastened to one another to define the plurality of cells some of which support fuel rods and others of which support control rod guide thimbles. A cross section of a prior art protective grid 40 attached to a bottom nozzle 12 is shown in FIG. 2. The fuel rod cells are designated by reference character 42 and the guide thimble cells are designated by reference character 46. Each of the fuel rod cells has dimples 54 for supporting the fuel rods within the cells. A guide thimble 18 having an end plug 48 is secured within a guide thimble support cell 46 by a thimble screw 50 that is screwed through the underside of the bottom nozzle 12 into the end plug 48 to secure the guide thimble 18 to the bottom nozzle 12. A spacer 52 is interposed between the bottom nozzle 12 and the end plug 48. FIG. 2 illustrates the basic geometry of a current protective grid joint typically employed in fuel assemblies with a “tube-in-tube” configuration, where the bottom grid does not have inserts. The “tube-in-tube” design refers to fuel assemblies that have control rod guide thimbles that include a dashpot that is formed from a tube inside the thimble cladding and employ grid straps that are constructed from Zircalloy or Inconel, and guide thimbles constructed from Zircalloy. In such an arrangement relatively short lengths of either Zircalloy or Inconel sleeves are welded or braised to the control rod guide thimble support cells. The Zircalloy guide thimbles 18 are then inserted through these sleeves and the guide thimbles are bulged at the sleeve location to establish a mechanical joint that affixes the grids to the guide thimbles at the appropriate elevations. In the tube-in-tube configuration, the protective grid has the spacer 52 inserted between the control rod guide thimble end plug 48 and the bottom nozzle 12 with the ends of the spacer wrapped around and welded to the walls of the adjacent fuel rod support cells 42. This configuration provides for a very rigid joint. Recently, cracking of the protective grid features has been identified which has led to fuel rod failures. These failures have been determined to be intergranular cracking, consistent with stress corrosion cracking. One of the sources of stress is the differential thermal expansion between the bottom nozzle 12 and the protective grid 40 since the bottom nozzle is made of stainless steel and the protective grid is made of Alloy-718. The stainless steel expands more during heat-up than does the Alloy-718, thus causing stresses in the protective grid, particularly near the attachment point. This invention provides a new means of attachment that will avoid the stresses that had previously built up during heat up of the reactor. FIG. 3 illustrates the attachment arrangement of this invention that uses the same spacer design 52 as the current configuration illustrated in FIG. 2, except that the hole 56 in the spacer 52 is larger. The spacer 52 is captured between either the bottom grid insert end plug (for a swaged dash-pot design) or the thimble tube end plug (for tube-in-tube designs, the latter being shown in FIG. 3). The key difference is that there is a step 58 in either the insert end plug or the guide tube end plug such as to provide a minimal lateral and axial clearance between the end plug 48 and the spacer 52. The lateral clearance 44 is just enough to accommodate tolerances and the differential in thermal expansion among the parts. Preferably, the axial clearance 60 is between 0.001 inch to 0.010 inch (0.003 to 0.025 cm) and preferably between 0.001 inch to 0.002 inch, (0.003 and 0.005 cm). This small clearance will allow for a small amount of relative movement between the parts during heat-up and expansion of the parts. The lateral clearance 44 is at least as, if not more important than the axial clearance 60. There is no substantial axial differential thermal expansion, only lateral. However, the clearance will be sufficiently small to preclude vibration of the grid during operation or significant movement of the grid prior to rod loading. Since a significant portion of the grid retention force is the interaction with the rods, and since the flow in the joint area is not high and the relative clearance of the parts is not large, vibration of the joint is not a significant concern. However, the clearance between the spacer 52 and the end plug 48 will be sufficient to significantly reduce the stresses experienced by the protective grid that were responsible for the intergranular cracking and fuel rod failures that have been experienced. 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 breath of the appended claims and any and all equivalents thereof. |
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claims | 1. A method for optimizing a binary mask pattern, the method comprising:determining, by a hardware processor, an evaluation value based on a comparison between a design pattern and a substrate pattern simulated based on the binary mask pattern;based on the evaluation value, using, by the processor, a gradient-based optimization method to generate a first adjusted binary mask pattern;determining, by the processor, a first updated evaluation value based on a comparison between the design pattern and a first updated substrate pattern simulated based on the first adjusted binary mask pattern;based on the first updated evaluation value, using, by the processor, a product of a Hessian matrix and an arbitrary vector to generate a second adjusted binary mask pattern; andsimulating, by the processor, a second updated substrate pattern based on the second adjusted binary mask pattern. 2. The method of claim 1, wherein the evaluation value is based on at least one selected from: an edge placement error (EPE) of the substrate pattern, a nominal process window condition, a mask error enhancement factor (MEEF), and/or a side-lobe printing indication value indicative of a possibility of side-lobe printing in the substrate pattern. 3. The method of claim 1, further comprising:based on a determination that the evaluation value is greater than or equal to a predetermined threshold, using, by the processor, the gradient-based optimization method to generate the first adjusted binary mask pattern; andbased on a determination that the evaluation value is less than the predetermined threshold, outputting the binary mask pattern for mask making. 4. The method of claim 1, further comprising:based on a determination that the first updated evaluation value is greater than or equal to a predetermined threshold, using, by the processor, the product of the Hessian matrix and the arbitrary vector to generate the second adjusted binary mask pattern; andbased on a determination that the first updated evaluation value is less than the predetermined threshold, outputting the first adjusted binary mask pattern for mask making. 5. The method of claim 1, further comprising determining, by the processor, a second updated evaluation value based on a comparison between the design pattern and the second updated substrate pattern. 6. The method of claim 5, further comprising:based on a determination that the second updated evaluation value is greater than or equal to a predetermined threshold, using, by the processor, a product of the gradient-based optimization method to generate a third adjusted binary mask pattern; andbased on a determination that the second updated evaluation value is less than the predetermined threshold, outputting the second adjusted binary mask pattern for mask making. 7. The method of claim 1, wherein the evaluation value corresponds to a similarity between the design pattern and the substrate pattern. 8. An apparatus for optimizing a binary mask pattern, the apparatus comprising:a processor; anda memory coupled to the processor, the memory storing instructions which, when executed by the processor, become operational with the processor to at least:determine an evaluation value based on a comparison between a design pattern and a substrate pattern simulated based on a binary mask pattern;based on the evaluation value, use a gradient-based optimization method to generate a first adjusted binary mask pattern;determine a first updated evaluation value based on a comparison between the design pattern and a first updated substrate pattern simulated based on the first adjusted binary mask pattern;based on the first updated evaluation value, use a product of a Hessian matrix and an arbitrary vector to generate a second adjusted binary mask pattern; andsimulate a second updated substrate pattern based on the second adjusted binary mask pattern. 9. The apparatus of claim 8, wherein the evaluation value is based on at least one selected from: an edge placement error (EPE) of the substrate pattern, a nominal process window condition, a mask error enhancement factor (MEEF), and/or a side-lobe printing indication value indicative of a possibility of side-lobe printing in the substrate pattern. 10. The apparatus of claim 8, wherein the memory comprises instructions operational with the processor to:based on a determination that the evaluation value is greater than or equal to a predetermined threshold, use the gradient-based optimization method to generate the first adjusted binary mask pattern; andbased on a determination that the evaluation value is less than the predetermined threshold, output the binary mask pattern for mask making. 11. The apparatus of claim 8, wherein the memory comprises instructions operational with the processor to:based on a determination that the first updated evaluation value is greater than or equal to a predetermined threshold, use the product of the Hessian matrix and the arbitrary vector to generate the second adjusted binary mask pattern; andbased on a determination that the first updated evaluation value is less than the predetermined threshold, output the first adjusted binary mask pattern for mask making. 12. The apparatus of claim 8, wherein the memory comprises instructions operational with the processor to determine a second updated evaluation value based on a comparison between the design pattern and the second updated substrate pattern. 13. The apparatus of claim 12, wherein the memory comprises instructions operational with the processor to:based on a determination that the second updated evaluation value is greater than or equal to a predetermined threshold, use a product of the gradient-based optimization method to generate a third adjusted binary mask pattern; andbased on a determination that the second updated evaluation value is less than the predetermined threshold, output the second adjusted binary mask pattern for mask making. 14. The apparatus of claim 8, wherein the evaluation value corresponds to a similarity between the design pattern and the substrate pattern. 15. A non-transitory computer-readable storage medium, comprising instructions for optimizing a binary mask pattern, which instructions, when executed by a processor, become operational with the processor to at least:determine an evaluation value based on a comparison between a design pattern and a substrate pattern simulated based on a binary mask pattern;based on the evaluation value, use a gradient-based optimization method to generate a first adjusted binary mask pattern;determine a first updated evaluation value based on a comparison between the design pattern and a first updated substrate pattern simulated based on the first adjusted binary mask pattern;based on the first updated evaluation value, use a product of a Hessian matrix and an arbitrary vector to generate a second adjusted binary mask pattern; andsimulate a second updated substrate pattern based on the second adjusted binary mask pattern. 16. The non-transitory computer-readable storage medium of claim 15, wherein the evaluation value is based on at least one selected from: an edge placement error (EPE) of the substrate pattern, a nominal process window condition, a mask error enhancement factor (MEEF), and/or a side-lobe printing indication value indicative of a possibility of side-lobe printing in the substrate pattern. 17. The non-transitory computer-readable storage medium of claim 15, wherein the instructions are operational with the processor to:based on a determination that the evaluation value is greater than or equal to a predetermined threshold, use the gradient-based optimization method to generate the first adjusted binary mask pattern; andbased on a determination that the evaluation value is less than the predetermined threshold, output the binary mask pattern for mask making. 18. The non-transitory computer-readable storage medium of claim 15, wherein the instructions are operational with the processor to:based on a determination that the first updated evaluation value is greater than or equal to a predetermined threshold, use the product of the Hessian matrix and the arbitrary vector to generate the second adjusted binary mask pattern; andbased on a determination that the first updated evaluation value is less than the predetermined threshold, output the first adjusted binary mask pattern for mask making. 19. The non-transitory computer-readable storage medium of claim 15, wherein the instructions are operational with the processor to determine a second updated evaluation value based on a comparison between the design pattern and the second updated substrate pattern. 20. The non-transitory computer-readable storage medium of claim 19, wherein the instructions are operational with the processor to:based on a determination that the second updated evaluation value is greater than or equal to a predetermined threshold, use a product of the gradient-based optimization method to generate a third adjusted binary mask pattern; andbased on a determination that the second updated evaluation value is less than the predetermined threshold, output the second adjusted binary mask pattern for mask making. |
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claims | 1. A fast reactor nuclear fuel element comprising:a metallic fuel slug,the fuel slug consisting essentially of a uranium (U) and zirconium (Zr) alloy; a protective coating layer of an oxide layer,the protective coating layer is coated on a surface of the fuel slug, which causesthe fuel slug to be coated with a single protective coating layer of an oxide layer,the single protective coating layer is formed by oxidation of the fuel slug, thickness of the single protective coating layer is in a range of 0.5 μm to 100 μm, andthe single protective coating layer is preformed on the fuel slug surface prior to fuel slug usage in a fast reactor,the single protective coating layer is configured to prevent interdiffusion between the fuel slug and a cladding tube, to prevent the cladding tube from thinning during fission operation in the fast reactor. 2. A nuclear fuel rod configured for use with a fast reactor comprising:a fast reactor nuclear fuel element of claim 1; anda cladding tube sealing the metal fuel slug. 3. The nuclear fuel rod as set forth in claim 2, wherein the cladding tube comprises one or more selected from the group consisting of iron (Fe), chromium (Cr), tungsten (W), molybdenum (Mo), vanadium (V), titanium (Ti), niobium (Nb), tantalum (Ta), silicon (Si), manganese (Mn), nickel (Ni), carbon (C), nitrogen (N), and boron (B). |
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051724022 | abstract | An exposure method for manufacture of semiconductor devices, includes moving a shutter having an edge so that the edge is related to a predetermined exposure region; projecting an exposure beam to the edge of the shutter and to at least a portion of the exposure region; determining a position of a shadow of the edge of the shutter formed by the exposure beam with respect to a predetermined coordinate system related to movement of a movable chuck; adjusting the shutter in accordance with the determination; placing a substrate on the chuck; moving the chuck so that the substrate is related to the exposure region; and controlling the exposure of the substrate with the exposure beam through the shutter. |
051805278 | claims | 1. Nuclear fuel pellets, consisting of: sintered grains of nuclear fuel substance having a continuous deposition phase in the grain boundaries of said sintered grains, said deposition phase consisting of beryllium oxide alone or a mixture of beryllium oxide and at least one other oxide selected from the group consisting of titanium, gadolinium, calcium, barium, magnesium, strontium, lanthanum, yttrium, ytterbium, silicon, aluminum, samarium, tungsten, zirconium, lithium, molybdenum, uranium and thorium, wherein the amount of beryllium oxide alone is 13.6 wt. % at maximum or wherein the amount of a mixture of beryllium oxide and said other oxides is 12.5 wt. % at maximum. 2. The nuclear fuel pellets of claim 1, wherein the amount of beryllium oxide is 1.5 wt. % at maximum. 3. The nuclear fuel pellets of claim 1, wherein said deposition phase consists of said mixture of beryllium oxide and at least one other oxide. 4. The nuclear fuel pellets of claim 1, wherein said deposition phase consists of beryllium oxide. 5. The nuclear fuel pellets of claim 1, wherein said deposition phase consists of beryllium oxide and titanium oxide. 6. The nuclear fuel pellets of claim 1, wherein said deposition phase consists of beryllium oxide and gadolinium oxide. 7. The nuclear fuel pellets of claim 1, wherein said deposition phase consists of beryllium oxide and silicon oxide. 8. The nuclear fuel pellets of claim 1, wherein said deposition phase consists of beryllium oxide and aluminum oxide. 9. The nuclear fuel pellets of claim 1, wherein said deposition phase consists of beryllium oxide, titanium oxide and gadolinium oxide. |
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H00009369 | description | DETAILED DESCRIPTION OF THE INVENTION Reference will now be made to the present preferred embodiments of the present invention, an example of which is illustrated in the accompanying drawings. FIG. 1 illustrates the power cycle of the present invention, for direct conversion of alpha-particle energy to electricity for a stellarator reactor. This power cycle provides an alternative scheme in energy conversion for deuterium-tritium (D-T) fueled reactors and could become an important method in energy conversion for advanced neutron-lean fueled (e.g. D-He.sup.3) reactors. The direct energy conversion is achieved by alternately compressing and expanding the plasma minor radius of a stellarator reactor 10. The cycle may be used in a stellarator reactor as shown by reactor 10 in FIG. 9. the cycle will now be discussed with reference to a single stellarator reactor 10. (A description of a two-reactor system is described subsequently.) Reactor 10 includes external toroidal magnetic confining coils 12, helical stabilizing coils 13, and vacuum vessel 19. A generator 15 provides electrical energy to coils 12 via line 34. Control means 37 operatively associated with lines 32 and 34 engage and disengage load 17 and generator 15 from toroidal coils 12 in response to plasma parameters. The cycle is composed of three stages. In a preferred embodiment of the present invention, ignited plasma 16 is thermally stable and in thermal balance at stage 0. (Conditions for an ignited plasma may be found in the published literature. For example, reference is made to Controlled Thermonuclear Reactions by Samuel Glasstone and Ralph Lovberg published by D. Van Nostrand Co., Inc., Princeton, N.J., 1960.) The plasma .beta. is slightly above .beta..sub.c. [.beta.=(P/B.sub.i.sup.2 /8.pi.), i.e. the ratio of plasma kinetic to the internal magnetic field pressure, and .beta..sub.c, the maximum attainable .beta., is set by the onset condition for MHD ballooning instabilities.] During the compression phase (from stage 0 to stage 1), plasma 16 is compressed adiabatically by increasing the external toroidal compressed magnetic field strength 14 generated by toroidal coils 12 and the plasma .beta. decreases. At stage 1, the end of the compression phase, .beta. is less that .beta..sub.c and the plasma 16 is no longer in thermal balance since the thermonuclear alpha-particle heating power exceeds the rate of energy loss (due to neoclassical transport, turbulent convection, and Bremsstrahlung radiation). During the heating phase (from stage 1 to stage 2), as the plasma temperature is driven up by the excess heating power, the plasma volume is kept constant by further increasing the external field strength 14. As .beta. approaches .beta..sub.c, the rate of energy loss increases until it balances the alpha-particle heating power when .beta. reaches .beta..sub.c. The plasma 16 is again in thermal balance and is thermally stable. This is stage 2 of the cycle. To complete the cycle, the external field 14 is then reduced so that the plasma 16 expands back to its original radius during the expansion phase (from stage 2 to stage 0). When the plasma 16 expands, the plasma .beta. tends to increase. However, .beta. is already at .beta..sub.c at stage 2, hence ballooning instabilities force .beta. to stay at .beta..sub.c through turbulent convection during the entire expansion phase. As a result, the plasma pressure during the expansion is higher than the corresponding pressure during the compression. Therefore, negative work is done on the plasma 16 during a complete. cycle. Note that if there is no .beta. limit, then more work can be obtained during a complete cycle. This work manifests itself as a back-voltage in the toroidal field coils 12 and direct electrical energy is obtained from this voltage. By operating two or more reactors in tandem, the cycle can be made self-sustaining. As an alternative cycle, net work is done on the external system by letting the plasma expand at constant pressure between stages 1 and 2, rather than keeping the plasma at constant volume. These two methods (heating phase at constant plasma volume and at constant plasma pressure) are discussed below as the preferred embodiments of the present invention. As will be recognized by those skilled in the art, there are many other possible methods, that can also result in net work done, e.g. the plasma minor radius varies sinusoidally during the cycle. If the external magnetic field 14 is considered to be a "piston," then the external system absorbs work done by the pumping action of the plasma 16 on the piston. This action will be referred to as "magnetic pumping". It is "inverse magnetic pumping" over a full cycle because work is done on the external system by the plasma 16. Note that this concept of magnetic pumping differs from the traditional definition which refers to "gyro-relaxation,". The detailed physical processes at, and between, various stages of the cycle are analyzed below. To simplify the analysis, the plasma column is modeled by a straight cylinder. The plasma density, temperature, and the magnetic field 18 are assumed to be uniform across the minor radius except for a sharp discontinuity across the boundary between the plasma 16 and the confining vacuum magnetic field 14. Throughout this analysis, the plasma is assumed to behave like an ideal MHD fluid. Due to the nonlinear temperature dependence of the alpha-particle heating power term and the power loss terms, the thermonuclear plasma in a stellarator can have more than one thermal equilibrium, i.e., the thermonuclear power can balance the power losses at different temperatures, or have no equilibrium at all. A qualitative discussion about the possible thermal equilibria and their stability is given here. The reactor parameters listed in Table I are used in the discussion here. TABLE I. ______________________________________ STELLARATOR REACTOR PARAMETERS ______________________________________ Plasma density (cm.sup.-3) 6 .times. 10.sup.14 Plasma temperature (keV) 10 Toroidal magnetic field (KG) 50 Plasma .beta. (%) 19.3 Major Radius (m) 10 Minor Radius (m) 2 .epsilon.h 0.1 ______________________________________ For a fixed plasma density (n=6.times.10.sup.14 cm.sup.-3), the thermonuclear alpha-particle heating power per unit volume is plotted versus plasma temperature as the solid curve in FIG. 2. In the same figure, the power loss per unit volume [due to neoclassical diffusion (discussed below) and Bremstrahlung radiation] as a function of temperature appears as the dashed curve. (The power loss due to turbulent convection is not included in this dashed curve but its effect on thermal equilibrium is disclosed below). FIG. 2 indicates that there are two equilibrium solutions. The first (point A) is thermally unstable. If the plasma temperature decreases slightly, the neoclassical diffusion and Bremsstrahlung radiation losses will begin to dominate and hence the plasma temperature will decrease to zero. On the other hand, if there is a slight increases in plasma temperature, the alpha-particle heating power will dominate and thus the plasma temperature will proceed on a thermal excursion until the loss rate matches the heating power at a stable thermal equilibrium, which is the second equilibrium solution (point C). (Similar discussions for tokamak reactors have been given by Conn, Fusion, Academic Press, N.Y. (1981), and by Kolesnichenko and Reznik, Plasma Physics and Controlled Nuclear Fusion Research, 1976, Proc., 6th Int. Conf. Berchtesgaden, 1976, vol. 3, IAEA, Vienna 1977, 347.) Thus, to start a stellarator reactor, it is only necessary to raise the plasma temperature to the unstable equilibrium at point A, even if the desired operating condition at the stable equilibrium is at a higher temperature. It is interesting to note that if a.sub.0 is reduced to 1.5 m, but all the other reactor parameters remain unchanged, then the stable thermal equilibrium occurs at some temperature between 7-8 keV. The stable thermal equilibrium (point C) in FIG. 2 requires a plasma temperature of approximately 11 keV. If .beta..sub.c =19.3%, then .beta. at point C exceed .beta..sub.c. As a result, pressure driven turbulent convection will increase the power loss, raise the loss curve, and force the stable equilibrium to occur at a lower plasma temperature (point B) such that .beta..congruent..beta..sub.c. (As .beta. approaches .beta..sub.c, the plasma will follow the broken curve in FIG. 2). After adiabatic compression, due to the increase in both the alpha-particle heating power and the power losses, the solid curve in FIG. 2 shifts upward and the equilibrium point shifts toward higher plasma temperature and power (the upper-right hand corner). As discussed below, the increase in the alpha-particle heating power is greater than the increase in the power losses. This implies that, immediately after compression the plasma temperature is located somewhere between the corresponding thermal equilibria (points A and B) of the shifted curves. Consequently, the plasma temperature continues to rise until it reaches a new stable equilibrium. Before the compression, the ignited plasma 16 is in thermal balance, at a stable thermal equilibrium. The plasma .beta. is slightly above .beta..sub.c. Thus, the plasma pressure gradient exceeds the critical pressure gradient by a small amount. Turbulent convective cells are driven by this excess pressure gradient and carry part of the outward particle and energy fluxes as discussed by Ho and Kulsrud, PPPL-2251; the rest of the fluxes are carried by neoclassical transport as discussed by Ho and Kulsrud, PPPL-2253. This is stage 0 in the power cycle. The plasma and magnetic field parameters are: ______________________________________ Plasma .beta. .beta..sub.0 = .beta..sub.c, Plasma pressure P.sub.0, Plasma minor radius: a.sub.0, Internal magnetic field: B.sub.i0, External magnetic field: B.sub.e0. ______________________________________ The subscript 0 refers to the physical quantities at stage 0. During the compression phase from stage 0 to stage 1, the plasma 16 is compressed adiabatically as the external toroidal magnetic field strength 14 is increased. Adiabatic compression occurs if the compression time is shorter than the burn time (the time for the thermonuclear alpha-particles to increase the plasma temperature by an amount comparable to itself). It is important for the compression to be adiabatic because otherwise, the alpha-particles could heat up the plasma and more work would be required during the compression phase. On the other hand, as explained below, the compression phase must be carried out slowly compared with .tau..sub.i and .tau..alpha. (the 90.degree. deflection times for ions and alpha-particles) so that the compression is three-dimensional. The plasma .beta. decreases during the compression because the internal magnetic field pressure increases faster than the plasma kinetic pressure. This can be shown explicitly if the plasma .beta. is expressed in terms of P.sub.0 and B.sub.i0. Using the adiabatic compression law (PV.sup..gamma. =const with .gamma.=5/3), the definition of .beta., and the frozen flux condition, the plasma .beta. can be expressed as ##EQU1## Here r.sub.v (t)=a.sub.0 /a(t) is the compression ratio. During the compression, r.sub.v increases from unity to a.sub.0 /a, and thus .beta. decreases. If .beta..sub.c is roughly constant, then the plasma .beta. is below .beta..sub.c after compression. This is stage 1 in the power cycle. The plasma and magnetic field parameters are: ______________________________________ Plasma .beta.: .beta..sub.1 < .beta..sub.0 = .beta..sub.c, Plasma pressure: P.sub.1 > P.sub.0, Plasma minor radius: a.sub.1 < a.sub.0, Internal magnetic field: B.sub.i1 > B.sub.i0, External magnetic field: B.sub.e1 > B.sub.e0. ______________________________________ The subscript 1 refers to the physical quantities at stage 1. After the adiabatic compression, the increase in alpha-particle heating power per unit volume is larger than the increase in neoclassical energy diffusion and Bremsstrahlung radiation losses per unit volume. Also, turbulent convective transport can be assumed to be absent after compression since .beta. is less than .beta..sub.c. This imbalance between the heating power and the power loss causes the plasma temperature to increase while the plasma volume is kept constant by further increasing the external magnetic field strength 14. The increase in temperature can be understood in more detail from the volume-averages energy balance equation ##EQU2## The first term on the right-hand side of this equation is the heating power from the thermonuclear alpha-particles. The first term inside the bracket is the energy loss rate due to neoclassical diffusion, i.e. ##EQU3## As discussed by Ho et al., PPPL-2253, the electron energy confinement time is ##EQU4## and the ion energy confinement time is EQU .tau..sub.E.sup.i .congruent..tau..sub.E.sup.e. Here the minor radius a.sub.m and the major radius R.sub.m are in meters, B.sub.4 is in 10KG, electron or ion density n.sub.14 is in 10.sup.14 cm.sup.-3, plasma temperature T.sub.4 is in 10 keV, .epsilon..sub.h is the depth of the helical magnetic well caused by external helical windings, and the normalized ambipolar electric field strength C.congruent.(e/T)(.differential..PHI./.differential.r)n(.differential.n/.d ifferential.r).sup.-1 can be approximated by unity. The second term inside the bracket in Eq. (2) is the convective energy loss rate. The last terms is the energy loss rate due to Bremsstrahlung radiation and is equal to cn.sup.2 .sqroot.T, with "c" a constant. Note that density is not a function of time during the heating phase since the plasma volume is held fixed. Also note that before the compression, thermal balance means that dT/dt=0. The ratio of the value of each term on the right-hand side of Eq. (2) after the adiabatic compression to the value of the corresponding term before the compression will now be studied. Because of the increase in plasma density and temperature after the adiabatic compression, the rate of thermonuclear alpha-particle energy production is larger than that before the compression by the ratio ##EQU5## Here 3.5 MeV is the energy of an alpha-particle generated from D-T reactions, and <.sigma.v<.sub.0 and <.sigma.v>.sub.1 are the Maxwellian reactivities at stage 0 and stage 1, respectively. If r.sub.v =1/0.6 amd T.sub.0 =10 keV, then T.sub.1 =19.8 keV. Using the formula for <.sigma.v>.sub.D-T given in NRL Plasma Formulary (D.L. Book Ed.), Naval Research Laboratory, Washington, D.C. (1980), Eq. (5) has a value of 32.1. To obtain the ratio of the neoclassical energy loss rate per unit volume after the compression to that before the compression, we let P.sub.neo .congruent.3nT/.sub..tau..sup.e. Then, it can be shown that ##EQU6## which has a value of 7.72 for r.sub.v =1/0.6. The turbulent convective transport is assumed to vanish at the end of the compression phase since .beta. drops below .beta..sub.c. Finally, the ratio of the Bremsstrahlung radiation energy loss rate after compression to that before the compression is ##EQU7## which has a value of 10.85 for r.sub.v =1/0.6. From Eqs. (5)-(7), we can conclude that alpha-particle heating will further increase the plasma temperature after the adiabatic compression since the relative increase in the alpha-particle heating power is larger than the relative increase in the energy loss rates. This phenomenon of plasma temperature rise after compression is of fundamental importance to the success of the power cycle of the present invention, since the plasma must have a higher pressure during the expansion phase than during the compression. As the temperature rises, the plasma .beta. increases since the plasma volume is held fixed. As .beta. approaches .beta..sub.c, the convective energy loss re-emerges and the convective energy loss rate gradually catches up with the increase in the alpha-particle heating power. After the compression, the plasma temperature asymptotically approaches the limit at which .beta.=.beta..sub.c in a characteristic time defined as the "thermal relaxation time" (see FIG. 7). At stage 2 in the power cycle, the plasma is again thermally stable and in thermal balance, at a stable equilibrium. The plasma and magnetic field parameters are: ______________________________________ Plasma .beta. .beta..sub.2 = .beta..sub.c, Plasma pressure: P.sub.2 > P.sub.1, Plasma minor radius: a.sub.2 = a.sub.1, Internal magnetic field: B.sub.i2 = B.sub.i1, External magnetic field: Be.sub.2 > B.sub.e1. ______________________________________ To complete the cycle, the external magnetic field 14 is decreased so that the plasma 16 expands back to its original minor radius. This is the expansion phase. When the plasma expands, the plasma .beta. tends to increase. [According to Eq. (1), .beta. increases as r.sub.v decreases]. However, .beta. is already at .beta..sub.c at stage 2, hence ballooning instabilities force .beta. to stay at .beta..sub.c (recall that .beta..sub.c is assumed to be a constant) through turbulent convection during the entire expansion phase. Consequently, the plasma pressure during the expansion phase can be expressed as ##EQU8## Upon applying the frozen flux condition, this expression can be written as ##EQU9## which varies exactly as though it has an adiabatic index .gamma.=2. As a result, the plasma pressure during the expansion is higher than the corresponding pressure during the compression. Therefore, negative work is done on the plasma 16 during a completer cycle. This work manifests itself as a mean back-voltage in the toroidal field coils 12, and direct electrical energy is obtained from this voltage. This electrical energy may be transfered to a load 17 via line 32. Using the pressure-volume (P-V) relation, the amount of work done on coils and the thermal efficiency of the cycle are calculated below. It is now clear that if the compression phase has been carried out faster than .tau..sub.i, then the compression would be two-dimensional (.gamma.=2) and the pressure variation during the compression would follow Eq. (8) instead of PV.sup.5/3 =const. Consequently, no net work would be done on the external system since the plasma pressure during the compression phase would equal the corresponding pressure during expansion. Finally, the cycle described here satisfies the Kelvin-Planck statement of the second law of thermodynamics by losing heat (obtained from thermonuclear alpha-particles) to the outside through turbulent convection. During the heating phase, between stages 1 and 2, the plasma can either be held at constant volume or be allowed to expand at constant pressure while receiving energy from the thermonuclear alpha-particles. In a complete cycle, both methods result in net work done on the external system. The work done and thermal efficiency for each of these methods are now calculated. The preferred embodiment of the thermonuclear inverse magnetic pumping power cycle with heating phase at constant plasma volume is discussed first. To calculate the amount of work delivered during this cycle, it is only necessary to consider the work performed by the plasma during the compression and expansion phases. No work is performed during the heating phase because the plasma volume is constant. The work done on the plasma during the adiabatic compression is ##EQU10## Invoking P.sub.0 =.beta..sub.c B.sub.i0.sup.2 /8.pi. and the pressure balance equation P.sub.0 +B.sub.i0.sup.2 8.pi.=B.sub.e0.sup.2 /8.pi., P.sub.0 can expressed as ##EQU11## Using this expression, .sub.0 W.sub.1 can be written as ##EQU12## where L=2.pi.R is the length of the system. The work done by the plasma during the expansion phase is calculated by using Eqs. (8) and (9). The result is ##EQU13## Therefore, the amount of net work done on the coils during a complete cycle is ##EQU14## This expression shows that either a higher compression ratio or a larger .beta..sub.c will give a larger amount of delivered work. The net work done normalized by the machine dependent parameters (1/8)a.sub.0.sup.2 L.beta..sub.c [1/(1+.beta..sub.c)]B.sub.e0.sup.2 is ##EQU15## which is plotted versus the compression ratio in FIG. 3. Although it is desirable to operate the cycle at a high compression ratio, the attainable compression ratio may depend on the highest achievable toroidal magnetic field. This field is limited by the allowable static and dynamic loading on the machine structure. The amount of work delivered by the cycle can be represented by the area of the triangle 0-1-2 in the pressure-volume diagram shown if FIG. 4. The performance of this cycle is characterized by the thermal efficiency .eta..sub.th which is defined as ##EQU16## where O.sub.H represents the heat obtained by the cycle (engine) from a heat source (thermonuclear alpha-particles). To calculate the heat received by the plasma during the heating phase, use the first law of thermodynamics, EQU Q.sub.H =.sub.1 U.sub.2 +.sub.1 W.sub.2. (14) Here .sub.1 U.sub.2 is the change in plasma internal energy between stages 1 and 2 and can be expressed as EQU .sub.1 U.sub.2 =3 a.sub.0.sup.2 Ln.sub.0 (T.sub.2 -T.sub.1). Since the plasma volume is held fixed during the heating phase, Q.sub.H =.sub.1 U.sub.2. From P.sub.2 =.beta..sub.e B.sub.i2.sup.2 /8.pi., the frozen flux condition, and the adiabatic compression law, it can be shown that ##EQU17## Using Eqs. (12) and (15), the thermal efficiency can be expressed as ##EQU18## The important thing to note is that the efficiency of this cycle is a function only of the compression ratio and increases with it. The thermal efficiency is plotted versus the compression ratio in FIG. 5. As the compression ratio approaches infinity, the thermal efficiency approaches a value of 2/3. The thermal efficiency can be visualized by looking at the temperature entropy (T-S) diagram for the cycle, FIG. 6. The thermal efficiency is the ratio of the area of the triangle 0-1-2 to the area beneath the path 1-2. Up to this point, the discussions have been restricted to the case in which there is a limiting .beta.. However, the cycle will become more efficient and more work can be obtained if .beta..sub.c is very high or if there is actually no .beta. limit (this situation may occur in a heliac). For this case the work required to compress the plasma is given by Eq. (10). The plasma pressure at stage 2 may now reach a higher value than in the case where there is a .beta. limit. [Note that turbulent convection is absent here since there is no .beta. limit.] During the expansion, the plasma pressure variation follows PV.sup.5/3 =const since .beta. will no longer be prevented from rising. Hence, ##EQU19## where the subscript 0' denotes conditions at stage 0'--the moment when the expansion phase is completed and the plasma volume returns to its original value at stage 0. At stage 0', P.sub.0' >P.sub.0 and the power losses are greater than the alpha-particle heating power. Thus, the plasma temperature will decrease. While the temperature is decreasing, the external magnetic field is reduced in order to keep the plasma at constant volume and heat diffuses to the outside by neoclassical transport. The cycle is completed when the plasma temperature and external magnetic field return to their original values at stage 0 (point C in FIG. 2). The net work is ##EQU20## where T.sub.0' can be related to T.sub.2 using the adiabatic law. The thermal efficiency is ##EQU21## which is the Otto cycle efficiency. Note that this cycle is identical to the Otto cycle. The preferred embodiment of the thermonuclear inverse magnetic pumping power cycle with heating phase at constant plasma pressure is now discussed. In this power cycle, the compressed plasma is allowed to expand at constant pressure until the plasma .beta. reaches .beta..sub.c. At this point (stage 2), the plasma radius is between the minor radius before the compression and that after the compression. Next, the plasma column is expanded further with .beta. staying at .beta..sub.c until the minor radius reaches the pre-compression value. The cycle is now complete. To calculate the amount of work delivered during this cycle, note that the work required to compress the plasma is the same as that of the previous cycle, see Eq. (10). To calculate the work done by the plasma on the confining field (.sub.1 W.sub.2 +.sub.2 W.sub.0), it is necessary to know the plasma minor radius at the end of the constant pressure heating phase. Starting with P.sub.2 =.beta..sub.c B.sup.2.sub.i2 /8.pi., using the frozen flux condition, and noting that P.sub.2 =P.sub.1, it can be shown that EQU a.sub.2 =a.sub.0 r.sub.v.sup.-5/6. (19) The work done by the plasma on the coils during the constant pressure heating phase is ##EQU22## Using Eq. (9), the work done by the plasma during the final constant .beta..sub.c expansion phase is ##EQU23## Therefore, the amount of net work done on the coils 12 during a completer cycle is ##EQU24## where W.sub.norm =2 r.sub.v.sup.4 5.sup./3 -(5/2)r.sub.v.sup.4/3 +1/2 is plotted versus the compression ratio in FIG. 3. Again, the amount of work delivered by this cycle is represented by the area of the triangle 0-1-3 in the pressure-volume diagram, FIG. 4. The thermal efficiency, which again depends only on the compression ration, is ##EQU25## The thermal efficiency is plotted versus the compression ratio in FIG. 5. As the compression ratio approaches infinity, the thermal efficiency approaches a value of 4/5. Now, the thermal efficiency is the ratio of the area of triangle 0-1-3 to the area beneath the path 1-3 in FIG. 6. Thus, for the same compression ration, this cycle delivers less work but at a higher thermal efficiency than the previous cycle. From the standpoint of reactor economics, it is probably the net work done, rather than the thermal efficiency, that is important. The power delivered by the power cycle via direct energy conversion depends on the period of the cycle. One of the major factors that governs the period is the thermal relaxation time, i.e. time for the plasma .beta. to reach .beta..sub.c after adiabatic compression. The rate of energy transfer of an individual alpha-particle to the background plasma 16 is now considered. The time evolution of the plasma temperature after the compression is also studied using the volume-averaged energy equation for electrons. From the numerical solution of this equation, the thermal relaxation time is estimated. The rate of thermonuclear alpha-particle energy transferred to the background plasma is given by Trubnikov, Review of the Plasma Physics (M. A. Leontovich, Ed.), Consultant Bureau, New York (1965), vol. 1, in the form ##EQU26## where .epsilon..sub..alpha. is the alpha-particle energy, and .tau..sup..alpha./D and .tau..sup..alpha./e are, respectively, the characteristic energy transfer time between the alpha-particle and electrons, and the characteristics energy transfer time between the alpha-particle and electrons. In this analysis, we assume T =T.sub.e =T.sub.i. To obtain the characteristic energy transfer time, not that after the compression (at stage 1), the plasma with stage 0 parameters give in Table I has n.sub.1 =16.7.times.10.sup.14 cm.sup.-3 and T.sub.i =19.8 keV if r.sub.v =1/0.6. Thus ##EQU27## where .epsilon..sub..alpha. (0)=3.5 MeV is the energy of an alpha-particle generated from D-T reactions, and m.sub.e and m.sub..alpha. are the electron and alpha-particle mass, respectively. Using these limits, the expressions for .tau..sup..alpha./e can be simplified accordingly. Trubnikov, cited above, showed that ##EQU28## For .epsilon..sub..alpha. (0)=3.5 MeV, it can be shown that .tau..sup..alpha./e =.tau..sup..alpha./D /57. Thus, at the time of birth of an alpha-particle, the rate of energy transfer to the electrons is about sixty times faster from an alpha-particle that to the deuterons. At the critical energy given by ##EQU29## the rate of energy transfer from an alpha-particle to the electrons is equal to that to the ions. At T.sub.1 =19.8 keV, .epsilon..sub..alpha.crit =0.29 MeV. Thus, the thermonuclear alpha-particles lose most of their energy to electrons and for practical purposes, the alpha-particles energy transfer rate can be approximated by ##EQU30## Using Eqs. (23) and (24), the characteristics energy transfer time can be expressed as ##EQU31## Substituting the values of density and temperature of the plasma immediately after the compression that Eq. (26) gives .tau..sup..alpha./e =0.05 sec. Note that using Eq. (4), it can be shown that after the compression, the plasma energy confinement time .tau..sub..epsilon. .congruent.0.32 sec. Hence .tau..sup..alpha./e <.tau..sub..epsilon.. To obtain the temporal evolution of the plasma temperature after the compression, assume T.sub.e =T.sub.i and use the volume-averaged energy balance equation for the plasma: ##EQU32## In this equation, the turbulent convective energy loss is not included since we have assumed that there is no convective loss for .beta.<.beta..sub.c (in reality, however, convective loss emerges gradually as .beta. approaches .beta..sub.c as was mentioned above). Let the time at the end of the compression phase be zero. Then, the power deposited by the alpha-particles to the background plasma per unit volume, P (t), at any time t after the compression can be expressed as ##EQU33## Here the first term on the right-hand side of this equation represents the alpha-particle power deposition at any time t>0 by all the alpha-particles generated in some intermediate time between 0.ltoreq.t'.ltoreq.t (0.gtoreq.t'.gtoreq.-.infin.); n.sub.0 is the density before the compression, and d.epsilon..sub..alpha. (t,t')/dt [given by Eq. (23)] represents the rate of energy transfer at time t, of an individual alpha-particle generated at some previous time t'. The factor (1+2r.sub.v.sup.2)/3 in the second term is the increase in alpha-particle energy due to two-dimensional adiabatic compression (compression is two-dimensional if the compression phase is carried out faster than .tau..sub..alpha.i - and 90.degree. deflection time between an alpha-particle and background ions). Equation (27) is an integrodifferential equation, but it can be converted into a second order differential equation by taking a time derivative. Using Eqs. (25) and (26), it can be shown that ##EQU34## Using this expression, we find that the time derivative of Eq. (28) can be written as ##EQU35## where <.sigma.v>.sub.t is the Maxwellian reactivity at time t. Then, after taking the time derivative of Eq. (27), using the above expression for dP.alpha./dt, and performing some straight forward algebra, it can be shown that This equation can be solved numerically. Two initial conditions are needed. The first one is EQU T(0)=r.sub.v.sup.4/3 T.sub.0 (30a) from the adiabatic law. [Note that T(0) denotes the plasma temperature at time 0 (stage 1) and T.sub.0 denotes the plasma temperature at stage 0.] To determine the second initial condition dT/dt.vertline..sub.t=0, we need to know P.alpha.(0). If the adiabatic compression time is faster that .tau..sub..alpha.i, then the alpha-particle heating power per unit volume immediately after the compression is increased from the corresponding heating power before the compression by the ratio ##EQU36## Here 0.sup.- denotes the time at the beginning of the compression. The second initial condition for Eq. (29) can now be written as ##EQU37## Using the initial conditions given by Eqs. (30a) and (30b), the solution of Eq. (29) for the reactor with parameters given in Table I with r.sub.v =1/0.6 is obtained and plotted versus time as the solid curve in FIG. 7. This figure shows that the plasma temperature asymptotically approaches a limit of 35.5 keV. If we let the thermal relaxation time for the plasma .beta. to reach .beta..sub.c be the time that it takes the plasma temperature to reach 90% of the limiting temperature at 35.5 kev, then this time is approximately 0.16, as illustrated in FIG. 7. This condition would represent the end of the heating phase. Note that the thermal relaxation time is somewhat larger than .tau..sup..alpha./e. In the limit that the relaxation time is much greater than .tau..sup..alpha./e, Eq. (28) can be simplified by assuming <.sigma.v>.sub.t' .apprxeq.<.sigma.v>.sub.t. Furthermore, the second term on the right-hand side of Eq. (28) is generally small compared to the first term and thus can be neglected. The power delivered to the plasma now becomes ##EQU38## which is the instantaneous fusion power. This result simplifies Eq. (27) to a first-order equation. The temporal evolution of temperature described by this simplified equation is plotted versus time as the dashed curve in FIG. 7. Finally, note that if the turbulent convective loss were included in the calculation, then the resulting power loss would be higher due to the turbulent convection as .beta. approaches .beta..sub.c and the rate of temperature rise would become slower. However, the thermal relaxation time would probably be about the same, since turbulent convection also forces the asymptotic limit of the plasma temperatures to drop to a lower value at which .beta.=.beta..sub.c. To make the power cycle self-sustaining, part of the work done by the plasma on the coils during the expansion phase must be stored in order to supply power for the next compression phase. However, the amount of energy to be stored is large compared with the net work done by the plasma during the cycle. Thus, even if the ratio of the energy lost (during the transfer to, plus the loss in the storage system) to the total energy transferred from the reactor to the storage system (this ratio is defined as the re-circulation inefficiency) is only a few percent, the total energy lost in recirculation may still exceed the work done during the cycle. Consequently, the power cycle may require a lower re-circulation inefficiency than can be provided by conventional energy storage systems, e.g. capactive, inductive, and inertial (motor-generator-flywheel). To obviate this, in a preferred embodiment of the present invention two (or more) stellerator reactors are operated in tandem. The major electrical energy loss in this system is the resistive dissipation in the coils 12, but this loss may be small compared with the net work performed by the cycle as is discussed below. The reactor system of this preferred consists of two identical stellerator reactors, 10 and 20 as shown in FIG. 9. Reactor 20 includes external magnetic confining coils 22, helical stabilizing coils 23 and and vacuum vessel 29. The cycle with heating phase at constant volume will be used for discussion here, however, as will be recognized by those skilled in the art other power cycles may also be used. The operation scenario is illustrated in FIG. 8. When the plasma in reactor 10 is expanding, some of the resulting work is transferred via line 44 and used to compress the plasma in reactor 20. When the expansion phase in reactor 10 is completed, the plasma in that reactor returns to its precompression state (stage 0) while the plasma in reactor 20 completes the compression phase and is at stage 1. The plasma is reactor 10 is now maintained at stage 0 temporarily while the external magnetic field strength in reactor 20 is increasing so that the plasma volume in reactor 20 can be kept constant as the plasma temperature is increasing. During this period, the power use to increase the magnetic field strength in reactor 20 comes either from the electrical power generated by the thermonuclear neutrons in reactor 10 or from that in reactor 20 itself. When the plasma in reactor 20 reaches thermal balance (stage 2), it is allowed to expand. Some of the resulting work obtained from reactor 20 during its expansion phase is transferred via line 42 and used to compress the plasma in reactor 10. The balance of the energy is transferred to load 27 via line 36. The cycle continues in this manner. The current in the coils 12 and 22 of reactor 10 and 20 respectively as a function of time is illustrated in FIG. 8. Note that this coupled reactor system is analogous to a two cylinder internal combustion engine. The averaged total electrical output power obtained from direct conversion is defined as ##EQU39## Here P.sub.l is the resistive power dissipation in the coils, .tau..sub.p is the period of one complete cycle, and .phi.dt is the cyclic time integral, i.e. time integration over the period .tau..sub.p. Having generally described the invention, the following specific example is given as further illustration thereof. The power cycle with heating phase at constant plasma volume is considered. Note that the neoclassical energy loss P.sub.neo, which could in principle be converted into electrically, is not included in Eq. (32). For a stellerator reactor 10 with reactor parameters given in Table I, the thermal relaxation time required by the plasma to reach stage 2 after the adiabatic compression with r.sub.v =1/0.6 is approximately 0.16 sec. If the compression and expansion phases are each carried out in 0.01 sec (note that .tau..sub.i =0(10.sup.-3) sec for the plasma with parameters given in Table I), then .tau..sub.p .apprxeq.0.18 sec. With this information and using Eq. (12), it can be shown that W.sub.net /.tau..sub.p =2.2 GW. If the plasma radius remains constant, then at r=a, the thermonuclear neutron power P.sub.n =12.2 GW. The electrical power obtained from the neutrons at a conversion efficiency .eta..sub.c =1/3 is .eta..sub.c P.sub.n =4.1 GW. Thus, W.sub.net /.tau..sub.p is about 50% of .eta..sub.c P.sub.n. Note that W.sub.net /.tau..sub.p for each reactor in the coupled stellarator system may be lower than the 2.2 GW since .tau..sub.p for the coupled system is longer (see FIG. 8). Also note that the actual values of W.sub.net /.tau..sub.p and P.sub.n should be lower than the results obtained here since the radial profiles of density and temperature must be taken into account properly. To calculate the resistive power dissipation in the coils, 12, note that ##EQU40## The factor T.sub.room /T.sub.coil is an approximation for the thermodynamic efficiency of the refrigeration cycle, i.e. ##EQU41## where T.sub.room and T.sub.coil are the room temperature and the cryogenic temperature of the cooled coils, respectively. The current in the coils 12 is given by ##EQU42## where c is the speed of light and N is the number of turns of the coil per meter. The coil resistance is expressed as ##EQU43## where l = 2.pi.a.sub.c LN is the total length of the coil (a.sub.c is the distance between the coil and the center of the plasma), A is the coil cross sectional area, and .eta. is the resistivity. If b is the width of the coil (measured along the direction of the minor radius), then A=b/N. Thus, Eq. (33) can be written as ##EQU44## Using the reactor parameters in Table I and setting a.sub.c =3 m, b=0.5 m, T.sub.room =293.degree. K., T.sub.coil =77.degree. K. (the boiling point for liquid nitrogen), it can be shown that the total resistive power dissipation in a copper coil during a complete cycle is on the order of a few percent of W.sub.net. Hence, .phi.P.sub.l dt can be neglected and P.sub.direct =2.2 GW. It may be thought that more neutron power could be obtained by increasing the confining magnetic field strength 14 and operating the plasma 16 at a higher pressure without pulsing the minor radius. However, this mode of operation is undesirable since the neutron wall load would exceed the present day engineering limit which is below 10 MW.multidot.m.sup.-2. A power cycle for direct conversion of alpha-particle energy into electricity for stellarator reactors has been described. The direct energy conversion is achieved by alternating compression and expansion of the plasma minor radius. For the stellarator reactor with parameters given in Table I, the averaged power obtained from the cycle with compression ratio 1/0.6 is about 50% of the electrical power obtained from the thermonuclear neutrons from the same reactor without compressing the plasma. Thus, the cycle provides an alternative scheme for extracting energy from D-T fueled reactors. This scheme can be used either alone or as a supplement to the electrical power generated from thermonuclear neutrons. For advanced neutron-lean fueled reactors, this power cycle may become an important scheme for energy conversion. 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 in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto. |
claims | 1. A method for testing a weld seam located on an inner surface of a reactor pressure vessel and connecting an outer circumference of an instrumentation nozzle leading into an interior of the reactor pressure vessel to the reactor pressure vessel, the method which comprises:inserting an ultrasound test probe into the instrumentation nozzle, coupling a transmitted ultrasound signal into the instrumentation nozzle in a region of the weld seam and receiving a reflected ultrasound signal with the ultrasound test probe for determining a presence of faults in the weld seam;generating the ultrasound signal with at least one linear ultrasound transducer array constructed from a plurality of transducer elements arranged next to one another in a longitudinal direction, the transducer array having a longitudinal direction extending parallel to the central axis; andcausing the transmitted ultrasound signal to propagate inside the instrumentation nozzle at an oblique angle to the central axis of the instrumentation nozzle by actuating the transducer elements of the transducer array with a time delay with respect to one another for adjusting the oblique angle. 2. The method according to claim 1, which comprises causing the transmitted ultrasound signal to propagate inside the instrumentation nozzle on a plane parallel to and spaced apart from the central axis of the instrumentation nozzle. 3. The method according to claim 1, which comprises operating the at least one ultrasound transducer array according to a pulse-echo technique. 4. The method according to claim 1, which comprises providing an ultrasound transducer assembly operable according to a transmitting/receiving technique and containing at least two ultrasound transducer arrays that are spaced apart from one another and mirror-symmetric to a plane containing the central axis. 5. The method according to claim 1, which comprises utilizing transverse waves for the transmitted ultrasound signal. 6. A device for testing a weld seam, located on an inner surface of a reactor pressure vessel, by which an outer circumference of an instrumentation nozzle leading into the reactor pressure vessel is welded onto the reactor pressure vessel, the device comprising:an ultrasound test probe configured for insertion into the instrumentation nozzle, said test probe having a longitudinal axis;at least one linear ultrasound transducer array formed with a plurality of transducer elements disposed next to one another in a longitudinal direction, said transducer array being disposed, in terms of the longitudinal direction, parallel to said longitudinal axis of said test probe inside said test probe;a control and evaluation device connected to said transducer array for actuating said transducer elements with a time delay; andwherein a transmission axis of said transducer elements is spaced apart from a central axis of the instrumentation nozzle when said ultrasound test probe is inserted in the instrumentation nozzle. 7. The device according to claim 6, wherein at least one linear ultrasound transducer array is one of at least two ultrasound transducer arrays disposed spaced apart from one another and mirror-symmetric to a plane containing said longitudinal axis of said ultrasound test probe, and wherein at least one of said at least two ultrasound transducer arrays is a transmitter and the other one is a receiver. 8. The device according to claim 6, wherein said ultrasound test probe is formed with a cylindrical coupling face, wherein at least one supporting element is disposed on a side facing away from said coupling face of said ultrasound test probe, and wherein said supporting element is resiliently supported on an inner surface of the instrumentation nozzle, when said ultrasound test probe is inserted in the instrumentation nozzle, and presses said coupling face onto the inner surface of the instrumentation nozzle. 9. The device according to claim 6, wherein said ultrasound transducer array is configured to produce transverse waves. |
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049869558 | abstract | The device comprises a rod (20) on which is mounted a means (22, 24, 25) for the support and displacement of a work tool which is movable in an axial direction of the rod (20) and in two directions perpendicular to this axial direction. The tool comprises tongs consisting of two arms which are articulated together about a spindle fixed on the means (22, 24, 25) for support and displacement in a direction parallel to the axis of the rod (20). The tongs comprise end jaws which are capable of gripping a fuel rod. The gripping of the tongs is controlled remotely and the positioning of these tongs on a fuel rod to be removed is checked by means of a video camera (26). |
abstract | Seals are positioned between abutting nuclear reactor components. Example seals are held in position by gravity, grooves, retainers, direct joining, or other mating structures to seal the abutting components. Compression of example seals drives the seals against the joining components, preventing fluid passage therebetween. Example seals may include a cavity opening to a higher pressure fluid outside the joined components to drive expansion or sealing of the seal. Seals may have a C-shaped, E-shaped, O-ring, coiled, helical, or other cross-section to provide such a cavity. Example seals may be flexible materials compatible with radiation and heat encountered in a nuclear reactor. Seals may be continuous or sectional about the abutment of the components. An annular seal may extend continuously around a perimeter of removably joined core plates, supports, shrouds, and/or chimney heads and structures. Seals can be installed between and in the components at any time access is available to the components. |
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summary | ||
description | FIG. 1 illustrates one exemplary embodiment of a model-based centralized diagnostic system 100. As shown in FIG. 1, the system 100 includes a set of assumption variables 110. The assumption variables represent the assumptions of the states of the various components of the system being diagnosed. Each assignment of a value to an assumption variable 110 has a cost. In various exemplary embodiments, an assignment of a value to an assumption variable 110 represents an assumption about the current state, such as normal or failure, of the corresponding component of the system being diagnosed. In various exemplary embodiments, the cost represents the prior probability of that assumption variable having that value, which corresponds to the prior probability of the corresponding component being in that state. In various exemplary embodiments, the cost may represent an energy used by the system, the desirability of a state for a component of the system being diagnosed, or any evaluative parameter used in various exemplary optimization tasks. The diagnostic system 100 also has a set of observation variables 120. Each observation variable 120 represents a quantity that may be observed by a corresponding sensor of the diagnostic system 100 that is attached to the system being diagnosed. Each observation variable 120 is assigned a value that cannot be unassigned, because that value is based on the output of the corresponding sensor and thus represents a current status of the system being diagnosed. Further, the diagnostic system 100 has a set of dependent variables 130. The values of the dependent variables 130 represent quantities that relate the set of assumption variables 110 to the set of observation variables 120. The diagnostic system 100 also has a set of constraint values 140 between the variables that describe the behavior of the modeled system being diagnosed. A constraint value 140 may be defined between two dependent variables 130, between an assumption variable 110 and a dependent variable 130, between a dependent variable 130 and an observation variable 120, or between an assumption variable 110 and an observation variable 120. In the diagnostic system 100, the observation variable o3 is constrained by the dependent variables d5 and d3. The value of the dependent variable d3 is in turn constrained by the dependent variables d1 and d2, whose values are constrained by the assumption variables a2 and a3. Given the constraint values 140, any choice of values assigned to the assumption variables 110 will enable the diagnostic system 100 to predict values for the observation variables 120 that would be expected in view of those values assigned to the assumption variables 110. Thus, given a set of values assigned to the observation variables 120 in view of the outputs of the corresponding sensors, a diagnosis of the system being diagnosed comprises a set of assignments of the values of the assumption variables 110 that results in a set of derived values for the observation variables 120 that are consistent with the assigned values of the observation variables 120 based on the sensors outputs. In various exemplary embodiments, if a probability is assigned to each value an assumption variable 110 can take, then the diagnosis with the highest likelihood may be obtained. Thus, with respect to the diagnostic system 100, if the diagnostic system 100 assigns values to the assumption variables a2 and a3 that are inconsistent with derived and assigned values for the observation variable o3, the diagnostic system 100 will have to change the values assigned to one or more of the assumption variables a2 or a3 to make the derived values for the observation variable o3 consistent with the assigned values for the observation variable o3. Similarly, the diagnostic system 100 may change the value assigned to the assumption variable a1, as the assumption variable a1 also constrains the observation variable o3 through the dependent variables d1 and d5. Choosing which assumption variable 110 to change depends on the cost of each value that can be assigned to the various assumption variables a1-a3, as well as the derived values for the observation variables that a new value assigned to an assumption variable 110 causes to change via the constraints. FIG. 2 illustrates a first embodiment of a distributed optimization-based diagnostic system 200 in accordance with the invention. As shown in FIG. 2, the distributed optimization-based diagnostic system 200 contains a first diagnostic subsystem 210 and a second diagnostic subsystem 220. The distributed optimization-based diagnostic system 200 is used to diagnose faults in a system to be diagnosed. The system to be diagnosed includes two distinct subsystems, where each subsystem to be diagnosed corresponds to or is modeled by, one of the first and second diagnostic subsystems 210 and 220. The first diagnostic subsystem 210 contains one or more assumption variables 212, one or more observation variables 214, and zero, one or more dependent variables 216. The variables are related by one or more constraints 218. Similarly, the second diagnostic subsystem 220 contains one or more assumption variables 222, one or more observation variables 224, and zero, one or more dependent variables 226, all related by one or more constraints 228. The one or more constraints 228 also relates one or more observation variables 214 and/or 224 and/or one or more dependent variables 216 and/or 226 between the first diagnostic subsystem 210 and the second diagnostic subsystem 220. In operation, the observation variables 214 of the first diagnostic subsystem 210 and the observation variables 224 of the second diagnostic subsystem 220 are set to values corresponding to sensor readings from the monitored device. A global diagnosis function 230 accepts values from the one or more assumption variables 212 of the first diagnostic subsystem 210 and the one or more assumption variables 222 of the second diagnostic subsystem 220 to produce a diagnosis. The diagnosis includes a minimal cost assignment of values to the assumption variables 212 and 222 that is consistent with the constraints 218 and 228. For example, when the current value assigned to the assumption variables 212 and/or 222 are inconsistent with observation variable o3, the second subsystem 230 can eliminate the inconsistency by changing the value assigned to the assumption variable a2. In various exemplary embodiments, changing the value assigned to this assumption variable 212 changes the probability of the overall set of values assigned to the assumption variables 212, and thus the diagnosis. Changing the value assigned to this assumption variable 212 may also have ramifications on one or more other observation variables 214 and/or 224, such as, for example, the observation variable o2 via the dependent variables d1 and d5. Alternately, in various exemplary embodiments, the first diagnostic subsystem 210 can change the value assigned to the assignment variables a1 or a3, engendering a different impact on the probability of the overall set of values assigned to the assumption variables 212 and the values for the observation variables 214. Thus, to maintain consistency with the values of the observation variables required by the outputs of the sensors, multiple diagnostic subsystems that generate local diagnoses must collaborate. In addition to producing the same results as a centralized diagnostic system, in various exemplary embodiments, this collaboration of diagnostic subsystems takes place in a manner that increases the amount of independent decision making or determinations that each local diagnostic subsystem can perform and reduces the amount of communication between the local diagnostic subsystems. FIG. 3 illustrates a second embodiment of a distributed diagnostic system that provides optimization-based diagnosis in accordance with the invention. As shown in FIG. 3, the distributed system 300 is similar to the distributed diagnostic system 200 of FIG. 2. Specifically, in FIG. 3, the distributed system 300 contains a first diagnostic subsystem 310 and a second diagnostic subsystem 320. The first diagnostic subsystem 310 contains one or more assumption variables 312, one or more observation variables 314, and one or more dependent variables 316. The assumption, observation and dependent variables 312, 314 and 316 are related by one or more constraints 318. The second diagnostic subsystem 320 contains one or more assumption variables 322, one or more observation variables 324, and one or more dependent variables 326, all related by one or more constraints 328. The first diagnostic subsystem 310 also contains one or more pseudo-observation variables 315. A pseudo observation variable 315 enables a local diagnostic system to be informed of the value required by a remote diagnostic subsystem for one of its dependent variables 316, and also allows the local diagnostic subsystem to find the actual cost of supporting the requested value for the remote dependent variable 315 through the existing diagnostic search. The second local diagnostic subsystem 310 also contains one or more pseudo-assumption variables 323. A pseudo-assumption variable 323 allows a local diagnostic subsystem to represent the cost of changing a dependent variable 326 when that dependent variable is stored in a remote diagnostic subsystem. FIG. 4 illustrates one exemplary embodiment of a diagnostic interface 400 that each local diagnostic subsystem must support in accordance with various exemplary embodiments of the systems and methods of this invention. In FIG. 4, the interface 400 provides six diagnostic subsystem interface portions 410-460. A local diagnostic subsystem, such as the subsystems 210, 220, 310 and/or 320, determines or derives the value of each local observation variable based on the most likely assignment of values to each local assumption variable. The first diagnostic subsystem interface portion 410 allows a local diagnostic subsystem to access information on other local diagnostic subsystems that allows this local diagnostic subsystem to determine those most likely assignments. The second diagnostic subsystem interface portion 420 enables a local diagnostic subsystem to determine or derive the likelihood of the second most likely value for each observation variable. The third diagnostic subsystem interface portion 430 enables a local diagnostic subsystem to find the most likely value assignments to the assumption variables based on a given assignment of the values for the observation variables. The fourth diagnostic subsystem interface portion 440 enables a local diagnostic subsystem to find the most likely assignment of the values to the assumption variables other than a present assignment of a value of an assumption variable, given an assignment of the values of the observation variables and that present value assigned to that assumption variable. The fifth diagnostic subsystem interface portion 450 enables a local diagnostic subsystem to update the likelihoods of the values that are assignable to an assumption variable. The sixth diagnostic subsystem interface portion 460 enables a local diagnostic subsystem to update the assignments to the observations. The interface 400 enables the values assigned to the assumption, observation and dependent variables of a local diagnostic subsystem to be used by another local diagnostic subsystem without that local diagnostic subsystem having to have any knowledge of the implementation of the first local diagnostic subsystem. That local diagnostic subsystem will have no indication that the value of one of its observation variables is in fact used as the value of the assumption variable of another local diagnostic subsystem, nor that that local diagnostic subsystem is participating in a decentralized diagnosis system. The interface 400 thus provides a framework for integrating heterogeneous diagnosis subsystems into a single diagnostic system. FIG. 5 is a flowchart outlining one exemplary embodiment of a distributed model-based diagnostic method in accordance with the invention. As shown in FIG. 5, operation of the process begins in step S100, and continues to step S110, where each local diagnostic subsystem of a distributed diagnostic system determines a local diagnosis that makes the values of the local assumption variables consistent with the values of the local observation variables received from the associated sensors. Next, in step S120, each local diagnostic subsystem coordinates its local diagnosis to the local diagnoses of one or more of the other local diagnostic subsystems to determine a global diagnosis. Then in step S130, the method ends. FIG. 6 is a flowchart outlining a second exemplary embodiment of a distributed model-based diagnostic method in accordance with the invention. As shown in FIG. 6, the method begins in step S200, and continues to step S210, where all local diagnostic subsystems that do not contain any pseudo-assumption variables are initialized by setting the values of their pseudo-observation variables to initial values. Next, in step S220, any remaining local diagnostic subsystems that contain one or more pseudo-assumption variables are initialized. The pseudo-assumption variables are initialized based on the initialized values for the corresponding pseudo-observation variables established in step S210. Then, in step S230, the system to be diagnosed is diagnosed in accordance with various exemplary embodiments of the invention. Finally, in step S240, the process ends. Once the diagnostic subsystems have been initialized, observation values obtained from the physical system are used to update the values of the observation variables within each diagnostic subsystem. The values of these observations may vary from the values of the observation variables assigned to the observation variables in steps S210 and S220. A distributed diagnosis must then be performed. FIG. 7 is a flowchart outlining an exemplary embodiment of a method to determine a local diagnoses that is consistent with one or more other local diagnosis according to the invention. It should be appreciated that, before step S305 is performed, the local diagnostic subsystems have been initialized, for example, in accordance with steps S210 and S220 of FIG. 6. The diagnostic process begins when an observation variable in the current local diagnostic subsystem changes from its current value. This change indicates for example, a potential fault in the corresponding component. As shown in FIG. 7, the local diagnostic method begins in step S300 and continues to step S305, where a local diagnosis is performed to determine a lowest-cost assignment of values to the assumption variables, including all local pseudo-assumption variables di-A, that is consistent with the new values of the observation variables, including all local pseudo-observation variables di-O. In particular, in step S305, an expected value, vi, for each pseudo-assumption value di-A is determined from the corresponding pseudo-observation variable di-O. Operation then continues to step S310. In step S310, a first or next pseudo-assumption variable of this local diagnostic subsystem, di-A, is selected. Next, in step S315, a determination is made whether the lowest-cost local diagnosis includes a change to the value of the currently selected pseudo-assumption variable, di-A. The lowest-cost local diagnosis is the most probable set of values for the assumption and pseudo-assumption variables of the local diagnostic subsystem given the current set of values for the observation and pseudo-observation variables that constrain the assumption and pseudo-assumption variables of this diagnostic subsystem. If not, operation jumps to step S355. Otherwise, operation continues to step S320, in which a second local diagnosis is performed with the value of the selected pseudo-assumption variable di-A set to its initialized value. This value, vi, corresponds to the current value of the associated pseudo-observation variable in a second local diagnostic subsystem. This second local diagnosis results in the determination of a maximum cost, cmax, that the local diagnostic subsystem is willing to xe2x80x9cpayxe2x80x9d to change the value of the selected pseudo-assumption variable di-A to the expected value, vi, for the current pseudo-assumption variable determined in step S305. Operation then continues to step S325. In step S325, the local diagnostic subsystem forwards the expected value vi and the maximum cost cmax to the second local diagnostic subsystem that contains the pseudo-observation variable, di-O, corresponding to the current pseudo-assumption variable di-A. Then, in step S330, a determination is made whether the second local diagnostic subsystem can change the value of the pseudo-observation variable di-O for a cost that is less than or equal to the maximum cost cmax. That is, the second local diagnostic subsystem determines whether a diagnosis local to that second local diagnostic subsystem in which the value of the corresponding pseudo-observation variable di-O is set to the expected value vi can be determined for a cost less than or equal to the maximum cost cmax. If not, operation continues to step S335. Otherwise operation jumps to step S345. In step S335, the second local diagnostic subsystem transmits the actual costs, cf, to the first diagnostic subsystem. Next, in step S340, the first diagnostic subsystem then uses the second local diagnosis determined in step S320. The second local diagnosis is used because the value of the selected pseudo-assumption variable di-A cannot be set to the expected value vi for a cost less than or equal to cmax. Operation then jumps to step S355. In contrast, in step S345, the second local diagnostic subsystem transmits the actual cost, cf, to the first local diagnostic subsystem. Next, in step S350, the first local diagnostic subsystem uses the lowest cost local diagnosis, in which the value of the current pseudo-assumption variable di-A is set to the expected value, vi. Operation then continues to step S355. In step S355, a determination is made whether any more pseudo-assumption variables di-A remain to be processed for this local diagnostic subsystem. If so, operation jumps to step S310. Otherwise, the method ends at step S360. In various exemplary embodiments, if the lowest cost local diagnosis includes a change to the value of the current pseudo-assumption variable di-A, an upper bound can be set on the cost the first local diagnostic subsystem is willing to pay to change the value of the corresponding pseudo-observation variable di-O. Thus, before requesting that a second local diagnostic subsystem perform a diagnosis to change the value of the corresponding pseudo-observation variable di-O to match the value of the current pseudo-assumption variable di-A, the value of the current pseudo-assumption variable di-A is fixed at its original value, and a second diagnosis is performed. The second diagnosis gives a maximum cost, Cmax, of making the local constraints consistent without changing the value of the current pseudo-assumption variable di-A. This is a maximum cost the first local diagnostic subsystem is willing to have attached to changing the value of the current pseudo-assumption variable di-A. Therefore, if the second local diagnostic subsystem cannot change the value of the corresponding pseudo-observation variable di-O to the expected value, vxe2x80x2, for a cost of cmax or less, the first local diagnostic subsystem is better off using the second diagnosis that did not involve changing the value of the current pseudo-assumption variable di-A. The first local diagnostic subsystem forwards the determined expected value, vxe2x80x2, and the maximum cost, cmax, for the corresponding pseudo-observation variable di-O to the second local diagnostic subsystem. If the second local diagnostic subsystem can produce a diagnosis that uses the expected value vi for the value of the corresponding pseudo-observation value di-O for a cost cf that is less than the maximum cost cmax, the actual cost, cf is returned to the first local diagnostic subsystem. The diagnosis involving a diagnosis that uses the expected value vi for the value of the corresponding pseudo-observation value di-O for a cost cf that is less than the maximum cost then becomes a local diagnosis of the first local diagnostic subsystem. If not, the first local diagnostic subsystem uses the determined second diagnosis at a cost of cmax and the value of the current pseudo-assumption variable di-A remains unchanged. Thus, for each diagnosis that requires a value of the pseudo-assumption variable di-A other than the expected value vi, a cost, ci, is assigned to that diagnosis. A local diagnostic subsystem will only find a diagnosis involving the pseudo-assumption variable di-A if it cannot find a diagnosis involving changing the values of one or more local assumption variables for a cost less than ci. Thus, a local diagnostic subsystem will only request a change to the corresponding pseudo-observation variable di-O in a second diagnostic subsystem when the cost of resolving a conflicting observation locally is too high. FIG. 8 is a data flow diagram illustrating a data flow for a first exemplary embodiment of a distributed diagnostic system 500 that implements optimization-based initialization and diagnosis according to the invention. In FIG. 8, the distributed diagnostic system 500 engages in a global diagnosis based on the local diagnoses of two local diagnostic subsystems 501 and 502. In various exemplary embodiments, any plural number of local diagnostic subsystems may be engaged in the global diagnosis. As shown in FIG. 8, a predicted value 505, vi, for a given pseudo-observation variable 510, dog, is predicted. Then, that given pseudo-observation variable 510, d1-0 is set to the predicted value 505. These are values representing one or more states of the component to be diagnosed. Next, the cost of consistency, that is, the cost to change the value of the given pseudo-observation variable 510 d1-0 to its next most likely value, is determined. The current value 505 for the given pseudo-observation variable 510 d1-O, and the cost of consistency 515 c1 are transmitted to the second diagnostic subsystem 502 that contains a pseudo-assumption variable 520, d1-A, corresponding to the pseudo-observation variable 510, d1-O. The second local diagnostic subsystem 502 then performs an initialization process by assigning observation values 525 to observation variables corresponding to sensor readings from the component being diagnosed by the second local diagnostic subsystem 502. Next, the lowest cost diagnosis 530 for these observations is determined. Then, a determination is made as to whether the lowest cost diagnosis 530 includes a value 535 for the pseudo-assumption variable, 520 that is different from the expected value 505. If so, then the cost of consistency 540, cmax or cxe2x80x2, is determined for a second diagnosis in which the pseudo-assumption variable di-A is set to v1, the new value 535 for the pseudo assumption variable 520. The second local diagnostic subsystem 502 transmits the new value 535, vxe2x80x2, the desired value for the given pseudo-observation variable 510, and the maximum cost 515 or 540, cmax or cxe2x80x2, back to the first local diagnostic subsystem 501. The first local diagnostic subsystem 502 attempts a local diagnosis in which the given pseudo-observation variable 510, d1-O, is set equal to the new value 535, vxe2x80x2 for a cost less than or equal to the cost of consistency 515 or 540, cmax or cxe2x80x2. If a local diagnosis is found in which the pseudo-observation variable 510, d1-O, is set equal to the new value 535, vxe2x80x2 for a cost less than or equal to the cost of consistency 510 or 540, cmax or cxe2x80x2, then, the first local diagnostic subsystem 501 transmits the actual cost 540, cf, to the second local diagnostic subsystem 502. Once the first local diagnostic subsystem 501 has received all of its pseudo-observations, the data flow illustrated in FIG. 8 can be repeated between the first local diagnostic subsystem 501 and any other local diagnostic subsystem(s) that are supplying its assumptions. The method illustrated in FIG. 7 and the data flow illustrated in FIG. 8 do not necessarily produce a globally optimal diagnosis. In FIG. 8, the second local diagnostic subsystem 502 will only request that the first local diagnostic subsystem 501 change the value 505 of the given pseudo-observation variable 510 d1-O if the second local diagnostic subsystem 502 cannot find a local diagnosis for a cost less than the cost of consistency 520, c1. Thus, the second local diagnostic subsystem 502 may instead prefer a local diagnosis of cost cxe2x80x2 where cxe2x80x2 is less than the cost of consistency 520, c1. In one or more embodiments of the invention, a third local diagnostic subsystem may exist that also has another pseudo-assumption, d1-A, corresponding to the given the pseudo-observation variable 510 d1-O. The third local diagnostic subsystem would also request a change to the value of the given pseudo-observation variable 510 d1-O if the third local diagnostic subsystem cannot find a local diagnosis of less than the cost of consistency 520, c1. For example, the third local diagnostic subsystem may choose a local diagnosis of cost cxe2x80x3 less than the cost of consistency 520, c1. In this case, the second local diagnostic subsystem 502 and the third local diagnostic subsystem are both considering a request to change the given pseudo-observation variable 510, d1-O, without knowledge of the other local diagnostic subsystem. A global diagnosis of cost cxe2x80x2+cxe2x80x3, is determined because both the cost of consistency 520, cxe2x80x3, the cost of consistency 520, and the cost of consistency 520, cxe2x80x2, are less than c1. However, there is no guarantee that cxe2x80x2+cxe2x80x3 is less than c1. That is, the second local diagnostic subsystem 502 changes its pseudo-assumption variable 520 for a cost cxe2x80x2 while the third local diagnostic subsystem changes its pseudo-assumption variable d1-A for a cost cxe2x80x3. However, the lowest total cost solution would have been for each of the second and third local diagnostic subsystems to change their pseudo-assumption variables to the predicted value 505 for a single cost of the cost of consistency 515, c1. Accordingly, a globally minimal cost solution to the constraint problem cannot be determined while considering only local decisions. FIG. 9 is a flowchart outlining an exemplary embodiment of a method for determining a global diagnosis at or close to a globally minimal cost according to the invention. As shown in FIG. 9, the method begins in step S500, and continues to step S510, where the number of diagnostic subsystems containing a pseudo-assumption variable, di-A, corresponding to a local variable, di-0, is determined. Next, in step S520, a determination is made whether the number of remote diagnostic subsystem containing the pseudo-assumption variable di-A is greater than one. If so, operation continues to step S530. Otherwise, operation jumps to step S590. In step S530, a first or next local diagnostic subsystem containing a pseudo-assumption variable di-A corresponding to the local variable di is selected. Next, in step S540, a global diagnosis is determined in which the pseudo-assumption variable di-A is changed with zero cost in the local diagnostic subsystem. Next, in step S550, a determination is made whether any more local diagnostic subsystems exist containing a pseudo-assumption variable di-A corresponding to the local variable di-0. If so, operation jumps to step S530. Otherwise, operation continues to step S560. In step S560, the actual cost to change the pseudo-assumption variable di-A in each local diagnostic subsystem is assigned. Next, in step S570, the global diagnosis with a minimum cost to change the pseudo-assumption variable di-A is determined. Next, in step S580, the minimum cost global diagnosis determined in step S570 is selected as the actual global diagnosis. Operation then jumps to step S595. In step S590, a distributed diagnosis is determined in which the pseudo-assumption variable di-A is changed with its actual cost in the local diagnostic subsystem. In various exemplary embodiments, step S590 can be implemented by the exemplary method illustrated by the flowchart as shown in FIG. 7. Operation then continues to step S595, where the method ends. FIG. 10 shows an exemplary embodiment of a local diagnostic subsystem 600 according to this invention. As shown in FIG. 10, the local diagnostic subsystem 600 includes a local diagnosis circuit, routine or application 610, a controller 620, a memory 630, and an input/output interface 640, each interconnected by one or more data/control busses and/or application programming interfaces 650. As shown in FIG. 10, one or more sensors 660 are connected over one or more links 662 to the input/output interface 640. Additionally, a network interface 670 is connected to the input/output interface 640 over a link 672. The network interface 670 enables the input/output interface 640 to communicate with an external network 680 over one or more links 682. Thus, the local diagnostic subsystem 600 may be in communication with, for example, other local diagnostic subsystems via the network 680. The local diagnostic subsystem 600 may instead or additionally be in communication with other local diagnostic subsystems in a peer-to-peer relationship via the input/output interface 640. Each of the links 662, 672 and 682 can be implemented using any known or later developed device or system for connecting the corresponding one or more sensors 660, the network interface 670, and the external network 680, respectively, to the local diagnostic subsystem 600, including a direct cable connection, a connection over a wide area network, a connection over an intranet, a connection over the Internet, or a connection over any other distributed processing network or system. In general, each of the links 662, 672 and 682 can be any known or later developed connection system or structure usable to connect the corresponding one or more sensors 660, the network interface 670, and the external network 680, respectively, to the local diagnostic subsystem 600. The input/output interface 640 inputs data from the network 680, and/or the one or more sensors 660 and outputs data to the network 680. The input/output interface 640 also outputs data to one or more of the controller 620, the memory 630 and/or the local diagnosis circuit, routine or application 610 and receives data from one or more of the controller 620, the memory 630 and/or the local diagnosis circuit, routine or application 610. The memory 630 includes one or more of a model portion 632, an observation portion 634, a local diagnosis portion 636, and an associated diagnostic subsystem portion 638. In various exemplary embodiments, the model portion 632 stores the variables and constraints which together model the component being diagnosed. Thus, the model portion 632 may contain one or more observation variables, one or more assumption variables, one or more dependent variables, and one or more constraints. In various exemplary embodiments, the model portion 632 can also contain one or more pseudo-observation variables and/or one more or more pseudo-assumption variables. In various exemplary embodiments, the observation portion 634 stores the sensor readings received from the one or more sensors 660 via the input/output interface 640. In various exemplary embodiments, the observation portion 634 also contains one more rules relating sensor readings to the observation values to be stored in the observation variables. In various exemplary embodiments, these rules are implemented as translation tables. In various exemplary embodiments, the rules are implemented as one or more logical statements stored in the observation portion 634 of the memory 630. In various exemplary embodiments, the local diagnosis portion 636 stores the assumption values for the assumption variables and associated costs relating to the various local diagnoses. In various exemplary embodiments, the local diagnosis portion 636 also stores the assumption values corresponding to one or more pseudo-assumption variables and/or the observation values corresponding to one or more pseudo-observation variables, and the associated costs to change the values of these variables. In various exemplary embodiments, the local diagnosis portion 636 stores various logical routines associated with the local diagnosis process. In various exemplary embodiments, the associated diagnostic subsystem portion 638 of the memory 630 holds information identifying other local diagnostic subsystems that contain pseudo-observation variables corresponding to the local pseudo-assumption variables of the local diagnostic subsystem 600 and pseudo-assumption variables corresponding to the local pseudo-observation variables of the local diagnostic subsystem 600. In various exemplary embodiments, the associated diagnostic subsystem portion 638 holds the various routines used by the local diagnosis circuit, routine or application 610 to manage the associated other local diagnostic subsystems. In various embodiments, the memory 630 stores one or more control routines used by the controller 620 to operate the local diagnostic subsystem 600. The memory 630 can be implemented using any appropriate combination of alterable, volatile or non-volatile memory or non-alterable, or fixed, memory. The alterable memory, whether volatile or non-volatile, can be implemented using any one or more of static or dynamic RAM, a floppy disk and disk drive, a writeable or rewriteable optical disk and disk drive, a hard drive, flash memory or the like. Similarly, the non-alterable or fixed memory can be implemented using any one or more of ROM, PROM, EPROM, EEPROM, an optical ROM disk, such as CD-ROM or DVD-ROM disk, and disk drive or the like. It should be understood that each of the circuit, routine or applications shown in FIG. 10 can be implemented as physically distinct hardware circuits within an ASIC, or using an FPGA, a PDL, a PLA or a PAL, a digital signal processor, or using discrete logic elements or discrete circuit elements. The particular form each of the circuits or routines shown in FIG. 10 will take is a design choice and will be obvious and predictable to those skilled in the art. FIG. 11 is a block diagram showing in greater detail one exemplary embodiment of the local diagnosis circuit, routine or application 610 shown in FIG. 10. As shown in FIG. 11, the local diagnosis circuit, routine or application 610 includes one or more of an initialization, circuit, routine or application 612, a local diagnosis circuit, routine or application 614, a diagnosis management circuit, routine or application 616, and/or a remote diagnostic subsystem management circuit, routine or application 618. In various exemplary embodiments, the initialization circuit, routine or application 612 initializes a local diagnostic subsystem 600 to values indicative of the normal functioning of the diagnosed physical system. In various exemplary embodiments, the initialization circuit, routine or application 612 interacts with the diagnosis management circuit, routine or application 616 and/or the remote diagnostic subsystem management circuit, routine or application 618 to participate in initializing one or more other local diagnostic subsystems. In various exemplary embodiments, the local diagnosis circuit, routine or application 614 determines a local diagnosis for the local diagnostic subsystem 600 to be used in a distributed diagnosis. In various exemplary embodiments, the diagnosis management circuit, routine or application 616 controls the local diagnosis circuit, routine or application 614 and interacts with the remote diagnostic subsystem management circuit, routine or application 618 to manage the local diagnostic information used in the distributed diagnosis. In various exemplary embodiments, the remote diagnoser management circuit, routine or application 618 implements the communication routines used in the distributed diagnosis framework. In various exemplary embodiments, the remote diagnostic subsystem management circuit, routine or application 618 maintains one or more databases indicating associated local diagnostic subsystems and pseudo-assumption variables and/or pseudo-observation variables and values. In various exemplary embodiments, the remote diagnostic subsystem management circuit, routine or application 618 implements logical routines useful in the coordination of associated local diagnostic subsystems. While this invention has been described in conjunction with the exemplary embodiments outlined above,it is evidenced that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention. |
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048812471 | claims | 1. A method of measuring the burnup of nuclear fuel comprising: (A) measuring the fast neutron counting rate of said nuclear fuel; (B) reading said burnup off a curve which expresses the relationship between neutron emission rate and burnup for a nuclear fuel of comparable history, where the emission rate which corresponds to said neutron counting rate is obained by multiplying said neutron counting rate by the ratio of the neutron emission rate given by said curve for nuclear fuel of comparable history and known burnup to its similarly measured counting rate, and is defined by the formula EQU n/s=1.34.times.10.sup.-3 3.92 (A) measuring the fast neutron counting rate of said nuclear fuel; (B) obtaining the burnup which corresponds to said counting rate from a fast neutron counting rate-burnup curve which is a neutron emission rate-burnup curve, where the scale of said counting rate given by said fast neutron counting rate-burnup curve is the product of (1) the scale of the emission rate of said neutron emission rate-burnup curve for nuclear fuel of comparable history and (2) the ratio of a similarly measured neutron counting rate of nuclear fuel of comparable history and known burnup to its neutron emission rate as given by said neutron emission rate-burnup curve, and is defined by the formula EQU n/s=1.34.times.10.sup.-3 3.92 where n/s equals neutron emission rate. (A) means for measuring the fast neutron counting rate of said nuclear fuel; (B) a curve giving the relationship between said fasat neutron counting rate and burnup which is defined by the formula EQU n/s=1.34.times.10.sup.-3 3.92 where n/s equals neutron emisson rate. (A) means for measuring the fast neutron counting rate of nuclear fuel; (B) a sample of nuclear fuel of comparable history and known burnup, for which, when placed in said means for measuring fast neutron counting rate, a fast neutron counting rate is obtainable; (C) a neutron emission rate-burnup curve giving the relationship between neutron emission rate and burnup, from which the neutron emission rate of said sample is obtainable, and the ratio of said neutron emission rate to said neutron counting rate of said sample is determinable, so that when said nuclear fuel is placed in said means for measuring fast neutron counting rate and is fast neutron counting rate is measured, its fast neutron counting rate can be multiplied by said ratio to give its neutron emission rate and the burnup of said nuclear fuel can be read off said neutron emission rate-burnup curve, said curve being defined by the formula EQU n/s=1.34.times.10.sup.-3 3.92 2. A method according to claim 1 including the additional step of calculating said curve. 3. A method according to claim 1 wherein said fast neutron counting rate is measured with a boron-10 lined neutron detector or a U-235 lined fission detector which is shielded from gamma rays by a gamma ray shield and from thermal neutrons by a thermal neutron shield, where a moderator which slows fast neutrons down to thermal neutrons is provided inbetween said detector and said thermal neutron shield. 4. A method accordinig to claim 3 wherein said moderator is selected from the group consisting of water, polyethylene, and mixtures thereof. 5. A method according to claim 3 wherein said gamma rays are shielded with lead. 6. A method according to claim 3 wherein said thermal neutrons are shielded with cadmium. 7. A method of measuring the burnup of nuclear fuel comprising: 8. Apparatus for determining the burnup of nuclear fuel comprising: 9. Apparatus according to claim 8 which includes a boron-10 lined neutron detector or a U-235 lined fission detector to measure said fast neutron counting rate, where said detector is provided with a gamma ray shield and a thermal neutron shield, and a moderator which slows fast neutrons down to thermal neutrons is positioned inbetween said detector and said thermal neutron shield. 10. Apparatus accordiing to claim 8 wherein said moderator is selected from the group consisting of water, polyethylene, and mixtures thereof. 11. Apparatus according to claim 9 wherein said gamma ray shield is lead. 12. Apparatus according to claim 9 wherein said thermal neutron shield is cadmium. 13. Apparatus for measuring the burnup of nuclear fuel comprising: 14. Apparatus according to claim 13 which includes a boron-10 lined neutron detector or a U-235 lined fission detector to measure said fast neutron counting rate, where said detector is provided with a gamma ray shield and a thermal neutron shieldd, and a moderator which slows fast neutrons down to thermal neutrons is positioned in between said detector and said thermal neutron shield. 15. Apparatus according to claim 14 wherein said moderator is selected from the group consisting of water, polyethylene, and mixtures thereof. 16. Apparatus according to claim 14 wherein said gamma ray shield is lead. 17. Apparatus according to claim 14 where said thermal neutron shield is cadmium. 18. Apparatus according to claim 8 wherein the scale of said fast neutron counting rate given by said curve is the product of the scale of the neutron emission rate of a neutron emission rate-burnup curve times the ratio of a similarly measured fast neutron couning rate of nuclear fuel of known burnup and comparable history to its neutron emission rate as given by said neutron emission rate-burnup curve. |
claims | 1. An observation instrument inside a thick-walled radiation shielded cell, wherein the instrument is arranged to be capable of extending inside a cavity passing through a wall of the cell, the instrument comprising two separate modules:a first module of the instrument comprising a biological protection shield, a camera for acquiring images of zones situated in the cell; anda travel mechanism for moving the camera between a retracted position to which the camera is retracted into the cavity and a deployed position for observing the inside of the cell, the travel mechanism being coupled to the camera and including an actuator for causing the camera to move between the retracted position and the deployed position; anda second module of the instrument comprising a dome that is substantially transparent to rays or radiation and that is arranged to be capable of receiving the camera therein when the camera is in the deployed position for observation;each of the two modules including a mutual bearing face, the two modules being capable of being put into mutual contact via their respective mutual bearing faces when the modules are engaged in the cavity,the camera being arranged between the dome and the shield, and being secured to the shield via the travel mechanismthe dome being provided at a first end of the instrumentthe actuator causing the camera to move between the retracted position away from the dome and the deployed position in which the camera extends inside the dome,the travel mechanism being arranged between the dome and the shield, andthe dome being separate from the camera, from travel mechanism, and from the shield of the instrument. 2. An instrument according to claim 1, wherein the dome is secured to a tubular sleeve fitted with two O-rings and is arranged to slide in a tubular bushing lining the cavity, the O-rings being arranged to be in contact with the bushing. 3. An instrument according to claim 1, wherein the dome comprises a substantially hemispherical wall. 4. An instrument according to claim 3, wherein the wall is made of a plastics material, in particular of polycarbonate. 5. An instrument according to claim 1, wherein the travel mechanism comprises:a first actuator for causing the sensor to move in translation along the longitudinal axis of the instrument;a second actuator for causing the sensor to move in turning about the longitudinal axis; anda third actuator for causing the sensor to move in pivoting about an axis that is substantially orthogonal to the longitudinal axis. 6. An instrument according to claim 1, wherein the camera includes a controlled or automatic focusing lens with a motor-driven zoom function. 7. An instrument according to claim 1, wherein the camera includes a motor-driven zoom function. 8. A cell including a wall pierced by a cavity and an instrument according to claim 1 that extends inside the cavity. 9. A cell according to claim 8, wherein the wall of the cell includes an abutment that is movable between a stop position in which the abutment prevents the dome from being expelled into the cell, and a release position in which the abutment allows the dome to be expelled into the cell. 10. An observation instrument for observing the inside of a thick-walled radiation shielded cell, wherein the instrument is arranged to be capable of extending inside a cavity passing through a wall of the cell, the instrument comprising two separate modules:a first module of the instrument comprising:a biological protection shield;a gamma ray detector for measuring gamma rays emitted in zones situated in the cell; anda travel mechanism for moving the detector between a retracted position in which the detector is retracted into the cavity and a deployed position for observing the inside of the cell, the travel mechanism being coupled to the detector and including an actuator for causing the detector to move between the retracted position and the deployed position; anda second module of the instrument comprising a dome that is substantially transparent to rays or radiation and that is arranged to be capable of sliding in the cavity, which dome is capable of receiving the detector therein when the detector is in the deployed position for observation;each of the two modules including a mutual bearing face, the two modules being capable of being put into mutual contact via their respective mutual bearing faces when the modules are engaged in the cavity,the detector being arranged between the dome and the shield and being secured to the shield via the travel mechanism,the dome being provided at a first end of the instrument,the actuator causing the detector to move between the retracted position away from the dome and the deployed position in which the detector extends inside the dome,the travel mechanism being arranged between the dome and the shield, andthe dome being separate from the detector, from the travel mechanism, and from the shield of the instrument. 11. An instrument according to claim 10, wherein the dome is secured to a tubular sleeve fitted with two O-rings and is arranged to slide in a tubular bushing (31) lining the cavity, the O-rings being arranged to be in contact with the bushing. 12. An instrument according to claim 10 wherein the dome comprises a substantially hemispherical wall. 13. An instrument according to claim 12, wherein the wall is made of a plastics material, in particular of polycarbonate. 14. An instrument according to claim 10, wherein the travel mechanism comprises:a first actuator for causing the detector to move in translation along the longitudinal axis of the instrument;a second actuator for causing the detector to move in turning about the longitudinal axis; anda third actuator for causing the detector to move in pivoting about an axis that is substantially orthogonal to the longitudinal axis. 15. A cell including a wall pierced by a cavity and an instrument according to claim 10 that extends inside the cavity. 16. A cell according to claim 15, wherein the wall of the cell includes an abutment that is movable between a stop position in which the abutment prevents the dome from being expelled into the cell, and a release position in which the abutment allows the dome to be expelled into the cell. |
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summary | ||
claims | 1. A method of surface finishing a cladding tube for a fuel element of a nuclear reactor core in which the cladding tube contains a plurality of fuel, comprising the steps of:heating the tube to thermal creep temperatures for the sapphire; andslowly drawing and/or pushing the heated tube through a plug and die set to reduce heights of ridges on respective inner and outer surfaces of the tube while limiting changes in the crystalline structure, especially the crystal orientation, of the bulk of the tube. 2. A method according to claim 1, wherein the plug and die set are dimensioned to provide substantially uniform wall thickness of the tube while reducing ridge height and limiting changes in the crystalline structure, especially the crystal orientation, of the bulk of the tube. 3. A method according to claim 1, wherein the forming displaces irregularities by producing shear along an “a” plane parallel to a principal “c” axis of the tube material. 4. A method according to claim 1, wherein the tube is drawn or pushed in a similar manner through a plurality of plug and die sets, each succeeding plug and die set having a slightly larger inner diameter and slightly smaller outer diameter, respectively, than its predecessor so as to reduce ridge height in successive steps, a final plug and die set having respective inner and outer diameters corresponding to finished outer and inner diameters of the tube. 5. A method according to claim 4, wherein the tube is allowed to thermally soak between die passes at a temperature slightly above the drawing temperature to alleviate any work hardening and make the ridges workable during subsequent drawing. 6. A method of surface finishing a sapphire tube by thermal creep differential expansion moulding using a mould that is made of a material that has a different coefficient of expansion than sapphire and is non-wettable by sapphire, the mould being sized and shaped to give desired diameters and surface uniformity of at least one of inner and outer surfaces of the tube, the method comprising:placing the rough sapphire tube in the mould and slowly heating the tube-mould assembly to the range of the creep temperature of the sapphire and causing pressure at an interface between the sapphire and the mould;maintaining the assembly at the upper end of the creep temperature range for a creep and soak period to allow creep to progress and relieve the stresses from the pressure upon the sapphire tube from the mould; andslowly cooling the assembly, allowing the sapphire tube to part from the mould so that it can be withdrawn. 7. A method according to claim 6, wherein the mould is configured and dimensioned to apply pressure to form the inner surface of the sapphire tube. 8. A method according to claim 6, wherein the mould is configured and dimensioned to apply pressure to form the outer surface of the sapphire tube. 9. A method according to claim 6, wherein the mould is configured and dimensioned to apply pressure to form both inner and outer surfaces of the sapphire tube at the same time. 10. The method according to claim 1 wherein the step of heating comprises heating to the tube to a temperature in the range of 1700-2000 degrees Celsius. 11. The method according to claim 6 wherein the step of heating comprises heating the tube-mold assembly to a temperature in the range of 1700-2000 degrees Celsius. |
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claims | 1. A method for processing toxic material, comprising:forming quasi-natural feldspar or artificial feldspar having a chemical formula of Ca(Al,Si)O2 with a toxic material, the quasi-natural or the artificial feldspar having a toxicity level equal or below an average toxicity level in a natural feldspar material present at a host site where the quasi-natural feldspar or the artificial feldspar will be permanently stored. 2. The method of claim 1, wherein forming comprises forming the quasi-natural feldspar or the artificial feldspar with the toxic material comprising a radioactive material. 3. The method of claim 2, wherein forming comprises forming the quasi-natural feldspar or the artificial feldspar with the radioactive material in liquid form or solid form. 4. The method of claim 2, wherein forming comprises forming the quasi-natural feldspar or the artificial feldspar with the radioactive material comprising depleted uranium. 5. The method of claim 2, wherein forming comprises forming the quasi-natural feldspar or the artificial feldspar with the radioactive material comprising medical radioactive material or other classified radioactive material. 6. The method of claim 2, wherein forming comprises forming the quasi-natural or the artificial feldspar with radioactive material comprising radioactive materials from a nuclear incident. 7. The method of claim 2, wherein forming comprises forming the quasi-natural or the artificial feldspar with the radioactive material comprising radioactive materials resulting from a nuclear detonation. 8. The method of claim 1, wherein forming comprises forming the quasi-natural feldspar or the artificial feldspar with the toxic materials comprising a toxic chemical or a reactive material. 9. The method of claim 1, wherein forming comprises forming the quasi-natural feldspar or the artificial feldspar with the toxic material comprising mine tailing material. 10. The method of claim 1, wherein forming the quasi-natural feldspar or the artificial feldspar comprises subjecting a job mix formula, including precursors for the quasi-natural feldspar or the artificial feldspar and the toxic material, to a temperature of at least about 1,100° C. 11. The method of claim 10, wherein forming the quasi-natural feldspar or the artificial feldspar comprises subjecting the job mix formula to the temperature of at least about 1,100° C. for about four hours or more. 12. The method of claim 11, wherein subjecting the job mix formula to the temperature of at least about 1,100° C. for about four hours or more comprises introducing the job mix formula into a continuous flow reactor. 13. The method of claim 1, wherein forming the quasi-natural feldspar or the artificial feldspar comprises subjecting the job mix formula to a temperature of about 800° C. to about 1,400° C. 14. The method of claim 13, wherein forming the quasi-natural feldspar or the artificial feldspar comprises subjecting the job mix formula to the temperature of about 800° C. to about 1,400° C. for about four hours or more. 15. The method of claim 14, wherein subjecting the job mix formula to the temperature of about 800° C. to about 1,400° C. for about four hours or more comprises introducing the job mix formula into a continuous flow reactor. 16. A method for processing toxic material, comprising:designing a job mix formula, including fly ash, for making an artificial feldspar having a chemical formula of Ca(Al,Si)O2;mixing the job mix formula with a toxic material to provide a mixture having a toxicity level equal to or below an average toxicity level in a natural feldspar material present at a host site where the artificial feldspar will be permanently stored;introducing the mixture into a continuous flow reactor to form the artificial feldspar. 17. The method of claim 16, wherein introducing the mixture into the continuous flow reactor comprises exposing the mixture to a temperature of about 800° C. to about 1,400° C. 18. The method of claim 17, wherein introducing the mixture into the continuous flow reactor comprises exposing the mixture to a temperature of at least about 1,100° C. 19. The method of claim 16, further comprising:leaving the mixture in the continuous flow reactor for about four hours or more. 20. A method for processing toxic material, comprising:designing a job mix formula, including fly ash, for making an artificial feldspar having a chemical formula of Ca(Al,Si)O2;mixing the fly ash and other components of the job mix formula with a toxic material to provide a mixture having a toxicity level equal to or below an average toxicity level in a natural feldspar material present at a host site where the artificial feldspar will be permanently stored;introducing the mixture into a continuous flow reactor to heat the job mix formula and the toxic material to a temperature of at least about 1,100° C. to form the artificial feldspar; andrapidly cooling the artificial feldspar, with a coating of silicon dioxide forming on each particle or piece of the artificial feldspar while rapidly cooling the artificial feldspar. |
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053612833 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, it is seen in FIG. 1 that the invention is generally indicated by the numeral 10. Locking arrangement 10 is integral to the guide tube assembly 12 and is designed to be reusable without the release of loose parts in the system. Locking arrangement 10 is generally comprised of a retainer sleeve 16 that cooperates with slots 18 in upper end fitting 14 to lock the guide tube assembly and upper end fitting together in their installed position. As seen in FIG. 4, retainer sleeve 16 is formed from a cylindrical tube that is provided with a plurality of flexible curved tabs 20 that extend outwardly and are spaced apart around the circumference of the tube substantially at the mid section of the tube. Tabs 20 are curved in the preferred embodiment as seen in FIG. 5 to provide for smoother operation. Tabs 22, which are optional, are located at the lower end of the tube and spaced around the circumference. Tabs 22 serve to center guide tube assembly 12 in the bore through upper end fitting 14 and provide a more rigid connection. Tabs 20 serve to retain guide tube 12 assembly and upper end fitting 14 in their installed position relative to each other. In the installed position, tabs 20 extend outwardly immediately above shoulder 24 defined at the lower end of each slot 18. This prevents upper end fitting 14 from being removed from guide tube assembly 12. As seen in FIGS. 1 and 2, upper end fitting 14 is provided with four vertically extending slots 18 that are spaced apart around bore 26 but do not extend the entire length of the bore. In order to provide the necessary resilient biasing action, retainer sleeve 16 is preferably made from a material that is used for springs and suitable for use in a nuclear application, such as nickel alloy 718. As seen in FIG. 1, guide tube assembly 12 is provided with an upper end sleeve 28 that serves as an attachment point for retainer sleeve 16. Upper end sleeve 28 may be attached to guide tube assembly 12 by any suitable means such as welding as indicated by the numeral 29. As best seen in FIGS. 1, 3 and 4, the retainer sleeve 16 of the invention is attached to upper end sleeve 28 by the use of lugs or rigid tabs 30 that extend around a portion of the circumference of upper end sleeve 28. Retainer sleeve 16 is provided with slots 32 that are sized to receive tabs 30. To provide a permanent connection, retainer sleeve 16 may also be attached to upper end sleeve 28 by any suitable method such as bonding or welding. Since guide tubes are usually relatively thin (approximately 19 mils), an upper end sleeve is normally included on guide tubes to provide a point for attachment to the upper end fitting and to provide the necessary support for a shoulder stop 34 seen in FIG. 1 to prevent the upper end fitting from moving down the guide tube assembly when the fuel assembly is in the vertical position. During assembly, the upper end fitting 14 is pushed over upper end sleeve 28 and sleeve retainer 16. The tabs 20 and 22 are forced inboard as the end fitting slides over the guide tube assembly. When end fitting 14 is fully seated, a rotation tool not shown is received in tooling slots 34 on the upper end of retainer sleeve 16. The tool is used to rotate retainer sleeve 16 until tabs 20 spring outboard into slots 18 in upper end fitting 14. The presence of tabs 20 at shoulders 24 serve to retain upper end fitting 14 and guide tube assembly 12 in their relative installed positions. Tabs 22 maintain pressure against the walls of the bore 26 through end fitting 14 to retain guide tube assembly 12 in a centered position and provide for a more rigid connection. Removal of end fitting 14 is accomplished by engaging a rotating tool with tooling slots 34 and rotating retainer sleeve 16 approximately forty-five degrees to force tabs 20 inboard and then sliding end fitting 14 upward. As seen in FIG. 2, slots 18 are preferably semicircular to provide for ease of operation in forcing tabs 20 inboard during rotation of retainer sleeve 16. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense. |
041529189 | summary | BACKGROUND OF THE INVENTION The present invention relates to a vertical rolling mill which is provided with at least a pair of rolling rolls having vertical axes of rotation. To explain the conventional rolling mills of this type reference is made to a rolling mill 31 shown in FIG. 1 as an example. A pair of spindle members 33 and 33' are connected to a driving member 32 and said spindle members are disposed directly above a stand 35 provided with a pair of rolling rolls 34 and 34'. The spindle members 33 and 33' are respectively connected with the rolling rolls 34 and 34' so as to drive them from above. Therefore, in the case of this rolling mill 31, at the time of replacing the stand 35, it is impossible to perform said replacing by lifting same with a machine, such as crane, etc., unless the stand 35 is shifted from the prescribed position for rolling indicated by the solid line to one side as indicated by the dotted line because the spindle members 33 and 33' obstruct it. Accordingly, provision of a mechanism 36 for the purpose of thus shifting the stand 35 sideways is indispensable. Besides, since much time is required in the work of replacing the stand 35, as stated above, in order to reduce the frequency of replacing, multicaliber-type rolls 34 and 34' provided with plural number of calibers for inserting the material-to-be-rolled have been adopted. Because of the adoption of this multicaliber-type roll, provision of a mechanism 37 for effecting vertical movement of the stand 35 in order to align all the calibers with the pass line appropriately is indispensable. Inasmuch as the rolling mill 31 is provided with the mechanisms 36 and 37 as stated above, it becomes large in size, complicated in structure and heavy in weight as a whole, necessitating a large-size foundation at the time of erecting it, and also a spacious site is required therefore. Accordingly, it is difficult to erect this rolling mill 31 among existing various machines for the rolling process in factories. Moreover, inasmuch as the stand 35 per se having said multicaliber-type rolls 34 and 34' is heavy in weight, the machine for use in lifting it, e.g., crane, etc., must be of a large size. The upper end of a lifting machine such as a large-sized crane and the like at the time of operation is close to the restricted height of factory buildings, and therefore it must be operated with prudence. Consequently, the work of replacing the stand 35 is inconvenient and is difficult to perform. As set forth above, the conventional rolling mills exemplified by the rolling mill 31 illustrated in FIG. 1 have been accompanied by various drawbacks such as enumerated in the foregoing. SUMMARY OF THE INVENTION The primary object of the present invention is to provide a vertical rolling mill which will eliminate the aforedescribed drawbacks of the conventional vertical rolling mills. Another object of the present invention is to provide a vertical rolling mill wherein at least a pair of spindle members, for the purpose of rotating at least a pair of rolling rolls having vertical axes of rotation, are juxtaposed below a sole plate installed on a frame on which is mounted a stand for supporting said rolling rolls in rotatable fashion. When said stand is mounted on said sole plate the rolling rolls are connected with the spindle members respectively so as to be driven thereby, whereby there is no necessity for shifting the stand sideways from the prescribed position for rolling beforehand at the time of lifting the stand in order to replace it with another stand. The replacing work can be performed by lifting the stand directly from the rolling position, and accordingly, provision of any particular mechanism for moving the stand can be dispensed with and the rolling mill can be of a small size and light weight compared with the conventional rolling mills, thereby facilitating the stand replacing work. The pair of rolling rolls are provided with a single caliber formed thereon whereby it is not necessary to provide any specific mechanism for effecting vertical movement of the stand necessary for aligning all the calibers with the pass line appropriately. Therefore, the rolling mill can be of small size and light weight compared with the conventional rolling mills employing a pair of multicaliber-type rolls and the foundation work at the time of erecting the rolling mill can be simplified. A further object of the present invention is to provide a vertical rolling mill wherein an upright portion is provided on the sole plate and extends upwardly at one side thereof. A guide face parallel to the direction of inserting the material-to-be-rolled between said pair of rolling rolls is formed on said upright portion. Another guide face which cooperates with this guide face is formed on the stand. The stand is further provided with an adjusting member for advancing or retracting said guide face. By the action of this adjusting member the horizontal position of the caliber can be adjusted at will. A still further object of the present invention is to provide a vertical rolling mill which comprises universal couplings as said spindle members, each of said couplings being of a self-standing and short length type and having its upper part provided with an engaging portion for the purpose of connecting the coupling with the lower end of the rolling roll so as to drive said roll. The interspace of the paired rolling rolls is not restricted at the time of installing them on the stand in rotatable fashion. Accordingly, a delicate, subtle adjustment of the caliber can be performed by slightly widening or narrowing said interspace. Because said coupling is of a self-standing and short length type, no coupling holder is required therefor and, moreover, the distance from the sole plate to the bottom of the reduction means can be shortened. An additional object of the present invention is to provide a vertical rolling mill wherein holding members are installed on the upright portion of the frame by disposing same on one side of the sole plate so as to hold the sole plate therebetween. Each of the holding members is provided with a projection so as to clamp said stand at the time of operation. The stand is provided with vertical grooves which cooperate with these projections, whereby when mounting the stand on the sole plate, the stand can be very easily fixed on a prescribed position on said table. |
claims | 1. A pulsed plasma thruster propellant module comprising: at least one propellant rod including: a first stage having a first propellant source having dimensions defining a first stage discharge length; a second stage having a second propellant source having dimensions defining a second stage discharge length, wherein the first stage discharge length is less than the second stage discharge length; and an ignition source for generating an ignition discharge across the first stage discharge length, wherein the first and second stages are designed such that said ignition discharge across the first discharge length initiates a subsequent ignition discharge across the second discharge length. 2. The propellant module as described in claim 1 , further comprising a passive impedance source designed to transmit the ignition discharge current from the first stage propellant source to the second stage propellant source. claim 1 3. The propellant module as described in claim 1 , wherein the ignition source includes a power supply in electrical communication with at least one ignition electrode. claim 1 4. The propellant module as described in claim 3 , further comprising a switch for connecting or disconnecting the electrical communication between the power supply and the at least one ignition electrode. claim 3 5. The propellant module as described in claim 1 , wherein the ignition source comprises: claim 1 a power supply; a first ignition electrode in electrical communication with the power supply; a second ignition electrode, wherein the first stage propellant source is disposed between the first and second ignition electrodes; and a third ignition electrode, wherein the second stage propellant source is disposed between the second and third ignition electrodes. 6. The propellant module as described in claim 5 , wherein the first, second and third ignition electrodes are cylindrical and arranged in a coaxial geometry. claim 5 7. The propellant module as described in claim 5 , wherein the first and second propellant sources are made of a non-conductive material. claim 5 8. The propellant module as described in claim 5 , wherein the electrodes are made of a conducting metal. claim 5 9. The propellant module as described in claim 5 , further comprising at least two propellant rods. claim 5 10. The propellant module as described in claim 5 , further comprising a passive impedance in electrical communication between the first and second stage, wherein the passive impedance transfers the ignition discharge from the first stage to the second stage. claim 5 11. The propellant module as described in claim 5 , further comprising a switch in electrical communication between the first and second stage for triggering the ignition discharge of the second stage. claim 5 12. The propellant module as described in claim 5 , further comprising a trigger capacitor in electrical communication with the ignition source, wherein the trigger capacitor provides an additional quantum of discharge energy to the ignition discharge across the first stage propellant source. claim 5 13. The propellant module as described in claim 5 , further comprising an RC circuit in electrical communication with the first stage, wherein the RC circuit impedes the voltage rise on the first stage and controls the firing frequency of the propellant module. claim 5 14. A propulsion unit comprising the propellant module described in claim 5 . claim 5 15. The propellant module as described in claim 1 , wherein the first and second stages comprise independent cylinders arranged in an adjacent relationship. claim 1 16. The propellant module as described in claim 15 , wherein the first stage includes: claim 15 wherein the second stage includes: a first ignition electrode in electrical communication with a power supply, and a second ignition electrode, wherein the first stage propellant source is disposed between the first and second ignition electrodes; and a third ignition electrode in electrical communication with the second ignition electrode, and a fourth ignition electrode, wherein the second stage propellant source is disposed between the third and fourth ignition electrodes. 17. The propellant module as described in claim 16 , wherein the first and second electrodes are arranged in a coaxial geometry and form a first propellant cylinder, and wherein the third and fourth electrodes are arranged in a coaxial geometry and form a second propellant cylinder. claim 16 18. The propellant module as described in claim 15 , wherein the first and second propellant sources are made of Teflon. claim 15 19. The propellant module as described in claim 15 , wherein the electrodes are made of a conducting metal. claim 15 20. The propellant module as described in claim 15 , further comprising a passive impedance in electrical communication between the first and second stage, wherein the passive impedance transfers the ignition discharge from the first stage to the second stage. claim 15 21. The propellant module as described in claim 15 , further comprising a switch in electrical communication between the first and second stage for triggering the ignition discharge of the second stage. claim 15 22. The propellant module as described in claim 15 , further comprising a trigger capacitor in electrical communication with the ignition source, wherein the trigger capacitor provides an additional quantum of discharge energy to the ignition discharge across the first stage propellant source. claim 15 23. The propellant module as described in claim 15 , further comprising an RC circuit in electrical communication with the first stage, wherein the RC circuit impedes the voltage rise on the first stage and controls the firing frequency of the propellant module. claim 15 24. The propellant module as described in claim 15 , further comprising at least two second stages. claim 15 25. The propellant module as described in claim 24 , further comprising a selector switch in electrical communication with the ignition source, wherein the selector switch determines which of the at least two second stages is ignited by the ignition discharge of the first stage. claim 24 26. A propulsion unit comprising the propellant module described in claim 15 . claim 15 27. The propellant module as described in claim 1 , further comprising: claim 1 a power source for generating an ignition voltage; a bundle of at least two propellant rods in electrical communication with the power source, the at least two propellant rods each including: a first electrode, a second electrode, and a propellant source disposed between the first and second electrodes having dimensions defining a discharge length; wherein the power source randomly applies the ignition voltage to one of the at least two propellant rods to generate an ignition discharge across the discharge length of said propellant rod until the propellant source within each propellant rod is exhausted. 28. The propellant module as described in claim 27 , wherein the ignition discharge is triggered by a triggering technique selected from the group consisting of: claim 27 self-triggered, triggered, and quasi-steady. 29. The propellant module of claim 27 wherein each of the at least two propellant rods are designed to enter an open-circuit condition such that no further ignition discharges occur across said discharge length once the propellant source has been expended. claim 27 30. The propellant module of claim 27 wherein each of the at least two propellant rods further comprises an insulating tube surrounding one end of the first electrode such that when the propellant source has been depleted sufficiently to expose the insulating tube an open-circuit condition is entered such that no further ignition discharges occur across the discharge length. claim 27 31. The propellant module of claim 27 wherein each of the at least two propellant rods further comprises a non-ablative material disposed between the first and second electrodes at one end of the propellant rod such that when the propellant source has been depleted sufficiently to expose the non-ablative material an open-circuit condition is entered such that no further ignition discharges occur across the discharge length. claim 27 32. The propellant module of claim 27 wherein the discharge length between the first and second electrodes of each of the at least two propellant rods increases at one end of the propellant rod such that when the propellant source has been depleted sufficiently to reach the increased discharge length an open-circuit condition is entered such that no further ignition discharges occur across said increased discharge length. claim 27 33. The propellant module as described in claim 27 , further comprising a propellant rod switch for directing the ignition voltage between the at least two propellant modules. claim 27 34. A propulsion unit comprising the propellant module described in claim 27 . claim 27 35. A propulsion unit comprising the propellant module described in claim 1 . claim 1 |
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050874110 | description | DESCRIPTION OF PREFERRED EMBODIMENT FIG. 1 shows an entire device recovery and for the elimination of radioactive waste in the water of the well 1 of a pressurized-water nuclear reactor. The device is used during a shutdown phase of the nuclear reactor, the vessel of which is open and communicates with the well 1. The device according to the invention comprises an aspiration pipe 2, a means for the handling and lifting of the pipe 2 which may consist of a travelling crane moving above the well of the reactor, the hook 3 of which is connected to the upper part of the pipe 2, and a pumping installation 4 connected by a flexible conduit 5 to the lower part of the pipe 2 ensuring the aspiration and the delivery of the water from the well. The pumping installation 4 placed on the edge 6 of the well 1, in the zone accessible to the operators ensuring the maintenance of the reactor, may be disposed in a biological protection enclosure to cover the case in which radioactive debris of small dimensions may be liable to come into contact with certain parts of the installation and to cause a certain contamination. The pipe 2 consists of a column 8 comprising three successive sections 8a, 8b, 8c extending along its axis ZZ'. The two upper sections 8a and 8b each consist of a tube of light alloy closed in a sealed manner at its ends, while the lower section 8c comprises openings in its wall permitting the filling thereof by water from the well. The column of water filling the section 8c ensures biological protection in the case where highly radioactive materials are found below the column 8. A handling bar 9 is fixed at the end of the upper section 8a of the column, which is suspended with its axis ZZ' in a vertical position from the hook 3 of the crane of the reactor, by means of the handling bar 9. At the lower end of the column 8 opposite to its end connected to the handling means 3, there is fixed an aspiration head 10 of difrustoconical shape, the upper part of which is connected to the flexible aspiration conduit 5 and the lower part of which comprises an aspiration connection 11 opening into the well 1. The various sections of the column are demountable, in such a manner as to permit the use of a pipe 2 of length appropriate to carry out the recovery of waste, at any location within the vessel of the reactor. FIG. 2 shows the upper part of the section 8c of the column 8 and its means for connection to the lower part of the section 8b. As can be seen in FIGS. 2 and 2A, the lower part of the section 8b comprises a shoulder 12 having two flats 13 carrying four attachment screws 14 traversing and fixed in a captive manner on this shoulder. The upper part of the section 8c is constituted by a widening 15, the shape of which in transverse cross-section corresponds to the shape of the shoulder 12 and which comprises, in particular, two flats 16 similar to the flats 13 of the shoulder 12. The widening 15 is pierced by four threaded blind holes each intended to receive a screw 14, in the course of the assembly of the sections 8b and 8c of the column. The assembly of the two sections is carried out by placing in coincidence the similar sections of the shoulder 12 and of the widening 15 and by screwing the screws 14 into the threaded holes of the widening 15. Two suspension arms 17 are fixed via a shaft 18, on the widening 15, at the location of the flats 16. A handling bar 20 is connected to the end of the arms 17. The suspension device consisting of the arms 17 and of the bar 20 may be displaced by pivoting about the shaft 18, the flats 13 and 16 in coincidence ensuring a sufficient displacement for the arms 17. In FIG. 2, the suspension device has been represented in solid lines in its position permitting the handling of the lower section 8c and in broken lines in a withdrawn position similar to that represented in FIG. 1 and corresponding to the assembled position of the column. Each of the successive sections of the column has an upper part similar to the upper part of section 8c and may permit the fixing of a suspension device consisting of arms and a bar. In particular, the handling bar 9 of the column 8 is connected to the upper section 8a by pivoting arms, in the same manner as the bar 20 of the lower section 8c. The suspension devices of the various sections of the column are therefore used either for the suspension of the pipe during the use of the aspiration device or at the moment of mounting of the column, a sufficient number of sections being assembled to obtain the desired length. FIG. 3 shows the lower part of the section 8c of the column 8 on which the aspiration head 10 is fixed. The lower part of the section 8c consists of a shoulder 23 carrying six attachment screws 24 connected in a captive manner to the shoulder 23. The shoulder 23 is furthermore pierced by a centering bore 25 opening at its lower end. The aspiration head 10 comprises an upper connection 26 with a widening 27 at its end, the cross-section of which corresponds to the cross-section of the shoulder 23 of the section 8c. The widening 27 comprises, at its end, a stub 28 intended to come into engagement in the centering bore 25 of the shoulder 23. The widening 27 further comprises six equidistant threaded holes in positions corresponding to the positions of the screws 24. The fixing of the aspiration head 10 at the lower end of column 8c is carried out by introducing the stub 28 into the opening 25 by orienting into the head in such a manner as to place the screws 24 in alignment with the threaded holes of the widening 27 and by ensuring the screwing of the screws 24 into the threaded holes. The aspiration head 10 comprises an aspiration conduit 30 at its upper part, to which conduit the flexible conduit 5 may be connected via a screwed connection 31. FIG. 4 shows the assembly of the parts constituting the aspiration head 10 and their connecting means. The casing of the aspiration head 10 is constituted by two hollow walls 32 and 33 of frustoconical shape, which may be connected, along their major bases in order to by flanges 34 and 35 form the difrustoconical casing represented in FIG. 1. The frustoconical hollow wall 32 constituting the upper part of the aspiration head in the service position, as represented in FIG. 1, is solid at its end, along its minor base, with the tubular connection 26 to which the aspiration conduit 30 is connected. The flange 34 is internally machined to form an annular seating 36 receiving, in the course of the mounting of the aspiration head, the peripheral edge of a filter support 38 against which the filter 39 of the aspiration head is placed. The flange 34 carries centering pins 37 intended to be inserted upon mounting of the aspiration head, in holes 44 provided in the flange 35 of the frustoconical wall 33. The centering pins and holes may respectively be located at 90.degree. from one another. In the course of the assembly of the aspiration head, the filter 39 placed along the entire cross-section of the major base of the frustoconical walls 32 and 33 ensures a separation of the internal volume of the aspiration head 10 into a first part situated within the wall 32 and disposed at the upper part of the aspiration head and a second part situated within the frustoconical wall 33 and disposed at the lower part of the aspiration head 10. The flange 34 carries a fixing plate 41 for a chain 40 connected at its other end to a small plate 41' fixed on the external wall of the lower frustoconical casing 33. The chain 40 permits, in the course of the demounting of the aspiration head 10, as represented in FIG. 4, the maintenance of a connection between the upper frustoconical wall 32 solid with the column and the lower frustoconical wall 33, while still permitting separation of the walls 32 and 33, sufficient for removal of the filter 39 from the aspiration head 10. The lower frustoconical wall 33 is solid, at its end corresponding to the minor base of the cone, with a nozzle 42 comprising internal recesses 43. This nozzle places the internal volume of the aspiration head, in its second part situated below the filter 39, in communication with the external medium, which may consist of the water of the well of the reactor. The flange 35 further carries two connecting devices such as 45, in diametrically opposite positions, permitting the assembly of the flanges 34 and 35 and thus of the walls 32 and 33 to constitute the casing of the aspiration head. Each of the devices 45 comprises an eyelet screw 46 mounted so as to be articulated, via a shaft 47, on a bearing 48, solid with the flange 35. A nut 49 is engaged on the threaded end of the screw 46. To assemble the two flanges and the two walls constituting the casing of the aspiration head, the two flanges are placed in coincidence, and the pins 37 come into engagement in the corresponding openings 44 of the flange 35. The eyelet screw 46 is withdrawn into a position parallel to the axis of the aspiration head, as represented in FIG. 5. The screw 46 then comes within a facing 50 machined radially, in the flange 34. The fixing of the two walls 32 and 33 is completed by tightening the nut 49 against the flange 34. The same operation is carried out for the two connecting devices 45. FIGS. 4 and 6 show the filter support plate 38 which is constituted by a rigid plate pierced by holes 52 traversing the plate 38 and disposed on the plate in regular pattern. The plate 38 also comprises two threaded radial holes 53, in diametrically opposite positions and opening onto the peripheral surface of the plate 38. The plate 38, whose diameter is very slightly less than the diameter of the seating 36, is placed in this seating in the course of the mounting of the aspiration head. The flange 34 is pierced by two radial holes in diametrically opposite positions. The plate 38 is oriented within the seating 36 in such a manner as to place the threaded holes 53 in alignment with the holes traversing the flange 34. Screws 55 engaged into these holes placed in alignment permit the assembly of the filter support plate 38 and of the frustoconical wall 32 to be carried out. The frustoconical wall 32 comprises an ejection device 56 constituted by a cylinder 57 traversing the wall 32, a rod 58 terminated by a pusher 59 mounted to slide in the cylinder 57, a thrust wheel 61 solid with the end of the rod 58 opposite to the pusher 52, and a return spring 62 intercalated between the thrust wheel 61 and the end of the cylinder 57. The cylinder 57 is disposed in such a manner that the pusher 59, the diameter of which is less than the diameter of the openings 52 of the filter support 38, is centered within one of the openings. As can be seen in FIGS. 4 and 7, the filter 39 is constituted by a network of crossed steel wires, like a metallic net, fixed within an annular support 63, the internal diameter of which is substantially equal to the diameter of the plate 38. The annular support 63 constituting the border of the filter 39 is placed between the four centering pins 37 which, in the course of the mounting of the filter, enter into openings 44 of the flange 35. In its assembled position, the wall of the filter 39 is in contact with the filter support plate 38 which ensures its retention against the pressure of the water passing through the aspiration head. The water passes through the filter support plate 38 via the openings 52. When the aspiration head is in the service position, the first part of its internal volume, situated above the filter 39 and within the wall 32, is in communication with the branch 30 connected by the conduit 5 to the aspiration installation 4. The second part of the internal volume of the aspiration head below the filter 39 and within the wall 33 is in communication via the nozzle 42 with the external medium constituted by the water of the well. When, in the course of the operations of maintenance and of recharging of the reactor, waste or debris has been located in the vessel, the column is mounted in such a manner as to provide access to the zones in which this waste or debris is located. It may thus become necessary to carry out the mounting of a larger or smaller number of sections such as 8a, 8b, 8c, fixed end to end. In an embodiment suitable for pressurized-water nuclear reactors of the current art, each column section has a length of 4.800 meters and the aspiration head a length close to 0.60 meter. The assembly of three successive sections 8a, 8b, 8c thus permits the achievement of a length of 15 meters, which is sufficient to undertake the recovery of waste or debris in any location whatever of the vessel of the reactor. The end of the aspiration head constituted by the nozzle 42 is placed in position in the immediate vicinity of the waste of which the recovery is being undertaken, it being possible for this positioning to be undertaken by means of the crane of the reactor and controlled by one or more submerged television cameras. It is thus possible to guide the end of the aspirating pipe to a specific location. In the case where the waste is resting on an accessible surface, it will be possible to achieve the placement of the end of the nozzle on this surface around the waste, in order to ensure effective aspiration. The pumping and delivery installation 4 is activated; this performs the aspiration of the water from the well of the reactor by the nozzle 42 and a delivery thereof to the upper part of the well. The water from the well is aspirated through the space formed between the internal recesses 43 and the surface on which the nozzle rests; this water which is aspirated and which circulates upwardly within the second part of the internal volume of the aspiration head below the filter, entrains the waste or debris which is retained against the surface of the filter 39, during such time as the aspiration in the head 10 is maintained. The water which has passed through the filter 39 and which is aspirated by the pump 4 therefore no any longer contain radioactive elements, so that no contamination of the pumping installation is produced. This installation 4 may therefore be placed on the floor 6 in the vicinity of the well, in a zone in which the operators entrusted with the maintenance of the reactor work. During the circulation of the water in the aspiration head, the filter 39 is maintained by the filter support 38 and does not undergo any damage, even in the case where a partial clogging of the filter gives rise to an increase in the pressure difference on either side of the filter. When the recovery of the debris or waste located in the vessel has been completed, their elimination is carried out by placing a container in proximity to the working zone and by bringing the nozzle 42 of the aspiration head into coincidence with the opening of the container intended for the storage of the radioactive waste. The aspiration is terminated by cutting off the power supply to the motor of the pump 4, so that the waste and debris retained against the filter by the aspiration fall back into the second part of the internal volume of the aspiration head and are then guided by the smooth internal surface of the wall 33 towards the nozzle 42 and the container for the storage of the waste. In the case where the debris recovered is highly radioactive, for example in the case of sintered pellets of combustible material, the filter becomes highly radioactive, so that it is necessary to undertake the demounting and elimination thereof before remounting the aspiration pipe, in order to avoid irradiating the operators ensuring the maintenance. There is then performed the remote unscrewing of the nuts 49 of the eyelet screws 46, by means of a box key mounted on a column. The eyelet screws 46 are set down towards the outside in such a manner as to separate the two flanges 34 and 35 and the two frustoconical walls 32 and 33. These two walls are uncoupled and the filter is ejected into a container for the storage of radioactive waste by means of the pusher device 56 which can be remotely operated by applying pressure to the wheel 61; this causes the displacement of the pusher 59 within the opening 52 of the plate 38 until the pusher 59 comes into contact with the filter 39, which it ejects into the container for the storage of waste. It should be noted that, in the course of the demounting of the aspiration head 10, the frustoconical lower wall 33 remains solid with the upper wall 32 and with the column, by virtue of the chain 40. The aspirating pipe 2, the head 10 of which no longer encloses any radioactive material, may be remounted at the upper level of the well. The mounting of a filter 9 in the aspiration head is then carried out. The aspirating pipe 2 is ready for a new operation of recovery and of elimination of radioactive waste. In the case where the debris recovered on the surface of the filter by aspiration is slightly radioactive, the aspiration head 10 of the pipe is not demounted, it being possible for the filter to be used for a new operation. The main advantages of the invention are to permit recovery of the radioactive waste under water and elimination of this waste, even where it is constituted by friable materials and/or by particles of small dimensions. Moreover, the recovery and elimination operations are carried out entirely remotely, under a large head of water; this eliminates the risk of irradiation of the operators. Finally, the parts of the device which are placed at the upper level of the well or which are to be remounted at this level in the course of operation are not subjected to any contamination under the effect of the highly radioactive waste. The aspiration head may have walls having an other than frustoconical geometric shape and the remotely demountable connecting means of these walls may be constructed in a different manner. The connecting means of the walls may have any number. It is possible to use any pumping, aspiration and delivery installation disposed either above or on the base of the well and any filtration wall having characteristics adapted to the size of the waste and to the depth of intervention. It is possible to connect a flexible pipe to the nozzle 42 of the aspiration head, and to fit to the end of the flexible pipe connections provided according to the location and the nature of the waste to be recovered (for example, recovery of debris from pellets within a fuel assembly). The column of the aspiration pipe may be constituted by any number of sections connected to one another by connecting means of any type. The aspiration pipe may be associated with any handling and lifting means for the placing in position thereof in the vessel. This means may be constituted by a handling and lifting means existing in the nuclear reactor or by a specially devised means. The device according to the invention may be used in the case of any nuclear reactor cooled with light water. |
description | The present application claims priority from Japanese Patent application serial no. 2013-224765, filed on Oct. 29, 2013, the content of which is hereby incorporated by reference into this application. Technical Field The present invention relates to a charged particle beam system and more particularly to a charged particle beam system suitable to a cancer treatment using an ion beam such as a proton, a helium ion, or a carbon ion. Background Art A charged particle beam irradiation system for irradiating an ion beam such as a proton, helium, or carbon to a tumor volume of a patient to treat a cancer includes an ion source, an accelerator, a beam transport system, and a rotating gantry and the rotating gantry includes an irradiation nozzle for irradiating the ion beam to the patient. The ion beam generated by the ion source is accelerated up to desired energy using the accelerator such as a synchrotron or a cyclotron and then is extracted from the accelerator to the beam transport system. The extracted ion beam is transported to the irradiation nozzle installed in the rotating gantry by the beam transport system. The rotating gantry is rotated, so that the irradiation nozzle is rotated around a rotation axis of the rotating gantry and is aligned with the irradiation direction of the ion beam with respect to the tumor volume of the patient on a treatment couch. Therefore, the tumor volume (the target volume) is irradiated with the ion beam transported to the irradiation nozzle in the irradiation direction set by the rotating gantry in accordance with a depth of the tumor volume, which is an irradiation target of the ion beam, from a body surface and with a shape of the tumor volume. An ion beam irradiation method using the irradiation nozzle can be broadly divided into a scatterer method and a scanning method. In the scatterer method, the ion beam is enlarged in a lateral direction of the tumor volume, which is an irradiation target, by a scatterer, and also enlarged in a depth direction of the tumor volume by using an SOBP (spread out of Bragg peak) filter. The tumor volume is irradiated with the enlarged ion beam. In the scanning method, in accordance with the shape of the target volume, the ion beam is moved in the lateral direction of the tumor volume by using a scanning magnet and in the depth direction of it by changing the energy of the ion beam is changed by the accelerator and the whole tumor volume is irradiated with the ion beam (refer to Japanese Patent Laid-Open No. 10(1998)-118204 and Japanese Patent Laid-open No. 2004-358237). When a human body is irradiated with the ion beam, the dose distribution as shown in FIG. 3 of Japanese Patent Laid-Open No. 10(1998)-118204 is shown in the depth direction of the human body, and the dose is maximized at the Bragg peak. Furthermore, the dose distribution reduces rapidly at a depth exceeding the Bragg peak. The cancer treatment using the ion beam uses the property that the dose is maximized at a depth exceeding the Bragg peak and the dose reduces rapidly at a depth exceeding the Bragg peak. Japanese Patent Laid-open No. 2010-32451 describes that in one charged particle beam irradiation system, ion beams different in kind, that is, a proton ion beam (a proton beam) and a carbon ion beam (a carbon beam) are switched and the tumor volume of the patient is irradiated with the proton ion beam or the carbon ion beam. Japanese patent No. 4632278 describes that in one charged particle beam irradiation system, ion beams different in kind, that is, any of a helium ion beam, a carbon ion beam, and an oxygen ion beam is injected into the synchrotron which is an accelerator, and the injected ion beam is accelerated by the synchrotron, and then the tumor volume of the patient is irradiated with any of these accelerated beams. H. Eickhoff et al., GSI Darmstadt, “TESTS OF A LIGHT-ION GANTRY SCECTION AS AN EXAMPLE OF PREPARATIONS FOR THE THERAPY FACILITY IN HEIDELBERG”, Proc. of EPAC 2002, Paris France describes similarly to Japanese Patent Laid-open No. 2010-32451 and Japanese patent No. 4632278 that in one charged particle beam irradiation system, a plurality of kinds of ion beams are switched and an irradiation target is irradiated with the switched ion beam. [Patent Literature 1] Japanese Patent Laid-Open No. 10(1998)-118204 [Patent Literature 2] Japanese Patent Laid-open No. 2004-358237 [Patent Literature 3] Japanese patent No. 4632278 [Non Patent Literature 1] H. Eickhoff et al., GSI Darmstadt, “TESTS OF A LIGHT-ION GANTRY SCECTION AS AN EXAMPLE OF PREPARATIONS FOR THE THERAPY FACILITY IN HEIDELBERG”, Proc. of EPAC 2002, Paris France To irradiate a treatment target (a tumor volume) existing in a deep position in a body with an ion beam, an underwater range of the ion beam needs to be made long so that the ion beam arrives at an irradiation target, and as the ion weight of the ion beam is increased, higher energy is necessary. As a result, in each of the accelerator, beam transport system, and rotating gantry which are apparatuses configuring the charged particle beam irradiation system, the curvature radius of the bending magnet used needs to be large. This is related to enlargement of the size of each apparatus and as a result, the charged particle beam irradiation system is made larger. The charged particle beam irradiation system for switching ion beams different in kind and irradiating the treatment target with one of them by the switching is structured so as to be able to irradiate it with a heaviest ion beam among those ion beams and the charged particle beam irradiation system is made larger in accordance with irradiation of the heaviest ion beam. For example, the charged particle beam irradiation system capable of performing switching between the proton ion beam and carbon ion beam and irradiating the irradiation target with one of them by the switching needs to be able to irradiate it with the carbon ion beam, so that the system is inevitably made larger. On the other hand, in the charged particle beam irradiation system using a light ion beam like the proton ion beam, the curvature radius of the bending magnet used in the accelerator, beam transport system, and rotating gantry becomes smaller, so that the accelerator, beam transport system, rotating gantry, and irradiation nozzle can be made smaller. By doing this, the charged particle beam irradiation system using a light ion beam can downsize compared with the charged particle beam irradiation system using a heavy ion beam like the carbon ion beam. However, the investigation of the inventors found that a problem arises that the light ion beam produces large sideward scattering by the irradiation nozzle, so that when the irradiation target is irradiated with the light ion beam, the beam size in the body increases or the dose reduction width (penumbra) at an end of the irradiation range increases, and the dose concentration to the irradiation target and the controllability of the dose distribution reduce. An object of the present invention is to provide a charged particle beam system which can downsize and wherein irradiation concentration of ion beam to an irradiation target and controllability of irradiation dose distribution can be improved. A feature of the present invention for attaining the above object is a charged particle beam system comprising: an ion source generating a plurality of kinds of ions different in weight from each other; an accelerator accelerating one kind of injected ions of the plurality of kinds of ions generated in the ion source; a beam transport system transporting an ion beam extracted from the accelerator, the ion beam including one kind of the injected ions; a rotating gantry setting an irradiation direction of each ion beam to an irradiation target; an irradiation nozzle installed in the rotating gantry, the irradiation nozzle irradiating each ion beam to an irradiation target in the irradiation direction; and a control apparatus, wherein the ion source is an ion source generating a first ion and a second ion that are heavier than first ions; and wherein the control apparatus is a control apparatus executing a first control accelerating a first ion beam including the first ions by controlling frequency of high-frequency voltage applied to a high-frequency acceleration apparatus so that an underwater range of the first ion beam becomes larger than a set underwater range of a second ion beam including the second ions and the first ion beam reaches the irradiation target when water equivalent depth of the irradiation target in the irradiation direction is larger than the set underwater range of the second ion beam, and a second control accelerating the second ion beam by controlling the frequency of the high-frequency voltage applied to the high-frequency acceleration apparatus so that an underwater range of the second ion beam becomes the set underwater range of the second ion beam or smaller than the set underwater range of the second ion beam and the second ion beam reaches the irradiation target when the water equivalent depth of the irradiation target in the irradiation direction of the second ion beam is the set underwater range of the second ion beam or smaller than the set underwater range of the second ion beam. It is preferable that the control apparatus further executes the first control to rotate the rotating gantry so that the irradiation direction of a first ion beam including the first ions from the irradiation nozzle fits to a first irradiation direction, and the second control to rotate the rotating gantry so that the irradiation direction of the second ion beam from the irradiation nozzle fits to a second irradiation direction. (1) A charged particle beam system which is other feature of the present invention for attaining the above object comprises: an ion source; an accelerator accelerating ions generated in the ion source; a beam transport system transporting an ion beam extracted from the accelerator; a rotating gantry setting an irradiation direction of the ion beam to an irradiation target; and an irradiation nozzle installed in the rotating gantry, the irradiation nozzle irradiating the ion beam to the irradiation target in the irradiation direction, wherein the ion source is an ion source generating a plurality of kinds of ions different in weight from each other; wherein the accelerator is an accelerator accelerating the plurality of kinds of ions so that an underwater range at highest energy after acceleration is different in an ion species; and wherein ions where a water equivalent depth (a water depth of equivalent attenuation) of the irradiation target in an irradiation direction determined by the rotating gantry is equal to an underwater range at the highest energy after the acceleration or lower are selected; and the selected ions are transported to the irradiation nozzle using the ion source, the accelerator, the beam transport system, and the rotating gantry, thereby irradiating the irradiation target with the selected ions from the irradiation nozzle. (2) A charged particle beam system which is other feature of the present invention for attaining the above object comprises: an ion source; an accelerator accelerating ions generated in the ion source; a beam transport system transporting an ion beam extracted from the accelerator; a rotating gantry setting an irradiation direction of the ion beam to an irradiation target; and an irradiation nozzle installed in the rotating gantry, the irradiation nozzle irradiating the ion beam to the irradiation target in the irradiation direction, wherein the ion source is an ion source generating a plurality of kinds of ions different in weight from each other; wherein the accelerator is an accelerator accelerating the plurality of kinds of ions so that an underwater range after the heaviest ion is accelerated to the highest energy becomes shorter than the underwater range after acceleration to the highest energy of ions of other than the heaviest ion; and wherein when a water equivalent depth of the irradiation target in the irradiation direction determined by the rotating gantry exceeds the longest underwater range of the heaviest ion, an ion except the heaviest ion among the plurality of ions is selected, and when the water equivalent depth of the irradiation target is equal to the longest underwater range of the heaviest ion or lower, the plurality of kinds of ions including the heaviest ion are selected, and then the selected ions are transported to the irradiation nozzle using the ion source, accelerator, beam transport system, and rotating gantry, thereby irradiating the irradiation target with the selected ions from the irradiation nozzle. (3) A charged particle beam system which is other feature of the present invention for attaining the above object comprises: an ion source; an accelerator accelerating ions generated in the ion source; a beam transport system transporting an ion beam extracted from the accelerator; a rotating gantry setting an irradiation direction of the ion beam to an irradiation target; and an irradiation nozzle installed in the rotating gantry, the irradiation nozzle irradiating the ion beam to the irradiation target in the irradiation direction, wherein the ion source is an ion source generating a plurality of kinds of ions different in weight from each other; wherein the accelerator is an accelerator accelerating the plurality of kinds of ions so that wherein an underwater range after acceleration of a heaviest ion to highest energy becomes shorter than an underwater range after acceleration to highest energy of ions lighter than said heaviest ion; wherein when a water equivalent depth of the irradiation target in an irradiation direction determined by the rotating gantry exceeds a longest underwater range of the heaviest ion, ions excluding the heaviest ion among the plurality of kinds of ions are selected, and when the water equivalent depth of the irradiation target is equal to the longest underwater range of the heaviest ion or lower, the heaviest ion are selected, and then the selected ions are transported to the irradiation nozzle using the ion source, the accelerator, the beam transport system, and the rotating gantry, thereby irradiating the irradiation target with the selected ions from the irradiation nozzle. (4) A charged particle beam system which is other feature of the present invention for attaining the above object comprises: an ion source; an accelerator accelerating ions generated in the ion source; a beam transport system transporting an ion beam extracted from the accelerator; a rotating gantry setting an irradiation direction of the ion beam to an irradiation target; and an irradiation nozzle installed in the rotating gantry, the irradiation nozzle irradiating the ion beam to the irradiation target in the irradiation direction, wherein the ion source is an ion source generating a plurality of kinds of ions different in weight from each other; wherein the accelerator is an accelerator in which an underwater range after accelerating each of the plurality of kinds of ions to the highest energy reduces in correspondence with an increase in the ion weight; and wherein when a water equivalent depth of the irradiation target in the irradiation direction determined by the rotating gantry exceeds an underwater range at the highest energy of the heaviest ion, ions except the heaviest ion among the plurality of ions are selected, and when the water equivalent depth of the irradiation target is equal to the underwater range at the highest energy of the heaviest ion or lower, the ions included in the plurality of kinds including the heaviest ion are selected, and then the selected ions are transported to the irradiation nozzle using the ion source, accelerator, beam transport system, and rotating gantry, thereby irradiating the irradiation target with the selected ions from the irradiation nozzle. (5) Each charged particle beam system described in the above items (1), (2), (3), and (4) comprises a control apparatus wherein the control apparatus compares the water equivalent depth of each of a plurality of layers divided in a depth direction in the irradiation target with the longest underwater range of each ion species, selects the ion species in which the underwater range corresponding to depth of the irradiation target becomes equal to the longest underwater range or lower, controls the energy of the selected ion species, thereby irradiating the irradiation target with the selected ions from the irradiation nozzle in the irradiation direction. (6) Each charged particle beam system described in the above items (1), (2), (3), and (4) comprises a scanning magnet scanning various kinds of ions in the irradiation nozzle; and a control apparatus, wherein the control apparatus controls an irradiation position and irradiation range of the ions in a lateral direction by controlling the scanning magnet based on a position and a range in the lateral direction of each of a plurality of volume elements divided in the irradiation target, compares the water equivalent depth of each volume element in the irradiation direction determined by the rotating gantry with the longest underwater range of different ion species, selects an ion species in which the water equivalent depth of each volume element becomes equal to the longest underwater range or lower, accelerates the ion species to energy for obtaining an underwater range for irradiating each volume element, thereby irradiating each volume element with a dose determined for each volume element. According to the present invention, the charged particle beam system can downsize, and the irradiation concentration of ion beam to the irradiation target is improved, and the controllability for the irradiation dose distribution in the irradiation target can be improved. The inventors investigated such irradiation of ion beam to an irradiation target that a charged particle beam system can be downsized and irradiation concentration of the ion beam to the irradiation target and controllability for an irradiation dose distribution can be improved. The investigation results will be explained below. When a human body is irradiated with the ion beam, a dose distribution in a depth direction of the human body as shown in FIG. 5 is shown and as mentioned above, the dose is maximized at the Bragg peak. In the body, the depth that the ion beam can arrive at beyond the depth showing the Bragg peak is called a range (defined as a depth when the dose becomes 50% of dose of the Bragg peak) of the ion beam. An example of a relation between an underwater range of each ion beam and kinetic energy per a nucleon on a body surface of a patient is shown in FIG. 6. For example, in a proton (H+) and a helium ion (He2+), the kinetic energy per a nucleon for obtaining the same underwater range is the same. However, in an ion heavier than the helium ion (for example, a carbon ion (C6+)), as the mass increases, the kinetic energy necessary to increase the underwater range increases. On the other hand, in the process of irradiation of the ion beam to the irradiation target in the body from the irradiation nozzle, a beam size of the ion beam increases due to the sideward scattering by the respective materials in the irradiation nozzle and the body. The sideward scattering of the ion beam in the irradiation nozzle becomes larger as the ion beam energy becomes smaller. The sideward scattering of the ion beam by the material in the body increases in correspondence with an increase in the underwater range. As a result, the size increase in the ion beam is conspicuous in a shallow position in the body as shown in FIG. 7. Further, the size increase in the ion beam becomes smaller as the ions included in the ion beam become heavier as shown in FIG. 7. The embodiments of the present invention reflected by the above investigation results will be explained below. A charged particle beam irradiating method according to example 1 shown in FIG. 1 which is a preferred embodiment of the present invention will be explained by referring to FIGS. 1, 2, and 3. The charged particle beam irradiating method of the present embodiment uses the proton ion beam and helium ion beam as an ion beam with which a tumor volume which is an irradiation target is irradiated. A charged particle beam system 5 used in the charged particle beam irradiating method of the present embodiment includes a charged particle beam generator 6, a beam transport system 21, a rotating gantry 27, an irradiation nozzle 30, and a control apparatus 33. The charged particle beam generator 6 uses a synchrotron accelerator 13 as an accelerator and as shown in FIG. 1, in addition to the synchrotron accelerator 13, includes an ion source 1 of a hydrogen molecule (H+), an ion source 2 of helium (He2+), a linear accelerator 20, and a switching magnet 3 switching the injection of hydrogen molecule ions and helium ions to the linear accelerator 20. A beam duct (a beam path) connected to the ion source 1 with a shutter 4A installed and a beam duct connected to the ion source 2 with a shutter 4B installed are joined to each other and then are connected to the linear accelerator 20. The switching magnet 3 is disposed at the junction of the beam duct connected to the ion source 1 and the beam duct connected to the ion source 2. A charge convertor 12 is disposed between the linear accelerator 20 and the synchrotron accelerator 13, concretely, between the linear accelerator 20 and an injector 11 which will be described later. The synchrotron accelerator 13 is provided with a high-frequency acceleration apparatus (an acceleration cavity) 17 applying a high-frequency voltage to the ion beam, a plurality of bending magnets 18, a plurality of quadrupole magnets 19, an extraction high-frequency electrode 15, and an extraction deflector 16 on a circular beam duct and these apparatuses are arranged along the circular beam duct as shown in FIG. 1. The synchrotron accelerator 13 includes the injector 11 which is a magnet injecting the ion beam extracted from the linear accelerator 20 into the circular beam duct. The beam transport system 21 includes a beam path 22 reaching the irradiation nozzle 30 and is structured by arranging a plurality of quadrupole magnets 23, a bending magnet 24, a plurality of quadrupole magnets 25, and a bending magnet 26 in this order on the beam path 22 and toward the irradiation nozzle 30 from the synchrotron accelerator 13. A part of the beam path 22 of the beam transport system 21 is installed on the rotating gantry 27 and the bending magnet 24, the plurality of quadrupole magnets 25, and the bending magnet 26 are also installed on the rotating gantry 27. The beam path 22 is connected to the circular beam duct of the synchrotron accelerator 13 in the neighborhood of the extraction deflector 16. The irradiation nozzle 30 includes two scanning magnets 32a and 32b and irradiation amount monitors 52a and 52b for measuring the irradiation amount as shown in FIG. 2. The irradiation amount monitors 52a and 52b are arranged on the downstream side of the scanning magnets 32a and 32b. The irradiation nozzle 30 is attached to the rotating gantry 27 and is disposed on the downstream side of the bending magnet 26. A treatment couch 28 on which a patient 29 lies is arranged so as to be opposite to the irradiation nozzle 30. When a tumor volume 40 of the patient 29 lying on the treatment couch 28 is irradiated with an ion beam 10, the rotating gantry 27 is rotated at a predetermined angle around a rotary shaft 35 before the irradiation of the ion beam 10, a beam axis of the irradiation nozzle 30 is adjusted to the irradiation direction of the ion beam 10 wherein the beam axis of the irradiation nozzle 30 is placed at a predetermined angle set in a treatment planning, and the beam axis of the irradiation nozzle 30 is directed to the tumor volume 40 of the patient 29 on the treatment couch 28. The linear accelerator 20 is structured so as to be able to individually accelerate hydrogen molecule ions and helium ions, though it accelerates the hydrogen molecule ions or helium ions injected from one ion source (the ion source 1 or the ion source 2) switched by the switching magnet 3 of the two ion sources 1 and 2 at the time of irradiation of the ion beam 10. The injection of ions (the hydrogen molecule ions or helium ions) to the linear accelerator 20 from one ion source of the ion sources 1 and 2 is controlled by the switching control of the switching magnet 3 by the control apparatus 33. The beam of the hydrogen molecule ions or helium ions accelerated by the linear accelerator 20 is extracted from the linear accelerator 20 and is injected into the circular beam duct of the synchrotron accelerator 13. When the hydrogen molecule ions are accelerated by the linear accelerator 20, a charge convertor 12B is operated by the control of the control apparatus 33, and the hydrogen molecule ions extracted from the linear accelerator 20 are converted to protons by the charge convertor 12B. Therefore, the beam of the hydrogen molecule ions extracted from the linear accelerator 20 becomes a proton ion beam by the charge convertor 12B and this proton ion beam is injected into the circular beam duct of the synchrotron accelerator 13 by the injector 11. The ion beam 10 injected into the circular beam duct is accelerated by increasing the frequency of the high-frequency voltage to be applied to a high-frequency acceleration apparatus 17 and circles in the circular beam duct which is a circular track. The high-frequency voltage is applied from a high-frequency power supply (not shown) connected to the high-frequency acceleration apparatus 17. The frequency of the high-frequency voltage to be applied to the high-frequency acceleration apparatus 17 is increased by controlling the high-frequency power supply by the control apparatus 33. When the ion beam 10 circling in the circular beam duct is accelerated, the frequency of the high-frequency voltage to be applied to the high-frequency acceleration apparatus 17 is increased and, the magnetic field strength of each bending magnet 18 and each quadrupole magnet 19 is also increased by the control of the control apparatus 33, and the energy of the ion beam 10 circling in the circular beam duct is accelerated up to predetermined energy. When the energy of the ion beam 10 which is accelerated and circles becomes the highest energy (the aforementioned predetermined energy) at the time of acceleration end, if an irradiation high-frequency voltage is applied to the extraction high-frequency electrode 15 by the control of the control apparatus 33, the irradiation high-frequency voltage is applied to the ion beam 10 circling in the circular beam duct. When the irradiation high-frequency voltage is applied to the ion beam 10, the ion beam 10 is extracted to the beam path 22 of the beam transport system 21 through the extraction deflector 16. The ion beam 10 is injected to the irradiation nozzle 30 through the beam path 22 and furthermore, the tumor volume 40 of the patient 29 on the treatment couch 28 is irradiated with the ion beam 10 from the irradiation nozzle 30. When it is extracted to the beam path 22 of the beam transport system 21 through the extraction deflector 16, the respective magnetic field strengths of each quadrupole magnet 23, the bending magnet 24, each quadrupole magnet 25, and the bending magnet 26 of the beam transport system 21 are increased so as to become equal to the magnetic field strength of each bending magnet 18 and each quadrupole magnet 19 which are adjusted when it becomes the highest energy at the time of acceleration end of the ion beam 10 circling in the circular beam duct of the synchrotron accelerator 13 by a control signal from the control apparatus 33. In the charged particle beam irradiating method of the present embodiment, the control apparatus 33 controls respectively the scanning magnets 32a and 32b so as to scan the ion beam 10 and irradiates each spot in each divided layer of the tumor volume 40 with the ion beam 10. The irradiation of the ion beam 10 by scanning the tumor volume 40 is executed, for example, by the irradiating method described in Japanese Patent Laid-open No. 2004-358237. The change of the irradiation position of the ion beam 10 in the depth direction of the tumor volume 40 is executed by change of each of the acceleration energy of the ion beam 10 and the Bragg peak position in the depth direction caused by changing the frequency of the high-frequency voltage applied to the high-frequency acceleration apparatus 17. The change of the irradiation position of the ion beam 10 in the depth direction of the tumor volume 40 is generally executed from the distal layer toward the proximal layer. In the present embodiment, as mentioned above, the proton ion beam and helium ion beam are used. The irradiation of the proton ion beam and helium ion beam to the tumor volume (the irradiation target) 40 of the patient 29 (refer to FIG. 3) using the charged particle beam system 5 will be explained below. A maximum water equivalent depth of the irradiation target to be treated in the present embodiment is 30 cm, the longest underwater range of the proton ion beam (a set underwater range of a first ion beam) is set to 30 cm, and the longest underwater range of the helium ion beam (a set underwater range of a second ion beam) is set to 4 cm. When the water equivalent depth of the irradiation target is 4 cm or smaller, the irradiation target is irradiated with the helium ion beam or the proton ion beam. When the water equivalent depth of the irradiation target is between 4 cm and 30 cm, the irradiation target is irradiated with the proton ion beam from the irradiation nozzle 30. By doing this, when the water equivalent depth is 4 cm or smaller, as shown in FIG. 7, the irradiation with the ion beam in which the sideward scattering is suppressed can be executed. When irradiating the helium ion beam to the tumor volume 40, the control apparatus 33 operates the ion source 2, opens the shutter 4B, controls the switching magnet 3, injects the helium ions generated by the ion source 2 to the linear accelerator 20, and accelerates it. At this time, the shutter 4A is closed. The helium ion beam extracted from the linear accelerator 20 is injected into the circular beam duct of the synchrotron accelerator 13 through the injector 11. When injecting the helium ion beam from the linear accelerator 20 into the circular beam duct of the synchrotron accelerator 13, the charge convertor 12 is not operated. To obtain an underwater range of 4 cm, the helium ion beam needs to be accelerated up to 69 MeV (magnetic rigidity of 2.4) per a nucleon which is the maximum energy after the acceleration required to obtain the underwater range (refer to FIGS. 6 and 8). The magnetic rigidity is a value obtained by multiplying the radius of the circular track of the ion beam by the bending magnetic field strength. FIGS. 6 and 8 show the underwater range of the ion beam and the energy and magnetic rigidity of the ion beam required to obtain the underwater range. To obtain a helium ion beam with an underwater range of 4 cm, the magnetic field strength of each bending magnet 18 and each quadrupole magnet 19 of the synchrotron accelerator 13 is increased based on a control signal from the control apparatus 33 so that a helium ion beam of 69 MeV per a nucleon which is the maximum energy after acceleration can circle, and furthermore, the energy of the helium ion beam is increased up to 69 MeV per a nucleon by increasing the frequency of the high-frequency voltage applied to the high-frequency acceleration apparatus 17 by the control apparatus 33. The helium ion beam is increased up to the energy necessary to reach the position of the tumor volume 40 which is irradiated with it. The respective magnetic field strengths of each quadrupole magnet 23, the bending magnet 24, each quadrupole magnet 25, and the bending magnet 26 of the beam transport system 21 are similarly controlled by the control apparatus 33 as mentioned above. The helium ion beam having energy of 69 MeV per a nucleon is extracted from the synchrotron accelerator 13 to the beam path 22 of the beam transport system 21, and the tumor volume 40 is irradiated with the helium ion beam from the irradiation nozzle 30. By the irradiation of the helium ion beam, the Bragg peak is formed in a position at a water equivalent depth of 4 cm in the depth direction from the body surface of the patient 28. When irradiating the proton ion beam to the tumor volume 40, the control apparatus 33 operates the ion source 1, opens the shutter 4A, controls the switching magnet 3, injects the hydrogen molecule ions generated by the ion source 1 to the linear accelerator 20. The injected hydrogen molecule ions are accelerated by the linear accelerator 20. At this time, the shutter 4B is closed. The hydrogen molecule ion beam extracted from the linear accelerator 20 becomes a proton ion beam by the charge convertor 12 as mentioned above and is injected into the circular beam duct of the synchrotron accelerator 13 through the injector 11. When injecting the hydrogen molecule ion beam from the linear accelerator 20 into the circular duct of the synchrotron accelerator 13, the charge convertor 12 is operated as mentioned above. In order to obtain an underwater range of 30 cm, the proton ion beam needs to be accelerated up to about 220 MeV (magnetic rigidity of 2.3) which is the maximum energy after the acceleration required to obtain the underwater range (refer to FIGS. 6 and 8). To obtain a proton ion beam of an underwater range of 30 cm, the magnetic field strength of each bending magnet 18 and each quadrupole magnet 19 of the synchrotron accelerator 13 is increased based on the control signal from the control apparatus 33 so that the proton ion beam of 220 MeV which is the maximum energy after acceleration can circle, and the energy of the proton ion beam is increased up to about 220 MeV by increasing the frequency of the high-frequency voltage applied to the high-frequency acceleration apparatus 17 by the control apparatus 33. That is, the energy of the proton ion beam is increased up to the energy necessary to reach the position of the tumor volume 40 which is irradiated with the proton ion beam. The respective magnetic field strengths of each quadrupole magnet 23, the bending magnet 24, each quadrupole magnet 25, and the bending magnet 26 of the beam transport system 21 are similarly controlled by the control apparatus 33 as mentioned above. The proton ion beam having energy of about 220 MeV is extracted from the synchrotron accelerator 13 to the beam path 22 of the beam transport system 21, and the tumor volume 40 is irradiated with this proton ion beam from the irradiation nozzle 30. A Bragg peak is formed in a position at a water equivalent depth of 30 cm in the depth direction from the body surface of the patient 28 by the irradiation of the proton ion beam. The irradiation amount monitors 52a and 52b can successively confirm the irradiation amount to the tumor volume 40 by the helium ion beam or the proton ion beam which are scanned by the scanning magnets 32a and 32b and the tumor volume 40 is irradiated with the helium ion beam or the proton ion beam. The irradiation to the tumor volume 40 in a lateral direction (a direction perpendicular to a beam axis of the irradiation nozzle 30) by the helium ion beam and the irradiation in the depth direction can be executed by the scanning of the helium ion beam by the scanning magnets 32a and 32b and the change of the acceleration energy of the helium ion beam. Further, the irradiation to the tumor volume 40 in the lateral direction by the proton ion beam and the irradiation in the depth direction can be executed by the scanning of the proton ion beam by the scanning magnets 32a and 32b and the change of the acceleration energy of the proton ion beam. The magnetic rigidity for accelerating the proton ion beam up to about 220 MeV which is the maximum energy and the magnetic rigidity for accelerating the helium ion beam up to 69 MeV per a nucleon which is the maximum energy are almost equal to each other and are about ½ of the magnetic rigidity for obtaining an underwater range of 30 cm of the helium ion beam. In the present embodiment, the radius of curvature of each bending magnet used in the synchrotron accelerator 13 and the beam transport system 21 can be suppressed compared with the case that the irradiation target is always irradiated with the helium ion beam (the maximum magnetic rigidity of 4.5) until the water equivalent depth of the irradiation target becomes 30 cm and as a result, the size of each bending magnet can downsize. Therefore, the size of the charged particle beam system 5 can downsize to about ½ or the magnetic field strength of those bending magnets can be suppressed to ½. FIG. 3 shows an example of a tumor volume 40 of the patient 29 which is irradiated with the helium ion beam and proton ion beam. The irradiation of the proton ion beam and helium ion beam to the tumor volume (the irradiation target) 40 of the patient 29 using the charged particle beam system 5 will be explained below. The tumor volume 40 which is an irradiation target is divided imaginarily into a plurality of volume elements 41 by the treatment planning using a treatment planning apparatus 9, as shown in FIG. 4. The irradiation direction of the ion beam, kind of the irradiated ion beam, energy of the irradiated ion beam, and irradiation amount of ion beam are determined for each volume element 41. These information is input from the treatment planning apparatus 9 to the control apparatus 33 as treatment planning information before start of the ion beam irradiation and is stored in a memory (not shown) of the control apparatus 33. In the present embodiment, as shown in FIG. 3, the rotation angle of the rotating gantry 27 is controlled by the control apparatus 33 and the tumor volume 40 is irradiated with the ion beam in the direction A and direction B. In the ion beam irradiation in the direction A, the water equivalent depth of the entire tumor volume 40 is 3 cm, which is lower than the underwater range of 4 cm from the body surface of the patient 29, and all the volume elements 41 are is irradiated with the helium ion beam. The helium ion beam is accelerated by the synchrotron accelerator 13 up to the energy after end of the acceleration capable of obtaining the underwater range suitable for each volume element 41 and is extracted to the beam path 22 of the beam transport system 21 after the acceleration. The rotating gantry 27 is rotated and the beam axis of the irradiation nozzle 30 is beforehand fitted to the direction A. The irradiation position of the helium ion beam in the lateral direction is set by the scanning of the helium ion beam by the scanning magnets 32a and 32b of the irradiation nozzle 30 and the volume elements 41 is irradiated with the helium ion beam until a dose of each volume element 41 becomes a planned dose amount. After the irradiation of the helium ion beam of the planned amount is confirmed by the irradiation amount monitors 52a and 52b, the irradiation of the helium ion beam to the volume elements 41 is stopped. Next, when the water equivalent depth of the volume element 41 which is irradiated with the helium ion beam is the same, the magnetic field strength of the scanning magnets 32a and 32b is changed and the next volume element 41 is irradiated with the helium ion beam. When the water equivalent depth of the volume element 41 is different, the acceleration energy of the helium ion beam is changed using the high-frequency acceleration apparatus 17 so that the underwater range of the irradiated helium ion becomes a value suitable for the water equivalent depth, and the irradiation position in the lateral direction is set by controlling the magnetic field of the scanning magnets 32a and 32b and the irradiation of the helium ion beam to the applicable volume element 41 is executed. Such irradiation of the helium ion beam is executed repeatedly and the irradiation of the helium ion beam in a predetermined amount is executed to the volume elements 41 of the entire tumor volume 40. After end of the irradiation of the helium ion beam in the direction A, the rotation angle of the rotating gantry 30 is changed and the beam axis of the irradiation nozzle 30 is fitted to the direction B. In the irradiation of the ion beam in the direction B, as shown in FIG. 3, the tumor volume 40 which is an irradiation target is located in a deeper position than an underwater range of 4 cm. Therefore, the irradiation of the proton ion beam is executed to all the volume elements 41 in the direction B. The irradiation procedure of the proton ion beam to each volume element 41 is the same as the case of the irradiation using the helium ion beam in the direction A. In the present embodiment, the irradiation of the helium ion beam in the direction A and the irradiation of the proton ion beam in the direction B, that is, the irradiation of an ion beam to the tumor volume 40 in different directions are executed, so that the dosage irradiated to healthy cells on the foreside of the tumor volume 40 is reduced. The tumor volume 40 is irradiated with the helium ion beam in the direction A until a dose of the tumor volume 40 becomes the above dose in a predetermined amount in the direction A, and the tumor volume 40 is irradiated with the proton ion beam in the direction B until a dose of the tumor volume 40 becomes other dose in a predetermined amount in the direction B. In the present embodiment, the tumor volume 40 is irradiated with the helium ion beam in the proximal water equivalent depth direction from the body surface of the patient 29 (for example, in the direction A giving a water equivalent depth of 3 cm) and the tumor volume 40 is irradiated with the helium ion beam in the distal water equivalent depth direction from the body surface of the patient 29 (for example, in the direction B giving a water equivalent depth of 10 cm or more), so that the bending magnets 18, 24, and 26 can downsize and the size of the charged particle beam system 5 can be made small. Further, the tumor volume 40 is irradiated with the helium ion beam in the direction A and the tumor volume 40 is irradiated with the proton ion beam in the direction B, so that an increase in the respective beam sizes of the helium ion beam and the proton ion beam can be suppressed and the irradiation concentration of each ion beam to the tumor volume 40 can be enhanced. Furthermore, the irradiation of the helium ion beam to the tumor volume 40 in the direction A and the irradiation of the proton ion beam to the tumor volume 40 in the direction B can enhance the controllability of the irradiation dose distribution in the tumor volume 40. In the present embodiment, the change of ion beams different in the ion species can be executed in a short period of time, so that two ion sources are used, though the ion generation gas is changed by one ion source, and a plurality of kinds of ion beams separately including ions different in weight are generated, and the irradiation target can be irradiated with the respective ion beams. A charged particle beam irradiating method according to embodiment 2 which is another preferred embodiment of the present invention will be explained below. In the charged particle beam irradiating method of the present embodiment, the same charged particle beam system 5 used in embodiment 1 is used. FIG. 9 shows an example of the tumor volume 40 of the patient 29 which is irradiated with the helium ion beam and proton ion beam. The irradiation of the proton ion beam and helium ion beam to the tumor volume (the irradiation target) 40A of the patient 29 using the charged particle beam system 5 will be explained below. A tumor volume 40A which is an irradiation target is positioned between the water equivalent depths of 2 cm and 7 cm from the body surface of the patient 28 in the direction A and in the direction B, the water equivalent depth of the tumor volume 40A from the body surface of the patient 28 exists in a deeper position than an underwater range of 4 cm of the helium ion beam (a set underwater range of a second ion beam). Similarly to embodiment 1, when the tumor volume 40 is divided by the plurality of volume elements 41, the beam axis of the irradiation nozzle 30 is fitted to the direction A, and the irradiation of the ion beam is executed in the direction A, each volume element 41 of the tumor volume 40 existing in a position where the water equivalent depth from the body surface is 4 cm or shallower is irradiated with the helium ion beam, and furthermore, each volume element 41 of the tumor volume 40 existing in a position where the water equivalent depth from the body surface is deeper than 4 cm is irradiated with the proton ion beam. Further, when the beam axis of the irradiation nozzle 30 is fitted to the direction B and the irradiation of the ion beam is executed in the direction B, all the volume elements 41 exist in a position where the water equivalent depth from the body surface is 10 cm or more, so that all the volume elements 41 is irradiated with the proton ion beam. Also in the present embodiment, the tumor volume 40 is irradiated with the ion beam from each of the directions A and B similarly to embodiment 1, so that the dosage irradiated to healthy cells on the foreside of the tumor volume 40 is reduced. The tumor volume 40 is irradiated with a dose in a predetermined amount by each irradiation of the helium ion beam and proton ion beam in the direction A and the irradiation of the proton ion beam in the direction B. When the volume elements exist in a position deeper than an underwater range of 4 cm, the volume elements are irradiated with the proton ion beam, and when the volume elements exist in a position of an underwater range of 4 cm or shallower, the volume elements are irradiated with the helium ion beam. The present embodiment can improve the irradiation concentration to the tumor volume 40 and the controllability of the irradiation dose distribution, similarly to embodiment 1. Particularly, in the present embodiment, all the volume elements existing in the region A where the depth from the body surface is a water equivalent depth of 4 cm or lower are irradiated with the helium ion beam, though all the volume elements existing in the region B exceeding a water equivalent depth of 4 cm are irradiated with the proton ion beam. In this way, in the irradiation of the ion beam from the direction A, the controllability of the dose distribution can be further improved in a combination of the volume elements which are irradiated with the helium ion beam and the volume elements which are irradiated with the proton ion beam. Further, the region A is irradiated with the helium ion beam having a small beam size and the region B is irradiated with the proton ion beam having a relatively large beam size, so that the irradiation can be finished in a short period of time by improving the dose concentration to the irradiation target. The charged particle beam irradiating method according to embodiment 3 which is other preferred embodiment of the present invention will be explained below. In the charged particle beam irradiating method of the present embodiment, a charged particle beam system having an irradiation nozzle 30A shown in FIG. 10 as a substitute for the irradiation nozzle 30 in the charged particle beam system 5 used in embodiment 1, is used. A structure of the charged particle beam system except the irradiation nozzle 30A used in the present embodiment is the same as that of the charged particle beam system 5. The scanning magnets 32a and 32b, the irradiation amount monitors 52a and 52b for measuring the irradiation amount, and a collimator 53 for determining the radiation field range in the lateral direction are installed in the irradiation nozzle 30A. Further, a range compensator 54 compensating the underwater range based on the shape of the irradiation target in the depth direction is installed in the lower part of the irradiation nozzle 30. The other structure of the charged particle beam system of the present embodiment is the same as the structure shown in FIG. 1. Also in the present embodiment, the proton ions and helium ions are used, the proton ions are accelerated up to the energy of the underwater range of 30 cm and the helium ions are accelerated up to the energy of the underwater range of 4 cm. The ion beam extracted from the synchrotron accelerator 13 is transported to the irradiation nozzle 30 installed in the rotating gantry 31 by the beam transport system 14. In the present embodiment, the tumor volume 40 is divided into a plurality of layers 42 in the depth direction as shown in FIG. 11. When the water equivalent depth of each layer adjusted to the range change by the range compensator is 4 cm or lower, each layer is irradiated with the helium ion beam and when it of each layer exceeds 4 cm, each layer is irradiated with the proton ion beam. In the present embodiment, the linear accelerator 12 and the synchrotron accelerator 13 are used as an accelerator, though as shown in FIG. 14, a cyclotron accelerator 55 for extracting the proton (H+) ion beam and helium (He2+) ion beam at fixed energy is used as an accelerator, and a metallic degrader 56 for permitting the ion beam to pass through is installed in the beam transport system, and the attenuation amount of the ion beam energy is controlled by changing the thickness of the degrader is changed. Thus, a similar system to each of embodiments 1 to 3 can be realized by using the cyclotron accelerator 55. When switching the proton ions and helium ions, the polarity of the switching magnet 3 shown in FIG. 14 is changed, and the magnetic field of a bending magnet 57 of the cyclotron accelerator 55, the resonance frequency control of a high-frequency accelerator 58, and the applied high-frequency and the voltage applied to an irradiation deflector 59 are changed and controlled. As a consequence, the proton ions or helium ions is accelerated and each layer in the tumor volume 40 is irradiated with the proton ions or helium ions. A charged particle beam irradiating method according to embodiment 4 which is other preferred embodiment of the present invention will be explained below. In the charged particle beam irradiating method of the present embodiment, a charged particle beam system 5A shown in FIG. 12 is used. The charged particle beam system 5A is provided with a charged particle generator 6A, the beam transport system 21, the rotating gantry 27, the irradiation nozzle 30, and the control apparatus 33. The charged particle generator 6A includes a helium ion source 2 (He2+), a carbon ion source 7 (C4+), the linear accelerator 20 and a linear accelerator 8, a charge converter 12B for charge-converting carbon ions (C4+) to carbon ions C6+, and the switching magnet 3 in addition to the synchrotron accelerator 13. The helium ion source 2 is connected to the linear accelerator 20 and the carbon ion source 7 is connected to the linear accelerator 8. The switching magnet 3 switches the injection of the helium ion beam extracted from the linear accelerator 20 and the carbon ion (C6+) beam extracted from the linear accelerator 8 to the circular beam duct of the synchrotron accelerator 13. The respective structures of the synchrotron accelerator 13, the beam transport system 21, the rotating gantry 27, and the irradiation nozzle 30 are the same as that of the charged particle beam system 5. Either the helium ion beam extracted from the linear accelerator 20 or the carbon ion (C6+) beam extracted from the linear accelerator 8 is injected to the synchrotron accelerator 13 by switching by the switching magnet 3. The ion beam (the helium ion beam or the carbon ion (C6+) beam) injected to the synchrotron accelerator 13 is accelerated similarly to embodiment 1 and is extracted to the beam path 22 of the beam transport system 21. The extracted ion beam is scanned by the scanning magnets 32a and 32b in the irradiation nozzle 30 and the predetermined positions of a tumor volume 40B (refer to FIG. 13) is irradiated with the scanned ion beam. In the synchrotron accelerator 13, the helium ion beam and the carbon ion beam are accelerated by the high-frequency acceleration apparatus 17 up to the maximum energy of 220 MeV per a nucleon (magnetic rigidity 4.5 Tm). By doing this, the helium ion beam becomes a longest underwater range of 30 cm and the carbon ion beam becomes a longest underwater range of 10 cm. The dose monitors 52a and 52b in the irradiation nozzle 30 successively confirm the respective irradiation amounts by the helium ion beam and by the carbon ion beam. The helium ion beam (or the carbon ion beam) is scanned in the lateral direction by the scanning magnets 32a and 32b according to the shape of the irradiation target and the tumor volume 40B is irradiated with the helium ion beam (or the carbon ion beam). In the depth direction of the tumor volume 40B, the acceleration energy of the helium ion beam (or the carbon ion beam) is changed and the Bragg peak depth and the underwater range of the ion beam are changed. In the present embodiment, a tumor volume 40B exists in the position shown in FIG. 13 in the body of the patient 29 and the ion beam is irradiated with the tumor volume 40B in the 3 directions A, B, and C. Prior to treatment, the tumor volume 40B is imaginarily divided into the minute volume elements 41 by the treatment planning similarly to FIG. 4. In the irradiation from the irradiation direction A, the water equivalent depth of the entire tumor volume 40B is 10 cm or larger and all the volume elements 41 is irradiated with the helium ion beam. The energy of the helium ion beam necessary for the irradiation to each volume element 41 and the irradiation amount thereof are beforehand determined by the treatment planning. The rotating gantry 31 is set at the angle beforehand determined by the treatment planning, and the helium ion beam is accelerated up to the energy for obtaining the underwater range suitable for the water equivalent depth of each volume element 41. The irradiation position in the lateral direction is adjusted by the scanning magnets 32a and 32b of the irradiation nozzle 30 and each volume element 41 is irradiated with the helium ion beam for the planned amount. After the volume element 41 is irradiated with the helium ion beam for the planned amount, the irradiation of the helium ion beam is stopped. When the water equivalent depth of the volume element 41 where is irradiated next with the helium ion beam is the same, the strength of the scanning magnets 32a and 32b is changed and the next volume element 41 is irradiated with the helium ion beam, and when the water equivalent depth of in the position of next volume element 41 is different, the acceleration energy of the helium ion beam is changed, and the irradiation position of the helium ion beam in the lateral direction is set by the scanning magnets 32a and 32b, and the irradiation of the ion beam is executed repeatedly. As a consequence, the irradiation of the ion beam to all the target volume is executed. In the irradiation from the direction B, the depth of each volume element is within a range from a water equivalent depth of 8 cm to 13 cm and each volume element within a range from a water equivalent depth of 10 cm to 13 cm is irradiated with the helium ion beam. The volume elements 41 at a water equivalent depth of 8 cm to 10 cm are irradiated with the carbon ion beam. In the case of the irradiation from the direction C, the depth of each volume element 41 is 10 cm or lower and each volume element 41 within the range is irradiated with the carbon ion beam. In the above embodiment, when the water equivalent depth is 10 cm or lower, any volume element 41 is irradiated with the carbon ion beam. However, each volume element 41 can be irradiated with the helium ion beam or carbon ion beam even when the water equivalent depth is 10 cm or lower. In this way, a high dose concentration and high dose distribution controllability are obtained and the irradiation time can be shortened. In the present embodiment, the linear accelerator 12 and the synchrotron accelerator 13 are used as an accelerator. However, by using the cyclotron accelerator 55 as an accelerator and a helium ion source (He2+) and a carbon ion source (C6+) as an ion source to accelerate the ions up to energy of 220 MeV/a nucleon as shown in FIG. 14, installing a metallic degrader 56 for permitting the respective ion beams to pass through in the beam transport system 21, and changing the thickness of the degrader 56 to control the attenuation amount of the ion beam energy, a similar system to embodiment 4 can be realized. When performing switching between the helium ion beam and the carbon ion beam, the polarity of the switching magnet 3 shown in FIG. 14 is changed, and the resonance frequency of the high-frequency accelerator 58 of the cyclotron accelerator 55 and the applied high-frequency are controlled. As a consequence, the ion beam is accelerated to a predetermined energy. In the present embodiment, the irradiation target is irradiated with the helium ion beam and the carbon ion beam. However, by adding a proton ion source and a proton linear accelerator to the present embodiment, accelerating the ion beams up to 220 MeV by the synchrotron accelerator, and adding the irradiation of the proton ion beam to the irradiation of the helium ion beam and carbon ion beam, the irradiation time can be shortened while enhancing the dose concentration to the irradiation target. 1: hydrogen molecule ion source, 2: helium ion source, 3: switching magnet, 5, 5A: charged particle beam system, 6, 6A: charged particle beam generator, 7: 8, 20: linear accelerator, 12, 12B: charge convertor, 13: synchrotron accelerator, 15: extraction high-frequency electrode, 16: extraction deflector, 17: high-frequency acceleration apparatus, 18, 24, 26: bending magnet, 19, 23, 25: quadrupole magnet, 21: beam transport system, 27: rotating gantry, 30, 30A: irradiation nozzle, 32a, 32b: scanning magnet, 33: control apparatus, 52a, 52b: irradiation amount monitor, 54: range compensator, 55: cyclotron accelerator, 56: degrader. |
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abstract | Substrates suitable for mirrors used at wavelengths in the EUV wavelength range have substrates (1) including a base body (2) made of a precipitation-hardened alloy, of an intermetallic phase of an alloy system, of a particulate composite or of an alloy having a composition which, in the phase diagram of the corresponding alloy system, lies in a region which is bounded by phase stability lines. Preferably, the base body (2) is made of a precipitation-hardened copper or aluminum alloy. A highly reflective layer (6) is preferably provided on a polishing layer (3) of the substrate (1) of the EUV mirror (5). |
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047327294 | claims | 1. A fast breeder reactor comprising: a reactor vessel, a reactor core constituted by a plurality of fuel assemblies and a plurality of control rod guide pipes disposed in said reactor vessel, a partitioning member disposed between said reactor vessel and said reactor core and serving to separate the inside space of said reactor vessel into an upper plenum and a lower plenum, a high-pressure plenum, a medium-pressure plenum whose pressure is lower than that of said high-pressure plenum but is higher than said upper plenum; and a means of introducing a coolant into said high-pressure plenum, wherein said high-pressure plenum is disposed below said reactor core, said medium-pressure plenum being disposed between said reactor core and said high-pressure plenum, and wherein there is provided a channel for introducing said coolant from said medium-pressure plenum into said control rod guide pipe, a partition plate separating said high-pressure plenum and said medium-pressure plenum, said partition plate supporting lower ends of said fuel assemblies and said control rod guide pipes and support members thereof, the lower ends of said fuel assemblies and said control rod guide pipes and said support members thereof extending across said medium-pressure plenum in a direction toward said high-pressure plenum without extending across said high-pressure plenum and ending in said partition plate, and means for introducing coolant from said high-pressure plenum to the lower ends of said fuel assemblies. 2. A fast breeder reactor comprising: a reactor vessel, a reactor core constituted by a plurality of fuel assemblies and a plurality of control rod guide pipes disposed in said reactor vessel, a partitioning member disposed between said reactor vessel and said reactor core and serving to separate the inside space of said reactor vessel into an upper plenum and a lower plenum, a high-pressure plenum, a medium-pressure plenum whose pressure is lower than that of said high-pressure plenum but is higher than said upper plenum, and a means of introducing a coolant into said high-pressure plenum, wherein said high-pressure plenum is disposed below said reactor core, said medium-pressure plenum being disposed between said reactor core and said high-pressure plenum, and wherein there is provided a first channel for introducing said coolant from said medium-pressure plenum into said control rod guide pipe and a second channel for introducing said coolant from said high-pressure plenum into the lower end portion of said fuel assemblies, a partition plate separating said high-pressure plenum and said medium-pressure plenum, said partition plate supporting lower ends of said fuel assemblies and said control rod guide pipes and support members thereof, the lower ends of said fuel assemblies and said control rod guide pipes and said support members thereof extending across said medium-pressure plenum in a direction toward said high-pressure plenum without extending across said high-pressure plenum and ending in said patition plate, and means for introducing coolant from said high-pressure plenum to the lower ends of said fuel assemblies. 3. In a fast breeder reactor comprising: a reactor vessel, a reactor core having a center zone and a peripheral zone surrounding said center zone and constituted by a plurality of core fuel assemblies arranged in said center zone, a plurality of blanket fuel assemblies arranged in said peripheral zone and control rod guide pipes in which control rods are guided therealong, said core blanket fuel assemblies each having an entrance nozzle in a lower end portion opened at lower end face thereof, and said control rod guides each having an entrance nozzle formed with at least one opening formed in a peripheral wall of a lower end portions thereof, a partitioning member disposed between said reactor vessel and said reactor core and delimiting the inside space of said reactor vessel into an upper plenum and a lower plenum; a high-pressure plenum laid below said reactor core; medium-pressure plenum whose pressure is lower than that of said high-pressure plenum but is higher than said upper plenum; and a means for introducing coolant into said high-pressure plenum, the improvement wherein said medium-pressure plenum is disposed between said reactor core and said high pressure-plenum, and said high and medium-pressure plenums are separated by a partition plate serving as a lower supporting plate for said core and blanket asssemblies and said control rod guide pipes, said partition plate being formed therein with through-holes receiving said entrance nozzles of said core and blanket fuel assemblies which extend across said medium-pressure plenum, said partition plate also being formed therein with recesses which receive said entrance nozzles of said control rod guide pipes which extend across the medium-pressure plenum, a partition wall having at least one orifice formed therein being disposed in said high-pressure plenum to define an annular plenum surrounding said high-pressure plenum, said annular plenum being communicated with said medium-pressure plenum through at least one opening formed in said partition plate while communicating with said high-pressure plenum through said orifice formed in said partition wall, whereby said core fuel asemblies are fed with coolant from said high-pressure plenum through said through-holes formed in said partition plate while said blanket fuel assemblies are fed with coolant from said annular plenum through said through-holes formed said partition plate, and said control rod guide pipes are fed with coolant from said medium-pressure plenum through the openings formed in the peripheral wall of said entrance nozzles of said control rod guide pipes. 4. In a fast breeder reactor comprising: a reactor vessel, a reactor core constituted by a plurality of fuel assemblies and control rod guide pipes in which control rods are guided therealong, said fuel assemblies each having an entrance nozzle in a lower end portion opened at a lower end face thereof, said entrance nozzle defining therein a flow passage, and said control rod guide pipes each having an entrance nozzle formed with at least one opening formed in a peripheral wall of lower end portions thereof, a partitioning member disposed between said reactor vessel and said reactor core and delimiting the inside space of said reactor vessel into an upper plenum and lower plenum; a high-pressure plenum disposed below said reactor core; a medium-pressure plenum whose pressure is lower than that of said high-pressure plenum but is higher than a pressure of said upper plenum; and a means for introducing coolant into said high-pressure plenum, the improvement wherein said medium-pressure plenum is disposed between said reactor core and said high-pressure plenum, and said high and medium-pressure plenums are separated by a partition plate serving as a lower supporting plate for said assemblies and said control rod guide pipes and support members thereof, said partition plate being formed therein with through-holes receiving said entrance nozzles of said fuel assemblies which extend across said medium-pressure plenum, said partition plate also being formed therein with recesses which receive said entrance nozzles of said control rod guide pipes which extend across said medium-pressure plenum, the lower ends of said fuel assemblies and said control rod guide pipes and said support members thereof extending across said medium-pressure plenum without extending across said high-pressure plenum and ending in said partition plate, means for introducing coolant from said high-pressure plenum to the lower ends of said fuel assemblies, said fuel assemblies being fed with coolant from said high-pressure plenum through said through-holes formed in said partition plate, and said control rod guide pipes being fed with coolant from said medium-pressure plenum through the at least one opening formed in the peripheral wall of said entrance nozzles of said control rod guide pipers, said flow passage in said entrance nozzle of each of said fuel assemblies having an upper section and a lower section with the upper section having a larger cross-sectional area than the lower section so that a pressure receiving area is obtained in said flow passage, at least one orifice being provided in said flow passage to enable a fuel assembly internal pressure which is effected upon said pressure receiving area, each of said through-holes in said partition plate being formed in a stepped shape to provide an annular shoulder part on which an annular bead is formed, the lower end face of said entrance nozzle abutting against said annular bead so that the pressure of said medium-pressure plenum acts upon a part of said lower end face outside of said annular bead while the pressure of said high-pressure plenum acts upon the remaining part of said end face inside of said annular bead, whereby a sufficient downward force is obtained by selecting a relationship among said fuel assembly internal pressure, the pressure of said medium-pressure plenum, said high-pressure plenum and said pressure receiving area, in order to prevent said entrance nozzle of said fuel assembly from lifting up from said annular bead. 5. A fast breeder reactor according to claim 2, wherein said high-pressure plenum and said medium-pressure plenum are located adjacent to each other with a supporting plate interposed therebetween, said supporting plate being provided with a multiplicity of recesses into which entrance nozzles that constitute the lower end portions of said fuel assemblies are inserted, and said second channel pierces through said supporting plate from the bottom surfaces of said recesses and constitutes an opening leading to said high-pressure plenum. 6. A fast breeder reactor according to claim 5, wherein an annular bead made in contact with the lower end surface of said entrance nozzle is disposed on the bottom surface of said recess concentrically with said second channel. 7. A fast breeder reactor according to claim 6, wherein a vertical section of said annular bead is a curved surface, and said curved surface is in contact with the lower end surface of said entrance nozzle. 8. A fast breeder reactor according to claim 6 or 7, wherein a transverse sectional area of said entrance nozzle radially outside of the point of contact between said entrance nozzle and said annular projection is larger than a transverse sectional area of said entrance nozzle within said point of contact. 9. A fast breeder reactor according to claim 2, wherein said high-pressure plenum and said medium-pressure plenum are communicated via a pressure-reducing means. 10. A fast breeder reactor according to claim 9, wherein said high-pressure plenum and said medium-pressure plenum are located adjacent to each other with a supporting plate interposed therebetween, said supporting plate being provided with a multiplicity of recesses in which entrance nozzles that constitute the lower end portions of said fuel assemblies are inserted, and said second channel pierces through said supporting plate from the bottom surfaces of said recesses and constitutes an opening leading to said high-pressure plenum. 11. A fast breeder reactor according to claim 10, wherein an annular bead made in contact with the lower end surface of said entrance nozzle is disposed on the bottom surface of said recess concentrically with said second channel. 12. A fast breeder reactor according to claim 11, wherein a vertical section of said annular bead is a curved surface, and said curved surface is in contact with the lower end surface of said entrance nozzle. 13. A fast breeder reactor according to claim 11 or 10, wherein a transverse sectional area of said entrance nozzle radially outside of the line of contact between said entrance nozzle and said annular projection is larger than a transverse sectional area of said entrance nozzle within said point of contact. |
046844910 | claims | 1. In a nuclear steam generator vessel having a part-spherical bottom wall cooperating with a horizontal tube sheet and a vertical divider plate to define a plenum having a nozzle, apparatus for retaining a nozzle seal in the nozzle against displacement into the plenum comprising: rigid beam means disposed in the plenum, attachment means connecting said beam means to the nozzle seal, anchor means connecting said beam means to the tube sheet, and coupling means bracing said beam means against the divider plate, whereby said beam means is securely braced between the tube sheet and the divider plate for transferring thereto forces coupled to said beam means from the nozzle seal. 2. The apparatus of claim 1, wherein said beam means is arcuate in shape. 3. The apparatus of claim 1, wherein said beam means extends substantially diametrically across the nozzle seal. 4. The apparatus of claim 3, wherein said anchor means is connected to the tube sheet adjacent to the vessel bottom wall. 5. The apparatus of claim 4, wherein said anchor means includes lateral brace means engageable with the vessel bottom wall. 6. The apparatus of claim 1, wherein said coupling means is disposed against the divider plate at the bottommost portion thereof. 7. The apparatus of claim 1, wherein said coupling means includes adjustment means for varying the overall dimensions of said apparatus. 8. The apparatus of claim 7, wherein said adjustment means includes replaceable spacer means disposed between said coupling means and said beam means. 9. In a nuclear steam generator vessel having a part-spherical bottom wall cooperating with a horizontal tube sheet and a vertical divider plate to define a plenum having a nozzle, apparatus for retaining a nozzle seal in the nozzle against displacement into the plenum comprising: first and second beam means respectively disposed in first and second intersecting planes and each having an inner end and an outer end, said first plane intersecting the nozzle seal and the divider plate, coupling means disposed in engagement with the divider plate and interconnecting said inner ends of said first and second beam means, first and second anchor means respectively anchoring said outer ends of said first and second beam means to the tube sheet, and attachment means connecting said first beam means to the nozzle seal, whereby said beam means is securely braced between the tube sheet and the divider plate for transferring thereto forces coupled to said beam means from the nozzle seal. 10. The apparatus of claim 9, wherein said first and second planes are disposed substantially vertically. 11. The apparatus of claim 10, wherein said first plane extends substantially diametrically across the nozzle seal. 12. The apparatus of claim 9, wherein each of said first and second beam means is arcuate in shape. 13. The apparatus of claim 12, wherein each of said first and second anchor means is connected to the tube sheet adjacent to the vessel bottom wall. 14. The apparatus of claim 13, wherein each of said first and second anchor means includes lateral brace means engageable with the vessel bottom wall. 15. The apparatus of claim 9, wherein said attachment means comprises clamp means releasably engageable with said first beam means and slidably movable with respect thereto. 16. The apparatus of claim 9, wherein said coupling means includes selectively replaceable spacer means coupled to said first beam means for selectively varying the effective length thereof. 17. The apparatus of claim 9, wherein said coupling means includes jacking means for urging said first and second beam means firmly against the tube sheet. 18. In a nuclear steam generator vessel having a part-spherical bottom wall cooperating with a horizontal tube sheet and a vertical divider plate to define a plenum having a nozzle, wherein a nozzle seal is retained in the nozzle by a retaining assembly anchored to the tube sheet at a predetermined location and having an adjustment portion with a selectively variable dimension, positioning apparatus for predetermining the variable dimension of the adjustment portion comprising: mounting means adapted to be mounted on the tube sheet at the predetermined location, frame means having dimensions equal to predetermined dimensions of the associated retaining assembly, means releasably connecting said frame means to said mounting means and to the nozzle seal in a measuring configuration such that the position of a predetermined point on said frame means defines the position of the adjustment portion of retaining assembly, and measuring means coupled to said frame means for measuring the distance from said predetermined point to the divider plate, thereby to determine the variable dimension of the adjustment portion of the retaining assembly. 19. The apparatus of claim 18, wherein said frame means includes first and second coplanar beams, said first beam extending between said mounting means and the nozzle seal and said second beam extending between the nozzle seal and said predetermined point. 20. The apparatus of claim 19, wherein the plane of said first and second beam means is disposed substantially vertically and extends diametrically across the nozzle seal and through the midline of the divider plate, said measuring means extending substantially perpendicular to the divider plate. |
summary | ||
H00002356 | summary | BACKGROUND OF THE INVENTION This invention pertains to the measurement of radial profiles of energy components of intense particle beams, and relates especially to neutral beams used in the heating of a fusion plasma. A number of approaches are currently being studied in the development of nuclear fusion as a long-term energy source. Several of the more promising approaches involve the confinement, by means of strong magnetic fields, of a highly energetic plasma possessing extremely high temperature and densities, so as to cause the fusing of atoms, such as deuterium and tritium, and the resulting production of energy. It has been found that one of the most efficient configurations for optimum plasma containment is in the form of a toroid or "doughnut". This has given rise to the tokamak fusion reactor design which is currently under intensive study by research groups in a number of countries. By means of a circular arrangement of powerful magnets, a toroidal magnetic field is formed for the confinement of an energetic plasma comprised primarily of protons and deuterons. Once generated, the confined energetic plasma must be sustained by means of an external source. Further, the plasma must be continuously re-fueled during reactor operation. One method of heating and fueling the plasma, and thus energizing the plasma particles confined, includes the injection of a beam of energetic neutrals into a plasma. Neutral beam injection methods have become technologically feasible with the recent development of efficient, high-power neutral beam modules such as those described in the following: V. D. Shafranov and E. I. Yurchenko, Nuclear Fusion 8, 329 (1968); L. D. Stewart, R. C. Davis, J. T. Hogan, T. C. Jernigan, O. B. Morgan, and W. L. Stirling, Garching/Munich Conference, 1973, paper E 12; W. L. Stirling, R. C. Davis, T. C. Jernigan, O. B. Morgan, J. J. Orzechowski, G. Schilling and L. D. Stewart, paper d-5 at Second International Conference on Ion Sources, Vienna, 1972; K. W. Ehlers and W. B. Kunkel, paper d-3 at Second International Conference on Ion Sources, Vienna, 1972; and W. L. Gardner et al, Rev. Sci. Inst. 53, 424 (1982). Since the beam power absorbed by the plasma exceeds the ohmic heating power, neutral beams cause significant heating. Neutral beams also provide a particle source to offset the fusion losses, and could be used to maintain an electric current in the plasma, as described in the following: T. Ohkawa, Nuclear Fusion 10, 185 (1970); R. J. Bickerton, Comments on Plasma Phys. and Controlled Fusion 1, 95 (1972); and J. D. Callen, J. F. Clarke and J. A. Rome, Garching/Munich Conference, 1973, paper E-14. The neutral beam injection method of plasma heating is currently being tested in a number of research facilities, including the Poloidal Divertor Experiment (PDX) located at the Princeton Plasma Physics Laboratory in New Jersey, the ISX-B project at the Oak Ridge National Laboratory, the Doublet III project at GA Technologies, and the ASDEX studies at the Institute for Plasma Physics in Garching, West Germany. A typical neutral beam injector consists of only a few basic parts. First, there is a plasma source, such as the duo-PiGatron. Ions extracted from the plasma meniscus are accessed through a multiple-aperture (approximately 2000, 3-4 mm diameter hole) plate. The ions are then accelerated in a multiple aperture accel-decel electrode system to typical energies of 40-50 keV, and enter a charge-exchange neutralization cell which contains a neutral gas such as H.sub.2 or D.sub.2. At the neutralization cell outlet, about 60-80% of the ions have been converted into energetic neutrals, which are then injected into the fusion plasma. Ions remaining at the end of the charge-exchange cell are bent out of the beam path by an ion deflection magnet usually contained within the vacuum enclosure of the injection system. As the energetic neutrals from the neutral beam penetrate into the confined fusion plasma, they undergo ionization by charge-exchange with the plasma ions. After being "ionized," the fast ions from neutral beam injection circulate around the fusion reactor along particle orbits that follow the magnetic field lines. Plasma heating results from the slowing down of the fast ions by collisions with the background plasma ions and the electrons. For fusion plasma heating, neutral beam efficiencies are found to be a very sensitive function of neutral species energy yields of the neutral beam. Hence, practical neutral beam injection systems should include a provision for accurate determination of energy species yields. High energy particle beams have also found wide use in science and industry. In typical applications, beams are first accelerated to a desired energy, and are then used to analyze or modify various targets. In nuclear research for example, particle beams are used to analyze the basic physical properties of subatomic systems, whereas in solid state physics research, particle beams are used to study the physical properties of surfaces, crystals, and thin films. Beams are also used to modify targets, as in the commercial production of radio-pharmaceuticals, ion-implanted semiconductor devices, and the heating of fusion reactor plasmas. Most particle beam applications require a control or knowledge of beam properties, such as energy, mass, charge, and species (i.e., energy components). Typical acceleration methods usually produce particle beams containing several different simultaneously-appearing atomic species. This is due to the variety of atomic processes that occur in the ion sources from which particle beams are extracted prior to acceleration. For example, a deuterium ion source is fed diatomic deuterium gas (D.sub.2) from a gas cylinder. The deuterium gas, upon entering the ion source, is decomposed into ions of atomic deuterium (D+), ions of diatomic molecular deuterium (D.sub.2.sup.+), and stable ions of triatomic molecular deuterium (D.sub.3.sup.+). The extraction and acceleration of these ions to an energy E produces a beam with three molecular species, each of which initially have the same energy. However, collisions of the molecular D.sub.2.sup.+ and D.sub.3.sup.+ beam species with gas in the beam acceleration system causes a decomposition of these molecular species into atomic particles having energies of one-half (E/2) and one-third (E/3) of the initial acceleration energy (E). Thus, the resulting beam can consist of particles having several different energies. Similar processes occur with other kinds of beams. In some applications, it is necessary to filter the ion beam using magnetic or electrostatic devices to prevent undesirable beam species from reaching the target. In other applications, such as the beam injecting systems used to heat the fusion reactor plasmas for example, pre-neutralization beam filtering is impractical due to the size, cost, and complexities involved. It is nevertheless desirable to know the neutral energy species content of such beams in order to optimize ion source performance in the beam-target interaction. Even in cases where beam filtering is used, it may be desirable to have the capability of detecting the presence of unwanted energy species resulting from system inefficiencies or defects. Several well-known methods of measuring the energy species content of particle beams are surveyed in an article by C. C. Tsai et al, Oak Ridge National Laboratory Technical Memo, ORNL TM-8360, Aug. 8, 1982. Each of these methods has limitations. For example, energy and momentum analysis methods which use electric/magnetic fields are limited to relatively low beam-currents, usually at a single point in the beam, and require that the beam particles be in a known ionic charge state. If the beam consists of neural particles, a gas-stripper cell or foil must be used to ionize the beam prior to analysis. Since the analysis still requires electric/magnetic fields, the same limitations just mentioned apply, with added complexity stemming from the gas handling and support requirements of gas cells or foils. Optical diagnostic methods of detecting the Doppler shift in the wavelength of light emitted by beam species moving at different velocities require relatively high background gas pressures to give detectable light output. The beam line regions having sufficient gas pressure for optical diagnostics are frequently located far from the target region, thereby allowing undetected changes to occur in the beam before the beam strikes the target. In the case of powerful neutral beams used to heat fusion reactor plasmas, optical species measurements must be made near the ion source, in a region containing both neutral and ionic particles which thereafter pass through a high gas density. Hence, measurements made with these diagnostic techniques must be extrapolated in order to estimate the state of the beam as it interacts with the target plasma. It is therefore an object of the present invention to provide particle beam energy species analyses applicable to either ion or neutral beams, that allows accurate, prompt, direct, position-dependent, in-situ measurements of the beam energy species. Operating tokamaks constitute a hostile environment for any in situ diagnostic technique, and concern over stray magnetic fields and electrical noise have discouraged proposals to consider sensitive particle in-situ measurements. It is an object of the present invention to provide analyses of the aforementioned type for fusion reactor plasmas which are heated by intense neutral beams, where heating efficiency is a sensitive function of D.degree.(E), the full energy species component of the heating beam. 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. 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 These and other objects of the present invention are provided for a particle beam having a full energy component at least as great as 25 keV, which is directed onto a beamstop target, such that Rutherford backscattering, preferably near-surface backscattering occurs. The geometry, material composition and impurity concentration of the beam stop are predetermined, using any suitable conventional technique. The energy-yield characteristic response of backscattered particles is measured over a range of angles using a fast ion electrostatic analyzer having a microchannel plate array at its focal plane. The knee of the resulting yield curve, on a plot of yield versus energy, is analyzed to determine the energy species components of various beam particles having the same mass. |
description | The present invention relates to a nuclear power plant, a method of replacement in the same, and a method of operating the same, and particularly to a nuclear power plant, a method of replacement in the nuclear power plant, and a method of operation in the nuclear power plant, suitable for operating and controlling a primary loop recirculation (PLR) pump. Boiling water reactors (BWR) including a primary loop recirculation (PLR) system with a PLR pump to provide a flow of coolant for cooling to control an output of the reactor are known. In a BWR plant, a so-called MfG set including a variable speed hydraulic coupling for variably controlling a rotation speed of a motor coupled to the PLR pump is used as a PLR power supply to control a recirculation flow rate. In the MfG set, power is supplied from a unit auxiliary middle voltage bus to an induction motor mechanically coupled to a variable rotation speed hydraulic coupling which is further mechanically coupled to a synchronous generator for generating power for driving the PLR pump motor, wherein the rotation speed control of the PLR pump motor is provided by controlling the variable speed hydraulic coupling. Upon controlling the flow rate in the core, kinetic momentum in the variable speed hydraulic coupling is controlled by a recirculation flow control signal from a reactor PLR control circuit to control the rotation speed of the PLR pump motor. Another prior art PLR power supply for driving the PLR pump motor using a current source inverter instead of the MfG set in the nuclear power plant is disclosed in Japanese laid-open patent application No. 8-80061. In this prior art, the use of the current source inverter eliminates the necessity of the auxiliary devices of the MfG set such as the variable hydraulic coupling, a rotation machine, and a hydraulic device. This structure improves maintainability, efficiency in a low output condition, and linearity in speed control. An aspect of the present invention provides a nuclear power plant capable of safely tripping a PLR (primary loop recirculation) pump at a high speed upon occurrence of a plant error such as turbine trip or load rejection. A further aspect of the present invention provides a method of replacement in a nuclear power plant including a conventional MfG set or a current source inverter to provide the nuclear power plant with a PLR power supply including a voltage source inverter capable of safely tripping a PLR pump at a high speed upon occurrence of a plant error such as the turbine trip or the load rejection. A further aspect of the present invention provides a method of operating a nuclear power plant with a PLR power supply including a voltage source inverter capable of safely tripping a PLR pump at a high speed upon occurrence of a plant error such as the turbine trip or the load rejection. A further aspect of the present invention provides a nuclear power plant comprising: a nuclear reactor; a PLR pump motor for driving a PLR pump to re-circulate coolant in the nuclear reactor; a unit auxiliary middle voltage bus; a first circuit breaker; a voltage source inverter electrically coupled to the unit auxiliary middle voltage bus through the first circuit breaker; and a second circuit breaker, the voltage source inverter supplying power to the PLR pump motor through the second circuit breaker. A further aspect of the present invention provides a method of replacement in a nuclear power plant with a PLR pump motor power supply system including a variable speed hydraulic coupling, a motor mechanically coupled to the variable speed hydraulic coupling, a first circuit breaker coupled to the motor, a generator mechanically coupled to the variable speed hydraulic coupling, and a PLR pump motor electrically coupled to the generator, comprising: removing the motor mechanically coupled to the variable speed hydraulic coupling and the synchronous mechanically coupled to the variable speed hydraulic coupling; providing a voltage source inverter; providing a second circuit breaker; and electrically coupling an output of the voltage source inverter to the PLR pump motor through the second circuit breaker. A further aspect of the present invention provides a method of replacement in a nuclear power plant with a PLR pump motor power supply system including a current source inverter, a first circuit breaker electrically coupled to the current source inverter, and a PLR pump motor electrically coupled to the current source inverter, comprising: removing the current source inverter; providing a voltage source inverter; providing a second circuit breaker; and electrically coupling the output of the voltage source inverter to the PLR pump motor through the second circuit breaker. A further aspect of the present invention provides a method of operating a nuclear power plant including a PLR pump motor for driving a PLR pump re-circulating coolant for the nuclear reactor, comprising: supplying power to the PLR pump motor through a unit auxiliary middle voltage bus, a first circuit breaker electrically coupled to the unit auxiliary middle voltage bus, a voltage source inverter electrically coupled to the first circuit breaker and a second circuit breaker electrically coupled to an output of the voltage source inverter; opening the second circuit breaker in response to a PLR pump trip signal; and stopping operation of the voltage source inverter in response to the PLR pump trip signal at the same time as the second circuit breaker is opened in response to the PLR pump trip signal. A further aspect of the present invention provides a nuclear power plant including a PLR pump motor, comprising: a unit auxiliary middle voltage bus for supplying power to the PLR pump motor; and a voltage source inverter electrically coupled to the unit auxiliary middle voltage bus for supplying drive power to the PLR pump motor. A further aspect of the present invention provides a method of replacement in a nuclear power plant with a PLR pump motor power supply system including an income circuit breaker receiving supply power, a PLR pump motor, and a drive circuit electrically coupled to the income circuit breaker for driving the PLR pump motor at a desired rotational speed, comprising: electrically isolating the income circuit breaker and the PLR pump motor from the drive circuit; providing a voltage source inverter; electrically coupling the voltage source inverter to the incoming circuit breaker; providing a circuit breaker; and electrically coupling an output of the voltage source inverter to the PLR pump motor through the circuit breaker. A further aspect of the present invention provides a method of replacement in a nuclear power plant with a PLR pump motor power supply system including a current source inverter, an income circuit breaker electrically coupled to the current source inverter, and a PLR pump motor electrically coupled to the current source inverter, comprising: electrically isolating the income circuit breaker and the PLR pump motor from the current source inverter; providing a voltage source inverter; electrically coupling the voltage source inverter to the circuit breaker; providing a circuit breaker; and electrically coupling the output of the voltage source inverter to the PLR pump motor through the circuit breaker. The same or corresponding elements or parts are designated with like references throughout the drawings. Prior to describing embodiments of the present invention, a related art PLR (primary loop recirculation) pump power supply system will be further argued. FIG. 2 illustrates a related art nuclear plant with a PLR pump power supply system using an inverter. This system includes a unit auxiliary middle voltage bus 1, an income circuit breaker 13 built in a supply transfer panel (not shown), a current source inverter 14, and an inverter control circuit 12 for controlling the current source inverter 14 in accordance with an inverter control signal 18 from a reactor recirculation flow control (RFC) circuit 9, which supplies power (for example, phase signals) to the PLR pump motor 7 for operation of the PLR pump 8. The current source inverter 14 acts as a current source, which does not allow no-load operation in which an output 54 of the inverter is opened. Thus, upon occurrence of an error in the plant such as turbine trip or load shut down, the income circuit breaker 13 for the current source inverter 14 is tripped in response to a recirculation pump trip (RPT) signal 17 from an RPT control circuit 10, and the current source inverter 14 is stopped through the inverter control circuit 12 to trip two PLR pumps 8. Therefore, it is difficult to trip the PLR pumps 8 with safety at a high speed because of the current source inverter 14. Will be described embodiments according to the present invention with reference to drawings. FIG. 1 illustrates a nuclear power plant according to an embodiment of the present invention. A PLR pump power supply system in the nuclear power plant in FIG. 1 comprises the unit auxiliary middle voltage bus 1, an income circuit breaker 2 electrically coupled to the unit auxiliary middle voltage bus 1, a voltage source inverter 15 electrically coupled to the income circuit breaker 2, two RPT circuit breakers (breakers) 6 electrically connected to an output 54 of the voltage source inverter 15, and the PLR pump motor 7 supplied with power (for example, phase signals) from the voltage source inverter 15 through the RPT circuit breakers 6. The first circuit breaker 6 is electrically coupled to the voltage source inverter 15 and is electrically connected to the second RPT circuit breaker 6 in series. The second RPT circuit breaker 6 is electrically coupled to the PLR pump motor 7 that mechanically coupled to the PLR pumps 8. The system further comprises an inverter control circuit 12 for controlling the voltage source inverter 15 in response to a control signal from the recirculation flow control (RFC) circuit 9 to supply power (phase drive signals) to the PLR pump motor 7, which drives the PLR pump 8. The income circuit breaker 2 electrically coupled to the unit auxiliary middle voltage bus 1 comprises only a trip coil for general switching operation. More specifically, an input 51 of the income circuit breaker 2 is electrically connected to the unit auxiliary middle voltage bus 1 with a cable. The output 52 of the income circuit breaker 2 is electrically connected to an input 53 of the voltage source inverter 15 with a cable. The output 54 of the voltage source inverter 15 is electrically connected to an input of the first RPT circuit breaker 6 with a cable. An output 56 of the first RPT circuit breaker 6 is electrically connected to an input 57 of the second RPT circuit breaker 6 with a cable or a bus bar. An output 58 of the second RPT circuit breaker 6 is electrically connected to the input 59 of the PLR pump motor 7 with a cable. The voltage source inverter 15 receiving power from the unit auxiliary middle voltage bus 1 through the income circuit breaker 2 is controlled by the inverter control circuit 12 supplied with a signal from the RFC circuit 9. The RFC circuit 9 supplies an inverter signal 18 for decreasing a deviation of a processed value of a flow rate in the core from a command value to the inverter control circuit 12 that operates the voltage source inverter 15 by PWM (Pulse Width Modulation) control to provide operation at a constant voltage/frequency ratio to control, i.e., increase, decrease, or keep constant, the rotation speed of the PLR pump motor 7. Generally, in the nuclear plant, when the turbine trip or the load shut down occurs during operation of the nuclear plant, to keep soundness of fuel, a recirculation pump trip control for moderating a transitional output increase of the reactor 11 is executed together with a scrum signal by tripping two PLR pumps 8 to rapidly decrease a reactor core flow. This control function is carried out by the RPT control circuit 10. The RPT control circuit 10 detects, when a turbine main steam stop valve (not shown) is closed by the turbine trip or when a turbine steam control valve (not shown) is closed due to the generator load rejection, the closing operation of these valves are detected by detection circuits, respectively, to generate the RPT signal 17. The RPT signal 17 is generated by 2-out of 4 logic to increase its reliability to prevent an error trip in the PLR pump 8 due to a signal failure or the like of devices. Further, to surely trip the PLR pump 8 upon occurrence of an error of the plant, devices to be tripped in response to the RPT signal 17 are multiplexed. In this embodiment, as cut off means responsive to the RPT signal, the RPT circuit breakers 6 are provided at the output 54 of the voltage source inverter 15 electrically connected in series to provide shutdown operation with both the RPT circuit breakers 6 by opening them for the purpose of multiplexing the trip operation devices to surely trip the PLR pump 8 upon an error in the nuclear plant. Further, after occurrence of the recirculation pump trip, since it is unnecessary to operate the voltage source inverter 15, the RPT control circuit 10 has a function for stopping the voltage source inverter 15 by supplying either of open signals for the two RPT circuit breakers 6 to the inverter control circuit 12 as described below. More specifically, the RPT control circuit 10 includes a delay timer 20. The RPT control circuit 10 detects, when a turbine main steam stop valve (not shown) is closed by the turbine trip or when a turbine steam control valve (not shown) is closed due to the generator load rejection, the closing operation of these valves are detected by detection circuits, respectively, to generate the RPT signal 17. In response to the RPT signal 17, the delay timer 20 measures a predetermined time interval. When the predetermined time interval is elapsed, a delayed PRT signal 19 is supplied to the inverter control circuit 12 to stop the inverter control circuit 12. However, the delay time may be zero or the RPT signal 17 may be supplied to the inverter control circuit 12 instead of the delayed PRT signal 19. In other words, the stop of the voltage source inverter 15 is at the same time as or after the open of the RPT circuit breakers 6. FIG. 3 illustrates a nuclear power plant provided by modifying the first embodiment. A PLR pump power supply system in the nuclear power plant in FIG. 3 comprises the unit auxiliary middle voltage bus 1, the income circuit breaker 2 electrically coupled to the unit auxiliary middle voltage bus 1, the voltage source inverter 15 electrically coupled to the income circuit breaker 2, the RPT circuit breaker 6 electrically connected to an output 54 of the voltage source inverter 15, and the PLR pump motor 7 supplied with power from the RPT circuit breaker 6. The system further comprises the inverter control circuit 12 for controlling the voltage source inverter 15 in response to the control signal from the RFC circuit 9 by supplying power to the PLR pump motor 7 to drive the PLR pump 8. More specifically, the input 53 of the voltage source inverter 15 is electrically connected to the output 52 of the income circuit breaker 2 with a cable and its output 58 is electrically connected to the PLR pump motor 7 with a cable. Upon occurrence of the turbine trip or the generator load rejection, to keep soundness of fuel, the RPT signals 17 are generated by the RPT control circuit 10. In this embodiment, in the RPT control circuit 10, the RPT signals 17 are independently generated through the 2-out of 4 logic and supplied to the RPT circuit breaker 6 for an opening operation and to the inverter control circuit 12 for stop of the voltage source inverter 15. This multiplexes the device to be tripped in response to the RPT signals, providing a structure surely tripping the PLR pump 8. The first and second embodiments have been described with examples in which the present invention is applied to a newly build nuclear power plant. However, this invention is applicable to existing nuclear power plates by replacing the existing devices to provide the structures of the first and second embodiments. If a nuclear power plant includes the PLR power supply system for the MfG set, replacement is done as shown in FIG. 4. First, are removed an induction motor 21 supplied with a power from the unit auxiliary middle voltage bus 1 through the income circuit breaker 2, a hydraulic coupling 22 mechanically connected to the induction motor 21, and a synchronous generator 23 mechanically coupled to the hydraulic coupling 22 supplying phase signals supplied to the PLR pump motor 7 through electrical and mechanical isolation. Second, the voltage source inverter 15 is installed and its input 53 is electrically connected to the unit auxiliary middle voltage bus 1 through the income circuit breaker 2. The output 54 of the voltage source inverter 15 is electrically coupled (electrically connected) to the PLR pump motor 7 through one RPT circuit breaker 6 or two RPT circuit breakers 6 with cables to supply voltage phase signals to the PLR pump motor 7. Further, the inverter control circuit 12, the RFC circuit 9, and the RPT control circuit 10 are installed and electrically coupled to devices as described in the first and second embodiments. This provides replacement in the nuclear power plant including PLR power supply system for the MfG set. According to the present invention, if a nuclear power plant is subjected to expanding its life by maintenance, the replacement of the system including the MfG set with the system including the voltage source inverter 15 provides the following an advantageous effect. In the case of an existing nuclear power plant including a power supply for the PLR pump for the MfG set, according to the present invention, maintainability, efficiency at a low output operation, and controllability of rotation speed, of the MfG set and auxiliary devices in the MfG set can be improved. Further, the existing circuit breaker 2 and cables from the existing circuit breaker 2 to the PLR pump motor 7 can be reused, which simplifies the modifying process. Further, this invention is also applicable to a nuclear power plant including a current source inverter to replace the current source inverter with the voltage source inverter. In the case of an existing nuclear power plant (FIG. 2) with the PLR power supply system for the PLR pump 7 including the current source inverter 14, first, the current source inverter 14 is electrically isolated (disconnected) from the PLR pump 7 and from the income circuit breaker 13 and is removed. The voltage source inverter 15 is installed on the side of the PLR pump motor 7 with respect to the income circuit breaker 13 that was electrically connected to the current source inverter. In other words, the voltage source inverter 15 is electrically connected to the income circuit breaker 13, corresponding to the income circuit breaker 2, to receive the power from the unit auxiliary middle voltage bus 1 via its input through the existing income circuit breaker 13. The voltage source inverter 15 is electrically connected, via its output, to the PLR pump motor 7 through newly provided RPT circuit breakers 6. Further, a cable for the RPT signal 17 of the RPT control circuit 10 is electrically isolated (disconnected) from the income circuit breaker 13, and is electrically connected to the first and second RPT circuit breakers 6 and 6 between the voltage source inverter 15 and the PLR pump motor 7. Thus, the power supply including the current source inverter 14 shown in FIG. 2 is modified as shown in FIG. 1. If a nuclear power plant including the existing MfG set was subjected to replacement with a current source inverter, it would be necessary to adjust control coefficients of the current inverter in a combination test with the PLR pump in advance. This is problematic because of a lot of days necessary for the replacement operation. Further, if the current source inverter 14 was used, to provide the PLR pump trip function, it would be necessary to install a circuit breaker including a double trip coil having a special specification on a unit auxiliary middle voltage bus panel. On the other hand, according to the present invention, the voltage source inverter 15 is used in the nuclear power plant, which eliminates the necessity of the combination test with the PLR pump. This enables the reduction in the number of replacement operations. Further, the nuclear power plant using the voltage source inverter 15 according to the present invention allows, as the income circuit breaker for supplying power to the PLR pump, use of a circuit breaker that is similar to a circuit breaker employing a general single trip coil. This eliminates the necessity of a power supply with a special specification on the unit auxiliary middle voltage bus, which provides a nuclear power plant with easiness in maintenance of the power supply panel at a low cost and with high speed and safe tripping of the PLR pump. The method of replacement of the power supply for the MfG set in the second embodiment may be modified. First, the power supply (a driving circuit) including the induction motor 21, the hydraulic coupling 22, and the synchronous generator 23 is electrically isolated from the income circuit breaker 2 and the PLR pump motor 7 without removal if there is a space for installation. More specifically, the income circuit breaker 2 is electrically disconnected from the induction motor 21 (FIG. 4), and the PLR pump motor 7 is electrically disconnected from the synchronous generator 23. Second, the voltage source inverter 15 is installed, and its input 53 is electrically connected to the unit auxiliary middle voltage bus 1 through the income circuit breaker 2. The output 54 of the voltage source inverter 15 is electrically coupled to the PLR pump motor 7 through one RPT circuit breaker 6 or two RPT circuit breakers 6 to supply voltage phase signals to the PLR pump motor 7 as similar to the second embodiment. Similarly, in the method of replacement of the power supply for the current source inverter set in the second embodiment may be modified. First, the current source inverter 14 (FIG. 2) is electrically isolated from the income circuit breaker 13 (2) and the PLR pump motor 7 without removal if there is space. More specifically, the income circuit breaker 13 is electrically isolated (disconnected) from the induction motor 21 shown in FIG. 4 (disconnected from the cable connected to the induction motor 21 at the induction motor 21), and the PLR pump motor 7 is electrically isolated (disconnected) from the synchronous generator 23 (disconnected from the cable connected to the synchronous generator 23 at the synchronous generator 23) without removal if there is a space for installation. Second, the voltage source inverter 15 is installed and its input 53 is electrically connected to the unit auxiliary middle voltage bus 1 through the income circuit breaker 13 (with the cable that was disconnected from the induction motor 21). The output 54 of the voltage source inverter 15 is electrically coupled to the PLR pump motor 7 through one RPT circuit breaker 6 or two RPT circuit breakers 6 to supply voltage phase signals to the PLR pump motor 7 as similar to the third embodiment. More specifically, the output 54 of the voltage source inverter 15 is electrically connected to the PLR pump motor 7 with the cable that was disconnected from the synchronous generator 23. In the second and third embodiments, the connection of the cable to the newly provided devices such as the voltage source inverter 15 is done after disconnection of the cable from device that became unused. However, for example, if the income circuit breaker 2 has auxiliary output terminals, it is possible to electrically connect the income circuit breaker 2 to the voltage source inverter 15 with newly provided cable before electrical isolation (disconnection) of the income circuit breaker 2 from the induction motor 21 or the current source inverter 14. Thus, the order of disconnection and connection processes can be reversed. However, the connection is done after installation of, for example, the voltage source inverter 15. In the first embodiment, the first and second RPT circuit breakers 6 and 6 are connected in series. Thus, the first and second RPT circuit breakers 6 and 6 are opened in response to the recirculation pump trip signal at the same time. This provides redundancy in the trip control, so that the voltage source inverter 15 can be stopped after the trip of the first and second RPT circuit breakers 6 and 6. However, the voltage source inverter 15 can be stopped at the same time as the first and second RPT circuit breakers 6 and 6. In the second embodiment, the RPT circuit breaker 6 and the voltage source inverter 15 shown in FIG. 3 are tripped at the same time in response to the recirculation pump trip signal to provide redundancy in the tripping control. |
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051035049 | abstract | Textile fabric shielding electromagnetic radiation, and clothing made thereof. The textile fabric is made of threads spun of textile fibers, containing cotton, and of steel fibers having a diameter of 6 to 10 .mu.m. The number of mixed yarn threads in warp direction and in weft direction each is 18 to 20 threads per cm, and the yarn fineness of the textile fabric is especially 38 to 40 tex. The textile fabric guarantees a shielding of 20 to 40 dB against electromagnetic radiation at a frequency of 10 GHz. The fabric has the quality of usual clothing, and the clothing thereof is designed with respect to proportions, seams, fasteners, and other special features in a manner such that especially people wearing pacemakers, or hospital and radar personnel, are protected against electromagnetic radiation. |
claims | 1. A scanning apparatus for scanning a beam in a single dimensional scan, the apparatus comprising:a. a source of radiation for generating a fan beam of radiation effectively emanating from a source axis and characterized by a width;b. an angle selector, stationary during the course of scanning, for limiting the angular extent of the scan; andc. a multi-aperture unit rotatable about a central axis in such a manner that beam fluence incident on a target is the same per revolution for different fields of view of the beam on the target. 2. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes rings of apertures spaced laterally along the central axis in such a manner that relative axial motion of the multi-aperture unit, relative to the x-ray beam plane, places a ring of apertures in the beam that is collimated by a corresponding opening angle in the angle selector. 3. A scanning apparatus in accordance with claim 1, wherein the angle selector includes a slot of continuously variable opening. 4. A scanning apparatus in accordance with claim 1, wherein the central axis is substantially coincident with the source axis. 5. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes rectangular slots. 6. A scanning apparatus in accordance with claim 1, wherein the source axis is forward-offset relative to the central axis. 7. A scanning apparatus in accordance with claim 1, further comprising a collimator for limiting at least one of a width of the beam and an angular extent of the scan. 8. A scanning apparatus in accordance with claim 7, wherein the collimator is a width collimator. 9. A scanning apparatus in accordance with claim 8, wherein the collimator is an inner collimator. 10. A scanning apparatus in accordance with claim 8, wherein the collimator is an outer collimator. 11. A scanning apparatus in accordance with claim 1, wherein the angle selector includes a plurality of discrete slots. 12. A scanning apparatus in accordance with claim 10, wherein the angle selector includes a shutter position. 13. A scanning apparatus in accordance with claim 1, wherein the source of radiation is an x-ray tube. 14. A scanning apparatus in accordance with claim 1, wherein the source of radiation is of a type generating a fan beam exceeding 60° in opening angle. 15. A scanning apparatus in accordance with claim 1, further comprising an enclosing conveyance for conveying the scanning apparatus past an inspection target. 16. A scanning apparatus in accordance with claim 1, wherein the scanning apparatus is coupled to a platform. 17. A scanning apparatus in accordance with claim 1, wherein the scanning apparatus is coupled to a platform in conjunction with at least one further scanning apparatus. 18. A scanning apparatus in accordance with claim 1, further comprising a filter disposed within the beam for changing the energy distribution of the beam. 19. A scanning apparatus in accordance with claim 18, wherein the filter is disposed on a filter tube adapted for selective insertion of a plurality of filters. 20. A scanning apparatus in accordance with claim 18, wherein the filter tube includes a beam shutter. 21. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes two nested, multi-aperture collimators. 22. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes an inner multi-aperture hoop characterized by a hoop axis, the inner multi-aperture hoop made of material opaque to the beam. 23. A scanning apparatus in accordance with claim 21, wherein the inner multi-aperture unit includes rings of apertures spaced laterally along the hoop axis in such a manner that relative axial motion of the inner multi-aperture unit, relative to the beam plane, places a ring of apertures in the beam that is collimated by a corresponding opening angle in the angle selector. 24. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes an outer multi-aperture hoop rotatable in registration with an inner multi-aperture hoop. 25. A scanning apparatus in accordance with claim 23, wherein the outer multi-aperture hoop includes a plurality of apertures configured as horizontal slots in such a manner as to define a minimum size of emitted pencil beams along a sweep direction of the beams. 26. A scanning apparatus in accordance with claim 23, wherein the inner multi-aperture hoop and the outer multi-aperture hoop are mechanically integral. 27. A scanning apparatus in accordance with claim 23, further comprising an outer variable width collimator for defining a width of the beam that enters or exits the outer multi-aperture hoop. 28. A scanning apparatus in accordance with claim 1, wherein radiation is emitted through a plurality of apertures at different angles with respect to the target, such that pencil beams of penetrating radiation sweep in alternation through the target in such a manner as to provide a stereoscopic view of an interior volume of the target. 29. A scanning apparatus in accordance with claim 1, further comprising a rotation assembly adapted to provide for rotation of the source of radiation about the source axis. 30. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes substantially rectangular through-holes. 31. A method for inspecting an object based on the transmission of x-rays through an object, the method comprising:a. generating a fan beam of radiation;b. collimating the width of the fan beam with a collimator that is stationary during the course of a scan of the object, the scan characterized by an extent;c. limiting the extent of the scan with an angle selector; andd. varying a field of view of the beam on the object by means of a multi-aperture unit rotatable about a central axis in such a manner that the resulting beam fluence on the target is the same per revolution for all selected scan angles. |
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046631097 | summary | BACKGROUND OF THE INVENTION This invention relates generally to apparatus for confining a plasma, and more particularly to a modular stellarator. In the development of a device to confine a thermonuclear plasma, an obvious choice was a torus with coils to produce a toroidal field spaced about the torus. However, this was soon found unsatisfactory. Because of the geometry of the torus, the toroidal field lines curved around the toroidal axis such that the force associated with the magnetic field gradient caused positively and negatively charged plasma particles to drift in opposite directions. This charge separation resulted in an electric field which destroyed the magnetic confinement. Consequently, in order to prevent charge separation in a torus, a poloidal magnetic field must be applied. The two major toroidal confinement devices: tokamaks and stellarators differ in the manner in which the poloidal magnetic field is applied. In a tokamak, the poloidal field is applied by introducing a toroidal current in the plasma. One drawback of the tokamak is that the large plasma current needed for confinement carries a large free energy that can be tapped by instabilities which destroy the confinement. Another drawback of the tokamak is the relatively small values of beta achievable--typically only up to 6%. The tokamak is also not a steady-state device; it only operates during pulsed operation. Beta, .beta., is the ratio of plasma particle pressure to the magnetic field. High values of beta are important for achieving high plasma temperatures and confinement times. High betas are essential if a fusion reactor using only deuterium fuel is to be realized. Currently, deuterium/tritium is the fuel or choice because the D-T reaction requires lower temperatures and confinement times than the D--D reaction. In a stellarator, the poloidal field is produced externally to the plasma, generally by current-carrying conductor wound helically around the torus. Stellarators with helically wound conductor and toroidal field coils are said to have interlocked coils because the helical conductor winds in and around the toroidal field coils. Stellarators are capable of achieving betas several times greater than in a tokamak and are also capable of steady-state operation. The major drawbacks of stellarators have been the complicated coil structure required and the lack of easy access to the inside of the machine for repair due to the helically wound conductor. Recently, several modular stellarator designs have been proposed. In a modular stellarator, both toroidal and poloidal fields are achieved by a single set of non-interlocking non-planar coils. These designs generally include a circular (non-helical) axis and hence do not have the high beta or stability of the more complicated interlocked stellarators. Although the non-planar coils are modular and easily replaceable, they are difficult to manufacture. Another version of a modular stellarator is built using only non-interlocked, circular coils on a helical axis. While this stellarator is easily maintainable and the coils easily manufactured, the most unattractive feature of this stellarator is that it has a maximum average B (magnetic field) at low .beta.--a magnetic hill. This condition implies instability for reactor grade plasmas. It has been determined that stellarators which have magnetic wells--minimum average B at low .beta.--have good stability properties. The measure of a magnetic well is determined by the sign of V", the second derivative of volume per unit toroidal flux. Hence, when V"<0, there is a magnetic well. The stability beta limit is .chi. 2/2A where .chi. is the rotational transform and A is the stellarator aspect ratio. (Rotational transform is the average twist or rotation of a magnetic field line in a magnetic surface. Aspect ratio is the ratio of the torus major radius to minor radius.) Hence a large rotational transform in the presence of a magnetic well gives a large beta. Therefore, it is an object of the present invention to provide a modular stellarator using planar coils having a magnetic well and large rotational transform. It is also an object of the present invention to provide a stable plasma confinement device using only toroidal field coils. It is another object of the present invention to provide a stellarator that can be easily maintained, dismantled and repaired. 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. SUMMARY OF THE INVENTION To achieve the foregoing and other objects and in accordance with the purposes of the present invention an apparatus for confining a plasma may comprise a closed endless tube; and a plurality of closed, curved, planar coils spaced about said tube, the centers of said coils defining a helical axis, said helical axis being substantially parallel to the axis of said tube, the plane of each coil being substantially perpendicular to said helical axis, the curve of each coil being defined in .rho., .theta. coordinates by the relationship: .rho.=a.sub.c +.delta..sub.2 cos 2.theta.+.delta..sub.3 cos 3.theta., where a.sub.c, .delta..sub.2, and .delta..sub.3 are constants and at least one of .delta..sub.2 and .delta..sub.3 is not equal to zero. When the helical axis is described by radius r.sub.o, pitch kr.sub.o, and period m, a.sub.c, .delta..sub.2, and .delta..sub.3 satisfy the relationship: |
052788822 | claims | 1. A zirconium alloy for use in light water nuclear core structure elements and fuel cladding, which comprises an alloy composition as follows: tin, in a range of 0.4 to 1.0 wt. %; iron, in a range of 0.3 to 0.6 wt. %; chromium, in a range of 0.2 to 0.4 wt. % nickel, in a range of up to 0.06 wt. %; silicon, in a range of 50 to 200 ppm; and oxygen, in a range of 1200 to 2500 ppm; and the balance being of zirconium. tin, in a range of 0.4 to 1.0 wt. %; iron, in a range of 0.3 to 0.6 wt. %; chromium, in a range of 0.2 to 0.4 wt. % nickel, present in a range from a measurable amount to 0.06 wt. %; silicon, in a range of 50 to 200 ppm; oxygen, in a range of 1200 to 2500 ppm; and the balance being of zirconium. 2. The alloy composition as set forth in claim 1, wherein said tin is typically about 0.5 wt. %. 3. The alloy composition as set forth in claim 1, wherein said iron is typically about 0.46 wt. %. 4. The alloy as set forth in claim 1, wherein said chromium is about 0.23 wt. %. 5. The alloy as set forth in claim 1, wherein said nickel is about 0.03 wt. %. 6. The alloy as set forth in claim 1, wherein said silicon is about 100 ppm. 7. The alloy as set forth in claim 1, wherein said oxygen is about 1800 to 2200 ppm. 8. The alloy as set forth in claim 1, wherein said alloy is irradiated in use. 9. The alloy as set forth in claim 7, wherein said oxygen level reduces hydrogen uptake for said alloy as compared to conventional Zircaloy-4. 10. A zirconium alloy for use in light water nuclear core structure elements and fuel cladding, which comprises a composition which includes tin in a range of 0.4 to 1.0 wt. % to improve corrosion resistance of said alloy in combination with iron in a range of 0.3 to 0.6 wt. %; chromium in a range of 0.2 to 0.4 wt. %; and alloying elements including nickel present in a range of a measurable amount to 0.06 wt. % to enhance the high temperature corrosion resistance of the alloy, silicon in a range of 50 to 200 ppm to reduce the hydrogen absorption by the alloy and to reduce variation of corrosion resistance with variation in the processing history of the alloy, oxygen in a range of 1200 to 2500 ppm as a solid solution strengthening alloying element; and the remainder zirconium. 11. The alloy composition as set forth in claim 10, wherein said tin is typically about 0.5 wt. %. 12. The alloy composition as set forth in claim 10, wherein said iron is typically about 0.46 wt. %. 13. The alloy as set forth in claim 10, wherein said chromium is about 0.23 wt. %. 14. The alloy as set forth in claim 10, wherein said nickel is about 0.03 wt. %. 15. The alloy as set forth in claim 10, wherein said silicon is about 100 ppm. 16. The alloy as set forth in claim 10, wherein said oxygen is about 1800 to 2200 ppm. 17. The alloy as set forth in claim 10, wherein said alloy is irradiated in use. 18. The alloy as set forth in claim 10, wherein said oxygen level reduces hydrogen uptake compared to Zircaloy-4. 19. A zirconium alloy consisting essentially of the following composition: 20. A zirconium alloy which comprises a composition consisting essentially of tin in a range of 0.4 to 1.0 wt. % to improve corrosion resistance of said alloy in combination with iron in a range of 0.3 to 0.6 wt. %; chromium in an amount in a range of 0.2 to 0.4 wt. %; and further comprising alloying elements including nickel present in a range of from a measurable amount to 0.06 wt. % to enhance the high temperature corrosion resistance of the alloy, silicon in a range of 50 to 200 ppm to reduce the hydrogen absorption by the alloy and to reduce variation of corrosion resistance with variation in the processing history of the alloy, and oxygen in a range of 1200 to 2500 ppm as a solid solution strengthening alloying element; and the remainder zirconium. 21. The alloy composition as set forth in claim 20, consisting essentially of said alloying elements. |
description | This application claims priority of Chinese Application No. 201710927155.3 filed on Sep. 29, 2017, the entire contents of which are hereby incorporated by reference. The application generally relates to imaging, and more specifically, relates to a system and method for tracking and/or correcting the focus position of a radiation source in an imaging device. During a computed tomography (CT) scanning, focus positions of X-ray beams emitted from an X-ray tube may change due to effects from external environments and other factors. For example, a rotation shaft of the X-ray tube may thermally expand due to heat accumulation, which may lead to a focus position offset, and have an impact on the scanning. Moreover, due to effects of environmental changes, in CT imaging, it is needed to perform an air correction. The focus position of the X-ray tube of the CT scanner during the air correction may be different from the focus position of the X-ray tube of the CT scanner during the scanning of a patient, which may cause artifacts in a reconstructed image. Therefore, there is a need for a method for tracking the position of the focus of the X-ray tube of a CT scanner to identify, reduce, or eliminate the impact of a focus position offset on imaging. In a first aspect of the present disclosure, an imaging device is provided. The imaging device may include an X-ray tube, a detector, and a collimator. The collimator may include an opening. The opening may have a plurality of opening widths along a first direction and a plurality of opening lengths along a second direction. The plurality of opening widths may include a first opening width and a second opening width. The first opening width may correspond to at least one end of the opening. The second opening width may correspond to a middle section of the opening, and the first opening width may be smaller than the second opening width. In some embodiments, the collimator may include a protrusion at at least one end in the second direction, and the protrusion may protrude into the opening. In some embodiments, the collimator may be an anti-scatter grid. The anti-scatter grid may include a plurality of sub-openings, and the plurality of sub-openings may be configured corresponding to a plurality of detection units of a detector. In some embodiments, the anti-scatter grid may include a body and a plurality of protrusions. The plurality of protrusions may be located at an edge of the body extending along the first direction. The plurality of protrusions may be arranged along the edge of the body, and each of the plurality of protrusions may partially block a corresponding detection unit. In a second aspect of the present disclosure, a method for determining a focus position offset of an X-ray tube of an imaging device is provided. The method may be implemented on at least one device each of which has at least one processor and storage. The method may include one or more of the following operations. A first ray intensity distribution detected by an edge detection unit of a detector of the imaging device may be obtained. The imaging device may include an X-ray tube, a detector, and a collimator. The collimator may include an opening and a protrusion. The protrusion may be configured at at least one end of the opening and protruding into the opening. The opening may have a plurality of opening widths along a first direction and a plurality of opening lengths along a second direction. A first opening width corresponding to at least one end of the collimator in the second direction may be smaller than a second opening width corresponding to a middle section of the collimator in the second direction. The edge detection unit may be located at an edge of the detector along the first direction. A size of the edge detection unit along the second direction may correspond to a size of the protrusion along the second direction. The first ray intensity distribution may correspond to a first focus position of the X-ray tube. A second ray intensity distribution detected by the edge detection unit may be obtained. The second ray intensity distribution may correspond to a second focus position of the X-ray tube. The focus position offset that is between the first focus position and the second focus position of the X-ray tube may be determined based on the first ray intensity distribution and the second ray intensity distribution. In some embodiments, the method may include one or more of the following operations. A first detection unit that corresponds to a boundary of the first ray intensity distribution may be determined. A second detection unit that corresponds to a boundary of the second ray intensity distribution may be determined. The focus position offset may be determined based on a distance between the first detection unit and the second detection unit. In a third aspect of the present disclosure, a method for tracking a focus position of an X-ray tube of an imaging device is provided. The method may be implemented on at least one device each of which has at least one processor and storage. The method may include one or more of the following operations. A ray intensity distribution detected by an edge detection unit of a detector of the imaging device may be obtained. The imaging device may include an X-ray tube, a detector, and a collimator. The collimator may include an opening and a protrusion. The protrusion may be configured at at least one end of the opening and protruding into the opening. The opening may have a plurality of opening widths along a first direction and a plurality of opening lengths along a second direction. The plurality of opening widths may include a first opening width and a second opening width. The first opening width may correspond to at least one end of the collimator in the second direction. The second opening width may correspond to a middle section of the collimator in the second direction, and the first opening width may be smaller than the second opening width. The edge detection unit may be located at an edge of the detector along the first direction. A size of the edge detection unit along the second direction may correspond to a size of the protrusion along the second direction. Each ray intensity of the ray intensity distribution may correspond to a focus position of the X-ray tube. A first boundary intensity and a second boundary intensity of the ray intensity distribution may be determined. A relationship between the first boundary intensity and the second boundary intensity may be determined. The focus position of the X-ray tube may be determined by consulting a mapping table based on the relationship between the first boundary intensity and the second boundary intensity. The mapping table may include a correspondence relationship between focus positions and the relationship between the first boundary intensity and the second boundary intensity. In a fourth aspect of the present disclosure, a system for tracking a focus position of an X-ray tube of an imaging device is provided. The system may include a storage device configured to store a computer program and a processor configured to communicate with the storage device. When executing the set of instructions, the processor may be configured to cause the system to: obtain a ray intensity distribution detected by an edge detection unit of a detector of the imaging device, wherein the imaging device includes an X-ray tube, a detector and a collimator, the collimator includes: an opening and a protrusion, the protrusion being configured at at least one end of the opening and protruding into the opening, the opening having a plurality of opening widths along a first direction and a plurality of opening lengths along a second direction, the plurality of opening widths including a first opening width and a second opening width, the first opening width corresponding to at least one end of the collimator in the second direction, the second opening width corresponding to a middle section of the collimator in the second direction, and the first opening width being smaller than the second opening width, wherein the edge detection unit may be located at the edge of the detector along the first direction, a size of the edge detection unit along the second direction may correspond to a size of the protrusion along the second direction, and each ray intensity of the ray intensity distribution may correspond to a focus position of the X-ray tube; determine a first boundary intensity and a second boundary intensity of the ray intensity distribution; determine a relationship between the first boundary intensity and the second boundary intensity; and determine, by consulting a mapping table, the focus position of the X-ray tube based on the relationship between the first boundary intensity and the second boundary intensity, wherein the mapping table includes a correspondence relationship between focus positions and the relationship between the first boundary intensity and the second boundary intensity. In a fifth aspect of the present disclosure, a calibration system for tracking a focus position of an X-ray tube of an imaging device is provided. The system may include a storage device configured to store a computer program and a processor configured to communicate with the storage device. When executing the set of instructions, the processor may be configured to cause the system to: obtain a first detector response corresponding to a first focus position by scanning a reference object; obtain a second detector response corresponding to a second focus position by scanning a target object; determine, by consulting a correction table, a third detector response corresponding to the first focus position and a fourth detector response corresponding to the second focus position, wherein the correction table includes a correspondence relationship between focus positions and detector responses; calibrate the first detector response based on the third detector response and the fourth detector response; obtain image data corresponding to the target object based on the calibrated first detector response and the second detector response; and generate an image based on the image data. In a sixth aspect of the present disclosure, a method for calibrating a focus position of an imaging device is provided. The method may be implemented on at least one device, each of which has at least one processor and storage. The method may include one or more of the following operations. A first detector response corresponding to a first focus position may be obtained by scanning a reference object. A second detector response corresponding to a second focus position may be obtained by scanning a target object. A third detector response corresponding to the first focus position and a fourth detector response corresponding to the second focus position may be determined by consulting a correction table. The correction table may include a correspondence relationship between focus positions and detector responses. The first detector response may be calibrated based on the third detector response and the fourth detector response. Image data corresponding to the target object may be obtained based on the calibrated first detector response and the second detector response. An image may be generated based on the image data. In some embodiments, the method may include one or more of the following operations. A calibration value may be determined based on the third detector response and the fourth detector response. The first detector response may be calibrated based on the calibration value. In some embodiments, the method may include one or more of the following operations. The first focus position and/or the second focus position may be determined based on a ray intensity distribution detected by an edge detection unit of a detector of an imaging device. The imaging device may include an X-ray tube, a detector, and a collimator. The collimator may include an opening and a protrusion. The protrusion may be configured at at least one end of the opening and protruding into the opening. The opening may have a plurality of opening widths along a first direction and a plurality of opening lengths along a second direction. The plurality of opening widths may include a first opening width and a second opening width. The first opening width may correspond to at least one end of the collimator in the second direction. The second opening width may correspond to a middle section of the collimator in the second direction, and the first opening width may be smaller than the second opening width. The edge detection unit may be located at an edge of the detector along the first direction. A size of the edge detection unit along the second direction may correspond to a size of a protrusion along the second direction. Each ray intensity of the ray intensity distribution may correspond to a focus position of an X-ray tube. In a seventh aspect of the present disclosure, a collimator is provided. The collimator may include an opening. The opening may have a plurality of opening widths along a first direction and a plurality of opening lengths along a second direction. The plurality of opening widths may include a first opening width and a second opening width. The first opening width may correspond to at least one end of the collimator in the second direction. The second opening width may correspond to a middle section of the collimator in the second direction, and the first opening width may be smaller than the second opening width. In some embodiments, the collimator may include a blade. In some embodiments, the blade may include a protrusion at at least one end in the second direction, and the protrusion may protrude into the opening. In some embodiments, the collimator may be an anti-scatter grid. In some embodiments, the anti-scatter grid may include a plurality of sub-openings, and the plurality of sub-openings may be configured corresponding to a plurality of detection units of a detector. In some embodiments, the anti-scatter grid may include a body and a plurality of protrusions. The plurality of protrusions may be located at an edge of the body and protruding along the first direction. Each of the plurality of protrusions may partially block a corresponding detection unit. In some embodiments, the opening may be a substantially rectangular opening, and at least one corner of the opening may include a protrusion protruding into the opening. In some embodiments, the collimator may include a pair of blocks disposed opposite to each other. The pair of blocks may define an opening, and at least one end of a block of the pair of blocks may include a protrusion protruding into the opening. Additional features 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 and the accompanying drawings or may be learned by production or operation of the examples. The features of the present disclosure may be realized and attained by practice or use of various aspects of the methodologies, instrumentalities and combinations set forth in the detailed examples discussed below. In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant disclosure. However, it should be apparent to those skilled in the art that the present disclosure may be practiced without such details. In other instances, well known methods, procedures, systems, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present disclosure. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present disclosure is not limited to the embodiments shown, but to be accorded the widest scope consistent with the claims. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise,” “comprises,” and/or “comprising,” “include,” “includes,” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that the term “system,” “unit,” “module,” and/or “block” used herein are one method to distinguish different components, elements, parts, section or assembly of different level in ascending order. However, the terms may be displaced by other expression if they achieve the same purpose. Generally, the word “module,” “unit,” or “block,” as used herein, refers to logic embodied in hardware or firmware, or to a collection of software instructions. A module, a unit, or a block described herein may be implemented as software and/or hardware and may be stored in any type of non-transitory computer-readable medium or other storage device. In some embodiments, a software module/unit/block may be compiled and linked into an executable program. It will be appreciated that software modules can be callable from other modules/units/blocks or from themselves, and/or may be invoked in response to detected events or interrupts. Software modules/units/blocks configured for execution on computing devices (e.g., data processing device 105 as illustrated in FIG. 1) may be provided on a computer readable medium, such as a compact disc, a digital video disc, a flash drive, a magnetic disc, or any other tangible medium, or as a digital download (and can be originally stored in a compressed or installable format that needs installation, decompression, or decryption prior to execution). Such software code may be stored, partially or fully, on a storage device of the executing computing device, for execution by the computing device. Software instructions may be embedded in a firmware, such as an EPROM. It will be further appreciated that hardware modules/units/blocks may be included of connected logic components, such as gates and flip-flops, and/or can be included of programmable units, such as programmable gate arrays or processors. The modules/units/blocks or computing device functionality described herein may be implemented as software modules/units/blocks, but may be represented in hardware or firmware. In general, the modules/units/blocks described herein refer to logical modules/units/blocks that may be combined with other modules/units/blocks or divided into sub-modules/sub-units/sub-blocks despite their physical organization or storage. It will be understood that when a unit, engine, module or block is referred to as being “on,” “connected to,” or “coupled to,” another unit, engine, module, or block, it may be directly on, connected or coupled to, or communicate with the other unit, engine, module, or block, or an intervening unit, engine, module, or block may be present, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. These and other features, and characteristics of the present disclosure, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, may become more apparent upon consideration of the following description with reference to the accompanying drawings, all of which form a part of this disclosure. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended to limit the scope of the present disclosure. It is understood that the drawings are not to scale. The following description is provided to help better understand methods or systems in the present disclosure. The imaging system described below may be applied in imaging, such as disease diagnosis and research, as well as industry. The imaging system may be a single-modality system, or a multi-modality system, including but not limited to a computed tomography (CT) system, a positron emission tomography (PET) system, a magnetic resonance imaging (MRI) system, an ultrasound scan (US) system, a single-photon emission computed tomography (SPECT) system, PET-CT, US-CT, PET-MRI or the like, or a combination thereof. The system and method disclosed herein may track and/or correct the focus position of a radiation source in an imaging device. The focus position of the radiation source (or referred to as a radiation generator) may shift due to, e.g., heat generated by the imaging device or a portion thereof, e.g., by the radiation source. Merely by way of example, the imaging device is a CT scanner, and the radiation generator of the CT scanner includes an X-ray tube. FIG. 1 is a schematic diagram illustrating an exemplary imaging system according to some embodiments of the present disclosure. The imaging system 100 may scan a target object, and generate an image related to the target object based on scanning signals. In some embodiments, the imaging system 100 may be a medical imaging system. The imaging system 100 may include a data acquisition device 101, a high voltage generator 102, a controller 103, a focus position tracker 104, a data processing device 105, and storage 106. The data acquisition device 101 may scan a target object, and obtain corresponding scanning signals. The data acquisition device 101 may be a computed tomography (CT) scanner, a positron emission tomography (PET) scanner, a magnetic resonance imaging (MRI) scanner, a medical electronic endoscope (MEE), or the like, or any combination thereof. In some embodiments, the data acquisition device 101 may be a CT device. Merely for illustration purposes, the data acquisition device 101 may be a CT device. The data acquisition device 101 may include a table 107, a radiation generator 108, a detector 109, and a gantry 110. The table 107 may support a target object (e.g., a patient to be diagnosed). During a CT scanning, the table 107 may move the target object to a specific location (e.g., a circular chamber of the gantry 110). The gantry 110 may support the radiation generator 108 and the detector 109. In some embodiments, the gantry 110, or a part thereof, may rotate around a rotation axis, thereby enabling the radiation generator 108 and the detector 109 to rotate around the target object. The radiation generator 108 may emit rays toward the target object. Typical rays may include an X-ray, neutrons, protons, heavy ions, or the like, or any combination thereof. The CT device may scan the target object by emitting rays from the radiation generator 108, and may obtain scanning data. During the scanning, the rays may penetrate the target object, and CT image data may be generated after the rays are detected by the detector 109. As an example, the radiation generator 108 may include an X-ray tube. The detector 109 may be have the shape of an arc. In some embodiments, the detector 109 may be a single-row detector or a multi-row detector. The multi-row detector may refer to a detector including multiple rows of detection units along the Z direction. In some embodiments, the detector 109 may include a plurality of channels arranged along the circumferential direction of the chamber of the gantry 110, each of which may receive X-rays of particular angles. The X-ray tube may rotate around the rotation axis of the gantry 110. During the CT scanning, a focus position of the X-ray tube may offset from an initial position due to heat generated by the X-ray tube. In some embodiments, when the CT data acquisition device scans air and a human body, respectively, in different scans corresponding focus positions of the X-ray tube may be different, which may lead to an error in the response of the detector 109. If air scan data containing the error is used to process human scan data to reconstruct an image, artifacts may occur. A response of the detector 109 may represent the intensity of a beam (X-ray) detected by the detector 109. In some embodiments, the focus position may be obtained through measurements. In some embodiments, a first focus position may be determined by the focus position tracker 104 based on response signals detected by one or more detection units of the detector 109. As used herein, a response signal may refer to a signal detected by, e.g., the detector 109. In some embodiments, a channel of the detector 109 may be operably coupled to one or more detection units (e.g., a detection unit column illustrated in FIG. 2) so as to receive X-rays of particular angles incident on the one or more detector units. The high voltage generator 102 may generate high voltage or heavy current. In some embodiments, the high voltage or the heavy current generated by the high voltage generator 102 may be transmitted to the radiation generator 108 for generating rays. The controller 103 may be associated with the data acquisition device 101, the high voltage generator 102, the focus position tracker 104, and/or the data processing device 105. In some embodiments, the controller 103 may control the data acquisition device 101 to scan a target object when the focus of the X-ray tube is located at different focus positions. For example, the controller 103 may control the radiation generator 108 and the detector 109 to rotate around the Z axis. In some embodiments, the controller 103 may control the data processing device 105 to perform data or image processing. As another example, the controller 103 may control the data processing device 105 to retrieve response signals from the storage 106, and reconstruct a CT image based on the response signals. In some embodiments, the controller 103 may control the data processing device 105 to acquire response signals directly from the detector 109, and reconstruct a CT image based on the response signals. The controller 103 may be a control element or a device. For example, the controller 103 may be a microcontroller unit (MCU), a central processing unit (CPU), a programmable logic device (PLD), an application specific integrated circuits (ASIC), a single chip microcomputer (SCM), a system on a chip (SoC), etc. The focus position tracker 104 may process and analyze input data to generate a processing result. For example, the focus position tracker 104 may process and analyze a parameter of the X-ray (e.g., the X-ray intensity) detected by the detector 109 to determine a focus position of the radiation generator 108. When the radiation generator 108 is an X-ray tube, the focus position tracker 104 may determine a focus position of the X-ray tube. During a CT scanning, the focus position tracker 104 may acquire response signals detected by the detector 109, determine a focus position of the X-ray tube based on the response signals, and store the response signals and the corresponding focus position in, e.g., the storage 106. In some embodiments, the focus position tracker 104 may be implemented on a server, or a server group. The server group may be centralized, for example, a data center. The server group may also be distributed, for example, a distributed system. The focus position tracker 104 may be implemented on a cloud server, a file server, a database server, an FTP server, an application server, a proxy server, a mail server, or the like, or any combination thereof. The focus position tracker 104 may be local or remote. In some embodiments, the focus position tracker 104 may include a storage device for storing data (e.g., the X-ray intensity detected by the detector 109, etc.) collected by the data acquisition device 101, programs that the focus position tracker 104 operates, and/or various data generated during operation of the focus position tracker 104. The focus position tracker 104 may access information (e.g., a correction table) stored in the storage device during the operation. The data processing device 105 may perform data processing, including, e.g., image processing. For example, during an air scan or the scanning of a patient, the data processing device 105 may process response signals detected by the detector 109 (or referred to as detector responses) corresponding to different focus positions, and may calibrate focus position offsets. Different focus positions and the detector responses corresponding to the different focus positions may be obtained by the focus position tracker 104 and may be stored in the storage 106. The data processing device 105 may access the storage 106 to acquire different focus positions and the detector responses corresponding to the different focus positions, and may process the acquired focus positions and detector responses. As another example, the data processing device 105 may determine response signals of the detector 109 by calculation, and may reconstruct an image based on the response signals. In some embodiments, the data processing device 105 may receive data from the storage 106 or an external data source, and may process the received data. The external data source may include one or more kinds of a hard disk, a USB storage, an optical disk, a flash memory, a cloud disk, etc. The data processing device 105 may including one or more processing elements, such as a central processing unit (CPU), a digital signal processor (DSP), a graphics processing unit (GPU), etc. In some embodiments, the data processing device 105 may also be a specialized processing element or device with a particular function. The data processing device 105 may be a local device, such as a console, a desktop computer, a local server, a cloud server with a data/image processing function, etc. The data processing device 105 may transmit a processing result (e.g., a reconstructed CT image) to the storage 106. The storage 106 may store information. The information may include scan data (e.g., detector response), a focus position corresponding to the scan data, a reconstructed image, a parameter input by a user, a data processing algorithm, or the like. The information stored in the storage 106 may be in the form of text, digits, audio, an image, or the like, or a combination thereof. In some embodiments, the storage 106 may store data (e.g., a parameter of X-ray detected by the detector 109, such as the X-ray intensity) collected from the CT device, programs the focus position tracker 104 operates, and various data generated during the operations of the focus position tracker 104. The focus position tracker 104 may access information (e.g., a mapping table) stored in the storage device during the operations. The storage 106 may also store instructions or codes executed by the data processing device 105 and/or the controller 103. When the data processing device 105 and/or the controller 103 execute the codes, the data processing device 105 may be caused to execute one or more functions of the imaging system 100 disclosed in the present disclosure. The storage 106 may include but not limited to various types of storage devices, such as a solid-state disk, a mechanical hard disk, a universal serial bus (USB), flash, a secure digital (SD) memory card, an optical disk, a random-access memory (RAM), a read-only memory (ROM), etc. In some embodiments, the storage 106 may be an internal storage device of the system, an external storage device of the system, a network storage device outside the system (e.g., a storage of a cloud storage server, etc.), or the like. Components in the imaging system 100 may be connected in wired or wireless manner. In some embodiments, the components in the imaging system 100 may be connected via a network. The network may include a local area network, a wide area network, a public network, a private network, a wireless local area network, a virtual network, a metropolitan area network, a public switched telephone network, or the like, or any combination thereof. For example, a network may use WIFI, Bluetooth, ZigBee, and/or other protocols to communicate. In some embodiments, the network may include a variety of network access points, for example, a wired or wireless access point, a base station or a network exchange point, or the like, or a combination thereof. Through an access point, a data source may be connected to the network and send information via the network. In some embodiments, the imaging system 100 may also communicate with an external device (e.g., a database, a terminal, an input/output interface, etc.). In some embodiments, the high voltage generator 102 in the imaging system 100 may be included in the data acquisition device 101. FIG. 2 is a schematic diagram illustrating an exemplary data acquisition device according to some embodiments of the present disclosure. As an example, the data acquisition device 101 may be a CT scanner. The CT scanner may include an X-ray tube 201, a front collimator 202, a detector 206, a post collimator 207, and a scanning table 204. The X-ray tube 201 may generate X-ray, which may pass through the front collimator 202, pass through a scan object 203 (e.g., air, a phantom, or a patient), and impinge on the detector 206. The front collimator 202 may control a width of the X-ray beam in z direction shown in FIG. 2, so as to determine the thickness of a scan layer. The detector 206 may include a detection unit array (including, for example, a detection unit 205). As shown in FIG. 2, detection units arranged along an x direction may be referred to as a detection unit column, and detection units arranged along the z direction may be referred to as a detection unit row. The radiation intensity of an X-ray beam received by the detector 206 may relate to the attenuation of the X-ray beam when passing through the scan object 203. Each detection unit of the detector 206 may generate a separate electric signal. The separate electric signal may represent a measured value of the beam received by each detection unit. Imaging may be achieved by obtaining the measured values from all of the detection units, respectively. The post collimator 207 may decrease the interference of scattered rays on the detector 206. The post collimator 207 may be mounted above the detector 206, and be in a position close to the upper surface of the detector 206. The post collimator 207 may also be mounted on the upper surface of the detector 206. During a CT scanning, an X-ray tube rotation shaft may thermally expand due to heat accumulation, resulting in a focus position offset or shift, which in turn may affect the imaging process. For example, the focus of the X-ray tube 201 may be at a first focus position during the scanning of a reference object and at a second focus point during the scanning of a target object. If the first focus position is different from the second focus position, the reconstructed image of the target object may be affected. The system and method described in the present disclosure may be used to mitigate or eliminate adverse effects caused by the offset between the first focus position and the second focus position. The reference object may include air, a phantom, etc. The phantom may be a water phantom, an organic glass phantom, etc. The target object may include a patient, a phantom, etc. FIG. 3 is a flowchart illustrating an exemplary process for calibrating a focus position offset according to some embodiments of the present disclosure. In 301, a correction table may be obtained. In some embodiments, during the scanning of a reference object, the correction table may record the correspondence between different focus positions of the X-ray tube and detector responses. The reference object may include air, a phantom, etc. The phantom may be a water phantom, an organic glass phantom, etc. The following description is made with reference to a reference object of air for illustration purposes, and not intended to limit the scope of the present disclosure. In some embodiments, the imaging system 100 may obtain a correction table from one or more external devices (e.g., a database, a terminal, etc.), or an internal storage device or element (e.g., the storage 106). In some embodiments, the correction table may be input by a user. In some embodiments, the imaging system 100 may scan the reference object using the data acquisition device 101, acquire a plurality of detector responses and the corresponding focus positions, and generate a correction table. Merely by way of example, when the data acquisition device 101 scans air or a phantom, the focus position tracker 104 may obtain focus positions, and record the focus positions and corresponding detector responses in the correction table. In some embodiments, one or more focus positions in the present disclosure may be acquired by the focus position tracker 104 using devices or methods illustrated in FIGS. 4 through 12. For example, the focus position tracker 104 may determine a focus position according to a response signal detected by the detector. In some embodiments, the focus positions may be determined in other manners. If the correction table already exists, the imaging system 100 may skip the operation of acquiring a correction table. In 302, a first detector response corresponding to a first focus position may be acquired by scanning a reference object. The reference object herein may be the same as or different from the reference object used for determining the correction table. For example, the reference object used for determining the correction table may be a phantom, and the reference object herein may be a phantom or air. Merely by way of example, the data acquisition device 101 may perform an air scan (or referred to as air calibration) before scanning a human body, and acquire a first detector response of the air calibration. The first detector response may correspond to a first focus position. The first focus position may refer to a focus position of the X-ray tube 201 when the data acquisition device 101 scans a reference object. In some embodiments, during the scanning of the reference object, the focus position tracker 104 may obtain the first response signal of the detector, and determine the first focus position corresponding to the first response signal. In 303, a second detector response corresponding to a second focus position may be acquired by scanning a target object. The target object may be a patient. The data acquisition device 101 may scan a certain part (e.g., an organ, such as a lung, a kidney, etc.) or a whole body of the patient, and acquire a second detector response. The second detector response may correspond to a second focus position. The second focus position may refer to a focus position of the X-ray tube 201 when the data acquisition device 101 scans a patient. In some embodiments, during the scanning of a patient, the focus position tracker 104 may acquire the second response signal of the detector, and determine the second focus position corresponding to the second response signal. In 304, a third detector response corresponding to the first focus position and a fourth detector response corresponding to the second focus position may be determined by consulting the correction table. In some embodiments, the correction table may include the first focus position and/or the second focus position. The imaging system 100 may retrieve the third detector response corresponding to the first focus position and/or the fourth detector response corresponding to the second focus position from the correction table. In some embodiments, the correction table does not include the first focus position and the second focus position. The imaging system 100 may determine the third detector response corresponding to the first focus position and/or the fourth detector response corresponding to the second focus position using one or more processing techniques. The one or more processing techniques may include interpolation, linear fitting, non-linear fitting, or the like. In 305, a calibration value may be determined based on the third detector response and the fourth detector response. In some embodiments, the calibration value may be a ratio, a product, a difference value, or a result of a power exponent function, or the like. The calibration value may be obtained by performing an operation on the third detector response and/or the fourth detector response. In some embodiments, the calibration value may be a difference value between the fourth detector response and the third detector response. In some embodiments, the calibration value may be a ratio of the fourth detector response to the third detector response. In 306, the first detector response may be calibrated based on the calibration value. In some embodiments, the data processing device 105 may calibrate the first detector response based on the calibration value. For example, when the calibration value is a difference value between the fourth detector response and the third detector response, the data processing device 105 may generate a calibrated first detector response by adding the difference value to the first detector response. As another example, when the calibration value is a ratio of the fourth detector response to the third detector response, the data processing device 105 may generate a calibrated first detector response by multiplying the ratio by the first detector response. In some embodiments, the calibration value may be generated in other manners. Moreover, a conversion may be performed considering a relationship between the scanned objects corresponding to the correction table and the first focus position, respectively. In 307, image data of the target object may be determined based on the calibrated first detector response and the second detector response. The data processing device 105 may determine the image data of the target object based on the calibrated first detector response and the second detector response. The data processing device 105 may reconstruct an image based on the imaging data. Exemplary CT reconstruction algorithms may include a filtered back protrusion reconstruction algorithm, a Radon inversion algorithm, a unary function Hilber transform algorithm, an iterative reconstruction algorithm, or the like. Merely for illustration purposes, the imaging system 100 may determine a correction table. The correction table may record a plurality of detector responses Detresp n (n=1, 2, 3 . . . ) and a plurality of focus positions Sp n=1, 2, 3 . . . ) corresponding to the plurality of detector responses Detresp n (n=1, 2, 3 . . . ), respectively. When the data acquisition device 101 scans a first reference object, the focus positions Sp n and the corresponding detector responses Detresp n may be recorded in the correction table. When the data acquisition device 101 scans a second reference object, a first detector response Detresp_sp_obj corresponding to a focus position Sp_obj may be obtained. The second reference object may be the same as or different from the first reference object. For example, the first reference object may be air, and the second reference object may be a phantom. As another example, the first reference object may be a phantom, and the second reference object may be air. As a further example, the first reference object may be air, and the second reference object may also be air. As still a further example, the first reference object and the second reference object may be phantoms of different materials. When the data acquisition device 101 scans a patient, a second detector response Detresp_sp_raw corresponding to a focus position Sp_raw may be obtained. By consulting the correction table and/or performing an interpolation, the data processing device 105 may obtain a third detector response Detresp_sp_obj_table corresponding to the focus position Sp_obj in the correction table, and a fourth detector response Detresp_sp_raw_table corresponding to the focus position Sp_raw in the correction table. Based on the detector response Detresp_sp_raw_table and the detector response Detresp_sp_obj_table, the data processing device 105 may determine a calibration value D according to Equation (1):D=Detresp_sp_raw_table−Detresp_sp_obj_table. (1)A calibrated first detector response new Detresp_sp_obj may be determine according to Equation (2):new Detresp_sp_obj=D+Detresp_sp_obj. (2)The data processing device 105 may obtain image data corresponding to the target object based on the calibrated first detector response and the second detector response, and reconstruct an image based on the image data. Merely for illustration purposes, the imaging system 100 may determine a correction table. When the data acquisition device 101 scans a first reference object, detector responses Detresp n (n=1, 2, 3 . . . ) and corresponding focus positions Sp n (n=1, 2, 3 . . . ) may be recorded in the correction table. When the data acquisition device 101 scans a second reference object, a first detector response Detresp_sp_obj corresponding to a focus position Sp_obj may be obtained. When the data acquisition device 101 scans a patient, a second detector response Detresp_sp_raw corresponding to a focus position Sp_raw may be obtained. By consulting the table and/or performing an interpolation, the data processing device 105 may obtain a third detector response Detresp_sp_obj_table corresponding to the focus position Sp_obj, and a fourth detector response Detresp_sp_raw_table corresponding to the focus position Sp_raw. According to the detector response Detresp_sp_raw_table and the detector response Detresp_sp_obj_table, the data processing device 105 may determine a calibration value R according to Equation (3):R=Detresp_sp_raw_table/Detresp_sp_obj_table (3)A calibrated first detector response may be determined according to Equation (4):new Detresp_sp_obj=R·Detresp_sp_obj. (4)The data processing device 105 may obtain image data corresponding to the target object based on the calibrated first detector response and the second detector response, and reconstruct an image based on the image data. In some embodiments, one or more focus positions described in the present disclosure may be tracked or determined by a collimator. The collimator may be used to determine a focus position offset of the X-ray tube 201 along the z direction as shown in FIG. 2. The collimator described in the present disclosure may track the focus position of the X-ray tube when a reference object and a target object are scanned, respectively so that errors introduced by an offset of the focus position may be corrected by eliminating or mitigating artifacts caused by the offset of the focus position. The collimator may include one or more openings. The collimator may have a certain width in a first direction (e.g., the z direction shown in FIG. 2), and a certain length in a second direction (e.g., the x direction shown in FIG. 2). The opening may have a plurality of opening widths in the first direction. An opening width corresponding to at least one end of the opening may be smaller than an opening width corresponding to a middle section of the opening. The opening width may refer to a width of the opening in the first direction. In some embodiments, opening widths corresponding to different sections of the opening or the collimator along the second direction may be different. For example, referring to FIGS. 4A-4F and FIGS. 5A-5F, the collimator may have one opening. An opening at at least one end of the collimator in the length direction (i.e., the x direction) may have an opening width smaller than that of an opening within a middle section of the collimator in the length direction. As used herein, the middle section may refer to a position or a portion including and/or in the vicinity of a center of the collimator (e.g., 530a in FIG. 5A) relative to the left end and the right end of the collimator. For instance, the middle section of the collimator may be a portion of, e.g., half, a third, a fourth, a fifth, of the entire length of the collimator in the middle of the collimator along the length direction of the collimator. In some embodiments, the collimator may have a plurality of openings. The opening width may refer to a width of one opening in the first direction, or a sum of the widths of the plurality of openings in the first direction. For example, referring to FIG. 11, a collimator 1100 has three openings 1101, 1102, and 1103. The opening width may refer to a width of the opening 1101, 1102, or 1103. The opening width may also refer to a sum of widths of the opening 1101, 1102, and 1103. In some embodiments, a single opening, e.g., an opening 530a in FIG. 5A, may be continuous in its width direction (i.e., the first direction). In some embodiments, a single opening, e.g., an opening 1201 in FIG. 12, may be discontinuous in its width direction, and the opening width may be a sum of several discontinuous widths. Referring to FIG. 12, a collimator 1200 may have an opening 1201. The opening width corresponding to an end of the opening 1201 in the second direction (i.e., the x direction) may be discontinuous. The opening width corresponding to the end of the opening 1201 in the second direction may be Σ di, where Σ represents a summation operator, di represents a distance between two adjacent protrusions, and i=1, 2, . . . , 7. In some embodiments, a collimator may be made of a material with a large density (e.g., plumbum) for shielding X-ray. In some embodiments, the collimator described in the present disclosure may take the form of a blade. For instance, the front collimator 202 may include a blade. At least one end of the blade along the second direction (i.e., the x direction) may have one or more protrusions. The protrusions may protrude into an opening included in the blade. A gap may be formed between two protrusions. The one or more protrusions may be formed as one-piece with or an integral part of the blade, or removably attached to the blade. FIGS. 4A to 4F are top views of exemplary collimators according to some embodiments of the present disclosure. The x direction and the z direction shown in FIG. 4A may correspond to the x direction and the z direction shown in FIG. 2, respectively. The blade may include a pair of blocks disposed opposite to each other (e.g., a block 440 and a block 450), which may define an opening (e.g., an opening 430a, 430b, 430c, 430d, 430e, or 430f). The blocks may shift along the first direction (e.g., the z direction of FIG. 4A) to determine a width of the opening. In some embodiments, at least one of the blocks (e.g., a block 440 and/or a block 450) may have a protrusion (e.g., protrusions 421, 422, 423, or 424) at at least one end in the second direction (e.g., the x direction shown in FIG. 4A), and the protrusion may protrude into the opening, and thus an opening at at least one end of the blade in the second direction may have an opening width smaller than that of an opening within a middle section of the blade in the second direction. For example, a cross-section of the block 440 (or the block 450) in the x-z plane may be of a concave shape, an “L” shape, or the like. In some embodiments, an opening width corresponding to a section of an opening of the collimator in the second direction may be referred to as a width at a position of the opening along the second direction formed by blocks arranged opposite to each other. For example, as shown in FIG. 4A, both ends of blocks 440 and 450 in the second direction (e.g., the x direction shown in FIG. 4A) may extend into the opening 430a, forming four protrusions (e.g., the protrusions 421, 422, 423, or 424). As another example, as shown in FIG. 4B, one end of the block 440 (or the block 450) in the second direction may extend into the opening 430b, forming a protrusion (e.g., the protrusion 422). Both ends of the block 450 (or the block 440) in the second direction may extend into the opening 430b, forming two protrusions (e.g., the protrusions 423, or 424). As another example, as shown in FIG. 4C, the ends of the block 440 and the block 450 at a same side in the second direction may extend into the opening 430c, respectively, each forming one protrusion (e.g., the protrusions 422 and 424). As another example, as shown in FIG. 4D, an end of the block 440 and an end of the block 450 on different sides in the second direction may extend into the opening 430d, respectively, each forming one protrusion (e.g., the protrusions 421 and 424). As a further example, as shown in FIG. 4E, both ends of the block 450 (or the block 440) in the second direction may extend into the opening 430e, forming two protrusions (e.g., the protrusions 423 and 424). As still a further example, as shown in FIG. 4F, one end of the block 450 (or the block 440) in the second direction may extend into the opening 430f, forming one protrusion (e.g., the protrusion 424). In some embodiments of the present disclosure, the collimator may have a substantially rectangular or square opening. At least one corner of the opening may include a protrusion that may protrude into the opening. FIG. 5A to FIG. 5F are top views of exemplary collimators according to some embodiments of the present disclosure. The collimators in FIGS. 5A through 5F may include a body of a same shape, for example, illustrated as the body 510. The x direction and z direction shown in FIG. 5A may correspond to the x direction and z direction shown in FIG. 2, respectively. The blade may include a plurality of openings with different widths (see, e.g., FIG. 11) along the first direction (e.g., the z direction shown in FIG. 5A). Among the plurality of openings of different widths, at least one of the plurality of openings may have a different width along the second direction (e.g., the x direction shown in FIG. 5A) relative to other openings of the plurality of openings. Further, a middle section of at least one of the openings in the second direction may have a greater width than that of at least one end in the second direction. As shown in FIGS. 5A-5F, for an opening having a width changing along the second direction (e.g., the x direction shown in FIG. 5A), at least one end of the blade in the second direction may extend into the opening to form one or more protrusions (e.g., protrusions 521, 522, 523 and/or 524), and thus an opening within a middle section of the blade in the second direction may have an opening width greater than that of an opening at at least one end of the blade in the second direction. In some embodiments, an opening width corresponding to a section of an opening of the collimator along the second direction may be referred to as a width corresponding to the section of the opening of a plurality of openings along the second direction. The plurality of openings may have different widths in the first direction. For example, as shown in FIG. 5A, both ends of the blade in the second direction may extend into an opening 530a, forming four protrusions (e.g., protrusions 521, 522, 523, and 524). As another example, as shown in FIG. 5B, one end of the blade in the second direction may extend into an opening 530b, forming two protrusions (e.g., protrusions 521 and 523). The other end of the blade in the second direction may extend into the opening 530b, forming another protrusion (e.g., a protrusion 524). As another example, as shown in FIG. 5C or FIG. 5D, both ends of the blade in the second direction may extend into an opening 530c (or 530d), forming two protrusions (e.g., protrusions 523 and 524 in FIG. 5C, or protrusions 521 and 524 in FIG. 5D). As a further example, as shown in FIG. 5E, one end of the blade in the second direction may extend into an opening 530e, forming two protrusions (e.g., protrusions 521 and 523). As still a further example, as shown in FIG. 5F, one end of the blade in the second direction may extend into an opening 530f, forming a protrusion (e.g., a protrusion 521). The blades shown in FIGS. 4A-4F and FIGS. 5A-5F may be implemented in the front collimator 202. The protrusions of the blades may shield one or more detection units located around the edges of the detector 206 in the second direction, while leave detection units within a middle section of the detector 206 in the second direction unshielded, thereby improving X-ray efficiency and image quality. When a focus position of the X-ray tube 201 shifts, the intensity of the X-ray impinging on the shielded detection units located around the edges of the detector 206 in the second direction may be reduced. A signal-noise ratio of the beam intensity variation, which may indicate the sensitivity of the beam intensity variation when the focus position is tracked, may be effectively improved due to the protrusions set at at least one corner of the opening of the collimator, thereby improving an accuracy for tracking the focus position. The second direction of the detector 206 may be the same as the second direction of the collimator. According to some embodiments of the present disclosure, the collimator may include an anti-scatter grid. For instance, the post collimator 207 may include an anti-scatter grid. FIG. 6A to FIG. 6C are top views of exemplary collimators according to some embodiments of present disclosure. The x direction and z direction shown in FIG. 6A may correspond to the x direction and z direction shown in FIG. 2, respectively. As shown in FIG. 6A to FIG. 6C, the anti-scatter grid may include a plurality of sub-openings. Each sub-opening may correspond to one or more detection units of the detector 206. For example, as shown in FIG. 6A, an anti-scatter grid may have a plurality of sub-openings (e.g., sub-openings 630a and 640a), and each sub-opening may correspond to a detection unit. As another example, as shown in FIG. 6B, an anti-scatter grid may have a plurality of sub-openings (e.g., a sub-opening 630b), and each sub-opening may correspond to a column of detection units. As still another example, an anti-scatter grid may have a plurality of sub-openings (e.g., sub-openings 630c and 640c illustrated in FIG. 6C), and each sub-opening in a beam direction may correspond to a row or a column of detection units or a detection unit. The anti-scatter grid may include a body (e.g., a body 610a, 610b, or 610c), and a plurality of protrusions (e.g., a protrusion 620). In some embodiments, the lengths of the protrusions (e.g., the protrusion 620) in the second direction (e.g., the x direction shown in FIG. 6A) may be the same as or smaller than the lengths of the sub-openings (e.g., the sub-opening 630a) in the second direction. Merely for illustration purposes, as illustrated in FIG. 6A, the length 650a of the protrusion 620 may be the same as or smaller than the length 660a of the sub-opening 630a. The plurality of protrusions may be located on the edges of the body in the first direction (e.g., the z direction shown in FIG. 6A), and the plurality of protrusions may be arranged along the first direction. Due to the presence of the protrusions, an opening including a plurality of sub-openings at at least one end of the anti-scatter grid in the second direction (e.g., 630a in FIG. 6A) may have an opening width smaller than that of an opening within a middle section of the anti-scatter grid in the second direction (e.g., 640a in FIG. 6A). In some embodiments, an opening width of the collimator in the second direction may refer to a width of an opening of a plurality of sub-openings in the anti-scatter grid along the second direction. For example, as shown in FIG. 6A, a width of the sub-opening 630a in the first direction (i.e., the z direction) may be smaller than a width of the sub-opening 640a in the first direction. As shown in FIG. 6B, a width of the sub-opening 630b in the first direction (i.e., the z direction) may be smaller than a width of the sub-opening 640b in the first direction. As shown in FIG. 6C, a width of the sub-opening 630c in the first direction may be smaller than a width of the sub-opening 640c in the first direction. As still another example, as shown in FIG. 6A, a sum of widths of sub-openings at one end of the anti-scatter grid in the second direction (e.g., a sum of opening widths of eight sub-openings in a row along the upper end of the body 610a) may be smaller than a sum of widths of sub-openings within a middle section of the anti-scatter grid in the second direction (e.g., a sum of opening widths of eight sub-openings in a row within a middle section of the body 610a). Merely for illustration purposes as illustrated in FIG. 6A, the anti-scatter grid may include six rows of sub-openings from the upper end to the lower end, and each row may have eight sub-openings. The total widths of a row of sub-openings at the upper end or the lower end may be smaller than the total widths of any one of the four rows of sub-openings between the upper end and the lower end due to the presence of the protrusions in the sub-openings at both the upper end and the lower end of the anti-scatter grid. The middle section may refer to a position or a portion including and/or in the vicinity of a center of the body 610a relative to the upper end and the lower end of the body 610a. For instance, the middle section of the collimator may be a portion of, e.g., half, a third, a fourth, a fifth, of the entire length of the collimator in the middle of the collimator along the length direction (i.e., the x direction in FIG. 6A) of the collimator. The sub-openings at the end of the anti-scatter may correspond to a row of detection units. The sub-openings within the middle section of the anti-scatter may correspond to another row of detection units. As shown in FIG. 6B, a sum of widths of sub-openings at one end of the anti-scatter grid in the second direction (e.g., a sum of opening widths of eight sub-openings along the upper end of the body 610b) may be smaller than a sum of widths of sub-openings within a middle section of the anti-scatter grid in the second direction (e.g., a sum of opening widths of eight sub-openings within a middle section of the body 610b). The sub-openings at the end of the anti-scatter may correspond to a row of detection units. The sub-openings within the middle section of the anti-scatter may correspond to another row of detection units. As shown in FIG. 6C, a sum of widths of sub-openings at one end of the anti-scatter grid in the second direction may be smaller than a sum of widths of sub-openings, including an opening 640c, within a middle section of the anti-scatter grid in the second direction. The middle section may refer to a position or a portion including and/or in the vicinity of a center of the body 610c relative to the upper end and the lower end of the body 610c. The sub-openings at the end of the anti-scatter may correspond to a row of detection units. The sub-openings within the middle section of the anti-scatter may correspond to another row of detection units. Each protrusion may be used for partially shielding an edge detection unit. An edge detection unit may refer to a detection unit located at an edge of the detector in the second direction. The detector may include multiple edge detector units positioned next to each other along the first direction (i.e., the z direction). For example, the edge detection units may include two rows of detection units of outermost layers of the detector 206 along the x direction, four rows of detection units of outermost layers of the detector 206 along the x direction, or six rows of detection units of outermost layers of the detector 206 along the x direction. In some embodiments, the sizes of the edge detection units in the second direction (also referred to as “x direction”) may correspond to the sizes of the protrusions in the second direction. As used herein, “correspond to” may indicate that an edge detection unit may be at least partially shielded by a protrusion in a beam direction. In some embodiments, the second direction may be perpendicular to the first direction. In some embodiments, each protrusion may partially shield an edge detection unit of the edge detection units. For example, each protrusion 620 may shield a left part of an edge detection unit as shown in FIGS. 6A-6C of the edge detection units. In some embodiments, each protrusion may also shield other parts of a detection unit of the edge detection units. The one or more protrusions may be formed as one-piece with or an integral part of the body, or removably attached to the body. In some embodiments, the protrusions may be directly connected to the body. In some embodiments, the protrusions, or may be attached to the body through a braced structure connected to the body. The post collimator 207 may include an anti-scatter grid structure shown in any one of FIGS. 6A-6C. A protrusion of the anti-scatter grid may shield a part of an edge detection unit of the detector 206 in the second direction. When a focus position of the X-ray tube 201 shifts, the intensity of the X-ray impinging on the shielded detection units located around the edges of the detector 206 in the second direction may be reduced. A signal-noise ratio of the beam intensity variation may be effectively improved, thereby improving an accuracy for tracking the focus position. FIG. 7 is a block diagram of a focus position tracker 104 according to some embodiments of the present disclosure. In some embodiments, a collimator (e.g., the collimator described in FIGS. 4A-4F, FIGS. 5A-5F or FIGS. 6A-6C) for tracking a focus position of the X-ray tube described in the present disclosure may partially shield edge detection units of the detector 206. When the focus position of the X-ray tube 201 shifts, the X-ray detected by the edge detection units may change accordingly. For instance, the X-ray intensity distribution may be changed. The focus position tracker 104 may include an intensity determination module 710 and a focus position determination module 720 to determine, for example, the X-ray intensity distribution and a focus position. Thus, offsets of the focus position may be determined based on the changes of the X-ray detected by the edge detection units. The intensity determination module 710 may determine X-ray intensity information. For example, X-ray intensity information may include a first boundary intensity and a second boundary intensity detected by edge detection units, and an X-ray intensity distribution detected by edge detection units. The edge detection units may refer to detection units located at an edge of the detector in the second direction. The X-ray intensity distribution detected by the edge detection units may represent a distribution of detection units that have detected X-ray emitted from the X-ray tube 201, when a focus of the X-ray tube 201 is located at a certain position. The X-ray intensity distribution detected by the edge detection units may also represent a distribution of X-ray intensity detected by each edge detection unit, when a focus of the X-ray tube is located at a certain position. The X-ray intensities detected by edge detection units located at two ends of a same row may be the first boundary intensity and the second boundary intensity of the X-ray intensity distribution, respectively. The boundary may correspond to a farthest detection unit of detection units arranged in the first direction along which the X-ray irradiates. The focus position determination module 720 may determine a focus position according to the X-ray intensity information. For example, the focus position determination module 720 may determine, according to a geometric relationship, an offset between an initial focus position and an offset focus position based on a first X-ray intensity distribution detected by edge detection units and a second X-ray intensity distribution detected by edge detection units. The first X-ray intensity distribution may correspond to the initial focus position. The second X-ray intensity distribution may correspond to the offset focus position. As another example, the focus position determination module 720 may determine, according to a mapping table, a current focus position (e.g., the offset focus position) of the X-ray tube 201 based on a ratio of a first boundary intensity to a second boundary intensity that are detected by the edge detection units. FIG. 8 is a flowchart illustrating an exemplary process for tracking a focus position according to some embodiments of the present disclosure. In 810, the intensity determination module 710 may obtain a first X-ray intensity distribution corresponding to the initial focus position of the X-ray tube 201. The first X-ray intensity distribution may be detected by one or more edge detection units. The first X-ray intensity distribution may represent a distribution of detection units that have detected X-ray emitted from the X-ray tube 201, when the focus of the X-ray tube 201 is located at an initial focus position. In 820, the intensity determination module 710 may obtain a second ray intensity distribution corresponding to the offset focus position of the X-ray tube 201. The second ray intensity distribution may be detected by one or more edge detection units. The second ray intensity distribution may represent a distribution of detection units that have detected X-ray emitted from the X-ray tube 201, when the focus of the X-ray tube 201 is located at an offset focus position. In 830, the focus position determination module 720 may determine an offset between the initial focus position and the offset focus position based on the first X-ray intensity distribution and the second X-ray intensity distribution. The focus position determination module 720 may determine a first detection unit located at one end of a row of detection units in the first X-ray intensity distribution, and a second detection unit located at the same end of the same row of detection units in the second X-ray intensity distribution. The focus position determination module 720 may determine the offset between the initial focus position and the offset focus position based on a distance between the first detection unit and the second detection unit. The distance between the first detection unit and the second detection unit may refer to a distance between the geometric centers of the two detection units. The focus position determination module 720 may determine the offset between the initial focus position and the offset focus position according to a geometric relationship between the distance of the two detection units and the offset between the initial focus position and the offset focus position. A current focus position (i.e., the offset focus position) may be obtained. Merely by way of example, the x direction, the y direction, and the z direction shown in FIG. 9 may correspond to the x direction, the y direction, and the z direction shown in FIG. 2, respectively. As shown in FIG. 9, detection units 1-9 may constitute a detection unit row of the edge detection units. The first X-ray intensity distribution corresponding to the initial focus position 201a may be associated with detection units 1-7. The second ray intensity distribution corresponding to the offset focus position 201b may be associated with detection units 3-9. Therefore, an offset between the initial focus position 201a and the offset focus position 201b may be determined based on a distance between corresponding detection units associated with the first X-ray intensity distribution and the second X-ray intensity distribution, respectively (e.g., a distance between detection units 1 and 3, a distance between detection units 2 and 4, a distance between detection units 3 and 5, a distance between detection units 4 and 6, etc.). The movement between the initial focus position 201a and the offset focus position 201b may be determined according to Equation (5):AB=(BE×CD)/EF, (5)where AB may represent the offset between the initial focus position 201a and the offset focus position 201b, BE may represent a distance between the X-ray tube 201 and the front collimator 202, EF may represent a distance between the detector 206 and the front collimator 202, CD may represent a distance between a first detection unit that is located at the boundary in the first direction corresponding to the first X-ray intensity distribution and a second detection unit that is located at the same boundary in the first direction corresponding to the second X-ray intensity distribution. FIG. 10 is a flowchart illustrating an exemplary process for tracking a focus position according to some embodiments of the present disclosure. In 1010, the intensity determination module 710 may determine a first boundary intensity and a second boundary intensity that are detected by edge detection units. For example, as shown in FIG. 9, when the X-ray tube 201 is located at a current focus position 201a, the intensity determination module 710 may determine an X-ray intensity (e.g., the first boundary intensity) detected by a detection unit 1 and an X-ray intensity (e.g., the second boundary intensity) detected by a detection unit 7. In 1020, the focus position determination module 720 may determine an X-ray intensity relationship between the first boundary intensity and the second boundary intensity. In this example, the X-ray intensity relationship may include, but are not limited to, an X-ray intensity ratio, or one or more other mathematical relationships. The X-ray intensity ratio may be a ratio of the first boundary intensity to the second boundary intensity, or a ratio of the second boundary intensity to the first boundary intensity. Another exemplary mathematical relationship may be y=kx+z, where x and y may represent one of the first boundary intensity and the second boundary intensity, respectively, and z may be a constant. Other types of relationships may be conceived by those skilled in the art in light of the embodiments of the present disclosure. In 1030, the focus position determination module 720 may determine a focus position based on the X-ray intensity relationship. In some embodiments, the focus position determination module 720 may determine the focus position according to a mapping table, which may record focus positions and corresponding X-ray intensities. The mapping table may record multiple sets of mapping relationships. A set of mapping relationships may include a mapping relationship between a focus position of the X-ray tube and a ratio of a first boundary intensity to a second boundary intensity described in connection with 1010 and 1020. The mapping table may also record information of detection units corresponding to the first boundary intensity and the second boundary intensity, respectively. Given detection units corresponding to the first boundary intensity and the second boundary intensity, and a ratio of the first boundary intensity to the second boundary intensity, the focus position determination module 720 may determine a focus position corresponding to the ratio by consulting the mapping table. If data in the mapping table is insufficient, the focus position may be obtained using conventional techniques, such as interpolation, extrapolation, etc. The mapping table may be determined in advance. In some embodiments, the focus position tracker 104 may generate the mapping table automatically. In some embodiments, a user (e.g., a doctor, an imaging engineer, a manufacture of a CT scanner, etc.) may input the mapping table into the focus position tracker 104. In some embodiments, the mapping table may be stored in a storage device (e.g., the storage 106). The focus position determination module 720 may obtain the mapping table by accessing the storage device. Having thus described the basic concepts, it may be rather apparent to those skilled in the art after reading this detailed disclosure that the foregoing detailed disclosure is intended to be presented by way of example only and is not limiting. Various alterations, improvements, and modifications may occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested by this disclosure, and are within the spirit and scope of the exemplary embodiments of this disclosure. Moreover, certain terminology has been used to describe embodiments of the present disclosure. For example, the terms “one embodiment,” “an embodiment,” and/or “some embodiments” mean that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Therefore, it is emphasized and should be appreciated that two or more references to “an embodiment” or “one embodiment” or “an alternative embodiment” in various portions of this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the present disclosure. Further, it will be appreciated by one skilled in the art, aspects of the present disclosure may be illustrated and described herein in any of a number of patentable classes or context including any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof. Accordingly, aspects of the present disclosure may be implemented entirely hardware, entirely software (including firmware, resident software, micro-code, etc.) or combining software and hardware implementation that may all generally be referred to herein as a “unit,” “module,” or “system.” Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable media having computer readable program code embodied thereon. A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including electro-magnetic, optical, or the like, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that may communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer readable signal medium may be transmitted using any appropriate medium, including wireless, wireline, optical fiber cable, RF, or the like, or any suitable combination of the foregoing. Computer program code for carrying out operations for aspects of the present disclosure may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C#, VB. NET, Python or the like, conventional procedural programming languages, such as the “C” programming language, Visual Basic, Fortran 2103, Perl, COBOL 2102, PHP, ABAP, dynamic programming languages such as Python, Ruby and Groovy, or other programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider) or in a cloud computing environment or offered as a service such as a Software as a Service (SaaS). Furthermore, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed processes and methods to any order except as may be specified in the claims. Although the above disclosure discusses through various examples what is currently considered to be a variety of useful embodiments of the disclosure, it is to be understood that such detail is solely for that purpose, and that the appended claims are not limited to the disclosed embodiments, but, on the contrary, are intended to cover modifications and equivalent arrangements that are within the spirit and scope of the disclosed embodiments. For example, although the implementation of various components described above may be embodied in a hardware device, it may also be implemented as a software only solution, e.g., an installation on an existing server or mobile device. Similarly, it should be appreciated that in the foregoing description of embodiments of the present disclosure, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the various inventive embodiments. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed subject matter requires more features than are expressly recited in each claim. Rather, inventive embodiments lie in less than all features of a single foregoing disclosed embodiment. In some embodiments, the numbers expressing quantities or properties used to describe and claim certain embodiments of the application are to be understood as being modified in some instances by the term “about,” “approximate,” or “substantially.” For example, “about,” “approximate,” or “substantially” may indicate ±20% variation of the value it describes, unless otherwise stated. Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. Each of the patents, patent applications, publications of patent applications, and other material, such as articles, books, specifications, publications, documents, things, and/or the like, referenced herein is hereby incorporated herein by this reference in its entirety for all purposes, excepting any prosecution file history associated with same, any of same that is inconsistent with or in conflict with the present document, or any of same that may have a limiting affect as to the broadest scope of the claims now or later associated with the present document. By way of example, should there be any inconsistency or conflict between the description, definition, and/or the use of a term associated with any of the incorporated material and that associated with the present document, the description, definition, and/or the use of the term in the present document shall prevail. In closing, it is to be understood that the embodiments of the application disclosed herein are illustrative of the principles of the embodiments of the application. Other modifications that may be employed may be within the scope of the application. Thus, by way of example, but not of limitation, alternative configurations of the embodiments of the application may be utilized in accordance with the teachings herein. Accordingly, embodiments of the present application are not limited to that precisely as shown and described. |
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053032764 | abstract | Fuel assembly including deflector vanes for deflecting a component of a fluid stream flowing past such fuel assembly. The fuel assembly comprises a lattice member having rhombic-shaped rod cells and generally rhombic-shaped thimble cells therethrough. A plurality of parallel fuel rods extend through respective ones of the rod cells and a plurality of parallel control rod guide thimble tubes extend through respective ones of the thimble cells. A plurality of deflector vanes are associated with each rod cell and are integrally attached thereto on the upstream edge of each rod cell. Each deflector vane extends above its associated rod cell and curvilinearly protrudes partially over the rod cell for deflecting a component of the fluid stream onto the exterior surface of the fuel rod that extends through the rod cell. The deflector vane and the rhombic shape of each rod cell coact to create a vortex centered about the longitudinal axis of the fuel rod for maintaining liquid substantially single-phase fluid flow along the exterior surface of the fuel rod, such that DNB is avoided even in the presence of high heat fluxes across the exterior surface of the fuel rod. |
051732521 | abstract | In a fuel bundle having a matrix of parallel side-by-side fuel rods supported between a lower tie plate and an upper tie plate, a new ferrule and spring construction for the required spacers used to maintain the fuel rods in their required precise side-by-side alignment is disclosed. Paired ferrules are each provided with apertures for capturing a single spring between the ferrules. The springs are provided with a continuously looping main body having protruding tabs on opposite sides of the springs. The paired ferrules are confronted at their respective apertures for the capture of the springs. The shape of the apertures permits insertion of the spring after the ferrules have been welded together. The springs are compressed while being inserted. After insertion the springs return to their original shape and are confined between the ferrules. After insertion of the fuel rods, the springs are compressed to an intermediate position, but are still confined within the ferrule apertures. The springs can be partially inserted into the ferrules and held in a compressed condition while the fuel rods are inserted. This reduces the forces on the fuel rods and reduces scratching of the fuel rods during bundle assembly. After the fuel rods are inserted, the springs are fully inserted. |
045487839 | claims | 1. For use in a cooling fluid filled cylindrical nuclear reactor pressure vessel to isolate a cooling fluid recirculation loop, said vessel containing a cylindrical fuel core shroud spaced from the sidewall of said vessel, said vessel having an outlet nozzle in the sidewall of said vessel adjacent said shroud coupled to an outlet conduit of said loop, said nozzle having a beveled seat formed in its inner end, compact collapsible plug apparatus for blocking said nozzle comprising: a plug having a tapered face portion generally mating with said beveled seat of said nozzle; gasket means mounted to said tapered face portion of said plug for sealing said plug to said beveled seat of said nozzle upon abutment between said face portion and said seat; maneuvering means attached to said plug for remotely positioning said plug in confronting relationship with said nozzle, said plug being maneuvered by said maneuvering means downward through the space between said shroud and said sidewall of said vessel to said confronting relationship; and jack means attached to said plug, said jack means including an extendable scissor assembly, said scissor assembly being remotely selectively extendable to bear against said shroud for providing a force between said shroud and said plug for urging and maintaining said tapered face portion of said plug in abutment with said beveled seat of said nozzle. 2. The apparatus of claim 10 wherein said plug is frusto-conical in shape and is formed with a hollow cavity, at least a portion of said cavity containing a closed-cell material whereby said plug is buoyant in said cooling fluid. 3. The apparatus of claim 1 including a remotely operable hydraulic actuating piston connected to said scissor assembly for selective extension and retraction thereof. 4. The apparatus of claim 1 wherein said maneuvering means comprises first and second cables, said first and second cables being attached at different locations to said plug for suspending said plug and for aligning said face portion of said plug adjacent said nozzle seat. |
description | Embodiments of the present invention as described herein are related to the following patent applications, all of which are incorporated by reference herein in their entirety: U.S. patent application Ser. No. 10/824,967, entitled “Method And Apparatus For Controlling Access To Memory Circuitry,” with inventors Glenn A. Baxter et al., filed Apr. 15, 2004; U.S. patent application Ser. No. 10/824,713, entitled “Method And Apparatus For Controlling Direct Access To Memory Circuitry,” with inventors Glenn A. Baxter et al., filed Apr. 15, 2004; U.S. patent application Ser. No. 10/824,715, entitled “Method And Apparatus For Communicating Data Between A Network Transceiver And Memory,” with inventors Christopher J. Borrelli et al., filed Apr. 15, 2004; and U.S. patent application Ser. No. 11/341,003, entitled “Architecture For Dynamically Programmable Arbitration Using Memory,” with inventor Jennifer R. Lilley, filed Jan. 27, 2006. 1. Technical Field Embodiments of the present invention relate to features of a versatile Multi-Port Memory Controller (MPMC) that can be included in a system to control access to memory from processors, devices, or buses. 2. Related Art A conventional processor-based system includes a processor along with a memory, and one or more peripheral devices. The memory stores data and instructions for the computing system. The peripheral devices can include components such as graphics cards, keyboard interfaces, and network interface cards. The computing system can include a system bus to facilitate communication among the processor and peripheral devices and the memory. With memory access provided through a system bus providing for processor and peripheral devices, arbitration must be performed to gain access to ports of the bus. However, on a shared bus, arbitration is a serial process. That is, a component must request bus access, be granted bus access to the exclusion of all other components, and then perform a memory transaction. The bus arbitration overhead may not allow the full bandwidth capabilities of the memory to be utilized. For instance, the memory is not being kept busy during the time when components are requesting and receiving access to the system bus. Conventional processor-based systems use some form of memory controller in order to access memory devices and provide arbitration to the memory for the processor and peripherals. Requirements for a memory controller to communicate with different type components and bus structures can decrease bandwidth from the normal operation of a bus-based system. To address the need to configure a memory controller to provide maximum bandwidth when used with various processor systems, a programmable logic device such as an Field Programmable Gate Array (FPGA) has been used to create the memory controller. FPGAs can be used to provide a wide variety of these memory controllers, including single port and multi port memory controllers. FIG. 1 shows a block diagram of an FPGA 102 that can be used as a memory controller. The FPGA 102 illustratively comprises programmable or configurable logic circuits or “blocks,” shown as CLBs 104, I/O Blocks (IOBs) 106, and programmable interconnects 108, as well as configuration memory 116 for determining the functionality of the FPGA 102. The FPGA 102 may also include an embedded processor block 114, as well as various dedicated internal logic circuits, illustratively shown as blocks of random access memory (“BRAM 110”), and digital clock management (DCM) blocks 112. For a memory controller, the components of the FPGA 102 can be used to control an external memory 150. Those skilled in the art will appreciate that the FPGA 102 may include other types of logic blocks and circuits in addition to those described herein. The IOBs 106, the CLBs 104, and the programmable interconnects 108 may be configured to perform a variety of functions. Notably, the CLBs 104 are programmably connectable to each other, and to the IOBs 106, via the programmable interconnect 108. Each CLB slice in turn includes various circuits, such as flip-flops, function generators (e.g., look-up tables (LUTs)), logic gates, and memory. The IOBs 106 are configured to provide input to, and receive output from, the CLBs 104. Configuration information for the CLBs 104, the IOBs 106, and the programmable interconnect 108 is stored in the configuration memory 116. The configuration memory 116 can include static random access memory (SRAM) cells. A configuration bit stream to program the configuration memory 116 can be produced from the program memory 120. The IOBs 106 can include transceiver circuitry configured for communication over any of a variety of media, such as wired, wireless, and photonic, whether analog or digital. The DCM blocks 112 provide well-known clock management circuits for managing clock signals within the FPGA 102, such as delay lock loop (DLL) circuits and multiply/divide/de-skew clock circuits. The processor block 114 comprises a microprocessor core, and typically associated control logic. Notably, such a microprocessor core may include embedded hardware or embedded firmware or a combination. A soft microprocessor 134 may be implemented using the programmable logic of the FPGA 102 (e.g., CLBs 104 and IOBs 106). As one example, the FPGA used to make an MPMC can be one selected from the Virtex-4 family of products, commercially available from Xilinx, Inc. of San Jose, Calif. To enable high data-rate communications (e.g., 1200 megabits per second full duplex), the FPGA can be configured as an MPMC with built-in arbitration logic. A typical MPMC will have a fixed number of ports to communicate with components connecting to a memory device. For example, the MPMC may include a port for communicating directly with a central processing unit (CPU) (e.g., an instruction-side processor local bus) and/or a port for communicating with a system bus. Current MPMC designs have performance issues because of their fixed or non-flexible implementation or architecture. Notably, the systems have a fixed implementation because the port types cannot be changed, and the number of ports remains fixed. Further, they have a fixed arbitration scheme. The systems tend to have port connections to two buses, one for high-speed entities, and one for low-speed entities. The implementation of each of these entities affects the performance such that the lowest performing device on each bus sets the highest frequency possible on that bus. Some system ports are typically dedicated for connection to a CDMAC to allow for direct memory access. Current systems therefore can suffer performance degradation depending on design constraints. It is desirable to define topologies to efficiently use the components of an FPGA to develop a memory controller. In particular, it is desirable to provide an MPMC that can allow source code to be efficiently changed dynamically to handle a desired number of ports, while maximizing system performance and providing compatibility with a number of different components including peripherals and memory devices that can be connected to the memory controller. According to embodiments of the present invention, a universal memory controller is provided that can be dynamically made compatible with multiple types of memory as well as multiple types of memory system organizations. Different system topologies are provided through configurable logic. The MPMC configuration provided offers substantially higher bandwidth to devices because of its architecture. It offers freedom of implementation so that customers can trade off area and performance. One implementation uses the resources provided by FPGA technology to efficiently implement the MPMC based system topology. In some embodiments of the present invention, an MPMC is provided with a self-aligning programmable state machine to provide dynamic compatibility between the MPMC and various memory devices. The self-alignment is provided using shift register look up tables (SRLs) connected to the output of the BRAM state machine forming a part of the MPMC controller. Unlike the fixed implementation of a BRAM-only state machine of conventional systems, this state machine is capable of being updated both dynamically, and statically by providing a delay input to the SRLs and/or updating its contents. This alignment is a key to supporting the dynamic nature of adaptation to various memory organizations, speeds, and timing requirements. In other embodiments of the present invention, configurable Port Interface Modules (PIMs) are provided on MPMCs ports to enable programmable connection to different type devices, processors, or buses. The PIMs include logic that can be programmed to provide functions ranging from the simple function of a simple direct link, such as a native port interface (NPI), to a more complex DMA such as a CDMAC. The PIMs allow for communication within a wealth of different system topologies. The PIM can further include protocol bridges to allow the PIM to communicate with other PIMs to form a master, slave or master/slave port or a combination thereof. As a master port, the PIM can shift communications from one port to the PIM of another port that provides the necessary translation from a device connected. In this manner, efficient use of the ports is made, and ports will be more available for memory access. Further, buses typically used to communicate with specialized dedicated ports will not be needed with the programmable PIMs, increasing overall port operation speed and reducing latency. Even with bridges external to the MPMC, the PIMs allow a processor to communicate with peripheral devices on different buses while not slowing down remaining devices on a bus communicating with memory over the MPMC. The processor can simultaneously perform instruction reads from memory while communicating with other peripheral devices. In further embodiments, the data path, address path and PHY interfaces of the MPMC are made highly configurable. In the data path, FIFOs according to embodiments of the present invention are alternatively formed from BRAMs, SRLs, LUT RAM or registers to accommodate different device parameters and operation speed. For example when a PLB typically requires a larger FIFO, a BRAM can be used, while a simple register can be used for an OPB. Further, operation speed at the front end can be adjusted to a different speed than the back end of the FIFO. In the address path, the addresses according to embodiments of the invention can be selectively multiplexed depending on the type memory used. For example, multiplexing can be provided with DRAM memory, and eliminated with SRAM where it is not usually required. Further, the address size can be dynamically adjusted. If an overlap between addresses of two ports occurs, in one embodiment addresses can be semaphored for protection or separation to prevent collisions. In another embodiment, aliasing of addresses can be provided so that when address size is adjusted, the physical addresses do not overlap. For the PHY interface, rather than a fixed device with registers and clocking, the PHY interface according to the present invention is parameterized to align with different memory device types. Instead of using a state machine to read a data address strobe (DAS), embodiments of the invention use logic to read and write a header, payload and footer of data words, compare the values, and adjust input data delays to provide precise data alignment relative to the clock. In still further embodiments of the present invention, intelligent pipelining is provided to allow control over a variety of pipeline stages in order to permit a customer to trade off FPGA area for maximum frequency performance. The pipelines can be optionally added for each port internal to the MPMC. In one example, the optional pipeline is used between the arbiter and control state machine of the MPMC for each port. The locations of these optional pipelines and their ability to be controlled on a per port basis, achieves greater flexibility and performance. The MPMC implemented using an FPGA can be programmed in some embodiments through a Graphical User Interface (GUI). The various embodiments of the GUI offer advantageous control over creation of prior MPMC-based systems. First, the GUI allows creation of multiple cores of a system rather than a single core, with an MPMC set to connect the core devices to a particular memory. The GUI can be data driven from user editable text files, and it can offer feedback on resource utilization, area, performance estimates, and performance measurements. It can provide performance feedback estimates based upon the current programmable settings for each port. The GUI can further provide performance data measured for the system back to the user. The GUI can intelligently set the arbitration of the system in such a way as to maximize system performance based upon the measured data. Further, the GUI can use the information entered to dynamically create an entire core for the MPMC and peripherals and processors on board the FPGA, and provide intelligent design rule checking both as information is being entered, as well as during operation when the GUI dynamically creates complex hardware. In still other embodiments, performance monitors (PMs) can be embedded within the MPMC to provide measurement of various aspects of performance. The measurements can be aggregated together to provide historical information. Additionally, the information collected can be used to dynamically alter the arbitration or any other relevant adjustable parameter within the MPMC. In one embodiment, the PM provides the performance measurement to an external agent for later additional processing and/or summarization. FIG. 2 is a block diagram depicting an exemplary FPGA 200 configured as a multi-port memory controller (MPMC) 210. The MPMC 210 includes general ports 2220 through 2223 (collectively referred to as ports 222). MPMC ports 222 may be connected to peripherals by a system bus, such as Processor Local Buses (PLBs) 2260 and 2261. Processor 205 and other peripheral devices 203 and 202 are shown connected to ports 2220 and 2221 by PLBs 2260 and 2261. PLB arbiter 206 provides bus arbitration for the peripherals on bus 2260, while PLB arbiter 204 provides arbitration for bus 2261. A communication direct memory access controller (CDMAC) 224 can provide a LocalLink to devices 207 and 208 over other ports, such as ports 2222 and 2223. An example of a LocalLink device is a Gigabit Ethernet Media Access Controller (GEMAC). The CDMAC 224 has ports configured to communicate with the devices 207 and 208 over a non-shared interface (e.g., a streaming interface to a direct memory access DMA port). The ports 222 are pre-configured with I/O paths capable of communicating with the various types of buses or point-to-point interfaces. Notably, each of the I/O paths of ports 2220-2224 include a data path interface (Data) 215, a control bus interface (Cntl) 219, and address bus interface (Addr) 218. The MPMC further includes port arbitration logic 216, data path logic 218, address path logic 212, and control logic 214. The data path logic 218 includes an interface to the data path interface 215 and to the memory 206. The address path logic 212 includes an input interface coupled to the address bus 218 and a memory interface coupled to external memory 150. The port arbitration logic 216 includes an interface coupled to the control bus 219, an interface coupled to the control logic 214, an interface coupled to the data path logic 218, and an interface coupled to the address path logic 212. The control logic 214 includes a memory interface coupled to external memory 150, an interface coupled to the data path logic 218, and an interface coupled to the address path logic 212. In operation, the port arbitration logic 216 executes a fixed arbitration algorithm to select one of the ports 222 for access to the memory 150. Notably, a plurality of the ports 222 may provide memory transaction requests to the port arbitration logic 216 simultaneously. The port arbitration logic 216 analyzes all pending transaction requests and provides a request acknowledgment to one of the ports 222 in accordance with the fixed arbitration algorithm. The port that “wins” then obtains access to external memory 150 and the requested memory transaction is performed. The port arbitration logic 216 provides port select data to each of the address path logic 212, the data path logic 218, and the control logic 214. The port select data includes the identity of the selected one of the ports 222. The address path logic 212 receives an address context from the selected one of the ports 222 using the port select data. Likewise, the data path logic 218 receives a data context from the selected one of the ports 222 using the port select data. After granting a transaction request from one of the ports 222, the port arbitration logic 216 provides a memory transaction request to the control logic 214. The control logic 214 processes the memory transaction request and determines a sequence of sub-transactions required to perform the desired memory transaction. Each of the sub-transactions comprises a sequence of memory operations for causing external memory 150 to perform a particular action. Thus, each memory transaction includes a sequence of memory operations. The control logic 214 drives the data path logic 218, the address path logic 212, and external memory 150 with control signals that execute memory operations in external memory 150. The data path logic 218 drives external memory 150 with data needed to perform the memory operations indicated by the control signals from the control logic 214. Likewise, the address path logic 212 drives external memory 150 with addresses needed to perform the memory operations indicated by the control signals from the control logic 214. The end result is that the requested memory transaction provided by the arbitration logic 216 is performed. The control logic 214 provides a complete signal to the port arbitration logic 216 to indicate when another memory transaction may be issued. In the example of FIG. 2, hardware is custom built for a four port MPMC using PLB interfaces for ports 2220 and 2221 and CDMAC interfaces for ports 2222 and 2223. The example of FIG. 2 further lacks a changeable PHY interface between external memory 150 and logic of the MPMC to enable communication with different forms of memory. Further, a means to customize all of the elements, such as through a Graphical User Interface (GUI), is not provided. FIG. 3 shows a block diagram of an MPMC 300 showing components constructed in accordance with one or more embodiments of the invention. FIG. 3 demonstrates the application of a changeable number of ports labeled 3400-340N to range from 0 to N, rather than the fixed four ports 2220-2223 shown in FIG. 2. Using a variable number of ports 3400-340N is advantageous because it allows a designer to begin with an existing design and morph the system topology to use more ports and improve performance over time. The ports 3400-340N are further connected to Port Interface Modules (PIMs) 3300-330N, illustrating that each port is changeable in what it can do, relative to the fixed type ports 2220-2223 of FIG. 2. The PIMs 3300-330N are shown connected to devices 3700-370N. Rather than being confined to specific types of peripherals or buses, or requiring use of a CDMAC, as in FIG. 2, the configurability of the PIMs 3300-330N allows various components to be attached as the devices 3700-370N. For convenience, the PIMs will be collectively referred to herein as PIMs 330. While this diagram shows the devices in a point-to-point configuration, many other configurations are possible, some of which are illustrated through subsequent figures. How a specific configuration is connected represents the ‘topology’ of the system built with the MPMC 300. In addition to the ports 3400-340N that provide an interface to components external to the MPMC, the memory controller 300 of FIG. 3 further includes a physical (PHY) interface 310 to connect to various memory devices, labeled as memory 350. The PHY Interface 310 is added to demonstrate the changeable nature of the interface, described in more detail subsequently, that is provided to connect with the different memories. The memory 350 is indicated without reference to whether the memory is internal or external, in contrast with FIG. 2 that specifically references an external memory. The memory 350 can be provided within the FPGA chip, or external to the FPGA, and is not confined to the external memory device as in FIG. 2. The memory 350 can further take various forms, for example the memory 350 can be a Dynamic Random Access Memory (DRAM) device, Static RAM (SRAM), Double Data Rate (DDR) DRAM, or other type of memory device known in the art. The memory 350 can further be internal BRAM included as part of the FPGA itself. The memory 350, FPGA 102, and various other devices, whether internal or external to the FPGA, may be integrated onto a single chip to form a single system-level integrated circuit (referred to as a “system-on-a-chip” or (SoC)). Similar to the address path logic 212, control logic 214, arbiter 216 and data path 218 of FIG. 2, the memory controller of FIG. 3 includes a different address path 312, control state machine 314, port arbiter 316, and data path 318 respectively. Also, similar to buses 215, 218 and 219 of FIG. 2, the topology of FIG. 3 includes a data bus 320, address bus 322 and control bus 324. Address path logic 312 receives address signals from ports 3400-340N via Port Interface Module (PIM) 3300-330N. Data path logic 318 includes bi-directional FIFOs between PIMs 330 and memory 350, via PHY interface 310. Data written to FIFOs of data path logic 318 is provided to the physical (PHY) interface 310 for sending to memory 350 once data from the port is selected for transmission. Similarly, data received from memory 350 is returned through PHY interface 310. Additional features of these new components are described in detail below. In sum, the versatility of the components illustrated in FIG. 3 provide a significant advantage over prior memory controllers, as can be appreciated by the remainder of this specification. FIG. 4 shows further details of the memory controller of embodiments of the present invention. The arbiter 316 receives control inputs provided from PIMs 3300-330N. The arbiter 316 analyzes all pending transaction requests from the PIMs 3300-330N and provides port select data indicating which port was granted access. One embodiment of an arbiter that can be used in conjunction with the present invention is described in U.S. patent application Ser. No. 11/341,003, referenced previously. The control state machine 314 receives the control information from arbiter 316 and includes circuitry to look up control data needed in BRAM 414. The control signals from BRAM 414 are provided through SRLs 416 to the address path logic 312, data path logic 318, and through a physical (PHY) interface 310 to memory 350. The control signals from the SRLs 416 of the control state machine 316 include port select data that identifies the selected port that will transmit data. The address path logic 312 receives an address context from the selected one of the ports. Likewise, the data path logic 318 receives a data context from the selected port. After granting a transaction request from one of the input ports, the port arbitration logic arbiter 316 provides a memory transaction request to the control state machine logic 314. The control state machine 314 processes the memory transaction request and determines a sequence of sub-transactions required to perform the desired memory transaction. Each of the sub-transactions comprises a sequence of memory operations for causing the memory to perform a particular action. The control state machine logic 314 drives the data path logic 318, the address path logic 312, and the PHY interface 310 with control signals directed to the memory 350 to execute memory operations. The data path logic 318 and address path logic 312 also drive the PHY interface 310 with data and address signals to perform the memory operations indicated by the control signals from the control state machine logic 314. The end result is that a requested memory transaction provided by the port arbitration logic arbiter 316 is performed. Self Aligning State Machine FIG. 5A shows additional details of the arbiter 316 and control state machine 314 of FIGS. 3 and 4. The arbiter 316 in one embodiment includes an arbiter BRAM 520 that receives request control signals from the ports 0-N connected to the memory controller. The appropriate port sequence is selected by a signal provided from the arbiter BRAM 520 that provides a signal indicating “which port” is selected through encoder 522 to optional pipeline 538 and to a multiplexer 512 of the control state machine 314. The arbiter 316 also provides a start signal through the optional pipeline 538 once a port is selected, and the “start sequence indicator” is then provided to the control state machine 314. A “Load” signal is likewise provided from the arbiter once an indication is received that the previous port access has been completed, in order to start the next memory transaction, if present. In the control state machine 314, each of ports 0-N has an assigned port address input module 5100-N. The port 0-N address modules 5100-N each include a transaction encoder 514 that chooses which sequence will be used in control BRAM 414. The transaction encoder 514 provides a start address based upon the transaction type requested by the port. The start address is provided to register 516 and then to multiplexer 512. Multiplexer 512 selects ‘which port’ is to be granted access from arbiter 316, and then provides the selected start address through optional pipeline register 538 to counter 530. Counter 530 then loads the start address when arbiter 316 tells it to do so. This then begins the sequence of operations to the memory. More details of the arbiter, particularly on how sequences are stored and selected for individual ports, is described in U.S. patent application Ser. No. 11/341,003 referenced previously. The BRAM 414 of the control path state machine 314 can have contents set to any number of values to permit any kind of control that a user requires. The state machine BRAM 414 provides information with several output paths that control the data path logic 318, address path logic 312 and PHY interface 310 as shown and described with respect to FIGS. 3 and 4. The sequence of memory transactions from port arbitration logic arbiter 316 of FIG. 5 are used by control state machine 314 to control a memory transaction stored in BRAM 414. Outputs of control BRAM 414 are provided from the controller through shift register look up tables (SRLs) 416. The SRLs 416 shown include separate registers to provide a signal ‘Control Complete’ from output Q0, ‘Control Stall’ from output Q1, and the ‘Control Data’ from outputs Q2-Q35. The initial address input to the BRAM 414 from counter 530 is used to set the initial sequence state of the state machine, as described previously. The basic function of the control state machine 314 is to play sequences of events. The BRAM control path in control state machine 314, in one exemplary embodiment can allow up to 16 sequences. The sequences can include: (1) word write, (2) word read, (3) 4-word cache-line write, (4) 4-word cache-line read, (5) 8-word cache-line write, (6) 8-word cache-line read, (7) 32-word burst write, (8) 32-word burst read, (9) 64-word burst write, (10) 64-word burst read, (11) No operation (NOP), (12) Memory refresh, and (13) Memory initialization. With the memory 350 being DDR2, DDR, SDRAM, and potentially other types that are driven by a memory controller, the read and write sequences can be divided into three stages: activate, read or write and precharge. Each of these stages has specific sequences of events to the data path 318, address path 312, PHY interface 310, and the arbiter 316 of FIG. 3. The sequences vary depending on the memory type (e.g., DDR2, double data-rate (DDR) Dynamic Random Access Memory (DRAM), a single data rate DRAM, or Synchronous DRAM (SDRAM)), memory style (e.g., discrete parts, unbuffered DIMM, or registered DIMM), memory configuration (number of bank, row and column address bits), PIM configuration (e.g., ISPLB PIM, DSPLB PIM, PLB PIM, OPB PIM, XCL PIM, CDMAC PIM, and/or NPI PIM), and clock frequency. The control state machine 314 of FIGS. 3, 4 and 5A can be configured to support any of these options because the contents of the BRAM 414 can be modified and the SRLs 416 have configurable delays. The SRLs 416 of the control state machine 414 connect, as illustrated in FIG. 4, partly to the PHY interface 310 to further make it easy to change the MPMC system in order to make it compatible with different types of memories. The PHY interface 310 is described in more detail subsequently. Counter 530 generates an address for the BRAM 414 and is used to play a sequence of events from BRAM 414. One of the port 0-n ADDR inputs 5100-n determines the base address of the selected sequence and is loaded into counter 530. The arbiter 316 contains a prioritized list of port numbers that have access to the control path BRAM state machine 414. Arbiter 316 will look at which ports are requesting access to the state machine and will determine when a new sequence will start and will send the ‘Start Sequence Indicator’ to load counter 530. Additionally, arbiter 316 will present the selected port to the address and data path via the ‘Which Port’ signal. The SRLs 416 provide output words that can be individually delayed by static and/or dynamic control in order to control different functions. After a sequence is begun to access BRAM 414, in every clock cycle the address increments by one unless the sequence calls for a stall (Cntrl_Stall) or until the sequence has finished and the state machine is ready to accept the next sequence. Each sequence continues until (Cntrl_Complete) is received from one of the SRLs 416 indicating the sequence has finished and the state machine is ready to accept the next sequence. The Cntrl_Stall and Control_Complete signals are provided as feedback through logic 541 to provide an increment (Inc) input to counter 530 to control and hold the state of counter 530 for a specified time until a sequence is complete. Once a sequence is indicated to be complete, the start sequence indicator ‘load’ signal can be provided from the arbiter 316 to indicate that a new sequence base address can be loaded and the next sequence can begin. Although Cntrl_Stall and Cntrl_Complete are illustrated and described, they show one embodiment for implementation of the system and are not specifically required. For example, the sequences could have a fixed length and timing or the high address in the sequence could be used to determine when an operation is complete. It can be appreciated by one of ordinary skill in the art that other types of control signals may be possible and that the above description is provided with the intent to illustrate the concepts. In one embodiment, the contents of the BRAM 414 can be read or written over a Device Control Register (DCR) bus. A processor included in the MPMC system with a DCR interface can, thus, be used to read and write the contents of the BRAM 414. As illustrated, processor signals are provided over the DCR bus to a B-side interface of BRAM 414. The DCR effectively provides an auto-incrementing keyhole register access to the BRAM 414, as described later. Note as well that the same DCR interface shown in FIG. 5A could also be attached to arbiter BRAM 520 within arbiter 316. FIG. 5B illustrates the function of the SRLs 416 with programmable delays. According to embodiments of the present invention, the SRLs 416 are controllable to provide different delays depending on the memory device(s) attached. Each SRL 416 has a delay parameter that can be set on a per-output basis. The delay parameter indicates the number of cycles that the BRAM data output should be delayed. If the parameter is set to zero, the SRL is bypassed. In some embodiments a register is added to the SRL 416 outputs in order to greatly improve timing within the MPMC. In operation as shown in FIG. 5B, the outputs 5400-540N of the Control BRAMs 414 are aligned with clocks Clk0. This may not be compatible with an attached memory. The SRLs 416 allow delayed staggering of the data outputs 5420-542N. The delay may be fixed at programming of an FPGA used to create the MPMC, or dynamically during memory operation. As shown in FIG. 5B, outputs 5420-542N are no longer aligned relative to Ck0. In one embodiment, the dynamic ability of the SRLs 416 is used to allow for altering the order of the content coming from control BRAM 414. Through the use of multiple SRLs 416 (not shown) per control BRAM 414 bit, and with the application of dynamic multiplexing logic (not shown), data bits are allowed to be effectively altered in the output. Bits are altered rather than simply delaying bits before data is sent to the PHY interface. For example, bit 544 can be swapped for bit 546, as illustrated in FIG. 5B. Each SRL 416 can be individually and dynamically adjusted as needed to provide appropriate delays. The control over the delay may be static and remain unchanged while the SRL 416 is in operation. It may also be dynamic in that other logic within the MPMC may alter the number of cycles that each individual SRL 416 delays in order to accomplish a specific purpose. Those skilled in the art will understand the value of being able to dynamically delay the outputs of the BRAM 414. Port Interface Modules (PIMs) Overview FIGS. 6A-6B, 9 and 10 illustrate how some embodiments of the present invention include Port Interface Modules (PIMs) that are versatile to allow decoupling of individual ports from a particular type of attached devices, processor or buses. The PIMs can include programmable logic forming a “bridge” that can be programmed to translate from one of a multiplicity of interfaces to enable compatibility with a particular type of processor, device or bus. Further, bridges can be provided within a PIM to enable bridging of signals entirely within the MPMC from one port to another port where the PIM is programmed to be compatible with that particular device. The structure and location of these bridges allows for the wealth of different system topologies. The PIMs can create high performance systems due to the way they allow transactions to be offloaded from various devices that wish to communicate with memory. Further, the bridges allow a processor to communicate with peripheral devices directly or through different buses while not slowing down remaining devices on the bus(es) communicating with memory via the MPMC. The processor(s) are also enabled to simultaneously perform instruction reads from memory while communicating with other peripheral devices. PIM Protocol Bridges FIGS. 6A-6B show architectures for different classes of Port Interface Module (PIMs), according to embodiments of the present invention. In FIG. 6A, a slave PIM 670 illustrates an example PIM that contains just a slave bus interface 672 with an interface to Native Port Interface (NPI) 674 via a memory bridge 675. Memory bridge 675 provides any required change (“bridge”) in protocol from the particular protocol on the slave bus interface 672 to the NPI 674 side to the MPMC. In some instances, there is no change in protocol and the PIM becomes a NPI PIM. FIG. 6B shows another class of PIM, a slave bridge PIM 630 illustrating a modification from slave PIM 670. In slave bridge PIM 630, two additional elements are added, namely arbiter 633 and bus bridge 637. Arbiter 633 is not to be confused with port arbiter 316, nor with PLB arbiter 730 or OPB arbiter 740 in FIG. 7. The function of arbiter 633 is to simply allow the master's transaction on the slave bus interface 632 to be directed toward memory via memory bridge 635, or to one or more bus bridge 637 toward one or more master/slave PIM 650. The arbiter 633 need not be a complex arbiter; it could, for example, switch the transaction based purely upon address. One skilled in the art will appreciate that many methods exist for creating arbiter 633. Note that PIM 650 can also be used in a so-called ‘master-only’ mode where the slave bus interface 652 and NPI 654 remain unconnected. This provides slave bridge PIM 630 with the ability to communicate with slaves on master bus interface 655. The bus bridge 637 is used, when requested, to provide the bus master from the slave bus interface 632 to generate master access via another PIM, such as the exemplary Master/Slave PIM 650. The provision of bus bridge 637 obviates the need for the significantly more complex bridge 750 and 760 as shown in FIG. 7B, and discussed subsequently. Further, the configuration with slave bridge PIM 630 permits the use of one or more bus bridges 637 within the same slave bridge PIM 630. Alternately, bus bridge 637 can itself be designed to communicate with multiple exemplary Master/Slave PIMs 650. It can be appreciated by one skilled in the art that the purpose of the bus bridge 637 is to provide directed access for point-to-point connection on slave bus interface 632 to one or more other master bus interfaces 655 advantageously providing a mechanism to “bypass” traditional bus bridges without sacrificing the point-to-point system topology, performance loss, and area requirements. Further it can be appreciated that systems can be better graphically represented to users since an entire function moves inside a block, and provides a cleaner and clearer viewpoint of the resulting topology. The master/slave PIM 650 is another example class of PIM. In this case, the master bus interface 655 is directly connected from Bus Bridge 637 through master/slave PIM 650 to master bus interface 655. It should be noted that master/slave PIM 650 could have additional logic contained within it between bus bridge 637 and master bus interface 655 as required by the application at hand. One skilled in the art will understand that many different embodiments of PIMs other than those shown in FIGS. 6A-6B are possible. For example, a PIM could be a master-only PIM similar to master/slave PIM 650 but missing slave bus interface 652, memory bridge 655 and interface to NPI 654. Further, additional functions can be placed within a PIM to accomplish other purposes. For example, a Direct Memory Access Controller (DMAC) could be embedded within a PIM to enable the PIM to master traffic on is local master bus interface 655 from within the PIM, and couple such a transaction to interface to NPI 654. This exemplary PIM according to the present invention can be referred to as a CDMAC PIM. MPMC Systems with Dedicated Bus Interfaces FIG. 7A shows a topology for a system including an MPMC 700 having ports connecting to devices such as processor 702, a Processor Local Bus (PLB) 731 and On-chip Peripheral Bus (OPB) 741. The MPMC 700 further connects to memory 350. The PLB 731 is shown connected to a PLB PIM at a port of the MPMC 700 and supports a processor 707 external to the MPMC 700 as well as on-chip device 705. A PLB arbiter 730 arbitrates connection of devices, such as processor 707 and on-chip device 705, to the PLB 731. The OPB 741 is shown connected to an OPB PIM at a port of the MPMC 700. The OPB 741 supports on-chip devices 708 and 709 and has arbitration provided by OPB arbiter 740. Processor 702 is directly connected to two separate ports of the MPMC 700, one providing an instruction side PLB (ISPLB) and another providing a data side PLB (DSPLB). One skilled in the art will understand the exemplary nature of FIGS. 7A and 7B and that differing numbers of devices are possible within the topologies shown. FIG. 7B illustrates an alternative MPMC system bus connection topology demonstrating a wide variety of devices that can be connected to the OPB and PLB buses illustrated generally in FIG. 7A to reduce the need for different MPMC port configurations. In this example topology, memory controller 710 is a single ported memory controller that interfaces to memory 350. The memory controller has a slave input from PLB 731. Processor 114 is a dual bus master on PLB 731. Similarly, an external processor 732 could be a single or dual bus master on PLB 731. This allows the MPMC to match existing shared bus systems and is an advantageous place to begin a system design prior to converting it to a multi-ported design. Other devices 733, 735 and 737 are connected to PLB 731 to illustrate how various master/slave, slave only, or master only devices can be supported, respectively. Device 733 is an exemplary master/slave device. An example of device 733 could be a Gigabit Ethernet controller that contains a DMA engine to move data to and from memory 350 via memory controller 710. Device 735 is an exemplary slave only device. That is, it only responds to bus transactions from masters on PLB 731. An example of device 735 could be a high speed USB serial controller. Device 737 is an exemplary master only device. That is, it only initiates bus transactions to slaves such as memory controller 710 on PLB 731. An example of device 737 could be a Video Controller which only gathers data from memory 350 and displays it on a CRT or LCD screen. In addition to the processors, devices, and memory controller 710, PLB 731 illustrates two example bridges that are conventional mechanisms to interconnect PLB 731 and OPB 741. The first, bridge out 750 allows the processors and other masters on PLB 731 to initiate transactions onto OPB 741 where slaves on OPB 741 can respond. The second, bridge in 760 allows master devices on OPB 741 to initiate transactions onto PLB 731, for example transactions to memory 350 via memory controller 710. These bridges are integral to this example system topology because they are the sole means for the masters on the buses to communicate with slaves on other buses. Devices 743, 745 and 747 are analogous to devices 733, 735 and 737, respectively, but are connected to a different protocol, in this case OPB 741. PIM Embodiments of Invention FIG. 8 illustrates an exemplary MPMC system topology illustrating how embodiments of the present invention can overcome the inefficiencies of the dedicated interfaces of FIGS. 7A and 7B. In particular, FIG. 8 illustrates how uniquely programmable PIMs can eliminate the need for devices external to the PIMs that are used in FIG. 7B and allow for connection of different type devices directly to a port. With the arrangement of FIG. 8, a number of differing processors with potentially differing bus interfaces can be connected to the MPMC via the uniquely programmed PIMs. Further, whereas in a typical system as shown in FIG. 7B where the processors must share their connections to the bus, this embodiment of FIG. 8 illustrates the performance advantageous separation of the processor buses into separate PIMs of an MPMC. FIG. 8 initially includes one or more processors 7321-2. The processors 7321-2 can be fixed devices, such as processor 114 or processor 124 described previously, or a soft processor such as processor 134 formed using FPGA logic. This illustrates the connectivity to MPMC 810 to one or more so-called “hard” processors (e.g., 114 and/or 124), one or more so-called “soft” processors (e.g., 134), and/or one or more external processors (e.g., 732). Note that it is not a requirement, and the processor(s) may also be connected to a single PIM, such as PIM 650, using an arbiter, such as OPB arbiter 740 over an OPB 741. FIG. 8 also shows exemplary connectivity for the peripheral devices, such as devices 733, 735 and 737 used in FIG. 7B, to the unique PIMs in accordance with the present invention. The devices 733, 735 and 737 connect to individual PLB PIMs of slightly differing types instead of through an external PLB to a single PIM. The types are illustrated by a reference number label for the PIM indicating one of the different PIM configurations shown in FIGS. 6A and 6B. Devices 733 and 735 are shown connected to PLB PIMs of type Master/Slave PIM 650. Note that device 735 differs from device 733 in that it is only a slave type device. In this example, the Master/Slave PIM 650 would only connect the master port to the device, and the slave port would be left unconnected (‘n.c.’ in FIG. 8). Device 737 connects to a PLB PIM 670 of type slave only since the device 737 only masters transactions. FIG. 8 further shows exemplary connectivity to PIMs for devices 7431, 7451 and 7471, shown connected to an OPB 741 in FIG. 7. This example also illustrates how devices 7432, 7452 and 7472 can still also be placed on an exemplary bus (OPB 741). Note that one device 7471 is directly connected to an OPB PIM of type Slave Only PIM 670, while the other device 7472 is connected via OPB 741 to a separate OPB PIM of type Master/Slave PIM 650. Similarly, there is one device 7451 connected directly to an OPB PIM and a second device 7452 connected via OPB 741 to an OPB PIM shared with the second device 7452. Additionally, the OPB 741 device 7431 is illustrated as connected to a master/slave style of PIM 650, while a similar device 7432 is connected through the OPB 741 to the OPB PIM 650. A number of advantages can be appreciated from the FIG. 8 example embodiment over conventional systems such as that shown in FIGS. 7A-7B. First, multiple entities can simultaneously access an MPMC. Simultaneous, MPMC access is enabled and performance is enhanced because entities are not required to access a single bus or small set of buses, enabling the performance of the system to be limited by memory controller performance instead of bus performance. Second, by separating the individual entity connections to the MPMC into point-to-point connections, instead of a bus connection, clock frequency of the interface can be improved. In one embodiment, the clock performance of the processor is doubled in speed, improving from 100 MHz to 200 MHz. Third, by separating the individual entities into point-to-point connections, the devices no longer interfere with one another. That is, in past systems, when devices shared the bus, they had to wait (latency) for access to the bus until other devices completed their access. Fourth, embodiments of the present invention permit shared bus systems to still be created. The OPB 741 used in FIG. 8 illustrates this. Use of the system bus may be advantageous if a system designer is not as concerned about speed as opposed to using up available MPMC PIMs or increasing FPGA resource utilization. As a fifth advantage, the example embodiment in FIG. 8 demonstrates the lack of bridge out 750 from FIG. 7B. Such bridge(s) are no longer needed with the new system topologies possible with embodiments of the present invention. Bus bridge out 750 is typically a large and complicated bridge because it has to handle many different types of transactions. Instead a comparable bridge is built into MPMC 810 of FIG. 8 specifically in slave bridge PIM 630 as bus bridge 637 as shown in FIG. 6B. This bridge is advantageously smaller than bridge out 750. The bridge formed in the PIM can run at higher clock frequencies because it can be made simpler than bridge out 750 as it has to respond to a smaller number of types of bus transactions. As a sixth advantage, similar to elimination of bridge out 750, embodiments of the present invention enable elimination of the bridge in 760 shown in FIG. 7B. This is because typically neither bridge 760 nor 750 is needed with the new system topologies possible using embodiments of the present invention. Bus bridge 760 is typically used because devices on the bus slave side of the bridge 760 want to gain access to memory via the bus master side of the bridge 760. In the example of FIG. 8, the devices all have direct access to PIMs of the MPMC 810. This has the advantage of not requiring a change in protocol. Without a protocol change, clock performance is increased while latency is decreased. As a seventh advantage, with embodiments of the present invention eliminating buses and their associated arbiter, arbitration will typically be done inside the memory controller and not within each possible bus. Memory controller performance can then improve because transactions can be more efficiently overlapped in the way that provides the highest possible data rate from the memory 350 using a single arbiter. In shared bus systems, the devices arbitrate for the memory on the bus, and thus the memory cannot take advantage of the parallel knowledge of what transactions are next. As an eighth advantage, the ports according to embodiments of the present invention can operate at differing frequencies, which permits the ports to match the best operating frequencies of the devices attached. In a typical share bus system as illustrated in FIG. 7B, the devices attached to any given bus must operate at that bus clock frequency. Thus, if a particular device is very complicated and thus has a slow clock frequency, the whole bus is limited to running at the frequency of the slowest device on the bus. With individual PIMs according to embodiments of the present invention, instead each device can operate at its own preferential clock frequency and the whole system can improve in performance since faster devices can now operate faster. Ninth, the arbitration in arbiter 316 in MPMC 810 is dynamically programmable, so the system performance can be modified as appropriate without the adverse effect of separate bus arbitration. For example, when the system is mainly using the processor(s) to execute code, a first arbitration algorithm can be used, whereas when devices are mainly communicating with memory 350, a second arbitration algorithm can be used that is more efficient for memory communication. In sum, the structure and location of the bridges in a PIM allow for a wealth of different system topologies. They create high performance systems due to the way they allow transactions to be offloaded from various devices that wish to communicate with memory. PIMs Forming NPI and CDMAC FIG. 9 illustrates an exemplary system topology wherein Native Port Interface (NPI) PIMs are provided in the MPMC 910. Note that this particular example does not show a processor connected. In some system topologies no processor is present, yet multiple devices still want to communicate with memory 350. As indicated previously, with an NPI PIM, the PIM does not need internal logic to translate from the device or processor connected to the port to be compatible with the memory. The Native Port Interface (NPI) devices 902, 904, 906, and 908 can be any kind of device which requires access to memory and which utilizes the NPI protocol to communicate with memory. An example NPI device could be a Video CODEC that captures video from a video input device and sends the video data to memory 350 as well as outputs different video data from memory and sends the video data to a video output device. Since PIMs are programmable and not dedicated to a particular port type, more ports on an MPMC will be available for the typical NPI device as opposed to conventional systems without such dedicated non-NPI interfaces. FIG. 9 also illustrates a Communication Direct Memory Access Controller (CDMAC) PIM that contains an embedded intelligent Direct Memory Access (DMA) engine optimized for communication style data access to memory. While most often DMA engines are controlled by processors, as can be appreciated by one skilled in the art, an intelligent DMA engine can be created which does not require a processor. One example usage of such an engine is to format conversion between one input video format and another output video format by properly moving data such that the NPI devices are provided correct data from memory. An advantage of having DMA engines embedded within the PIMs according to some embodiments of the present invention is that the DMA engine alleviates either the processor or other devices from needing complicated internal DMA engines. The DMA engines can additionally offload the processor connected to its port to another port by directly doing so in a so-called “memcopy” function where memory is copied from one set of memory locations to another set of memory locations without requiring processor access to the memory to perform the copying. This saves significant processing cycles while also having substantially faster execution time to do the copy. In some embodiments, the memcopy function can be done within the PIM using much larger memory transactions than the processor can generate, which further reduces the amount of time the memory is ‘busy’. By minimizing the time the memory is being used by the memcopy, even greater bandwidth is made available to other PIMs that want access to memory 350. PIM Performance Monitor (PM) PM Provided Inside PIM FIG. 10A illustrates a Performance Monitor (PM) 1000 included in a PIM 330, illustrating how the PM 1000 can be connected. The PM 1000 allows the user to measure the performance of the transactions within the PIM 330. It can be appreciated that PM 1000 can be connected on the port interface to NPI 674 side of PIM 330 and/or on the Port Slave Bus Interface 672 side. The PM 1000 can be connected to other elements within PIM 330, as required by the PIM in order to measure what is desired. In operation, the PM allows a system to view the performance of a port over time. The PM monitors each transaction and keeps a histogram of the execution time of each type of transaction, including separation for read and write access. The PM can perform a variety of measurements. The Performance Monitor 1000 also has a per-port performance monitor interface 1001. The performance monitor interface 1001 is generally connected to a processor through a bus interface that is appropriate to that processor. However, it can also be connected to hardware that reads the performance monitor periodically to provide feedback control or other control to the system. In either case, performance monitor interface 1001 is intended as the means of reading and writing the relevant data captured by the performance monitor 1000. In one embodiment of the present invention, the PM 1000 captures the transactions on the NPI 674 side of the PIM 330. For example, the PM 1000 can capture each byte read separately from each 16-bit word read. The PM 1000 counts how many clock cycles the transaction took to execute, and then accumulates the number of times this type of transaction has occurred at the measured number of clock cycles, providing a histogram of all the types of transactions of various execution times. It should be appreciated by one skilled in the art that many differing types of measurements are possible. For example, the PM 1000 could be built to measure the aggregate data rate on each side of the interfaces. Since the PM 1000 contains a readable and writable performance monitor interface 1001, and the PM 1000 can be implemented on a per-port basis within the MPMC, the PM 1000 can also act as a control mechanism for dynamically settable parameters with a given PIM 330. That is, if a particular PIM requires some control functions such as setting up a dynamically adjustable base address, the PM 1000 provides a simple means to read or write registers within a given PIM 330 or anywhere else within the MPMC structure. With a PIM having dynamically programmable arbitration and including per-port PMs, an advantageous dynamic selection of arbitration schemes can be performed. Either software or hardware within the arbiter 316 and control state machine 314 can automatically adjust the arbitration scheme based upon detected performance from a PM to maximize the system level performance. PM Structure Provided Inside or Outside PIM In some embodiments of the present invention, the MPMC can have PMs attached to various locations within the MPMC, yet outside the PIM, in order to measure some aspect of performance. For example, in many instances a user wishes to know how much data over how much time has been transferred to/from the memory 350. In one embodiment, the PM would measure the total number of bytes transferred to/from the memory 350 over a specific amount of time. In another embodiment, the PMs are used to measure the length of time that each type of transaction takes to execute. This information is accumulated in a memory within the PM and read out at a later time. By accumulating each type of transaction and the time each transaction time takes into separate ‘buckets’, the PM can contain the data of a histogram of the time each type of transaction takes. This information can be read from the PM's memory either via hardware that affects the state of the MPMC, or via hardware that communicates the information outside the MPMC for a computer or person to look at. It can be appreciated by those skilled in the art that many different types of measurements are possible, including directly measuring the memory 350. The PM then should be understood to not be limited exclusively to the domain shown in FIGS. 10A-10D, nor to the measurements described above. Any form of measurement can be stored in the PM's memory, and it is only requires logic structurally similar to that shown in FIG. 10B to produce the PM. FIG. 10B shows an exemplary block diagram to illustrate principles of creating performance monitors. BRAM 1006 is used to store the contents of the measured data. For example, BRAM 110 from FIG. 1 could be used to store the measured data. BRAM 1006 can be dual ported, as shown in FIG. 10B. One side of BRAM 1006 is used to input the measurements while the other side is made available for hardware and/or software to read and write the contents of the PM's storage element (e.g., BRAM 1006). It should be noted that a single ported memory could also be used if sufficient logic is added to share the port. In one embodiment, the BRAM 1006 of the PM has a memory interface bus 1005 which can be coupled to DCR to BRAM connection logic 1004. It should be noted that in some embodiments, memory interface bus 1005 can be attached to one or more BRAMs, such as BRAM 1036 and/or BRAM 1046, which may or may not be contained within a PM or other part of the system. For example, memory interface bus 1005 could be attached to Control BRAM 414 as shown in FIG. 5A and/or arbiter BRAM 520, as well one or more performance monitors 1000 shown in FIG. 10. The DCR to BRAM connection logic 1004 is designed to translate the DCR Interface 1002 transactions into the transactions that BRAM 1006 can understand in order to read and/or write to BRAM 1006. It can be appreciated by one skilled in the art that any kind of interface could replace DCR Interface 1002 as a means to communicate with the BRAM 1006. For example, a hardware state machine could replace DCR to BRAM connection logic 1004 and provide feedback to arbiter 316 of FIGS. 3, 4 and 5A The PM's main purpose is to measure performance. In one embodiment, the performance measured is a histogram of the amount of time each type of transaction takes to execute. FIG. 10B demonstrates such an embodiment, though this example is provided to illustrate the major principles. Measurement envelope logic 1016 is used to keep track of how much time a given event is to be measured for. By the application of single clock cycle high pulses on the ‘Start Event’ and ‘Stop Event’ in sequence, an enveloping signal is created which is used to control a counter. The counter simply counts how many clock cycles have elapsed between the start and stop events. This information is then fed forward into lower order address management logic 1014. The count value, as well as scaling information is then used to determine which ‘time bucket’ within memory is to be chosen. Note that along with lower order address management logic 1014, the exemplary PM provides upper order address management logic 1012. Upper order address management logic 1012 is where the particular transaction type, along with whether the transaction is a read or a write is encoded to provide a unique ‘transaction bucket’. In order to build a histogram, accumulation must take place. The accumulator logic 1010 serves the accumulation purpose by reading the data specified by the current address through the address management logic 1014 and 1012, accumulating it, and then writing it back to the same current address. This provides an additional registration of an event within the bucket specified by the combination of transaction bucket and time bucket. Using the scaling function of lower order address management logic 1014, the time bucket can be scaled, for example, allowing one bin to hold one and two clocks or one, two, three or four clocks of accumulation. While this results in lower granularity of time counted, it offers a larger view over all time. The PM of the example embodiment, illustrated in FIG. 10B allows for the measurement of a histogram of transaction types and execution times of that transaction. FIG. 10C illustrates an example embodiment of how the BRAM 1006 might have its internal memory organized. The BRAM memory organization illustrates 16 different transaction buckets 1051-1066. Each transaction bucket is broken down into 32 time buckets. Each time bucket represents a 32-bit value that can accumulate the number of times a transaction's execution time has occurred for that specific transaction. For example, transaction bucket 1051 corresponds to a byte read transaction, while transaction bucket 1052 corresponds to a byte write transaction. Similarly, transaction bucket 1063 corresponds to a burst read of 256 words while transaction bucket 1064 corresponds to a burst write of 256 words. Note that in some instances, not all of the memory space is used in BRAM 1006, and thus, for example, transaction bucket 1065 and 1066 are left unused. Importantly, each of the time buckets within a transaction bucket can accumulate 232 events, since there are 32-bits of data available in BRAM 1006. The 32 time buckets contained within each transaction bucket correspond to a count of how many clocks the specified transaction took to execute. For example, if the scaling is set to count each clock separately, the minimum measured time is 2 cycles, and if a count of 3 is measured, then the second time bin within the transaction would have one added to it. As each subsequent transaction's time is counted, a count of one is added to each corresponding transaction and time bin. In some embodiments, the PM uses a DCR bus interface, as shown in FIG. 10B. Some bus interface types, such as DCR have very small address footprints, and therefore could not directly address all of the memory available within a single PM, let alone multiples PMs across multiple ports. In these types of systems, a so-called ‘keyhole’ register set is introduced which permits the memory(ies) to be fully addressed and read and written. FIG. 10D is an example embodiment for BRAM access registers 1080 provided to give a keyhole to access the memory. Read and writes are done to the BRAM access registers 1080 in order to set, clear, or read the data on the PMs or other BRAMs in the system. The register BRAM data 1070 is provided as the means of a conduit for the data that will go to or from the BRAM 1006, etc. The register labeled “WHICH BRAM” 1074 is used to determine which BRAM will actually be communicated with (e.g., BRAM 1006, BRAM 1036 or BRAM 1046). Similarly register 1072 is used to specify where within the BRAM the read or write will take place. (e.g., where within the BRAM Memory Organization of FIG. 10C). An optional register, data bandwidth 1076 can be provided which gives access to an aggregate data bandwidth number for the measured element (logic not shown in FIG. 10B.). For example, data bandwidth 1076 can be used to get an average, peak bandwidth, or both. In some embodiments, address space may be left unutilized by BRAM access registers 1080 It can be appreciated that the example PM embodiment illustrated in FIGS. 10A-10D is to illustrate the principles of measurement, accumulation, reading, writing, and control. Those skilled in the art will recognize a number of methods exist to measure a variety of performance related elements, as well as communicate information content to and from the memory in the PM. Each of those can replace the front end and/or back end logic shown in FIG. 10B. Configurable Data Path, Address Path, PHY Interface, and Pipelining Data Path The data path 318, as illustrated in FIG. 4, can be configured on a per-port and/or per-direction basis. The FIFOs 422, 424 and optional pipeline register 426 that receive and transmit data through the data path can be built, for example, from BRAMS, SRLs, LUT RAM or Registers. Read and write paths created through the FIFOs 422, 424 and optional pipeline registers 426, 428 are independent. The size of FIFOs 422, 424 and optional pipeline registers 426, 428 can be adjusted according to embodiments of the invention. To provide efficient operation, the FIFOs for each data port may be changed or adjusted depending on the device or bus attached to a port. Examples of how data path can be morphed or changed are as follows. First, a DSPLB can only do certain transactions, but the DSPLB transactions will dictate minimum FIFO size. Using an SRL based FIFO can be an appropriate choice. In contrast, a PLB can do many transactions and will require a larger storage area, so it likely will be desirable to use BRAM to make the larger FIFO. Lastly, an OPB will typically only use a single word read/write, so a register-type FIFO may be desirable. For latency control, if FIFO front and back end communicate at different speeds, the type and size of the FIFO can be adjusted in some embodiments of the invention. Previous structures forced fixed type with both end speeds fixed. With adjustable FIFOs, the front and back end speed can be selected depending on attached devices. FIFOs can further be constructed to accommodate different width memories and NPI sizes according to embodiments of the invention. The optional pipeline registers 426, 428 can be programmably connected from the data path 318 through the PHY interface 310 (which also has registers configurable to accommodate different width memories) to the memory 350 to create a highly configurable data path. Additionally, optional pipeline registers 426, 428 can be used to adjust latencies within the system, act as temporary data storage elements for data realignment when PIMs 330 and memory 350 are of differing size, or act as simple retiming elements to advantageously improve the data path timing. The variable data path allows for different size memory data widths while maintaining a constant interface to the ports and/or different size port widths while maintaining a constant memory data width. Additionally, the configurable data path allows for management of differing clock ratios between the memory 350 and the PIMs 330. For example, changing the memory to PIM clock ratio from 1:1 to 1:2 requires the data path to be in a different physical configuration to properly accumulate and forward data on both sides of the data path. The configurable data path therefore yields high flexibility in implementation area, frequency of operation and architectural functionality. The programmable data path can also include optional timing management logic (TML) 429 as shown in FIG. 4. This TML 429 is designed to create replicated optional pipeline registers 426 in the data paths to manage the number of loads for each data bit. The TML 429 can be used to keep the data paths that are at high frequency from being heavily loaded by the lower frequency data paths. This has two major effects. First, the latency on the high frequency data path is lower than on the slower frequency data path. Second, the operational frequency of the high frequency data path can now be met, or even enhanced due to how the loads are organized. Significantly, the TML logic is applied on a per-port, per-direction basis. In some embodiments, it is preferable to have a single large centralized storage element (e.g., FIFO) per direction between PHY 310 and FIFOs 422, 424. Using optional large centralized FIFOs 425, 427, typically made from a BRAM, allows the FIFO 422 and/or FIFO 424 storage requirements to be lowered. For example, when a large number of ports are used, FIFOs 422 and 424 can consume a significant amount of logic real estate of the overall MPMC. Adding a ‘front-end’ FIFO may allow the FIFOs 422, 424 to be simple register or smaller SRL based FIFOs. In some embodiments, optional large centralized FIFOs 425 and 427 can serve another advantageous purpose. In many systems, it is desirable to decouple the frequency of memory 350 from the frequency of ports 340. It is further desirable to run memory 350 at the highest possible clock rate that memory 350 is allowed to operate in order to gain additional data bandwidth. Using optional large centralized FIFOs 425, 427 permits the decoupling of frequencies across a single domain. The very high clock rate of memory 350 can have its data path very lightly loaded by directly connecting only to FIFOs 425 and 427. This smaller loading increases the frequency that the memory side of the FIFO may be able to run at. In yet another embodiment using the optional large centralized FIFOs 425, 427, the data path FIFOs 422, 424 may be able to be removed entirely. By using a BRAM for FIFOs 425, 427, the data from memory 350 can be placed in differing locations within the BRAM corresponding to the port that the data corresponds to. With appropriate adjustments to arbiter 316 and control state machine 314, it is possible to eliminate one or more of the FIFO 422 and/or FIFO 424 from the data path. In such embodiments, the ports ‘share’ the data from the dual ported BRAM. One side attaches to memory 350 via PHY 310 and optional pipeline 426. The other side is shared by the NPI. In another embodiment, multiple BRAMs could be used in order to increase the aggregate data bandwidth possible so that the port side of the FIFOs 425, 427 can be increased. Note that this differs from the normal data path 318 in that there is no longer one FIFO per port per direction. Instead the ports have ‘logical’ FIFOs by their address context within optional centralized FIFOs 425, 427. Address Path Like the data path 318, the address path 312 is also programmable according to embodiments of the invention. The address can be programmed to be multiplexed or non-multiplexed by including multiplexers 415. An SRAM type memory may not use a multiplexed address, while a DRAM type memory may. Thus, the multiplexers 415 of FIG. 4 can be optionally included or not included. Multiplexers 417 are used to choose which port's address will be selected and ultimately presented to memory 350 via PHY 310. In some embodiments, per port FIFOs 412 are included in order to allow for transactions to be queued. This gives the MPMC arbiter 316 a priori information to begin arbiting for access to the memory long before it is needed. The result is a substantially more efficient use of both memory 350, and the bus(es) connected to ports 340. In other embodiments, per port FIFOs 412 may be single registers (e.g, a 1 deep FIFO). In still other embodiments, typically where the entire system is fully synchronous at a single rate, FIFOs 412 may be eliminated entirely in order to reduce latency. In some embodiments, the address size can be dynamically adjusted based on the memory device. In one embodiment, the address size is dynamically changed based on type of memory that is addressed. In this case, additional multiplexers (not shown) are used to ‘reconfigure’ the address to match the memory device requirement. This is a particularly important when two disparate memories are present as part of memory 350. For example, if two DIMMs that have differing addressing requirements are present within the system, accommodation must be made within address path 312 in order to be able to properly accommodate each DIMM. In some embodiments, the address of each port is independently settable. With adjustable addresses, each port can have address space of its own. However, an overlap between two addresses can also be generated. In some occasions, this is a desirable effect. The address path 312 permits address overlapping, address offset, address replication and address aliasing between ports. FIGS. 11A-11B illustrate various types of addressing based on this potential address overlap, offset, replication and aliasing. FIG. 11A illustrates the concepts of address overlap, offset, replication and aliasing using an example of how five different ports might be setup according to embodiments of the present invention in a five port MPMC. Memory physical address space 1190 graphically shows how the five ports might appear within the physical address space of memory 350. Note that Port 0 and Port 1 have some address space within the memory that overlaps. Port 2 (and 2A as described below) has address space that is effectively doubled in size from the perspective of the port, but is only ½ the size in the actual memory. For example, the addressees specified when Port 2 communicates in address range 0x3000—0000 to 0x4000—0000 will actually result in memory transactions in the corresponding address range of 0x2000—0000 to 0x3000—0000 respectively. Port 3 demonstrates a simple offset of address such that the port address and memory address are the same, but are offset from where, for example, Port 0 will communicate with memory. Port 4 demonstrates the concept of aliasing. That is, the address the port uses to communicate with memory is aliased to the memory in a different location (e.g., port access to 0x2000—0000 corresponds to 0x0000—0000 in the memory). Lastly, Port 5 illustrates a simple large range of addresses that encompass all the other ports ranges of addresses. In such a situation, Port 5, and Port 5 alone can communicate with every location of memory that any other port communicates with. To provide further delineation, Port 0, Port 4, part of Port 5 and part of port 1 all share the same memory. However, Port 2 cannot talk to any of the memory that Port 0, Port 1 and Port 4 have access to. FIG. 11B demonstrates the Ports logical address space 1100. This diagram usefully shows how each port has a base address and high address. Port 0 has base address 1102 and high address 1104. Similarly, Port 1 has base address 1112 and high address 1114 while Port 2 has base address 1122 and high address 1124. Port 3 has base address 1132 and high address 1134. Port 4 has base address 1142 and high address 1144. Lastly, Port 5 has base address 1152 and high address 1154. FIG. 11B also shows the following significant items: First, base address 1102 of Port 0 and base address 1152 of Port 5 are set the same. Second, the high address 1114 of Port 1 and base address 1122 of Port 2 as well as base address 1132 of Port 3 are set the same. Third note that base address 1112 of Port 1 is set higher than base address 1102 but lower than high address 1104 of Port 0. The results from these configurations demonstrate overlap 1172 where Port 0 and Port 1 share a part of their address space. This is useful for inter process communications (IPC) so that the shared part of the memory is available to both parts, but there is additional unique memory available for each port separately. Another configuration demonstrated in FIG. 11B is offsets 1174, 1177 and 1178. Here we see that the address of Port 1, Port 2 and Port 3 are each offset from the bottom of the ports logical address space, respectively. Offsetting is useful to achieve either overlapping of addresses, as described above, or to simply separate address spaces between ports. An example of the latter might be where Port 1 and Port 2 are tied to processors each of which is running a separate operating system that requires its memory space to be separate. Yet another configuration is shown via replication 1176 in FIG. 11B. Here the address from Port 2 is actually doubled in apparent size. That is, only ½ of the address space will be physically available in memory, but access by the port to either region will result in access to the memory within the ½ space. An excellent use for this is when a system has a video graphics controller and wishes to ensure that the video data does not go through the cache of the processor. The processor would keep the lower ½ cacheable and the upper ½ uncacheable. When the processor wanted to write data to the video screen, it would access the upper ½ and not alter the contents of its cache. FIG. 11B also demonstrates a fourth memory configuration via alias 1179. In this situation, the port believes that the memory is located far away from the bottom part of memory. For example the port will talk to address range 0x8000—0000 to 0x9000—0000, but will actually be communicating to the physical memory at address range 0x0000—0000 to 0x1000—0000. This can be useful for many purposes including apparent separation in the system between ports for debugging purposes. In some instances, systems have requirements on a port that it appear to be at a different address location but still see memory at the apparent physical address. According to some embodiments of the present invention, provisions are additionally made to prevent collisions between overlapping addresses depending on programming of address size. For example, semaphores may be used to avoid or prevent collisions. This can be true of either an overlap in the physical memory space, and/or each port's logical address space. FIGS. 11A-B demonstrate the wealth of possible address configurations which are possible due to the highly configurable nature of address path 312. Those skilled in the art will understand that these configurations can be mixed and matched on a per port basis, or even in some embodiments on a per port, per address, per direction basis. That is, read and write address could differ for each port, as well as each port having multiple logical address ranges that map to multiple physical memory address ranges using the above styles of configurations. PHY Interface The PHY interface 310 according to some embodiments of the present invention is provided that can be parameterized so that data is aligned to match the type of memory connected to the MPMC. The PHY Interface 310 according to some embodiments of the invention is more than a conventional group of registers with clocking. The PHY interface 310 provides for versatile data alignment. Instead of using a state machine to read data and look for a data address strobe (DAS) or column address strobe (CAS) to align data before sending/receiving to/from the PHY interface, embodiments of the PHY layer of the present invention look at data itself. As shown in FIG. 12, the PHY of embodiments of the present invention include data alignment state machine 1210 to read and write the header, payload and footer to/from memory 350 and use the header, payload and footer information to provide precise data alignment using delay 1230 before data is applied to flip-flops 1214. A specific data-training pattern is used that conceptually includes a header, payload and footer. The header is used to identify an edge within the data whereas the payload and footer are used together to ascertain which edge is the first edge of the intended data. The footer also serves to ensure that last edge of data can be fully captured. The data alignment state machine 1210 is typically only used during initialization of memory 350. During the training period, state machine 1210 must communicate with multiplexer 1250 to force write data to memory 350 at the appropriate time. The state machine 1210 will control the delay element to properly set the delay upon completion of the training. In one embodiment state machine 1210 begins with the delay set to some value, and steps through each delay value possible until it identifies when data first starts being aligned correctly, and then continues on until it has exhausted the maximum value of the delay, memorizing the points where the data first started to be correct, and where it first stopped being correct. State machine 1210 will then reset the delay 1230 to the midway point between where data first started being correct and where it last was correct. With the PHY embodiments of the present invention, latency is reduced and data alignment is more efficient. Unlike conventional MPMCs that aligned the data 4 or 8 bits at a time using data strobes, the present PHY embodiment can also align individual bits. With sufficient FPGA input/output hardware, it is also capable of adjusting read and/or write timing on a per-port basis. This is strongly advantageous because it can correct for common mistakes in printed circuit board routing between an FPGA and connected memory device. Further still, the present PHY interface embodiments are capable of easily connecting to different memory types. While the primary function of the PHY interface is data alignment, it can be appreciated by those skilled in the art that the PHY interface can easily be altered to accommodate a number of different types of memory including SDRAM, DDR SDRAM, DDR2 SDRAM, SRAM, BRAM, RLDRAM, and nearly any other memory technology which the input/outputs of the FPGA can communicate with. Intelligent Pipelining In one embodiment, optional pipeline registers 538 as illustrated in FIG. 5A are included to control provision of the initial sequence and other control signals from the arbiter BRAM 520 to the control state machine 314. The optional pipelines 538 can be selectively added on each port between the arbiter 316 and control state machine 314 of the memory controller. The additional signals include an indication of which port has been granted memory access as well as an indicator of when a sequence has started. The optional pipelining can achieve improved performance, particularly when a large number of ports are used. The optional pipelining of registers shown can likewise be included in other areas of the memory controller. For example, as shown in FIG. 4, optional pipelining 426 and 428 can be used in the data path logic 318. Further the optional pipelines 411 can be used in the address path logic 312. Intelligent pipelining allows user program control over a variety of pipeline stages in order to permit a customer to trade off FPGA area for maximum frequency performance. The location of these optional pipelines and their ability to be controlled on a per-port basis achieves greater flexibility and performance. In some embodiments of an MPMC of the present invention, the optional pipelines can be dynamically employed as needed. For example, if two disparate DIMMs make up memory 350, one configuration of the optional pipelines can be used when communicating with the first DIMM, whereas a second differing configuration can be used when communicating with a second DIMM. This dynamic ability advantageously provides the best performance for both DIMMs. In some embodiments, the characteristics of the MPMC for configuring the intelligent pipelining, address path, data path, control path and PHY path are obtained by reading so-called Serial Presence Detect (SPD) Read Only Memory (ROM) typically found on Dual Inline Memory Modules (DIMMs). The SPD ROM is well known in the art. In some embodiments some or all of the variables that affect the MPMC can be read from the SPD ROM, and then enacted in the MPMC structure. This could include configuring the address path, data path, control path, number, type and size of FIFOs used, as well as other memory unique information. In some embodiments, the MPMC's function can be altered dynamically depending upon which of several DIMMs the MPMC is communicating with. This is particularly useful when multiple disparate DIMMs are placed within a system. Versatile Graphical User Interface The MPMC implemented using an FPGA can be programmed in some embodiments through a Graphical User Interface (GUI) that provides advantages over prior art. First, the GUI allows system topology creation as well as programming of the MPMC to form a complete project that can be run through Electronic Design Automation (EDA) tools. Previously, GUIs only allowed programming of a single core at one time. With embodiments of the present invention, the GUI can be data driven from user editable text files. It can also offer feedback on resource utilization. Further, it can provide performance feedback estimates based upon the current programmable settings for each port. The GUI can allow users to create sets of data for their configurations of an MPMC and to reuse those for future projects. The GUI uses the information entered to dynamically create an entire core for the MPMC as well as peripherals and processors while providing intelligent design rule checking both as information is being entered, as well as during operation when the GUI dynamically creates complex hardware. The GUI can also be used to display information content from the Performance Monitor(s) within an MPMC system. In some embodiments, this information can be used to dynamically update the arbitration scheme currently in use in the MPMC system. Thus the GUI need not only be used for configuration of the MPMC based system. FIGS. 13-17 provide screen shots of a GUI demonstrating an example GUI according to embodiments of the present invention. The screen shots are presented to illustrate some key components for a GUI that are advantageous in configuring MPMCs in an FPGA. Additionally, the screen shots can help elucidate new principles in GUI development that are advantageous outside their use with MPMC systems. FIG. 13 shows an example of the main or “Base Configuration” tab 1316 of the GUI. Here a user will have the opportunity to load past configurations, set various options that affect what is built, create the MPMC core as a standalone entity, or create an entire system based upon the present settings within the GUI. Importantly, a design may first be loaded that is identifiable in a user editable text file 1300 selected using drop down menu 1304 and loaded using button 1302. The GUI displayed can be used to change parametrics of the MPMC and/or system. The text files that contain the MPMC configuration information can be copied and placed within a directory that the GUI creates. These files are then dynamically available from the drop down menu tab 1304 of preconfigured MPMC cores. FIG. 13 further shows settings in region 1306 and region 1307 of the memory 350 to be attached to the MPMC. These are used to read in specific manufacturer memory devices and to intelligently control what configuration the MPMC will need to be in. The physical memory configuration information is also text file data driven using region 1307, and file information can be added to by the user, the author of the GUI, or a memory manufacturer. Additionally, the text files used for region 1307 permit the drop down boxes in region 1307 to have their content dynamically set based upon the organization structure of those text files. The act of selecting an element from the final drop down box in region 1307 results in loading the specified file content into the GUI and advantageously intelligently setting various MPMC control parameters. It should be appreciated by those skilled in the art that these techniques can be applied to many differing types of GUIs. FIG. 13 further shows the configuration of the PIMs in regions 1308. Each port can have a different type of PIM as shown in the Port Type drop down field 1309, and can further have the Performance Monitors (PM) enabled or disabled by check box 1310 as needed. Each port can also have its clock frequency set using box 1312. Address configuration information can be provided using boxes 1314. The GUI contains intelligence to guide users and help them prevent mistakes. These include dynamic rule checking to ensure entered data conforms to the format and type of information required, as well as pop-up dialogs when an error or warning is encountered. Further, each data entry point contains mouse over text that helps to explain what the data entry point is for. FIG. 13 also demonstrates the use of tabs to organize information presentation to the user. Significantly, in FIG. 13, the “Base Configuration” tab 1316 was designed so that most users would never have to use the other tabs, and yet still perform the configuration they wished to achieve. The other tabs are available when additional user control is desired. FIG. 14 shows additional per-port configuration information. In this case, the data path configuration is shown that can be accessed using the “Data Path Configuration” tab 1400. Here is where the user will specify some of the common constraints that are used to determine the size, style and operation of the data path FIFOs referred to in FIG. 4. Additionally, FIG. 14 shows an example of area utilization reports, here the “BRAM Management Report” 1402. It can be appreciated by one skilled in the art that additional information could be reported such as the total FPGA area, predicted frequencies of operation, and fit for a particular FPGA. Further, a “thermometer” 1404 is provided in the management report area 1402 that can graph as well as turn various colors to represent how close to fully utilized the number of elements which are provided within the selected FPGA are. For example, it turns yellow to indicate when the configuration is close to exhausting the resources, and red when the resources are exhausted. This provides additional visual clues that are important to the user in order to correctly configure the MPMC. FIG. 14 also shows an example of user control over pipelining for the individual data path ports using regions 1406. This includes “Read Pipeline” and “Write Pipeline” fields that all pipeline control using check boxes. In some embodiments, the pipelining is automatically set based upon other choices the user has made in the GUI. For example, when the user loaded a particular manufacturer's part number for memory 350 in region 1307, specific information within the file loaded will cause a design rule check which will result in specific ports having their pipeline stages independently enabled/disabled. This kind of intelligence greatly assists a user from making a mistake, and is one essential component to so-called ‘ease of use’. FIG. 15 shows an example of the static arbitration configuration means selected using the “Arbiter Configuration” tab 1500. Here, the user has the freedom to load and save configurations, again of user editable text files, to effect a particular arbitration scheme. Significantly, the GUI allows multiple algorithms to be stored and/or loaded using tabs 1502, including default algorithms. FIG. 15 further illustrates another example means to control and configure the pipeline stages, this time within the arbiter using check boxes 1504. These are loaded by the load button 1302 on FIG. 13, or in some embodiments by intelligent design rule checking, but are still changeable by the user within the Arbiter Configuration tab 1500 in region 1504. FIG. 15 also demonstrates an easy means to adjust important arbiter characteristics, and guides the user in so doing. For example, the total number of time slots is settable using drop down 1506, which then enables or disables the editability of the timeslots. Within each timeslot 1508, the dynamic rule checking ensures that the typed in data is of the correct form, and notifies the user via colorization of the text when it is incorrect. Lastly, the arbiter configuration tab 1500 of the GUI offers information in the aliasing of the port names to the port numbers. Entering data in the Time Slot editable boxes is done via port number to keep it easier to understand and less work to type—but the user needs to know what interface each port number corresponds to. The GUI provides the Port Base Configuration field 1510 in FIG. 15 to assist the user in knowing the context of each port. FIG. 16 shows the “Memory Info” tab 1600. This tab is significant for two reasons. First, it provides a highly detailed summary to the user of specific parameters that a selected memory device to attach to an MPMC requires. Second, it illustrates the application of a completely dynamically generated content of the GUI from English text files. The former is of interest to users because they may wish to verify that the data the GUI will be using matches what the selected memory actually requires. The latter is significant because data driven files populate the content of the GUIs fields for this tab. For example, based purely upon the Part_Number 1602, the remaining fields within the GUI are automatically loaded when the user selected the Part_Number from region 1307 in FIG. 13. An array of English text files, indexed by Part_Number, are used to populate the remaining fields. For example, the parameter 1604 fields, value 1606 fields, and unit 1608 fields from within Memory Timing Information box 1610 are all populated from the contents of this text file dynamically. Additionally, when the text file is read in, populating the visible data shown in FIG. 15, it also loads the so-called “mouse over” information. This is the information that pops up when a user pauses the mouse pointer over an element to help explain the purpose of the particular element. This is a significant embodiment because it means that many disparate types of memory can be added simply by adding a text file and the compiled source code of the GUI does not need to change. One skilled in the art will recognize the value of not having to maintain the GUI to add completely new features. This aspect of the present invention is readily usable in many other applications than MPMCs. FIG. 17 demonstrates the “Error Log” tab file 1700 that is produced upon running the GUI to configure the MPMC or the MPMC system. In addition to writing a log file to a specific location, the log file is also shown within the context of the GUI. This prevents a user from having to waste time looking for another application beyond the GUI to have all relevant information. FIGS. 13-17 also demonstrate a number of buttons on the bottom, such as buttons 1702 shown in FIG. 17. These buttons are used to control the creation of MPMC core or system, as well as provide direct access to the documentation related to MPMC. Additionally, the buttons demonstrate a third function that is a control function, global in scope to the GUI. In this case, that function is to Left Justify Ports, from the button 1704 of that name, causing any gaps in the ports shown in FIG. 13 and FIG. 14 to be removed. It can be appreciated that other global scope functions could be included within these buttons and that these buttons differ in function from the documentation or program control functions. In some embodiments of the present invention, different frequencies are allowed to be used within the memory control portion of MPMC. This affects the address path 312, control path state machine 314, port arbiter 316 and in some instances, portions of data path 318. Memory 350 is often a double data rate memory where the data appears on both edges of the clock. There are two typical methods to handle this situation, namely double the output width or double the frequency of the data path. Doubling the frequency of the data path is typically difficult, and thus the usual alternative choice of doubling the output width is selected. However, there is an additional opportunity available to slow down paths within the MPMC based upon some memory technologies. In some instances, including DDR memory, it is possible to run the address and control signals to the memory at ½ the speed of the clock. In some embodiments of the present invention, the PHY interface 310 can contain I/O registers that are clocked at the normal clock rate of the memory, but are fed by information clocked at ½ that rate, and the I/O registers have asynchronous set/reset pins. The control logic (address path 312, control state machine 314, port arbiter 316, and parts of data path 316) is altered as needed to operate at this ½ clock rate of memory 350. Additionally, some extra logic can be placed within control state machine 314 which runs at the clock frequency of memory 350 and is used to drive the previously mentioned set/reset signals going to the I/O registers within the PHY interface 310. These signals are used to make the signals coming from PHY interface 310 appear as though they are clocked by the memory clock. For example, in DDR memory, there is an activate command followed by a no operation command. The PHY interface would be handed just the activation command at ½ the clock speed of memory 350, but also would be handed the set/reset signals to effect the no operation command at the right time. The net effect of these combinations is the ability to run the memory 350 at much higher effective clock rates than previously possible. It can be appreciated by one skilled in the art that the logic structures of embodiments described herein could be implemented advantageously using Programmable Logic Device (PLD) technology, more specifically, FPGA style PLDs. However, other implementations are possible using other technologies, such as an Application Specific Integrated Circuit (ASIC), standard cell, or even full custom. These implementations can be “fixed” from the originally programmable implementations in order to accomplish a specific purpose. As such, the present invention need not be limited exclusively to FPGA technology, as one skilled in the art can appreciate. Although the present invention has been described above with particularity, this was merely to teach one of ordinary skill in the art how to make and use the invention. Many additional modifications will fall within the scope of the invention, as that scope is defined by the following claims. |
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description | Referring initially to FIG. 1, a separation device in accordance with the present invention is shown and generally designated 10. As shown, the separation device 10 includes a substantially cylindrical wall 12 that surrounds a chamber 14 and extends from a closed end 16 to an open end 17. As shown in FIG. 2, the cylindrical wall 12 defines a longitudinal axis 18. In the preferred embodiment of the present invention, the wall 12 is formed with a plurality of holes 20a-d to allow a working gas to be introduced into the chamber 14. Although four holes 20a-d are shown, it is to be appreciated that the size, shape and number of holes 20a-d shown for introducing a working gas into the chamber 14 is merely exemplary. Referring now with cross reference to FIGS. 1 and 2, it can be seen that coils 22a-d are mounted on the outside of the wall 12. For the present invention, a current source (not shown) can be used to pass an electrical current through the coils 22a-d to generate a magnetic field, B, in the chamber 14. For the present invention, a magnetic field that is oriented substantially parallel to the longitudinal axis 18, and is substantially uniform in strength throughout the chamber 14 is preferably established. For some applications, small magnetic mirrors (not shown) can be established near the ends 16, 17 of the wall 12 to axially confine the plasma within the chamber 14. Although four coils 22a-d are shown mounted on the outside of the wall 12 to generate a uniform magnetic field in the chamber 14, it is to be appreciated that these coils 22a-d are merely exemplary, and that the size, shape and number of coils 22a-d can be varied in accordance with the present invention. Furthermore, it is to be appreciated that other methods known in the pertinent art for establishing a uniform, axially aligned magnetic field in the chamber 14 can be used for the present invention. In accordance with the present invention, as shown in FIGS. 1 and 2, a plurality of ring electrodes 24a-c, are positioned in the chamber 14 near the closed end 16 of the wall 12. As shown, each ring electrode 24a-c is preferably positioned to be concentrically centered on the longitudinal axis 18. For the present invention, the ring electrodes 24a-c can be staggered axially to reduce sputtering of the electrodes 24a-c by the ion beam exiting the chamber 14 (note: axially staggered electrodes not shown). With this combination of structure, a voltage source (not shown) can be connected to the electrodes 24a-c to establish a radially oriented electric field, E, in the chamber 14. Referring still to FIG. 2, it can be seen that an elongated central electrode 28 is positioned in the chamber 14 and oriented substantially along the longitudinal axis 18. Preferably, as shown, the outer surface of the central electrode 28 is formed with a plurality of disk-shaped projections 30 that extend radially outward from the longitudinal axis 18. In accordance with the present invention, the projections 30 are provided to minimize loss of the central electrode 28 to the plasma in the chamber 14 due to sputtering of the central electrode 28. Although disk-shaped projections 30 are shown, it is to be appreciated that any surface feature known in the pertinent art, such as a beehive configuration (not shown), that effectively minimizes sputter loss can be used on the surface of the central electrode 28 in conjunction with the present invention. In some embodiments, a voltage source (not shown) can be connected to apply a voltage between the wall 12 and the central electrode 28 to establish part or all of the required radially oriented electric field in the chamber 14. Thus, a radially oriented electric field is established by either the ring electrodes 24a-c, the wall 12 and central electrode 28, or both. Importantly, the radially oriented electric field is directed inwardly from the wall 12 towards the central electrode 28, and accordingly, the central electrode 28 functions as a cathode while the wall 12 functions as an anode. As shown, the central electrode 28 is distanced from the wall 12 by a distance 29. As further shown in FIG. 2, the central electrode 28 is preferably formed with a gas-box 32 for the purpose of recycling working gas that has accumulated at the central electrode 28. As shown, channels 34 are formed in the central electrode 28 to allow working gas to pass into the gas-box 32 from the chamber 14. Once inside the gas-box 32, the working gas is able to travel in the direction of arrow 36 and into a duct 38 that is located outside of the wall 12. In the preferred embodiment of the present invention, the duct 38 is routed along the outside of the wall 12 to deliver working gas from the gas-box 32 to the holes 20a-d in the wall 12 for subsequent reintroduction into the chamber 14. Also shown, a control valve 40 is preferably installed along the duct 38 to selectively meter the working gas through the duct 38. Although only one duct 38 is shown to deliver working gas from the gas-box 32 to the holes 20a-d, it is to be appreciated that any number of ducts 38 can be provided to deliver working gas from the gas-box 32 to the holes 20a-d. In the preferred embodiment of the present invention, the chemical mixture requiring separation is formed into tiles 42 and mounted on the inside of the wall 12 facing the chamber 14, as shown in FIGS. 2 and 3. In an alternative embodiment of the present invention (not shown), the wall 12 can be made of the chemical mixture requiring separation. In accordance with the present invention, the chemical mixture can be a mixture, aggregate or alloy of two or more constituents. Each constituent, in turn, can be a chemical element, isotope or chemical compound. One chemical mixture that is particularly applicable for the present invention is a metallic alloy of Zirconium and Hafnium. The operation of the present invention can best be appreciated with reference to FIGS. 2 and 3. Once the constituents of the chemical mixture are known, the working gas can be selected. Specifically, the chemical mixture will be separated into constituent(s) having relatively low mass to charge ratios in the plasma and constituent(s) having relatively high mass to charge ratios in the plasma. Preferably, the working gas is selected to have a mass to charge ratio in the plasma that is between the low mass to charge ratio constituent and the high mass to charge ratio constituent. Further, a noble element is preferably used as the working gas. For the case where the chemical mixture requiring separation is a metallic alloy of Zirconium and Hafnium, the working gas is preferably Xenon. To create a plasma in the chamber 14, the chamber 14 is first evacuated and then filled with the working gas using the holes 20a-d in the wall 12. Next, a plasma is created from the working gas in the chamber 14 by energizing the ring electrodes 24a-c. Upon obtaining a plasma in the chamber 14, the strengths of the electric and magnetic fields are adjusted to control the trajectories of the ions to effect separation of the chemical mixture. In one embodiment, the electric and magnetic fields are adjusted to cause the Larmor diameter of the working gas to be slightly smaller than the distance 29 between the central electrode 28 and the anode (i.e. the tiles 42). Generally, a relatively large electric field is required to initially create a plasma from the working gas and a smaller electric field necessary to establish the proper ion trajectories. Once the strengths of the electric and magnetic fields have been properly adjusted, molecules/atoms of the working gas that are ionized near the wall 12 are directed on trajectories (shown by exemplary arrow 44) toward the central electrode 28. Specifically, the strengths of the magnetic and electric fields are established such that the Larmor diameter of the working gas ions in the fields is somewhat smaller than the distance 29 between the wall 12 and the central electrode 28. Near the central electrode 28, a portion of the working gas ions that were directed toward the central electrode 28 (i.e. arrow 44) will undergo electron exchange reactions with neutrals atoms that are present there, creating fast neutrals that are directed on trajectories (shown by exemplary arrow 46) towards the tiles 42. Another portion of the working gas ions that were directed toward the central electrode 28 (i.e. arrow 44) will strike the central electrode 28, neutralize, and contribute to the neutral gas pressure in the gas-box 32. It is to be appreciated that the fast neutrals that are produced have sufficient energy to strike the chemical mixture near the wall 12 and sputter the chemical mixture into the chamber 14 where a plasma has been established from the working gas. In the plasma, the sputtered chemical mixture is dissociated into its constituents, and the constituents are ionized. Due to the strengths and orientations of the electric and magnetic fields in the chamber 14, ionized constituents having a relatively high mass to charge ratio are placed on trajectories that are directed towards the central electrode 28 (i.e. orbital trajectories of large radius, shown by exemplary arrow 48). Specifically, the strengths of the magnetic and electric fields are established such that the Larmor diameter of the high mass to charge ratio ions in the fields is larger than the distance 29 between the wall 12 and the central electrode 28. Upon striking the central electrode 28, these ions are captured. On the other hand, ions having a relatively low mass to charge ratio are placed on small radius, orbital trajectories (shown by exemplary arrow 50). Specifically, the strengths of the magnetic and electric fields are established such that the Larmor diameter of the small mass to charge ratio ions in the crossed electric and magnetic fields is smaller than the diameter of the chamber 14. As such, these ions are directed out of the chamber 14 through the open end 17. The result is an essentially pure ion beam containing almost exclusively ions of relatively low mass to charge ratio exiting from the open end 17 of the wall 12. During the operation of the present invention, neutrals of the working gas are accumulated near the central electrode 28 and depleted near the wall 12. Denoting the direct ion current to the cathode as I and the charge exchange flux as xcex930, energetic ions that reach the cathode due to direct loss (particle flow I/e) and energetic neutrals that are produced due to charge exchange of these ions with neutral gas near the cathode (xc2xdxcex930) both sputter the cathode and create a flow of neutrals from the cathode, n0cV0. Here n0c is neutral density of the sputtered atoms near the cathode and V0 is average velocity of the sputtered ions. It is further assumed that about one-half (xc2xd) of the charge exchange neutrals can reach the cathode and about one-half (xc2xd) can reach the anode. The dependence of this partition on attenuation of the beam has been neglected. The ratio xcex2 can be defined as: Ratio xcex2=xcex930/(I/e). The flux of fast neutrals that end up on the cathode, are neutralized, and contribute to the pressure in the gas-box 32, can be expressed as a function of ion current: Gc=(I/e)(1+xcex2/2). The flux of fast neutrals in the direction of the anode is: Ga=(I/e)xcex2/2 which is smaller than the gas flow from the anode: n0a less than V0 greater than S=(I/e)(1+xcex2). Here n0a is the neutral density of the sputtered atoms near the anode. Accordingly, to sustain the discharge, a bypass for the gas flow can be provided. Assuming Knudsen flow in the bypass duct 38: Ga=Sduct(D/L) less than V0 greater than (n0cxe2x88x92n0a). Here S=xcfx80D2/4, D is duct 38 diameter and L is duct 38 length. As indicated above, the gas conductance in the duct 38 can be controlled by a valve, and, hence, the ratio n0a/n0c can be varied if necessary. Table 1 below provides exemplary parameters for a small-scale device to separate a Zirconium-Hafnium alloy. While the particular methods and devices as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims. |
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043550029 | abstract | First nuclear fuel elements in which a fissionable material in which a burnable poison is incorporated is loaded and second nuclear fuel elements in which a fissionable material in which no burnable poison is incorporated is loaded are disposed in a nuclear fuel assembly. Content of the fissionable material in the first nuclear fuel element is less than about 72% of that of the fissionable material in the second nuclear fuel element adjacent to the first nuclear fuel element. |
abstract | This invention relates to a control method for a pressurized water nuclear reactor, which comprises a core generating thermal power and means of acquiring magnitudes representative of core operating conditions. The method comprises a step to regulate the temperature of the primary coolant, if the temperature of the primary coolant for a given thermal power is outside a predefined set temperature interval (ΔTREF) depending on the reactor power. The set temperature interval (ΔTREF) is characterized by variable amplitude (ΔT) on a thermal power range between N % and 100% nominal power, where N is between 0 and 100 and comprises a zero amplitude at 100% nominal power, a zero amplitude at N % nominal power. |
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052251543 | claims | 1. A fuel assembly for a nuclear reactor, comprising a fuel cladding tube of three-layer structure having an outer surface layer to be in contact with reactor water of the nuclear reactor, which outer surface layer is made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy containing Nb, Sn and Mo consisting by weight of 0.5 to 2.2% Nb, 0.5 to 1.5% Sn, 0.1 to 0.8% Mo, and the balance Zr and incidental impurities, an inner surface layer to be in contact with nuclear fuel, which inner surface layer is made of pure zirconium, and an intermediate layer made of a high ductility alloy which is higher in ductility than the outer surface layer and which is higher in strength than the inner surface layer, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 2. A fuel assembly for a nuclear reactor, comprising a fuel spacer of three-layer structure having outer surface layers to be in contact with reactor water of the nuclear reactor, which outer surface layers are made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy containing Nb, Sn and Mo consisting by weight of 0.5 to 2.2% Nb, 0.5 to 1.5% Sn, 0.1 to 0.8% Mo, and the balance Zr and incidental impurities, and an intermediate layer adjacent to the outer surface layers, which intermediate layer is made of a high ductility alloy higher in ductility than the outer surface layers, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 3. A fuel assembly for a nuclear reactor, comprising a fuel channel box of three-layer structure having outer surface layers to be in contact with reactor water of the nuclear reactor, which outer surface layers are made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy containing Nb, Sn and Mo consisting by weight of 0.5 to 2.2% Nb, 0.5 to 1.5% Sn, 0.1 to 0.8% Mo, and the balance Zr and incidental impurities, and an intermediate layer adjacent to the outer surface layers, which intermediate layer is made of a high ductility alloy higher in ductility than the outer surface layers, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 4. A fuel assembly for nuclear reactor of any one of the claims 1 to 3, wherein the high ductility alloy forming the intermediate layer consists of a Zr-based alloy containing Sn, Fe and Ni. 5. A fuel assembly for nuclear reactor of the claim 4, wherein the high ductility alloy forming the intermediate layer consists by weight of 0.5 to 2.0% Sn, 0.05 to 0.4% Fe, 0.03 to 0.2% Ni, and the balance Zr and incidental impurities. 6. A fuel assembly for nuclear reactor of any one of the claims 1 to 3, wherein the high ductility alloy forming the intermediate layer is a Zr-based alloy containing Sn, Fe, Ni and Cr. 7. A fuel assembly for nuclear reactor of the claim 6, wherein the high ductility alloy forming the intermediate layer consists by weight of 0.5 to 2.0% Sn, 0.05 to 0.4% Fe, 0.03 to 0.2% Ni, 0.05 to 0.15% Cr, and the balance Zr and incidental impurities. 8. A fuel assembly for nuclear reactor of any one of the claims 1 to 3, wherein the high ductility alloy forming the intermediate layer is a Zr-based alloy containing Sn, Fe, Ni, Cr and Mo. 9. A fuel assembly for nuclear reactor of the claim 8, wherein the high ductility alloy forming the intermediate layer consists by weight of 0.5 to 2.0% Sn, 0.05 to 0.4% Fe, 0.03 to 0.2% Ni, 0.05 to 0.15% Cr, 0.01 to 0.8% Mo, and the balance Zr and incidental impurities. 10. A fuel assembly for nuclear reactor of any one of the claims 1 to 3, wherein the high ductility alloy forming the intermediate layer consists of Zr and incidental impurities. 11. A fuel assembly for nuclear reactor of any one of the claims 1 to 3, wherein the high ductility alloy forming the intermediate layer consists by weight of 0.1 to 0.7% Nb, and the balance Zr and incidental impurities. 12. A fuel assembly for nuclear reactor of any one of the claims 1 to 3, wherein the high ductility alloy forming the intermediate layer is a stainless steel containing carbon, the carbon being included in an amount, by weight, up to 0.08%, and the stainless steel also containing, by weight, 0-2.0% Mn, 0-1.00% Si, 16.0 to 20.0% Cr, 8.00 to 14.00% Ni, 0-3.00% Mo, and the balance Fe and incidental impurities. 13. A fuel assembly for nuclear reactor of any one of the claims 1 to 3, wherein the high ductility alloy forming the intermediate layer is a Cu-based alloy consisting by weight of 0-3.0% Pb, 0-6.0% Fe, 0-0.5% Zn, 0-11.0% Al, 0-2.0% Mn, 0-33.0%; Ni, and the balance Cu and incidental impurities. 14. A fuel assembly for nuclear reactor of claim 1, wherein in the fuel cladding tube the thickness of the outer surface layer to be in contact with the reactor water of the nuclear reactor is 10 to 30% of the total thickness of the cladding tube. 15. A method of producing a fuel assembly for nuclear reactor of any one of the claims 1 to 3, 14 and 28, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding when assembling the three-layer structure. 16. A method of producing a fuel assembly for nuclear reactor of claim 2, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding the end face of a tubular or plate-like member. 17. A method of producing the fuel assembly for nuclear reactor of any one of the claims 1 and 14, wherein the fuel cladding tube is produced by a process comprising the steps of: inserting a cylindrical billet of an alloy, which becomes an intermediate layer, into another cylindrical billet which becomes an outer surface layer in contact with the reactor water of the nuclear reactor; inserting into the intermediate layer billet a cylindrical billet which becomes an inner surface layer; integrating all of these billets by welding each end face thereof; extruding the integrated billets at a temperature of 500.degree. to 800.degree. C.; and repeating both cold working and annealing thereof by a plurality of times. 18. A method of producing the fuel assembly for nuclear reactor of claim 2, wherein the cylindrical fuel spacer is produced by a process comprising the steps of: inserting a cylindrical billet of an alloy, which becomes an intermediate layer, into another cylindrical billet which becomes an outer surface layer in contact with the reactor water of the nuclear reactor; inserting into the intermediate layer billet a cylindrical billet which becomes an inner surface layer and which is made of the same material as the outer surface layer; integrating all of the billets by welding each end face thereof; extruding the integrated billets at a temperature not less than 610.degree. C.; and repeating both cold working and annealing thereof by a plurality of times. 19. A method of producing the fuel assembly for nuclear reactor of claim 17, wherein the welding is effected under a pressure not more than 1.times.10.sup.-4 Torr. 20. A method of producing the fuel assembly for nuclear reactor of claim 17, wherein an intermediate annealing between adjacent two cold workings is effected at a temperature of 610.degree. to 750.degree. C. 21. A method of producing the fuel assembly for nuclear reactor of claim 17, wherein the fuel cladding tube is subjected to a heat treatment comprising the steps of heating the surface layer of or heating the total thickness of the cladding tube at a temperature of 800.degree. to 900.degree. C. after the final hot working but before the final cold working, and then quenching it. 22. A method of producing the fuel assembly for nuclear reactor of claim 3, wherein the fuel channel box is produced by a process comprising the steps of: inserting a plate of an alloy, which becomes an intermediate layer, between plate members which become outer surface layers in contact with the reactor water of the nuclear reactor; integrating them by welding each end face thereof; extruding the integrated members at a temperature of 500.degree. to 800.degree. C.; and repeating both cold working and annealing thereof by a plurality of times. 23. A method of producing the fuel assembly for nuclear reactor of any one of claims 22 and 46, wherein an intermediate annealing between adjacent two cold workings is effected at a temperature of 610.degree. to 750.degree. C. 24. A method of producing the fuel assembly for nuclear reactor of claim 22, wherein the fuel channel box is subjected to a heat treatment comprising the steps of heating it at a temperature of 800.degree. to 900.degree. C. after the final hot working but before the final cold working, and then quenching it. 25. A member for a fuel assembly for a nuclear reactor, comprising a three-layer structure having an outer surface layer of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy containing Nb, Sn and Mo consisting by weight of 0.5 to 2.3% Nb, 0.5 to 1.5% n, 0.1 to 0.8% Mo, and the balance Zr and incidental impurities, which outer surface layer is to be in contact with reactor water of the nuclear reactor, and an intermediate layer of a high ductility alloy which is higher in ductility than the Zr-based alloy containing Nb, Sn and Mo and which is higher in strength than pure Zr, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 26. A member for a fuel assembly of claim 25, wherein the three-layer structure further includes an inner surface layer, such that the inner surface layer and outer surface layer sandwich the intermediate layer, the inner surface layer being made of pure zirconium. 27. A fuel assembly for nuclear reactor of claim 3, wherein in the channel box a thickness of each of the outer surface layers is 20 to 35% of the total thickness of the channel box. 28. A member for a fuel assembly of claim 25, wherein the Zr-based alloy containing Nb, Sn and Mo has a tensile strength of at least 70 kgf/mm.sup.2 at room temperature. 29. A member for a fuel assembly of claim 25, wherein the high ductility alloy has a tensile strength of 45-60 kgf/mm.sup.2 at room temperature and an elongation rate of at least 25%. 30. A method of producing a fuel assembly for nuclear reactor of claim 5, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding when assembling the three-layer structure. 31. A method of producing a fuel assembly for nuclear reactor of claim 5, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding when assembling the three-layer structure. 32. A method of producing a fuel assembly for nuclear reactor of claim 6, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding when assembling the three-layer structure. 33. A method of producing a fuel assembly for nuclear reactor of claim 7, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding when assembling the three-layer structure. 34. A method of producing a fuel assembly for nuclear reactor of claim 8, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding when assembling the three-layer structure. 35. A method of producing a fuel assembly for nuclear reactor of claim 9, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding when assembling the three-layer structure. 36. A method of producing a fuel assembly for nuclear reactor of claim 10, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding when assembling the three-layer structure. 37. A method of producing a fuel assembly for nuclear reactor of claim 11 comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding when assembling the three-layer structure. 38. A method of producing a fuel assembly for nuclear reactor of claim 12, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding when assembling the three-layer structure. 39. A method of producing a fuel assembly for nuclear reactor of claim 13, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding when assembling the three-layer structure. 40. A method of producing a fuel assembly for nuclear reactor of claim 10, comprising the step of effecting a heat-treatment at a temperature of 400.degree. to 700.degree. C. after welding the end face of a tubular or plate-like member. 41. A method of producing the fuel assembly for nuclear reactor of claim 18, wherein the welding is effected under a pressure not more than 1.times.10.sup.-4 Torr. 42. A method of producing the fuel assembly for nuclear reactor of claim 18, wherein an intermediate annealing between adjacent two cold workings is effected at a temperature of 610.degree. to 750.degree. C. 43. A method of producing the fuel assembly for nuclear reactor of claim 18, wherein the cylindrical fuel spacer is subjected to a heat treatment comprising the steps of heating the surface layer of or heating the total thickness of the cylindrical fuel spacer at a temperature of 800.degree. to 900.degree. C. after the final hot working but before the final cold working, and then quenching it. 44. A method of producing the fuel assembly for nuclear reactor of claim 2, wherein the fuel spacer is produced by a process comprising the steps of: inserting a plate of an alloy, which becomes an intermediate layer, between plate members which become outer surface layers in contact with the reactor water of the nuclear reactor; integrating them by welding each end face thereof; extruding the integrated members at a temperature of 500.degree. to 800.degree. C.; and repeating both cold working and annealing thereof by a plurality of times. 45. A method of producing the fuel assembly for nuclear reactor of claim 44, wherein the fuel spacer is subjected to a heat treatment comprising the steps of heating it at a temperature of 800.degree. to 900.degree. C. after the final hot working but before the final cold working, and then quenching it. 46. A fuel assembly for a nuclear reactor, comprising a fuel cladding tube of three-layer structure having an outer surface layer to be in contact with reactor water of the nuclear reactor, which outer surface layer is made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy containing Nb, Sn and Mo consisting by weight of 0.5 to 2.2% Nb, 0.5 to 1.5% Sn, 0.1 to 0.8% Mo, and the balance Zr and incidental impurities, an inner surface layer to be in contact with nuclear fuel, which inner surface layer is made of pure zirconium, and an intermediate layer made of a high ductility alloy which is higher in ductility than the outer surface layer and which is higher in strength than the inner surface layer, wherein the high ductility alloy forming the intermediate layer consists by weight of 0.5 to 2.0% Sn, 0.05 to 0.4% Fe, 0.03 to 0.2% Ni, 0.05 to 0.15% Cr, 0.01 to 0.8% Mo, and the balance Zr and incidental impurities, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 47. A fuel assembly for nuclear reactor, comprising a fuel spacer of three-layer structure having outer surface layers to be in contact with reactor water of the nuclear reactor, which outer surface layers are made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy having properties that no nodular corrosion or corrosion of white color occurs when the alloy is exposed to steam of a pressure of 105 kgf/cm.sup.2 at 500.degree. C. for 24 hours, and having a tensile strength of at least 70 kgf/mm.sup.2 at room temperature, and an intermediate layer adjacent to the outer surface layers, which intermediate layer is made of a high ductility alloy higher in ductility than the outer surface layers, wherein the high ductility alloy forming the intermediate layers consists by weight of 0.5 to 2.0% Sn, 0.05 to 0.4% Fe, 0.03 to 0.2% Ni, 0.05 to 0.15% Cr, 0.01 to 0.8% Mo, and the balance Zr and incidental impurities, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 48. A fuel assembly for a nuclear reactor, comprising a fuel channel box of three-layer structure having outer surface layers to be in contact with reactor water of the nuclear reactor, which outer surface layers are made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy having properties that no nodular corrosion or corrosion of white color occurs when the alloy is exposed to steam of a pressure of 105 kgf/cm.sup.2 at 500.degree. C. for 24 hours, and having a tensile strength of at least 70 kgf/mm.sup.2 at room temperature, and an intermediate layer adjacent to the outer surface layers, which intermediate layer is made of a high ductility alloy higher in ductility than the outer surface layers, wherein the higher ductility alloy forming the intermediate layer consists by weight of 0.5 to 2.0% Sn, 0.05 to 0.4% Fe, 0.03 to 0.2% Ni, 0.05 to 0.15% cr, 0.01 to 0.8% Mo, and the balance Zr and incidental impurities, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 49. A fuel assembly for a nuclear reactor, comprising a fuel cladding tube of three-layer structure having an outer surface layer to be in contact with reactor water of a nuclear reactor, which outer surface layer is made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy containing Nb, Sn and Mo consisting by weight of 0.5 to 2.2% Nb, 0.5 to 1.5% Sn, 0.1 to 0.8% Mo, and the balance Zr and incidental impurities, an inner surface layer to be in contact with nuclear fuel, which inner surface layer is made of pure zirconium, and an intermediate layer made of a high ductility alloy, which is higher in ductility than the outer surface layer and which is higher in strength than the inner surface layer, wherein the high ductility alloy forming the intermediate layer is a stainless steel, containing carbon, the carbon being included in an amount, by weight, of not more than 0.08% C, and the stainless steel also containing, by weight, 0-2.0% Mn, 0-1.00% Si, 16.0 to 20.0% Cr, 8.00 to 14.00% Ni, 0-3.00% Mo, and the balance Fe and incidental impurities, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 50. A fuel assembly for a nuclear reactor, comprising a fuel spacer of three-layer structure having outer surface layers to be in contact with reactor water of the nuclear reactor, which outer surface layers are made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy having properties that no nodular corrosion or corrosion of white color occurs when the alloy is exposed to steam of a pressure of 105 kgf/cm.sup.2 at 500.degree. C. for 24 hours, and having a tensile strength of at least 70 kgf/mm.sup.2 at room temperature, and an intermediate layer adjacent to the outer surface layers, which intermediate layer is made of a high ductility alloy higher in ductility than the outer surface layers, wherein the high ductility alloy forming the intermediate layer is a stainless steel, containing carbon, the carbon being included in an amount, by weight, of not more than 0.08% C, and the stainless steel also containing, by weight, 0-2.0% Mn, 0-1.0% Si, 16.0 to 20.0% Cr, 8.00 to 14.00% Ni, 0-3.00% Mo, and the balance Fe and incidental impurities, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 51. A fuel assembly for a nuclear reactor, comprising a fuel channel box of three-layer structure having outer surface layers to be in contact with reactor water of the nuclear reactor, which outer surface layers are made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy having properties that no nodular corrosion or corrosion of white color occurs when the alloy is exposed to steam of a pressure of 105 kgf/cm.sup.2 at 500.degree. C. for 24 hours, and having a tensile strength of at least 70 kgf/mm.sup.2 at room temperature, and an intermediate layer adjacent to the outer surface layers, which intermediate layer is made of a high ductility alloy higher in ductility than the outer surface layers, wherein the high ductility alloy forming the intermediate layer is a stainless steel, containing carbon, the carbon being included in an amount, by weight, of not more than 0.08% C, and the stainless steel also containing, by weight, 0-2.0% Mn, 0-1.00% Si, 16.0 to 20.0% cr, 8.00 to 14.00% Ni, 0-3.00% Mo, and the balance Fe and incidental impurities, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 52. A fuel assembly for a nuclear reactor, comprising a fuel cladding tube of three-layer structure having an outer surface layer to be in contact with reactor water of the nuclear reactor, which outer surface layer is made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy containing Nb, Sn and Mo consisting by weight of 0.5 to 2.2% Nb, 0.5 to 1.5% Sn, 0.1 to 0.8% Mo, and the balance Zr and incidental impurities, an inner surface layer to be in contact with nuclear fuel, which inner surface layer is made of pure zirconium, and an intermediate layer made of a high ductility alloy, which is higher in ductility than the outer surface layer and which is higher in strength than the inner surface layer, wherein the high ductility alloy forming the intermediate layer is a Cu-based alloy consisting by weight of 0-3.0% Pb, 0-6.0% Fe, 0-0.5 Zn, 0-11.0% Al, 0-2.0% Mn, 0-33.0% Ni, and the balance of Cu and incidental impurities, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 53. A fuel assembly for a nuclear reactor, comprising a fuel spacer of three-layer structure having outer surface layers to be in contact with reactor water of the nuclear reactor, which outer surface layers are made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy having properties that no nodular corrosion or corrosion of white color occurs when the alloy is exposed to steam of a pressure of 105 kgf/cm.sup.2 at 500.degree. C. for 24 hours, and having a tensile strength of at least 70 kgf/mm.sup.2 at room temperature, and an intermediate layer adjacent to the outer surface layers, which intermediate layer is made of a high ductility alloy higher in ductility than the outer surface layers, wherein the high ductility alloy forming the intermediate layer is a Cu-based alloy consisting by weight of 0-3.0% Pb, 0-6.0% Fe, 0-0.5% Zn, 0-11.0% Al, 0-2.0% Mn, 0-33.0% Ni, and the balance Cu and incidental impurities, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 54. A fuel assembly for a nuclear reactor, comprising a fuel channel box of three-layer structure having outer surface layers to be in contact with reactor water of the nuclear reactor, which outer surface layers are made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy having properties that no nodular corrosion or corrosion of white color occurs when the alloy is exposed to steam of a pressure of 105 kgf/cm.sup.2 at 500.degree. C. for 24 hours, and having a tensile strength of at least 70 kgf/mm.sup.2 at room temperature, and an intermediate layer adjacent to the outer surface layers, which intermediate layer is made of a high ductility alloy higher in ductility than the outer surface layers, wherein the high ductility alloy forming the intermediate layer is a Cu-based alloy consisting by weight of 0-3.0% Pb, 0-6.0% Fe, 0-0.5% Zn, 0-11.0% Al, 0-2.0% Mn, 0-33.0% Ni, and the balance Cu and incidental impurities, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 55. A fuel assembly for a nuclear reactor, comprising a fuel cladding tube of three-layer structure having an outer surface layer to be in contact with reactor water of the nuclear reactor, which outer surface layer is made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy containing Nb, Sn and Mo consisting by weight of 0.5 to 2.2% Nb, 0.5 to 1.5% Sn, 0.1 to 0.8% Mo, and the balance Zr and incidental impurities, an inner surface layer to be in contact with nuclear fuel, which inner surface layer is made of pure zirconium, and an intermediate layer made of a high ductility alloy, which is higher in ductility than the outer surface layer and which is higher in strength than the inner surface layer, a thickness of the outer surface layer being 10% to 30% of the total thickness of the cladding tube, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 56. A fuel assembly for a nuclear reactor, comprising a fuel channel box of three-layer structure having outer surface layers to e in contact with reactor water of the nuclear reactor, which outer surface layers are made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy having properties that no nodular corrosion or corrosion of white color occurs when the alloy is exposed to steam of a pressure of 105 kgf/cm.sup.1 at 500.degree. C. for 24 hours, and having a tensile strength of at least 70 kgf/mm.sup.2 at room temperature, and an intermediate layer adjacent to the outer surface layers, which intermediate layer is made of a high ductility alloy higher in ductility than the outer surface layers, a thickness of each of the outer surface layers being 20 to 35% of the total thickness of the fuel channel box, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 57. A fuel assembly for a nuclear reactor, comprising a fuel spacer of three-layer structure having (a) outer surface layers to be in contact with reactor water of the nuclear reactor, which outer surface layers are made of a Zr-based alloy containing Nb, Sn and MO, the Zr-based alloy having properties that no nodular corrosion or corrosion of white color occurs when the alloy is exposed to steam of a pressure of 105 kgf/cm.sup.2 at 500.degree. C. for 24 hours, and having a tensile strength of at least 70 kgf/mm.sup.2 at room temperature, and (b) an intermediate layer adjacent to the outer surface layers, which intermediate layer is made of a high ductility alloy higher in ductility than the outer surface layers, the intermediate layer being made of a material selected from the group consisting of Zr-based alloy, stainless steel alloy and copper-based alloy, having a tensile strength of 45 to 60 kgf/mm.sup.2 at room temperature and an elongation rate of at least 25%, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 58. A fuel assembly for a nuclear reactor, comprising a fuel channel box of three-layer structure having (a) outer surface layers to be in contact with reactor water of the nuclear reactor, which outer surface layers are made of a Zr-based alloy containing Nb, Sn and Mo, the Zr-based alloy having properties that no nodular corrosion or corrosion of white color occurs when the alloy is exposed to steam of a pressure of 105 kgf/cm.sup.2 at 500.degree. C. for 24 hours, and having a tensile strength of at least 70 kgf/mm.sup.2 at room temperature, and (b) an intermediate layer adjacent to the outer surface layers, which intermediate layer is made of a high ductility alloy higher in ductility than the outer surface layers, the intermediate layer being made of a material selected from the group consisting of Zr-based alloy, stainless steel alloy and copper-based alloy, having a tensile strength of 45 to 60 kgf/mm.sup.2 at room temperature and an elongation rate of at least 25%, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 59. A member for a fuel assembly of claim 25, wherein the outer surface layer has a thickness that is 10% to 60% of the total thickness of the three-layer structure. 60. A member for a fuel assembly of claim 59, wherein the three-layer structure includes an inner surface layer, which has a thickness that is 5-20% of the total thickness of the three-layer structure. 61. A member for a fuel assembly for a nuclear reactor, comprising a three-layer structure having an outer surface layer of a Zr-based alloy containing Nb, Sn and Mo, which outer surface layer is to be in contact with reactor water of the nuclear reactor, and an intermediate layer of a high ductility alloy which is higher in ductility than the Zr-based alloy containing Nb, Sn and Mo and which is higher in strength than pure Zr, a thickness of the intermediate layer being 25%-85% of a total thickness of the three-layer structure. 62. A member for a fuel assembly of claim 61, wherein the intermediate layer is made of a material selected from the group consisting of Zr-based alloy, stainless steel and copper-based alloy. 63. A member for a fuel assembly of claim 62, wherein the outer surface layer has a thickness that is 10%-60% of the total thickness of the three-layer structure. 64. A member for a fuel assembly of claim 63, wherein the three-layer structure includes an inner surface layer, which has a thickness that is 5-20% of the total thickness of the three-layer structure. 65. A member for a fuel assembly of claim 64, said member being selected from the group consisting a fuel cladding tube, a fuel channel box and a fuel spacer. 66. A member for a fuel assembly of claim 64, wherein the three-layer structure includes an inner surface layer, made of Zr, the intermediate layer being higher in strength than the inner surface layer. |
059490845 | summary | CROSS-REFERENCE TO RELATED APPLICATIONS Not Applicable STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not Applicable REFERENCE TO A MICROFICHE APPENDIX Not Applicable BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains generally to shielding for radioactive materials and more particularly to a lightweight storage container for radioactive materials. 2. Description of the Background Art At the present time, there are approximately 560,000 tons of depleted uranium hexaflouride under storage in 50,000 cylinders which cost about $10,000,000 annually to maintain. Putting the depleted uranium to practical use would cut the maintenance costs significantly. One such use of depleted uranium is as shielding material for radioactive materials. Using the depleted uranium in such a manner is not only useful, but also serves to eliminate the depleted uranium from the environment. The storage and/or transportation of radioactive materials require effective shielding to protect the operating personnel and the surrounding environment. The storage and/or transportation of radioactive materials have been accomplished using canisters, containers, receptacles or vessels that possess photon and neutron absorption capability and sufficient structural strength. The radiation absorption capability shields the environment and operating personnel from radiation emitted by the radioactive materials, while structural strength allows the vessel to withstand normal handling and storage stresses and even some accidental impacts upon the vessel. One such known storage vessel utilizes a hollow body having lateral walls and a base formed unitarily with one another and open at an upper end. The walls of the body have an outer layer, an intermediate layer and an inner layer. The outer and intermediate layers are cast unitarily from a carbon containing ferrous metal of copper alloy while the intermediate layer consists of a cast matrix phase within which heavy metal particles, such as depleted uranium, are embedded to absorb radiation. A plurality of separate channels disposed longitudinally within the outer layer is filled with neutron absorptive material, and a removable cover is fitted over the upper end after the radioactive has been placed therein. The multi-layer configuration of such storage vessels result in a shielding system that is large dimensionally and in mass, thus limiting the quantity of radioactive material that can be stored, especially when storage area is limited. Without the separate longitudinal channels containing the neutron absorptive material, the vessel would be ineffective, as depleted uranium is useless by itself for neutron absorption. Such a large multi-layer configuration also requires ancillary cooling systems to dissipate heat generated by the enclosed radioactive material. Accordingly, there is a need for a radiation storage vessel that combines the functions of attenuating photon radiation, neutron absorption and shock mitigation from impact, while minimizing the thickness of the vessel's walls and weight such that the vessel can be more readily transported and a larger quantity of radioactive material can be stored in a given area. The foregoing reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicant's acknowledged duty of candor in disclosing information which may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these teach or render obvious, singly or when considered in combination, applicant's claimed invention. BRIEF SUMMARY OF THE INVENTION The present invention is a vessel for the storage and transportation of radioactive materials. The vessel generally comprises a mixture of small metal particles, preferably but not necessarily spherical, embedded in a matrix that contains neutron moderating and absorbing material. The use of spherical particles, however, assures maximum density of packing so that the thickness of the vessel's wall is minimized while allowing sufficient space in the interstices between the particles for the neutron absorber/moderator. The composite mixture of metal particles and neutron absorbing matrix is poured into an annular space between an inner vessel that is used to contain the radioactive material and an outer casing that serves both as a form for the shielding system and a protective covering. The metal particles are composed of depleted uranium, lead or other like material. The inclusion of neutron absorbing material within the matrix eliminates the need for a separate layer of neutron absorptive materials thus reducing the weight and amount of space occupied by the vessel. An object of the invention is to provide a radioactive material storage vessel which attenuates photon radiation, absorbs neutron emissions and mitigates shock from impacts. Another object of the invention is to provide a radioactive material storage vessel which minimizes thickness and weight so that a larger quantity of radioactive material can be stored in a minimum amount of space therein, thereby maximizing the efficiency of the storage system. Another object of the invention is to provide a radioactive material storage vessel which minimizes thickness and weight so that the vessel is more readily transportable. Another object of the invention is to provide a radioactive material storage vessel in which heat generated by the radioactive contents can be more easily dissipated by thermal conduction. Still another object of the invention is to provide a radioactive material storage vessel which allows retrieval of the metal components of the storage vessel using conventional techniques. Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. |
047284900 | description | DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like are words of convenience and are not to be construed as limiting terms. In General Referring now to the drawings, and particularly to FIGS. 1 to 7, there is shown a nuclear fuel assembly, generally designated 10, for a BWR to which the improved features of the present invention can be advantageously applied. The fuel assembly 10 includes an elongated outer tubular flow channel 12 that extends along substantially the entire length of the fuel assembly 10 and interconnects an upper support fixture or top nozzle 14 with a lower base or bottom nozzle 16. The bottom nozzle 16 which seves as an inlet for coolant flow into the outer channel 12 of the fuel assembly 10 includes a plurality of legs 18 for guiding the bottom nozzle 16 and the fuel assembly 10 into a reactor core support plate (not shown) or into fuel storage racks, for example in a spent fuel pool. The outer flow channel 12 generally of rectangular cross-section is made up of four interconnected vertical walls 20 each being displaced about ninety degrees one from the next. Formed in a spaced apart relationship in, and extending in a vertical row at a central location along, the inner surface of each wall 20 of the outer flow channel 12, is a plurality of structural ribs 22. The outer flow channel 12, and thus the ribs 22 formed therein, are preferably formed from a metal material, such as an alloy of zirconium, commonly referred to as Zircaloy. Above the upper ends of the structural ribs 22, a plurality of upwardly-extending attachment studs 24 fixed on the walls 20 of the outer flow channel 12 are used to interconnect the top nozzle 14 to the channel 12. For improving neutron moderation and economy, a hollow water cross, generally designated 26, extends axially through the outer channel 12 so as to provide an open inner channel 28 for subcooled moderator flow through the fuel assembly 10 and to divide the fuel assembly into four, separate, elongated compartments 30. The water cross 26 has a plurality of four radial panels 32 composed by a plurality of four, elongated, generally L-shaped, metal angles or sheet members 34 that extend generally along the entire length of the channel 12 and are interconnected and spaced apart by a series of elements in the form of dimples 36 formed in the sheet members 34 of each panel 32 and extending therebetween. The dimples 36 are provided in opposing pairs that contact each other along the lengths of the sheet members 34 to maintain the facing portions of the members in a proper spaced-apart relationship. The pairs of contacting dimples 36 are connected together such as by welding to ensure that the spacing between the sheet members 34 forming the panels 32 of the central water cross 26 is accurately maintained. The hollow water cross 26 is mounted to the angularly-displaced walls 20 of the outer channel 12. Preferably, the outer, elongated longitudinal edges 38 of the panels 32 of the water cross 26 are connected such as by welding to the structural ribs 22 along the lengths thereof in order to securely retain the water cross 26 in its desired central position within the fuel assembly 10. Further, the inner ends of the panels together with the outer ends thereof define the inner central cruciform channel 28 which extends the axial length of the hollow water cross 26. Also, the water cross 26 has a lower flow inlet end 39 and an opposite upper flow outlet end 40 which each communicate with the inner channel 28 for providing subcoolant flow therethrough. Disposed within the channel 12 is a bundle of fuel rods 42 which, in the illustrated embodiment, number sixty-four and form an 8.times.8 array. The fuel rod bundle is, in turn, separated into four mini-bundles thereof by the water cross 26. The fuel rods 42 of each mini-bundle, such being sixteen in number in a 4.times.4 array, extend in laterally spaced apart relationship between an upper tie plate 44 and a lower tie plate 46 and connected together with the tie plates comprise a separate fuel rod subassembly 48 within each of the compartments 30 of the channel 12. A plurality of grids or spacers 50 axially spaced along the fuel rods 42 of each fuel rod subassembly 48 maintain the fuel rods in their laterally spaced relationship. Coolant flow paths and cross-flow communication are provided between the fuel rod subassemblies 48 in the respective separate compartments 30 of the fuel assembly 10 by a plurality of openings 52 formed between each of the structural ribs 22 along the lengths thereof. Coolant flow through the openings 52 serves to equalize the hydraulic pressure between the four separate compartments 30, thereby minimizing the possibility of thermal hydrodynamic instability between the separate fuel rod subassemblies 48. As seen generally in FIG. 4 and in greater detail in FIGS. 6-8, each spacer 50 includes a plurality of interleaved inner straps 54 having opposite terminal end portions 56 and being arranged in an egg-crate configuration to define a plurality of inner cell openings 58. Dimples 60 and springs 62 are formed in the straps 54 so as to project into the inner cell openings 58 and hold respective ones of the fuel rods 42 received therethrough in spaced apart and generally parallel extending relation to one another. The spacer 50 also includes an outer peripheral strap 64 attached to the respective terminal end portions 56 of the inner straps 54 so as to define a number of perimeter cell openings 66 into which others of the dimples 60 and springs 62, also being formed in the outer strap, extend to hold other ones of the fuel rods 42 in the spaced apart parallel relation. The perimeter cell openings 66 are arranged in the form of a ring which encompasses the inner cell openings 58 as a group. Portions of the inner straps 54 define a border, generally indicated as 68, which surrounds the group of inner cell openings 58 and separates them from the perimeter cell openings 66. The above-described basic components of the BWR fuel assembly 10 are known in the prior art, such as in the fuel assembly disclosed in the patent to Barry et al cited above, and have been discussed in sufficient detail herein to enable one skilled in the art to understand the feature of the present invention presented hereinafter. For a more detailed description of the construction of the BWR fuel assembly, attention is directed to the above-mentioned Barry et al patent. Improved Spacer for Avoiding CHF Performance Degradation The present invention provides improved features at least in the limiting CHF ones of the spacers 50 (i.e., the uppermost three spacers) of the fuel assembly 10. Referring to FIGS. 4 and 6-9, these features comprise a plurality of coolant flow diverting scoops 70 mounted on the outer peripheral strap 64. Basically, each of the scoops 70 is composed of a mounting portion 72 and a coolant flow deflecting portion 74 connected at its outer end 76 to the lower end of the mounting portion. The mounting portions 72 of the scoops 70 are in the form of flat extensions of the respective spacer outer strap 64 which extend downwardly therefrom, for instance from three to six inches, and generally parallel to the fuel rods 42 and are disposed in laterally spaced apart relation from one another along the upstream side of the spacer 50. The flow deflecting portions 74, having longitudinally tapered and arcuate-shaped configurations, extend inwardly from respective lower ends of the mounting portions 72 within the respective spaces between the ones of the fuel rods 42 received through the perimeter cell openings 66 of the spacer 50. Also, the flow deflecting portions 74 of the scoops 70 extend along and in spaced relation downwardly from the upstream side of the spacer 50 and particularly from the respective ones of the terminal end portions 56 of the inner straps 54. The flow deflecting portions 74 terminate at inner ends 78 being disposed generally below the border 68, as seen in FIG. 6, defined by portions of the inner straps 54. As depicted in FIGS. 7 and 9, the outer end 76 of the arcuate-shaped flow deflecting portion 74 of each scoop 70 is spaced farther from its respective one of the inner strap terminal end portions 56 than its inner end 78 such that it extends in an inclined relation thereto across the path of a portion of the coolant flowing upwardly toward the perimeter cell openings 66. Such inclined relation of the scoop flow deflecting portion 74 achieves scooping of liquid coolant from along the channel 12 and water cross panels 32 and redistributes it to the fuel rods 42 extending through the inner cell openings 58 of the spacer 50 just upstream of the same. Preferably, at least the three uppermost ones of the spacers 50 have the scoops 70 mounted as just described on their upstream sides. It is thought that the invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that varrious changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof. |
summary | ||
041479386 | abstract | The disclosure is directed to a fire resistant nuclear fuel cask employing reversibly thermally expansible bands between adjacent cooling fins such that normal outward flow of heat is not interfered with, but abnormal inward flow of heat is impeded or blocked. |
claims | 1. A method of forming a diode assembly for producing a pulsed fusion event in a z-pinch driver, the method comprising:providing a fusionable fuel source material including a lithium compound formed of one or more lithium isotopes and one or more hydrogen isotopes;heating the fusionable fuel source material under controlled conditions in a vacuumed environment such that a surface of the fusionable fuel source material decomposes to lithium metal and a hydrogen isotopic gas leaving an inner core of undecomposed fusionable fuel source material; andextracting the hydrogen isotopic gas from the vacuumed environment to form the diode assembly having a lithium metal outer sheath integrally formed around the inner core of undecomposed fusionable fuel source material. 2. The method of claim 1 wherein the fusionable fuel source material is selected from a group consisting of 6LiD, 6LiT, 7LiD, and 7LiT. 3. The method of claim 1 wherein the controlled conditions include a vapor pressure ranging from about 2.2 torr to about 11.1 torr. 4. The method of claim 1 wherein the surface of the fusionable fuel source material is heated to a temperature ranging from about 400° C. to about 680° C. 5. The method of claim 1 wherein the surface of the fusionable fuel source material is heated to a temperature ranging from about 600° C. to about 660° C. 6. The method of claim 1 wherein the controlled conditions include a vapor pressure ranging from about 2.2 torr to about 11.1 torr and the surface of the fusionable fuel source material being heated to a temperature ranging from about 400° C. to about 680° C. 7. The method of claim 6 wherein the heating step includes raising the vapor pressure of the vacuumed environment as the temperature of the surface of the fusionable fuel source material increases. 8. The method of claim 1 further comprising controlling a thickness of the lithium metal outer sheath between about ten microns and about 150 microns by selecting the controlled conditions to include a temperature between about 560° C. to about 660° C. and a heating time between about one hour to about three hours. 9. The method of claim 1 wherein the heating step includes controlling a thickness of the lithium metal outer sheath by adjusting an amount of time in which the fusionable fuel source material is heated under controlled conditions in the vacuumed environment. 10. The method of claim 1 wherein the heating and extracting steps are performed in a sealed vessel having a separator disposed between the fusionable fuel source material and an interior surface of the sealed vessel. |
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claims | 1. A method of volumetric oxidative treatment of spent nuclear fuel (SNF) of uranium dioxide, the method comprising thermal processing a reaction mass of SNF element fragments in oxidative environment, said thermal processing being carried out in at least one reaction chamber in two phases, the first phase being performed at 400-650° C. for 60-360 minutes in the gas stream of air additionally comprising carbon dioxide in the amount of 1-4 volume %, the second phase being performed at 350-450° C. for 30-120 minutes in the gas stream of air that includes water steam in the amount corresponding to the dew point of gas-vapor mixture at 30-40° C., the both phases being performed with a repeated mechanical activation of the reaction mass. 2. The method according to claim 1, wherein an hourly rate of the gas stream at said first and second phases is about 10-50 full exchanges of a reaction chamber volume at each phase. 3. The method according to claim 1, further providing preheating the gas stream up to an internal temperature of the at least one reaction chamber before the gas stream enters the at least one reaction chamber at said first phase and second phase, respectively. 4. The method according to claim 1, wherein the gas stream of air at the second phase is oxygen enriched. 5. The method according to claim 1, wherein the at least one reaction chamber includes two reaction chambers, the first phase being carried out in one of the two reaction chambers, the second phase being carried out in another of the two reaction chambers. 6. A method of volumetric oxidative treatment of spent nuclear fuel (SNF) of uranium dioxide, the method comprising thermal processing a reaction mass of SNF element fragments in oxidative environment, said thermal processing being carried out in at least one reaction chamber in two phases, the first phase being performed at 400-650° C. for 60-360 minutes in the gas stream of air additionally comprising carbon dioxide in the amount of 1-4 volume %, the second phase being performed at 350-450° C. for 30-120 minutes in the gas stream of air that includes water steam in the amount corresponding to the dew point of gas-vapor mixture at 30-40° C., an hourly rate of the gas stream being about 10-50 full exchanges of the at least one reaction chamber volume at each phase, the both phases being performed with a repeated mechanical activation of the reaction mass. 7. The method according to claim 6, further providing preheating the gas stream up to an internal temperature of the at least one reaction chamber before the gas stream enters the at least one reaction chamber at said first phase and second phase, respectively. 8. The method according to claim 6, wherein the gas stream of air at the second phase is oxygen enriched. 9. The method according to claim 6, wherein the at least one reaction chamber includes two reaction chambers, the first phase being carried out in one of the two reaction chambers, the second phase being carried out in another of the two reaction chambers. 10. A method of volumetric oxidative treatment of spent nuclear fuel (SNF) of uranium dioxide, the method comprising thermal processing a reaction mass of SNF element fragments in oxidative environment, said thermal processing being carried out in a reaction chamber in two phases, the first phase being performed at 400-650° C. for 60-360 minutes in the gas stream of air additionally comprising carbon dioxide in the amount of 1-4 volume %, the second phase being performed at 350-450° C. for 30-120 minutes in the gas stream of air that includes water steam in the amount corresponding to the dew point of gas-vapor mixture at 30-40° C., the both phases being performed with a repeated mechanical activation of the reaction mass, the gas stream being preheated up to an internal temperature of the reaction chamber before the gas stream is used at said first phase and second phase. 11. The method according to claim 10, wherein the gas stream of air at the second phase is oxygen enriched. 12. The method according to claim 10, wherein an hourly rate of the gas stream is about 10-50 full exchanges of the reaction chamber volume at each phase. 13. The method according to claim 10, wherein the reaction chamber includes a first and a second reaction chambers, the first phase being carried out in the first reaction chamber and the second phase being carried out in the second reaction chamber. |
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051942143 | claims | 1. A tube plugging device, comprising: a first member having a bore at least partially therethrough, said bore having a portion with inside diameter threads; a second member disposed in said bore of said first member; an annular locking cup, disposed in said bore of said first member, having an inward open end portion and an outward open end portion, said inward open end portion having outside diameter threads corresponding to said inside diameter threads of said first member for threaded engagement of said locking cup and said first member; at least one of said second member and said locking cup having at least one recess therein, the other of said second member and said locking cup deformable to engage said recess for securing said first member, said second member, and said locking cup together; and said outside diameter threads of said locking cup having a deformed portion, said deformed portion including at least two segments of said outside diameter threads having at least one protuberance positioned between a crest and a root of said outside diameter threads and having at least one portion of a root of said deformed portion offset from a root of the remainder of said deformed portion, said offset of said root being axially aligned with said protuberance for resisting the threading of said locking cup into and out of said first member for preventing the inadvertent separation of said first member, said second member, and said locking cup. a shell having a closed end, an open end, and an outer wall defining a chamber in said shell and having inside diameter threads positioned near said open end; bolt means disposed in said open end of said shell; an annular locking cup, disposed in said open end of said shell, having an inward open end portion and an outward open end portion, said inward open end portion having outside diameter threads corresponding to said inside diameter threads of said shell for threaded engagement of said locking cup and said shell; at least one of said bolt means and said locking cup having at least one recess therein, the other of said bolt means and said locking cup deformable to engage said recess for securing said shell, said bolt means, and said locking cup together; and said outside diameter threads of said locking cup having a deformed portion, said deformed portion including at least two segments of said outside diameter threads having at least one protuberance positioned between a crest and a root of said outside diameter threads and having at least one portion of a root of said deformed portion offset from a root of the remainder of said deformed portion, said offset of said root being axially aligned with said protuberance for resisting the threading of said locking cup into and out of said shell for preventing the inadvertent separation of said shell, said bolt means, and said locking cup. installing said shell within an open end of a tube; deforming threads of said locking cup into a deformed portion including at least two segments of outside diameter threads having at least one protuberance positioned between a crest and a root of said outside diameter threads and having at least one portion of a root of said deformed portion offset from a root of the remainder of said deformed portion, said offset of said root being axially aligned with said protuberance for providing resistance to the threading and unthreading of said locking cup into and out of said shell; threading said locking cup with said deformed portion into said threaded bore of said shell; disposing said bolt means through a bore of said locking cup and through said threaded bore of said shell; and crimping said deformable portion of said locking cup into said recess of said bolt means. seating an outside diameter surface of said locking cup against an edge of said shell by providing a torque sufficient to create an interference between said outside diameter surface and said edge for sealing a chamber within said shell to prevent fluid flow through said tube; and seating an outside diameter taper of said bolt means against an inside diameter taper of said locking cup by providing a torque sufficient to create an interference between said outside diameter taper and said inside diameter taper for sealing said chamber within said shell to prevent fluid flow through said tube. 2. The plugging device according to claim 1, wherein said deformed portion of said outside diameter threads of said locking cup comprises at least two segments of said outside diameter threads deformed so that a pitch of said outside diameter threads of said deformed portion is offset from a pitch of the remainder of said outside diameter threads of said locking cup for resisting the unthreading of said locking cup from said first member. 3. The plugging device according to claim 1, wherein said second member comprises at least one recess positioned at an end of said second member for engaging said outward open end portion of said locking cup for securing said first member, said second member, and said locking cup together. 4. The plugging device according to claim 1, wherein said plugging device further comprises a third member, disposed in said bore of said first member for expanding said first member into sealing engagement when installed in a tube, and having a bore therethrough with inside diameter threads corresponding to outside diameter threads of said second member for threaded engagement of said second member and said third member. 5. The plugging device according to claim 4, wherein said inside diameter threads of said third member and said outside diameter threads of said second member have a different pitch than a pitch of said inside diameter threads of said first member and said outside diameter threads of said locking cup for providing an additional fastening feature to secure said first member, said second member, said third member, and said locking cup together. 6. The plugging device according to claim 4, wherein said first member is a shell having a closed end, an open end, and an outer wall defining a chamber in said shell for plugging a tube. 7. The plugging device according to claim 6, wherein said second member is bolt means having a shaft and a bolt head, disposed in said open end of said shell, for sealing said chamber defined by said shell. 8. The plugging device according to claim 7, wherein said third member is an expander member having a bore therethrough with inside diameter threads for threaded engagement with said shaft of said bolt means. 9. A tube plug for plugging a tube, comprising: 10. The plugging device according to claim 9, wherein said deformed portion of said outside diameter threads of said locking cup comprises at least two segments of said outside diameter threads deformed so that a pitch of said outside diameter threads of said deformed portion is offset from a pitch of the remainder of said outside diameter threads of said locking cup for resisting the unthreading of said locking cup from said shell. 11. The tube plug according to claim 9, wherein said bolt means comprises at least one recess positioned at an end of said bolt means for engaging said outward open end portion of said locking cup for securing said shell, said bolt means, and said locking cup together. 12. The tube plug according to claim 9, wherein said tube plug further comprises an expander member, disposed in said chamber of said shell for expanding said outer wall of said shell into sealing engagement when installed in a tube, and having a bore therethrough with inside diameter threads corresponding to outside diameter threads of said bolt means for threaded engagement of said bolt means and said expander member. 13. The tube plug according to claim 12, wherein said inside diameter threads of said expander member and said outside diameter threads of said bolt means have a different pitch than a pitch of said inside diameter threads of said shell and said outside diameter threads of said locking cup for providing an additional fastening feature to secure said shell, said bolt means, said expander member, and said locking cup together. 14. The tube plug according to claim 9, wherein said locking cup further comprises an outside diameter surface positioned between said inward open end portion of said locking cup and said outward open end portion of said locking cup for sealingly abutting a plug face of said shell positioned at said open end of said shell, for sealing said chamber of said shell to prevent fluid flow through said tube plug. 15. The tube plug according to claim 9, wherein said bolt means further comprises an outside diameter taper positioned between opposite ends of said bolt means for sealingly abutting an inside diameter taper of said locking cup positioned between said inward open end portion and said outward open end portion of said locking cup, for sealing said chamber of said shell to prevent fluid flow through said tube plug. 16. The tube plug according to claim 9, wherein said shell further comprises a plurality of lands surrounding said outer wall of said shell for sealing engagement when installed in a tube for preventing fluid flow through said tube. 17. A method for plugging a tube, including a shell having a threaded bore at least partially therein, bolt means with a threaded portion and at least one recess, and an annular locking cup with a deformed portion and a deformable portion, comprising the steps of: 18. The method according to claim 17, further comprising the steps of: 19. The method according to claim 17, further comprising the step of threading said bolt means into a bore of an expander member disposed in said shell for providing an additional fastening feature due to the difference in pitch of threads of said expander member and said bolt means as compared to the pitch of threads of said shell and said locking means for securing said shell, said expander member, said bolt means, and said locking cup together. |
summary | ||
abstract | A nuclear power plant comprising a primary coolant circuit, a steam-water circuit separated from the primary coolant circuit and a steam generator connected to the primary coolant circuit and the steam-water circuit to transfer heat from the primary coolant circuit into the steam-water circuit has at least one dosing point in the steam-water circuit to inject a reducing agent into the steam-water circuit, wherein the reducing agent is an organic compound consisting of carbon, hydrogen and oxygen. Furthermore, a method for operating said nuclear power plant and the use of the method for downtime preservation of the secondary side of a steam generator of a nuclear power plant are provided. |
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062140868 | summary | FIELD OF THE INVENTION The present invention relates to a method and apparatus that simultaneously provides both hot and cold DRI (direct reduced iron) from a continuous gravity-fed supply of hot DRI material, as from a conventional direct reduction furnace. BACKGROUND OF THE INVENTION Sponge iron, metallized pellets, briquettes, or reduced metal materials such as direct reduced iron ("DRI"), nickel, or the like, are produced by the direct reduction of ores or metal oxides. Large quantities of metallized iron pellets are made in the direct reduction process wherein particulate iron oxide is reduced substantially to metallic iron by direct contact with a reducing gas such as a mixture of hydrogen and carbon monoxide. Throughout this specification and appended claims, the term "metallized pellets" is intended to include metal-bearing pellets such as sponge iron, briquettes, DRI, other compacted forms of reduced metal and the like which contain at least 80 percent of their metal in the metallic state with the balance being primarily in the form of metallic oxide. For these purposes, iron carbide is considered iron in the metallic state. "Metallized" in this specification does not mean coated with metal, but means nearly completely reduced to the metallic state. For ease of discussion and visualization, the majority of this specification will describe the invention as it relates to DRI, although it should be understood that the invention functions equally well with other forms of "metallized pellets" of any size, or any metal. A problem associated with the use of DRI as a raw material to make steel or other products is its inherent tendency to reoxidize upon exposure to air or water. Exposure of a mass of hot DRI to atmospheric air and moisture causes re-oxidation of the metal ("rusting") with a significant loss of metallization. The re-oxidation also produces heat that can dramatically raise the temperature of a mass of DRI. The process of reoxidation also releases water-bound hydrogen into the immediate environment. Under proper conditions, hot DRI can ignite the liberated hydrogen resulting in additional heat, formation of additional hydrogen and possibly an explosion within transfer piping or within storage units. DRI must be removed from a direct reduction furnace in order to be useful. Methods are needed to transport DRI while reducing the risk of re-oxidation. One common method of reducing this risk of re-oxidation is to cool the hot DRI material to a sufficiently low temperature (less than about 100.degree. C.), to prevent the ignition of any hydrogen that is released by the oxidation process. One drawback to this method is that current DRI production systems are typically "all or nothing" propositions with respect to cooling. Either all of the hot DRI material exiting a particular furnace is cooled or none of it is cooled. A known method of transfer is the pneumatic transfer of hot DRI materials through piping from a furnace to an exterior storage unit. Drawbacks to this method include: extensive piping is required to transfer hot DRI through significant elevation changes, input of additional energy is required to the gases utilized in pneumatic transfer, additional opportunities are present for oxygen intake into transfer piping, and size reduction of hot DRI from nugget-size to particulate-size occurs during the transfer to remote storage units because of abrasion and impact. The present invention does not employ pneumatic transfer, and instead provides a method and apparatus for removing continuous output of hot DRI material from a direct reduction furnace and gravitationally transferring the output for subsequent processing or storage. The invention may simultaneously provide hot DRI material for subsequent steps such as melting or briquetting. The invention may also cool DRI material for transport, storage, or other use. The disclosure of the invention refers to elements or components in the Midrex process. The Midrex process and apparatus for direct reduction are disclosed in the following U.S. Patents: U.S. Pat. No. 3,748,120 entitled "Method of Reducing Iron Oxide to Metallic Iron", U.S. Pat. No. 3,749,386 entitled "Method for Reducing Iron Oxides in a Gaseous Reduction Process", U.S. Pat. No. 3,764,123 entitled "Apparatus for Reducing Iron Oxide to Metallic Iron", U.S. Pat. No. 3,816,101 entitled "Method for Reducing Iron Oxides in a Gaseous Reduction Process", and U.S. Pat. No. 4,046,557 entitled "Method for Producing Metallic Iron Particles", all of which are hereby incorporated herein by reference. SUMMARY OF THE INVENTION The invention is a system for providing both hot and cold DRI from a continuous gravity-fed supply of hot DRI material. The invention is an apparatus for the simultaneous discharge of hot direct reduced iron (DRI) material and cold DRI material from a continuous supply of hot DRI. The invention has a furnace discharge section, a hot discharge section, and a cold discharge section. The furnace discharge section has a pair of discharge outlets for discharging DRI material, and a plurality of feeders. The hot discharge section gravitationally receives hot DRI from the first discharge outlet of the hot discharge cone and conveys the hot DRI through a conduit or pipe to a melting furnace or a hot transport vessel. The cold discharge section gravitationally receives hot DRI material from the other discharge outlet of the furnace discharge section, conveys the DRI to a cooler through a conduit cools the hot DRI, and discharges cold DRI. OBJECTS OF THE INVENTION The principal object of the present invention is to provide an improved method to simultaneously provide both hot and cold DRI from a continuous supply of hot DRI material. Another object of this invention is to provide an improved method to simultaneously provide both hot and cold DRI from a continuous supply of hot DRI material, the hot DRI being delivered at a temperature of at least 700.degree. C. A further object of this invention is to provide apparatus for producing simultaneously both hot and cold DRI from a continuous supply of hot DRI material |
claims | 1. An X-ray apparatus for deriving X-ray absorbing information and X-ray phase information of an object to be detected comprising:a splitting element for splitting spatially X-rays generated by an X-ray generator into X-ray beams;a detector unit for detecting intensities of the X-rays, based on the X-rays split by said splitting element and transmitted through the object, the intensity of the X-rays changing according to an X-ray phase shift during the transmitting of the X-rays through the object, and also changing according to an X-ray position change; anda calculating unit for calculating an X-ray transmittance image as the X-ray absorbing information, and an X-ray differential phase contrast image or an X-ray phase shift contrast image as the X-ray phase information by using the intensities of the X-rays, whereinsaid splitting element forms X-ray beams by splitting the X-rays, and the X-ray beams have two or more widths at said detector unit,said calculating unit calculates the X-ray absorbing information and the X-ray phase information, based on a changing, in correlation between the changing of the phase of the X-rays and the changing the intensity of the X-rays in said detector unit, the correlation being changed according to the width of X-ray beam,wherein said splitting element comprises a slit array formed by line and space such that a slit width changes periodically between two or more slit widths, andwherein said slit array formed by line and space is formed by arranging alternatingly two slits of different widths. 2. The X-ray apparatus according to claim 1, further comprising an X-ray optical element arranged between said splitting element and said detector unit, and formed from an element for converting the position change quantity generated by the phase shift through the object into the intensity change of the X-rays. 3. The X-ray apparatus according to claim 2, wherein said element forming the X-ray optical element comprises a plurality of members absorbing or transmitting the X-rays arranged perpendicularly to an X-ray incident direction, and said member is formed into a triangular prism shape to have absorbing capability gradient so that an X-ray absorbing quantity or an X-ray transmitting quantity changes according to an X-ray incident position. 4. The X-ray apparatus according to claim 2, wherein said element forming the X-ray optical element comprises a plurality of shields shielding a part of the X-rays arranged perpendicularly to an X-ray incident direction, so that an area shielded by said shield changes according to an X-ray incident position. 5. The X-ray apparatus according to claim 1, further comprising an optical element arranged between said splitting element and said detector unit,wherein an element forming said optical element comprises a plurality of phosphors sensing the X-rays arranged perpendicularly to an X-ray incident direction, to have a light emitting quantity gradient so that the light emitting quantity of the phosphor changes according to an X-ray incident position. 6. The X-ray apparatus according to claim 1, further comprising an optical element arranged between said splitting element and said detector unit,wherein an element forming the optical element comprises a plurality of optical filters arranged perpendicularly to an X-ray incident direction, so that a light transmittance of said filters changes according to an X-ray incident position. 7. The X-ray apparatus according to claim 2, wherein said calculating unit calculates the X-ray transmittance image and the X-ray phase shift image of the object, under an assumption that the X-rays being transmitted to said elements forming said X-ray optical element and being adjacent to each other contain information of the same position of the object. 8. The X-ray apparatus according to claim 1, further comprisingan optical element comprising a plurality of elements arranged between said splitting element and said detector unit, whereinsaid calculating unit calculates the X-ray transmittance image and the X-ray position change of the object, under an assumption that the X-rays being transmitted to elements forming the X-ray optical element and being adjacent to each other contain information of the same position of the object. 9. An X-ray apparatus for deriving X-ray absorbing information and X-ray phase information of an object to be detected comprising:a splitting element for splitting spatially X-rays generated by an X-ray generator into X-ray beams;a detector unit for detecting intensities of the X-rays, based on the X-rays split by said splitting element and transmitted through the object, the intensity of the X-rays changing according to an X-ray phase shift during the transmitting of the X-rays through the object, and also changing according to an X-ray position change;a calculating unit for calculating an X-ray transmittance image as the X-ray absorbing information, and an X-ray differential phase contrast image or an X-ray phase shift contrast image as the X-ray phase information by using the intensities of the X-rays; andan X-ray optical element arranged between said splitting element and said detector unit, and formed from an element for converting the position change quantity generated by the phase shift through the object into the intensity change of the X-rays, whereinsaid splitting element forms X-ray beams by splitting the X-rays, and the X-ray beams have two or more widths at said detector unit,said calculating unit calculates the X-ray absorbing information and the X-ray phase information, based on a changing, in correlation between the changing of the phase of the X-rays and the changing the intensity of the X-rays in said detector unit, the correlation being changed according to the width of X-ray beam, anda plurality of the elements each forming the X-ray optical element include a first element and a second element, and said calculating unit calculates the X-ray transmittance image and the X-ray position change of the object according to following mathematical expressions: I 1 ′ A I 1 = a 1 d + b 1 I 2 ′ A I 2 = a 2 d + b 2 whereI1 is an intensity of X-rays being transmitted through the first element when the object is not arranged between the X-ray generator and the detector unit,I2 is an intensity of X-rays being transmitted through the second element when the object is not arranged between the X-ray generator and the detector unit,I1′ is an intensity of X-rays being transmitted through the first element when the object is arranged between the X-ray generator and the detector unit,I2′ is an intensity of X-rays being transmitted through the second element when the object is arranged between the X-ray generator and the detector unit,A is X-ray transmittance,d is X-ray position moving quantity,a1 and b1 are constants determined based on a relation between the X-ray intensity ratio and the X-ray position moving quantity of the width of the X-ray incident in the first element, anda2 and b2 are constants determined based on a relation between the X-ray intensity ratio and the X-ray position moving quantity of the width of the X-ray incident in the second element. 10. An X-ray apparatus for deriving X-ray absorbing information and X-ray phase information of an object to be detected comprising:a splitting element for splitting spatially X-rays generated by an X-ray generator into X-ray beams;a detector unit for detecting intensities of the X-rays, based on the X-rays split by said splitting element and transmitted through the object, the intensity of the X-rays changing according to an X-ray phase shift during the transmitting of the X-rays through the object, and also changing according to an X-ray position change;a calculating unit for calculating an X-ray transmittance image as the X-ray absorbing information, and an X-ray differential phase contrast image or an X-ray phase shift contrast image as the X-ray phase information by using the intensities of the X-rays; andan optical element arranged between said splitting element and said detector unit, and including a first element and a second element, and wherein said calculating unit calculates the X-ray transmittance image and the X-ray position change of the object according to following mathematical expressions: I 1 ′ A I 1 = a 1 d + b 1 I 2 ′ A I 2 = a 2 d + b 2 whereI1 is an intensity of the X-rays being transmitted through the first element when the object is not arranged between the X-ray generator and the detector unit,I2 is an intensity of the X-rays being transmitted through the second element when the object is not arranged between the X-ray generator and the detector unit,I1′ is an intensity of the X-rays being transmitted through the first element when the object is arranged between the X-ray generator and the detector unit,I2′ is an intensity of the X-rays being transmitted through the second element when the object is arranged between the X-ray generator and the detector unit,A is X-ray transmittance,d is X-ray position moving quantity,a1 and b1 are constants determined based on a relation between the X-ray intensity ratio and the X-ray position moving quantity of the width of the X-ray beam incident on the first element, anda2 and b2 are constants determined based on a relation between the X-ray intensity ratio and the X-ray position moving quantity of the width of the X-ray beam incident in the second element, whereinsaid splitting element forms X-ray beams by splitting the X-rays, and the X-ray beams have two or more widths at said detector unit, andsaid calculating unit calculates the X-ray absorbing information and the X-ray phase information, based on a changing, in correlation between the changing of the phase of the X-rays and the changing the intensity of the X-rays in said detector unit, the correlation being changed according to the width of X-ray beam. 11. The X-ray apparatus according to claim 10, wherein said splitting element comprises a slit array formed by line and space such that a slit width changes periodically between two or more slit widths. 12. The X-ray apparatus according to claim 11, wherein said slit array formed by line and space is formed by arranging alternatingly two slits of different widths. |
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052232093 | description | Referring now to the single FIGURE of the drawing in detail, there is seen a filter 2 disposed inside a containment 1 of a nuclear power plant. The filter 2 is provided for the purpose of filtering a gas-steam mixture that can be produced inside the containment 1 if a major malfunction should occur. In the event of such a malfunction, the release of considerable quantities of heat must be expected, which causes a large proportion of the water present inside the containment 1 to evaporate and causes the pressure inside the containment 1 to rise. When the calculated design pressure of the containment 1 is reached, the same gas-steam mixture is then released to the outside, while filtered by the filter 2, for pressure relief. The filter includes a container having a cylindrical middle part including outer and inner concentric walls 4 and 5 with lower ends being joined together by a curved base 8. The walls 4 and 5 have upper ends being joined together and closed off from the outside by a likewise curved cap 9. The walls 4 and 5 form an annular chamber 6, which surrounds an inner chamber 10. The first inner chamber 10 communicates with the second annular chamber 6 through openings located immediately below the cap 9. Inside the inner chamber 10, mist collectors 13 are secured to the upper end of the chamber 10, immediately in front of the openings in the wall 5. Filter mats 11 are disposed inside the upper half of the annular chamber 6. The filter mats 11 have a radially inner surface which communicates in a non-illustrated manner with the openings covered by the mist collectors 13 and a radially outer surface which communicates with another opening 18 leading outside, from which the filtered gas-steam mixture is carried out of the containment 1 through a pipe 19 penetrating the containment 1. The radially outer wall 4 is also pierced by an overpressure line 32, through which the annular chamber 6 is relieved through the use of an overpressure valve 33, if an impermissibly high pressure should arise. In order to avoid convection over the entire height of the annular chamber 6, a perforated and/or slit convection barrier 12 is provided immediately below the filter mats 11. The inner chamber 10 is filled with a washing fluid 3 to an extent of 30 to 80%, and preferably approximately half, prior to initiation of operation of the filter 2. The annular chamber 6 between the walls 4 and 5 is filled virtually completely with heat-conducting fluid 7 below the convection barrier 12. In the exemplary embodiment, water is provided as both the washing fluid 3 and the heat-conducting fluid 7. The supply of the filter material, that is of the gas-steam mixture, into the filter 2 from the interior of the containment 1, is effected through a horizontal segment 15 that is located toward an upper end of a pipe 14 disposed vertically in the middle of the inner chamber 10. The pipe 14 has a lower end with horizontally extending feed pipes 16 disposed in a radial or star pattern, for short Venturi nozzles 17. Normally, and particularly during nuclear power plant operation according to plan, the horizontal segment 15 is blocked off from the interior of the containment 1 through both a check valve 22 located in a line 21, and a bursting disk 23. The interior of the filter 2 also communicates with a primary loop of the nuclear power plant in a non-illustrated manner. This communication is also blocked off during normal operation. During normal operation of the nuclear power plant, the pipe 19 originating at the opening 18 leading outside is also closed. This is effected by shutoff fixtures 25, which can uncover or unblock the pipe 19 so that it is open toward not only a throttle 28 but also a further bursting disk 26 and a chimney 27. A measuring filter 30 is provided parallel to the throttle 28 and to a further shutoff fixture 29 located between the throttle 29 and the bursting disk 26. A replenishment line 24 for washing fluid 3 communicates with the inner chamber 10 through the base 8. The replenishment line 24 penetrates the containment 1 and has a free end which is closed by shutoff fixtures 31 during normal operation. If a major malfunction occurs inside the containment 1, then as mentioned above a considerable proportion of the water present as coolant inside the containment 1 will evaporate, causing the pressure to rise inside the containment, which is immediately hermetically sealed off in gas-tight fashion from the outside when a malfunction occurs. Parallel to the evaporation of some of the water, a number of other reactions also occur, by means of which gases and/or vapors are also produced and/or released. As a result of all of these processes, the pressure prevailing inside the containment 1 sooner or later may reach the design pressure of the containment 1. This depends substantially on the quantity of heat released. However, the temperature inside the containment also increases simultaneously with the pressure. As a result, the entire contents of the containment, thus including the filter 2 as well, are heated. The temperature of the contents of the containment 1 already reaches 100.degree. C. long before the calculated design pressure is approached. Since the interior of the filter 2 is sealed off hermetically from the outside and an inert gas cushion above the washing fluid is provided, the pressure inside the filter housing and the line elements connected to it rises as well, so that water provided as the heat-conducting fluid 7 and as the washing fluid 3 will not yet boil. Since heat transfer fins 20 are provided on the walls 4 and 5 in order to improve the heat transfer from the wall 4 to the heat-conducting fluid and from the fluid to the wall 5, the amount of heat given up to the heat-conducting fluid 7 by the wall 4 is especially high, so that a containment vessel temperature of 150.degree. C., for example, is quickly reached. Accordingly, when the bursting disk 23 responds, the temperature of the washing fluid 3 is 150.degree. C., for example, which is the temperature that has been reached by then inside the containment 1. Thus the gas-steam mixture flowing through the line 21, the horizontal segment 15 and the pipe 14 and through the feed pipes 16 to the short Venturi nozzle 17, will be only insignificantly if at all warmer, than the washing fluid 3. Accordingly, when the gas-steam mixture mixes with the washing fluid 3 in the short Venturi nozzles 17, only an insignificant portion of the water steam will condense out of the gas-steam mixture, so that the gas-steam mixture emerging upward from the washing fluid 3 and also flowing out through the mist collectors or separators 13 and the filter mats 11 to the opening 18 leading to the outside substantially has the same composition as the mixture carried into the filter through the line 21. The gas-team mixture flowing into the filter 2 through the short Venturi nozzles 17 undergoes a pressure drop from 2000 to 200 hPa in this process, so that immediately after the response of the bursting disk 23, washing fluid 3 and heat-conducting fluid 7 evaporate. Since in contrast to the washing fluid, the heat-conducting fluid is not replenished, it is soon evaporated, and as a result the thermal bridge between the interior of the containment 1 and the interior of the filter 2 is broken. Due to the removal of the heat of evaporation, the temperature of the washing fluid 3 is approximately 10.degree. to 2.degree. lower than the temperature of the inflowing gas-steam mixture. After the response of the bursting disk 23, the pressure, which is lowered merely by the aforementioned amount, prevails in the filter 2. This pressure is almost equivalent to the pressure in the interior of the containment 1, so that only a relatively small volumetric flow of gas-steam mixture has to be filtered. Moreover, because of the accommodation of filter mats 11 in the chamber 6 annularly surrounding the inner chamber 10, a very compact, space-saving structure for the filter 2 is made possible. When the filter 2 is in operation for a relatively long period, filter material dripping out of the filter mats 11 will collect in the lower part of the chamber 6 and as a result will re-create a thermal bridge to the washing fluid 3. Nevertheless, this process proceeds so slowly that it presents no threat or substantial impairment to the filtration. In any case, during continuous operation of the filter, only relatively small losses of washing fluid need be expected, because only the quantity of heat contained in the filter material itself flows through the filter 2. However, as long as the partial pressure of the water steam in the gas-steam mixture is lower than the boiling pressure corresponding to the temperature of the washing fluid, some of the washing fluid will evaporate. As a result, heat is removed from the washing fluid, and in other words the temperature is lowered, until the boiling pressure is equal to the partial pressure. |
abstract | A base portion for use in a bottom nozzle of a fuel assembly in a nuclear reactor includes a top surface, a bottom surface, and a plurality of vertical wall portions arranged in a generally squared grid-like pattern which extend between the bottom surface and the top surface and which define a plurality of non-circular passages passing between the bottom surface and the top surface through the base portion. |
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claims | 1. An X-ray diaphragm having four blades which are arranged in a surrounding relation to four sides so as to form a pyramidal X-ray beam with an X-ray focus as a vertex,the four blades having such a structure that the blades are fitted in one another in the form of parallel crosses at portions corresponding to four-corner edges of the pyramid, wherein one of the blades is configured to move from a first position parallel to a second position. 2. An X-ray diaphragm according to claim 1, wherein each of the blades has a plurality of cross beams, the cross beams of the blades being formed such that the adjacent cross beams are fitted in each other. 3. An X-ray diaphragm according to claim 1, wherein the distance between the mutually opposed blades is variable. 4. An X-ray diaphragm according to claim 1, wherein the diaphragm is configured to rotate. 5. An X-ray diaphragm according to claim 1, wherein the diaphragm is configured to rotate in a plane parallel to an axis of an X-ray tube. 6. An X-ray irradiator comprising:an X-ray tube;an X-ray diaphragm having four blades which are arranged in a surrounding relation to four sides so as to form a pyramidal X-ray beam with an X-ray focus as a vertex; anda collimator for collimating the X-ray beam formed by the X-ray diaphragm,the four blades having such a structure that the blades are fitted in one another in the form of parallel crosses at portions corresponding to four-corner edges of the pyramid, wherein one of the blades is configured to move from a first position parallel to a second position. 7. An X-ray irradiator according to claim 6, wherein each of the blades has a plurality of cross beams, the cross beams of the blades being formed such that the adjacent cross beams are fitted in each other. 8. An X-ray irradiator according to claim 6, wherein the distance between the mutually opposed blades is variable. 9. An X-ray irradiator according to claim 8, wherein the X-ray diaphragm is interlocked with the collimator. 10. An X-ray irradiator according to claim 6, wherein the X-ray diaphragm and the collimator are rotatable in a plane parallel to an axis of the X-ray tube. 11. An X-ray apparatus comprising:an X-ray tube;an X-ray diaphragm having four blades which are arranged in a surrounding relation to four sides so as to form a pyramidal X-ray beam with an X-ray focus as a vertex, wherein a first one of the blades is configured to fit with a second one of the blades, wherein the first one of the blades is conflaured to form a plurality of parallel crosses within the second one of the blades, wherein the parallel crosses are formed at an edge of a pyramid formed by the blades, and wherein the first one of the blades is configured to move from a first position parallel to a second position; anda collimator for collimating the X-ray beam formed by the X-ray diaphragm and directing the collimated beam to an object to be radiographed. |
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041487451 | summary | BACKGROUND OF THE INVENTION In reprocessing spent nuclear fuels and/or blanket materials, phosphoric acid esters (mixed with hydrocarbons) are frequently used as solvent for extracting actinide elements. When such solvent is used for a prolonged period of time, radiolysis or chemical reactions give rise to undersized decomposition products. Although some of these products can be removed by cleaning steps, no complete separation is possible. Because of the pronounced complexing properties of decomposition products there is an increased, disturbing extraction of fission products, such as zirconium-95, from the aqueous phase into the organic phase loaded with actinides. However, an increase in fission product concentration of the organic phase not only reduces the extraction efficiency for the actinides and the separation efficiencies both of the actinides from the fission products and the actinides from each other and the degree of purity of the individual actinides but also enhances the radiolytic processes in the organic phase and, in addition, aggravates the phase separation by generating turbidities and colloids in the interface between the organic and aqueous phases. For full utilization the solvent should be recycled. However, in that case a cumulation of unfavorable influences cannot be avoided, and the usefulness of a solvent batch is limited despite the decontamination step following every application. The rate at which a batch becomes unusable for further application is a function of such factors as the burnup level of the nuclear fuels and blanket materials, respectively, their concentration in the aqueous phase, the number of recycles of a batch (number of application steps), etc. Solvent mixtures which have become useless in this way, or must be termed useless, represent strongly radioactively contaminated organic wastes and are separated first into their phosphoric acid ester and hydrocarbon constituents by means of the addition of phosphoric acid, the ester, e.g. tributyl phosphate (TBP), combining with phosphoric acid into an adduct insoluble in hydrocarbons, which adduct is further decomposed after separation from the hydrocarbons. The hydrocarbons can be removed by burning. Various methods of TBP removal have so far been employed, but either they are unfeasible because of their environmental impact or they require relatively large expense in terms of time, facilities, cost, etc. It was suggested, for instance, to burn liquid organic wastes containing phosphoric acid esters. However, this generates highly corrosive gases carrying with them radioactive material and phosphorpentoxide aerosols. The usual type of filters for gases containing radioactive materials are plugged up within a very short time, corrode and thus become ineffective. The combustion or flue gases, therefore, must first be scrubbed and the phosphorpentoxide must be neutralized before there can be a final filtering step. Moreover, it was suggested to discharge all solutions containing TBP into the ground in arid areas with a low population density. However, only some of the radioactive materials will be retained in the soil components, while most of them will pass through the layers of soil together with the organic liquid and may reach ground water. Distillation processes can be used only for the more or less effective separation of TBP from hydrocarbons, but this neither removes the TBP nor prepares it in any way for non-polluting storage. In addition, disadvantages connected with the methods outlined above give rise to some hazards, such as radioactive materials getting into the biocycle, organic liquids entering ground water, generation of easily flammable gases, and explosions in distillation plants. Another technique which has been suggested in the prior art is the incorporation of TBP into polyethylene, as disclosed in U.S. Pat. No. 3,463,738 to Fitzgerald et al. Products produced by mixing polyethylene, with the addition of heat with either a mixture of tributyl phosphate and alkane hydrocarbon or with tributyl phosphate which had previously been separated from the alkane hydrocarbon, are solid gels which, during storage in containers for a period of time exhibit undesirable shrinkage as the result of a discharge of liquid. The solid polyethylene-containing bodies no longer contact the container walls. This shrinkage results in an environmental danger because the containers may break, for example, by mechanical force when the containers are stacked, or due to corrosion, and this breakage would enable the radioactive liquid to escape. Since the possibility of this discharge liquid entering the biocycle cannot be dependably excluded, the process for solidifying and removing radioactive organic waste liquids with the aid of polyethylene is unsuitable in view of the safety and environmental protection problems involved. In an article by Burns, Solidification of Low- and Intermediate-Level Wastes, ATOMIC ENERGY REV., 9(3) pages 583 to 584, Sept., 1971, it is stated that limited experiments were carried out which show that it is possible to introduce chemical sludges, which contained about 50% water, into plastic wastes comprised of a mixture of polyethylene and polyvinyl chloride. In discussing the results obtained with the waste plastic mixture of polyethylene and polyvinyl chloride Burns states that the tests were experimental in nature, that the activity in wastes was kept to tracer levels, and that it would be advisable to carry out further experiments before coming to definite conclusions concerning the use of such waste plastic mixtures with aqueous chemical sludges. Burns does not disclose that such waste plastic mixtures can be used for solidification of organic phosphoric acid ester wastes. SUMMARY OF THE INVENTION The present invention provides a method which safely avoids the disadvantages and hazards connected with previous practices for the removal of spent phosphoric acid esters contaminated with radioactive materials. At the same time, phosphoric acid esters are brought into a state suitable for introduction into a secular store for radioactive wastes, i.e. they are not able to flow and they do not corrosively attack container material. Minimum leachability of the radioactive materials incorporated in this state is ensured by the present method in order to satisfy the environmental protection requirements. In addition, the overall cost of storing reprocessing plant waste is minimized. The products of the present invention do not exhibit shrinkage when placed in containers as a result of a discharge of liquid, and thus do not present any danger to the environment should the container in which it is placed break. The products formed by the method of the present invention closely contact the container walls of the container in which they are stored even after years of storage and do not discharge any liquids. These products are safe with respect to the environment which has to be protected and are suited for the permanent solidification of spent phosphoric acid ester organic waste liquids. The products can be in the form of a rubber-like mass which retains its volume and which assures permanent solidification. The present invention thus relates to a method of preparing, for nonpulluting storage, phosphoric acid esters used in reprocessing spent nuclear fuels and/or blanket materials and to obtained products. In accordance with the present invention, phosphoric acid esters which have been separated from hydrocarbon and which contain radionuclides and decomposition products are contacted with a solidification matrix which consists of crushed polyvinyl chloride (PVC), in a weight ratio of phosphoric acid ester to PVC of 5 to 1 or less. In a further aspect of the invention, a method is provided for preparing phosphoric acid ester used in reprocessing spent nuclear fuels and/or blanket materials for non-polluting storage, which phosphoric acid ester has been separated from hydrocarbon, which comprises contacting the separated phosphoric acid ester containing radionuclides and decomposition products with crushed polyvinyl chloride (PVC) to form a liquid mixture having a weight ratio of phosphoric acid ester to PVC of 5 to 1 or less, adding spent ion exchanger contaminated with radionuclides to the liquid mixture of phosphoric acid ester and PVC by stirring to form a resulting liquid mixture having a minimum PVC content of about 14 weight percent and then permitting the resulting liquid mixture to cool until a solid mass is formed which consists of the phosphoric acid ester, the PVC, and the spent ion exchanger. The use of polyvinyl chloride as the sole solidification matrix component in accordance with the present invention, enables large quantities of the phosphoric acid ester to be absorbed. Thus, for example, the solid mass can contain equal quantities of phosphoric acid ester and polyvinyl chloride, and, in fact, can contain significantly greater quantities of phosphoric acid than polyvinyl chloride. Thus, the weight ratio of phosphoric acid ester to polyvinyl chloride can be, for example, 1:1, or can be even higher, such as 7:1.5. The upper limit for the ratio is 5:1 and this corresponds to a composition comprising about 83 weight percent phosphoric acid ester relative to about 17 weight percent PVC. The ratio, for example, can be from 1.47:1, which corresponds to a composition comprising about 59.5 weight percent phosphoric acid ester relative to about 40.5 weight percent PVC, to 3:1, which corresponds to a composition comprising about 75 weight percent phosphoric acid ester relative to about 25 weight percent PVC. Ratios of phosphoric acid ester to PVC of up to 3:1 are particularly suited for forming a rubber-like mass which retains its volume and which assures permanent solidification. In the embodiment of the invention where spent ion exchange materials contaminated with radionuclides are added and form part of the final solid mass, the use of such ion exchange materials enables the amount of radioactive material in the solid mass to be increased up to 86%, comprised of the phosphoric acid ester and spent ion exchanger, and enables the amount of PVC used to be decreased down to 14%. In the present invention, spent ion exchange material is the only component which can be incorporated into mixtures of organic phosphoric acid esters and PVC. The ratio of organic phosphoric acid ester to PVC in this embodiment of the invention can be the same as those set forth above for the embodiment where PVC is the sole other component of the solidification product. DESCRIPTION OF THE PREFERRED EMBODIMENTS In one embodiment, phosphoric acid esters with tributyl phosphates as the dominating component are mixed with PVC chips at temperatures below the softening point of PVC, and the mixture is kept at room temperature until a solid, homogeneous mass is generated. In another embodiment, phosphoric acid esters with TBP as the dominating component are homogeneously mixed with PVC chips at temperatures above the softening point of PVC; the heat added to attain these temperatures is allowed to act upon at least one of the noted ingredients of the mixture; and the mixture is left to cool so as to form a solid mass. In order to minimize addition of inactive ingredients to the PVC mixture and thus prevent an increase in the resulting volume of radioactive waste (solidification products fit for secular storage), a preferred embodiment provides (a) for addition (with stirring) of spent ion exchanger (contaminated with radionuclides) to the liquid mixture of TBP and PVC in an amount in the order of 20 weight % referred to the weight of the sum of TBP, PVC and ion exchanger and (b) for letting the resulting mixture cool until a solid mass has been generated. Although incorporation of radioactive material contaminated ion exchanger in a non-flowable (phosphoric acid ester)/PVC mass provides safe means for storing the radioactive material contained therein and incorporation in a similar mass of ion exchanger (whether spent or not) which has a capacity for absorbing the phosphoric acid ester provides means for reducing the proportion of PVC required to attain a non-flowable mass, a double advantage results when radioactive material contaminated spent ion exchanger having a capacity for absorbing the phosphoric acid ester is incorporated in such masses. Illustrative of ion exchangers which have the noted capacity even when they are spent and are contaminated with radioactive material are, e.g., polystyrene resins containing sulfonic acid groups or polystyrene resins containing trimethylammonium groups. Regulations on the shipment of radioactive wastes to a place of secular storage and on secular storage proper require previous treatment of the wastes in a way which ensures that the environment is not contaminated even when waste containers are accidentally damaged. Hence, the requirements to be fulfilled, e.g., by TBP-PVC product masses as far as mechanical strength is concerned can be low and can be limited to the requirement that the product must not be able to flow. As a consequence, very favorable mixing ratios of TBP and PVC as a solidifying agent can be achieved in order to minimize any increase in volume of radioactive waste. Commercial grade relatively pure PVC can be used to generate products (containing only 20 weight % or less PVC) which are of a soft, jelly like consistency, but not able to flow. If PVC grades containing large amounts of plasticizer or filler are used, of course much less favorable mixing ratios must be condoned. PVC softens at temperatures above 100.degree. C., immediately forming homogeneous mixtures when stirred in the presence of TBP, which mixtures solidify on cooling. Because of the toxicity of TBP and its content of radioactive substance, however, heating requires precautionary measures and should be avoided. When TBP and crushed PVC are left as a mixture, the PVC absorbs the liquid TBP; when sufficient PVC is present, it swells so that no liquid is left after only 24 hours. Within a few weeks a compact mass forms which hardly differs from the corresponding product generated under the influence of heat. An alternative provides for heating TBP to a slightly elevated temperature, feeding it into crushed PVC in a container and producing a homogeneous solution by a short period of stirring. One of the advantages of the present method is that bound TBP is not volatile during storage. A sample kept in open air for 16 months did not show any detectable loss of weight. Other waste products, such as spent radioactively contaminated ion exchangers, can also be included in the produced mixtures. Since some ion exchangers are capable of absorbing TBP, with ensuing swelling, smaller amounts of PVC (relative to TBP) will suffice to generate a product of sufficient strength in the presence of such ion exchangers. Another advantage of the present invention is that the PVC waste mixtures of the present invention do not shrink during solidification. The products produced in accordance with the present invention loosely contact the container walls even after years of storage and do not discharge any liquids. |
claims | 1. A passive residual heat removal system, comprising:a reactor pressure vessel;a reactor core placed in the reactor pressure vessel;a primary containment vessel including a drywell to surround the reactor pressure vessel, and a suppression chamber internally provided with a suppression pool;a vent line connecting the drywell and the suppression pool, the vent line being fitted with a plurality of openings in the suppression pool;a coolant pool filled with a coolant and provided above the primary containment vessel;a heat exchanger placed under the coolant in the coolant pool;a steam suction line connecting the drywell and the heat exchanger;a condensate storage tank disposed below the heat exchanger and above an upper end of the reactor core;a first condensate discharge line connecting the condensate storage tank and the heat exchanger;a non-condensate gas discharge line connected at a first end thereof to an upper section of the condensate storage tank and at a second end thereof to the suppression pool, the second end of the non-condensate gas discharge line being open at a position higher than a highest opening of the vent line in the suppression pool;a second condensate discharge line connected at a first end thereof to a position below that section of the condensate storage tank to which the first end of the non-condensate gas discharge line is connected, and at a second end thereof to the suppression pool, the second end of the second condensate gas discharge line being open at a position lower than a lowest opening of the vent line in the suppression pool; anda condensate return line connected at a first end thereof to a position below that section of the condensate storage tank to which the first end of the second condensate discharge line is connected, and at a second end thereof to a side portion of the reactor pressure vessel, the side portion being above the upper end of the core;wherein the open end of the second condensate discharged line, positioned in the suppression pool, is branched into a plurality of horizontal lines, with condensate discharge ports being formed at distal ends of the branched horizontal lines. 2. A passive residual heat removal system, comprising:a reactor pressure vessel;a reactor core placed in the reactor pressure vessel;a primary containment vessel including a drywell to surround the reactor pressure vessel, a suppression chamber internally provided with a suppression pool, and a pedestal formed directly under the reactor pressure vessel, as space that is demarcated atop from the drywell;a vent line connecting the drywell and the suppression pool, the vent line being fitted with a plurality of openings in the suppression pool;a coolant pool filled with a coolant and provided above the primary containment vessel;a heat exchanger placed under the coolant in the coolant pool;a steam suction line connecting the drywell and the heat exchanger;a condensate storage tank disposed below the heat exchanger and above an upper end of the reactor core;a first condensate discharge line connecting the condensate storage tank and the heat exchanger;a non-condensate gas discharge line connected at a first end thereof to an upper section of the condensate storage tank and at a second end thereof to the suppression pool, the second end of the non-condensate gas discharge line being open at a position higher than a highest opening of the vent line in the suppression pool;a second condensate discharge line connected at a first end thereof to a position below that section of the condensate storage tank to which the first end of the non-condensate gas discharge line is connected, and at a second end thereof to the pedestal; anda condensate return line connected at a first end thereof to a position below that section of the condensate storage tank to which the first end of the second condensate discharge line is connected, and at a second end thereof to a side portion of the reactor pressure vessel, the side portion being above the upper end of the core;wherein parallel branches are provided on part of the condensate return line, a squib valve is provided as a condensate return valve on one of the parallel branch lines, and an air-operated valve is provided as another condensate return valve on the other branch line. 3. The passive residual heat removal system according to claim 1, further comprising:a depressurization line connecting the reactor pressure vessel and the primary containment vessel, and a depressurization valve opening/closing the depressurization line. 4. The passive residual heat removal system according to claim 1, wherein:a ratio of V/Q between the amount of coolant, V (m3), in the condensate storage tank, and thermal output power Q (GW) of the core under rated operation, is at least 20. 5. A nuclear power plant facility, comprising the passive residual heat removal system according to claim 1. |
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claims | 1. A rectangular frame system with one to two discoid radiation filters for filtering the spectrum of a tanning radiator, with an upper plate, a lower plate and two to three marginal members wherein two marginal members lie opposite one another and the join the upper plate to the lower plate the upper plate having a first opening whose perimeter describes a circle, an ellipse, a rectangle or a polygon, and the lower plate has a rectangular second opening, the second opening having a greater area than the first opening, and on the two oppositely lying marginal members, which border on the side of the frame system at which no marginal member is provided, at least two double spring clips are arranged such that between the lower plate and the double spring clips a first radiation filter is clamped. 2. A rectangular frame system according to claim 1 , wherein the first radiation filter is an interference filter. claim 1 3. A rectangular frame system according to claim 1 , wherein the first radiation filter is of rectangular shape. claim 1 4. A rectangular frame system according to claim 1 , wherein the first radiation filter has a width and a length ranging from 215 mm to 240 mm. claim 1 5. A rectangular frame system according to claim 4 , wherein the first radiation filter has a width of 225 mm and a length of 230 mm. claim 4 6. A rectangular frame system according to claim 1 , wherein a second radiation filter is clamped between the upper plate and the double spring clips. claim 1 7. A rectangular frame system according to claim 6 , wherein the second radiation filter is an ultraviolet filter or an infrared filter. claim 6 8. A rectangular frame system according to claim 7 , wherein the second radiation filter is of rectangular shape. claim 7 9. A rectangular frame system according to claim 8 , wherein the second radiation filter has a width and a length ranging from 215mm to 240 mm. claim 8 10. A rectangular frame system according to claim 9 , wherein the second radiation filter has a width of 225 mm and a length of 230 mm. claim 9 11. A rectangular frame system according to claim 6 , wherein the double spring clips are configured such that the second radiation filter can be inserted from the side of the frame at which no marginal member is present, between the upper plate and the double spring clips. claim 6 12. A rectangular frame system according to claim 6 , wherein the first radiation filter has on its side facing away from the second radiation filter an imprint or an adhesive label. claim 6 13. A rectangular frame system according to 12 , wherein the imprint or label has an opaque marginal area. 14. A rectangular frame system according to claim 1 , wherein the double spring clips are arranged half-way between the upper plate and the lower plate. claim 1 15. A rectangular frame system according to claim 1 , wherein the double spring clip is formed from at least one bent metal wire. claim 1 16. A rectangular frame system according to claim 15 , wherein the double spring clip is shaped according to FIG. 3 a. claim 15 17. A rectangular frame system according to claim 15 , wherein the double spring clip is shaped according to FIG. 3 . claim 15 18. A rectangular frame system according to claim 1 , wherein the double spring clip is formed from at least one flat spring plate. claim 1 19. A rectangular frame system according to claim 1 , wherein the double spring clips are configured such that the first radiation filter can be inserted from the side of the frame system on which no marginal member is present, between the lower plate and the double spring clips. claim 1 20. A rectangular frame system according to claim 1 , wherein on the side of the frame system at which no marginal member is present a device is provided to prevent the one to two radiation filters from slipping back. claim 1 21. A rectangular frame system according to claim 1 , wherein on the side of the frame system that is opposite the side on which no marginal member is present, a device is provided and/or a third marginal member to prevent the dropping out of the one to two radiation filters. claim 1 22. A tanning module with a housing, a tridimensional reflector disposed on or in the housing, and with a rectangular frame system according to claim 1 , on one side of the housing , wherein the first radiation filter covers the radiation emitting area of the reflector and the lower plate faces away from the reflector. claim 1 23. A tanning module according to claim 22 , wherein the rectangular frame system can be released from the housing through a swivelling mechanism. claim 22 24. A tanning module according to claim 23 , wherein the rectangular frame system is hooked into the housing. claim 23 25. A tanning module according to claim 24 , wherein the rectangular frame system is hooked into an opening according to FIG. 8 in the housing. claim 24 26. A tanning module according to claim 23 , wherein the rectangular frame system is fixed in position by means of a snap mechanism. claim 23 27. A tanning module according to claim 22 , wherein a perimeter of the reflector parallel to the radiation emitting area describes a circle, an ellipse, a rectangle or a polygon. claim 22 28. A tanning module according to claim 27 , wherein the reflector is formed of facets and the perimeter of the reflector parallel to the radiation emitting area describes a polygon with twelve corners. claim 27 29. A tanning module according to claim 28 , wherein the reflector has a height of 90 mm to 95 mm, and the dodecagon has in the plane of the radiation emitting area a maximum diameter (corner to corner) ranging from 210 to 230 mm. claim 28 30. A tanning module according to claim 29 , wherein the reflector has a height of 93.6 mm. claim 29 31. A tanning module according to claim 29 , wherein the dodecagon has in the plane of the radiation emitting area a maximum diameter (corner to corner) of 210 mm. claim 29 32. A tanning module according to claim 28 , wherein the reflector has a height ranging from 110 mm to 125 mm, and the dodecagon has in the plane of the radiation emitting area a maximum diameter (corner to corner) ranging from 170 mm to 200 mm. claim 28 33. A tanning module according to claim 32 , wherein the reflector has a height of 118.7 mm. claim 32 34. A tanning module according to claim 32 , wherein the dodecagon has in the plane of the radiation emitting area a maximum diameter (corner to corner) of 184 mm. claim 32 35. A tanning module according to claim 28 , wherein the reflector has a height ranging from 75 mm to 90 mm, and the dodecagon has in the plane of the radiation emitting area a maximum diameter (corner to corner) ranging from 205 mm to 235 mm. claim 28 36. A tanning module according to claim 35 , wherein the reflector has a height of 83.3 mm. claim 35 37. A tanning module according to claim 35 , wherein the dodecagon has in the plane of the radiation emitting area a maximum diameter (corner to corner) of 220. claim 35 |
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