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claims | 1. An X-ray device, for half-scanning, the device comprising:a radiation source;a detector disposed in a beam path of the radiation source behind an object;a rotating plate comprising a rotary shaft provided adjacent to the radiation source in the beam path, the rotary shaft extending perpendicularly through a center axis of a radiation cone, wherein one side of the rotary shaft comprises X-ray-absorbing material; anda scanner that is operable to scan the object and the detector in only some portions to record two half-images, the two half-images being joined together to produce an X-ray image. 2. The X-ray device as defined by claim 1, wherein the X-ray-absorbing material ends a short distance from the rotary shaft. 3. The X-ray device as defined by claim 1, wherein the plate is essentially rectangularly symmetrical to the rotary shaft, and the second half comprises a frame that is operable as a balance. 4. The X-ray device as defined by claim 1, wherein in the time intervals between the half-image radiation exposure time slots, the X-radiation is interrupted. 5. The X-ray device as defined by claim 4, wherein the radiation source is operable in a pulsed mode. 6. The X-ray device as defined by claim 4, wherein in the time intervals between the half-image radiation exposure time slots, a screen is operable to interrupt the beam path of the radiation source. 7. The X-ray device as defined by claim 4, wherein the plate is operable to rotate at twice or a higher multiple of the speed of normal operation. 8. The X-ray device as defined by claim 1, wherein the object includes a patient. 9. The X-ray device as defined by claim 1, wherein images are partially overlapped. 10. The X-ray device as defined by claim 1, wherein the plate is essentially rectangularly symmetrical to the rotary shaft, and the second half comprises a plate of X-ray permeable material. 11. The X-ray device as defined by claim 7 wherein the plate is operable to avoid a doubled or higher-multiple image frequency. 12. The X-ray device as defined by claim 7, wherein two half-images are recorded upon each revolution. 13. The X-ray device as defined by claim 11, wherein two half-images are recorded upon each revolution. 14. The X-ray device as defined by claim 11, wherein the X-ray absorbing material is coated on the plate. 15. In a method of creating an X-ray image using a plate disposed between a radiation source and an object to be irradiated, the plate comprising a shaft, a first half that includes an X-ray absorbing material, and a second half that transmits radiation from the radiation source, the method comprising:directing radiation from the radiation source to the object;creating a first half of an image;rotating the plate; andcreating a second half of an image. 16. The method of creating an X-ray image as defined in claim 15, comprising combining the first half of an image with the second half of an image. 17. An X-radiation plate for suppressing scattered radiation where the plate is disposed between a radiation source and an object to be irradiated, the plate comprising:a rotatable shaft,a first half that includes an X-ray absorbing material, anda second half that comprises a frame forming only a single aperture that allows transmission of radiation from the radiation source,wherein the first half is connected to the rotatable shaft such that rotation of the rotatable shaft allows for recording X-ray half-images. 18. The X-radiation plate as defined by claim 17, wherein the X-ray absorbing material blocks out X-ray images. 19. The X-radiation plate as defined by claim 17, wherein the first half is rectangular. |
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052308618 | claims | 1. A fuel assembly for a light-water nuclear reactor comprising a plurality of vertical fuel rods which are arranged, in spaced relationship in a lateral direction, between a bottom tie plate and a top tie plate, the bottom tie plate defining through-going, vertical channels for conducting water through the bottom tie plate and into spaces between the fuel rods and horizontal channels which cross the vertical channels, and wherein helical springs with horizontal symmetry axis are positioned in said horizontal channels so as to extend across said vertical channels. 2. A fuel assembly according to claim 1, said helical springs extend along substantially the whole length of the horizontal channels. 3. A fuel assembly according to claim 1 wherein the bottom tie plate includes horizontal channels at spaced first and second vertical levels in the bottom tie plate, and wherein helical springs are positioned in the horizontal channels at said first and second vertical levels. 4. A fuel assembly according to claim 3, wherein said horizontal channels in said first level extend in parallel in a first direction and said horizontal channels in said second level extend in parallel in a second direction, said second direction being perpendicular to said first direction. 5. A fuel assembly according to claim 1, wherein the bottom tie plate includes horizontal channels which have no helical springs therein. 6. A fuel assembly according to claim 1, wherein the bottom tie plate defines side edges and wherein some of said horizontal channels extend to said side edges to be in open communication with the spaces between the fuel rods thereabove. 7. A fuel assembly for a boiling-water reactor according to claim 1, including tie fuel rods having end plugs which extend into said bottom tie plate, said end plugs having horizontal slots and wherein said helical springs are adapted to extend through said horizontal slots in said end plugs to lock the tie fuel rods in position. |
abstract | A method for selecting a loading map for a nuclear reactor core including the following steps: a) providing production data relating to the nuclear fuel assemblies, b) providing neutron data which are representative of the operation of the core, c) calculating the three-dimensional distribution of the local power in the core, d) calculating the extreme value reached by at least one thermomechanical parameter within the nuclear fuel assemblies, and e) selecting, in accordance with the extreme values calculated, a loading map from the loading maps envisaged. |
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claims | 1. An x-ray imaging configuration, comprising: means to support a sample; and a body of a substance excitable by an appropriate incident beam to generate x-ray radiation, the body being arranged with respect to said sample support means so that said radiation irradiates said sample; wherein said body is a divided or patterned array of spaced apart body portions, each of which, when excited by said incident beam, generates an x-ray beam of accurately predictable source size. 2. An x-ray imaging configuration according to claim 1 , wherein said substance is excitable by an electron beam to generate x-ray radiation. claim 1 3. An x-ray imaging configuration according to claim 1 , wherein said substance is excitable by an incident focused beam of electromagnetic radiation to generate x-ray radiation. claim 1 4. An x-ray imaging configuration according to claim 1 , wherein said body portions are retained on a common substrate. claim 1 5. An x-ray imaging configuration according to claim 1 , further comprising an energy detector. claim 1 6. An x-ray imaging configuration according to claim 1 , wherein said body portions are about 0.21 xcexcm in width. claim 1 7. An x-ray microscope or microprobe comprising: means to generate an electron beam; means to support a sample; and a body of a substance excitable by said electron beam to generate x-ray radiation, the body being arranged with respect to said sample support means so that said radiation irradiates said sample; wherein said body is a divided or patterned array of body portions, each of which, when excited by said electron beam, generates an x-ray beam of accurately predictable source size. 8. An x-ray microscope or microprobe according to claim 7 , wherein said body portions are about 0.2 xcexcm in width. claim 7 9. An x-ray microscope or microprobe according to claim 7 , wherein the electron beam is focused in operation to a width in the range of 10 to 1000 nm in said body of excitable substance. claim 7 10. An x-ray microscope or microprobe according to claim 7 , wherein said body portions are retained on a common substrate. claim 7 11. An x-ray microscope or microprobe according to claim 7 , further including an energy detector. claim 7 12. An apparatus for irradiating a sample with x-ray radiation for imaging the sample, comprising: a sample holder for mounting a sample; and a substance excitable by an appropriate incident beam to generate x-ray radiation, the substance being disposed in spaced relationship with said sample holder, such that x-ray radiation generated from said substance irradiates the sample mounted to said sample holder, and thereafter exits the sample holder for detection external to the sample holder, wherein said sample holder and said substance are adapted and dimensioned to be inserted in a complementary holder of an electron microscope at a position where the electron beam of the microscope is focused on said substance, to thereby generate x-ray radiation. 13. The apparatus according to claim 12 wherein said substance is excitable by an incident focused beam of electromagnetic radiation to generate x-ray radiation. claim 12 14. The apparatus according to claim 12 wherein said substance comprises a patterned array of x-ray generating material retained on a common substrate. claim 12 15. The apparatus according to claim 12 wherein said sample holder comprises a chamber arranged to be hermetically sealed after placement of a sample in the chamber. claim 12 16. The apparatus according to claim 12 wherein said sample holder is adapted to be enclosed, and said sample holder includes an x-ray transparent window by which the said x-ray radiation exits the sample holder for detection. claim 12 17. The apparatus according to claim 12 , further comprising an energy detector disposed in spaced relationship with said sample holder external to said sample holder. claim 12 18. A method for irradiating a sample with x-ray radiation for imaging the sample, comprising: disposing the sample in a sample holder in spaced relationship with a substance excitable by an appropriate incident beam to generate x-ray radiation and inserting the sample holder and said substance in a complementary holder of an electron microscope at a position where the electron beam of the microscope is focused on said substance; and irradiating said substance with an electron beam to cause the substance to generate x-ray radiation to irradiate the sample for detection external to the sample holder. 19. The method of claim 18 , further comprising the step of: claim 18 detecting at least a portion of the radiation exiting the sample holder after it has irradiated the sample, to provide an image of one or more internal boundaries or other features of the sample. |
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047117575 | abstract | Position indicating device for producing an indication of the position of a displaceable structure, the device including:. a plurality of sensing elements extending along a defined path such that each element is associated with a respective location along the defined path, each element being operative to respond to the presence of a position representing member when the member extends from a starting point to the respective location associated with that element, the elements being coupled into respective pairs of elements, with each pair of elements having an output producing a signal only when a single element of its respective pair is responding to the presence of the member; a plurality of signal producing members each operative for producing a signal representing a predetermined logic state in response to a predetermined input signal; and circuit components operatively connecting the outputs to the signal producing members for causing a signal at each output to produce a predetermined input signal at a corresponding signal producing member and for causing a predetermined input signal to be produced at at least one signal producing member by a signal at at least two of the outputs. |
abstract | An integrated head assembly (100) is disclosed for a nuclear reactor. The preferred integrated head assembly includes a lift assembly (150) that supports the reactor vessel closure head (90) and integrated head assembly for removal, a separate support structure (202) supported by a ring beam (151) that sits atop the reactor vessel closure head, a shroud assembly (200), a seismic support system (300), a baffle assembly (500), a missile shield (400), and a CRDM cooling system. The CRDM cooling system draws cooling air into the baffle assembly, downwardly past the CRDMs (96), outwardly to upright air ducts (600), upwardly to an upper plenum (680), and out of the assembly through the air fans (190). |
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052672751 | claims | 1. Apparatus for sealing a joint between a base surface and a mating end surface of a hollow body, said base surface and mating end surface joint having a compression gasket means therebetween, which gasket means requires the application of a compression preload force applied through said hollow body to create an effective seal, said apparatus being characterized by: means for creating an asymmetric preload force; said means for creating an asymmetric preload force having a ring-shape with circumferentially directed and radially directed slots and which applies the created forced to the hollow body end opposite said seal in an effective force loading pattern substantially in register with said gasket means. a ring of substantial axial depth having an asymmetric radial structure defined by a plurality of radially inwardly and circumferentially directed through slots. 2. The apparatus of claim 1 in which-the ring-shaped means for creating an asymmetric preload force has a radial structure such that the effective force loading pattern creates an asymmetric preload force on said gasket means. 3. The apparatus of claim 2 in which the ring-shaped means for creating an asymmetric preload force radial structure is created by slots open to the periphery thereof. 4. The apparatus of claim 3 in which the ring-shaped means for creating an asymmetric force is a body of a given thickness with slots cut in the body transversely to the direction of preloading force to render some areas in register with the gasket means of a different spring constant than other such areas. 5. The apparatus of claim 4 in which the joint surrounds a leak path to be sealed and said leak path is between a reactor vessel cavity having an inclined or non-planar surface and the interior of a stub tube/nozzle tube assembly. 6. The apparatus of claim 1 in which the base surface is inclined and said hollow body has a vertical axis. 7. The apparatus of claim 1 in which the base surface is non-planar. 8. A preloading force element for use with a hollow body comprising: |
053207866 | abstract | Cold pressed UC.sub.2 fuel compacts are sintered at temperatures greater than about 1850.degree. C. while in contact with a sintering facilitator material, e.g., tantalum, niobium, tungsten or a metal carbide such as uranium carbide, thereby allowing for a reduction in the overall porosity and leaving the desired product, i.e., a highly dense, large-grained uranium dicarbide. The process of using the sintering facilitator materials can be applied in the preparation of other carbide materials. |
claims | 1. An apparatus for determining state of a positively charged particle used in imaging a tumor of a patient, comprising:a first time of flight detector element;a second time of flight detector element;a main controller communicatively linked to both said first time of flight detector element and said second time of flight detector element, said main controller comprising a beam state determination system;a beam transport path of the positively charged particle passing sequentially from an accelerator, through a nozzle system, above a patient positioning system, through said first time of flight detector element, and at least into said second time of flight detector element;said beam state determination system configured to: (1) receive a first signal related to an initial time of passage of the positively charged particle through said first time of flight detector, (2) receive a second signal related to an arrival time of the positively charged particle to said second time of flight detector element, (3) calculate a difference in time between the initial time of the first signal and the arrival time of the second signal, and (4) determine a property of the positively charged particle with the difference in time, the property comprising at least one of:(1) a velocity of the positively charged particle; and(2) an energy of the positively charged particle, andan energy degrading element positioned in said beam transport path between said first time of flight detector element and said second time of flight detector element. 2. The apparatus of claim 1, said second time of flight detector element further comprising:an x/y-position detection array, an x/y-plane perpendicular to a z-axis from said nozzle system to said second time of flight detector element. 3. The apparatus of claim 1, said energy degrading element further comprising:a film layer consisting essentially or six of fewer protons per atom. 4. The apparatus of claim 3, said energy degrading element further comprising:a film layer substantially coating and within three millimeters of a front x/y-axis surface of said second time of flight detection element. 5. The apparatus of claim 1, further comprising:an x-axis position detector configured to detect an x-axis position of the positively charged particle; anda y-axis position detector configured to detect a y-axis position of the positively charged particle,said x-axis position detector and said y-axis position comprising spacing elements of a pathlength between said first time of flight detector and said second time of flight detector, said beam state determination system further comprising a computing platform configured to calculate at least one of: (1) a velocity of the positively charged particle and (2) an energy of the positively charged particle from the pathlength and the difference in time. 6. An apparatus for determining state of a positively charged particle used in imaging a tumor of a patient, comprising:a first time of flight detector element;a second time of flight detector element;a main controller communicatively linked to both said first time of flight detector element and said second time of flight detector element, said main controller comprising a beam state determination system;a beam transport path of the positively charged particle passing sequentially from an accelerator, through a nozzle system, above a patient positioning system, through said first time of flight detector element, and at least into said second time of flight detector element;said beam state determination system configured to: (1) receive a first signal related to an initial time of passage of the positively charged particle through said first time of flight detector, (2) receive a second signal related to an arrival time of the positively charged particle to said second time of flight detector element, and (3) calculate a property of the positively charged particle, the property comprising at least one of:(1) a velocity of the positively charged particle; and(2) an energy of the positively charged particle,an x-axis position detector configured to detect an x-axis position of the positively charged particle;a y-axis position detector configured to detect a y-axis position of the positively charged particle,said x-axis position detector and said y-axis position detector positioned in the beam transport path between the nozzle system and the first time of flight detector. 7. The apparatus of claim 6, said x-axis position detector comprising a first ionization strip detector and said y-axis position detector comprising a second ionization strip detector. 8. An apparatus for determining state of a positively charged particle used in imaging a tumor of a patient, comprising:a first time of flight detector element;a second time of flight detector element;a main controller communicatively linked to both said first time of flight detector element and said second time of flight detector element, said main controller comprising a beam state determination system;a beam transport path of the positively charged particle passing sequentially from an accelerator, through a nozzle system, above a patient positioning system, through said first time of flight detector element, and at least into said second time of flight detector element;said beam state determination system configured to: (1) receive a first signal related to an initial time of passage of the positively charged particle through said first time of flight detector, (2) receive a second signal related to an arrival time of the positively charged particle to said second time of flight detector element, and (3) calculate a property of the positively charged particle, the property comprising at least one of:(1) a velocity of the positively charged particle; and(2) an energy of the positively charged particle,a scintillation detector configured to stop the positively charged particles, said second time of flight detector element positioned between said first time of flight detector element and said scintillation detector. 9. A method for determining state of a positively charged particle used in imaging a patient, comprising the steps of:providing a first time of flight detector element;providing a second time of flight detector element;communicatively linking a main controller to both said first time of flight detector element and said second time of flight detector element, said main controller comprising a beam state determination system;transporting the positively charged particle along a beam transport path sequentially from an accelerator, through a nozzle system, through a position above a patient positioning system, through a first time of flight detector element, and at least into a second time of flight detector element;said beam state determination system: (1) receiving a first signal related to an initial time of passage of the positively charged particle through said first time of flight detector, (2) receiving a second signal related to an arrival time of the positively charged particle to said second time of flight detector element, and (3) determining a property of the positively charged particle, the property comprising at least one of:(1) a velocity of the positively charged particle; and(2) an energy of the positively charged particle,further comprising at least one of the steps of:calculating a residual velocity of the positively charged particle after passing through a patient position;determining a velocity of the positively charged particle using a distance between the first time of flight detector element and the second time of flight detector element; anddetermining an energy of the positively charged particle using the first signal, the arrival time, and a pathlength of the positively charged particle between the first time of flight detector and the second time of flight detector; andgenerating an image of the patient with the property. 10. The method of claim 9, further comprising the steps of:determining at least two x-axis positions of the positively charged particles between the position above the patient positioning system and the second time of flight detector element using a first pair of detectors;determining at least two y-axis positions of the positively charged particles between the position above the patient positioning system and the second time of flight detector element using a second pair of detectors. 11. The method of claim 9, further comprising the step of:reducing velocity of the positively charged particle, by at least thirty percent, after passage through the patient position using a time of flight degrader, said time of flight degrader comprising a film of material less than ten millimeters thick. 12. The method of claim 9, further comprising the step of:increasing a time interval of the positively charged particle passing between said first time of flight detector and said second time of flight detector from less than one hundred nanoseconds to greater than ten microseconds using a carbon film between said first time of flight detector and said second time of flight detector. 13. The method of claim 9, further comprising the step of:determining a pathlength of the positively charged particle between said first time of flight detector and said second time of flight detector. 14. The method of claim 13, further comprising the step of:generating a set of residual energies for a corresponding set of the positively charged particles for each of a set of relative rotational alignments of a patient support relative to the nozzle system and first time of flight detector; andgenerating a three-dimensional positive charge tomographic image of a tumor of the patient. 15. The method of claim 14, further comprising the step of:rotating said patient support. 16. The method of claim 14, further comprising the step of:rotating a curved and cantilevered gantry arm, supporting a beamline section of the beam transport path directing the positively charged particle, about a rotation axis, the rotation axis within five degrees of horizontal. |
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abstract | A real time monitoring system of a spent fuel pool includes a detection unit configured to detect condition information using a sensor installed in the spent fuel pool; an input storage unit configured to receive and store configuration information of a spent fuel, history information related to burnup, and a normal value and a limit value of current condition information; an operation and determination unit configured to calculate the current condition information of the spent fuel by using the condition information detected by the detection unit and the configuration information and the history information stored in the input storage unit and configured to determine a risk level by comparing the current condition information with the limit value corresponding to the risk level; and a display unit configured to display the current condition information calculated by the operation and determination unit and configured to display the determined risk level. |
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054105781 | claims | 1. A nuclear propulsion rocket, comprising: a. a pressure vessel; b. a reactor core in said pressure vessel having a plurality of nuclear fuel elements wherein each nuclear fuel element comprises: c. a radial reflector between said pressure vessel and said reactor core; and d. a rocket nozzle in fluid communication with the interior of said pressure vessel. a. a pressure vessel; b. a reactor core in said pressure vessel having a plurality of nuclear fuel elements wherein each nuclear fuel element comprises: c. a radial reflector between said pressure vessel and said reactor core; d. a control drum received in said radial reflector; and e. a rocket nozzle in fluid communication with the interior of said pressure vessel. 2. The nuclear propulsion reactor of claim 1, further comprising a control drum received in said radial reflector. 3. The nuclear propulsion reactor of claim 1, wherein said nuclear fuel is provided with a plurality of axial bores along the full length of said fuel. 4. The nuclear propulsion reactor of claim 1, further comprising an upper and lower nozzle formed from reflector material in each of said hexagonal housings. 5. The nuclear propulsion reactor of claim 1, further comprising a flow passageway for coolant around said rocket nozzle. 6. The nuclear propulsion reactor of claim 1, wherein said radial reflector is formed from beryllium. 7. A nuclear propulsion rocket, comprising: 8. The nuclear propulsion reactor of claim 7, further comprising an upper and lower nozzle formed from reflector material in each of said hexagonal housings. 9. The nuclear propulsion reactor of claim 7, further comprising a flow passageway for coolant around said rocket nozzle. 10. The nuclear propulsion reactor of claim 7, wherein said radial reflector is formed from beryllium. |
abstract | A system for storing high level radioactive waste. In one embodiment, the invention can be a system including an overpack body extending along a vertical axis and having a cavity for storing high level radioactive waste, the cavity having an open top end and a floor; an overpack lid positioned atop the overpack body to enclose the open top end of the cavity; an air inlet vent for introducing cool air into the cavity, the air inlet vent extending from an opening in an outer surface of the overpack body to an opening in the floor, the opening in the outer surface of the overpack body extending about an entirety of a circumference of the outer surface of the overpack body; and an air outlet vent in the overpack lid for removing warmed air from the cavity. |
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abstract | In one embodiment, the method includes determining the safety limit minimum critical power ratio using the operating limit minimum critical power ratio, a change-in-critical-power-ratio distribution bias and a change-in-critical-power-ratio distribution standard deviation. |
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claims | 1. A shield for absorbing radiation emitted by a target during operation of a cyclotron, wherein the target is located within a target enclosure, comprising:an inner box structure having a recess for receiving the target enclosure;a first plurality of shield elements arranged in a layered configuration about the inner box structure to form a first shielding arrangement having first shielding characteristics;an outer box structure for receiving the inner box structure and the first plurality of shield elements; anda second plurality of shield elements arranged in a layered configuration about the outer box structure to form a second shielding arrangement having second shielding characteristics. 2. The shield according to claim 1, wherein the first and second plurality of shield elements includes at least one shield element fabricated from 30% borated polyethylene. 3. The shield according to claim 1, wherein the first and second plurality of shield elements includes at least one shield element fabricated from 5% borated polyethylene. 4. The shield according to claim 1, wherein the first and second plurality of shield elements includes at least one shield element fabricated from lead. 5. The shield according to claim 1, wherein the first and second plurality of shield elements includes at least one shield element fabricated from polyethylene. 6. The shield according to claim 1, wherein the first and second plurality of shield elements are removable. 7. The shield according to claim 1, wherein the inner and outer box structures are fabricated from steel. 8. The shield according to claim 1, further including a cover fabricated from aluminum. 9. The shield according to claim 1, wherein the shield shields against neutron and gamma radiation. 10. A shield for absorbing radiation emitted by a target during operation of a cyclotron, wherein the target is located within a target enclosure, comprising:an inner box structure having a recess for receiving the target enclosure;a first plurality of shield elements arranged in first and second orientations about the inner box structure to form a first shielding arrangement having first shielding characteristics;an outer box structure for receiving the inner box structure and the first plurality of shield elements; anda second plurality of shield elements arranged in the first and second orientations about the outer box structure to form a second shielding arrangement having second shielding characteristics. 11. The shield according to claim 10, wherein the first orientation is horizontal and the first and second plurality of shield elements are arranged above and below the inner and outer box structures. 12. The shield according to claim 10, wherein the second orientation is vertical and the first and second plurality of shield elements are arranged on sides and to the rear of the inner and outer box structures. 13. The shield according to claim 10, wherein the first and second plurality of shield elements includes at least one shield element fabricated from 30% borated polyethylene. 14. The shield according to claim 10, wherein the first and second plurality of shield elements includes at least one .shield element fabricated from 5% borated polyethylene. 15. The shield according to claim 10, wherein the first and second plurality of shield elements includes at least one shield element fabricated from lead. 16. The shield according to claim 10, wherein the first and second plurality of shield elements includes at least one shield element fabricated from polyethylene. 17. The shield according to claim 10, wherein the first and second plurality of shield elements are removable. 18. A shield arrangement for absorbing radiation emitted by a target during operation of a cyclotron, wherein the target is located within a target enclosure, comprising:an inner box structure having a recess for receiving the target enclosure;a first plurality of removable shield elements arranged about the inner box structure to form a first shielding arrangement having first shielding characteristics;an outer box structure for receiving the inner box structure and the first plurality of shield elements;a second plurality of removable shield elements arranged about the outer box structure to form a second shielding arrangement having second shielding characteristics wherein the inner and outer box structures and first and second plurality of shield elements form a layered shield assembly; anda movable shield for receiving the layered shield assembly. 19. The shield according to claim 18, wherein the first and second plurality of shield elements are removable. 20. The shield according to claim 18, wherein the shield shields against neutron and gamma radiation. 21. A shield arrangement for absorbing radiation emitted by a target during operation of a cyclotron, wherein the target is located within a target enclosure, comprising:an inner box structure having a first size and a recess for receiving the target enclosure;a first plurality of first shield elements arranged about the inner box structure wherein the first shield elements are reconfigurable to provide additional or less shielding or to accommodate an alternate size inner box structure wherein the first shield elements form a first shielding arrangement having first shielding characteristics;an outer box structure having a second size for receiving the inner box structure and the first plurality of shield elements;a second plurality of second shield elements arranged about the outer box structure wherein the second shield elements are reconfigurable to provide additional or less shielding or to accommodate an alternate size outer box structure wherein the second shield elements form a second shielding arrangement having second shielding characteristics and wherein the inner and outer box structures and first and second plurality of shield elements form a layered shield assembly; anda movable shield for receiving the layered shield assembly. |
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abstract | In some aspects, a monochromatic x-ray component for producing monochromatic x-ray radiation from broadband x-ray radiation is provided. The monochromatic x-ray component comprises a housing configured to be positioned proximate a broadband x-ray source, at least one first target arranged to receive broadband x-ray radiation emitted from the broadband x-ray source when the housing is positioned proximate the broadband x-ray source, the at least one first target configured to produce first monochromatic x-ray radiation in response to the received broadband x-ray radiation, and at least one second target to receive at least some of the first monochromatic x-ray radiation produced by the at least one first target when the at least one second target is positioned within the monochromatic x-ray component, the at least one second target configured to produce second monochromatic x-ray radiation in response to the received first monochromatic x-ray radiation. |
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051695928 | abstract | An emergency stop of a pressurized water reactor to be protected is triggered when the nuclear power (ET) thereof reaches an emergency stop limit (LP). The value of this limit is lower with lower operating temperatures (ST) of the reactor. |
042008042 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 and 2 illustrate the system of an embodiment of the invention with FIG. 1 showing the system in assembled form and ready for packaging or storage. To facilitate understanding of the invention, reference is first made to FIGS. 3-5 which illustrate the shielded syringe portion of the invention. The core of the shielded syringe includes the basic elements of a conventional disposable-type plastic syringe, as labeled in the drawings by reference numeral 110. The syringe 110 has a plastic body or barrel 111, a rear flange 112, a plunger 113 and a tip 114. The plunger 113 has a conventional head or tip 117, typically formed of rubber, which is coupled to a plunger stem 118 by a novel shielding plug 119. The plug 119 is formed of a high density radiation-shielding material, such as lead or tantalum or plated lead. The plug has a cylindrical central portion which conforms generally to the inner circumference of the barrel 111, a front retaining nub 119A which is inserted in an aperture in the rear of tip 117, and a rear retaining nub 119B which snaps into and seats in the front end of the plunger stem 118. The plug 119 serves to shield the operator using the device against radiation emitted axially from the rear of the barrel. This radiation, which would typically and dangerously be directed toward the body of the operator, is generally not satisfactorily shielded in the prior art. The syringe body has volumetric indicia disposed in a longitudinal pattern along its barrel as shown at 115. A generally cylindrical body 130 is formed of a radiation-shielding material, such as lead, and is proportioned such that its inner surface conforms generally to the outer surface of the syringe barrel 111. The body 130 tapers inwardly at its front end at 138 and has an elongated rectangular slot 139 extending along one side thereof, the slot being in registration with the indicia 15 on the barrel 111. The surface containing the slot is flat on top and a pair of panels 131 and 132, which can be formed integrally of the same radiation-shielding material such as lead, are spaced slightly from the parallel edges of the slot and extend outwardly from the flat surface. A transparent radiation-shielding member 140 is of elongated rectangular shape and may be formed of leaded glass typically having a thickness which is substantially greater than that of the body 130. The member 140 is encased in a rectangular casing 141 which is opened at the top and bottom thereof. Pairs of lips 142 and 143 retain the member 140 within the casing 141. The top edge of the casing slants upward at the front thereof as shown at 145 so that the front end protrudes slightly above the top of the encased member 140. In the present embodiment the casing 141 is formed of material such as rigid plastic and the member 140 is snapped into the casing 141 for permanent retention therein and reuse in a manner to be described. The casing is proportioned to slideably fit within the panels 131 and 132 of body 130 such that the transparent shielding member 140 overlays the periphery of the slot 139 in body 130. As will be described, the encased member 140 is typically inserted in the shielded syringe at the time when it is to be used to inject a patient. A shell 150 is preferably formed of rigid plastic and is proportioned to generally conform in shape to the outer surface of the body 130. Specifically, the shell 150 has a pair of side panels 151 and 152 which cover and extend above the body panels 131 and 132, respectively. The panels 151 and 152 have lips 153 and 154, respectively, which define an elongated slot that is in registration with the slot 139 in body 130. The front end of the shell 150 is about half opened and has an approximately semicircular wall 156 having a circular aperture therein which receives the tip 114 of the syringe 110. The tip 114 is provided with an annular groove which is retained in the aperture as seen in FIG. 4. A cylindrical shroud 157 extends axially from the wall 156 and protrudes slightly above the top edge of the wall. The shroud 157, which may typically be formed integrally with the body, has an annular protrusion at 158. To assemble the disposable portion of the device described thus far, the syringe 110, with its plunger in place, is inserted into the body 130. The syringe flange 112 has a wall member 112A formed on the inner surface thereof which serves as a spacer between the rear end of the body 130 and the flange. The syringe and body are then inserted into the open-ended rear of the shell. The rear edge of the shell fits over the periphery of wall 119 and is secured to the flange 112 by any suitable means, such as an epoxy bond. This assembly comprises the portion of the shielded syringe which is most suitable for disposability. FIG. 4 also shows the manner in which a standard needle can be mounted over the syringe tip and is conveniently retained within the shroud 157 by the annular protrusion 158. This eliminates the need for screwing in the needle and facilitates more convenient operation. However, it will be understood that a standard needle mounting, such as a Luer-lock mounting, can be employed. In accordance with the invention, an aliquot of radioisotope-containing fluid is loaded into the syringe barrel before packaging. In the embodiment of FIGS. 1 and 2, a multipurpose sub-assembly is provided to deal with the presence of the radioisotope fluid. A radiation-shielding unit 210 includes a cover 210 which is proportioned at least large enough to cover the slot 139 (FIG. 5). In the present embodiment, a flange 212 extends downwardly from the front edge of the cover 211 and is formed integrally therewith. A hollow shroud 213, having a closed front end, protrudes from the flange at a position thereon which is in registration with the position of the tip 114 of the syringe. The rear end of the cover 211 has a reduced thickness, as shown, to fit over the flange 112. A protruding rear handle 215 has an indented neck portion 216 which extends from the rear edge of the cover 211. In the present embodiment, the shielding unit 210, including the cover 211, the front flange 212, the shroud 213 and the necked handle 215 are integrally formed of a single piece of radiation-shielding material, such as lead. The lead may be plastic coated or plated, if desired. The embodiment of FIGS. 1 and 2 further includes a horseshoe-shaped clip 230 which may be formed of any suitable material, but is preferably formed of plastic. The plunger stem 118 has a pair of slots in opposite sides of one of its cross panels, as depicted in dotted line in FIG. 2 (the stem itself being shown in dashed line). The slots are referred to by reference numerals 118A and 118B. The clip 230 is proportioned to engage the slots 118A and 118B when the plunger 110 is in its fully extended position. The spaced ends 231 and 232 of the clip are proportioned to engage the neck 216 of the rear handle of shielding unit 210 when the unit is positioned in place over the slot 139 (see dashed line depiction in FIG. 2). Operation of the invention is as follows: at the packaging facility, the aliquot of radioisotope is indroduced into the barrel 111 of syringe 110. The shielding unit 210 is positioned over the slot in the syringe shielding body with the shroud 213 covering the protruding tip of the syringe. The clip 230 is then engaged with the slots in the plunger stem, the ends of the clip engaging the neck portion of the rear handle 215 of unit 210. Depressions 231A and 232A are provided in the clip, and a retaining wire is wrapped around the depressed regions. The clip is formed of a material, such as plastic, which is sufficiently flexible to yield slightly to engage the plunger and cover unit. The overall system is typically stored in a carton for transporting. It is seen that the clip serves to retain the plunger in the fully extended position to prevent accidental depression thereof during shipping. The clip also retains the shielding unit 210 in place. The shielding unit, in conjunction with the disposable shielded syringe, is seen to render the radioisotope material completely shielded, the cover 211 providing shielding above the aperture, and the front flange and shroud providing shielding forwardly of the syringe body. The shielding plug 119 (FIG. 4) provides shielding in the rear axial direction. When the assembly is to be used, it is removed from its carton and the wire 250 and clip 230 are removed. This serves to release the plunger 110 for subsequent activation and also to release the shielding unit 210 which can now be removed. If desired, the reusable optically-transparent radiation-shielding member 140 (FIGS. 3-5, and in dashed line in FIG. 2) can now be inserted over the slot 139 to provide shielding during usage while still allowing the operator to view the contents of the shielded syringe. In the present embodiment, the encased transparent shielding member 140 is inserted in the shell through the front opening therein and is retained from sliding out during use by the protruding portion of the shroud 157. If desired, an assay can be performed prior to insertion of the leaded glass shielding member. After injection of the unit dose of radioisotope into the patient, the leaded glass shielding member 140 is removed for use in conjunction with other disposable systems, and the remainder of the system can be discarded (removal being facilitated by the raised edge of the casing (145) which can be grasped such as by using the thumb and finger). Thus, virtually complete shielding is provided from the time of packaging until use, handling of radioisotope materials is eliminated, and the inconvenience of handling shielding media and of measuring are all eliminated. The portion of the system which is disposable is relatively inexpensive to manufacture and the relatively expensive leaded-glass is reusable. In addition to the advantages in safety and convenience, the need to clean contaminated shields is eliminated. The invention has been described with reference to a particular embodiment, but variations within the spirit and scope of the invention will occur to those skilled in the art. For example, it will be recognized that the shielding unit 210 could be in the form of a lead slug (having the shape of the member 140--see the dashed outline of FIG. 2) in those situations where the full front shielding is considered unnecessary. |
044951396 | claims | 1. A container for radioactive waste, said container comprising: a massive metallic vessel having an interior adapted to receive radioactive waste and having a mouth formed with inner and outer spaced generally planar and annular vessel shoulders and formed therebetween with a nonplanar intermediate annular vessel surface; a massive metallic cover formed with a plug fitted in said mouth and having respective inner and outer plug shoulders closely juxtaposed with said vessel shoulders and a nonplanar intermediate annular plug surface complementary to said intermediate vessel surface; an inner ring seal engaged snugly between said inner shoulders; a pair of generally concentric and spaced outer ring seals engaged snugly between said outer shoulders and forming an annular outer chamber therebetween; an intermediate ring seal engaged snugly between said intermediate surfaces and forming therebetween and with said inner ring seal an annular inner chamber and therebetween and with said outer ring seals an intermediate chamber, said cover being formed with respective inner, intermediate, and outer passages each having one end opening into the repective chamber and another end; and means on said cover at the other ends of said passages for sampling gases therein and in the respective chambers. 2. The radioactive-waste container defined in claim 1 wherein said cover has an outwardly directed surface formed with a recess into which said other ends open and in which said means are provided. 3. The radioactive-waste container defined in claim 1, further comprising a second cover overlying the first-mentioned cover and fixed to said vessel. 4. The radioactive-waste container defined in claim 1, further comprising means for securing said cover to said vessel at said mouth. 5. The radioactive-waste container defined in claim 1 wherein said shoulders are planar and parallel. 6. The radioactive-waste container defined in claim 1 wherein said intermediate surfaces are surfaces of revolution. 7. The radioactive-waste container defined in claim 6 wherein said intermediate surfaces are substantially cylindrical. 8. The radioactive-waste container defined in clain 1, further comprising a body of tracer gas at above-ambient pressure in said vessel. 9. The radioactive-waste container defined in claim 1, further comprising bolts securing said cover to said vessel. 10. The radioactive-waste container defined in claim 1 wherein said means are valves. |
abstract | A method of storing heat includes moving a portion of a heated fluid from at least one reactor core to at least one tank having solid media, storing heat from the portion of the heated fluid in the solid media, and transferring the stored heat from the solid media to a fluid that can be used by a power plant to generate electrical energy. A system for storing heat in a nuclear power plant includes at least one tank comprising solid media structured and arranged to store heat and an arrangement structured and arranged to pass a first fluid through the at least one tank, transfer heat from the first fluid to the solid media, store the heat in the solid media, and transfer the heat from the solid media to a second fluid. This Abstract is not intended to define the invention disclosed in the specification, nor intended to limit the scope of the invention in any way. |
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abstract | Systems, assemblies and methods for thermally managing a grazing incidence collector (GIC) for EUV lithography applications are disclosed. The GIC thermal management assembly includes a GIC mirror shell interfaced with a jacket to form a sealed chamber. An open cell, heat transfer (OCHT) material is disposed within the metal chamber and is thermally and mechanically bonded with the GIC mirror shell and jacket. A coolant is flowed in an azimuthally symmetric fashion through the OCHT material between input and output plenums to effectuate cooling when the GIC thermal management assembly is used in a GIC mirror system configured to receive and form collected EUV radiation from an EUV radiation source. |
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summary | ||
claims | 1. A concentrated irradiation type radiotherapy apparatus, comprising:a radiation source configured to generate radioactive rays in a beam direction for both treatment and imaging;a radiation detector configured to detect radioactive rays transmitted through a subject;a rotating mechanism configured to rotate the radiation source and the radiation detector about a rotating axis;a reconstruction unit configured to reconstruct image data based on an output of the radiation detector; anda collimator unit equipped in the radiation source and configured to form the radioactive rays according to a subject to be treated, the collimator unit includinga plurality of collimator plates disposed along the rotating axis, each of said plurality of collimator plates having a face on a substantially common plane perpendicular to the beam direction and being individually movable in a length direction perpendicular to the beam direction around an aperture, each collimator plate of said plurality of collimator plates being in direct contact with at least one adjacent collimator plate adjacent in a width direction perpendicular to both the beam direction and the length direction, anda mechanism for selectively moving one or more of said plurality of collimator plates, wherein said plurality of collimator plates includesa plurality of central collimator plates, each central collimator plate of said plurality of central collimator plates having a first X-ray transmittivity along the beam direction, anda plurality of non-central collimator plates, each non-central collimator plate of said plurality of non-central collimator plates having a second X-ray transmittivity along the beam direction, the second X-ray transmittivity being lower than the first X-ray transmittivity, the plurality of non-central collimator plates sandwiching the plurality of central collimator plates, each of the plurality of central collimator plates and each of the plurality of non-central collimator plates having a substantially equal width in the width direction and substantially equal length in the length direction. 2. The concentrated irradiation type radiotherapy apparatus of claim 1, whereinone of the plurality of central collimator plates has a thickness in the beam direction smaller than a thickness in the beam direction of one of the plurality of non-central collimator plates. |
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description | This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2016/066458, filed Jul. 12, 2016, published as WO 2017/009302 on Jan. 19, 2017, which claims the benefit of European Patent Application Number 15176653.2 filed Jul. 14, 2015. These applications are hereby incorporated by reference herein. The present invention relates to imaging of an object of interest with enhanced X-ray radiation, and relates in particular to an X-ray imaging apparatus and an X-ray imaging system. For X-ray imaging, and in particular for X-ray mammography or for X-ray tomosynthesis, the bremsstrahlung of an X-ray source is utilized. The lifetime and the reliability of an X-ray source often depend on the workload of the X-ray source, wherein the workload relates to the rate between the power of the generated X-ray radiation and the possible maximal power of the X-ray radiation. Different levels of X-ray radiation power may be required. For example, in particular X-ray mammography, a higher power level of the X-ray source may be needed when scanning women with larger and thicker breasts. Increasing the maximal power of an X-ray radiation source would, however, increase the costs of a respective X-ray apparatus or system. For example, DE 41 30 039 A1 relates to an arrangement of an X-ray source and a collimator for generating collimated X-ray radiation, which is guided from an exit of the collimator to an object receiving space. It has been shown that X-ray radiation utilization of the X-ray radiation generated by the X-ray source has an effect on lifetime and reliability of the X-ray source. JP2009250910 A discloses a system for generation of highly monochromatic X-rays by means of Bragg reflection on crystals. Thus, there is a need to provide enhanced X-ray radiation utilizable for imaging, increased lifetime and reliability, while keeping the costs at a moderate level. The object of the present invention is solved by the subject-matter of the independent claims, wherein further embodiments are incorporated in the dependent claims. It should be noted that the following described aspects of the invention apply for the X-ray imaging apparatus and also for the X-ray imaging system. According to a first aspect of the present invention, an X-ray imaging apparatus is provided, comprising a source for generating X-ray radiation emitting a polychromatic spectrum of x-ray energies, an object receiving space for arranging an object of interest for X-ray imaging, an X-ray collimator arrangement, and an X-ray mirror arrangement. The X-ray collimator arrangement comprises at least a pre-collimator arranged between the source and the object receiving space for providing collimated X-ray radiation to the object receiving space. Further, the X-ray mirror arrangement is arranged between the source and the pre-collimator. The X-ray mirror arrangement comprises a set of two mirrors for guiding X-ray radiation of the source by providing total reflection of the whole polychromatic spectrum of x-ray energies of a part of the X-ray radiation in order to deflect the part of the X-ray radiation towards the pre-collimator such that in the region of the object receiving space enhanced radiation is provided in form of unreflected primary X-ray radiation in combination with secondary X-ray radiation by total reflection. The mirrors of the set of two mirrors are facing one another with an angle of spread larger than zero, such that the set of mirrors providing an X-ray entrance having an entrance width and an X-ray exit having an exit width, which is smaller than the entrance width. The pre-collimator relates to an optical element comprising at least one aperture, wherein each aperture can be formed as a slit. The mirror can also be referred to as an X-ray mirror. The term “total reflection” refers to a reflection of an X-ray radiation wave, which strikes a boundary of a medium at an angle smaller than a particular critical angle with respect to a plane level to the boundary. The critical angle is the angle of incidence below which the total internal reflection occurs. In an example, the critical angel Θc is defined as:Θc≈1.6*10{circumflex over ( )}(−3)*ρ{circumflex over ( )}(0.5)*λ, where ρ [g/cm3] relates to the density of the medium and λ [Å] relates to the wavelength of the X-ray radiation wave. The set of two mirrors can also be referred to as the set of mirrors. The “object-receiving space” relates to a space designated for arranging the object of interest. The object-receiving space may comprise an object support arrangement, for example a pair of paddles to hold and (temporarily) fix a breast for X-ray examination (e.g. screening) purposes. The angle of spread relates to an acute angle of the two mirrors of the set of mirrors. The acute angle preferably corresponds to a double of an angle between an inward surface line of one of the mirrors and a longitudinal axis of the set of mirrors. The effect of total reflection is absolute as long as the incident angle of the x-rays is smaller than the critical angle for the energy of the x-rays. The larger the energy, the smaller the critical angle of total reflection. Nevertheless for all energies in the polychromatic spectrum emitted by the x-ray source total reflection will take place. Hence monochromaticity of the source is not required neither particularly desirable. According to an exemplary embodiment, the primary X-ray radiation forms a primary beam cone (also referred to as “cone beam”) between the source and the pre-collimator, wherein the mirrors of the set of mirrors so-to-speak abut outside on the primary beam cone, and the angle of spread corresponds to a cone angle of the primary beam cone with a maximum deviation to the cone angle of 10%. The cone angle relates to an acute angle of the cone. The acute angle preferably corresponds to a double of an angle between a surface line of the cone and a cone longitudinal axis. The “deviation” relates to a deviation in a plane defined by the surface line of the primary beam cone and longitudinal axis of the primary beam cone. According to an exemplary embodiment, a length LM of each mirror of the set of mirrors is arranged, such that the inequality LM≤LMmax=LW/(Θc2−Θm) holds, wherein: LW is the width of the exit of the set of mirrors, Θc2 is the critical angle of reflection at a mirror of the set of mirrors, and Θm is the angle of spread of the mirrors of the set of mirrors. The length of a mirror preferably relates to an extension of the mirror in a direction of the longitudinal axis of the respective set of mirrors or in a direction with an angle to the longitudinal axis corresponding to an angle between an inward surface of the mirror and this longitudinal axis. According to an exemplary embodiment, the exit of the set of mirrors abuts to an aperture of the pre-collimator. According to an exemplary embodiment, each mirror of the sets of mirrors comprises a substrate with a coating layer for providing the total reflection. Between the coating layer and the substrate, a boundary is provided that is configured to reduce scatter radiation from incoming radiation that is not reflected but passes a mirror surface and enters the coating layer. According to a second aspect of the invention, an X-ray imaging system is provided. The imaging system comprises an X-ray imaging apparatus according to one of the previously examples, a detector for detecting X-ray radiation passing the object receiving space of the apparatus, an imaging processing unit, and an imaging output unit. The imaging processing unit is configured to receive signals from the detector and to compute image data of an object of interest arrangeable in the object receiving space based on these signals, and the imaging output unit is configured to provide an image data for further purpose. According to an aspect of the invention, an X-ray imaging apparatus is provided, which enables enhanced intensity of the X-ray radiation provided in an object receiving space of the X-ray imaging. A higher intensity of the X-ray radiation at the object receiving space allows improving the imaging quality. The object receiving space should be applied with X-ray radiation of the X-ray source of the X-ray apparatus. However, a limitation with respect to the lateral extension of this X-ray radiation is needed. Otherwise, X-ray radiation may be applied to the object receiving space without improving the imaging quality, since detectors for detecting X-ray radiation usually have a limited lateral extension. In order to fulfill both objections, the X-ray imaging apparatus provides a collimator and a set of two mirrors. The collimator comprises an aperture and is provided between the source and the object receiving space. The collimator provides collimated X-ray radiation to the object receiving space. The set of mirrors is provided between the collimator and the source. The mirrors of the set of mirrors are tapered and being opened to the source. Between the aperture of the collimator and the source, an X-ray beam cone is formed, whereas the X-ray waves (i.e. X-ray radiation) of the X-ray beam cone pass the aperture unreflected. The inward surfaces of the mirrors of the set of mirrors are facing each other and border to the outer surface of the beam cone. This configuration reduces the number of reflections of X-ray beams, which impinge one of the mirrors with an angle of incidence other than zero and smaller than a critical angle of total reflection. Further, the length of each mirror of the set of mirrors is limited, such that preferably a maximum of one or two total reflections for the same X-ray beam occurs. This limits an increase of an angle of reflection of the reflected X-ray radiation with respect to a longitudinal axis of the set of mirrors and thus limits the lateral extension of the X-ray radiation applied to the object receiving space. The part of the X-ray radiation generated by the source and being reflected at the mirrors is called the secondary X-ray radiation. Contrary to Bragg reflection total reflection functions for all angles and energies for which the condition of total reflection is satisfied and guarantees that many energy components of the primary radiation will be subject to total reflection and thus be part of the secondary X-ray radiation. The method is thus effective in combination with a polychromatic x-ray spectrum. The secondary X-ray radiation superposes the primary X-ray radiation at the object receiving space, wherein the primary X-ray radiation is formed by the X-ray radiation generated by the source and passing the set of mirrors and the collimator unreflected. Therefore, the intensity of the X-ray radiation at the object receiving space is increased, while the lateral extension of the X-ray radiation at the object receiving space is limited. Accordingly, by using the same source, an increase of the imaging quality is achievable without increasing significantly a dose of X-ray radiation to an object of interest not effectively utilized for imaging. At the same time, a decrease in lifetime for the source is prevented, since the X-ray radiation provided by the source is utilized more efficiently. These and other aspects of the present invention will become apparent from and be elucidated with reference to the embodiments described hereinafter. FIG. 1 shows an example of an X-ray imaging apparatus 2. The X-ray imaging apparatus 2 comprises a source 4 for generating X-ray radiation, an object receiving space 6 for arranging an object of interest for X-ray imaging, an X-ray collimator arrangement 8, and an X-ray mirror arrangement 10. The X-ray collimator arrangement 8 comprises at least a pre-collimator 12. The pre-collimator 12 is arranged between the source 4 and the object receiving space 6 for providing collimated X-ray radiation to the object receiving space 6. The X-ray mirror arrangement 10 is arranged between the source 4 and the pre-collimator 12. The X-ray mirror arrangement 10 comprises a set of two mirrors 14 for guiding X-ray radiation of the source 4 by providing a total reflection of a part 16 of the X-ray radiation in order to deflect the part 16 of the X-ray radiation towards the pre-collimator 12, such that, in the region of the object receiving space 6, enhanced radiation is provided in form of an unreflected primary X-ray radiation 18 in combination with a secondary X-ray radiation 20 by total reflection. The mirrors 22 of a set of mirrors 14 are facing one another with an angle of spread θm larger than zero, such that the set of mirrors 14 providing an X-ray entrance 24 having an entrance width UW and an (X-ray) exit 26 having an exit width LW, which is smaller than the entrance width UW. The source 4 can also be referred as X-ray source. The source 4 is preferably of the kind, which is generally known in the state of the art. The source 4 is preferably provided as a rigid X-ray source unit, in particular such as the x-ray focus of a stationary or rotation anode x-ray tube or as a radio-active γ-emitter. It is to be noted that rigid attachments or mounting features are not further shown. In an example, the source 4 is the focus of an X-ray tube emitting a polychromatic (white) spectrum of x-ray energies. The source 4 is adapted for generating X-ray radiation. In particular, the X-ray radiation generated by the source 4 has energy between 20 keV and 40 keV. Preferably, the source 4 comprises a wavelength filter, which is adapted for suppressing or damping X-ray radiation having a wavelength corresponding to the energy of more than 20 keV. The object receiving space 6 is adapted for arranging the object of interest for X-ray imaging. Thus, the object receiving space 6 relates to a space designated for arranging the object of interest. The object receiving space 6 may comprise an object support arrangement (not shown), for example a pair of pads to hold and temporarily fix a breast for X-ray examination purposes, in particular for screening purposes. For the pre-collimator 12, collimators are provided of a kind that are generally known in the state of the art. For example, the pre-collimator 8 comprises a plate, in particular an X-ray absorbing plate, with at least one hole, which is adapted for being passed by X-ray radiation. Accordingly, an aperture 36 of the pre-collimator 12 can be formed by the hole. Further preferred, the aperture 36 is formed as a slit. The aperture 36 or the slit, respectively, are adapted for being passed by X-ray radiation. X-ray radiation passing the pre-collimator 12, and in particular the aperture 36 or a slit of the pre-collimator 12, reaches the object receiving space 6. X-ray radiation of the source 4 directed to the pre-collimator 12, but not passing the pre-collimator 12 through an aperture 36 of the pre-collimator 12, will instead impinge on a surface of the pre-collimator 12. The X-ray radiation impinging this surface of the pre-collimator 12 will very likely not reach the object receiving space 6. Instead, this X-ray radiation will very likely be absorbed by the pre-collimator 12. Accordingly, the X-ray radiation usually has not a sufficient effect for being utilized for imaging an object of interest being arranged in the object receiving space 6. In order to improve the utilization of the total available X-ray radiation emitted from the source 4 for imaging an object of interest being arranged in the object receiving space 6, the X-ray mirror arrangement 10 is provided and arranged between the source 4 in the pre-collimator 12. As mentioned above, the X-ray mirror arrangement 10 comprises at least one set of two mirrors 14. The set of two mirrors 14 is also referred as the set of mirrors 14. The set of mirrors 14 has the purpose of guiding at least a part 16 of the X-ray radiation generated by the source 4 towards the pre-collimator 12. Without the mirrors, this part 16 of the X-ray radiation would impinge the surface of the pre-collimator 12 and would thus be absorbed by the pre-collimator 12 without a sufficient effect for being utilized for imaging an object of interest. Hence, the set of mirrors 14 is adapted for guiding a part 16 of the X-ray radiation generated by the source 4 to the pre-collimator 12 by providing total reflection of the part 16 of the X-ray radiation of the source 4 in order to deflect the part 16 of the X-ray radiation to the pre-collimator 12, in particular to the aperture 36 of the pre-collimator 12, such that, in the region of the object receiving space 6, enhanced radiation is provided. Generally, in the object receiving space 6, the primary X-ray radiation 18 is provided, which passes the mirror arrangement 10 and the pre-collimator 12 unreflected. Further, the secondary X-ray radiation 20 is provided in the object receiving space 6, namely by being previously totally reflected at one of the mirrors 22 of the set of mirrors 14 of the mirror arrangement 10. Accordingly, the part 16 of the X-ray radiation of the source 4 being totally reflected at one of the mirrors 22 forms the secondary X-ray radiation 20 in the object receiving space 6. The primary X-ray radiation 18 and the secondary X-ray radiation 20 are superposed in the object receiving space 6 and thus increase the intensity of the X-ray radiation provided to the object receiving space 6. As a result, higher intensity of the X-ray radiation in the object receiving space increases the imaging quality. Alternatively, the output of the source 4 can be reduced without decreasing the imaging quality, while increasing the lifetime of the source 4. Furthermore, a higher intensity of the X-ray radiation in the object receiving space allows a reduction of a measurement time for imaging an object of interest. Each of the mirrors 22 of the set of mirrors 14 is adapted for totally reflecting X-ray radiation. Accordingly, each of the mirrors 22 can also be referred to as X-ray mirror. The mirrors 22 preferably relate each to a plate with a suitable low atomic number mirror material, in particular with a atomic number lower than nine. The mirrors 22 further preferably relate each to a plate of a glass-ceramic. As an example, each mirror 22 can comprise a lithium aluminosilicate glass-ceramic. A mirror of that kind may have a specific density of 2.53. However, this is just one example for the specific density. Generally, a wide range of possible specific densities for the X-ray mirrors 22 is possible. Basically, total reflection occurs at the mirror 22 in case the mirror 22 has, with respect to the X-ray radiation, an optically thinner medium at a boundary surface to the space between the source 4 and the mirror 22. Since refractive indices in the X-ray radiation regime are smaller than 1, an X-ray total reflection can be observed upon grazing incidents on any material given the incidence occurs within the critical angle of incidence θc. A simplified critical angle of incidence can be calculated as follows: θc=1.6×10−3×(ρ)−0.5×λ, wherein ρ being the density in the units of g/cm3 and λ denotes the X-ray wavelength in Å. The critical angle of incidence θc is typically in the order of a few mrad (milli-rad). For example, the critical angle of total reflections may be between 0.5 mrad and 2 mrad. In order to achieve total reflection with larger angles, the density of the material being used has to be increased, or metallic coating can be used, for example with silver or gold. In order to achieve total reflection with smaller angles, the density of the material being used for a mirror has to be decreased. For example, each mirror may comprises at least one plastic mirror layer, preferably having low atomic number elements. When using such mirrors for the set of mirrors 14, an enhancement in radiation in the object receiving space 6 is made possible. The term total reflection refers to a reflection of the X-ray radiation wave being provided from the source 4, when the respective X-ray radiation wave strikes a boundary of the mirror 22 at an angle smaller than the critical angle with respect to a plain level of the boundary. In order to increase the radiation in the object receiving space by combining the primary X-ray radiation 18 and the secondary X-ray radiation 20, the mirrors 22 of the set of mirrors 14 are facing one another with an angle of spread θm larger than zero. Accordingly, the set of mirrors 14 provides an X-ray entrance 24 having an entrance width UW for entering X-ray radiation of the source 4. In order to provide X-ray radiation to the object receiving space 6, the set of mirrors 14 provides the X-ray exit 26 with the exit width LW, which is smaller than the entrance width UW. A part of the X-ray radiation of the source 4 may pass the set of mirrors 14 unreflected, in order to form the primary X-ray radiation in the object receiving space 6. Another part 16 of the X-ray radiation of the source 4 impinges on at least one of the mirrors 22 with an incidence angle θi with respect to the plain level of the boundary surface of the mirror 22 smaller than the critical angle θc, such that total reflection occurs. The X-ray radiation totally reflected leaves the set of mirrors 14, at least in part, through the X-ray exit 26, in order to form the secondary radiation 22. Since the X-ray imaging apparatus 2 is adapted for providing a combination of the primary X-ray radiation 18 and the secondary X-ray radiation 20 in the object receiving space 6, an increase of a total flux of the X-ray radiation is provided in the object receiving space 6. It is to be noted, that the increase is caused by the tapered arrangement of the mirrors 22 of the set of mirrors 14 and its arrangement between the source 4 and the pre-collimator 12. Consequently, the X-ray imaging apparatus 2 is a cost efficient improvement for increasing the intensity of the X-ray radiation usable for imaging of an object of interest in the object receiving space 6. Further, the source 4 is not necessarily being operated at its power limits for providing sufficient flux in case larger or thicker objects of interest are arranged in the object receiving space 6 for imaging. Instead, the mirror arrangement 10 allows using the same source 4 for generating a sufficient X-ray radiation flux. Consequently, the lifetime of the source 4 increases and reduced costs for a premature source replacement are provided. Furthermore, the imaging quality may be increased in case of thick objects of interest to be placed at the object receiving space 6 for imaging, since the intensity of the enhanced X-ray radiation may be sufficient for screening such an object of interest. In case the X-ray imaging apparatus is used for mammography or tomosynthesis, scanning times for women can be improved, in particular reduced. In an example, the pre-collimator 12 comprises a plate with an aperture 36. The plate of the pre-collimator 12 is preferably adapted for absorbing X-ray radiation, in particular for absorbing X-ray radiation provided by the source 4. In order for providing an enhanced X-ray radiation with the pre-collimator 12 to the object receiving space 6, the mirrors 22 of the set of mirrors 14 are preferably tapered, such that a part 16 of the X-ray radiation generated by the source 4 is totally reflected and thereby focused to the aperture 36 of the pre-collimator 12. In an example, the exit 26 of the set of mirrors 14 is aligned with the aperture 26 of the pre-collimator 12. Accordingly, the X-ray radiation totally reflected by one of the mirrors 22 may be reflected to the exit 26 of the set of mirrors 14, and thus, being reflected to the aperture 36 of the pre-collimator 12. In case the aperture 36 of the pre-collimator 12 and the exit 26 of the set of mirrors 14 are aligned, the reflected X-ray radiation can pass the aperture 36 and consequently provide the secondary X-ray radiation to the object receiving space 6. Further, the set of mirrors 14 and the aperture 36 of the pre-collimator 12 are preferably coaxially aligned with respect to a common longitudinal axis. In an example, the aperture 36 of the pre-collimator 12 is arranged as a slit. Accordingly, the pre-collimator 12 may be referred to as a slit pre-collimator. In an example, the mirrors 22 of the set of mirrors 14 are each arranged as planar mirrors having planar mirror surfaces. In particular, the surfaces are polished. According to an alternative example, the mirrors 22 of the set of mirrors 14 are arranged as curved mirrors 22, preferably each comprising a curved mirror surface. The surfaces are preferably polished. In a further example, the mirrors 22 of the set of mirrors 14 are preferably mirror-segments of one common mirror. In an example, a source width SW of the source 4 is larger than the entrance width UW of the entrance 24 of the set of mirrors 14. This increases the enhancement of the X-ray radiation provided in the object receiving space 6, since the mirrors 22 of the set of mirrors 14 can reflect a part 16 of the X-ray radiation of the source 4 at their total length LM. In a further example, the exit width LW is smaller than the entrance width UW of the set of mirrors 14. According to a further example, the source width SW of the source 4 is larger than the exit width LW of the exit 26 of the set of mirrors 24. It is further preferred that a width AW of the aperture 36 corresponds to the exit width LW of the exit 26 of the set of mirrors 14. Alternatively, it is preferred that the width AW of the aperture 36 of the pre-collimator 12 is smaller than the exit width LW of the exit 26. According to a further example, the source width SW of the source 4 is larger than an aperture width AW of the aperture 36 of the pre-collimator 12. FIG. 2 shows an example of the X-ray imaging apparatus 2, comprising the source 4, the object receiving space 6, the pre-collimator 12, arranged between the object receiving space 6 and the source 4, and the set of mirrors 14, which is arranged between the pre-collimator 12 and the source 4. The set of mirrors 14 comprises two mirrors 22, which are tapered, such that the entrance width UW of the entrance 24 of the set of mirrors 14 is larger than the exit width LW of the exit 26 of the set of mirrors 14. The exit 26 of the set of mirrors 14 is preferably aligned with an aperture 36 of the pre-collimator 12 with respect to a common longitudinal axis A. Accordingly, the X-ray radiation passing the set of mirrors 14 and the pre-collimator 12 unreflected will provide a primary X-ray radiation 18 to the object receiving space 6. According to a further example, exemplary shown in FIG. 2, the primary X-ray radiation will form a primary beam cone 28 between the source 4 and the pre-collimator 12. Preferably, a width of the primary beam cone 28 is defined at one end by the width SW of the source 4 and at the other end by the width AW of the aperture 36 of the pre-collimator 12. Preferably, the mirrors 22 of the set of mirrors 14 abut to the outside on the primary beam cone 28. Accordingly, the angle of spread θm preferably corresponds to a cone angle θk of the primary beam cone 28 with a maximum deviation to the cone angle θk of 10%. The cone angle θk relates to an acute angle of the primary beam cone 28, which corresponds to a double of an angle φk between a surface line 30 of the primary beam cone 28 and a longitudinal axis of the primary beam cone 28. Preferably, the cone longitudinal axis corresponds to the common longitudinal axis A of the set of mirrors 14 and the aperture 36 of the pre-collimator 12. In an example, the mirrors 22 of the set of mirrors 14 directly abut to the outside surface of the primary beam cone 28. In this case, the angle of spread θm of the mirrors 22 of the set of mirrors 14 and the cone angle θk of the primary beam cone 28 correspond exactly to each other. In case the angle of spread θm of the mirrors 22 of the set of mirrors 14 is larger or smaller than the cone angle θk, the mirrors 22 abuts preferably at least partly at the outside surface of the primary beam cone 28. The deviation between the cone angle θk and the angle of spread θm is preferably limited to 10%. By limiting this deviation, a large decrease of lateral resolution of the X-ray radiation provided at the object receiving space 6 is prohibited. In an example, the X-ray imaging apparatus 2 comprises a detector plane 32 for arranging a detector (not shown). Preferably, the mirror arrangement 8 and the collimator arrangement 10 are arranged between the source 4 and the detector plane 32. According to a further example shown in FIG. 3, the X-ray imaging apparatus 2 is provided with the mirror arrangement 10 comprising at least one of the set of mirrors 14, wherein a length LM of each mirror 22 of the set of mirrors 14 is arranged, such that the image quality LM≤LMmax=LW/(θc2−θm) holds, wherein LW relates to the width of the exit 26 of the set of mirrors 14, θc2 relates to the critical angle of reflection at the mirrors 22 of the set of mirrors 14, and θm relates to the angle spread of the mirrors 22 of the set of mirrors 14. Limiting the length LM of each of the mirrors 22 of the set of mirrors 14 has the effect that a number of reflections of the X-ray radiation provided by the source 4 are limited, in particular to a second or first order reflection within the set of mirrors 14. It is to be noted, that a reflection angle θr of an X-ray beam of the X-ray radiation reflected by the mirrors 22 of the set of mirrors 14 with respect to a common longitudinal axis A of the set of mirrors 14 increases with each reflection at a mirror 22 of the set of mirrors 14. Accordingly, second order reflected X-ray beams, or an even higher order reflected X-ray beam, may pass the exit 26 of the set of mirrors 14, the aperture 36 of the pre-collimator 12 and the object receiving space 6 without being picked up by a detector which is arrangeable at the detector plane 32. A detector usually has a limited width for detecting X-ray radiation. Since a second order or an even higher order reflected X-ray beam has a higher reflection angle θr, the respective X-ray beam may pass over the detector at the detector plane 32 and impinges at the detector plane 32 at a position, where the detector may not be arranged at. Accordingly, these X-ray beams would add an X-ray dose to an object of interest, in particular to a patient, without increasing the image quality. Since the above example shows a limitation for the length LM of the mirrors 22 of the set of mirrors 14, which provides a significant reduction of second order or higher reflected X-ray radiation beams at the mirrors 22 of the set of mirrors 14, the X-ray dose not utilized for the image quality is significantly reduced. In an example, the length LM of each mirror 22 of the set of mirrors 14 is between 0.8×LMmax and 1.2×LMmax, in particular between 0.9×LMmax and 1.0×LMmax. As previously explained, the arrangement for the length LM of each mirror 22 of the set of mirrors 14 provide a very good reduction of second order or higher order reflections of X-ray radiation beams within the set of mirrors 14. Thus, by limiting the length LM close to the length LMmax a technical effect as described above is provided at least similarly. In an example, the critical angle of reflection θc2 is defined as θc2=1.6×10−3×ρ(0.5)×λ, wherein ρ [g/cm3] relates to the density of the mirrors and λ [Å] relates to the wavelength of the X-ray radiation. In a further example, the X-ray radiation of the source 4 is filtered, such that the primary X-ray radiation and the part of the X-ray radiation being reflected at the set of mirrors 14 have an energy within an energy-bandwidth between 20 keV and 40 keV, in particular between 25 keV and 35 keV. At an energy of 25 keV, the wavelength of the X-ray radiation is about λ=0.5 Å. A preferred material for the mirrors 22 of the set of mirrors 14 is lithium aluminosilicate which preferably has a density of about ρ=2.53 g/cm3. According to a further example, in particular shown in any of the preceding FIGS. 1 to 3, the exit 26 of the set of mirrors 14 abuts to the aperture 36 of the pre-collimator 12. Preferably, an end of the set of mirrors 14 facing the pre-collimator 12 directly abuts to a surface of the pre-collimator facing the set of mirrors 14. Further, preferably, the exit 26 of the set of mirrors 14 borders on to a rim of the aperture 36, in particular formed by the pre-collimator 12. In a further example, the exit width LW of the exit 26 of the set of mirrors 14 corresponds to an aperture width AW of the aperture 36 of the pre-collimator 12. As exemplarily pointed out previously, the exit 26 of the set of mirrors 14 and the aperture 36 of the pre-collimator 12 are preferably aligned to a common longitudinal axis A. In case the exit 26 and the aperture 36 have corresponding widths, namely the exit width LW and aperture width AW, respectively, it is very likely, that X-ray radiation passing the exit 26 will also pass the aperture 36. FIG. 4 shows a further example of the X-ray imaging apparatus 2 with respect to the primary X-ray radiation 18 and the secondary X-ray radiation 20. The primary X-ray radiation 18 passes the mirror arrangement 14 and the collimator arrangement 8 unreflected and thus creates a primary spot 34 at the detector plane 32. The primary spot 34 preferably relates to the area at the detector plane 32, where at least 75%, in particular at least 85%, of the unreflected X-ray radiation with respect to its distribution reaches the detector plane 32. According to a further example, exemplarily shown in FIG. 4, a secondary spot 38 at the detector plane 32 is created by the secondary X-ray radiation 20, which has been previously totally reflected at one of the mirrors 22 of the set of mirrors 14. The secondary spot 38 preferably relates to the area at the detector plane 32, where at least 75%, in particular at least 85%, of the reflected X-ray radiation with respect to its distribution reaches the detector plane 32. In an example, a spot width KP of the secondary spot 38 is larger than a spot width SP of the primary spot 34. Preferably, the secondary spot 38 and the primary spot 34, each at the detector plane 32, are overlapping each other. Accordingly, an enhanced X-ray radiation is provided in the object receiving space 6. In a further example, the spot width KP of the secondary spot 38 is larger than the aperture width AW of the aperture 36 of the pre-collimator 12 or as the exit width LW of the exit 26 of the set of mirrors 14. A spot width SP of the primary spot 34 is preferably larger than the aperture width AW of the aperture 36 of the pre-collimator 12 or the exit width LW of the exit 26 of the set of mirrors 24. In an example, the spot width KP of the secondary spot 38 is in the range between 1.05×S and 1.5×S, where S relates to the amount of the spot width SP of the primary spot 34. This provides a large overlap between the primary spot 34 and the secondary spot 38, which helps increasing the intensity of the X-ray radiation in the object receiving space 6 and thus the utilization of the X-ray radiation for imaging an object of interest. According to a further example, the mirror arrangement 10, and in particular the length LM of each mirror 22 of the set of mirrors 14, are arranged, such that at least 50% of the secondary X-ray radiation 20 impinges at the primary spot 34 at the detector plane 32. According to a further example, as exemplary shown in FIG. 5, the set of mirrors 14 is arranged such that for the part 16 of X-ray radiation of the source 4 to be reflected at the set of mirrors 14, a maximum of one or two total reflections at the mirrors 22 of the set of mirrors 14 occur. Assuming that the exit width LW of the exit 26 of the set of mirrors 14 is given by a system design of the X-ray imaging apparatus 2 and that the angle of spread θm is given by a cone angle θk of the primary beam cone 28, it is preferred to adapt the length LM of each of the mirrors 22 of the set of mirrors 14 to limit the number of reflections at the mirrors 22 of the set of mirrors 14. Accordingly, it is preferred that the length LM of the mirrors 22 is adapted such that for the part 16 of the X-ray radiation to be totally reflected at at least one of the mirrors 22 of the set of mirrors 14 a maximum of one or two total reflections at the mirrors 22 of the set of mirrors 14 occur. By limiting the number of total reflections, the angle of reflection θr of the secondary X-ray radiation 29 (with respect to a common longitudinal axis A of the set of mirrors 14 and the aperture 36 of the pre-collimator 12) is limited. Limiting the angle of reflection θr of the secondary X-ray radiation 20, in particular with respect to the X-ray beams thereof, will limit the spot width KP of the secondary spot 38 and thus provides an increase in image quality of an object of interest. According to a further example, as exemplary shown in FIG. 6, the pre-collimator 12 comprises at least two apertures 36, wherein, for each aperture 36 of the pre-collimator 12, the mirror arrangement 10 comprises an associated set of two mirrors 14. Accordingly, for each aperture 36 of the pre-collimator 12, a set of mirrors 14 is preferably provided, wherein the two mirrors 22 of each set of mirrors 14 is preferably formed as one of the set of mirrors 14 as exemplary described previously. The sets of mirrors 14 can be integrally formed. In particular, the set of mirrors are preferably made of the same means. In a further example, the mirrors of the set of mirrors are fasten together in order to form a rigidly fixed unit. This unit can be pre-build. A pre-collimator 12 comprising at least two apertures 36 allows providing enhanced X-ray radiation at two different areas 40, 42 in the object receiving space 6. Accordingly, this allows providing a first pair of a primary spot 34 and secondary spot 38 to be spaced apart from a further pair a primary spot 34 and a secondary spot 38. Thus, imaging can be performed in parallel at the two separated areas 40, 42. Parallel imaging reduces the total time for imaging an object of interest. For example, two apertures 36 with an associated set of two mirrors 14 are provided as shown in FIG. 6. In further examples, more than two, e.g. three, four, five, six, seven, eight, nine or ten, or more than ten apertures 36 with a respective associated set of two mirrors 14 are provided. In an example, 15, 20, 25, 30 or more, or also numbers inbetween, apertures 36 are provided with associated sets of mirrors 14. According to a further example, as exemplary shown in FIG. 7, the collimator arrangement 10 of the X-ray imaging apparatus 2 comprises a post-collimator 44. Preferably, the object receiving space 6 is arranged between the pre-collimator 12 and the post-collimator 44. It is further preferred that the mirror arrangement 10 and the collimator arrangement 8 are arranged between the source 4 and the detector plane 32. Accordingly, X-ray radiation passing the mirror arrangement 10 and the collimator arrangement 8 is utilized for imaging an object of interest, which can be arranged in the object receiving space 6 between the pre-collimator 12 and the post-collimator 44 of the collimator arrangement 8. Preferably, the post-collimator 44 comprises at least one aperture 46. The at least one aperture 46 is preferably adapted for being passed by X-ray radiation. The remaining post-collimator 44 is preferably adapted for absorbing X-ray radiation. The at least one aperture 46 of the post-collimator 44 can be aligned with an aperture 36 of the pre-collimator with respect to a common longitudinal axis. In a further example, the post-collimator 44 comprises at least two apertures 46. For each aperture 36 of the pre-collimator 12, the post-collimator 44 preferably comprises an associated aperture 46, in particular formed by one of the apertures 46 of the post-collimator 44. In an example, an aperture 36 of the pre-collimator 12 and an aperture 46 of the post-collimator 44 are aligned with respect to a common axis, in particular to an optical axis intersecting the source 4, especially at its focal centre, such that the aperture 36 of the pre-collimator 12 and the aperture 46 of the post-collimator 44 are forming an aperture-pair of the collimator arrangement 8. The Collimator arrangement 8 preferably comprises at least two aperture-pairs. In a further example, each aperture 36, 46 of the collimator arrangement 8 is formed as a slit. Correspondingly, each aperture-pair can be formed as a slit-pair of the collimator arrangement 8. According to a further example, exemplary shown in FIG. 8, the X-ray imaging apparatus 2 comprises a detector arrangement 48. Preferably, the detector arrangement 48 is arranged at the detector plane 32. Correspondingly, the mirror arrangement 10 and the collimator arrangement 8 are preferably arranged between the source 4 and the detector arrangement 48. The detector arrangement 48 comprises at least one detector 50. In an example, the detector 50, one of the at least one apertures 46 of the post-collimator 44, one of the at least one apertures 36 of the pre-collimator 12, and an exit 26 of a set of mirrors 14 are aligned with respect to a common longitudinal axis. The alignment is preferably with respect to an optical axis as the common axis intersecting the source 4, in particular its focus-centre. This provides a good imaging quality. In an example, for each aperture 46 of the post-collimator 44 an associated detector 50 of the detector arrangement 48 is provided. Preferably, an aperture width KW of each aperture 46 of the post-collimator 44 is smaller than the detector width DW of the associated detector 50. Accordingly, each detector 50 is preferably adapted for detecting the X-ray radiation passing the associated aperture 46 of the post-collimator 44. In FIG. 9, an example of the mirror 22 of the set of mirrors 14 is shown. The mirror 22 shown is exemplary for each of the two mirrors 22 of each set of mirrors 14. In an example, each mirror 22 of the set of mirrors 14 comprises a substrate 52 with a coating layer 54 for providing total reflection, wherein, between the coating layer 54 and the substrate 52, a boundary 56 is provided, which is configured to reduce scatter radiation from an incoming radiation that is not reflected but passes a mirror surface 58 and enters the coating layer 54. Preferably, the density of the substrate 52 is higher than the density of the coating layer 54. In an example, the boundary 56 is flat, in particular as flat as could be. However, in a further example, the boundary may have a roughness. Accordingly, it is hard to ensure that an angle of incidence θi is smaller than the critical angle θc for every wave of X-ray radiation impinging the boundary 46. At the boundary 46, the X-ray radiation may be totally reflected only at small fractions thereof. However, at very low incidence angles θi a microscopic roughness appears more and more flat. Therefore, in reality, a microscopic roughness will have only impact on the total reflection of the X-ray radiation for incident angles θi close to the critical angle θc. According to a further example, exemplary shown in FIG. 10, the boundary 56 has a randomly rough structured surface profile. In case an X-ray radiation beam is being reflected at the boundary 56, the randomly rough structured surface profile of the boundary 56 provides an effective beam reduction for suppressing reflected beam parts in such a way that the reflection conditions for the reflected beam parts are not fulfilled at the boundary 56. Accordingly, the reflected beam parts of the X-ray radiation are absorbed at the boundary 56 from the substrate 52 or the coating layer 54. As an effect thereof, a reduction of a scatter radiation from the incoming radiation when impinging at the boundary 56 is provided. An alternative configuration for the boundary 56 is exemplary shown in FIG. 11. According to an example, the boundary 56 has a periodical profile with a periodic height h between 0.05 mm (millimeter) and 1.5 mm, and a period p between 0.5 mm and 5 mm. The analogous effect as described previously with respect to the random rough surface applies for the periodical profile. Accordingly, analogue reference is made. According to a further example, a thickness t of the coating layer is between 10 nm (nanometer) and 25 nm. According to a further example, the coating layer comprises a material with an atomic number at the most of 9. According to a further example (not further shown), between the coating layer 54 and the substrate 52, an uneven interface region is provided at the boundary 56. The interface region can be formed by the surfaces of the substrate 52 and the coating layer 54 facing each other. According to an alternative example, the interface region is formed by a further layer, which is provided between the substrate 52 and the coating layer 54 and connecting the coating layer 54 with the substrate 52. According to a further example, exemplary shown in FIG. 12, an X-ray imaging system 60 is provided. The imaging system 60 comprises an X-ray imaging apparatus 2 according to one of the previously examples, the detector 50 for detecting X-ray radiation passing the object receiving space 6 of the apparatus 2, and an imaging processing unit 62, as well as an imaging output unit 64. The imaging processing unit 62 is configured to receive signals from the detector 50 and to compute image data of an object of interest 76 arrangeable in the object receiving space 6 based on the signals, and the imaging output unit 64 is configured to provide an image data for further purpose. Preferably, a signal connection 66 is provided, which connects the detector 50 with the imaging processing unit 62. Accordingly, the imaging processing unit 62 can obtain signals from the detector 50 via the signal line 66. A signal from the detector 50 preferably corresponds to detected X-ray radiation. The imaging processing unit 62 can be configured for processing the received signals from the detector 50 to compute an image in form of image data of an object of interest 76, which, when arranged in the object receiving space 6, can be applied with X-ray radiation from the source 4. The image data, which can be computed by the image processing unit 62, can be provided to the output unit 64. For transmitting the image data, a further signal line 68 can be provided for connecting the image processing unit 62 with the output unit 64. The output unit 64 is configured to provide the image data for further purpose. In an example, the output unit 64 can be a display or a monitor. In a further example, the output unit 64 can be configured to transmit the image data to a further unit (not shown). In an example, the system 60 further comprises a mounting arrangement 70 for mechanically connecting the source 4, the mirror arrangement 14, the collimator arrangement 8 and the detector 50. Furthermore, an actuator 72 coupled to the mounting arrangement 70 to displace the mounting arrangement 70, and a control unit 74 to control the actuator 72 can be provided. The control unit 74 may be configured to receive signals from the detector 50 and to compute a control signal based on the received signals from the detector 50. In an example, the control unit 74 receives signals from the detector via a further signal line 78. Control signals from the control unit 74 can be sent to the actuator 72 via a further signal line 80. Preferably, the control unit 74 receives via a further signal line (not shown) signals from the source 4 or an associated controller. In a further example, the control unit 74 controls the actuator 72 via the control signal sent to the actuator 72 and on the bases of the signals received. In particular, the control unit 74 controls the actuator 72 such that the mounting arrangement 70 is moved linearly or along a trajectory between a first position and a second position. As they are mechanically connected to the mounting arrangement 70, the source 4, the mirror arrangement 14, the collimator arrangement 8 and the detector 50 are moved correspondingly. Preferably, the object of interest 76 is held by a holder (not shown). The holder is not mechanically connected to mounting arrangement, such that the movement of the mounting arrangement will not apply to the holder. Accordingly, when the actuator 72 moves the mounting arrangement 70 and the elements mechanically connected to it, a relative movement is provided with respect to the holder and consequently to the object of interest 76. Accordingly, the object of interest 76 can be imaged at several different positions between the first position and the second position of the mounting arrangement 70, and thus being scanned. The control unit 74 can control the actuator 72 in open loop or in close loop. For the close loop control, a position sensor (not shown) for detecting the position of the detector 50 or the mounting arrangement 70 can be provided for the system 2. The detected position can be provided to the control unit 74 or the image processing unit 62. In case of scanning the object of interest 76, for each image taken a detected position can be associated. This allows computing a quasi continuous image of the object of interest 76. In an example, the imaging processing unit 62 or the controller unit 74 can receive signals from the source 4 or an associated controller (not shown) for controlling the source 4, in order to control the X-ray radiation, in particular with respect to its intensity, emitted by the source 4. While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims. In the claims, the word “comprising” does not exclude other elements, and the indefinite article “a” or “an” does not exclude a plurality. A single collimator or another unit may fulfill the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. |
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055966152 | claims | 1. A fuel assembly for a nuclear reactor comprising fuel assembly elements, said fuel assembly elements comprising: a fuel sheath tube; a spacer tier holding said fuel sheath tube; and a channel box for containing a plurality of said sheath tubes, wherein at least one fuel assembly element comprises a Zr-containing matrix alloy, wherein an average crystal grain size of said matrix alloy is in the range of 1000 nm or less. a) mechanically mixing a Zr-containing metal and an alloying element, the alloying element being chosen from a group consisting of: Fe, Cr, Ni, Nb, Mo, Te, Bi, and Sn, whereby a Zr alloy is produced; b) subjecting the Zr alloy to an isostatic pressure, whereby a pressure-treated Zr alloy is produced; c) crystallizing the pressure-treated Zr alloy in a temperature range of between a crystallization temperature of the pressure-treated Zr alloy and a maximum crystallization temperature, said maximum crystallization temperature being 200 degrees C. above the crystallization temperature of the pressure-treated Zr alloy, whereby a Zr matrix alloy is produced; d) forming the Zr matrix alloy into a shape of the fuel assembly element. hydrogenation of the Zr-containing metal; crushing of the Zr-containing metal into a powder, and; dehydrogenation of the powder. 2. A fuel assembly as in claim 1 wherein said average crystal grain size is in the range of 100 nm or less. 3. A fuel assembly as in claim 1 wherein at least one of said fuel assembly elements comprises a Zr alloy having a random crystal orientation. 4. A fuel assembly as in claim 1 wherein at least one fuel assembly element comprises a Zr alloy having greater than about 0.02 wt % of Fe. 5. A fuel assembly as in claim 4 wherein at least one fuel assembly element comprises a Zr alloy having at least about 0.05 to 30 wt % of Fe, and an average crystal grain size of said Zr alloy is in the range of 100 nm or less. 6. A fuel assembly as in claim 1 wherein at least one fuel assembly element comprises a ZrFe.sub.2 intermetallic compound containing at least about 33 atomic percent Zr. 7. A fuel assembly as in claim 1 wherein at least one fuel assembly element comprises a ZrFe.sub.2 intermetallic compound containing at least about 66 atomic percent Fe. 8. A fuel assembly as in claim 7 wherein at least one fuel assembly element comprises a ZrFe.sub.2 intermetallic compound containing at least about 33 atomic percent Zr. 9. A fuel assembly as in claim 1 wherein at least one fuel assembly element comprises a Zr(Fe, Ni, Cr, Sn).sub.2 intermetallic compound containing a range of Zr between about 30 and about 35 atomic percent. 10. A fuel assembly as in claim 1 wherein at least one fuel assembly element comprises a Zr(Fe, Ni, Cr, Sn).sub.2 intermetallic compound containing a range of (Fe, Ni, Cr, Sn) of between about 65 and about 70 atomic percent. 11. A fuel assembly as in claim 10 wherein at least one fuel assembly element comprises a Zr(Fe, Ni, Cr, Sn).sub.2 intermetallic compound containing a range of Zr between about 30 and about 35 atomic percent. 12. A fuel assembly element for a nuclear reactor comprising a Zr-containing matrix alloy comprising an average crystal grain size of 1000 nm or less. 13. A fuel assembly element as in claim 12 wherein said average crystal grain size is less than about 100 nm. 14. A fuel assembly element as in claim 12 wherein said Zr-containing metal comprises a Zr alloy having at least about 0.02 wt % of Fe. 15. A fuel assembly element as in claim 14 wherein said Zr-containing metal comprises a Zr alloy having at least about 0.05 to 30 wt % of Fe and an average crystal grain size of said Zr alloy is in the range of 100 nm or less. 16. A fuel assembly element as in claim 12 said Zr-containing metal comprises a ZrFe.sub.2 intermetallic compound containing at least about 33 atomic percent Zr. 17. A fuel assembly element as in claim 12 wherein said Zr-containing metal comprises a ZrFe.sub.2 intermetallic compound containing at least about 66 atomic percent Fe. 18. A fuel assembly element as in claim 17 wherein said Zr-containing metal comprises a ZrFe.sub.2 intermetallic compound containing at least about 33 atomic percent Zr. 19. A fuel assembly element as in claim 12 wherein said Zr-containing metal comprises a Zr(Fe, Ni, Cr, Sn).sub.2 intermetallic compound containing a range of Zr between about 30 and about 35 atomic percent. 20. A fuel assembly element as in claim 12 wherein said Zr-containing metal comprises a Zr(Fe, Ni, Cr, Sn).sub.2 intermetallic compound containing a range of (Fe, Ni, Cr, Sn) of between about 65 and about 70 atomic percent. 21. A fuel assembly element as in claim 20 wherein said Zr-containing metal comprises a Zr(Fe, Ni, Cr, Sn).sub.2 intermetallic compound containing a range of Zr between about 30 and about 35 atomic percent. 22. A fuel assembly element manufacturing method comprising: 23. A method as in claim 22 wherein said crystallizing occurs during said subjecting, wherein said subjecting comprises subjecting the Zr alloy to an isostatic pressure at a temperature lower than the crystallization temperature of the Zr alloy. 24. A method as in claim 22 wherein said crystallizing comprises working the pressure-treated Zr alloy at a temperature range between about 100 degrees C. and about 200 degrees C. 25. A method as in claim 24 wherein said subjecting occurs at a temperature above the crystallizing temperature for said Zr alloy. 26. A method as in claim 22 wherein said mechanically mixing comprises: 27. A method as in claim 26 wherein said dehydrogenation comprises heating in a vacuum atmosphere. 28. A method as in claim 22 wherein said Zr-containing metal comprises a powder of pure Zr. 29. A method as in claim 22 wherein said Zr-containing metal comprises a powder of a Zr alloy. 30. A method as in claim 22 wherein the temperature is never allowed above about 650 degrees C. 31. A method as in claim 22 further comprising hot-working, performed below about 650 degrees C. 32. A method as in claim 22 further comprising annealing, performed at a temperature higher than about 530 degrees C. |
051568187 | description | DESCRIPTION OF THE FIRST EMBODIMENT As seen in FIG. 1 the first embodiment of the centrifugal casting apparatus includes a frame 10 comprised of a pair of generally parallel rectangular sub-frames 12 which are spaced apart from each other by a plurality of cross members 13. A rotatable bifurcated casting mold 20 intended for casting of both an impact resistant radiation barrier shell and radioactive waste materials is supported for rotation about a first axis (vertical as seen in FIG. 1) in the frame by swivels 22, 24 at the top and bottom of the mold to be described. The mold 20 is comprised of two separable mold halves 26, 28 (FIG. 2) which are held together by a plurality of fluid actuated latch members 30 which will be described with reference to FIG. 8. The mold halves are respectively moveable away from each other to the left and right as seen in FIG. 2 by a pair of linear actuators 32 which preferably have rotatable threaded male ends 34 which are receivable into female threaded apertures 36 (FIG. 1) in the mold halves. Means for rotating and longitudinally moving the actuators are conventional and are not shown. The frame 10 (FIG. 1) is supported for rotation about a second (horizontal) axis which is perpendicular to the plane of the first axis of rotation mentioned above. The frame support is comprised of a pair of pedestals 40, 42 having roller supports 44, 46 mounted thereon for supporting a pair of concentric half axles 48, 50 on which the mold frame is rotatably mounted as shown. A drive motor 51 (FIG. 2) is provided for actuating a pair of drive chains 52, 54 trained around a pair of drive sprockets 58, 60 which are in turn affixed to the left hand half axle 48 which is comprised of an outer drive portion 49 and an inner drive portion 53. The radially outer drive portion 49 of the half axle is fixedly attached to the frame 10 whereby the first drive chain 52 rotates the frame 10 about the horizontal axis of the half axles 48, 50. The second drive chain 54 is fixedly attached to the sprocket 60 which drives the radially inner portion 53 of the concentric drive axles, the inner end of which is seen extending through a bearing to the inside of the frame. A third drive chain 66 for rotating the mold about the first (vertical as seen in FIG. 1) axis is trained around a drive sprocket 62 mounted on the inner end of the inner drive portion 53 of the axle and is trained around a pair of idler pulleys 68 and into engagement with a mold drive sprocket 72 also seen in FIG. 4. Turning now to FIG. 2, the separable mold halves 26, 28 are shown in closed or latched operative centrifugal casting position and, in phantom, are shown in the open position. Opening of the mold is accomplished by longitudinally extending the pair of rotatable linear actuators 32 such that the male threaded ends 34 engage the female threaded apertures 36 (FIG. 1) provided in the mold halves following which the actuators are rotated to affix the male ends to the mold halves. The actuators are then linearly retracted to open the mold. It will be appreciated that the actuators are shown schematically and comprise only one of a number of possible different forms of mold opening and closing means which might be used. Mechanical latches or magnetic affixation of the actuators to metallic receptor plates on the mold halves may be used instead of rotatable linear actuators provided with threaded ends. When the mold halves 26, 28 are in the closed and latched position, castable radioactive waste materials as well as radioactive shielding materials, shell forming materials and chemicals for immobilizing radioactive waste may be fed from sources 74, 76, 78, 80 thereof into the mold via a feeder mixer mechanism 82 and feed wand 86 (FIG. 1) which is received in an axial inlet passageway 88 of the top mold support swivel 22 mounted between the parallel sub-frames 12 as seen in FIG. 1. Means are also provided for heating and cooling the mold walls in the embodiment shown in FIG. 2. These means are comprised of a heat transfer fluid conduit 90 which has a fluid supply inlet 92 and which is connected to a pump 94 and valve controlled branch conduits 96, 98 having means 100, 102 for heating and for cooling the heat transfer fluid disposed in series with the pump in the conduit 90. Heat transfer fluid is admitted through a valved inlet fluid passageway 110 which extends through the inner drive portion 53 of the left hand support axle 48, thence via a fluid inlet line 112 to the stationary portion 22a of the top mold support swivel 22 which is mounted between cross members 13 in the frame (FIG. 4). The rotatable portion 22b of the top swivel is sealingly engageable with the top surface of the mold halves such that fluid communication is provided between the swivel 22 and fluid passageways 120 in the mold halves. At the lower portion of the mold as best seen in FIGS. 2 and 4, the bottom swivel 24 serves as both a mold support and a fluid outlet. The lower, non-rotatable portion 24b of the bottom swivel is affixed to and mounted in frame cross members 13. A flexible heat transfer fluid outlet line 122 extends from the lower swivel 24 to an outlet passageway 130 of the heat fluid transfer conduit disposed coaxially in the right hand mold support half axle 50. FIG. 3 is a horizontal cross section of the mold apparatus taken at line 3--3 of FIG. 4 showing the mold halves in open position and, in phantom, the mold halves in closed position. Each mold half has a plurality of generally vertically oriented heat fluid transfer passageways 120 extending therethrough to permit heat transfer fluid to flow axially of the mold to thus rapidly heat or cool the mold walls and mold contents. The inner configuration of the mold is preferably of a hexagonal or octagonal shape to result in finished cast monoliths of complimentary external shape which are easy to stack or pack together without lost space between adjacent monoliths. FIG. 4 is a vertical cross section of the mold apparatus taken at line 4--4 on FIG. 3 and shows the mold being comprised preferably of a pair of C-shaped sidewall members 132, 134 to each of which are affixed a half of a top mold plate 136 and a half of a bottom mold plate 138. Each of the two halves of the top plate 136 and each of the two halves of the bottom plate 138 is provided with a plurality of radially extending bores 140, 142 for transmitting heat transfer fluid from axially extending fluid inlets 146 at the top of the mold to the vertically extending passageways 120 in the C-shaped sidewall members of the mold. Sealing engagement between the upper and lower exterior surfaces of the mold halves and the respectively adjacent swivels is provided by a pair of parallel tracks 152 and grooves 154 and preferably by rubber seals disposed in grooves 172 in the mold top surface which extend transversely to the track and groove seals to be described. As seen in FIG. 4, the mold is supported at the bottom on the bottom swivel 24 which is fixedly attached between spaced parallel lower frame cross members 13. The upper surface of the rotatable portion 24a of the bottom swivel is provided with a pair of spaced parallel tracks 148 which are sealingly received in a pair of spaced parallel grooves 150 on the bottom surfaces of the bottom mold plates 138 whereby the grooves and tracks may be aligned parallel with the axis of the linear mold actuators 32 to open and close the mold to bring the fluid passageways 120 in the mold into registry with mating fluid passageways in the rotatable portion 24a of the bottom swivel. Similarly, at the top of the mold seen also in FIG. 5, the top swivel 22 is preferably spring biased downwardly against the upper mold surfaces so that it is sealingly engaged therewith via a similar groove and track arrangement to that provided at the bottom mold swivel 24 except that here the tracks 152 are provided on the top surface of the mold and the grooves 154 are provided on the underside of the top swivel. Chamfered camming edges 156, 160 in the locations shown on the upper mold tracks 152 and the grooves 154 on the upper mold support swivel 22 are provided to ensure that the upper swivel is raised slightly against the spring bias as the mold halves engage the swivels during movement of the mold halves together to close the mold. Similarly, at the bottom of the mold (FIG. 4), chamfers are provided on the slideably engaging surfaces of the grooves 150 and tracks 148 of the lower mold surface and bottom swivel, respectively. Compressible elongated round rubber seals disposed in grooves 172 may be provided at the locations shown with the grooves 172 extending transversely between the track and groove seals previously described whereby the rubber seals may be compressed as the mold halves are moved together adjacent the upper and lower swivels 22, 24 (FIG. 2). A consumable casting support 180 (FIG. 4) comprised of a generally flat disc or base plate 182 of peripheral shape complementary to the preferably hexagonal or octagonal shape of the mold cavity is provided at the bottom of the mold cavity. The consumable casting support has keying edges 184 as shown for locking the support to the cast materials. A boss 186 is provided on the upper surface (as shown) of the base plate and has a vertically extending drain recess 190 and an enlarged bore 192 concentric therewith which provides a horizontally extending support shoulder for the cast monolith. Means for rotating the mold about its axis (vertical as seen in FIG. 4) is provided by a mold drive shaft 200 having a keyed or splined end 202 engageable with a mating keyway or internal splines 204 on the upper rotatable part of the lower mold support swivel and in the lower mold end pieces. The drive shaft has an axially extending mold drain passageway 206 in fluid communication with the drain recess 190 in the casting support 180 and an upper supporting end which abuts the internal support shoulder in the boss 186. A rack and pinion mechanism 210 is connected to the drive shaft 200 as shown for lowering the shaft to thus remove it from the interior of the consumable casting support after the mold has been opened and the casting has been grasped and independently supported by, e.g., a forklift provided with grasping tongs. Clearance is provided for non-interfering longitudinal movement of the splined drive shaft through the lower portion of the swivel 24. FIGS. 3 and 6 show a winder 220 for applying a filament strand or tape of reinforcing and radiation shielding material to the exterior surface of the cast monolith. As shown schematically, preferably the winder is horizontally moveable on a track 222 into and out of operative position and is vertically movable on a guide support 224 (FIG. 7) to permit the winding of the exterior surface of the monolith to take place vertically from end to end as the monolith is supported for rotation by the drive shaft 200 engaged with the support shoulder on the underside of the boss 186 after the mold halves 132, 134 have been removed. Access of a forklift truck or the like to remove cast monoliths from the mold is from the front with the winder 220 being disposed at the rear of the apparatus as seen in FIG. 6. Alternatively, the cast monoliths may be oriented in a generally horizontal position for removal as will be described below. FIG. 7 is a right side elevation view of the apparatus which shows the movement of the winder 220 along the vertically extending guide support 224. Also seen in FIG. 7 is a radiation detector 230 for detecting leakage radiation from the monolith. Heat curing lamps 232 are also optionally provided. Feed of contents to be centrifugally cast in the mold is provided by the vertically extending feed wand 86 which is moved by a linear piston/cylinder actuator 234 into and out of a manually rotatable ball valve 89 (FIGS. 1 and 4) which controls the opening and closing of the top swivel inlet passageway 88. A quick release latch mechanism for opening and closing the mold halves is seen in FIG. 8 to comprise a plurality of individual latches 30 pivotally mounted to one mold half and spring biased into engagement with a catch 31 on the other mold half. A linear actuator 240 for releasing the latches is comprised of a cylinder and piston which is actuated by a fluid pressure control line 242 as desired when the casting apparatus is stationary. The latches 30 are preferably spring biased to the closed position. OPERATION OF THE FIRST EMBODIMENT Centrifugally cast monoliths comprised of immobilized radioactive waste solidified and encapsulated in a radiation impermeable shield are formed by first orientating the closed and latched casting mold in a position such that its axis of rotation is generally vertical as seen in FIG. 2 or slightly inclined from the vertical. The mold drain is closed by inserting the lower end of the feed wand 86 into the drain recess 190 (FIG. 4). Radiation barrier shield forming materials such as polypropylene and powdered resin boron particles are then fed from supply sources 78 (FIG. 2) thereof to the mixer feeder 82 which transmits a flowable charge of volume calculated to provide a barrier wall of selected thickness, e.g. 1/4". The shield forming materials are then discharged at high pressure from radial apertures in the feed wand against the sidewall of the mold cavity as the feed wand is left in place with its lower end blocking the drain. The mold is rotated during the placement of the shielding materials solely about the axis of rotation defined by the upper and lower swivels 22, 24 during introduction of the charge into the mold to maintain the powdered shielding materials in engagement with the side walls of the mold. When the calculated volume charge of material has been completely injected into the mold, the feed wand 86 is removed therefrom while the mold continues to be rotated to prevent the charge from clogging the drain recess 190. The ball valve 89 at the top mold support swivel is then rotated to close the top swivel inlet passageway after the feed wand is withdrawn. The frame drive means is then actuated to rotate the frame 10 about the horizontal frame support axis seen in FIGS. 1 and 2 whereby the mold is rotated biaxially at a selected speed to centrifugally distribute the radiation shielding material uniformly on the end walls as well as the side walls of the mold. Preferably, this thickness will be slightly less than the vertical extent of the boss 186. Careful control of the two rotation speeds of the mold about the two axes of rotation is necessary to ensure that the drain recess 190 remains unobstructed during placement of the radiation barrier wall materials. Rapid curing and solidification of the shielding material in place on the inner surfaces of the mold cavity is accomplished during the biaxial rotation of the mold by pumping hot heat transfer fluid through the fluid transfer circuit which includes the passageways in the mold walls. This heats the mold to a temperature to rapidly melt the particulate shielding materials to form the radiation barrier. The heating ordinarily need not take place for more than about 45 seconds but the time will vary in practice depending upon the selected materials and intended barrier wall thickness. The mold 20 is then rapidly cooled to solidify the barrier wall by circulating cold heat transfer fluid through the mold passageways 120. After the mold and heat cured radiation barrier have been cooled to ambient temperature, the mold rotation is terminated and the mold is again oriented such that its axis of rotation is substantially vertical and the ball valve 89 is opened for reception of the inlet feed wand 86 to introduce castable radioactive waste material. The feed wand 86 is inserted into the mold through the open ball valve and top swivel inlet passageway with the discharge end of the wand 86 being again placed closely adjacent the bottom of the mold cavity to block the drain recess 190. Rotation of the mold about its axis is then commenced. Radioactive waste and castable radioactive waste immobilization materials such as polyorganic compounds or cementitious materials or the like are then discharged to the mixer feeder 82 and pumped into the mold in correct proportions which result in a castable and hardenable mixture. The mold is uniaxially rotated about its axis of rotation during feed of the mixed radioactive waste and waste immobilization materials to densely compact the waste inside of the formed radiation barrier. Excess liquid squeezed out of the castable materials during the centrifugal casting thereof is removed via the drain as the feed wand 86 is gradually withdrawn out of the mold as casting proceeds to completion. As casting of the mixed radioactive waste and immobilization materials progresses substantially to completion, the unfilled portion of the mold gradually shrinks and ultimately is in the shape of a centrally located generally cylindrical portion aligned with the axis of rotation of the mold. Casting of the radioactive materials is terminated when the mold is substantially filled except for the cylindrical unfilled mold central portion of a predetermined diameter not less than the diameter of the drain recess 190 which must remain unobstructed during casting. Since castings containing some types of radioactive waste such as Gamma radiation and other chemical waste often generate heat, it is a relatively simple matter to insert a consumable elongated generally cylindrical heat removal pipe (not shown) in the cylindrical unfilled portion of the mold after the casting is substantially complete if substantial heat generation is expected. The heat removal pipe is typically a ceramic conduit which can be finally affixed in place by injection of grout or cement into the annular clearance space left between the cast radioactive waste and the heat removal pipe. Placement of the heat removal pipe, if desired, in the cast monolith can take place either before or after removal of the mold parts from the monolith. A particularly important feature of the invention is the fact that the mold is removed from the monolith (rather than the monolith being removed from the mold) leaving the monolith supported (by the drive shaft 200) with its axis substantially vertical by a single consumable base plate 180 after the centrifugal casting operation is completed. Alternatively, two base plates can be used, one at either end of the monolith, whereby the monolith can be oriented with its axis generally horizontal and supported at each of its ends by the base plates which remain temporarily connected to the frame. The radiation detector 230 (FIG. 7) is placed in close proximity to the cast monolith to determine if detected leakage radiation exceeds a predetermined threshold level. If the castings are seen to be emitting excessive radiation despite the presence of the centrifugally cast radiation barrier, additional radiation barrier material can easily be applied by the winder 220 to the exterior of the monolith before it is removed from the apparatus. Although additional radiation shielding material can be applied e.g., by a spray on coating while rotating the monolith about its axis, a particularly advantageous manner of applying additional radiation shielding material consists of rotating the casting and thereby drawing a strand or tape of filamentary composite fiber material from the winder 220 to wind it onto the exterior surface of the monolith. Such wound on material provides additional structural support if needed as well as additional radiation barrier where required. A particularly advantageous material for this purpose comprises resin impregnated filaments selected from the group consisting of carbon, boron, fiberglass, polyester, organic fiber, metal fiber and composites thereof. The winder 220 is moveable on a track 222 so that it can be moved into and out of operative locations in proximity to the rotating mold apparatus as desired. Full details of the winder mechanism are not provided since it is believed well within the skill of the average person in the art to provide a suitable means for winding filamentary material onto the casting as it is supported in the apparatus. The completed monolith may be removed from the centrifugal casting apparatus by first orienting the mold such that its axis of rotation is generally vertical as seen in FIG. 1. The mold halves will have been withdrawn to the open position leaving the cast monolith supported on its base plate by engagement of the end of the drive shaft 220 with the shoulder on the undersurface of the boss 186. The frame is accessible from the front (as seen in FIG. 1) of the apparatus to a forklift provided with gripping tongs or other apparatus which is capable of grasping the monolith (which at this time is supported merely from below by the drive shaft) to hold the monolith independently of the support provided from below. Subsequently, the rack and pinion 210 mechanism is actuated to lower the drive shaft completely from the cast monolith and out of engagement therewith. The cast monolith is then easily removed from the centrifugal casting apparatus. Alternatively, as indicated above, the finished monolith may be supported in the frame by consumable end pieces provided at both ends of the monolith. The monolith is then oriented such that its axis is horizontal so that a material lift may be employed to support the monolith from below before disconnecting the frame support from the consumable end pieces. Although the presently preferred method of supporting and removing the cast monolith is by first orienting it in the vertical position shown, it will be appreciated by persons skilled in the art that, with some modification, the cast monolith could be oriented horizontally with support from both ends similar to that currently shown in the single ended support provided by the drive shaft and rack and pinion mechanism. THE SECOND EMBODIMENT AND OPERATION THEREOF Since it is occasionally more economical to use pre-formed impact resistant radiation barrier shells 250 which are shipped separately to the jobsite, a modified second embodiment of the invention is seen in FIG. 9 to comprise a bifurcated mold in which the fluid conduits needed for heating and cooling the mold halves are unnecessary due to the use of pre-formed shells. Each pre-formed shell 250 will ordinarily comprise a multi-layer shell having an external layer 252 of impact resisting material and an inner layer 254 of radiation barrier material. Parts of the second embodiment which are common to those of the first embodiment are identified with the same reference numerals and will not be described again. An axially extending hub 260 at either end of the pre-formed shell is provided for supporting the shell by apparatus to be described. An annular retaining collar 262 is mounted in the frame at the location shown and is moveable with respect to the frame along an axis (vertical as seen in FIG. 9) by a linear actuator 264 or by a rack and pinion or similar well known mechanism whereby the collar 262 may easily be slipped onto and off of the shell hub 260 when a shell is to be placed in the apparatus or a finished monolith is to be removed. At the lower end of the apparatus (as seen in FIG. 9) the stationary portion of swivel 24 is mounted in the frame 10 and its rotatable portion is affixed to a rotatable chuck 270 having radially moveable jaws for gripping and releasing the shell hub 260. Drive chain 66 is trained around affixed to drive sprocket 72 which is fastened to the rotatable portion of the swivel 24. Due to the insulation provided by the pre-formed shell adjacent the interior wall of the mold, it is more efficient to cure the added cast radiation barrier material (if needed) from the inside of the mold cavity than by heating the mold walls as was done in the first embodiment. When it is determined that the radioactive waste to be disposed of emits more radioactivity than can be effectively blocked by the pre-formed shell, a charge of castable radiation shielding material may be injected from the feed wand 86 into the shell 250. The mold halves 26, 28 are closed about the shell 250 to provide the necessary structural support during the high speed biaxial casting and curing of the additional radiation barrier and the actuators 32 are then removed to the inoperative position. Rotation of the mold and shell about the axis of the shell is commenced to evenly distribute the charge about the vertically extending sides of the shell 250. Subsequently, a detachable elongated electrically energized heating wand 276 is placed by actuator 234 in the shell and is held axially therein by disposing one of the ends of the wand in the fluid drain 190 in the lower shell hub 260 and the other end in the inlet in the upper shell hub 262. Electrical power is supplied to the wand during biaxial rotation of the mold by electrical leads 282 extending through the left hand axle to the stationary portion of an electrical swivel 284 and by leads 283 extending from the rotatable portion of the electrical swivel 284 to a stationary electrical collar 286 mounted in the frame. The power receiving end collar 277 of the heating wand is affixed to and rotatably contacts the electrical collar 286 whereby the wand 276 may be energized to heat and cure the radiation barrier material during simultaneous rotation of the pre-manufactured shell 250 about two mutually perpendicular axes. Fluids generated during waste casting are removed from the shell by the shell drain 190 which continues through the swivel and a drain conduit 288 to a fluid swivel 290 axially aligned with the right hand frame support bearing. A vacuum pump, not shown, facilitates drainage of excess liquids during casting. The winding apparatus shown with the first described embodiment of the invention is not strictly necessary but may optionally be provided with the second (FIG. 9) embodiment since the FIG. 9 embodiment provides a pre-formed shell which has enough impact resistance for structurally supporting the monolith and provides a means of casting additional radiation shielding material inside the shell if needed. Persons skilled in the art will readily appreciate that various modifications can be made from the preferred embodiment thus the scope of protection is intended to be defined only by the limitations of the appended claims. |
abstract | The present disclosure discloses a micro-nuclear battery. The micro-nuclear battery comprises a base frame comprising a bottom, a top and a side wall; a cantilever structure having a free end hung in the air and a fixed end fixed to the side wall of the base frame and provided with a piezoelectric component thereon; and a radiation unit comprising an upper radioactive source and a lower radioactive source configured to emit electrons to the free end and respectively arranged at positions in inner surfaces on the top and the bottom of the base frame corresponding to the free end of the cantilever structure, wherein a width of the free end is greater than a width of the fixed end. |
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summary | ||
claims | 1. A system comprising:a first pole section;a second pole section coupled to the first pole section;a tubular female end portion on an end of the first pole section and including a pair of connecting slots;a male end portion on an end of the second pole section, the male end portion insertable into the female end portion and having a connecting pin extending therethrough, opposing ends of the connecting pin insertable into the connecting slots and radially transitionable to a hook section of the respective connecting slots;a locking nut threadingly engaged with the male end portion, the locking nut rotatable to longitudinally transition the locking nut into contact with the female end portion to retain the connecting pins in the hook section of the respective connecting slots to fixedly couple the male end portion with the female end portion; anda biased locking sleeve assembly slidably and rotatably mounted on a locking assembly portion of the second pole, the locking sleeve assembly including,a locking sleeve having a collar portion and neck portion;a plunger slidingly positioned within an interior of the collar portion; anda biasing device located within the interior of the collar portion, between the neck portion and the plunger, for forcing the plunger against the locking nut to prevent rotation thereof,the neck portion including at least one retraction slot selectively engageable with a locking sleeve retaining pin on the second pole section to place the locking sleeve in an unlocked position and allow rotation of the locking nut. 2. The system of claim 1, wherein,the locking sleeve neck portion comprises a plurality of locking slots engageable with a locking sleeve retaining pin extending through the locking assembly portion to place the locking sleeve in a locked position, andif the locking sleeve is in the locked position, the biasing device exerts a locking load on the locking nut, via the plunger, sufficient to inhibit rotation of the locking nut that would otherwise allow the locking nut to longitudinally transition away from the female end portion and allow the opposing ends of the connecting pin to radially transition from the hook section to a backbone section of the connecting slots to allow separation of the male and female end portions. 3. The system of claim 2,wherein the load on the locking nut, via the biasing device and plunger, is reduced to allow rotation of the locking nut and separation of the male and female end portions, when the locking sleeve is in the unlocked position. 4. The system of claim 3, wherein the locking slots comprise slots radially located within an interior surface of a distal end portion of the locking sleeve neck portion and the locking sleeve retaining pin extends through the locking assembly portion such that opposing ends of the retaining pin are insertable into the locking slots to retain the locking sleeve in the locked position. 5. The system of claim 4, wherein the retraction slots comprise a pair of opposing slots formed in the interior surface of the distal end portion of the locking sleeve neck portion such that the opposing ends of the retaining pin are insertable into the retraction slots to retain the locking sleeve in the unlocked position, the retraction slots having a greater longitudinal length than the locking slots. 6. The system of claim 5, further comprising:a protection sleeve mounted on the locking assembly portion, the protection sleeve including a protective hood that extends over the retaining pin and is sized to receive the locking sleeve neck portion. 7. The system of claim 6, wherein the locking sleeve neck portion comprises an alignment indicator on an exterior surface of the neck portion indicative of the location of the retraction slots formed in the interior surface of the neck portion. 8. The system of claim 2, wherein the locking slots have a length sized to position a distal end of the locking sleeve collar portion in close proximity to the locking nut when the locking sleeve is in the locked position such that when the locking nut is rotated to longitudinally transition the locking nut toward the locking sleeve, the locking nut will abut the distal end of the locking sleeve collar portion preventing the locking nut from longitudinally transitioning a sufficient distance to allow separation of the male and female end portions. 9. A system comprising:a first pole section;a second pole section coupled to the first pole section;a tubular female end portion on an end of the first pole section, the tubular female end portion including a pair of opposing substantially J-shaped connecting slots, each having a backbone section open at a distal end of the female end portion;a male end portion on an end of the second pole section, the male end portion having a connecting pin extending therethrough, the male end portion insertable into the female end portion such that opposing ends of the connecting pin are insertable into the backbone sections of the connecting slots and radially transitionable to a hook section of the respective connecting slots;a locking nut threadingly engaged with the male end portion at a proximal end of the male end portion, the locking nut rotatable to longitudinally transition the locking nut into contact with the female end portion such that the connecting pin ends are retained in the hook sections of the connecting slots to fixedly interlock the male end portion with the female end portion;a locking sleeve retaining pin extending through a locking sleeve assembly portion of the second pole between the locking nut and a proximal end of the locking sleeve assembly portion; anda biased locking sleeve assembly slidably and rotatably mounted on the locking sleeve assembly portion between the locking nut and the locking sleeve retaining pin, the locking sleeve assembly including,a locking sleeve having a collar portion and neck portion;a plunger slidingly positioned within an interior of the collar portion; anda biasing device located within the interior of the collar portion, between the neck portion and the plunger, for forcing the plunger against the locking nut to prevent rotation thereof,the neck portion including at least one retraction slot selectively engageable with a locking sleeve retaining pin on the second pole section to place the locking sleeve in an unlocked position and allow rotation of the locking nut. 10. The system of claim 9, wherein the locking sleeve neck portion comprises a plurality of locking slots engageable with the locking sleeve retaining pin to place the locking sleeve in a locked position, andwherein the biasing device exerts a locking load on the locking nut, via the plunger, sufficient to prevent or considerably inhibit rotation of the locking nut and separation of the locking nut and female end portion when the locking nut has been transitioned into contact with the female end portion and moved the connecting pin into the hook sections of the connecting slots, when the locking sleeve is in the locked position. 11. The system of claim 10, wherein the load on the locking nut, via the biasing device and plunger, is reduced to allow rotation of the locking nut and separation of the male and female end portions, when the locking sleeve is in the unlocked position. 12. The system of claim 11, wherein the locking slots comprise slots radially located within an interior surface of a distal end portion of the locking sleeve neck portion and the locking sleeve retaining pin extends through the locking sleeve assembly portion between the locking sleeve and locking sleeve assembly portion proximal end such that opposing ends of the retaining pin are insertable into the locking slots to retain the locking sleeve in the locked position. 13. The system of claim 12, wherein the retraction slots comprise a pair of opposing slots formed in the interior surface of the distal end portion of the locking sleeve neck portion such that the opposing ends of the retaining pin are insertable into the retraction slots to retain the locking sleeve in the unlocked position, the retraction slots having a greater longitudinal length than the locking slots. 14. The system of claim 13, further comprising a protection sleeve mounted on the locking sleeve assembly portion, the protection sleeve including a protective hood that extends over the retaining pin and is sized to receive the locking sleeve neck portion. 15. The system of claim 14, wherein the locking sleeve neck portion comprises an alignment indicator on an exterior surface of the neck portion indicative of the location of the retraction slots formed in the interior surface of the neck portion. 16. The system of claim 10, wherein the locking slots have a length sized to position a distal end of the locking sleeve collar portion in close proximity to the locking nut when the locking sleeve is in the locked position such that when the locking nut is rotated to longitudinally transition the locking nut toward the locking sleeve, the locking nut will abut the distal end of the locking sleeve collar portion preventing the locking nut from longitudinally transitioning a sufficient distance to allow the connecting pin ends from moving out of the hook sections, thereby preventing separation of the male and female end portions. 17. The system of claim 9, wherein the first pole section comprise a tool that includes the tubular female end portion for having the male end portion inserted therein to fixedly interlock the male end portion with the tool. |
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description | The present invention concerns a nuclear reactor. In current practice nuclear reactors include a core, positioned in the lower part of the main vessel of the reactor, immersed in the primary fluid and formed of fuel elements supported by a supporting grid or suspended from the upper part. Reactor control rods are furthermore interposed between the fuel elements; exceptionally, in small-medium sized fast reactors, the control rods are positioned on the periphery of the core within the innermost crown of reflective/shielding elements. Generally the control rods are replaced by using the same replacement means used for replacement of the fuel elements and to avoid interference with said means it is necessary to disconnect them from their motor-drive element before refueling. In patent application GE2015A000036, with amphora-shaped hydraulic separation structure, the shielding element crowns are eliminated, but nothing is said about the positioning of the control rods and their management during refueling operations, therefore the methods of the current state of the art apply. An object of the present invention is to provide a nuclear reactor that overcomes the drawbacks highlighted of the known solutions and has further construction and safety advantages. The present invention therefore concerns a nuclear reactor, as defined in the attached claim 1, with ancillary characteristics and plant configurations defined in the dependent claims. With reference to FIG. 1, showing in particular a nuclear reactor 1 cooled by liquid metal or molten salts, the nuclear reactor 1 comprises a substantially cup- or pool-shaped vessel 2, a radially external fixed closing structure 3 and a radially internal mobile closing structure 4, positioned above the vessel 2 with the fixed closing structure 3 positioned radially on the outside and around the mobile closing structure 4. The mobile closing structure 4 is a component consisting of various elements such as a plurality of rotating plugs at the same time forming part of the fuel transfer means and the primary containment structures, known in the art and therefore not described in detail. The vessel 2 contains a core 5 and a hydraulic separation structure 6 delimiting a hot manifold 7 and a cold manifold 8 in which a primary cooling fluid F circulates for cooling the core 5. The primary fluid F has a free surface which in normal operation of the reactor 1 is at different levels H1, H2 in the manifolds 7,8. Inside the vessel 2, circulation pumps 9 are housed for circulating the primary fluid F, in addition to heat exchangers 10, through which the primary fluid F flows to transfer the power generated in the core 5 to a secondary fluid, and other components which are known and not illustrated. It is understood that the circulation pumps 9 of the primary fluid F and the heat exchangers 10 can also be positioned outside the vessel 2. The hydraulic separation structure 5 preferably has an amphoralike shape, according to the solution known from patent application GE2015A000036, and is suspended from the closure structure 3 of the vessel 2. The mobile closing structure 4 is positioned above the core 5 along a central axis of the reactor 1 and the fixed closing structure 3 is positioned, with reference to the central axis of the reactor 1, radially external to the mobile closing structure 4 and around the mobile closing structure 4, which is therefore radially internal to the radially external fixed closing structure 3. In other words, the mobile closing structure 4 and the fixed closing structure 3 are respectively radially internal and radially external with respect to the central axis of the reactor 1 and to the core 5. With reference also to FIGS. 2-5, the core 5 comprises a plurality of fuel elements 11 which have respective active parts 12 and respective service parts 13; in particular, the service part 13 of each fuel element 11 comprises a foot 14 and a head 15 respectively positioned at the bottom and at the top of the fuel element 11 and a connection shaft 16 connecting the active part 12 and the head 15. The heads 15 of the fuel elements 11 are circumferentially contained within the upper portion 17 of the separation structure 6 of which it constitutes the mechanical connection to the external fixed closing structure 3. The upper portion 17 of the separation structure 6 contains at the top also the internal mobile closing structure 4. The reactor is characterized by three distinct types of control rods 18a and shutdown rods 18b, 18c which are inserted in respective penetrations 19a, 19b, 19c of the external fixed closing structure 3 and are therefore located outside the internal mobile closing structure 4 and outside the upper portion 17 of the separation structure 6, and re-enter lower down in the separation structure 6 through respective ducts 20a, 20b, 20c engaging the radially wider lower portion 21 of said separation structure 6 and extend above the free level H2 of the cold manifold 8. The control rods 18a and shutdown rods 18b, 18c extend downwards in proximity of the core 5, with respective end portions 22a, 22b, 22c provided with respective absorbers 23a, 23b, 23c. The rods 18a perform the function of control of the reactor by means of motorized rotation around the axis A of the control mechanism 30a to bring respective absorbers 23a from a position 24 farther from the active part 12 of the core 5 to a position 25 of maximum proximity via intermediate positions 26. The rods 18b perform the function of shutdown of the reactor by means of translation along respective axes B to bring respective absorbers 23b from a higher position at maximum distance from the active part 12 of the core 5 to a position facing it at maximum proximity. Said translation along respective axes B can be performed by means of the control mechanism 30b with motorized movement or with release and gravitational fall according to known technologies. The rods 18c perform the function of shutdown of the reactor by means of translation along respective axes C to bring respective absorbers 23c from a lower position 26, facing the feet 14, at maximum distance from the active part 12 of the core 5, to a higher position 27 facing the active part 12 of the core 5 and at maximum proximity to it. The shutdown rods 18c, designed for application to reactors with high density primary coolant, are provided with a float 28 consisting of a cylindrical casing 29 containing gas inside it which, as the level H1 of the hot manifold 7 varies, determines the position of the absorber 23c with respect to the active part 12 of the core 5 in a condition of disconnection from the control mechanism 30c. With reference also to FIGS. 6a, 6b and 6c, the shutdown rod 18c is provided with a non-return device 31 consisting of a plurality of levers 32 which, forced by an elastic element 33, engage on the saw tooth-shaped internal profile 34 of the cylindrical duct 35 in which the shutdown rod 18c runs. A gripper 36, known in the art, belonging to a control device 30c, also known in the art, can translate along the axis C of the shutdown rod 18c and, by means of a longer stroke of the external bar 37 with respect to the internal bar 38 and an interaction of cams 39 and latches 40 of the control device 30c, engage on the head 41 of the shutdown rod 18c with the possibility of movement towards the top of the latter. With reference also to FIG. 6c, the continuation of the stroke of the external bar 37 with respect to the bar 38 internal to it allows the shaped end 42 of the gripper 36 to engage on the upper internal profile 43 of the levers 32, disengaging them from the saw tooth-shaped internal profile 34 of the cylindrical duct 35, also permitting controlled vertical sliding of the shutdown rod 18c. From the above, the advantages of the present invention are evident. The support of the control rods 18a and shutdown rods 18b and 18c on the outside of the mobile internal closing structure 4 and on the outside of the core 5 guarantees complete mechanical decoupling between the core 5 of the reactor and the control rods 18a and shutdown rods 18b and 18c and in particular the thermal expansions or swellings of the fuel elements subject to neutron irradiation do not interfere with the movement of the rods. Refuelling can be carried out without having to disconnect the control mechanisms 30a, 30b, 30c of the control rods 18a and shutdown rods 18b and 18c so that it is possible to move the mobile closing structure 4 which, in the traditional solutions, constitutes the support of the control rods. The control rods 18a and shutdown rods 18b and 18c do not occupy positions inside the core 5, which can consequently be reduced in diameter. The absence of structural material of the control and shutdown rods inside the core 5 allows reduction of the quantity of fissile material inside the core. The absence of positions intended for control and shutdown rods inside the core 5 reduces the heterogeneity of the core and the associated power and temperature gradients. The three systems of control rods 18a and shutdown rods 18b and 18c are differentiated from one another. The shutdown system 18c controlled by float allows shutdown of the core due to increase in the level H1 of the primary coolant following slow-down of the circulation pumps 9, whatever the cause, and therefore constitutes a particularly reliable and diversified passive shutdown system of the reactor in the presence of a reduction in the primary coolant flow rate. The shutdown system 18c controlled by float cannot be de-activated by a subsequent uncontrolled acceleration of the primary pumps 9 due to the non-return device 31 which can be de-activated only by restoring the mechanical connection between shutdown rod 18c and its control mechanism 30c. Lastly it is understood that numerous modifications and variations can be made to the reactor described and illustrated here that do not depart from the scope of the attached claims. |
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description | This patent application claims the benefit of priority under 35 U.S.C. §119 from Korean Patent Application No. 10-2013-0164738 filed Dec. 19, 2013, the contents of which are incorporated herein by reference. 1. Field of the Invention The present disclosure relates to a method for manufacturing oxide fuel pellets and oxide fuel pellets manufactured thereby. 2. Description of the Related Art Nuclear power generation uses heat generated by the nuclear fission. Oxide fuel pellets are put into a zirconium alloy cladding tube to seal each of both ends of the zirconium alloy cladding tube by welding, thereby manufacturing a fuel rod. Then, several fuel rods to several hundred fuel rods are bundled with each other to manufacture one assembly or bundle. The assembly or bundle may be fed into a light-water type power reactor or heavy-water type power reactor. Here, heat generated from the oxide fuel pellets is transferred into cooling water that flows around the fuel rods through the cladding tube via the oxide fuel pellets. A nuclear fuel may be prepared as cylindrical or globular oxide fuel pellets that are manufactured by compacting and sintering a single or mixed material of oxides such as uranium (U), plutonium (Pu), or thorium (Th). The oxide fuel pellets are generally formed of uranium dioxide (UO2). Alternatively, the oxide fuel pellets may be formed of a material that is prepared by adding at least one of other nuclear fuel materials such as oxides of Pu, Th, Gd, and Er to uranium dioxide (UO2). Particularly, the oxide fuel pellets may be formed of (U,Pu)O2, (U,Th)O2, (U,Gd)O2, (U,Er)O2, (U,Pu,Gd)O2, or (U,Th,Pu)O2. Uranium dioxide (UO2) pellets may be widely known as the nuclear fuel pellets. A method for manufacturing the uranium dioxide (UO2) pellets includes a process of adding and mixing a lubricant into/with uranium oxide powder that is used as a starting material to perform a preliminary compaction process at a pressure of about 1 ton/cm2, thereby manufacturing slug, a process of pulverizing the slug to produce granules, a process of adding and mixing a lubricant into/with the produced granules to perform a compression-compaction process, thereby manufacturing green pellets having a theoretical density (T.D) of about 50%, and a process of sintering the green pellets at a temperature of about 1,600° C. to about 1,800° C. for about 2 hours to about 4 hours under a hydrogen-containing gas atmosphere. The manufactured uranium dioxide pellets may have a density of about 95% of a theoretical density and a grain size of about 5 μm to about 25 μm. However, when the green pellets are sintered at a high temperature of about 1,600° C. or more under the hydrogen atmosphere as described above, the risk of explosion of hydrogen may be involved. Also, electricity may be excessively consumed due to the sintering at the high temperature, and thus, the above-described manufacturing process may be uneconomical. Also, in the low-temperature sintering method according to the related art, a method in which a sintering process is performed at a low temperature (about 1,400° C. or less) under an atmosphere in which a ratio of carbon dioxide/carbon monoxide is adjusted. However, in the low-temperature sintering method, it may be difficult to adjust the ratio of carbon dioxide/carbon monoxide, and thus it may be difficult to manufacture oxide fuel pellets that are adequate for nuclear fuel specification. Thus, while the inventors study methods for manufacturing oxide fuel pellets, the inventors have developed a method in which green pellets are manufactured by using nuclear fuel powder containing uranium dioxide (UO2), and the manufactured green pellets are sintered and reduced by using an atmosphere gas at a low-temperature of about 1,400° C. to manufacture oxide fuel pellets that are adequate for nuclear fuel specification. Embodiments of the present invention are directed to provide a method for manufacturing oxide fuel pellets and oxide fuel pellets manufactured thereby. According to an aspect of the present invention, there is provided a method for manufacturing oxide fuel pellets, the method including: (step 1) preparing nuclear fuel powder containing uranium dioxide (UO2+x, x=0 to 0.20); (step 2) compacting the nuclear fuel powder prepared in step 1 to manufacture green pellets; sintering the green pellets manufactured in step 2 at a temperature of about 1,200° C. to about 1,400° C. by using an atmosphere gas; and reducing the green pellets sintered in step 3 at a temperature of about 800° C. to about 1,000° C. by using a reducing atmosphere gas. According to another aspect of the present invention, there is provided oxide fuel pellets manufactured by the above-described method. The present invention provides a method for manufacturing oxide fuel pellets. The method for manufacturing the oxide fuel pellets includes a process (step 1) of preparing nuclear fuel powder containing uranium dioxide (UO2+x, x=0 to 0.20), a process (step 2) of compacting the nuclear fuel powder prepared in step 1 to manufacture green pellets, a process (step 3) of sintering the green pellets manufactured in step 2 at a temperature of about 1,200° C. to about 1,400° C. by using an atmosphere gas, and a process (step 4) of reducing the green pellets sintered in step 3 at a temperature of about 800° C. to about 1,000° C. by using a reducing atmosphere gas. The present invention provides a low-temperature sintering reduction method for adjusting the oxide fuel pellets, which are used as a nuclear fuel and fed into a nuclear power plant, to be adequate for nuclear fuel specification. The oxide fuel pellets that are adequate for the nuclear fuel specification may have a sintering density ranging from about 94.0% to about 96.5% of a theoretical density (T.D) and a grain size of about 5 μm to about 25 μm. Hereinafter, the method for manufacturing the oxide fuel pellets in each of the processes according to the present invention will be described in detail. First, in the method for manufacturing the oxide fuel pellets according to the present invention, step 1 may be a process of preparing nuclear fuel powder containing uranium dioxide (UO2+x, x=0 to 0.20). In step 1, nuclear fuel powder containing uranium dioxide manufactured in a wet or dry manner is prepared as a raw material for manufacturing the oxide fuel pellets. Particularly, in step 1, the nuclear fuel powder may be prepared by performing a pretreatment process. In one example of the pretreatment process of the nuclear fuel powder, to improve fluidity of the uranium dioxide (UO2+x, x=0 to 0.20) manufactured in a wet or dry manner, a preliminary compaction process is performed at a predetermined pressure (about 300 MPa or less) to form preliminary slug, and then, the slug passes through a granulator having a sieve with a diameter of about 1 mm or less to form granules having a particle size of about 1 mm or less. Since the nuclear fuel powder that is formed with the granules through the above-described pretreatment process has good fluidity, the granules having a predetermined particle size may be manufactured. Also, an amount of lubricant may be mixed with the granules to reduce frication between granules and friction between the granules and a die wall, thereby prevent cracks from occurring. Here, the nuclear fuel powder manufactured in step 1 may further contain gadolinia (Gd2O3) or plutonium oxide (PuO2). Although the nuclear fuel powder contains only the uranium dioxide to manufacture the uranium dioxide fuel pellets, if the nuclear fuel powder containing burnable poison such as gadolinia (Gd2O3) is used as described above, mixed oxide fuel pellets such as UO2—Gd2O3 may be manufactured. Also, when the nuclear fuel powder contains the nuclear fission material such as plutonium oxide (PuO2), mixed oxide fuel pellets such as UO2—PuO2 may be manufactured. Next, in the method for manufacturing the oxide fuel pellets according to the present invention, step 2 may be a process for compacting the nuclear fuel powder prepared in step 1 to manufacture the green pellets. Particularly, the process of manufacturing the green pellets in step 2 may be performed under a compaction pressure of about 100 MPa to about 500 MPa. If the process of manufacturing the green pellets in step 2 is performed under a compaction pressure of about 100 MPa or less, it may be difficult to deal with the green pellets due to their weak properties and obtain a sintering density that is used for the oxide fuel pellets. On the other hand, if the process of manufacturing the green pellets is performed under a compaction pressure of about 500 MPa or more, it may be difficult to manufacture the green pellets, involve the possibility of an occurrence of cracks, and increase a sintering density corresponding to the increase in the compaction pressure. The compaction in step 2 may be performed through the conventional method. The green pellets manufactured by the compaction process may have an annular, solid, or rectangular shape that is adequate for the following process. Next, in the method for manufacturing the oxide fuel pellets according to the present invention, step 3 may be a process for sintering the green pellets manufactured in step 2 at a temperature of about 1,200° C. to about 1,400° C. by using an atmosphere gas. To manufacture the oxide fuel pellets adequate from the nuclear fuel specification in the related art, the green pellets are sintered at a high temperature (about 1,600° C. or more) for two hours or more under a hydrogen atmosphere. However, when the green pellets are sintered at a high temperature under the hydrogen atmosphere as described above, the risk of explosion of hydrogen may be involved. Also, electricity may be excessively consumed due to the sintering at the high temperature, and thus, the above-described manufacturing process may be uneconomical. Also, in the low-temperature sintering method according to the related art, the sintering process is performed at a low temperature (about 1,400° C. or less) under an atmosphere in which a ratio of carbon dioxide/carbon monoxide is adjusted. However, in the low-temperature sintering method, it may be difficult to adjust the ratio of carbon dioxide/carbon monoxide, and thus it may be difficult to manufacture oxide fuel pellets that are adequate for the nuclear fuel specification. For this, in step 3, the green pellets are sintered at a temperature of about 1,200° C. to 1,400° C. by using the atmosphere gas. In step 4 that is the next process, the sintered green pellets are reduced by using the reducing atmosphere gas to manufacture the oxide fuel pellets that are adequate for the nuclear fuel specification. Particularly, the sintering in step 3 may be performed under a gas atmosphere of carbon dioxide, nitrogen, or argon. When the sintering in step 3 is performed under the oxidative gas atmosphere such as carbon dioxide or the inert gas atmosphere such as nitrogen or argon, since an O/U ratio of the uranium dioxide power manufactured in the wet or dry manner is about 2.15, excessive oxygen may exist. Thus, the excessive oxygen may promote the sintering to increase the sintering density and grain size. On the other hand, when the sintering in step 3 is performed under the hydrogen gas atmosphere, the existing excessive oxygen may be reduced and thus do not exist. Thus, to obtain the desired sintering density and grain size, the sintering may be performed at a high temperature of about 1600° C. or more. When the sintering is performed under the oxidative gas atmosphere such as the carbon dioxide (CO2) than the inert gas atmosphere such as nitrogen or argon, the gas atmosphere may be oxidized to further increase the sintering density and grain size. However, since the oxidative gas atmosphere such as the carbon dioxide causes global warming, when the sintering is performed by using nitrogen or argon, the sintering process may be environmentally friendly. Also, the sintering in step 3 may be performed for about 2 hours or more, more preferably, about 2 hours to about 8 hours. If when the sintering in step 3 is performed for about 2 hours or less, the manufactured oxide fuel pellets may not be suitable in grain size for the nuclear fuel specification. Next, in the method for manufacturing the oxide fuel pellets according to the present invention, step 4 may be a process for reducing the green pellets sintered in step 3 at a temperature of about 800° C. to about 1,000° C. by using a reducing atmosphere gas. Since the green pellets sintered in step 3 do not have an O/U ratio of about 2.00 that is required for the nuclear fuel specification, the green pellets may be reduced at a temperature of about 800° C. to about 1,000° C. by using the reducing gas atmosphere while being cooled after the sintering to reduce the green pellets into UO2. Thus, the UO2 oxide fuel pellets may be manufactured from UO2+x through the reduction process. As the reduction in step 4 is performed, high-quality UO2 oxide fuel pellets without having cracks may be manufactured. Here, since the manufactured UO2 oxide fuel pellets have an O/U ratio of about 2.0, the UO2 oxide fuel pellets may be superior in quality. Although the reduction in step 4 is performed at the temperature of about 800° C. to about 1,000° C. for about 1 hour to about 5 hours, the present invention is not limited thereto. The sintering and reduction in steps 3 and 4 may be continuously performed. That is, after the sintering in step 3 is performed, a hydrogen gas may be injected to convert the gas atmosphere into the reducing atmosphere. Thus, the sintering and reduction may be continuously performed without intermission. Here, when the sintering is performed under the atmosphere gas such as carbon dioxide, nitrogen, or argon, the hydrogen gas may be immediately injected to create the reducing atmosphere. In an example of the sintering and reduction processes according to the present invention, as schematically illustrated in FIG. 1, the method for manufacturing the oxide fuel pellets according to the present invention performs the low-temperature sintering process at a temperature of about 1,200° C. to 1,400° C. under the activated gas atmosphere or inert gas atmosphere to convert the gas atmosphere into the reducing gas atmosphere while performing the cooling process, thereby performing the reduction process at a temperature of about 800° C. to about 1,000° C. As a result, the oxide fuel pellets that are adequate for the nuclear fuel specification may be manufactured. Also, the present invention may provide the oxide fuel pellets manufactured by the above-described method. The oxide fuel pellets manufactured according to the present invention may be suitable for the oxide fuel pellets that are adequate for the nuclear fuel specification. In the related art, to manufacture the oxide fuel pellets that are adequate for the nuclear fuel specification, the oxide fuel pellets may be sintered at a high temperature (about 1,600° C. or more) for about 2 hours or more under the hydrogen atmosphere or may be sintered at a low temperature (about 1,400° C. or less) under an atmosphere in which a ratio of carbon dioxide/carbon monoxide is adjusted. However, the manufacturing methods may have low economic feasibility and stability, and it may be difficult to adjust the ratio of the atmosphere gas. On the other hand, the oxide fuel pellets manufactured by the above-described method according to the present invention may be sintered at a temperature of about 1,200° C. to about 1,400° C. to solve the above-described low economic feasibility and stability. Also, since the oxide fuel pellets are manufactured under the single gas atmosphere, the manufacturing process may be easy. Here, the oxide fuel pellets may have a density ranging from about 94.0% to about 96.5% of a theoretical density (T.D) and a grain size of about 5 μm to about 25 μm. Thus, the oxide fuel pellets may be suitable for the oxide fuel pellets that are adequate for the nuclear fuel specification. Hereinafter, following embodiments and experimental examples according to the present invention will be described in detail. However, the following embodiments and experimental examples may be exemplified merely as illustrative purpose, and thus the technical scope of the present invention is not limited thereto. Step 1: Natural uranium dioxide powder (ex-ADU UO2, specific surface area: 5.72 m2/g, O/U ratio: 2.13) manufactured in a wet manner was prepared. Step 2: The uranium dioxide prepared in step 1 may be pressed at a pressure of about 150 MPa by using a hydraulic press to manufacture green pellets. Here, each of the green pellets has a diameter of about 10.0 mm, a length of about 10 mm, and a weight of about 3.6 g to about 4.5 g. Also, the green pellet has a density of about 42% to about 43%. Step 3: The green pellets manufactured in step 2 were sintered at a temperature of about 1,200° C. with a heating rate of about 4° C./minute for about 2 hours under a carbon dioxide (CO2) atmosphere. Step 4: After step 3 is performed, the green pellets were cooled up to a temperature of about 1,000° C. with a cooling rate of about 4° C./minute, and then the carbon dioxide was replaced with a hydrogen gas to perform a reduction process for 2 hours to manufacture oxide fuel pellets. The same process as Embodiment 1 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 1 was performed to manufacture oxide fuel pellets. When the green pellets are manufactured at the pressure of about 300 MPa, a green density was about 48% to about 49% of the theoretical density. The same process as Embodiment 1 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 1 was performed to manufacture oxide fuel pellets. When the green pellets are manufactured at the pressure of about 450 MPa, a green density was about 52% to about 53% of the theoretical density. The same process as Embodiment 1 except that the green pellets are sintered for about 5 hours in step 3 of Embodiment 1 was performed to manufacture oxide fuel pellets. The same process as Embodiment 4 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 4 was performed to manufacture oxide fuel pellets. The same process as Embodiment 4 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 4 was performed to manufacture oxide fuel pellets. The same process as Embodiment 1 except that the green pellets are sintered at a temperature of about 1,300° C. in step 3 of Embodiment 1 was performed to manufacture oxide fuel pellets. The same process as Embodiment 7 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 7 was performed to manufacture oxide fuel pellets. The same process as Embodiment 7 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 7 was performed to manufacture oxide fuel pellets. The same process as Embodiment 7 except that the green pellets are sintered for about 5 hours in step 3 of Embodiment 7 was performed to manufacture oxide fuel pellets. The same process as Embodiment 10 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 10 was performed to manufacture oxide fuel pellets. The same process as Embodiment 10 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 10 was performed to manufacture oxide fuel pellets. The same process as Embodiment 1 except that the green pellets are sintered at a temperature of about 1,400° C. in step 3 of Embodiment 1 was performed to manufacture oxide fuel pellets. The same process as Embodiment 13 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 13 was performed to manufacture oxide fuel pellets. The same process as Embodiment 13 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 13 was performed to manufacture oxide fuel pellets. The same process as Embodiment 13 except that the green pellets are sintered for about 5 hours in step 3 of Embodiment 13 was performed to manufacture oxide fuel pellets. The same process as Embodiment 16 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 16 was performed to manufacture oxide fuel pellets. The same process as Embodiment 16 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 16 was performed to manufacture oxide fuel pellets. The same process as Embodiment 1 except that the green pellets are not sintered under carbon dioxide (CO2) atmosphere, but sintered under an argon (Ar) atmosphere in step 3 of Embodiment 1 was performed to manufacture oxide fuel pellets. The same process as Embodiment 19 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 19 was performed to manufacture oxide fuel pellets. The same process as Embodiment 19 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 19 was performed to manufacture oxide fuel pellets. The same process as Embodiment 19 except that the green pellets are sintered for about 5 hours in step 3 of Embodiment 19 was performed to manufacture oxide fuel pellets. The same process as Embodiment 22 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 22 was performed to manufacture oxide fuel pellets. The same process as Embodiment 22 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 22 was performed to manufacture oxide fuel pellets. The same process as Embodiment 19 except that the green pellets are sintered at a temperature of about 1,300° C. in step 3 of Embodiment 19 was performed to manufacture oxide fuel pellets. The same process as Embodiment 25 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 25 was performed to manufacture oxide fuel pellets. The same process as Embodiment 25 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 25 was performed to manufacture oxide fuel pellets. The same process as Embodiment 25 except that the green pellets are sintered for about 5 hours in step 3 of Embodiment 25 was performed to manufacture oxide fuel pellets. The same process as Embodiment 28 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 28 was performed to manufacture oxide fuel pellets. The same process as Embodiment 28 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 28 was performed to manufacture oxide fuel pellets. The same process as Embodiment 19 except that the green pellets are sintered at a temperature of about 1,400° C. in step 3 of Embodiment 19 was performed to manufacture oxide fuel pellets. The same process as Embodiment 31 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 31 was performed to manufacture oxide fuel pellets. The same process as Embodiment 31 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 31 was performed to manufacture oxide fuel pellets. The same process as Embodiment 31 except that the green pellets are sintered for about 5 hours in step 3 of Embodiment 31 was performed to manufacture oxide fuel pellets. The same process as Embodiment 34 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 34 was performed to manufacture oxide fuel pellets. The same process as Embodiment 34 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 34 was performed to manufacture oxide fuel pellets. The same process as Embodiment 1 except that the green pellets are not sintered under carbon dioxide (CO2) atmosphere, but sintered under a nitrogen (N2) atmosphere in step 3 of Embodiment 1 was performed to manufacture oxide fuel pellets. The same process as Embodiment 37 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 37 was performed to manufacture oxide fuel pellets. The same process as Embodiment 37 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 37 was performed to manufacture oxide fuel pellets. The same process as Embodiment 37 except that the green pellets are sintered for about 5 hours in step 3 of Embodiment 37 was performed to manufacture oxide fuel pellets. The same process as Embodiment 40 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 40 was performed to manufacture oxide fuel pellets. The same process as Embodiment 40 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 40 was performed to manufacture oxide fuel pellets. The same process as Embodiment 37 except that the green pellets are sintered at a temperature of about 1,300° C. in step 3 of Embodiment 37 was performed to manufacture oxide fuel pellets. The same process as Embodiment 43 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 43 was performed to manufacture oxide fuel pellets. The same process as Embodiment 43 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 43 was performed to manufacture oxide fuel pellets. The same process as Embodiment 43 except that the green pellets are sintered for about 5 hours in step 3 of Embodiment 43 was performed to manufacture oxide fuel pellets. The same process as Embodiment 46 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 46 was performed to manufacture oxide fuel pellets. The same process as Embodiment 46 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 46 was performed to manufacture oxide fuel pellets. The same process as Embodiment 37 except that the green pellets are sintered at a temperature of about 1,400° C. in step 3 of Embodiment 37 was performed to manufacture oxide fuel pellets. The same process as Embodiment 49 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 49 was performed to manufacture oxide fuel pellets. The same process as Embodiment 49 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 49 was performed to manufacture oxide fuel pellets. The same process as Embodiment 49 except that the green pellets are sintered for about 5 hours in step 3 of Embodiment 49 was performed to manufacture oxide fuel pellets. The same process as Embodiment 52 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Embodiment 52 was performed to manufacture oxide fuel pellets. The same process as Embodiment 52 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Embodiment 52 was performed to manufacture oxide fuel pellets. The same process as Embodiment 1 except that the green pellets are sintered at a temperature of about 1,000° C. in step 3 of Embodiment 1 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 1 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 1 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 1 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 1 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 1 except that the green pellets are sintered for about 5 hours in step 3 of Comparative Example 1 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 4 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 4 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 4 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 4 was performed to manufacture oxide fuel pellets. The same process as Embodiment 1 except that the green pellets are sintered at a temperature of about 1,100° C. in step 3 of Embodiment 1 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 7 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 7 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 7 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 7 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 7 except that the green pellets are sintered for about 5 hours in step 3 of Comparative Example 7 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 10 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 10 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 10 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 10 was performed to manufacture oxide fuel pellets. The same process as Embodiment 19 except that the green pellets are sintered at a temperature of about 1,000° C. in step 3 of Embodiment 19 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 13 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 13 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 13 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 13 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 13 except that the green pellets are sintered for about 5 hours in step 3 of Comparative Example 13 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 16 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 16 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 16 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 16 was performed to manufacture oxide fuel pellets. The same process as Embodiment 19 except that the green pellets are sintered at a temperature of about 1,100° C. in step 3 of Embodiment 19 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 19 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 19 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 19 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 19 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 19 except that the green pellets are sintered for about 5 hours in step 3 of Comparative Example 19 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 22 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 22 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 22 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 22 was performed to manufacture oxide fuel pellets. The same process as Embodiment 37 except that the green pellets are sintered at a temperature of about 1,000° C. in step 3 of Embodiment 37 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 25 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 25 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 25 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 25 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 25 except that the green pellets are sintered for about 5 hours in step 3 of Comparative Example 25 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 28 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 28 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 28 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 28 was performed to manufacture oxide fuel pellets. The same process as Embodiment 37 except that the green pellets are sintered at a temperature of about 1,100° C. in step 3 of Embodiment 37 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 31 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 31 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 31 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 31 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 31 except that the green pellets are sintered for about 5 hours in step 3 of Comparative Example 31 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 34 except that the uranium dioxide powder is pressed at a pressure of about 300 MPa by using the hydraulic press in step 2 of Comparative Example 34 was performed to manufacture oxide fuel pellets. The same process as Comparative Example 34 except that the uranium dioxide powder is pressed at a pressure of about 450 MPa by using the hydraulic press in step 2 of Comparative Example 34 was performed to manufacture oxide fuel pellets. TABLE 1AtmosphereTemperaturePressureClassificationgas(° C.)(MPa)TimeEmbodiment 1Carbon12001502Embodiment 2dioxide300Embodiment 3(CO2)450Embodiment 41505Embodiment 5300Embodiment 6450Embodiment 713001502Embodiment 8300Embodiment 9450Embodiment 101505Embodiment 11300Embodiment 12450Embodiment 1314001502Embodiment 14300Embodiment 15450Embodiment 161505Embodiment 17300Embodiment 18450 TABLE 2AtmosphereTemperaturePressureClassificationgas(° C.)(MPa)TimeEmbodiment 19Argon12001502Embodiment 20(Ar)300Embodiment 21450Embodiment 221505Embodiment 23300Embodiment 24450Embodiment 2513001502Embodiment 26300Embodiment 27450Embodiment 281505Embodiment 29300Embodiment 30450Embodiment 3114001502Embodiment 32300Embodiment 33450Embodiment 341505Embodiment 35300Embodiment 36450 TABLE 3AtmosphereTemperaturePressureClassificationgas(° C.)(MPa)TimeEmbodiment 37Nitrogen12001502Embodiment 38(N2)300Embodiment 39450Embodiment 401505Embodiment 41300Embodiment 42450Embodiment 4313001502Embodiment 44300Embodiment 45450Embodiment 461505Embodiment 47300Embodiment 48450Embodiment 4914001502Embodiment 50300Embodiment 51450Embodiment 521505Embodiment 53300Embodiment 54450 TABLE 4AtmosphereTemperaturePressureClassificationgas(° C.)(MPa)TimeComparativeCarbon10001502Example 1dioxideComparative(CO2)300Example 2Comparative450Example 3Comparative1505Example 4Comparative300Example 5Comparative450Example 6Comparative11001502Example 7Comparative300Example 8Comparative450Example 9Comparative1505Example 10Comparative300Example 11Comparative450Example 12ComparativeArgon10001502Example 13(Ar)Comparative300Example 14Comparative450Example 15Comparative1505Example 16Comparative300Example 17Comparative450Example 18Comparative11001502Example 19Comparative300Example 20Comparative450Example 21Comparative1505Example 22Comparative300Example 23Comparative450Example 24ComparativeNitrogen10001502Example 25(N2)Comparative300Example 26Comparative450Example 27Comparative1505Example 28Comparative300Example 29Comparative450Example 30Comparative11001502Example 31Comparative300Example 32Comparative450Example 33Comparative1505Example 34Comparative300Example 35Comparative450Example 36 (1) Analysis of Sintering Density and Grain Size of Oxide Fuel Pellet Depending on Sintering Under Carbon Dioxide Atmosphere To confirm the sintering density and grain size of the oxide fuel pellets manufactured by the manufacturing method according to the present invention, sintering densities of the oxide fuel pellets manufactured in Embodiments 1 to 18 and Comparative Examples 1 to 12 were measured in an immersion method, grain sizes were measured in the Heyn's lineal intercept (ASTM E112) method, and their results were illustrated in FIGS. 2 to 4. As illustrated in FIGS. 2 and 3, the oxide fuel pellets that are adequate for the nuclear fuel specification has a sintering density ranging from about 94.0% to about 96.5% of a theoretical density (T.D), and manufacturing conditions of the oxide fuel pellets having a density within the above-described sintering density range are as follows. When a sintering time is about 2 hours, a compaction pressure is about 400 MPa or more in case of a sintering temperature of about 1,000° C., a compaction pressure is about 280 MPa or more in case of a sintering temperature of about 1,100° C., a compaction pressure is about 210 MPa or more in case of a sintering temperature of about 1,200° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,300° C., and a compaction pressure is about 420 MPa or less in case of a sintering temperature of about 1,400° C. Also, when a sintering time is about 5 hours, a compaction pressure is about 300 MPa or more in case of a sintering temperature of about 1,000° C., a compaction pressure is about 210 MPa or more in case of a sintering temperature of about 1,100° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,200° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,300° C., and a compaction pressure is about 250 MPa or less in case of a sintering temperature of about 1,400° C. Further, as illustrated in FIG. 4, it was confirmed that the oxide fuel pellets that are adequate for the nuclear fuel specification has a grain size of about 5 μm or more, and manufacturing conditions of the oxide fuel pellets having a grain size within the above-described grain size range are as follows: a temperature of about 1,200° C. or more and a sintering time of about 2 hours or more. Here, it was confirmed that the compaction pressure has a slight influence on the grain size. As described above, conditions adequate for manufacturing the oxide nuclear fuel pellets, that are adequate for the nuclear fuel specification, having the conditions in which the theoretical density (T.D) of about 94.0% to about 96.5% and the grain size of about 5 μm or more are as follows. When a sintering time is about 2 hours, a compaction pressure is about 210 MPa or more in case of a sintering temperature of about 1,200° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,300° C., and a compaction pressure is about 420 MPa or less in case of a sintering temperature of about 1,400° C. When a sintering time is about 5 hours, a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,200° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,300° C., and a compaction pressure is about 250 MPa or less in case of a sintering temperature of about 1,400° C. (2) Analysis of Sintering Density and Grain Size of Oxide Fuel Pellet Depending on Sintering Under Argon Atmosphere To confirm the sintering density and grain size of the oxide fuel pellets manufactured by the manufacturing method according to the present invention, sintering densities of the oxide fuel pellets manufactured in Embodiments 19 to 36 and Comparative Examples 13 to 24 were measured in an immersion method, grain sizes were measured in the Heyn's lineal intercept (ASTM E112) method, and their results were illustrated in FIGS. 5 to 7. As illustrated in FIGS. 5 and 6, the oxide fuel pellets that are adequate for the nuclear fuel specification has a sintering density ranging from about 94.0% to about 96.5% of a theoretical density (T.D), and manufacturing conditions of the oxide fuel pellets having a density within the sintering density range are as follows. A sintering time is about 2 hours, a compaction pressure is about 370 MPa or more in case of a sintering temperature of about 1,000° C., a compaction pressure is about 220 MPa or more in case of a sintering temperature of about 1,100° C., a compaction pressure is about 220 MPa or more in case of a sintering temperature of about 1,200° C., and a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,300° C. Also, when a sintering time is about 5 hours, a compaction pressure is about 270 MPa or more in case of a sintering temperature of about 1,000° C., a compaction pressure is about 170 MPa or more in case of a sintering temperature of about 1,100° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,200° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,300° C., and a compaction pressure is about 300 MPa or less in case of a sintering temperature of about 1,400° C. Further, as illustrated in FIG. 7, it was confirmed that the oxide fuel pellets that are adequate for the nuclear fuel specification has a grain size of about 5 μm or more, and manufacturing conditions of the oxide fuel pellets having a grain size within the above-described grain size range are as follows: a temperature of about 1,200° C. or more and a sintering time of about 2 hours or more. Here, it was confirmed that the compaction pressure has a slight influence on the grain size. As described above, conditions adequate for manufacturing the oxide nuclear fuel pellets, that are adequate for the nuclear fuel specification, having the conditions in which the theoretical density (T.D) of about 94.0% to about 96.5% and the grain size of about 5 μm or more are as follows. When a sintering time is about 2 hours, a compaction pressure is about 200 MPa or more in case of a sintering temperature of about 1,200° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,300° C., and a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,400° C. When a sintering time is about 5 hours, a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,200° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,300° C., and a compaction pressure is about 300 MPa or less in case of a sintering temperature of about 1,400° C. (3) Analysis of Sintering Density and Grain Size of Oxide Fuel Pellet Depending on Sintering Under Nitrogen Atmosphere To confirm the sintering density and grain size of the oxide fuel pellets manufactured by the manufacturing method according to the present invention, sintering densities of the oxide fuel pellets manufactured in Embodiments 37 to 54 and Comparative Examples 25 to 36 were measured in an immersion method, grain sizes were measured in the Heyn's lineal intercept (ASTM E112) method, and their results were illustrated in FIGS. 8 to 10. As illustrated in FIGS. 8 and 9, the oxide fuel pellets that are adequate for the nuclear fuel specification has a sintering density ranging from about 94.0% to about 96.5% of a theoretical density (T.D), and manufacturing conditions of the oxide fuel pellets having a density within the sintering density range are as follows. A sintering time is about 2 hours, a compaction pressure is about 350 MPa or more in case of a sintering temperature of about 1,000° C., a compaction pressure is about 200 MPa or more in case of a sintering temperature of about 1,100° C., a compaction pressure is about 190 MPa or more in case of a sintering temperature of about 1,200° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,300° C., and a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,400° C. Also, when a sintering time is about 5 hours, a compaction pressure is about 270 MPa or more in case of a sintering temperature of about 1,000° C., a compaction pressure is about 190 MPa or more in case of a sintering temperature of about 1,100° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,200° C., a compaction pressure is about 190 MPa or more in case of a sintering temperature of about 1,300° C., and a compaction pressure is about 320 MPa or less in case of a sintering temperature of about 1,400° C. Further, as illustrated in FIG. 10, it was confirmed that the oxide fuel pellets that are adequate for the nuclear fuel specification has a grain size of about 5 μm or more, and manufacturing conditions of the oxide fuel pellets having a grain size within the above-described grain size range are as follows: a temperature of about 1,200° C. or more and a sintering time of about 2 hours or more. Here, it was confirmed that the compaction pressure has a slight influence on the grain size. As described above, conditions adequate for manufacturing the oxide nuclear fuel pellets, that are adequate for the nuclear fuel specification, having the conditions in which the theoretical density (T.D) of about 94.0% to about 96.5% and the grain size of about 5 μm or more are as follows. When a sintering time is about 2 hours, a compaction pressure is about 190 MPa or more in case of a sintering temperature of about 1,200° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,300° C., and a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,400° C. When a sintering time is about 5 hours, a compaction pressure is about 190 MPa or more in case of a sintering temperature of about 1,200° C., a compaction pressure is about 150 MPa or more in case of a sintering temperature of about 1,300° C., and a compaction pressure is about 320 MPa or less in case of a sintering temperature of about 1,400° C. In the method for manufacturing the oxide fuel pellets according to the present invention, the sintering may be performed at a low temperature of about 1,200° C. to about 1,400° C. to manufacture the economical and safe oxide fuel pellets that are adequate for the nuclear fuel specification. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. |
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claims | 1. A filter for use in adjusting a spectrum of passing radiation, said filter comprising:a support plate having an aperture for passage therethrough of radiation, the support plate being disc-shaped and having a circumference;a plurality of filter plates supported by the support plate within the circumference and having mutually different filter characteristics; anda moving device configured to selectively move the plurality of filter plates to a first position to close the aperture and a second position to open the aperture, the moving device configured to bias the plurality of filter plates to the second position and to extend the plurality of filter plates radially inwardly toward the first position. 2. A filter according to claim 1, wherein the moving device comprises:a spring device configured to operate the plurality of filter plates in a direction away from the aperture;a plurality of ratchet plates supported by the support plate in proximity to the plurality of filter plates, each of the plurality of ratchet plates comprising a notched portion;a first support point positioned to pivotably support the plurality of filter plates on the support plate;a second support point positioned to pivotably support the plurality of ratchet plates on the support plate;a leaf spring connected to the plurality of filter plates and the plurality of ratchet plates, the leaf spring configured to cause the plurality of filter plates and the plurality of ratchet plates to pivot interlockedly with each other; anda pawl engageable with the notched portion of each of the plurality of ratchet plates, the pawl configured to move in order to pivot the plurality of ratchet plates, thereby making the plurality of filter plates movable to the first position to close the aperture. 3. A filter according to claim 2, wherein the support plate is formed with the aperture at a center thereof. 4. A filter according to claim 2, further comprising a ring configured to rotate along the circumference of the support plate, the ring comprising the pawl. 5. A filter according to claim 1, wherein the support plate comprises a top layer and a bottom layer parallel to each other, and the plurality of filter plates are supported by the top layer and the bottom layer. 6. A filter according to claim 5, wherein the support plate is formed with the aperture at a center thereof. 7. A filter according to claim 5, further comprising a ring configured to rotate along the circumference of the support plate, the ring comprising a pawl. 8. A filter according to claim 1, wherein the support plate is formed with the aperture at a center thereof. 9. A filter according to claim 8, further comprising a ring configured to rotate along the circumference of the support plate, the ring comprising a pawl. 10. A filter according to claim 1, further comprising a ring configured to rotate along the circumference of the support plate, the ring comprising a pawl. 11. An X-ray imaging system for use in radiographing a subject with X-ray passing through a filter, the X-ray imaging system comprising:an X-ray irradiator; anda filter positioned with respect to the X-ray irradiator, the filter comprising:a support plate having an aperture for passage therethrough of radiation, the support plate being disc-shaped and having a circumference;a plurality of filter plates supported by the support plate within the circumference and having mutually different filter characteristics; anda moving device configured to selectively move the plurality of filter plates to a first position to close the aperture and a second position to open the aperture, the moving device configured to bias the plurality of filter plates to the second position and to extend the plurality of filter plates radially inwardly toward the first position. 12. An X-ray imaging system according to claim 11, wherein the moving device comprises:a spring device configured to operate the plurality of filter plates in a direction away from the aperture;a plurality of ratchet plates supported by the support plate in proximity to the plurality of filter plates, each of the plurality of ratchet plates comprising a notched portion;a first support point positioned to pivotably support the plurality of filter plates on the support plate;a second support point positioned to pivotably support the plurality of ratchet plates on the support plate;a leaf spring connected to the plurality of filter plates and the plurality of ratchet plates, the leaf spring configured to cause the plurality of filter plates and the plurality of ratchet plates to pivot interlockedly with each other; anda pawl engageable with the notched portion of each of the plurality of ratchet plates, the pawl configured to move in order to pivot the plurality of ratchet plates, thereby making the plurality of filter plates movable to the first position to close the aperture. 13. An X-ray imaging system according to claim 12, wherein the support plate is formed with the aperture at a center thereof. 14. An X-ray imaging system according to claim 12, wherein the filter further comprises a ring configured to rotate along the circumference of the support plate, the ring comprising the pawl. 15. An X-ray imaging system according to claim 11, wherein the support plate comprises a top layer and a bottom layer parallel to each other, and the plurality of filter plates are supported by the top layer and the bottom layer. 16. An X-ray imaging system according to claim 15, wherein the support plate is formed with the aperture at a center thereof. 17. An X-ray imaging system according to claim 15, wherein the filter further comprises a ring configured to rotate along the circumference of the support plate, the ring comprising a pawl. 18. An X-ray imaging system according to claim 11, wherein the support plate is formed with the aperture at a center thereof. 19. An X-ray imaging system according to claim 18, wherein the filter further comprises a ring configured to rotate along the circumference of the support plate, the ring comprising a pawl. 20. An X-ray imaging system according to claim 11, wherein the filter further comprises a ring configured to rotate along the circumference of the support plate, the ring comprising a pawl. |
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summary | ||
claims | 1. A decoding method of maximum a posteriori probability for receiving and decoding encoded data obtained by encoding information of length N, characterized by comprising: performing a backward repetitive operation which is a repetitive operation from back to front in terms of time in order starting from the end of encoded data and, while this operation is being performed, saving first to m 1 th results of the backward repetitive operation that correspond to first to m 1 th items of encoded data; performing a forward repetitive operation which is a repetitive operation from front to back in terms of time in order from first to m 1 th items of encoded data and, while this operation is being performed, outputting first to m 1 th operational results as results of decoding; again performing a backward repetitive operation in order starting from the end of encoded data and, while this operation is being performed, saving (m 1 +1)th to m 2 th results of the backward repetitive operation; performing a forward repetitive operation in order from (m 1 +1)th to m 2 th items of encoded data and, while this operation is being performed, outputting (m 1 +1)th to m 2 th operational results as results of decoding; and subsequently outputting all results of decoding up to an Nth result in similar fashion. 2. A decoding method of maximum a posteriori probability for calculating a kth forward probability using first to kth items of encoded data obtained by encoding information of length N, obtaining a kth backward probability using Nth to kth items of encoded data, and outputting a kth decoded result using these probabilities, characterized by comprising: calculating backward probabilities in a reverse direction from an Nth backward probability to a first backward probability and saving an m 1 th backward probability to the first backward probability; calculating first forward probabilities, obtaining a first decoded result using the first forward probabilities and the first backward probabilities that have been saved and similarly obtaining second to m 1 th decoded results; subsequently calculating backward probabilities in the reverse direction from the Nth backward probability to an (m 1 +1)th backward probability and saving an m 2 th backward probability to the (m 1 +1)th backward probability; calculating (m 1 +1)th forward probabilities, obtaining an (m 1 +1)th decoded result using the (m 1 +1)th forward probabilities and the (m 1 +1)th backward probability that has been saved, and similarly obtaining (m 1 +2)th to m 2 th decoded results; and subsequently obtaining (m 2 +1)th to Nth decoded results. 3. A decoding method of maximum a posteriori probability for receiving and decoding encoded data obtained by encoding information of length N, characterized by comprising: performing a backward repetitive operation which is a repetitive operation from back to front in terms of time in order starting from the end of encoded data and, while this operation is being performed, saving first to m 1 th, m 2 th, m 3 th . . . results of the backward repetitive operation that correspond to first to m 1 th, m 2 th, m 3 th . . . items of encoded data; performing a forward repetitive operation which is a repetitive operation from front to back in terms of time in order from first to m 1 th items of encoded data and, while this operation is being performed, outputting first to m 1 th operational results as results of decoding; subsequently saving results while performing m 2 th to (m 1 +1)th backward repetitive operations utilizing said m 2 th result of the backward repetitive operation; performing a forward repetitive operation in order from (m 1 +1)th to m 2 th items of data and, while this operation is being performed, outputting (m 1 +1)th to m 2 th operational results as results of decoding; and subsequently outputting all results of decoding up to an Nth result in similar fashion. 4. A decoding method of maximum a posteriori probability for calculating a kth forward probability using first to kth items of encoded data obtained by encoding information of length N, obtaining a kth backward probability using Nth to kth items of encoded data, and outputting a kth decoded result using these probabilities, characterized by comprising: calculating backward probabilities in a reverse direction from an Nth backward probability to a first backward probability, discretely saving an m s th backward probability, m (sxe2x88x921) th backward probability, . . . , m 2 th backward probability and continuously saving an m 1 th backward probability to the first backward probability; calculating first forward probabilities, obtaining a first decoded result using the first forward probabilities and the first backward probabilities that have been saved and similarly obtaining second to m 1 th decoded results; subsequently calculating and saving backward probabilities up to an (m 1 +1)th backward probability starting from the m 2 th backward probability that has been saved; calculating (m 1 +1)th forward probabilities, obtaining an (m 1 +1)th decoded result using the (m 1 +1)th forward probabilities and the (m 1 +1)th backward probability that has been saved, and similarly obtaining (m 1 +2)th to m 2 th decoded results; and subsequently obtaining (m 2 +1)th to Nth decoded results. 5. A decoding method of maximum a posteriori probability according to claim 4 , characterized in that the number of backward probabilities saved continuously is about N xc2xd . claim 4 6. A decoder for calculating a kth forward probability using first to kth items of encoded data obtained by encoding information of length N, obtaining a kth backward probability using Nth to kth items of encoded data, and outputting a kth decoded result using these probabilities, characterized by comprising: a backward probability calculation unit for calculating backward probabilities; a backward probability saving unit for saving backward probabilities that have been calculated; a forward probability calculation unit for calculating forward probabilities; a decoded result calculation unit for obtaining a kth decoded result using a kth forward probability and a kth backward probability that has been saved; and a controller for controlling operation timings of said backward probability calculation unit, said forward probability saving unit and said decoded result calculation unit; wherein (1) said backward probability calculation unit calculates backward probabilities in a reverse direction from an Nth backward probability to a first backward probability and saves an m 1 th backward probability to first backward probability in said backward probability saving unit; said forward probability calculation unit calculates a first forward probability to an m 1 th forward probability; and said decoded result calculation unit calculates a kth decoded result using the kth forward probability (k=1 to m 1 ) that has been calculated and the kth backward probability that has been saved; (2) said backward probability calculation unit subsequently calculates backward probabilities in the reverse direction from the Nth backward probability to an (m 1 +1)th backward probability and saves an m 2 th backward probability to the (m 1 +1)th backward probability in said backward probability saving unit; said forward probability calculation unit calculates an (m 1 +1)th forward probability to an m 2 th forward probability; and said decoded result calculation unit calculates a kth decoded result using the kth forward probability (k=m 1 +1 to m 2 ) that has been calculated and the kth backward probability that has been saved and (3) subsequently similarly obtains (m 2 +1)th to Nth decoded results. 7. A decoder for calculating a kth forward probability using first to kth items of encoded data obtained by encoding information of length N, obtaining a kth backward probability using Nth to kth items of encoded data, and outputting a kth decoded result using these probabilities, characterized by comprising: a backward probability calculation unit for calculating backward probabilities; a backward probability saving unit for saving backward probabilities that have been calculated; a forward probability calculation unit for calculating forward probabilities; a decoded result calculation unit for obtaining a kth decoded result using a kth forward probability and a kth backward probability that has been saved; and a controller for controlling operation timings of said backward probability calculation unit, said forward probability saving unit and said decoded result calculation unit; wherein (1) said backward probability calculation unit calculates backward probabilities in a reverse direction from an Nth backward probability to a first backward probability, discretely saves an m s th backward probability, m (sxe2x88x921) th backward probability, . . . , m 2 th backward probability in said backward probability saving unit and continuously saves an m 1 th backward probability to the first backward probability; said forward probability calculation unit calculates a first forward probability to an m 1 th forward probability; and said decoded result calculation unit calculates a kth decoded result using the kth forward probability (k=1 to m 1 ) that has been calculated and the kth backward probability that has been saved; (2) said backward probability calculation unit subsequently calculates, and saves in said backward probability saving unit, backward probabilities up to an (m 1 +1)th backward probability starting from the m 2 th backward probability that has been saved; said forward probability calculation unit calculates an (m 1 +1)th forward probability to an m 2 th forward probability; and said decoded result calculation unit calculates a kth decoded result using the kth forward probability (k=m 1 +1 to m 2 ) that has been calculated and the kth backward probability that has been saved and (3) subsequently similarly obtains (m 2 +1)th to Nth decoded results. 8. A decoder according to claim 7 , characterized in that the number of backward probabilities saved continuously is about N xc2xd . claim 7 |
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description | The present application constitutes a continuation of U.S. patent application Ser. No. 14/201,386, entitled SYSTEMS, DEVICES, AND METHODS FOR LOWERING DENTAL X-RAY DOSAGE INCLUDING FEEDBACK SENSORS, naming Roderick A. Hyde, Edward K. Y. Jung, Jordin T. Kare, Tony S. Pan, Charles Whitmer, Lowell L. Wood, Jr. as inventors, filed 7, Mar., 2014, which is currently co-pending or is an application of which a currently co-pending application is entitled to the benefit of the filing date. If an Application Data Sheet (ADS) has been filed on the filing date of this application, it is incorporated by reference herein. Any applications claimed on the ADS for priority under 35 U.S.C. §§119, 120, 121, or 365(c), and any and all parent, grandparent, great-grandparent, etc. applications of such applications, are also incorporated by reference, including any priority claims made in those applications and any material incorporated by reference, to the extent such subject matter is not inconsistent herewith. The present application is related to and/or claims the benefit of the earliest available effective filing date(s) from the following listed application(s) (the “Priority Applications”), if any, listed below (e.g., claims earliest available priority dates for other than provisional patent applications or claims benefits under 35 USC §119(e) for provisional patent applications, for any and all parent, grandparent, great-grandparent, etc. applications of the Priority Application(s)). In addition, the present application is related to the “Related Applications,” if any, listed below. None If the listings of applications provided above are inconsistent with the listings provided via an ADS, it is the intent of the Applicant to claim priority to each application that appears in the Priority Applications section of the ADS and to each application that appears in the Priority Applications section of this application. All subject matter of the Priority Applications and the Related Applications and of any and all parent, grandparent, great-grandparent, etc. applications of the Priority Applications and the Related Applications, including any priority claims, is incorporated herein by reference to the extent such subject matter is not inconsistent herewith. In an aspect, the present disclosure is directed to, among other things, an intra-oral x-ray imaging system. In an embodiment, the intra-oral x-ray imaging system includes an intra-oral x-ray sensor configured to acquire intra-oral x-ray image information associated with a patient. In an embodiment, the intra-oral x-ray imaging system includes an x-ray beam limiter assembly including a controllable x-ray collimator module. In an embodiment, the controllable x-ray collimator module includes an x-ray beam collimation adjustment mechanism that is responsive to one or more inputs including information associated with a border position of the intra-oral sensor. In an embodiment, the intra-oral x-ray imaging system includes an x-ray beam limiter assembly configured to adjust an x-ray beam field of view. In an embodiment, the intra-oral x-ray imaging system includes an x-ray collimator module operably coupled to the intra-oral x-ray sensor and the x-ray beam limiter assembly. In an embodiment, the x-ray collimator module is configured to adjust an x-ray beam field of view responsive to one or more inputs including information associated with a border position of the intra-oral sensor. In an embodiment, the intra-oral x-ray imaging system includes an x-ray beam limiter assembly having one or more shutters (e.g., spring-loaded shutters, solenoid activated shutters, relay device activated shutters, electro-mechanical shutters, etc.). In an embodiment, during operation, the x-ray collimator module is configured to vary a shutter aperture associated with at least one of the one or more shutters responsive to the one or more inputs. In an embodiment, the intra-oral x-ray imaging system includes an x-ray beam limiter assembly having one or more aperture diaphragms. In an embodiment, during operation, the x-ray collimator module is configured to vary a diaphragm aperture of the one or more aperture diaphragms responsive to one or more inputs including information associated with a border position of the intra-oral sensor. In an aspect, the present disclosure is directed to, among other things, an intra-oral x-ray imaging device. In an embodiment, the intra-oral x-ray imaging device includes circuitry configured to determine a position (e.g., location, spatial placement, locality, spatial location, physical location, physical position, etc.) or an orientation (e.g., angular position, physical orientation, attitude, etc.) of an intra-oral x-ray sensor. In an embodiment, the intra-oral x-ray imaging device includes circuitry configured to adjust an x-ray beam field of view responsive to one or more inputs from the circuitry configured to determine the position or orientation of the intra-oral x-ray sensor. In an embodiment, the intra-oral x-ray imaging device includes circuitry configured to acquire intra-oral x-ray image information associated with a patient. In an embodiment, the intra-oral x-ray imaging device includes circuitry configured to generate one or more parameters associated with a field of view setting. In an aspect, the present disclosure is directed to, among other things, an intra-oral x-ray imaging method. In an embodiment, the intra-oral x-ray imaging method includes automatically determining an intra-oral x-ray sensor border position and an intra-oral x-ray sensor orientation. In an embodiment, the intra-oral x-ray imaging method includes varying an x-ray beam field of view parameter (e.g., a field of view size, a diameter dimension, a field of view position parameter, an x-ray field collimation parameter, etc.) responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation. In an embodiment, the intra-oral x-ray imaging method includes acquiring intra-oral x-ray image information associated with a patient. In an embodiment, the intra-oral x-ray imaging method includes generating at least one parameter associated with an x-ray imaging mode (e.g., adult panoramic mode, child panoramic mode, high-dose-rate mode, low-dose-rate mode, moderate-dose-rate mode, mandible mode, occlusion mode, maxillary mode, panoramic mode, pulsed fluoroscopy mode, temporomandibular joint mode, etc.) responsive to automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation. In an embodiment, the intra-oral x-ray imaging method includes varying an x-ray beam aim parameter responsive to automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation. In an aspect, the present disclosure is directed to, among other things, an intra-oral x-ray sensor. In an embodiment, the intra-oral x-ray sensor includes an x-ray image component configured to acquire intra-oral x-ray image information associated with a patient. In an embodiment, the intra-oral x-ray sensor includes an intra-oral radiation shield structure configured to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%. For example, in an embodiment, oral x-ray sensor includes an intra-oral radiation shield structure having one or more high-atomic number (high-Z) materials in an amount sufficient to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%. In an aspect, the present disclosure is directed to, among other things, an intra-oral x-ray sensor. In an embodiment, the intra-oral x-ray sensor includes circuitry configured to communicate intra-oral x-ray sensor position information to a remote x-ray source. In an embodiment, the circuitry configured to communicate intra-oral x-ray sensor position information to the remote x-ray source includes one or more wired or wireless connections to the remote x-ray source. In an embodiment, the intra-oral x-ray sensor includes circuitry configured to communicate intra-oral x-ray sensor orientation information to the remote x-ray source. In an embodiment, the intra-oral x-ray sensor includes circuitry configured to verify an x-ray beam characteristic associated with the remote x-ray source. In an embodiment, the intra-oral x-ray sensor includes circuitry configured to communicate an x-ray beam field of view parameter to the remote x-ray source responsive to verifying an x-ray beam characteristic. In an embodiment, the intra-oral x-ray sensor includes circuitry configured to determine remote x-ray source and intra-oral x-ray sensor alignment before communicating an activation instruction to the remote x-ray source for imaging. In an embodiment, the intra-oral x-ray sensor includes circuitry configured to acquire a low intensity x-ray pulse to determine remote x-ray source and intra-oral x-ray sensor alignment before communicating an activation instruction to the remote x-ray source for imaging. In an aspect, the present disclosure is directed to, among other things, an intra-oral x-ray sensor operation method. In an embodiment, the intra-oral x-ray sensor operation method includes communicating intra-oral x-ray sensor position information to a remote x-ray source. In an embodiment, the intra-oral x-ray sensor operation method includes communicating intra-oral x-ray sensor orientation information to a remote x-ray source. In an embodiment, the intra-oral x-ray sensor operation method includes verifying an x-ray beam characteristic associated with the remote x-ray source. In an embodiment, the intra-oral x-ray sensor operation method includes communicating an x-ray beam field of view parameter to the remote x-ray source responsive to verifying an x-ray beam characteristic. In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. Radiographs (e.g., intra-oral radiographs, panoramic radiographs, cephalo radiographs, etc.) are essential and valuable diagnostic tools in dentistry. An objective of dental radiography is to obtain the highest quality images possible, while keeping patients' exposure risk to a minimum. Exposure to radiation may cause cancer, birth defects in the children of exposed parents, and cataracts. A major concern is the delayed health effects arising from chronic cumulative exposure to radiation. One way to reduce a patient's radiation burden is to employ low-dose practices. FIGS. 1A and 1B show an intra-oral x-ray imaging system 100 in which one or more methodologies or technologies can be implemented such as, for example, reducing patient exposure to x-rays, reducing amount of scatter, transmission, or re-radiation during imaging, or improving x-ray image quality. In an embodiment, the intra-oral x-ray imaging system 100 includes one or more intra-oral x-ray sensors 102. In an embodiment, at least one of the one or more intra-oral x-ray sensors 102 is configured to acquire intra-oral x-ray image information 104 associated with a patient. In an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray source 105 operably coupled to one or more intra-oral x-ray sensors 102. In an embodiment, the intra-oral x-ray imaging system 100 includes one or more power sources. In an embodiment, during operation, x rays from the x-ray source 105 pass through the body of the patient striking hard and soft tissue. In an embodiment, a portion of the x-ray beam is deflected, a portion of the x-ray beam is scattered, a portion of the x-ray beam is absorbed, a portion triggers release of characteristic radiation, etc. Intra-oral x-ray image information (e.g., diagnostic dental x rays) is acquired by positioning a part of the body to be examined between a focused x-ray beam and the intra-oral x-ray sensors 102. In an embodiment, the intra-oral x-ray imaging system 100 includes one or more modules. For example, in an embodiment, the intra-oral x-ray imaging system 100 includes x-ray collimator module 106. In an embodiment, the collimator module 106 is operably coupled to an intra-oral x-ray sensor 102 and an x-ray beam limiter assembly 108. For example, in an embodiment, the collimator module 106 is operably coupled to an intra-oral x-ray sensor 102 via a wired or wireless connection 103. In an embodiment, the x-ray beam limiter assembly 108 includes a controllable x-ray collimator module 106. In an embodiment, the controllable x-ray collimator module 106 includes an x-ray beam collimation adjustment mechanism that is responsive to one or more inputs including information associated with a border position of the intra-oral sensor 102. For example, in an embodiment, the x-ray collimator module 106 is configured to vary a shutter aperture 114 associated with at least one of the one or more shutters responsive one or more inputs including information associated with a position of the intra-oral sensor 102, a border position of the intra-oral sensor 102, a position of an intra-oral x-ray sensor centroid, or the like. In an embodiment, a module includes, among other things, one or more computing devices such as a processor (e.g., a microprocessor), a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like, or any combinations thereof, and can include discrete digital or analog circuit elements or electronics, or combinations thereof. In an embodiment, a module includes one or more ASICs having a plurality of predefined logic components. In an embodiment, a module includes one or more FPGAs, each having a plurality of programmable logic components. In an embodiment, the x-ray collimator module 106 includes a module having one or more components operably coupled (e.g., communicatively, electromagnetically, magnetically, ultrasonically, optically, inductively, electrically, capacitively coupled, or the like) to each other. In an embodiment, a module includes one or more remotely located components. In an embodiment, remotely located components are operably coupled, for example, via wireless communication. In an embodiment, remotely located components are operably coupled, for example, via one or more receivers, transmitters, transceivers, antennas, or the like. In an embodiment, the x-ray collimator module 106 includes a module having one or more routines, components, data structures, interfaces, and the like. In an embodiment, a module includes memory that, for example, stores instructions or information. For example, in an embodiment, the x-ray collimator module 106 includes memory that stores, for example, one or more of intra-oral x-ray sensor border position information, intra-oral x-ray sensor centroid information, intra-oral x-ray sensor dimension information, intra-oral x-ray sensor orientation information, intra-oral x-ray sensor position information, intra-oral x-ray sensor specific collimation information, or the like. For example, in an embodiment, the x-ray collimator module 106 includes memory that, for example, stores reference collimation information (e.g., reference collimation shape information, reference collimation size information, reference collimation separation information, etc.), intra-oral x-ray sensor position or orientation information, x-ray image information associated with a patient, or the like. Non-limiting examples of memory include volatile memory (e.g., Random Access Memory (RAM), Dynamic Random Access Memory (DRAM), or the like), non-volatile memory (e.g., Read-Only Memory (ROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Compact Disc Read-Only Memory (CD-ROM), or the like), persistent memory, or the like. Further non-limiting examples of memory include Erasable Programmable Read-Only Memory (EPROM), flash memory, or the like. In an embodiment, the memory is coupled to, for example, one or more computing devices by one or more instructions, information, or power buses. For example, in an embodiment, the x-ray collimator module 106 includes memory that, for example, stores reference collimation information (e.g., reference collimation shape information, reference collimation size information, reference collimation separation information, etc.), intra-oral x-ray sensor position or orientation information, x-ray image information associated with a patient, or the like. In an embodiment, a module includes one or more computer-readable media drives, interface sockets, Universal Serial Bus (USB) ports, memory card slots, or the like, and one or more input/output components such as, for example, a graphical user interface, a display, a keyboard, a keypad, a trackball, a joystick, a touch-screen, a mouse, a switch, a dial, or the like, and any other peripheral device. In an embodiment, a module includes one or more user input/output components, user interfaces, or the like, that are operably coupled to at least one computing device configured to control (electrical, electromechanical, software-implemented, firmware-implemented, or other control, or combinations thereof) at least one parameter associated with, for example, controlling activating, operating, or the like, an x-ray beam limiter assembly 108. In an embodiment, a module includes a computer-readable media drive or memory slot that is configured to accept signal-bearing medium (e.g., computer-readable memory media, computer-readable recording media, or the like). In an embodiment, a program for causing a system to execute any of the disclosed methods can be stored on, for example, a computer-readable recording medium (CRMM), a signal-bearing medium, or the like. Non-limiting examples of signal-bearing media include a recordable type medium such as a magnetic tape, floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), Blu-Ray Disc, a digital tape, a computer memory, or the like, as well as transmission type medium such as a digital or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link (e.g., receiver, transmitter, transceiver, transmission logic, reception logic, etc.). Further non-limiting examples of signal-bearing media include, but are not limited to, DVD-ROM, DVD-RAM, DVD+RW, DVD-RW, DVD-R, DVD+R, CD-ROM, Super Audio CD, CD-R, CD+R, CD+RW, CD-RW, Video Compact Discs, Super Video Discs, flash memory, magnetic tape, magneto-optic disk, MINIDISC, non-volatile memory card, EEPROM, optical disk, optical storage, RAM, ROM, system memory, web server, or the like. In an embodiment, the x-ray collimator module 106 is configured to adjust an x-ray beam field of view responsive to one or more inputs including information associated with a border position of the intra-oral sensor 102. For example, in an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray beam limiter assembly 108 having at least one collimator 110. In an embodiment, the collimator 110 includes a barrier 112 with a variable aperture 114 configured to vary the size and shape of an x-ray beam so as to substantially match the size of an intra-oral x-ray sensor detection region 126a (shown in FIG. 2B). In an embodiment, the collimator 110 implements filtration and collimation techniques and methodologies that reduce a patient's radiation burden. For example, in an embodiment, during operation, activation of the collimator 110 results in a reduction of the size and shape of the x-ray beam, resulting in a reduction of the volume of irradiated tissue in the patient. In an embodiment, activation of the collimator 110 also results in the elimination of one or more divergent portion of an x-ray beam. In an embodiment, the x-ray collimator module 106 is operably coupled to the intra-oral x-ray sensor 102 and the x-ray beam limiter assembly 108, and is configured to adjust an x-ray beam field of view responsive to one or more inputs from the intra-oral x-ray sensor 102 indicative of a border position of the intra-oral sensor 102. The variation of the x-ray beam field of view can comprise a change in the beam size, the beam shape, the beam orientation, or the like. In an embodiment, the x-ray beam expands as it propagates from the x-ray beam limiter assembly 108 towards the patient and the intra-oral x-ray sensor 102. For example, the x-ray propagation can be calculated by assuming straight line x-ray trajectories, allowing the propagation and expansion of the beam to be calculated by knowledge of the relative positions of the x-ray source 105 (e.g., internal components such as an x-ray beam emitter and elements of the x-ray beam limiter assembly 108) and the intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is configured to adjust the x-ray beam field of view such that a border position of the expanding x-ray substantially corresponds (e.g., matches, minimizes overfilling, minimizes underfilling, substantially fills the sensor area, etc.) to a border position of the intra-oral x-ray sensor 102 as the propagating beam arrives at it. In an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray beam limiter assembly 108 having an automatic aperture control mechanism including one or more mechanical diaphragms, (e.g., spring-loaded diaphragm, solenoid activated diaphragm, relay device activated diaphragm, electro-mechanical diaphragm, electromagnetic diaphragm, etc.) The mechanical diaphragm can include a plurality of aperture blades that interact with each other to create the aperture through which the x-rays are projected. In an embodiment, the x-ray collimator module 106 is configured to vary an aperture 114 associated with at least one of the one or more aperture blades included in a mechanical diaphragm responsive one or more inputs indicative of a position of the intra-oral sensor 102, a border position of the intra-oral sensor 102, a position of an intra-oral x-ray sensor centroid, or the like. In an embodiment, the x-ray collimator module 106 is configured to vary an aperture 114 associated with at least one of the one or more mechanical aperture diaphragms responsive one or more inputs indicative of an orientation of the intra-oral sensor 102. In an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray beam limiter assembly 108 having one or more aperture diaphragms. In an embodiment, the x-ray collimator module 106 is configured to vary a diaphragm aperture of the one or more aperture diaphragms responsive to one or more inputs indicative of an orientation or a border position of the intra-oral sensor 102. The diaphragm adjusts the aperture blades to provide the appropriately sized and shaped aperture. In an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray beam limiter assembly 108 having a collimator 110 including a collimator aperture. In an embodiment, the collimator aperture shape can be a geometrical shape including and regular geometric shapes, such as circular, rectangular, triangular, or the like, as well as irregular geometric shapes. In an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray beam limiter assembly 108 including one or more blades, radiation source shutters, wedges, and the like. In an embodiment, the x-ray collimator module 106 is configured to adjust the x-ray beam field size by actuating a change in a separation distance between a collimator aperture and an x-ray source 105 responsive to one or more inputs including information associated with an orientation or a border position of the intra-oral sensor 102. For example, in an embodiment, the x-ray collimator module 106 is operably coupled to a separation distance adjustment mechanism responsive to one or more inputs including information associated with an orientation or a border position of the intra-oral sensor 102. In an embodiment, the x-ray collimator module 106 is operably coupled to a collimator-and-x-ray source assembly configured to adjust the x-ray beam field size by actuating a change in a separation distance between a collimator aperture and an x-ray source 105 responsive to one or more inputs including information associated with an orientation or a border position of the intra-oral sensor 102. In an embodiment, the x-ray beam limiter assembly 108 includes a primary collimator and a secondary collimator. In an embodiment, the x-ray beam limiter assembly 108 includes a variable aperture collimator. In an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray beam limiter assembly 108 having a plurality of selectively actuatable absorber blades configured to form a focal plane shutter. In an embodiment, the focal plane shutter is positioned immediately or right in front of the intra-oral sensor 102. In an embodiment, the focal plane shutter is positioned immediately or right in front of a film-based analog x-ray sensor, a dental digital x-ray sensor, a charge-coupled device (CCD) sensor, complementary metal-oxide-semiconductor (CMOS) sensor, and the like. In an embodiment, the x-ray collimator module 106 is configured to adjust the x-ray beam field size by actuating one or more of the plurality of selectively actuatable absorber blades responsive one or more inputs including information associated with an orientation or a border position of the intra-oral sensor 102. In an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray beam limiter assembly 108 configured to adjust an x-ray beam field size. In an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray beam limiter assembly 108 configured to reduce the size of the x-ray beam at the point of contact with the intra-oral sensor to the size of the intra-oral sensor 102 detection area so as to reduce a patient exposure to x-rays. In an embodiment, the x-ray beam limiter assembly 108 includes one or more aperture diaphragms. In an embodiment, the x-ray beam limiter assembly 108 includes one or more circular aperture diaphragms having mechanical extensions (e.g., aperture blades, radiation source shutters, wedges, etc.) configured to form part of a focal plane shutter. In an embodiment, the x-ray beam limiter assembly 108 includes a shutter assembly having one or more opposing pair shutters. In an embodiment, the x-ray beam limiter assembly 108 includes at least a first-stage shutter and a second-stage shutter. In an embodiment, the intra-oral sensor 102 is configured to work together with the x-ray source 105 to reduce unnecessary patient exposure to x-rays. For example, in an embodiment, the x-ray beam limiter assembly 108 includes an aperture shaped and sized to direct an x-ray beam that provides a beam area that coincides with the detector area of the intra-oral sensor 102. During operation, the x-ray emitter and the intra-oral sensor 102 placed in the patient's mouth may not align exactly, resulting in an x-ray beam projection that is too big, too small, misoriented, etc. In an embodiment, this is fixed by translating or rotating an aperture or by translating or rotating the x-ray emitter. In an embodiment, the x-ray beam limiter assembly 108 includes at least one x-ray beam-limiting aperture configured to translate (laterally and/or longitudinally) relative to an x-ray emitter. In an embodiment, the x-ray beam limiter assembly 108 includes at least one x-ray beam-limiting aperture configured to rotate relative to an x-ray emitter. In an embodiment, the x-ray beam limiter assembly 108 includes at least one x-ray emitter configured to translate (laterally and/or longitudinally) relative to an x-ray beam-limiting aperture. In an embodiment, the x-ray beam limiter assembly 108 includes one or more diaphragms formed from high atomic number (high-Z) materials. For example, in an embodiment, the x-ray beam limiter assembly 108 includes one or more shutters formed from materials including elements have an atomic number greater than or equal to 37 (Rubidium or higher). In an embodiment, the x-ray beam limiter assembly 108 includes one or more shutters formed from materials including elements have an atomic number greater than or equal to 72 (Hafnium or higher). In an embodiment, the x-ray beam limiter assembly 108 includes one or more x-ray filters. For example, in an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray beam limiter assembly 108 including one or more x-ray compensating filters 117 such as a wedge 117a formed from aluminum, ceramic, high-density plastic, etc., that is placed over an oral cavity region during radiography to compensate for differences in radiopacity. In an embodiment, the x-ray compensating filter is configured to limit the x-rays passing through based upon the varying thickness of the filter. In an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray beam limiter assembly 108 including one or more positive beam limitation devices configured to automatically collimate the x-ray beam to the size of the intra-oral x-ray sensor detection region at the point of contact with the intra-oral x-ray sensor 102. In an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray beam limiter assembly 108 including one or more positive beam limitation devices configured to automatically collimate the x-ray beam so as to substantially match the size of an intra-oral x-ray sensor detection region 126a (shown in FIG. 2B). In an embodiment, the x-ray beam limiter assembly 108 includes an extension cone or an extension cylinder. In an embodiment, the x-ray collimator module 106 is configured to interface with one or more components via one or more wired or wireless connections. For example, in an embodiment, the x-ray collimator module 106 is in wireless communication with the x-ray beam limiter assembly 108. In an embodiment, the x-ray collimator module 106 is operably coupled to the x-ray beam limiter assembly 108 via one or more wired connections. In an embodiment, the x-ray collimator module 106 is in wireless communication with the intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is in wireless communication with an x-ray source 105. In an embodiment, the intra-oral x-ray sensor 102 is in wireless communication with an x-ray source 105. In an embodiment, the x-ray collimator module 106 is configured to adjust the x-ray beam field size responsive to the one or more inputs, such as one or more inputs including information associated with a location of a corner position of the intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is configured to adjust the x-ray beam field size responsive to the one or more inputs including information associated with a location of an edge position of the intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is configured to adjust the x-ray beam field size responsive to the one or more inputs including information associated with a location of a reference position on the intra-oral x-ray sensor 102 having a specified offset from a corner of the intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is configured to adjust the x-ray beam field size responsive to the one or more inputs including information associated with a location of a reference position on the intra-oral x-ray sensor having a specified offset from an edge of the intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is configured to adjust the x-ray beam field size responsive to the one or more inputs including information associated with an edge orientation of the intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is configured to adjust the x-ray beam field size responsive to one or more inputs from the x-ray collimator module 106 indicative of an intra-oral x-ray sensor position or orientation. In an embodiment, the position and/or orientation of the intra-oral x-ray sensor is determined relative to the position and/or orientation of at least one of the x-ray source 105, the collimator module 106, the x-ray beam limiter assembly 108, an x-ray beam emitter, and an external reference point. For example, in an embodiment, during operation, the x-ray collimator module 106 is configured to adjust the x-ray beam field size responsive to one or more inputs from the x-ray collimator module 106 indicative of an intra-oral x-ray sensor border position. In an embodiment, during operation, the x-ray collimator module 106 is configured to adjust the x-ray beam field size responsive to one or more inputs from the x-ray collimator module 106 indicative of an intra-oral x-ray sensor centroid 126 position. In an embodiment, during operation, the x-ray collimator module 106 is configured to adjust the x-ray beam field size responsive to one or more inputs from the x-ray collimator module 106 indicative of an intra-oral x-ray sensor angular orientation. In an embodiment, the x-ray collimator module 106 is configured to adjust the x-ray beam field size responsive to one or more inputs from the x-ray collimator module 106 indicative of an intra-oral x-ray sensor dimension. In an embodiment, the x-ray collimator module 106 is configured to generate one or more parameters associated with an x-ray beam limiter assembly 108 configuration responsive to one or more inputs from an intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is configured to generate at least one parameter associated with an x-ray imaging mode (e.g., adult panoramic mode, child panoramic mode, high-dose-rate mode, low-dose-rate mode, moderate-dose-rate mode mandible mode, occlusion mode, maxillary mode, panoramic mode, pulsed fluoroscopy mode, temporomandibular joint mode, etc.) responsive to one or more inputs from an intra-oral x-ray sensor 102. In an embodiment, the intra-oral x-ray imaging system 100 includes a field of view module 107 operable to generate one or more parameters associated with a field of view setting (e.g., field of view size, field of view shape, wide field of view, narrow field of view, field of view extension, horizontal field of view, vertical field of view, diagonal field of view, magnification, increase, decrease, etc.) responsive to one or more inputs from the x-ray collimator module 106 indicative of an intra-oral x-ray sensor position, orientation, or the like. In an embodiment, the intra-oral x-ray imaging system 100 includes one or more intra-oral x-ray sensors 102 configured to acquire intra-oral x-ray image information 104 associated with a patient. In an embodiment, the intra-oral x-ray imaging system 100 includes an x-ray image component 116 operably coupled to one or more intra-oral x-ray sensors 102. Non-limiting examples of intra-oral x-ray sensors 102 include film-based analog x-ray sensors, dental digital x-ray sensors, charge-coupled device (CCD) sensors, complementary metal-oxide-semiconductor (CMOS) sensors, and the like. In an embodiment, the intra-oral x-ray imaging system 100 includes one or more intra-oral x-ray sensors 102 having at least one scintillator plate. In an embodiment, the intra-oral x-ray imaging system 100 includes one or more intra-oral x-ray sensors 102 having at least one scintillator layer. In an embodiment, a scintillator layer is vapor-deposited onto an optical fiber coupled to a photo-sensor integrated into a CCD or CMOS chip. Further non-limiting examples of intra-oral x-ray sensors 102 includes scintillators (e.g., inorganic scintillators, thallium doped cesium iodide scintillators, scintillator-photodiode pairs, scintillation detection devices, etc.), dosimeters (e.g., x-ray dosimeters, thermoluminescent dosimeters, etc.), optically stimulated luminescence detectors, photodiode arrays, charge-coupled devices (CCDs), complementary metal-oxide-semiconductor (CMOS) devices, or the like. In an embodiment, the intra-oral x-ray sensor 102 includes one or more transducers that detect and convert x-rays into electronic signals. For example, in an embodiment, the intra-oral x-ray sensor 102 includes one or more x-ray radiation scintillation crystals. In an embodiment, the intra-oral x-ray sensor 102 includes one or more thallium doped cesium iodide crystals (e.g., cesium iodide crystals doped with thallium CsI(Tl)). In an embodiment, during operation the intra-oral x-ray sensor 102 includes a computing device that processes the electronic signals generated by the one or more transducers to determine one or more of intensity, energy, time of exposure, date of exposure, exposure duration, rate of energy deposition, depth of energy deposition, and the like associated with each x-ray detected. In an embodiment, during operation, incident x-ray radiation interacts with one or more detector crystalline materials (e.g., cadmium zinc telluride, etc.) within the intra-oral x-ray sensor 102, which results in the generation of a current indicative of, for example, the energy of the incident x-ray radiation. In an embodiment, the intra-oral x-ray sensor 102 includes an amorphous-carbon substrate coupled to a Cesium Iodide (CsI) scintillator. In an embodiment, the intra-oral x-ray sensor 102 includes a fiber optic plate (FOP) coupled to a CsI scintillator. In an embodiment, the intra-oral x-ray sensor 102 includes an aluminum substrate coupled to a CsI scintillator. In an embodiment, the intra-oral x-ray sensor 102 includes a scintillator configured to reduce scattering. For example, in an embodiment, the intra-oral x-ray sensors 102 includes thallium-doped-Cesium Iodide (CsI:TI) having columnar structure deposited on a substrate operably coupled to a CMOS/CCD sensor. See e.g., Zhao et al. X-ray imaging performance of structured cesium iodide scintillators. Med. Phys. 31, 2594-2605 (2004) which is incorporated herein by reference. The columnar structure of CsI helps to selectively pass a portion of the x-ray bean onto a CMOS/CCD sensor forming part of the intra-oral x-ray sensor 102. In an embodiment, the intra-oral x-ray sensor 102 includes a substrate that acquires at least a portion of penetrating x-ray radiation stimulus and transduces the penetrating x-ray radiation stimulus acquired by the intra-oral x-ray sensor 102 into an image or at least one measurand indicative of an x-ray flux throughput during an integration period of the intra-oral x-ray sensor 102. In an embodiment, an x-ray image component 116 component is operably coupled to an intra-oral x-ray sensor 102 having one or more x-ray radiation fluoroscopic elements. In an embodiment, the intra-oral x-ray sensor 102 includes one or more phosphorus doped elements (e.g., ZnCdS:Ag phosphorus doped elements). In an embodiment, the intra-oral x-ray sensor 102 includes one or more amorphous silicon thin-film transistor arrays. In an embodiment, the intra-oral x-ray sensor 102 includes one or more phosphors. In an embodiment, the x-ray image component 116 is operably coupled to one or more active pixel image sensors. In an embodiment, the x-ray image component 116 is operably coupled to one or more complementary metal-oxide-semiconductor sensors. In an embodiment, the x-ray image component 116 is operably coupled to one or more complementary metal-oxide-semiconductor active pixel sensors. In an embodiment, the intra-oral x-ray imaging system 100 includes at least one intra-oral x-ray sensor 102 wirelessly coupled to the x-ray collimator module 106. In an embodiment, the intra-oral x-ray imaging system 100 includes at least one intra-oral x-ray sensor 102 wired or wirelessly coupled to an x-ray source 105. In an embodiment, the intra-oral x-ray imaging system 100 includes an intra-oral x-ray sensor module 109 operably coupled to the intra-oral x-ray sensor 102 and the x-ray collimator module. In an embodiment, the intra-oral x-ray sensor module 109 is configured to generate one or more of intra-oral x-ray sensor dimension information, intra-oral x-ray sensor orientation information, or intra-oral x-ray sensor position information responsive to one or more inputs from the x-ray image sensor 102 or the x-ray collimator module 106. In an embodiment, the x-ray collimator module 106 is in wireless communication with the intra-oral x-ray sensor module. In an embodiment, during operation, the intra-oral x-ray imaging system 100 is configured to determine the position and orientation of the intra-oral x-ray sensor 102, and to adjust an x-ray beam field of view responsive to determining the position and orientation of the intra-oral x-ray sensor 102. For example, in an embodiment, the intra-oral x-ray imaging system 100 includes a camera, a sensor, a component, etc., configured to acquire image information associated with a position or an orientation of the intra-oral x-ray sensor 102. In an embodiment, the camera acquires an image involving one or more beacons 118, phosphors 120, retroreflectors 122, or the like that are configured to indicate the position or orientation of the intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is operably coupled to one or more sensors, components, etc., configured to determine, indicate, communicate, broadcast, etc., a border position of the intra-oral sensor 102. In an embodiment, the x-ray collimator module 106 is operably coupled to one or more beacons 118, phosphors 120, retroreflectors 122, or the like configured to determine, indicate, communicate, broadcast, etc., a border position of the intra-oral sensor 102. For example, during operation, the x-ray collimator module 106 is configured to acquire one or more inputs from one or more beacons 118 indicative of the position or orientation of the intra-oral x-ray sensor 102. In an embodiment, during operation, the x-ray collimator module 106 is configured to acquire one or more electrical, acoustic, or electromagnetic inputs from one or more beacons 118 indicative of the position or orientation of the intra-oral x-ray sensor 102. In an embodiment, during operation, the x-ray collimator module 106 is configured to acquire one or more inputs from a sensor configure to detect a florescence associated with one or more phosphors 120, and to generate information indicative of the position or orientation of the intra-oral x-ray sensor 102 based on the one or more inputs from the sensor. In an embodiment, the x-ray collimator module 106 is operably coupled to one or more sensors configured to generate one or more outputs indicative of the position or orientation of the intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is operably coupled to one or retroreflectors configured to indicate the position or orientation of the intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is operably coupled to one or more beacons 118 configured to indicate, communicate, convey, etc., position information or orientation information associated with an intra-oral x-ray sensor 102. Non-limiting examples of beacons 118 include infrared emitters, ultraviolet emitters, visible emitters, electromagnetic energy emitters, ultrasound emitters, and the like. Further non-limiting examples of beacons 118 include magnetic field generators, inductors, capacitors, or the like. In an embodiment, during operation, the x-ray collimator module 106 adjusts an x-ray beam field of view responsive to detecting one or more emitted signals from a beacon 118. In an embodiment, the x-ray collimator module 106 is operably coupled to one or more beacons 118 configured to emit an ultrasonic output. In an embodiment, the x-ray collimator module 106 is operably coupled to one or more beacons 118 configured to emit an ultrasonic output that is detectable through tissue. In an embodiment, the x-ray collimator module 106 is operably coupled to one or more phosphors 120 configured to indicate the position or orientation of the intra-oral x-ray sensor 102. Non-limiting examples of phosphors 120 include infrared phosphors, ultraviolet phosphors, visible phosphors, x-ray phosphors, and the like. Further non-limiting examples of phosphors 120 include phosphors having a peak emission wavelength associated with an optical window in biological tissue. See e.g. J. Phys. D: Appl. Phys. 46 (2013) 375401 (5pp) which is incorporated herein by reference. In an embodiment, the x-ray collimator module 106 is operably coupled to one or more phosphors 120 configured to provide a signal through the patient's skin (i.e. cheek, gum, or teeth). In an embodiment, the x-ray collimator module 106 is operably coupled to one or more phosphors 120 having a peak emission wavelength ranging from about 650 nanometers to about 900 nanometers. In an embodiment, during operation, the border position of the intra-oral sensor 102 is signaled by one or more phosphors 120. In an embodiment, during operation, the x-ray collimator module 106 adjusts an x-ray beam field of view responsive to detecting one or more phosphors 120 and determining a border position of the intra-oral sensor 102 based on determining the location of the one or more phosphors 120. In an embodiment, the intra-oral x-ray sensor comprises a position sensor 124 configured to determine border position data, and a transmitter configured to transmit a signal indicative of the border position data. In an embodiment, the border position data includes X, Y, and Z coordinates. In an embodiment, the border position data includes one or more parameters that define a specific location in a two-dimensional object or three-dimensional object. In an embodiment, the border position data includes one or more position parameters associated with an intra-oral x-ray sensor border. In an embodiment, the border position data includes one or more position parameters associated with an intra-oral x-ray sensor centroid 126. Non-limiting examples of position sensors 124 include local positioning system (e.g., analogous to GPS-type sensors) sensors configured to interact with room-based reference signals. In an embodiment, the position sensor 124 includes a magnetic sensor responding to room-based magnetic fields. In an embodiment, the position sensor 124 includes one or more accelerometer 128. In an embodiment, the position sensor 124 includes a multi-accelerometer or accelerometer-gyro package that keeps track of the motion involved in putting intra-oral x-ray sensor 102 into the patient's mouth. In an embodiment, the x-ray collimator module 106 is configured to adjust the x-ray beam to minimize the portion of the x-ray beam that misses (e.g., overfills) the intra-oral x-ray sensor 102. In an embodiment, the x-ray collimator module 106 is further configured to adjust the x-ray beam to maximize an amount of the x-ray beam that impacts the intra-oral x-ray sensor 102, e.g., to minimize underfilling it. FIG. 2A shows an intra-oral x-ray imaging device 200 in which one or more methodologies or technologies can be implemented such as, for example, reducing patient exposure to x-rays, reducing amount of scatter, transmission, or re-radiation during imaging, or improving x-ray image quality. In an embodiment, the intra-oral x-ray imaging device 200 includes circuitry 202 configured to determine a position and an orientation of an intra-oral x-ray sensor 102. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 includes circuitry configured to determine border position information of the intra-oral x-ray sensor 102. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 includes circuitry configured to determine an intra-oral x-ray sensor centroid position. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 includes an image sensor 203 configured to detect one or more optic devices 204 (e.g., retroreflectors, beacons, emitters, etc.) indicative of an intra-oral x-ray sensor border position, an intra-oral x-ray sensor position, or an intra-oral x-ray sensor orientation. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to an embedded orientation detection component 206. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 and the one or more acoustic transducers 232 form part of an integrated component. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more magnetic compass based sensors 208. For example, in an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more embedded magnetic compass sensors 210. In an embodiment, the circuitry 202 configured to determine position and the orientation of the intra-oral x-ray sensor 102 and the one or more embedded magnetic compass sensors 210 form part of an integrated component. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 forms part of an integrated image sensor configured to detect one or more optic devices 204 (e.g., retroreflectors, beacons, emitters, etc.) In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more local positioning system based sensors 124. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more acceleration sensors 214. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to at least two acceleration sensors 214 in a substantially perpendicularly arrangement. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more multi-axis accelerometers 216. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more orientation-aware sensors 218. For example, in an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor is operably coupled to one or more gyroscopes 220. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more electrolytic fluid based sensors 222. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to a two-axis tilt sensor 224 configured to detect an intra-oral x-ray sensor roll or yaw angle. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to a two-axis tilt sensor 224 configured to detect an intra-oral x-ray sensor pitch angle. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more inductors 226. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more active optic devices 228. For example, in an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more optical emitter that emit an electromagnetic energy signal that provides information associated with the position and the orientation of the intra-oral x-ray sensor 102. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more active acoustic emitters. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more passive optics devices 230 (e.g., retroreflectors, phosphors, etc.). In an embodiment, during operation, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 by emitting an interrogation signal that is reflected back by the one or more retroreflectors. The reflected signal is use to generate information associated with the position and the orientation of the intra-oral x-ray sensor 102. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 is operably coupled to one or more acoustic transducers 232 configured to generate an output indicative of an intra-oral x-ray sensor border position and an intra-oral x-ray sensor orientation. In an embodiment, the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102 and the one or more acoustic transducers 232 form part of an integrated component. In an embodiment, the intra-oral x-ray sensor 102 includes an integrated component including one or more optic devices 204, orientation detection component 206, magnetic compass based sensors 208, embedded magnetic compass sensors 210, local positioning system based sensors 124, more acceleration sensors 214, multi-axis accelerometers 216, orientation-aware sensors 218, gyroscopes 220, electrolytic fluid based sensors 222, two-axis tilt sensors 224, inductors 226, optic devices 228, passive optics devices 230, acoustic transducers 232, or the like. In an embodiment, the intra-oral x-ray imaging device 200 includes circuitry 234 configured to adjust an x-ray beam field of view (FOV) responsive to one or more inputs from the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102. For example, in an embodiment, the circuitry 234 configured to adjust the x-ray beam field of view is operably coupled to at least one of the x-ray collimator module 106 or the x-ray beam limiter assembly 108, and is configured to generate one or more control signal that actuates the x-ray collimator module 106 or the x-ray beam limiter assembly 108 to adjust an x-ray beam FOV responsive to one or more inputs from the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102. In an embodiment, the intra-oral x-ray imaging device 200 includes circuitry 236 configured to acquire intra-oral x-ray image information associated with a patient. In an embodiment, the intra-oral x-ray imaging device 200 includes circuitry 238 configured to generate one or more parameters associated with a field of view setting. In an embodiment, the circuitry 238 configured to generate one or more parameters associated with a field of view setting includes circuitry configured to generate the one or more parameters associated with the field of view setting responsive to one or more inputs from the circuitry 202 configured to determine the position and the orientation of the intra-oral x-ray sensor 102. FIG. 3A shows an intra-oral x-ray sensor 102 in which one or more methodologies or technologies can be implemented such as, for example, reducing patient exposure to x-rays, reducing amount of scatter, transmission, or re-radiation during imaging, or improving x-ray image quality. In an embodiment, the intra-oral x-ray sensor 102 includes an x-ray image component 116 configured to acquire intra-oral x-ray image information 104 associated with a patient. In an embodiment, the x-ray image component 116 includes circuitry 236 configured to acquire intra-oral x-ray image information associated with a patient. In an embodiment, the intra-oral x-ray sensor 102 includes an intra-oral radiation shield structure 302 configured to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%. In an embodiment, the intra-oral radiation shield structure 302 includes one or more high atomic number (high-Z) materials in an amount sufficient to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%. For example, in an embodiment, at least a portion of the intra-oral radiation shield structure 302 is formed from materials including elements have an atomic number greater than or equal to 37 (Rubidium or higher). In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is formed from materials including elements have an atomic number greater than or equal to 72 (Hafnium or higher). In an embodiment, the intra-oral radiation shield structure 302 includes one or more materials having a K-edge greater than 15 kiloelectron volts in an amount sufficient to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%. Non-limiting examples of materials having a K-edge greater than 15 kiloelectron volts include elements have an atomic number greater than or equal to 37 (Rubidium or higher). In an embodiment, the intra-oral radiation shield structure 302 includes one or more materials having an L-edge greater than 10 kiloelectron volts in an amount sufficient to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%. Non-limiting examples of materials having an L-edge greater than 10 kiloelectron volts include elements have an atomic number greater than or equal to 69 (Thulium or higher). In an embodiment, the intra-oral radiation shield structure 302 includes a mixture of materials having a K-edge greater than 15 kiloelectron volts, materials having an L-edge greater than 10 kiloelectron volts, or high atomic number (high-Z) materials in an amount sufficient to reduce at least one of x-ray scattering, transmission, or re-radiation by at least 50%. Referring to FIG. 3B, in an embodiment, the intra-oral x-ray sensor 102 includes a laminate structure having multiple layers. For example, in an embodiment, the intra-oral x-ray sensor 102 includes one or more of radiation shield layers 304, 306, electronic circuit layers 308, sensor layers 310, scintillator layers 312, protection layers 314, etc. In an embodiment, the intra-oral radiation shield structure 302 includes a laminate structure having at least a first layer 304. In an embodiment, the intra-oral radiation shield structure 302 includes a laminate structure having at least a first layer 304 and a second layer 306, the second layer having an x-ray attenuation profile different from the first layer. In an embodiment, the intra-oral radiation shield structure 302 includes a laminate structure having at least a first layer 304 and a second layer 306, the second layer 306 having an attenuation coefficient different from the first layer 304. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of one or more x-ray shielding materials. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of one or more x-ray radio-opaque materials (e.g., barium sulfate, silicon carbide, silicon nitride, alumina, zirconia, etc.). In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of one or more x-ray attenuating materials. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of one or more x-ray attenuating ceramic materials. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of multiple layers, each layer having an xx-ray attenuation coefficient different from another. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of one or more ferromagnetic materials. Ferromagnetic materials include those materials having a Curie temperature, above which thermal agitation destroys the magnetic coupling giving rise to the alignment of the elementary magnets (electron spins) of adjacent atoms in a lattice (e.g., a crystal lattice). In an embodiment, one or more of the plurality of x-ray shielding particles include one or more ferromagnets. Non-limiting examples ferromagnetic materials include crystalline ferromagnetic materials, ferromagnetic oxides, materials having a net magnetic moment, materials having a positive susceptibility to an external magnetic field, non-conductive ferromagnetic materials, non-conductive ferromagnetic oxides, ferromagnetic elements (e.g., cobalt, gadolinium, iron, or the like), rare earth elements, ferromagnetic metals, ferromagnetic transition metals, materials that exhibit magnetic hysteresis, and the like, and alloys or mixtures thereof. Further non-limiting examples of ferromagnetic materials include chromium (Cr), cobalt (Co), copper (Cu), dysprosium (Dy), europium (Eu), gadolinium (Gd), iron (Fe), magnesium (Mg), neodymium (Nd), nickel (Ni), yttrium (Y), and the like. Further non-limiting examples of ferromagnetic materials include chromium dioxide (CrO2), copper ferrite (CuOFe2O3), europium oxide (EuO), iron(II, III) oxide (FeOFe2O3), iron(III) oxide (Fe2O3), magnesium ferrite (MgOFe2O3), manganese ferrite (MnOFe2O3), nickel ferrite (NiOFe2O3), yttrium-iron-garnet (Y3Fe5O12), and the like. Further non-limiting examples of ferromagnetic materials include manganese arsenide (MnAs), manganese bismuth (MnBi), manganese (III) antimonide (MnSb), Mn—Zn ferrite, neodymium alloys, neodymium, Ni—Zn ferrite, and samarium-cobalt. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of iron oxides. Non-limiting examples of iron oxides include copper ferrite (CuOFe2O3), iron(II, III) oxide (FeOFe2O3), iron(III) oxide (Fe2O3), magnesium ferrite (MgOFe2O3), manganese ferrite (MnOFe2O3), nickel ferrite (NiOFe2O3), yttrium-iron-garnet (Y3Fe5O12), ferric oxides, ferrous oxides, and the like. In an embodiment, one or more of the plurality of x-ray shielding particles include at least one iron oxide. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of one or ferrimagnetic materials. In an embodiment, one or more of the plurality of x-ray shielding particles include one or more ferrimagnets (e.g., soft ferrites, hard ferrites, or the like). Non-limiting examples of ferrimagnetic materials include ferrimagnetic oxides (e.g., ferrites, garnets, or the like). Further non-limiting examples of ferrimagnetic materials include ferrites with a general chemical formula of AB2O4 (e.g., CoFe2O4, MgFe2O4, ZnFe2O4) where A and B represent various metal cations. In an embodiment, A is Mg, Zn, Mn, Ni, Co, or Fe(II); B is Al, Cr(III), Mn(III) or Fe(III), and O is oxygen. In an embodiment, A is a divalent atom of radius ranging from about 80 pm to about 110 pm (e.g., Cu, Fe, Mg, Mn, Zn, or the like), B is a trivalent atom of radius ranging from about 75 pm to about 90 pm, (e.g., Al, Fe, Co, Ti, or the like), and O is oxygen. Non-limiting examples of ferrimagnetic materials include iron ferrites with a general chemical formula MOFe2O3 (e.g., CoFe2O4, Fe3O4, MgFe2O4, or the like) where M is a divalent ion such as Fe, Co, Cu, Li, Mg, Ni, or Zn. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of at least a first ferrimagnetic material and a second ferromagnetic material, the second ferrimagnetic material having one or more absorption edges different from the first ferrimagnetic material. In an embodiment, the intra-oral radiation shield structure 302 includes a laminate structure having at least a first layer 304 and a second layer 306, the second layer having a different ferrimagnetic material composition from the first layer. Non-limiting examples of ferrimagnetic materials include materials having a magnetization compensation point, materials that are associated with a partial cancellation of antiferromagnetically aligned magnetic sublattices with different values of magnetic moments, or material having different temperature dependencies of magnetization. See e.g., Kageyama et al., Weak Ferrimagnetism, Compensation Point, and Magnetization Reversal in Ni(HCOO)2.2H2O, Physical Rev. B, 224422 (2003). In an embodiment, at least a portion of the intra-oral radiation shield structure 302 comprises one or more paramagnetic materials. In an embodiment, the intra-oral radiation shield structure 302 is removably attachable to the intra-oral x-ray sensor 102. For example, in an embodiment, at least a portion of the intra-oral radiation shield structure 302 is removably attachable to the intra-oral x-ray sensor 102, behind a sensor layer 310. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 includes two or more layers secured to each other to form structure 302. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of one or more x-ray radio-opaque materials. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of one or more x-ray attenuating materials. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of one or more x-ray attenuating ceramic materials. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of at least a first x-ray radio-opaque material and a second x-ray radio-opaque material, the second x-ray radio-opaque material having a different x-ray opacity profile from the first x-ray radio-opaque material. In an embodiment, the intra-oral radiation shield structure 302 includes a laminate structure having at least a first layer 304 and a second layer 306, the second layer 306 having a different opacity profile from the first layer 304. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is formed from at least one x-ray attenuating material, x-ray radio-opaque material, or x-ray attenuating ceramic material. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is formed from at least one ferromagnetic material, ferrimagnetic material, or paramagnetic material. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of one or more high-Z, high-density, materials. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of at least a first x-ray attenuating ceramic material and a second x-ray attenuating ceramic material, the second x-ray attenuating ceramic material having a different x-ray attenuation profile from the first x-ray attenuating ceramic material. In an embodiment, the intra-oral radiation shield structure 302 includes a laminate structure having at least a first layer 304 and a second layer 306, the second layer 306 having a different x-ray attenuation profile from the first layer 304. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of at least a first x-ray shielding material and a second x-ray shielding material, the second x-ray shielding material having one or more absorption edges different from the first x-ray shielding material. In an embodiment, at least one of the first x-ray shielding material or the second x-ray shielding material includes at least one material that absorbs x-rays at one or more frequencies and fluoresce x-rays at one or more lower frequencies. In an embodiment, at least one absorption edge of the second x-ray shielding material is selected to maximize absorption of x-rays fluoresced by the first x-ray shielding material. In an embodiment, at least a portion of the second x-ray shielding material is mounted between an x-ray image detector and a portion of the first x-ray shielding material on the intra-oral x-ray sensor 102. In an embodiment, at least a portion of the second x-ray shielding material is intermixed with at least a portion of the first x-ray shielding material. In an embodiment, at least a portion of the second x-ray shielding material is interlayered with at least a portion of the first x-ray shielding material. In an embodiment, at least a portion of the intra-oral radiation shield structure 302 is composed of at least a first x-ray shielding material and a second x-ray shielding material, the second x-ray shielding material having a different absorption edge profile from the first x-ray shielding material. In an embodiment, the intra-oral radiation shield structure 302 includes a laminate structure having at least a first layer 304 and a second layer 306, the second layer 306 having a different x-ray absorption edge profile from the first layer 304. In an embodiment, the second x-ray shielding material includes one or more K-edges, or one or more L-edges, different from the first x-ray shielding material. In an embodiment, the second x-ray shielding material includes at least one K-edge having an energy level lower than at least one K-edge of the first x-ray shielding material. In an embodiment, at least one of the first x-ray shielding material or the second x-ray shielding material includes at least one of lead (Pb), tantalum (Ta), or tungsten (W). In an embodiment, the second x-ray shielding material comprises an x-ray mass attenuation coefficient different from the first x-ray shielding material. In an embodiment, the intra-oral radiation shield structure 302 includes one or more x-ray shielding agents. For example, in an embodiment, the intra-oral radiation shield structure 302 includes a composition having a carrier fluid and a plurality of x-ray shielding particles each having at least a first x-ray shielding agent and a second x-ray shielding agent, the second x-ray shielding agent having one or more absorption edges different from the first x-ray shielding agent. In an embodiment, the intra-oral radiation shield structure 302 includes at least a first x-ray shielding agent and a second x-ray shielding agent, the second x-ray shielding agent having one or more absorption edges different from the first x-ray shielding agent. In an embodiment, the intra-oral radiation shield structure 302 includes at least a first x-ray shielding agent and a second x-ray shielding agent. In an embodiment, at least one of the first x-ray shielding agent or the second x-ray shielding agent includes at least one of mercury (Hg), lead (Pb), tantalum (Ta), or tungsten (W). In an embodiment, at least one of the first x-ray shielding agent or the second x-ray shielding agent includes at least one of teflon (C2F4), lead (II) oxide (PbO), or silicon nitride (Si3N4). In an embodiment, at least one of the first x-ray shielding agent or the second x-ray shielding agent includes at least one of boron, molybdenum, neodymium, niobium, strontium, tungsten yttrium, or zirconium, or combinations thereof. In an embodiment, at least one of the first x-ray shielding agent or the second x-ray shielding agent includes at least one of barium sulfate (BaSO4), boron nitride (BN), boron carbide (B4C), boron oxide (B2O3), or barium oxide (BaO). In an embodiment, at least one of the first x-ray shielding agent or the second x-ray shielding agent includes at least one of strontium oxide (SrO), zinc oxide (ZnO), or zirconium dioxide (ZrO2). In an embodiment, at least one of the first x-ray shielding agent or the second x-ray shielding agent includes at least one of SiO2—PbO-alkali metal oxide glass, CaO—SrO—B2O3 glass, or boron-lithium glass. In an embodiment, at least one of the first x-ray shielding agent or the second x-ray shielding agent includes borated high density polyethylene. In an embodiment, at least one of the first x-ray shielding agent or the second x-ray shielding agent includes at least one of mylar (C10F18O4), parylene-C (C8H7C1), parylene-N(C8H8), poly(methyl methacrylate) (PMMA), polycarbonate (C16H14O3), polyethylene, or ultra-high molecular weight polyethylene. In an embodiment, a portion of the intra-oral radiation shield structure 302 is configured to have an x-ray shielding lead equivalence of about 0.25 millimeters to about 0.5 millimeters. For example, in an embodiment, a portion of the intra-oral radiation shield structure 302 includes a sufficient amount of x-ray shielding materials to have an x-ray shielding lead equivalence of about 0.25 millimeters to about 0.5 millimeters. In an embodiment, x-ray shielding lead equivalence is configured based on an anticipated x-ray spectrum. In an embodiment, a portion of the intra-oral radiation shield structure 302 has an x-ray shielding lead equivalence of greater than about 0.25 millimeters. In an embodiment, a portion of the intra-oral radiation shield structure 302 includes a plurality of x-ray shielding particles. In an embodiment, a portion of the intra-oral radiation shield structure 302 extends outwardly beyond a terminal border of an x-ray image detector forming part of the intra-oral x-ray sensor 102. In an embodiment, the intra-oral radiation shield is structured and dimensioned to conform to a portion of an oral cavity. In an embodiment, a portion of the intra-oral radiation shield structure 302 is flexible or jointed so as to conform to a portion of an oral cavity. Referencing FIG. 3A, in an embodiment, the intra-oral x-ray sensor 102 includes an embedded orientation detection component 316 configured to generate information associated with at least one of an intra-oral x-ray sensor orientation, an intra-oral x-ray sensor position, an intra-oral x-ray sensor dimension, or an intra-oral x-ray sensor centroid position. In an embodiment, the embedded orientation detection component 316 is operably coupled to one or more orientation sensors 318. For example, in an embodiment, the embedded orientation detection component 316 is operably coupled to one or more magnetic compass based sensors. In an embodiment, the embedded orientation detection component 316 is operably coupled to one or more embedded magnetic compass sensors. In an embodiment, the embedded orientation detection component 316 is operably coupled to one or more local positioning system based sensors 320. In an embodiment, the embedded orientation detection component 316 is operably coupled to at least two acceleration sensors 322 in a substantially perpendicularly arrangement. In an embodiment, the embedded orientation detection component 316 is operably coupled to at least one gyroscope 324. In an embodiment, the embedded orientation detection component 316 is operably coupled to at least one electrolytic fluid based sensor 326. In an embodiment, the embedded orientation detection component 316 is operably coupled to at least one transmitter (wired or wireless) configured to report position or orientation information to the remote x-ray source 105. In an embodiment, the embedded orientation detection component 316 is operably coupled to a two-axis tilt sensor 328 configured to detect an intra-oral x-ray sensor pitch angle and an intra-oral x-ray sensor roll angle. In an embodiment, the embedded orientation detection component 316 is operably coupled to at least one multi-axis accelerometer 330. In an embodiment, the embedded orientation detection component 316 is operably coupled to one or more orientation-aware sensors 332. In an embodiment, the embedded orientation detection component 316 is operably coupled to one or more inductors 334. In an embodiment, the embedded orientation detection component 316 is operably coupled to one or more acoustic transducers 336. In an embodiment, the x-ray image component 116 is operably coupled to one or more dental digital x-ray sensors. In an embodiment, the x-ray image component 116 is operably coupled to one or more dental digital x-ray sensors. In an embodiment, the x-ray image component 116 is operably coupled to one or more charge-coupled devices 338. In an embodiment, the x-ray image component 116 is operably coupled to one or more active pixel image sensors 340. In an embodiment, the x-ray image component 116 is operably coupled to one or more complementary metal-oxide-semiconductor sensors 342. In an embodiment, the x-ray image component 116 is operably coupled to one or more complementary metal-oxide-semiconductor active pixel sensors 344. In an embodiment, the intra-oral x-ray sensor 102 includes one or more passive optics devices 204 configured to indicate an intra-oral x-ray sensor border position. In an embodiment, the intra-oral x-ray sensor 102 includes one or more active optic devices 228 (e.g., beacons, acoustic emitters, optical emitters, etc.) configured to generate an output indicative of an intra-oral x-ray sensor border position. In an embodiment, the intra-oral x-ray sensor 102 includes a beacon component 346 configured to convey information associated with at least one of a sensor position or a sensor orientation. In an embodiment, the beacon component 346 is operably coupled to a transducer configured to generate an output indicative of an intra-oral x-ray sensor border position. In an embodiment, the beacon component 346 is operably coupled to one or more transducers configured to generate an output indicative of an intra-oral x-ray sensor border position. In an embodiment, the beacon component 346 is operably coupled to one or more active optic devices configured to generate an output indicative of an intra-oral x-ray sensor border position. In an embodiment, the beacon component 346 is operably coupled to one or more inductors configured to generate an output indicative of an intra-oral x-ray sensor border position. In an embodiment, the beacon component 346 is operably coupled to one or more accelerometers configured to generate an output indicative of an intra-oral x-ray sensor orientation. In an embodiment, the beacon component 346 is operably coupled to one or more gyroscopes configured to generate an output indicative of an intra-oral x-ray sensor orientation. In an embodiment, the beacon component 346 is operably coupled to one or more electrolytic fluid based sensors 326 configured to generate an output indicative of an intra-oral x-ray sensor orientation. In an embodiment, the intra-oral x-ray sensor 102 includes an x-ray backscatter component 348 operably coupled to the x-ray image component 116. In an embodiment, the x-ray backscatter component 348 is configured to modify the intra-oral x-ray image information responsive to one or more inputs from the x-ray image component 116 indicative of backscatter, i.e., to computationally remove image noise resulting from backscattered x-rays. In an embodiment, the intra-oral x-ray sensor 102 includes circuitry 352 configured to communicate intra-oral x-ray sensor position information to a remote x-ray source 105. In an embodiment, communication with the remote x-ray source 105 can be wired or wirelessly connected to the intra-oral x-ray sensor 102. In an embodiment, the circuitry 352 configured to communicate the intra-oral sensor 102 position to the remote x-ray source 105 comprises one or more of a receiver, transmitter, or transceiver. In an embodiment, the circuitry 352 configured to communicate the intra-oral sensor 102 position to the remote x-ray source 105 comprises a wireless transmitter. In an embodiment, the circuitry 352 configured to communicate the intra-oral sensor 102 position is operably coupled to one or more radiation reflecting elements (e.g., prisms retro-reflectors, etc.). In an embodiment, the circuitry 352 configured to communicate the intra-oral sensor 102 position is operably coupled to a modulatable reflector. In an embodiment, the intra-oral x-ray sensor 102 includes circuitry 354 configured to verify an x-ray beam characteristic associated with the remote x-ray source 105. In an embodiment, the circuitry 354 configured to verify the x-ray beam characteristic associated with the remote x-ray source 105 includes circuitry configured to determine x-ray beam centroid information associated with the remote x-ray source 105. In an embodiment, the circuitry 354 configured to verify the x-ray beam characteristic associated with the remote x-ray source 105 includes circuitry configured to determine a spatial pattern associated with an x-ray beam received from the remote x-ray source 105. In an embodiment, the circuitry 354 configured to verify the x-ray beam characteristic associated with the remote x-ray source 105 includes circuitry configured to determine a spatial alignment associated with an x-ray beam received from the remote x-ray source 105. In an embodiment, the circuitry 354 configured to verify the x-ray beam characteristic associated with the remote x-ray source 105 includes circuitry configured to determine lateral overlap information associated with an x-ray beam received from the remote x-ray source 105 and an intra-oral x-ray sensor 102. In an embodiment, the intra-oral x-ray sensor 102 includes circuitry 356 configured to communicate an x-ray beam field of view parameter to the remote x-ray source 105 responsive to verifying an x-ray beam characteristic. In an embodiment, the circuitry 356 configured to communicate the x-ray beam field of view parameter to the remote x-ray source 105 comprises one or more of a receiver, transmitter, or transceiver. In an embodiment, the circuitry 356 configured to communicate the x-ray beam field of view parameter to the remote x-ray source 105 comprises a wireless transmitter. In an embodiment, the intra-oral x-ray sensor 102 includes circuitry 358 configured to generate intra-oral x-ray sensor orientation information. In an embodiment, the circuitry 358 configured to generate intra-oral x-ray sensor orientation information is operably coupled to one or more embedded magnetic compasses. In an embodiment, the circuitry 358 configured to generate the intra-oral x-ray sensor orientation information is operably coupled to one or more electrolytic fluid based sensors 222. In an embodiment, the circuitry 358 configured to generate the intra-oral x-ray sensor orientation information is operably coupled to one or more acceleration sensors. In an embodiment, the circuitry 358 configured to generate the intra-oral x-ray sensor orientation information is operably coupled to one or more multi-axis accelerometers 330. In an embodiment, the circuitry 358 configured to generate the intra-oral x-ray sensor orientation information is operably coupled to at least two acceleration sensors in a substantially perpendicularly arrangement. In an embodiment, the circuitry 358 configured to generate the intra-oral x-ray sensor orientation information is operably coupled to one or more orientation-aware sensors 332. In an embodiment, the intra-oral x-ray sensor 102 includes circuitry 360 configured to generate intra-oral x-ray sensor position information. In an embodiment, the circuitry 360 configured to generate the intra-oral x-ray sensor position information is operably coupled to one or more local positioning system based sensors. In an embodiment, the circuitry 360 configured to generate the intra-oral x-ray sensor position information is operably coupled to one or more inductors 334. In an embodiment, the circuitry 360 configured to generate the intra-oral x-ray sensor position information is operably coupled to one or more active optic devices (e.g., photodetectors, imagers, CCD detectors, CMOS detectors, etc.). In an embodiment, the circuitry 360 configured to generate the intra-oral x-ray sensor position information is operably coupled to one or more acoustic transducers 336 configured to generate an output indicative of an intra-oral x-ray sensor border position and an intra-oral x-ray sensor orientation. In an embodiment, the circuitry 360 configured to generate the intra-oral x-ray sensor position information is operably coupled to one or more border indicating beacon devices 118. In an embodiment, the intra-oral x-ray sensor 102 includes circuitry 362 configured to determine remote x-ray source 105 and intra-oral x-ray sensor alignment before communicating an activation instruction to the remote x-ray source 105 for imaging. In an embodiment, the intra-oral x-ray sensor 102 includes circuitry 364 configured to acquire a low intensity x-ray pulse to determine remote x-ray source 105 and intra-oral x-ray sensor alignment before communicating an activation instruction to the remote x-ray source 105 for imaging. In an embodiment, the intra-oral x-ray sensor 102 includes an integrated component including one or more of the circuitry 352 configured to communicate the intra-oral sensor 102 position is operably coupled to a modulatable reflector; the circuitry 354 configured to verify an x-ray beam characteristic associated with the remote x-ray source 105; the circuitry 356 configured to communicate an x-ray beam field of view parameter to the remote x-ray source 105 responsive to verifying an x-ray beam characteristic; the circuitry 358 configured to generate intra-oral x-ray sensor orientation information; the circuitry 360 configured to generate intra-oral x-ray sensor position information; the circuitry 362 configured to determine remote x-ray source 105; the circuitry 364 configured to acquire a low intensity x-ray pulse to determine remote x-ray source 105 and intra-oral x-ray sensor alignment before communicating an activation instruction to the remote x-ray source 105 for imaging; or the like. FIGS. 4A-4C show an intra-oral x-ray imaging method 400. At 410, the intra-oral x-ray imaging method 400 includes automatically determining an intra-oral x-ray sensor border position and an intra-oral x-ray sensor orientation. At 412, automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes wirelessly detecting an intra-oral x-ray sensor beacon output indicative of the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation. At 414, automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes detecting at least one passive reflector associated with an intra-oral x-ray sensor and generating intra-oral x-ray sensor border position information and intra-oral x-ray sensor orientation information. At 416, automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes detecting a transducer response associated with an intra-oral x-ray sensor 102 and generating intra-oral x-ray sensor border position information and intra-oral x-ray sensor orientation information. At 418, automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes detecting a reference component associated with an intra-oral x-ray sensor 102 and generating intra-oral x-ray sensor border position information responsive to detecting the reference component. At 420, automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes detecting a reference component associated with an intra-oral x-ray sensor 102 and generating intra-oral x-ray sensor orientation information responsive to detecting the reference component. At 422, automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes acquiring at least one parameter from an accelerometer associated with an intra-oral x-ray sensor 102 and generating the intra-oral x-ray sensor orientation responsive to acquiring the at least one parameter from the accelerometer. At 430, the intra-oral x-ray imaging method 400 includes varying an x-ray beam field of view parameter responsive to one or more inputs including information associated with a location of the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation. At 432, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with an intra-oral x-ray sensor border position and an intra-oral x-ray sensor orientation includes varying the collimation size or the collimation shape of an external x-ray source 105 operably coupled to the intra-oral x-ray sensor 102. At 434, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes varying the x-ray beam field of view parameter sufficient to minimize overfilling of the intra-oral x-ray sensor 102. At 436, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes varying the x-ray beam field of view parameter sufficient to minimize underfilling of the intra-oral x-ray sensor 102. At 438, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes varying one or more parameters associated with a field of view setting responsive to automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation. At 440, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes varying a shutter aperture setting. At 442, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes varying a diaphragm aperture setting. At 444, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes varying a separation between a collimator aperture and an x-ray beam emitter within x-ray source 105. At 446, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes varying an orientation between a collimator aperture and an x-ray beam emitter within x-ray source 105. At 448, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes actuating one or more selectively actuatable absorber blades forming part of a focal plane shutter. At 450, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes actuating an x-ray beam limiter assembly 108 configured to adjust an x-ray beam field size. At 452, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes generating one or more parameters associated with an x-ray beam field size adjustment responsive to automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation. At 454, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes generating one or more x-ray beam limiter assembly 108 setting parameters responsive to automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation. At 456, varying the x-ray beam field of view parameter responsive to one or more inputs including information associated with the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation includes actuating at least one liquid absorber. At 460, the intra-oral x-ray imaging method 400 includes acquiring intra-oral x-ray image information associated with a patient. At 462, acquiring the intra-oral x-ray image information associated with the patient includes acquiring one or more intra-oral radiographic images. At 464, acquiring the intra-oral x-ray image information associated with the patient includes acquiring intra-oral radiographic view information. At 466, acquiring the intra-oral x-ray image information associated with the patient includes acquiring a periapical view image of at least one anterior or posterior tooth. At 468, acquiring the intra-oral x-ray image information associated with the patient includes acquiring a bitewing view image of at least one tooth crown. At 470, acquiring the intra-oral x-ray image information associated with the patient includes acquiring an occlusal view image of a palate. At 472, acquiring the intra-oral x-ray image information associated with the patient includes acquiring a posterior periapical image. At 474, acquiring the intra-oral x-ray image information associated with the patient includes acquiring an anterior periapical image. At 478, the intra-oral x-ray imaging method 400 includes generating at least one parameter associated with an x-ray imaging mode (e.g., adult panoramic mode, child panoramic mode, high-dose-rate mode, low-dose-rate mode, moderate-dose-rate mode mandible mode, occlusion mode, maxillary mode, panoramic mode, pulsed fluoroscopy mode, temporomandibular joint mode, etc.) responsive to automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation. At 480, the intra-oral x-ray imaging method 400 includes varying an x-ray beam aim parameter responsive to automatically determining the intra-oral x-ray sensor border position and the intra-oral x-ray sensor orientation. At 490, the intra-oral x-ray imaging method 400 includes communicating intra-oral x-ray sensor position information to a remote x-ray source 105. At 492, communicating the intra-oral x-ray sensor position information to the remote x-ray source 105 includes communicating intra-oral x-ray sensor dimension information to the remote x-ray source 105. At 494, communicating the intra-oral x-ray sensor position information to the remote x-ray source 105 includes communicating intra-oral x-ray sensor orientation information to the remote x-ray source 105. At 496, communicating the intra-oral x-ray sensor position information to the remote x-ray source 105 includes communicating one or more outputs indicative of an intra-oral x-ray sensor border position. At 498, the intra-oral x-ray imaging method 400 includes communicating intra-oral x-ray sensor orientation information to a remote x-ray source 105. FIG. 5 shows an intra-oral x-ray sensor operation method 500. At 510, the intra-oral x-ray sensor operation method 500 includes verifying an x-ray beam characteristic associated with the remote x-ray source 105. At 520, the intra-oral x-ray sensor operation method 500 includes communicating an x-ray beam field of view parameter to the remote x-ray source 105 responsive to verifying an x-ray beam characteristic. At 522, communicating the x-ray beam field of view parameter to the remote x-ray source 105 includes communicating a parameter associated with a change in separation between a collimator aperture 114 and the remote x-ray source 105. At 524, communicating the x-ray beam field of view parameter to the remote x-ray source 105 includes communicating a parameter associated with actuating one or more electro-mechanical collimation edges. At 526, communicating the x-ray beam field of view parameter to the remote x-ray source 105 includes communicating a parameter associated with displacing, moving, or rotating one or more collimation edges. At 528 communicating the x-ray beam field of view parameter to the remote x-ray source 105 includes communicating a parameter associated with adjusting a relative position of an x-ray beam emitter within the remote x-ray source 105 and a collimator 110 to improve alignment of the x-ray beam to the sensor. At 530, the intra-oral x-ray sensor operation method 500 includes activating a discovery protocol that allows an intra-oral x-ray sensor 102 and the remote x-ray source 105 to identify each other and to negotiate information. At 540, the intra-oral x-ray sensor operation method 500 includes determining a remote x-ray source 105 and intra-oral x-ray sensor alignment. At 550, the intra-oral x-ray sensor operation method 500 includes communicating an activation instruction to the remote x-ray source 105 for imaging responsive to determining the remote x-ray source 105 and intra-oral x-ray sensor 102 alignment. At 560, the intra-oral x-ray sensor operation method 500 includes detecting a low intensity x-ray pulse to determine remote x-ray source 105 and intra-oral x-ray sensor alignment. At 570, the intra-oral x-ray sensor operation method 500 includes communicating an activation instruction to the remote x-ray source 105 for imaging responsive to detecting the low intensity x-ray pre-pulse to determine remote the x-ray source 105 and intra-oral x-ray sensor 102 alignment. It is noted that FIGS. 4A-4C and 5 denotes “start” and “end” positions. However, nothing herein should be construed to indicate that these are limiting and it is contemplated that other or additional steps or functions can occur before or after those described in FIGS. 4A-4C and 5. The claims, description, and drawings of this application may describe one or more of the instant technologies in operational/functional language, for example as a set of operations to be performed by a computer. Such operational/functional description in most instances can be specifically-configured hardware (e.g., because a general purpose computer in effect becomes a special purpose computer once it is programmed to perform particular functions pursuant to instructions from program software). Importantly, although the operational/functional descriptions described herein are understandable by the human mind, they are not abstract ideas of the operations/functions divorced from computational implementation of those operations/functions. Rather, the operations/functions represent a specification for the massively complex computational machines or other means. As discussed in detail below, the operational/functional language must be read in its proper technological context, i.e., as concrete specifications for physical implementations. The logical operations/functions described herein are a distillation of machine specifications or other physical mechanisms specified by the operations/functions such that the otherwise inscrutable machine specifications may be comprehensible to the human mind. The distillation also allows one of skill in the art to adapt the operational/functional description of the technology across many different specific vendors' hardware configurations or platforms, without being limited to specific vendors' hardware configurations or platforms. Some of the present technical description (e.g., detailed description, drawings, claims, etc.) may be set forth in terms of logical operations/functions. As described in more detail in the following paragraphs, these logical operations/functions are not representations of abstract ideas, but rather representative of static or sequenced specifications of various hardware elements. Differently stated, unless context dictates otherwise, the logical operations/functions are representative of static or sequenced specifications of various hardware elements. This is true because tools available to implement technical disclosures set forth in operational/functional formats—tools in the form of a high-level programming language (e.g., C, java, visual basic), etc.), or tools in the form of Very high speed Hardware Description Language (“VIDAL,” which is a language that uses text to describe logic circuits—)—are generators of static or sequenced specifications of various hardware configurations. This fact is sometimes obscured by the broad term “software,” but, as shown by the following explanation, what is termed “software” is a shorthand for a massively complex interchanging/specification of ordered-matter elements. The term “ordered-matter elements” may refer to physical components of computation, such as assemblies of electronic logic gates, molecular computing logic constituents, quantum computing mechanisms, etc. For example, a high-level programming language is a programming language with strong abstraction, e.g., multiple levels of abstraction, from the details of the sequential organizations, states, inputs, outputs, etc., of the machines that a high-level programming language actually specifies. See, e.g., High-level Programming Language, Wikipedia. Wikimedia Foundation, 18 Jan. 2014. Web. 4 Feb. 2014. In order to facilitate human comprehension, in many instances, high-level programming languages resemble or even share symbols with natural languages. See, e.g., Natural Language, Wikipedia. Wikimedia Foundation, 14 Jan. 2014. Web. 4 Feb. 2014. It has been argued that because high-level programming languages use strong abstraction (e.g., that they may resemble or share symbols with natural languages), they are therefore a “purely mental construct” (e.g., that “software”—a computer program or computer—programming—is somehow an ineffable mental construct, because at a high level of abstraction, it can be conceived and understood in the human mind). This argument has been used to characterize technical description in the form of functions/operations as somehow “abstract ideas.” In fact, in technological arts (e.g., the information and communication technologies) this is not true. The fact that high-level programming languages use strong abstraction to facilitate human understanding should not be taken as an indication that what is expressed is an abstract idea. In an embodiment, if a high-level programming language is the tool used to implement a technical disclosure in the form of functions/operations, it can be understood that, far from being abstract, imprecise, “fuzzy,” or “mental” in any significant semantic sense, such a tool is instead a near incomprehensibly precise sequential specification of specific computational—machines—the parts of which are built up by activating/selecting such parts from typically more general computational machines over time (e.g., clocked time). This fact is sometimes obscured by the superficial similarities between high-level programming languages and natural languages. These superficial similarities also may cause a glossing over of the fact that high-level programming language implementations ultimately perform valuable work by creating/controlling many different computational machines. The many different computational machines that a high-level programming language specifies are almost unimaginably complex. At base, the hardware used in the computational machines typically consists of some type of ordered matter (e.g., traditional electronic devices (e.g., transistors), deoxyribonucleic acid (DNA), quantum devices, mechanical switches, optics, fluidics, pneumatics, optical devices (e.g., optical interference devices), molecules, etc.) that are arranged to form logic gates. Logic gates are typically physical devices that may be electrically, mechanically, chemically, or otherwise driven to change physical state in order to create a physical reality of Boolean logic. Logic gates may be arranged to form logic circuits, which are typically physical devices that may be electrically, mechanically, chemically, or otherwise driven to create a physical reality of certain logical functions. Types of logic circuits include such devices as multiplexers, registers, arithmetic logic units (ALUs), computer memory devices, etc., each type of which may be combined to form yet other types of physical devices, such as a central processing unit (CPU)—the best known of which is the microprocessor. A modern microprocessor will often contain more than one hundred million logic gates in its many logic circuits (and often more than a billion transistors). See, e.g., Logic Gates, Wikipedia. Wikimedia Foundation, 2 Apr. 2014. Web. 4 Feb. 2014. The logic circuits forming the microprocessor are arranged to provide a microarchitecture that will carry out the instructions defined by that microprocessor's defined Instruction Set Architecture. The Instruction Set Architecture is the part of the microprocessor architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external Input/Output. See, e.g., Computer Architecture, Wikipedia. Wikimedia Foundation, 2 Feb. 2014. Web. 4 Feb. 2014. The Instruction Set Architecture includes a specification of the machine language that can be used by programmers to use/control the microprocessor. Since the machine language instructions are such that they may be executed directly by the microprocessor, typically they consist of strings of binary digits, or bits. For example, a typical machine language instruction might be many bits long (e.g., 32, 64, or 128 bit strings are currently common). A typical machine language instruction might take the form “11110000101011110000111100111111” (a 32 bit instruction). It is significant here that, although the machine language instructions are written as sequences of binary digits, in actuality those binary digits specify physical reality. For example, if certain semiconductors are used to make the operations of Boolean logic a physical reality, the apparently mathematical bits “1” and “0” in a machine language instruction actually constitute a shorthand that specifies the application of specific voltages to specific wires. For example, in some semiconductor technologies, the binary number “1” (e.g., logical “1”) in a machine language instruction specifies around +5 volts applied to a specific “wire” (e.g., metallic traces on a printed circuit board) and the binary number “0” (e.g., logical “0”) in a machine language instruction specifies around −5 volts applied to a specific “wire.” In addition to specifying voltages of the machines' configuration, such machine language instructions also select out and activate specific groupings of logic gates from the millions of logic gates of the more general machine. Thus, far from abstract mathematical expressions, machine language instruction programs, even though written as a string of zeros and ones, specify many, many constructed physical machines or physical machine states. Machine language is typically incomprehensible by most humans (e.g., the above example was just ONE instruction, and some personal computers execute more than two billion instructions every second). See, e.g., Instructions per Second, Wikipedia. Wikimedia Foundation, 13 Jan. 2014. Web. 4 Feb. 2014. Thus, programs written in machine language—which may be tens of millions of machine language instructions long—are incomprehensible. In view of this, early assembly languages were developed that used mnemonic codes to refer to machine language instructions, rather than using the machine language instructions' numeric values directly (e.g., for performing a multiplication operation, programmers coded the abbreviation “mult,” which represents the binary number “011000” in MIPS machine code). While assembly languages were initially a great aid to humans controlling the microprocessors to perform work, in time the complexity of the work that needed to be done by the humans outstripped the ability of humans to control the microprocessors using merely assembly languages. At this point, it was noted that the same tasks needed to be done over and over, and the machine language necessary to do those repetitive tasks was the same. In view of this, compilers were created. A compiler is a device that takes a statement that is more comprehensible to a human than either machine or assembly language, such as “add 2+2 and output the result,” and translates that human understandable statement into a complicated, tedious, and immense machine language code (e.g., millions of 32, 64, or 128 bit length strings). Compilers thus translate high-level programming language into machine language. This compiled machine language, as described above, is then used as the technical specification which sequentially constructs and causes the interoperation of many different computational machines such that humanly useful, tangible, and concrete work is done. For example, as indicated above, such machine language—the compiled version of the higher-level language—functions as a technical specification which selects out hardware logic gates, specifies voltage levels, voltage transition timings, etc., such that the humanly useful work is accomplished by the hardware. Thus, a functional/operational technical description, when viewed by one of skill in the art, is far from an abstract idea. Rather, such a functional/operational technical description, when understood through the tools available in the art such as those just described, is instead understood to be a humanly understandable representation of a hardware specification, the complexity and specificity of which far exceeds the comprehension of most any one human. Accordingly, any such operational/functional technical descriptions may be understood as operations made into physical reality by (a) one or more interchained physical machines, (b) interchained logic gates configured to create one or more physical machine(s) representative of sequential/combinatorial logic(s), (c) interchained ordered matter making up logic gates (e.g., interchained electronic devices (e.g., transistors), DNA, quantum devices, mechanical switches, optics, fluidics, pneumatics, molecules, etc.) that create physical reality representative of logic(s), or (d) virtually any combination of the foregoing. Indeed, any physical object which has a stable, measurable, and changeable state may be used to construct a machine based on the above technical description. Charles Babbage, for example, constructed the first computer out of wood and powered by cranking a handle. Thus, far from being understood as an abstract idea, it can be recognizes that a functional/operational technical description as a humanly-understandable representation of one or more almost unimaginably complex and time sequenced hardware instantiations. The fact that functional/operational technical descriptions might lend themselves readily to high-level computing languages (or high-level block diagrams for that matter) that share some words, structures, phrases, etc. with natural language simply cannot be taken as an indication that such functional/operational technical descriptions are abstract ideas, or mere expressions of abstract ideas. In fact, as outlined herein, in the technological arts this is simply not true. When viewed through the tools available to those of skill in the art, such functional/operational technical descriptions are seen as specifying hardware configurations of almost unimaginable complexity. As outlined above, the reason for the use of functional/operational technical descriptions is at least twofold. First, the use of functional/operational technical descriptions allows near-infinitely complex machines and machine operations arising from interchained hardware elements to be described in a manner that the human mind can process (e.g., by mimicking natural language and logical narrative flow). Second, the use of functional/operational technical descriptions assists the person of skill in the art in understanding the described subject matter by providing a description that is more or less independent of any specific vendor's piece(s) of hardware. The use of functional/operational technical descriptions assists the person of skill in the art in understanding the described subject matter since, as is evident from the above discussion, one could easily, although not quickly, transcribe the technical descriptions set forth in this document as trillions of ones and zeroes, billions of single lines of assembly-level machine code, millions of logic gates, thousands of gate arrays, or any number of intermediate levels of abstractions. However, if any such low-level technical descriptions were to replace the present technical description, a person of skill in the art could encounter undue difficulty in implementing the disclosure, because such a low-level technical description would likely add complexity without a corresponding benefit (e.g., by describing the subject matter utilizing the conventions of one or more vendor-specific pieces of hardware). Thus, the use of functional/operational technical descriptions assists those of skill in the art by separating the technical descriptions from the conventions of any vendor-specific piece of hardware. In view of the foregoing, the logical operations/functions set forth in the present technical description are representative of static or sequenced specifications of various ordered-matter elements, in order that such specifications may be comprehensible to the human mind and adaptable to create many various hardware configurations. The logical operations/functions disclosed herein should be treated as such, and should not be disparagingly characterized as abstract ideas merely because the specifications they represent are presented in a manner that one of skill in the art can readily understand and apply in a manner independent of a specific vendor's hardware implementation. At least a portion of the devices or processes described herein can be integrated into an information processing system. An information processing system generally includes one or more of a system unit housing, a video display device, memory, such as volatile or non-volatile memory, processors such as microprocessors or digital signal processors, computational entities such as operating systems, drivers, graphical user interfaces, and applications programs, one or more interaction devices (e.g., a touch pad, a touch screen, an antenna, etc.), or control systems including feedback loops and control motors (e.g., feedback for detecting position or velocity, control motors for moving or adjusting components or quantities). An information processing system can be implemented utilizing suitable commercially available components, such as those typically found in data computing/communication or network computing/communication systems. The state of the art has progressed to the point where there is little distinction left between hardware and software implementations of aspects of systems; the use of hardware or software is generally (but not always, in that in certain contexts the choice between hardware and software can become significant) a design choice representing cost vs. efficiency tradeoffs. Various vehicles by which processes or systems or other technologies described herein can be effected (e.g., hardware, software, firmware, etc., in one or more machines or articles of manufacture), and that the preferred vehicle will vary with the context in which the processes, systems, other technologies, etc., are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may opt for a mainly hardware or firmware vehicle; alternatively, if flexibility is paramount, the implementer may opt for a mainly software implementation that is implemented in one or more machines or articles of manufacture; or, yet again alternatively, the implementer may opt for some combination of hardware, software, firmware, etc. in one or more machines or articles of manufacture. Hence, there are several possible vehicles by which the processes, devices, other technologies, etc., described herein may be effected, none of which is inherently superior to the other in that any vehicle to be utilized is a choice dependent upon the context in which the vehicle will be deployed and the specific concerns (e.g., speed, flexibility, or predictability) of the implementer, any of which may vary. In an embodiment, optical aspects of implementations will typically employ optically-oriented hardware, software, firmware, etc., in one or more machines or articles of manufacture. The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely examples, and that in fact, many other architectures can be implemented that achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected”, or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably coupleable,” to each other to achieve the desired functionality. Specific examples of operably coupleable include, but are not limited to, physically mateable, physically interacting components, wirelessly interactable, wirelessly interacting components, logically interacting, logically interactable components, etc. In an embodiment, one or more components may be referred to herein as “configured to,” “configurable to,” “operable/operative to,” “adapted/adaptable,” “able to,” “conformable/conformed to,” etc. Such terms (e.g., “configured to”) can generally encompass active-state components, or inactive-state components, or standby-state components, unless context requires otherwise. The foregoing detailed description has set forth various embodiments of the devices or processes via the use of block diagrams, flowcharts, or examples. Insofar as such block diagrams, flowcharts, or examples contain one or more functions or operations, it will be understood by the reader that each function or operation within such block diagrams, flowcharts, or examples can be implemented, individually or collectively, by a wide range of hardware, software, firmware in one or more machines or articles of manufacture, or virtually any combination thereof. Further, the use of “Start,” “End,” or “Stop” blocks in the block diagrams is not intended to indicate a limitation on the beginning or end of any functions in the diagram. Such flowcharts or diagrams may be incorporated into other flowcharts or diagrams where additional functions are performed before or after the functions shown in the diagrams of this application. In an embodiment, several portions of the subject matter described herein is implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), or other integrated formats. However, some aspects of the embodiments disclosed herein, in whole or in part, can be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. In addition, the mechanisms of the subject matter described herein are capable of being distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal-bearing medium used to actually carry out the distribution. Non-limiting examples of a signal-bearing medium include the following: a recordable type medium such as a floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, a computer memory, etc.; and a transmission type medium such as a digital or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link (e.g., transmitter, receiver, transmission logic, reception logic, etc.), etc.). While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to the reader that, based upon the teachings herein, changes and modifications can be made without departing from the subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the subject matter described herein. In general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). Further, if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to claims containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense of the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense of the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). Typically a disjunctive word or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms unless context dictates otherwise. For example, the phrase “A or B” will be typically understood to include the possibilities of “A” or “B” or “A and B.” With respect to the appended claims, the operations recited therein generally may be performed in any order. Also, although various operational flows are presented in a sequence(s), it should be understood that the various operations may be performed in orders other than those that are illustrated, or may be performed concurrently. Examples of such alternate orderings includes overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise. While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. |
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abstract | The invention provides a system for collecting metal in an electrorefining process, the system having a hollow cathode; and a container defining an upwardly extending surface adapted to be received by the hollow cathode. An embodiment of the invention provides for metal reduction to occur on laterally facing and medially facing surfaces of the cathode such that electrolyte resides between surfaces of the cathode. Also provided is a metal electrorefining process having the steps of subjecting molten salt containing metal moieties to electrolysis wherein reduced metal accumulates in a cathode-cup construct in a first position; raising the construct to a second position above the molten salt while subjecting the construct to heat from the molten salt; withdrawing the cathode from the construct into a vestibule to the electrorefiner to a third position; and removing the cathode and cup from the electrorefiner to a fourth position. |
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047568780 | description | DETAILED DESCRIPTION Referring to FIG. 1, the fuel assembly includes an upper tie plate 2, a lower tie plate 4, and numerous fuel rods 6 extending between the tie plates. There are also a number of guide tubes 8 for control rods, which bind the upper and lower tie plate together. There is also a top-end assembly 12 which may include hold-down springs 14, which maintain the assembly in its proper position in the reactor. Cooling water flows upwardly through the assembly, as indicated by arrow 16. Spaced at intervals along the heighth of the assembly are a number grid spacers 18. A partial plan view of such a grid spacer is shown in FIG. 2. This spacer is of the type described and claimed in U.S. Pat. No. 4,077,843, granted Mar. 7, 1978 to John F. Patterson and Barney S. Flora, and assigned to the assignee of the present application. This patent may be consulted for a detailed description and is expressly incorporated by reference in this disclosure. FIG. 3 shows a partial perspective of this grid spacer with the bottom shown uppermost, the flow of water being indicated by the arrows 20,20'. Referring to FIGS. 2 and 3, the grid spacer includes a perimeter strip 22, which is in the form of a square encircling the entire member. There are also a plurality of grid members 24 and a second set of grid members 26 arranged at right angles to members 24. These two sets of grid members define grid apertures through which the fuel rods, some of which are shown in "phantom" lines, extend. Mounted on certain grid members are spring strips 28 (FIG. 3) which carry springs 30, one of which extends into each of the apertures formed by the grid members. The grid members 24,26 are deformed to produce dimples 31, which are of the "flow-through" type, i.e., open at their tops and bottoms. The bottom or leading edges of grid members 24,26 are convexly contoured, while the top or trailing edges (shown at the bottom of FIG. 3) are preferably tapered. FIGS. 4a and 4b are illustrations of this. During manufacture of the strips, the edges which are to be the leading edges may be coined as shown at 32 in FIG. 4a, while the edges which are to be trailing edges may be coined to a more acute angle, as shown at 34 in the same Figure. If used in this form, a reduction in flow resistance will be attained. However, improved results are secured by etching each of the edges in acid. This produces, very nearly, the shapes shown in FIG. 4b at 32' and 34'. It will be noted that the leading edge 32' has assumed, essentially, a semi-cylindrical cross-section, while the end of tapered portion 34' has been rounded. Another method of rounding the leading edges is illustrated by FIGS. 3, 5a, and 5b. In this method, after the grid spacer has been assembled, an electron beam 36 (FIG. 3) is focused on the edges and traversed therealong. The power of the beam and the rate of travel are correlated to produce a local melting. The surface tension of the molten metal draws it into, very nearly, a perfect semicylindrical shape. FIGS. 5a and 5b reproduce greatly enlarged photographs of cross-sections of such a strip after treatment by the electron beam. The shape shown in FIG. 5a was produced by a beam of 0.5 milliampere moving at a speed of 20 inches per minute along the strip of zircaloy-4 which was about 0.02 inch thick. The shape shown in FIG. 5b was the result of using a beam of 0.6 milliampere on the same type of strip at the same velocity. A suitably-powered laser beam could be substituted for the electron beam with the same results. The beam can be traversed relative to the grid members by the use of a conventional "X-Y table." In FIGS. 6 and 7, we show a deflecting-type grid. This grid is disclosed and claimed in application Ser. No. 838,768, entitled "Mixing Grid," filed on Mar. 12, 1986 by John F. Patterson, et al., and assigned to the assignee of this application. That application is expressly incorporated herein by reference. In this type of grid, the grid members are made up of pairs of strips 38,40 and 38',40', which may be welded together at their intersections. These plates are formed with matching channels 42,44, and 42',44', which are curved to deflect the cooling fluid as more fully-described in the above cited application. During their manufacture, these strips may be sheared at an angle, as shown in FIG. 8a. When placed together, the composite strip will assume the form shown in FIG. 8b, approximating that of FIG. 4a. If desired, the assembled strip may be etched to approximate the form shown in FIG. 4b. However, the form of grid spacer shown in FIG. 6 has, inherently, a very low resistance, and the etching step may not be worthwhile. Still another method of producing the rounded edge or edges is to direct a stream of a thick mixture of abrasive and an organic polymer through a grid, the strips preferably having the form shown in FIG. 4a or FIG. 8b. If the stream is surged back and forth, both edges of the strips will be rounded to the form shown in FIG. 5c. This is a convenient way of producing a form of strip, approximately that shown in FIG. 4b. FIG. 5c, which is based on a photograph, show on a greatly enlarged scale, the cross-sectional shape of the edges produced by this method. EXPERIMENTAL EXAMPLES EXAMPLE I In the following tests, grid spacers were incorporated in test fuel assemblies, including fuel rods of standard size and spacing (pitch) and the pressure drop across a spacer was measured at a water velocity typical of that present in operating nuclear reactors. The spacer was then removed from the assembly, the lower edges of all grid members rounded, and then replaced in the assembly. The pressure drop was again measured, and the reduction in pressure drop produced by rounding was determined. Results are shown in Table I, where in the types of spacer designated under "Test Piece" were as follows: A. A 6.times.6 intermediate grid of the type shown in FIGS. 1, 1a, and 1b of application Ser. No. 838,768, having double strips. The edges were rounded by hand grinding. B. A 6.times.6 test spacer made from a 17.times.17 spacer for a pressurized water reactor fuel assembly. Rounding was by electron-beam melting. C. A 5.times.5 test spacer made from a 9.times.9 spacer for a boiling water reactor fuel assembly. Rounding was by electron-beam melting. TABLE I ______________________________________ STRIP ROD ROD THICK- % REDUCTION TEST PITCH DIAM. NESS IN SPACER PIECE (IN.) (IN.) (IN.) PRESSURE DROP ______________________________________ A 0.496 0.376 2 .times. 0.012 10 B 0.496 0.376 0.020 7 C 0.572 0.424 0.020 8 ______________________________________ EXAMPLE II A full-sized 14.times.14 fuel assembly of the type used in pressurized water reactors (designated "D") was utilized for test purposes. Some of the grid strips were 0.026 inches and some 0.020 inches thick. Some of the spacers were of standard form and some had the lower edges of the grid strips rounded by electronbeam melting. The pressure drop, under rates of water flow typical of reactor operating conditions, was measured across various spacers, and the average reduction obtained by rounding was determined. Results are shown in Table II. TABLE II ______________________________________ STRIP ROD ROD THICK- % REDUCTION TEST PITCH DIAM. NESS IN SPACER PIECE (IN.) (IN.) (IN.) PRESSURE DROP ______________________________________ D 0.550 0.417 0.026/0.020 6.5 ______________________________________ The following experiments involved the use of a stiff but flowable abrasive composition comprising a viscous carrier laden with abrasive granules, such as is described in U.S. Pat. No. 3,909,217, granted Sept. 30, 1975, to Kenneth E. Perry. The mixture was of doughlike consistency and contained 16 mesh and 36 mesh grains of silicon carbide. It approximated the composition of Example 3 of the above patent. EXAMPLE III A 6.times.6 test spacer of the type shown in FIGS. 2 and 3 having an overall height of three inches was made up, and its pressure drop determined in the same manner as described in Example I above. An identical test spacer (designated Test Piece E) was abraded by pushing the composition described in the preceeding paragraph back and forth through it at 100 pounds per square inch for 150 cycles over a period of 80 minutes, in directions perpendicular to the plane defined by the lower edges of the grid members. After cleaning, it was found, on inspection, that the top and bottom edges of grid members 24,26, dimples 31, and to a lesser degree, springs 30, received the form shown in 5c. Results, tabulated in the same manner as in the previous examples, are shown in Table III. TABLE III ______________________________________ STRIP ROD ROD THICK- % REDUCTION TEST PITCH DIAM. NESS IN SPACER PIECE (IN.) (IN.) (IN.) PRESSURE DROP ______________________________________ E 0.496 0.376 0.020 20 ______________________________________ EXAMPLE IV A full-size 15.times.15 spacer of the type shown in FIGS. 2 and 3 was abraded in the manner described in Example III. Since the spacers are subjected to a force on the order of 5,000 pounds in each direction during processing, it is important to incorporate support across the spacer span. This spacer was processed for 145 cycles at 100 psi over a period of 196 minutes. This grid (designated Test Piece F) was mounted with other spacers in a test assembly described in Example II and the pressure drop across it determined. Results are shown in Table IV. TABLE IV ______________________________________ STRIP ROD ROD THICK- % REDUCTION TEST PITCH DIAM. NESS IN SPACER PIECE (IN.) (IN.) (IN.) PRESSURE DROP ______________________________________ F 0.550 0.417 0.018 22.5* ______________________________________ *Average of two runs. While we have described several embodiments of our invention in considerable detail, it will be apparent to those skilled in the art that various changes can be made. We therefore wish our invention to be limited solely by the scope of the appended claims. |
description | This application is a continuation of application Ser. No. 10/483,596, filed on Feb. 10, 2004 now U.S. Pat. No. 6,946,656, which is hereby incorporated by reference in its entirety. The present invention relates to a charged particle beam device and relates in particular to a measurement method and device thereof for inspecting or measuring the dimensions and shape of a pattern formed on a sample piece. The greater scale of integration and miniaturization of semiconductor devices in recent years has resulted in many diverse patterns being formed on the wafer and makes it ever more important to evaluate and measure the dimensions and shapes of these patterns. How fast these measurement points can be detected is critical for quickly and automatically testing the numerous measurement points. During fast detection of measurement points, it is necessary to focus on the pattern after shifting to the measurement point and to also set the desired magnification (scale) for observing that point. In charged particle optical systems, the conditions for focusing on the wafer are determined by the acceleration voltage of the charged particle supply, the voltage applied to the wafer, and the height of the wafer. In the method disclosed for example in JP-A No. 126573/1999, a laser beam is irradiated onto the wafer, the height of the wafer is detected by using that reflected light, and the height information obtained in this way is fed back to an objective lens control system serving as one control device for the charged particle optical system, and the necessary excitation voltage is applied to the objective lens at the same time that movement to the observation point ends. In recent years however, more and more wafers are being found to contain a static electrical charge or electrostatic charge that still remains even when the wafers are electrically grounded. The cause of this static or electrostatic charge may for example be due to a fixed electrical potential from splitting (split polarization) of polarized material within the resist due to friction during applying of the resist coating by a spin coater. Another possible cause is residual electrical charges from etching that uses plasma. These residual electrostatic charges remaining on the sample can cause the focus of the charged particle beam to deviate and are a cause of magnification fluctuations and measurement errors in the charged particle beam device. A method is disclosed for example in JP-A No. 176285/1995 for resolving the focus deviation problem by storing a focus offset value for each measurement point on a scanning electron microscope to prevent focus deviations from interfering with automatic measurement. Another method is disclosed in JP-A No. 52642/2001 for installing electrometers at multiple points in proximity to the sample inside a vacuum and feeding a retarding voltage back as a value based on those measurement results. However, the technology disclosed in JP-A No. 176285/1995 has the following problems. The electrostatic voltage on the wafer is determined by the temperature and humidity, state of the resist and plasma intensity in that manufacturing process, so the electrostatic voltage is not a fixed value even on wafers undergoing the same manufacturing process. So even if the focus deviation is stored in a file for making automatic measurements, the focus deviation has to be updated (rewritten) for each wafer. A long time is therefore needed to measure a wafer and this delay caused productivity to drop. The electrostatic electrical potential also still remained unchanged on the wafer so that the actual accelerating voltage is different from the accelerating voltage actually needed. This differential causes differences in contrast and tiny structures to appear in secondary charged particle phenomenon that are formed. Other problems also still unresolved included errors in controlling the magnification, etc. In the method disclosed in JP-A No. 52642/2001, using electrometers installed within a vacuum, the electrostatic electrical potential cannot be measured without moving to the measurement point so a long time was required to make a measurement at one point. Another problem is that when a breakdown occurred, the charged particle and stage in the vacuum unit has to be exposed to the outside air so that maintenance of the equipment is difficult. Yet another problem is that the multiple electrometers have to be adjusted to constantly provide the same output. A first object of the present invention is to provide a device and method for detecting the characteristic electrostatic charge state of the sample without having to also measure the electrostatic charge at each measurement point. A second object of the present invention is to provide a method ideal for reducing or eliminating measurement errors or fluctuations in magnification due to electrostatic charges, a magnification adjustment method, and a device to implement these methods. To achieve the first object, a technique is proposed in the present invention for measuring the electrical potential distribution on the sample by utilizing a static electrometer to measure the voltage on the sample during movement of the sample being loaded by the loader of the charged particle beam device. To achieve the second object, a technique is proposed in the present invention for measuring electrostatic charges at specified points on the sample, and from that electrostatic charge quantity then isolating and measuring the wide area electrostatic charge. As another method to achieve the second object, the electrostatic charge quantity at specified locations is irradiated under at least two charged particle irradiation conditions, and a fitting coefficient is formed that expresses changes in the electrostatic charge voltage from changes in the irradiation conditions, and the pattern dimensions are then corrected based on the feedback coefficient thus formed. The best modes for carrying out the invention are described next in detail using the specific embodiments of the present invention. The embodiments of the present invention are described next while referring to the drawings. The example in the embodiment was described as using a scanning electron microscope (SEM). However, the present invention is not limited to this and other charged particle beam devices such as ion beam irradiation devices can be used. The example in the present embodiment also describes detecting secondary electrons and/or reflected electrons which are one type of charged particle. However, the present invention is not limited to this and may detect other charged particles such as secondary ions, etc. FIG. 1 shows the overall structure of the present invention. An integrated controller 42 controls the overall device via the charged particle optical system controller 41, stage controller 40, and wafer conveyor 28, based on the observation position information, wafer information and acceleration voltage of the charged particle entered by the operator from the user interface 43. The wafer conveyor 28 extracts the wafer from the wafer cassette 29 using the conveyor arm 30 after receiving an instruction from the integrated controller 42. The wafer conveyor 28 opens the gate valve 26b separating the sample exchange chamber 25 maintained in a vacuum from an external section connecting to the outer atmosphere. The wafer conveyor 28 loads the wafer into the sample exchange chamber. The wafer inserted in the sample exchange chamber is conveyed to a sample chamber 24 via the gate valve 26a and is clamped onto the sample stage 21. The charged particle optical system controller 41 controls a high voltage controller 34, a retarding controller 33, a condenser lens controller 35, an amplifier 36, an alignment controller 37, a deflection signal controller 44, and an objective lens controller 39 according to instructions received from the integrated controller 42. A primary charged particle beam 13 pulled from the charged particle supply 11 by the pull-up electrode 12 is irradiated onto the wafer 19 after being focused by the condenser lens 14 and objective lens 18. During the above process, the path of the charged particle beam is aligned by the alignment coil 16. The upper part of the wafer is also scanned two-dimensionally by a signal received by the deflecting coil 17 from a deflecting signal controller via a deflecting signal amplifier 38. In the following description, a signal for changing the optical conditions of the charged particle beam is sent to each optical element and calculated in a section called a controller, control device or control processor, etc. A retarding voltage (negative voltage when using an electron microscope) is applied to the wafer from the retarding controller 33 to decelerate the charged particle beam. The irradiating of the primary charged particle beam 13 onto the wafer 19 causes secondary charged electrons 20 to be emitted from the wafer. These secondary electrons 20 are then trapped by the secondary charged electron detector 15 and are used via an amplifier as luminance signals for the secondary charged electron display device 46. The secondary charged electron display device deflection signal is synchronized with the deflection signal from the deflection coil so the pattern shape of the wafer is faithfully reproduced on the secondary charged electron display device. In order to test and observe the pattern on the wafer at high speed, a sample stage detects the wafer height when the wafer has moved to the desired observation point. The focus of the objective lens must then be aligned according to that height. A function is therefore installed in order to detect that wafer height by using light. The sample stage position detector 32 detects the position of the sample stage. At the point where the sample stage is close to the desired position, a height detection laser emitter 22 irradiates light towards the wafer. This reflected light is received by the position sensor 23 and the wafer height detected from that received light position. The amount of focus determined according to this detected height is then fed back to the objective lens. The focus is therefore already set when the sample stage arrived at the specified position and the pattern can be automatically detected without the intervention of the operator. If there is no electrostatic charge on the wafer, the excitation current required for focusing the objective lens is generally expressed by the following function (1).Iobj=F(Vo, Vr, Z) (1)Here, Iobj is the excitation current for the objective lens when there is no electrostatic charge on the wafer, F is the function for calculating the excitation current of the objective lens, Vo is the voltage of the charged particle supply, Vr is the wafer electrical potential, (retarding voltage applied to the wafer), Z is the height of the wafer. The function F can be derived by electron optical simulation or by actual measurement. A fixed focus control can be used to establish a relation shown in formula (1) for applying a retarding voltage with a electrical potential equivalent to a wafer usually having no electrostatic charge. However, when the wafer itself contains an electrostatic charge then the excitation current value required by the objective lens is as shown in formula (2). The focus current will differ depending on whether the wafer holds or does not hold an electrostatic charge.Iobj′=F(Vo, Vg′, Z) (2) Therefore, due to this difference the focus cannot be aligned no matter how accurately the height is detected, so the secondary charged particle image will appear blurred, detection at the observation point will fail and automatic measurement will be impossible. Here Iobj′ is the excitation current of the objective lens when the wafer holds an electrostatic charge, Vg′ is the total voltage of the retarding voltage Vr and the wafer electrostatic voltage ΔVg or in other words, Vg=Vr+ΔVg. The electrostatic charge on the wafers differs according to factors such as the resist and the material in the underlayer but in most cases is in a concentric circular shape. The present invention measures the amount of electrostatic charge in this concentric circular shape on the wafer and then uses this electrical potential as feedback. The wafer stored inside the wafer cassette is extracted by the conveyor arm 30 (conveyor mechanism) and is measured by the probe 31 while being conveyed in the sample exchange chamber. The measured value is reported to the charged particle optical system device via the static electrometer 45. In the example described in the present embodiment, the probe for measuring the electrical potential on the sample is above the movement path of the sample being conveyed by the conveyor mechanism and installed at a position separated from the material. However the present invention is not limited to this example. The probe for example may be installed on the movement path of the device for delivering and accepting the sample in the preheat chamber from the sample chamber, or the device for conveying the sample into the preheat chamber from the outside. In the above example, the wafers tended to have an electrostatic charge in a concentric circular shape. So the overall electrical potential across the entire sample can be found by measuring the electrical potential distribution in a linear shape including the center position on the wafer surface. The following description shows an example particularly effective for measuring this kind of electrical potential distribution with a scanning electron microscope on a sample such as a semiconductor wafer. FIG. 2 is a drawing showing the relative positions of the wafer cassette, and the conveyor arm as an essential element of the sample loader device, and the wafer, and static electrometer and sample exchange chamber. The wafer is extracted by the conveyor arm 30 from the wafer cassette 29 and conveyed into the sample exchange chamber 25. The probe 31 of the static electrometer is clamped onto the clamp bed 53 above the conveyor path of the wafer and further so that the center line 52 aligns with the wafer center line 51 above the wafer. The static electrometer probe measures the voltage of both the wafer and the grounded conveyor arm so that a more accurate value can be obtained by calibrating the wafer electrical potential based on the ground potential of the conveyor arm. The position the wafer will pass is a permanently fixed position, and since the probe is also clamped to the clamp bed, the relation of these two positions will not change so stable measurements can always be made. The probe is outside of the vacuum so even if the probe becomes defective, it can easily be repaired or replaced. In the present embodiment, the probe was installed outside the vacuum to make handling easier. However, the invention is not limited to this and the probe may be installed anywhere along the path of the wafer. Also in this embodiment, the wafer is moved so that the center of the probe is aligned with the center line of the wafer. However the present invention is not limited to this example. As described above, the electrostatic charge on the wafer is a concentric circular shape in most cases. When the distribution of this electrostatic charge takes the form of a so-called peak, where the wafer center is the highest point and the electrostatic charge becomes lower towards the edge of the wafer, even if the probe center is somewhat offset from the centerline of the wafer, the overall electrical potential distribution can be determined. The overall electrical potential distribution can therefore also be determined from a linear shaped electrical potential distribution that is offset from the wafer center. FIG. 3 is a chart expressing the electrostatic charge voltage measured from the surface electrical potential as a distribution coefficient above the wafer surface. FIG. 3 also shows the retarding feedback procedure. The conveyor arm for the wafer does not usually operate at a constant speed so even if the measurement time is a fixed period time-wise, the coordinates on the wafer will not be at fixed intervals from each other. However an electrical potential corresponding to accurate coordinates can be obtained if the coordinates on the wafer are calculated from the speed pattern of the conveyor arm during the electrical potential measurement. A distribution function for the electrical potential can be made based on this acquired data. An approximate expression is first created as an even function (quartic function in FIG. 3) based on all of this acquired data. Next, the differential at each measurement point versus this approximate expression is calculated. The electrical potential measurement value contains an error. When this differential (value) is larger than an established threshold, it is excluded since the error in the measurement is large. An approximate expression is once again formed without the excluded data. This process is repeated several times and ends when the differential for all values is smaller than the threshold. The function made in this way is a function expressing the distance from the center of the wafer as the electrical potential. The electrical potential for making the correction is calculated from this function, and from the stage coordinates acquired from the stage controller device. This correction voltage is supplied to the wafer via the retarding controller shown in FIG. 1. Data is acquired each time the wafer under observation is conveyed to the sample exchange chamber. This data is valid until wafer observation ends and an instruction to return the wafer to the original wafer cassette is issued. The embodiment of the present invention was described above. In the embodiment of the invention, a method was described for feeding back the measured electrostatic charge of the wafer unchanged, as retarding voltage. However, the electrostatic charge voltage made be converted to an excitation current for the objective lens and fed back. In that case however, the retarding voltage and the wafer electrostatic charge voltage added together should not exceed the voltage of the charged particle power supply. If the voltage of the charged particle power supply for example is −2000 volts, then when the charged particle voltage needed for beaming onto the sample is −300 volts, the retarding voltage applied to the wafer must be −1700 volts. Under these conditions, consider the case when observing a wafer having a maximum electrostatic charge of −290 volts. Here, the primary charged particle beam can still reach the sample even if a voltage is applied as a retarding voltage to correct the −290 volt static charge, or even if that voltage is converted to an excitation current and applied to the objective lens. However, on a wafer with a maximum electrostatic charge of −310 volts, the combined retarding voltage and electrostatic voltage will total −2010 volts thus exceeding the charged particle power supply voltage. In that case, the primary charged particle beam will not be able to reach the sample and is reflected away. A voltage of 310 volts must be applied as a retarding voltage to compensate for the −310 volts. The measured voltage may also be fed back to the charged particle power supply instead of applying it as a retarding voltage. Also in the embodiment of the present invention, instead of using a magnetic field lens whose high inductance makes high speed control difficult as the feedback destination for the retarding voltage, an electrostatic lens may be installed as the objective lens, or an electrostatic lens separately installed along with a magnetic field lens. A focus correction value based on the electrostatic charge voltage can then be fed back to these static lenses. Among other methods for aligning the focus, when the SEM employs the so-called boosting method wherein a positive voltage is applied to tubular electrodes inside the objective lens, the focus can be aligned by adjusting this positive voltage. Most other technology for aligning the focus of the electron beam may also be utilized. In the present invention, one static electrometer probe is installed to align with the center of the wafer; however, multiple probes may also be installed. FIG. 4 is a drawing of a structure for measuring the entire wafer surface with multiple probes arrayed along the wafer conveyance path. Here, multiple probes 31 are arrayed in a matrix on the clamp bed. In this case, the wafer 19 is temporarily stopped at a specified position along the conveyance path and the electrostatic charge measured at the respective points. This method has the advantages that there is no need to worry about the relation between speed or coordinates since the conveyor arm has stopped. Another advantage is that a distribution coefficient can be obtained even when the electrostatic charge does not have a symmetrical distribution. Also, the measuring points have already been established so that during fully automatic inspection of the semiconductor pattern width or fault inspection with the scanning electron microscope, those measurement points or the electrostatic charge near those points can be selectively tested and feedback then applied. The present embodiment need not only use just feedback based on the quantity of electrostatic voltage, but may also combine it with other information to find a feedback value for the retarding voltage. Further, when a problem has occurred in the static electrometer due to any number of causes, and feedback is applied to the retarding voltage, conversely the focus value itself might then deviate. In such cases another means may be installed to evaluate the focus. When a problem then appears in the focus evaluation value, then a means may also be installed to perform fault diagnosis of the static electrometer, stop the focus feedback process based on the electrostatic charge measurement, and warn the operator of the abnormality. As explained above, the present invention is capable of correcting the electrostatic charge even on wafers where focus offsets have occurred due to electrostatic charges and the success (pass) rate for pattern detection during automatic measurement has dropped. The present invention is also capable of automatically measuring wafers in the same way as wafers with no electrostatic charge. The invention further has the merit that the electrostatic charge voltage can be measured on each wafer so that measurement files are not needed and also that the file does not have to be revised according to whether or not there is an electrostatic charge or the size of that charge. In view of the problems in making accurate tests and measurements in particular when different electrostatic charge phenomenon occur in the sample (semiconductor wafer, etc.), the embodiment described next relates to a device and method allowing highly precise testing and measurement even when different electrostatic charge phenomenon. In a charged particle beam device, output information from a secondary charged particle detector is synchronized with the scanning by the charged particle beam and reproduced on an image display device as described above. The ratio of distance A between two points on the scanned image on the CRT (or display device) versus the distance a between two points on the sample, is the observation magnification MSEM.MSEM=A/a The distance a between two points on the sample is usually in inverse proportion to the observation magnification MSEM since the screen on the display device is a fixed size. By therefore measuring the distance A between the two points on the scanned image on the display, and dividing A by the observation magnification MSEM, we can derive the line dimension as a=A/MSEM. Along with the advances in miniaturization in the semiconductor industry in recent years, the SEM is being used in place of the optical microscope in semiconductor fabrication processes or in testing after the fabrication process (for example, electrical operation tests or dimension measurements using the electron beam). In the sample (wafer) used by the semiconductor industry as the insulation, fluctuations in the insulation are occurring over time due to irradiation by the primary electron beam and causing deterioration in the scanned image. A typical technology to resolve this problem was disclosed in JP-A No. 151927/1993 constituting a predose method wherein the SEM emitted (irradiated) a primary electron beam at a magnification different from the magnification during observation, and a static charge was progressively generated on the surface of the sample. A retarding method and a boosting method were next developed as disclosed in JP-A No. 171791/1997. In these methods, the retarding voltage applied to the sample was adjusted, and by observation with a primary electron beam having a low acceleration voltage below one kilovolt, a positive static charge was formed on the insulation. These methods generated a stable surface static charge for recreating the image and further attained a high resolution of approximately 3 nanometers. Following this, a method was developed utilizing a SEM as in JP-A No. 200579/2000 wherein instead of a primary electron beam during the usual observation, an energy electron beam was first irradiated (onto the sample) to progressively generate a surface electrostatic charge. These methods allowed easily generating a stable, high surface electrostatic voltage and permitted observations of electrical potential contrast based on the difference in electrostatic charge voltage and the film remaining on the bottom of contact holes with a high aspect ratio. However, when observing under the condition of this surface electrostatic charge voltage, it was found that a fluctuation of some several percent occurred in the measurement dimension values as the surface electrostatic charge was increased. Due to ever shrinking sizes in the semiconductor process, these fluctuations in measurement dimensions exceeded their allowable thresholds. The cause of the problem was fluctuations in observation magnification MSEM accompanying the surface electrostatic charge. FIG. 9 is a concept drawing showing an electronic optical system composed of a scanning deflector, objective lens and sample. This figure shows the relation of the coil current I7 of scanning deflector 107 to the optical magnification Mobj of objective lens 106 and observation magnification MSEM. The primary electron beam 101 emitted radially from one point on the crossover surface focused on one point on the wafer 108 surface. When the emission point of an imaginary primary electron is separated by an amount 1 from the center axis using the scanning deflector 107, it deviates by Mobj on the sample surface. When the conversion coefficient of the scanning deflector 107 and the coil current are respectively set as K and I7, the distance a between two points on the sample can be calculated with the next formula.a=KMobjI7 (4)Also, when the conversion coefficient of the CRT (display) is L, the distance A between two points on the scanning image on the CRT is shown in the next formula.A=LI7 (5)Here, considering the case where the optical magnification has shifted from Mobj to Mobj′, the electrical current for scanning the distance between two points a on the sample changes from I7 to I7′, and the distance between two points A on the scanning image of the CRT changes to A′.a=KMobjI7′ (6)A′=LI7′ (7)The observation magnification consequently changes from MSEM to MSEM′.Mobj′=(Mobj/Mobj′)MSEM (8)Using the following formula allows making correct dimension measurements even if the observation magnification has shifted.a=A′/MSEM′ (9)Being able to calculate the optical magnification Mobj and Mobj′ with good accuracy regardless of whether there is an electrostatic charge, allows measuring dimensions with high accuracy. FIG. 10A through 10C are drawings showing the principle of a surface electrostatic charge on the wafer. The retarding voltage Vr is applied to the wafer substrate. FIG. 10A shows the case where the wafer has a characteristic electrostatic charge prior to observation by SEM, because of friction from the spin coater applying the resist coating, or from etching with plasma. The electrostatic voltage in FIG. 10A spans the entire surface of the wafer and is therefore called the wide area electrostatic voltage ΔVg. The wide area electrostatic voltage in the vicinity of the observation point is Vg=Vr+ΔVg. The optical magnification Mobj at wide area electrostatic voltage Vg is expressed by the following formula (1).Mobj=M(Vo, Vg, Z) (10) The function M can be found by electronic optical simulation or by actual measurement. The electrostatic voltage ΔVs from the electron beam irradiation on the other hand, is localized as shown in FIG. 10B and is called a localized electrostatic voltage. When both electrostatic charges overlap, the localized voltage in FIG. 10C is Vs=Vg+ΔVs. FIG. 11 is a drawing showing the mechanism by which the wide area electrostatic voltage Vg and localized electrostatic voltage ΔVs make the optical magnification Mobj of the objective lens change. The wide area electrostatic voltage Vg varies the electrical potential within the objective lens 106a so that an electrostatic lens is formed on the sample and the focus deviates. When this focus is aligned, a marked change occurs in the excitation current I6. This I6 changes and also the energy beamed onto the sample fluctuates so that energy concentrates as in track 1a, and the optical magnification Mobj fluctuates. Conversely however, Vg can be estimated from the amount of fluctuation in I6. The electrostatic voltage ΔVs from the electron beam irradiation is localized so there is almost no effect on the excitation current I6. Regardless of this, the localized electrostatic voltage ΔVs forms a minute static lens 108b so that the primary electrons 101 are concentrated along the track as in 101b, and makes the optical magnification Mobj fluctuate greatly. The above description therefore confirms that the wide area electrostatic charge exerts a large effect on the focus and the localized electrostatic charge exerts a large effect on the magnification. As shown above, the two electrostatic phenomenon have completely different characteristics. The extent of the effect exerted on the focus and magnification by each electrostatic phenomenon is different so that high accuracy correction cannot be achieved even if correcting each of them separately is attempted. To solve this problem, the wide area electrostatic voltage ΔVg and the localized electrostatic voltage ΔVs, can be isolated and measured, or a means to estimate them can be installed and a means to calculate the correct optical magnification Mobj can then be achieved based on this data. Correcting the deflection intensity of the scanning deflector based on the amount of magnification correction allows accurately displaying a two-dimensional scanning image at the specified observation magnification. Simplifying the magnification correction of the measurement length value itself will prove effective in measurement of dimensions in the semiconductor process. The effect of the present invention is shown by referring to FIG. 12 and FIG. 13. FIG. 12 shows the magnification fluctuation sensitivity coefficient Tg when the wide area electrostatic voltage Vg has fluctuated within a range from −0.6 kV to −1.5 kV versus a retarding voltage Vr=−1.2 kV. The magnification fluctuation quantity ΔMg=(Mobj′−Mobj) can be calculated from Tg and ΔVg by the following formula.ΔMg/Mobj=Tg*ΔVg (11)Here, the Tg fluctuated due to the wide area electrostatic voltage Vg and observation conditions prior to the electrostatic charge. Therefore each of these observation conditions found by calculation or experiment per the graph of FIG. 8 must be stored. Also, instead of using the formula (11), the magnification Mobj or the Mobj′ may be found directly from the wide area electrostatic voltage Vg. On the other hand, FIG. 13 shows the magnification fluctuation sensitivity coefficient Ts when the beam irradiation area has fluctuated at a retarding voltage Vr=−1.2 kV. The magnification fluctuation amount ΔMs=(Mobj′−Mobj) can be calculated from Ts and ΔVs by the next formula.ΔMs/Mobj=Ts*ΔVs/Vacc (12)Here, Ts is the fluctuation due to the beam irradiation area size and observation conditions prior to the electrostatic charge. The formula (12) shows a good proportional relationship with the magnification correction ΔMs and localized electrostatic voltage ΔVs. The Ts can be grouped into four sections according to the beam irradiation area (in other words, the beam magnification). A magnification lower than 50 times is regarded as a wide area electrostatic charge. The section from 50 times to 500 times is a transition region from a wide area static charge to a localized static charge. The section from 500 times to 5,000 times is regarded as largely a fixed value. A high magnification from 5,000 times shows a trend for Ts to gradually diminish. Therefore, one side of the irradiation area may preferably be from 10 μm to 300 μm, so as to contain a section where the magnification fluctuation sensitivity coefficient Ts includes a section with a largely fixed value from 500 to 5,000 times. This kind of section allows maintaining the estimated accuracy of the correction value and reduces the number of data that must be stored in advance. FIG. 5 shows a first working example of the SEM of the present embodiment. The primary electron beam 101 from the cathode (negative electrode) 104 is focused by a condenser lens 105, and two-dimensional scanning of the wafer 108 further performed by the scanning deflector 107. The primary electron beam 101 applies a negative retarding voltage to the wafer 108 via the sample stage 109 so that the beam is decelerated in the decelerating magnetic field between the objective lens 106 and the wafer 108, and the beam on the wafer 108 is narrowed even further by the lens action of objective lens 106. Secondary electrons 102 are emitted when the primary electron beam 101 irradiates onto the wafer 108. The magnetic field created between the objective lens 106 and the wafer 108 functions as an accelerating magnetic field on the secondary electrons 102 that were generated to pull these secondary electrons 102 into electron beam passage holes of objective lens 106 and these secondary electrons 102 then rise while subject to the lens effect rendered by the magnetic field of objective lens 106. These rising secondary electrons 102 strike the conversion electrode 110 with high energy, to newly generate secondary electrons 103. These secondary electrons 103 are pulled towards the scintillator 111 that was applied with a positive voltage of approximately 10 kV. Light is emitted when the secondary electrons 103 strike the scintillator 111. Though not shown in the drawing, this light is supplied to a photoelectron multiplier tube via a light guide, converted into electrical signals, and after being amplified, the output is used for brightness modulation of the CRT. The explanation of FIG. 5, described the control processor as being integrated with the scanning electron microscope, or a subsection of the microscope. Needless, to say, the invention is not limited to this example, and a separately installed control processor as described next may be utilized instead of integrated with a scanning electron microscope. In that case, a notification medium for conveying the detection signal detected by the secondary electron detector to the control processor, and conveying the signal from the control processor to the deflector or lens of the scanning electron microscope is required. An input/output terminal is also needed for input or output of the signal conveyed by that notification medium. Further, a control processor to install a program for implementing the following described processing in a storage medium, and comprising a means for supplying the necessary signals to a scanning electron microscope having an image memory, and also executing that program may be used. The device of the present embodiment contained a static electrometer as described for example in the first embodiment as a measurement means (voltage differential measurement device) for measuring the wide area electrostatic voltage ΔVg. The wide area electrostatic voltage on the wafer has a concentric circular shape so that the electrical potential distribution of the entire sample can be known by measuring the electrical potential distribution in a linear shape including the center position on the wafer. Therefore the method as described for the first embodiment wherein a static electrometer probe 114 is clamped along the conveyance path of the wafer 108, and the movement of the conveyor arm 181 to measure along a linear shape is applicable. The wide area electrostatic voltage ΔVg is expressed as a function of the distance r from the wafer center by utilizing the measurement data, and each the measurement point is moved, a voltage Vr is fed back for the retarding voltage. Also, the voltage that the primary electron beam 101 beams onto the wafer 108 is generally made a fixed voltage value Vacc=V0+Vg. Here, V0 is equivalent to the voltage of the cathode 104. This embodiment also contains a secondary electron energy filter as a measurement means (voltage differential measurement device) for the localized electrostatic voltage ΔVs. A mesh electrode 112 for example, is installed below the conversion electrode 110. The voltage applied by this mesh electrode 112 is swept using the wide area electrostatic voltage Vg as a reference point, and the signal conversion quantity of the secondary electrons (so-called S curve) measured. The S curve at the observation point of the actual sample and the S curve measured on a conductive sample surface are compared, and the shift voltage set as the localized electrostatic voltage ΔVs. The electrostatic correction controller 120 measures the wide area electrostatic voltage Vg, and executes an S curve measurement sequence up to acquiring of a localized electrostatic voltage ΔVs. The amount of magnification compensation is then calculated based on the excitation current for the objective lens 106 and the Vg and ΔVs that were found, and the deflection intensity of the scanning deflector 107 then corrected. In view of the fact that a localized static charge exerts a large effect on magnification compared to the wide area electrostatic charge, the present embodiment corrects the magnification by subtracting a value equivalent to the wide area electrostatic charge, from an electrostatic charge (localized electrostatic charge) at a specified location. In measuring electrostatic charges merely by using an energy filter, the localized and wide area electrostatic charges (at least an area larger than the scanning area, for example an area larger than an observation area with a magnification of 50 times) are detected in a compounded state. So the present embodiment, by subtracting the electrostatic charge at the electron beam scanning locations measured by static electrometer 114, from the electrostatic charge measured by the energy filter, the localized electrostatic change can be measured based on the actual electron beam without depending on the wide area charge. This embodiment also allows adjusting the deflection range of the scanning deflector based on the magnification fluctuation quantity ΔMs acquired from the above described calculation method. This embodiment also allows correcting the measured length (or end measurement) value. When adjusting the deflecting range of the scanning deflector and that scanning deflector is the electromagnetic type, the electrical current required for correcting the magnification fluctuation quantity ΔMs, can be added to or subtracted from the original deflection current to make the adjustment. An accurate measurement length value can also be calculated by multiplying or dividing the magnification fluctuation ratio by the measurement length acquired by a measurement length method used in scanning electron microscopes of the known art and using the result for feedback to the measurement length value. In the present embodiment, the wide area electrostatic charge and localized electrostatic charge were measured while isolated from each other, however methods for adjusting the scanning deflector and methods for correcting the measurement length are not limited to this method. FIG. 6 shows a second working example of the present embodiment. In this example, a means to measure the sample height has been added instead of the static electrometer of the previous working example. For example, a laser emission device 115 for detecting the sample height at the point in time that the sample stage 109 has approached the specified measurement point, beams a laser light 116 towards the wafer 108. A so-called Z sensor here is a position sensor 117 receives that reflected light and detects the wafer height from the position that the light was received. The wide area electrostatic voltage Vg is determined from this data on the sample height and excitation current of the objective lens when exactly focused so that if the relation of these three physical quantities are calculated by test or by an electronic optical simulation, then the wide area electrostatic voltage Vg can be estimated without having to directly measure the voltage. In this embodiment, the electrostatic correction controller 120 executes an S curve measurement sequence until the localized electrostatic voltage ΔVs is obtained and sample height measurement with the Z sensor are obtained for estimating the wide area electrostatic voltage Vg. Further, the magnification correction quantity is calculated based on the excitation current for the objective lens and by the Vg, ΔVs found the same way as in the previous working example, and the deflection intensity of the scanning deflector 107 or the acquired length value is corrected. A different working example of the embodiment is described next. This example is an SEM comprising the static electrometer and the sample height measurement means of the two previous working examples. Since this working example contains these two means, the wide area electrostatic voltage Vg and localized electrostatic voltage ΔVs can be measured with even high accuracy and greater stability. In other words, if the first approximation value Vg(1) found from the measurement data of static electrometer probe 114 or by the appropriate expression, and the objective lens excitation current for exact focus estimated and combined with the sample height data from the Z axis sensor, then the exact focusing task (so-called auto-focus) can be completed in a short time. An accurate wide area electrostatic voltage Vg can be calculated from the differential between the excitation current of the autofocus that was found and the excitation current of the objective lens calculated from Vg(1). If the Vg is correct, then the ΔVs=ΔVs−Vg which is the differential versus the localized surface voltage Vs can be accurately calculated, and the magnification correction will have greater accuracy. FIG. 7 is a more detailed view for describing the energy filter for the above embodiment. A mesh electrode 112 is installed enclosed from above and below by the grounded mesh electrode 113 and the secondary electron conversion electrode 110 above it. The mesh electrode 112 voltage is swept using the wide area electrostatic voltage Vg or the first approximation value Vg(1) as reset values. The S curve (secondary electron distribution when the voltage applied to the energy filter is changed) is then measured. The grounded mesh electrode 113 prevents the magnetic field of the mesh electrode 112 from unwanted expansion towards the conversion electrode 110, etc. A fixed quantity of secondary electrons 102 strikes the lower mesh electrode 113 without requiring the voltage of the mesh electrode 112, and create a fixed quantity of new secondary electrons 130. These secondary electrons 130 are attracted towards the scintillator 131 to which a positive voltage of approximately 10 kilovolts has been applied. The S curve can be measured with high accuracy by standardizing the current I11 from the scintillator 111 with the current I31 from scintillator 131. Images can be displayed on the CRT the same as the case with the scintillator 111. FIG. 8 is a drawing for describing in more detail the electrostatic correction controller 120 for the above three working examples. This electrostatic correction controller 120 is composed of a static electrometer data table 201, an autofocus controller 202, a wide area static electrometer processor 203, an energy filter voltage controller 204 for automatically measuring the S curve, a localized electrostatic voltage processor 205, and a magnification correction processor 206. First of all, data on the voltage V14 for coordinates of the sample measured by the static electrometer or the fitting coefficient are stored in the static electrometer data table 201. The corresponding wide area electrostatic voltage ΔVg is measured each time the observation point is moved, and the retarding voltage Vg (=Vr) to the sample stage 109 is adjusted so as to satisfy the desired acceleration voltage Vacc=V0+ΔVg+Vr. The autofocus controller 202 calculates the excitation current I6(1) for the acceleration voltage Vacc set with the sample stage height data Z1 from the Z sensor, and by sweeping the vicinity of this electrical current, search for the excitation current I6 for an exact focus. Next, when there is a differential between I6(1) and I6, the wide area static electrometer processor 203 decides that an error has occurred in Vacc, and corrects the ΔVg, to find an accurate wide area electrostatic voltage Vg. The energy filter voltage controller 204 on the other hand, measures the S curve in a non-charged state, and stores it in the localized electrostatic voltage processor 205. In the S curve measurement sequence, the applied voltage V12 of mesh electrode 112 is swept using the wide area electrostatic voltage Vg or its estimated value Vg(1), as a reference just as described above, and changes in the electrical current I11 of the secondary electrons are measured. The electrical current I31 from the scintillator 31 can also be standardized here. The data to be stored may be data that was already processed such as the S curve itself, or filter voltages in excess of a threshold, filter voltages with a maximum S curve slope. The S curve varies somewhat depending on the sample material so data may also be recorded for each sample so that calculation accuracy can be enhanced from then onwards. The localized electrostatic voltage processor 205 selects the S curve to be used as the reference, and calculates the localized electrostatic voltage ΔVs from the amount of voltage shift. Finally, the magnification correction processor 206 uses the respective formulas (1) and (2) from the wide area electrostatic voltage Vg and localized electrostatic voltage ΔVs to calculate the magnification correction amounts ΔMg and ΔMs. By then correcting the electrical current I7 of the scanning deflector with the inverse of the total magnification M+ΔMg+ΔMs, an image can always be observed at the desired magnification regardless of the electrostatic voltage. An effective method for boosting the processing speed when automatically processing large numbers of wafers on a semiconductor production line, is to reduce the number of S curve measurements by the energy filter. With an identical circuit pattern, and identical material, the localized electrostatic voltage ΔVs will be the same (for each wafer) so a ΔVs that was already measured can be utilized. In some cases, one S curve measurement for each wafer will also suffice. When a new S curve is measured, it is automatically added to the database of localized electrostatic voltage processor 205. In the present embodiment, the fluctuation in the magnification rate can be calculated with high accuracy for dimension measurement and image observation of the insulation material of the sample. Also, fluctuations in the measurement length value can be corrected by setting a fixed desired magnification rate or magnification change. Dimensions can in this way be controlled with high accuracy in the currently ultra-miniaturized semiconductor fabrication process. A supplementary result also obtained is that image quality is stabilized since the energy of the primary electron beam irradiation onto the sample can be controlled to a high degree of accuracy. Further, by monitoring the localized electrostatic voltage ΔVs, the destruction of the dielectric (insulation) by excessively large electrostatic charges can be prevented, and an electrostatic voltage or index thereof can be obtained for bottom surface observation via large aspect ratio contact holes. The localized electrostatic voltage ΔVs varies the optical magnification Mobj of the objective lens as described using FIG. 11. The electrostatic voltage ΔVs is localized due to electron beam irradiation so there is almost no effect on the excitation current I6. Regardless of this, the localized electrostatic voltage ΔVs forms a minute electrostatic lens 108b. This lens causes the track 101a of the primary electron beam to be deflected by the global (wide area) electrostatic charge so as to concentrate onto the track 101b and make the optical magnification Mobj greatly fluctuate as described in the previous embodiment. Yet another method is described next for making accurate tests and measurements that are otherwise difficult due to different, overlapping electrostatic phenomenon. The present embodiment proposes a method for correcting the magnification fluctuation using the localized electrostatic voltage ΔVs and calculating the correct optical magnification Mobj. The magnification fluctuation brought about by the localized electrostatic charge is dependent on the localized electrostatic voltage ΔVs. The localized electrostatic voltage ΔVs is dependent on the electron beam irradiation magnification (in the present embodiment, this is hereafter called the predose magnification, mainly in order to describe electron beam irradiation prior to using electron beam for testing and measurement) Mpre and magnetic field near the sample surface and the type of sample. FIG. 14 shows the localized electrostatic voltage ΔVs, when the predose magnification Mpre was varied at boosting voltages of 0.5 kV and 5 kV. The boosting referred to here is a method for installing a cylindrical electrode to be applied with a positive voltage within the objective lens so that the electron beam within the objective lens can at least reach a high acceleration to pass through the objective lens. FIG. 14 shows the results when the surface electrical potential was measured after varying the predose magnification while a voltage of 0.5 kV was applied to the cylindrical electrode, and while 5 kV was applied. This boosting technology is disclosed in detail for example in JP-A No. 171791/1997 (U.S. Pat. No. 5,872,358). When the predose magnification and the sample surface electrical field are used as parameters for varying the localized electrostatic voltage ΔVs, then the localized electrostatic voltage ΔVs can be calculated in the following fitting function from the boosting voltage Vb, retarding voltage Vr, fitting coefficients A1 and a1, and predose magnification Mpre parameters.ΔVs=A1(Vb−Vr)/Mpre+a1 (13) Also, the magnification fluctuation quantity ΔM/Mobj can be calculated from ΔVs using the magnification sensitivity coefficient Ts.ΔM/Mobj=Ts*ΔVs (14)FIG. 15 shows the magnification fluctuation sensitivity coefficient Ts, when the beam irradiation area (∝1/predose magnification=1/Mpre) was varied at a retarding voltage of Vr=−1.2 kV. Ts can be grouped into four sections according to the beam irradiation area. A section with a low magnification rate below 50 times is regarded as a global electrostatic charge. A section from 50 times up to 500 times is a transition region from the global electrostatic charge to a localized electrostatic charge. A section from 500 times up to 5,000 times is regarded as largely fixed. A section with a high magnification from 5,000 times upward has a tendency for the Ts to diminish. Therefore, if the magnification fluctuation sensitivity coefficient Ts of the irradiation area is set as an irradiation area (1 side is from 10 μm to 300 μm) equivalent to a magnification of 500 times to 5,000 times regarded as a fixed area, then the number of pre-stored data can be reduced while still maintaining the estimated correction value accuracy. When the true value and actual measured value of the pattern dimensions are respectively set as L, Lex, the magnification fluctuation quantity B=ΔM/Mobj, can be calculated from the following formula.L/Lex=1+B (15)When estimating the true measured length using formula (13), formula (14), formula (15), the unknown coefficients are A1 and a1. Therefore, if the (Vb−Vr) proportional to the electrical field of the sample surface or the predose magnification Mpre, is changed and results from measuring two or more points are utilized, then the true measurement length L value can be estimated. This method has the advantage that when observing an unknown insulation sample, the true measurement length can be estimated by changing the charge location of the sample surface or the predose magnification Mpre, and measuring two or more different localized electrostatic voltage ΔVs. Also, when using this method, instead of a fitting coefficient having a predose magnification and surface charge location as electrostatic variable parameters to vary the localized electrostatic voltage ΔVs, as shown in formula (13); the same results can be obtained with another fitting coefficient having the energy of the input beam, irradiation time and electrons within the sample and the degree of hole movement as the charge variable parameters. By storing fitting coefficients a1 and A1 in the memory, true dimension values can be estimated by using the measurement length value for one predose magnification and surface electrical field. The fitting coefficient a1 used in formula (13) on the other hand, is not dominated by the predose magnification and surface electrical field. Therefore, by substituting in the formula (13), formula (14) and formula (15) for irregularities in the a1 utilized when correcting the measurement length of the same type of sample, the reliability of the adjusted parameters used to make the correction can be evaluated by means of the deviation in measurement length. FIG. 16 is a graph showing the relation of the measurement length value before correction to the measurement length value after correction versus predose magnification. By storing the magnification fluctuation amount B for each predose magnification calculated from the true dimension values and measurement length before correction, the true dimension value can be estimated from the measurement length value of one observation condition. When performing the predose, a high contrast image can be obtained by utilizing the optimal acceleration voltage shown in JP-A No. 200579/2000 and higher accuracy measurement results can be obtained. A function for estimating the true dimension values (per the means of the first working example of the embodiment) by utilizing the measurement length value of multiple points where the charge variable parameters for varying the localized electrostatic voltage were changed, is described next in an example using electrostatic correction controller 120 of FIG. 5 and FIG. 6. FIG. 17 is a block diagram of the electrostatic correction controller 120. The electrostatic correction controller 120 is comprised largely of a global electrostatic correction section 302 and localized electrostatic correction section 303. The localized electrostatic correction section 303 sets the measurement conditions (charge variable parameters, acceleration voltage, and primary electron beam irradiation time during predose) via 313a. The measurement length measured per the conditions that were set is input from an input device (not shown in drawing) via 313b to the localized electrostatic correction section 303. A magnification fluctuation amount B for correcting the localized electrostatic charge based on the measurement conditions that were set and the measurement length that was input, are input via 313d to the electrostatic charge corrector unifier section 304. Also, the magnification fluctuation amount calculated in the global electrostatic correction section 302 is also input to the electrostatic charge corrector unifier section 304 via 313e. The dimensions whose varied measurement length was corrected by the effect of the global electrostatic charge and localized electrostatic charge, was output from the magnification fluctuation amount derived in the respective correction section of global electrostatic correction section 302 and localized electrostatic correction section 303 that were input from the electrostatic charge corrector unifier section 304. FIG. 18 is a flow chart showing the process for correcting the measurement length value. First of all, the charge variable parameters and measurement conditions are set in step s101. Next, in step s102, the electron beam irradiates the sample to create an electrostatic charge according to the conditions set in step s101. In step s103, the measurement length value Lex is acquired by measurement under the charge variable parameters established in step s101 or step s109. In step s104, a decision is made whether the measurement length Lex acquired in step s103 has sufficient accuracy. When decided the measurement length was not sufficiently accurate, the observation condition settings of step s101 are corrected. In step s106, a decision is made whether data has been collected enough times for correction in step s107. If there is not enough data, then different charge variable parameters are set in step s109 and measurement length again measured. In step s107, the measurement length value is corrected by using the measurement length value measured in step s105 and the charge variable parameters established in step s102 and step s109. The measurement length value corrected in step s108 is output to the monitor. By using the localized electrostatic correction in the present embodiment, the true dimension value can be estimated with high accuracy by making two or more measurements with different localized electrostatic voltages, even on samples of materials and shapes that have had no preliminary measurement. Further, the measurement speed is improved because no preliminary measurement with an energy filter is required for each magnification. FIG. 19A and FIG. 19B show drawings of sample electrostatic charges when the predose magnification was changed and the sample given an electrostatic charge. During length measurement at respective magnifications using two or more different predose magnifications, a stable localized electrostatic charge can be quickly formed by using the following procedure. The sample 108 hold two types of electrostatic charges; a global (wide area) electrostatic charge Vg spanning the entire surface and a localized electrostatic voltage ΔVs created by the electron irradiation. In FIG. 19A, a residual electrostatic region 108d can be formed when the predose magnification is raised during observation after that predose magnification was observed in a small state. The localizes static charge correction is badly effected unless sufficient time is taken for the charge on the residual electrostatic region to sufficiently weaken. However if the predose magnification is lowered after observation of a large predose magnification as shown in FIG. 19B, then there is no residual electrostatic region, so measurement can start immediately after the predose ends since no weakening time is required. Using the above procedure allows rapid observation with good accuracy in an electrostatic region. The second working example of the embodiment of the present invention is described next while referring to FIG. 20 and FIG. 21. In this embodiment, the memory section 301 in the electrostatic correction controller 120, contains a database of fitting constants for functions expressing the magnification fluctuation amount B or localized electrostatic voltage ΔVs. Measurement conditions (charge variable parameters, acceleration voltage, and primary electron beam time during predose) from localized electrostatic correction section 303 via 313a are set here. The measurement length value measured under the preset conditions, is input via 313b to the localized electrostatic correction section 303. The magnification fluctuation amount B or the charge variable parameters are input to the memory section 301 via 313g. The ΔVs matching the charge variable parameters input in memory section 301 and fitting coefficient linked to the variable change parameters or the magnification fluctuation amount B are input to the localized electrostatic correction section 303 via 313h. After correction of the measurement length value calculated using the data that was input, the measurement length value is output via 313d. FIG. 21 is a flow chart showing the measurement procedures when storing the correction data. The charge variable parameters and measurement conditions are set in step s201. Next, in step s202, the electron beam irradiates the sample to create an electrostatic charge according to the conditions set in step s201. In step s203, the measurement length value Lex is acquired by measurement under the charge variable parameters established in step s201 or step s209. In step s204, a decision is made whether the measurement length Lex acquired in step s203 has sufficient accuracy. When decided the measurement length was not sufficiently accurate, the observation condition settings of step s209 are corrected. In step s206, fitting coefficients for showing the magnification fluctuation amount B or the Vs, derived previously under the same charge variable parameters as correction data are loaded from the memory section 301. In step S207, a decision is made if correction is possible or not from the measurement length value Lex that was acquired and from the charge variable parameters established in step s201 or step s208. When decided that correction is impossible, the observation conditions are reset in step s209. In step s208, the measurement length value Lex measured in step s205 is input to the localized electrostatic correction section 303. The measurement length value is at the same time obtained after correction by the localized electrostatic correction section 303, using this data. Performing localized electrostatic correction using this embodiment, allows shortening the time required for measurement length since this localized electrostatic correction can be performed from a measurement length value measured under one charge variable parameter for a sample measured once and having at least the same pattern and same condition. If the optimal predose conditions such as shown in JP-A No. 200579/2000 in step s201 are set, then stable measurements can be made with high accuracy. In the third working example of the present embodiment, in order to increase the reliability of the corrected measurement length, the memory section 301 contains a database holding fitting coefficients for fitting coefficients for magnification fluctuation amount B or Vs, and measurement conditions of the same type sample previously measured. In this embodiment by utilizing a memory section 301 containing the above described database, the measurement length value can be quantitatively evaluated by means of the differential in accuracy after localized electrostatic correction. A threshold value is set from the differential of this measurement length value. If a measurement length exceeding this threshold setting is measured, then this measurement is judged as abnormal and a decision is made whether the cause of the abnormal measurement is effects from impurities on the sample surface or an abnormal electrostatic charge, etc. The procedure used in this embodiment is shown next. First of all, the procedure for constructing the database is shown. The localized electrostatic voltage ΔVs of the sample is changed, and adjusted coefficients for localized electrostatic voltage at multiple points are derived from measurement length values measured between the same points. The fitting coefficients for the fitting coefficients of localized electrostatic voltage ΔVs, for the same type sample from between different two points are found in the same way. Among the multiple fitting coefficients found by repeating this process, the irregularities of fitting coefficient a1 not dependent on the charge variable parameters are extracted. Irregularities of fitting coefficient a1 and irregularities of the fitting coefficient a1 corrected with the length measurement differential are stored in the memory section 301. Next, the procedure for deciding if there is an abnormal electrostatic charge is shown by using the database that was formed. When the measurement length value derived from the changing the charge variable parameter and measuring the measurement length (each time the sample is replaced or a length measurement made) exceeds the threshold value found from the differential with the stored length measurement value in the memory section 103, then a screen display as shown in FIG. 22A and FIG. 22B appears and the user is notified of an abnormal electrostatic charge. When the fitting coefficient a1 currently utilized in this correction is within the thresholds found from the irregularities of the previously measured fitting coefficient a1 stored in memory section 301, this shows there is no abnormality and the localized electrostatic charge is judged to be normal. When the fitting coefficient a1 currently utilized in this correction exceeds the thresholds found from the irregularities of the previously measured fitting coefficient a1 stored in the memory section 301, this shows that an abnormal electrostatic charge has occurred. Utilizing this embodiment therefore allows knowing whether a localized electrostatic charge is abnormal or not so that the length measurement can be found with a high degree of reliability. The fourth working example of the present embodiment combines the functions of all the above embodiments. A flow chart of the process of the present embodiment is shown in FIG. 23. In step s1, a decision is made whether or not there is correction data in the memory section 301 for the current observation sample. When the correction data needed for the current measurement length does not exist (no correction data), the process in the flow of loop 1 in step s100 shown in the first working example is performed to derive the post-correction measurement length value L. In step s120 and step s160 the correction results are shown on a screen, and whether or not the currently used correction data will be used from the next time onwards is decided. If to be used from the next time onwards, then the correction data is stored in the memory section 301 in step s170. In step s1 when there is correction data, the flow of loop 2 starts and the processing shown in the second working example is performed to derive a post-correction measurement length L. The correction results displayed on the screen area shown in FIG. 22A and FIG. 22B. When the evaluation shown in the third working example is made and an abnormal electrostatic charge is detected in step s210, a warning is displayed and loop 3 starts. By repeatedly performing the procedure shown in the first working example multiple times, a fitting coefficient a1 is output under multiple conditions. In step s300, an fitting function is made using an average value for irregularities in the multiple fitting coefficients found in step s100. The reliability of the currently formed fitting function is evaluated from the differential in measurement lengths from irregularities in multiple fitting coefficient a1. If decided that the fitting function is not reliable, then the process returns once again to step s100. When decided in step s300 that a fitting function was obtained that is sufficiently reliable versus abnormal electrostatic charges, the calculation results for the measurement length differential and post-correction measurement length values using the fitting function currently made in step s120 are displayed on the screen. By performing localized electrostatic correction using the present embodiment, during length measurement of the same patterns cut into the same insulation piece sample, the measurement length process can be performed at higher speeds and with more uniform accuracy. The fifth working example of the present embodiment described here utilizes a scanning electron microscope comprising an ultraviolet beam device 314 for minimizing effects on the previously measured electrostatic charge. FIG. 24 is a block diagram showing the scanning electron microscope comprising an ultraviolet beam device 314. The reference number 113 in the drawing denotes the input device for entering the measurement conditions. By irradiating the sample with an ultraviolet beam from the ultraviolet beam device 314 for each observation, the electrostatic charge accumulated on the sample from the previous measurement can be reset so that stable measurement of dimensions can be performed. The embodiments can therefore calculate the amount of fluctuation in observation magnification with high accuracy for making dimension measurements and image observation of the insulation sample. The dimensions in the currently ultra-miniaturized semiconductor fabrication process can in this way be controlled in a short time with high accuracy. |
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062018469 | abstract | A method of jacketing a body of fissionable material within a nonfissionable jacket having a cup-shaped body open at one end and a cap effecting closure at said end comprising the steps of inserting the cup-shaped body into a tightly fitting cup-shaped sleeve; completely submerging said assembly in a bonding bath of a molten metallic bonding material, allowing the inner body to fill with molten bonding material; dipping the fissionable body into the open end of said assembly while under the surface of the bonding bath; closing the open end of the assembly with the cap while under the surface of the bonding bath; removing the complete assembly from the bonding bath; quenching in cold water; and removing the sleeve. |
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claims | 1. A neutron beam transmission adjusting device, comprising:a neutron beam transmission unit that comprises a neutron reactant and is capable of modulating at least any one selected from the group consisting of an energy and a flux of a neutron beam transmitted through the neutron beam transmission unit,wherein the neutron beam transmission unit contains a hydrogel containing water, a polymer, and a mineral. 2. The neutron beam transmission adjusting device according to claim 1,wherein the neutron beam transmission adjusting device is used, with the neutron beam transmission adjusting device disposed between a source of the neutron beam and an irradiation target to be irradiated with the neutron beam on a path of the neutron beam, andwherein the neutron beam transmission unit is configured to perform a modulation in an accordance with a lesion site condition of the irradiation target. 3. The neutron beam transmission adjusting device according to claim 2,wherein the neutron beam transmission unit has a shape conforming to a surface of the irradiation target. 4. The neutron beam transmission adjusting device according to claim 1,wherein the neutron reactant contains at least any one selected from the group consisting of a boron atom, a lithium atom, and a gadolinium atom. 5. The neutron beam transmission adjusting device according to claim 1,wherein the neutron beam transmission unit has a thickness distribution. 6. The neutron beam transmission adjusting device according to claim 1,wherein the neutron beam transmission unit has a concentration distribution of the neutron reactant. 7. The neutron beam transmission adjusting device according to claim 1,wherein the neutron beam transmission unit is deformable. 8. A neutron beam adjusting method, comprising:when irradiating an irradiation target of a neutron beam from a source of the neutron beam with the neutron beam, disposing the neutron beam transmission adjusting device according to claim 1 between the source of the neutron beam and the irradiation target of the neutron beam on a path of the neutron beam. 9. The neutron beam adjusting method according to claim 8, further comprising:performing a modulation with the neutron beam transmission adjusting device in an accordance with a condition of the irradiation target of the neutron beam. 10. A method for producing a neutron beam transmission adjusting device, the method comprising:producing a neutron beam transmission adjusting device according to claim 1 using a three-dimensional object producing apparatus. 11. The method for producing a neutron beam transmission adjusting device according to claim 10,wherein the three-dimensional object producing apparatus is a material jetting type. 12. The method for producing a neutron beam transmission adjusting device according to claim 10,wherein producing the neutron beam transmission adjusting device using the three-dimensional object producing apparatus comprising producing the neutron beam transmission adjusting device based on object formation data corresponding to a lesion site condition of an irradiation target to be irradiated with a neutron beam. 13. The method for producing a neutron beam transmission adjusting device according to claim 12, further comprising:controlling a thickness distribution of the neutron beam transmission unit based on the object formation data. 14. The method for producing a neutron beam transmission adjusting device according to claim 12, further comprising:controlling a concentration distribution of the neutron reactant in the neutron beam transmission unit based on the object formation data. 15. A cancer treating method, comprising:using a neutron beam transmission adjusting device according to claim 1. 16. The cancer treating method according to claim 15, further comprising:when irradiating an irradiation target of a neutron beam from a source of the neutron beam with the neutron beam, disposing the neutron beam transmission adjusting device between the source of the neutron beam and the irradiation target of the neutron beam on a path of the neutron beam. 17. The cancer treating method according to claim 15, further comprising:performing a modulation using the neutron beam transmission adjusting device in an accordance with a lesion site condition of the irradiation target of the neutron beam. |
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abstract | An illumination optical unit for EUV projection lithography includes a field facet mirror and a pupil facet mirror. A correction control device, which is used for the controlled displacement of at least some field facets that are usable as correction field facets, which are signal connected to displacement actuators, is embodied so that a correction displacement path for the correction field facets is so large that a respective correction illumination channel is cut off at the margin by the correction pupil facet so that the illumination light partial beam is not transferred in the entirety thereof from the correction pupil facet into the object field. |
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description | The present application is a continuation of U.S. patent application Ser. No. 12/641,378, filed Dec. 18, 2009, to be issued as U.S. Pat. No. 8,266,823, which in turn is a divisional of U.S. patent application Ser. No. 11/45,785, filed on Jun. 6, 2005, the entirety of which is hereby incorporated by reference. The present invention relates generally to the field of storing spent nuclear fuel, and specifically to the field of preparing spent nuclear fuel for dry storage. The storage, handling, and transfer of HLW, such as spent nuclear fuel, requires special care and procedural safeguards. In the operation of nuclear reactors, hollow zircaloy tubes tilled with enriched uranium, known as fuel assemblies, are burned up inside the nuclear reactor core. It is customary to remove these fuel assemblies from the reactor after their energy has been depleted down to a predetermined level. Upon depletion and subsequent removal, this spent nuclear fuel (“SNF”) is still highly radioactive and produces considerable heat, requiring that great care be taken in its subsequent packaging, transporting, and storing. Specifically, the SNF emits extremely dangerous neutrons and gamma photons. It is imperative that these neutrons and gamma photons be contained at all times subsequent to removal from the reactor core. In defueling a nuclear reactor, it is common place to remove the SNF from the reactor and place the SNF under water, in what is generally known as a spent fuel pool or pond store. The pool water facilitates cooling of the SNF and provides adequate radiation shielding. The SNF is stored in the pool for a period long enough to allow the decay of heat and radiation to a sufficiently low level to allow the SNF to be transported with safety. However, because of safety, space, and economic concerns, use of the pool alone is not satisfactory when the SNF needs to be stored for a considerable length of time. Thus, when long-term storage of SNIP is required, it is standard practice in the nuclear industry to store the SNF in a dry state subsequent to a brief storage period in the spent fuel pool, i.e., storing the SNF in a dry inert gas atmosphere encased within a structure that provides adequate radiation shielding. One typical structure that is used to store SNF for long periods of time in the dry state is a storage cask. Storage casks have a cavity suitably sized to receive a canister of SNF and are designed to be large, heavy structures made of steel, lead, concrete and an environmentally suitable hydrogenous material. Typically, storage casks weigh about 150 tons and have a height greater than 15 ft. A common problem associated with storage casks is that they are too heavy to be lifted by most nuclear power plant cranes. Another common problem is that storage casks are generally too large to be placed in spent fuel pools. Thus, in order to store SNF in a storage cask subsequent to being cooled in the pool, the SNF must be removed from the pool, prepared in a staging area, and transported to the storage cask. Adequate radiation shielding is needed throughout all stages of this transfer procedure. As a result of the SNF's need for removal from the spent fuel pool and additional transportation to a storage cask, an open canister is typically submerged in the spent fuel pool prior to the SNF being removed from the reactor core. The SNF is then placed directly into the open canister while submerged in the water. However, even after sealing, the canister alone does not provide adequate containment of the SNF's radiation. A loaded canister cannot be removed or transported from the spent fuel pool without additional radiation shielding. Thus, apparatus and methods that provide additional radiation shielding during the transport of the SNF have been developed. The additional radiation shielding is typically achieved by positioning the canisters in large cylindrical containers called transfer casks while submerged within the pool. Similar to storage casks, transfer casks have a cavity suitably sized to receive the canister and are designed to shield the environment from the radiation emitted by the SNF within. In facilities utilizing transfer casks to transport loaded canisters, an empty canister is first placed into the cavity of an open transfer cask. The canister and transfer cask are then submerged in the spent fuel pool. Previously discharged SNF from reactors located in wet storage is moved into the submerged canister (which is within the transfer cask and filled with water). The loaded canister is then fitted with its lid, enclosing the SNF and the water from the pool within the canister. The loaded canister and transfer cask are then removed from the pool by a crane and set down in a staging area to prepare the SNF-loaded canister for storage or transportation in a dry condition. In order for an SNF-loaded canister to be properly prepared for dry storage or transportation, the United States Nuclear Regulatory Commission (“NRC”) requires that the SNF and interior of the canister be adequately dried before the canister is sealed and transferred to the storage cask. Specifically. NRC regulations mandate that the vapor pressure (“vP”) within the canister be at or below 3 Torr (1 Torr=1 mm Hg) before the canister is backfilled with an inert gas and sealed. Vapor pressure is the pressure of the vapor over a liquid at equilibrium, wherein equilibrium is defined as that condition where an equal number of molecules are transforming from the liquid phase to gas phase as there are molecules transforming from the gas phase to liquid phase. Requiring a low vP of 3 Torr or less assures an adequately dry space in the canister interior suitable for long-term SNF storage or transportation. Currently, nuclear facilities comply with the NRC's 3 Torr or less vP requirement by performing a vacuum drying process. In performing this process, the bulk water that is within the canister is first drained from the canister. Once the bulk of the liquid water is drained, a vacuum system is coupled to the canister and activated so as to create a sub-atmospheric pressure condition within the canister. The sub-atmospheric condition within the canister facilitates evaporation of the remaining liquid water while the vacuum helps remove the water vapor. The vP within the canister is empirically ascertained through a vacuum-and-hold procedure. If necessary, the vacuum-and-hold procedure is repeated until the pressure rise during a prescribed test duration (30 minutes) is limited to 3 Torr. Once the vacuum drying passes the acceptance test, the canister is backfilled with an inert gas and the canister is sealed. The transfer cask (with the canister therein) is then transported to a position above a storage cask and the SNF-loaded canister is transferred into the storage for long-term storage. Current methods of satisfying the NRC's 3 Torr or less vP requirement are time consuming, manually intensive and prone to error from line and valve leakages. Any time the canister must be physically approached for vacuum monitoring and dryness testing, there is the risk of exposing the work personnel to high radiation. Moreover, the creation of sub-atmospheric conditions in the canister requires expensive vacuum equipment and can cause complicated equipment problems. It is therefore an object of the present invention to provide a method und system for drying a canister loaded with HLW. Another object of the present invention is to provide a method and system for drying a canister loaded with HLW without physically accessing the contents of the canister to ensure that an acceptable level of dryness has reached within the canister. Yet another object of the present invention is to provide a method and system for drying a canister loaded with HL W without subjecting the interior of the canister to sub-atmospheric conditions. Still another object of the present invention is to provide a method and system for drying a canister loaded with HL W without using expensive vacuum equipment. A further object of the present invention is to provide a method and system for preparing an SNF-loaded canister for dry storage that is easy to implement and for tune efficient. A yet further object of the present invention is to provide a method and system for preparing a canister loaded with HL W for dry storage in a more cost effective manner. These objects and other objects are met by the present invention which in one aspect is a method of drying a cavity loaded with “HL W” comprising: a) flowing a non-reactive gas through the cavity; b) repetitively measuring dew point temperature of the nonreactive gas exiting the cavity; and c) upon the dew point temperature of the non-reactive gas exiting the cavity being measured to be at or below a predetermined dew point temperature for a predetermined time, discontinuing the flow of the non-reactive gas and sealing the cavity. By ensuring that the non-reactive gas coming out of the cavity has a dew point temperature that is at or below the predetermined dew point temperature for the predetermined period of time, it is ensured that the cavity is adequately dry (i.e., that the vP of the non-reactive gas within the cavity is below a desired level without the need to physically measure the vP therein). In some embodiments, the predetermined dew-point temperature is selected so that a desired vapor pressure is achieved within the cavity, such as 3 Torr or less. The flow rate of the non-reactive gas through the cavity determines the predetermined time for a specified dryness level (i.e., a predetermined dew point temperature). The predetermined dew point temperature and the predetermined time for any sized cavity volume canister can be determined through experimentation or simulation. In some embodiments, the inventive method may further comprise the steps of d) drying the non-reactive gas that exits the cavity after the dew point temperature is measured; and e) re-circulating the dried non-reactive gas through the cavity. The drying step can be performed by contacting, the non-reactive gas with a desiccant or by chilling the non-reactive gas. In some embodiments, the non-reactive gas will be circulated through the cavity at a predetermined flow rate. The predetermined flow rate can be chosen so that the volume of the cavity is turned over 25 to 50 times during the predetermined time. In some embodiments, the predetermined dew point temperature can be in a range of approximately 20 to 26° F., and the predetermined time is in a range of approximately 25 to 35 minutes. In one embodiment, it is preferred that the predetermined dew point temperature be approximately 22.9° F. and the predetermined time be approximately 30 minutes. Suitable non-reactive gases include, without limitation, nitrogen, carbon dioxide, light hydrocarbon gases, or a noble gas selected from a group consisting of helium, argon, neon, radon, krypton, and xenon. In another aspect, the invention can be a system for drying a cavity loaded with HLW comprising a canister forming the cavity, the cavity having an inlet and an outlet; a source of non-reactive gas; means for flowing the non-reactive gas from the source of non-reactive gas through the cavity; and means for repetitively measuring the dew point temperature of the non-reactive gas exiting the cavity. The dew point temperature measuring means can be any type of a direct moisture-sensing device e.g., a hygrometer, or by other means, e.g. gas chromatography, mass spectroscopy etc. In some embodiments, the system can further comprise means for drying the nonreactive gas. Suitable drying means include the use of a chiller, freezer, and/or condenser or the use of desiccant. In such an embodiment, the drying means will be located downstream of the dew point temperature measuring means. Embodiments of the system that comprises a drying means can also comprise means for re-circulating the desired non-reactive gas from the drying means hack into the non-reactive gas source. This can be accomplished through the use of a recirculation line. In some embodiments, the system can be automated, and will further include: a controller operably coupled to the dew point temperature measuring means. In such an embodiment, the dew point temperature measuring means is preferably adapted to create signals indicative of the measured dew point temperature of the non-reactive gas and transmit the signals to the controller. The controller is adapted to analyze the signals and upon determining that the signals indicate that the measured dew point temperature is at or below the predetermined dew point temperature for the predetermined time, the controller is further adapted to (1) cease flow of the non-reactive gas through the cavity; and/or (2) activate a means for indicating that the cavity is dry. In one embodiment, the system will further comprise a spent fuel cask. In such at embodiment, the canister will be positioned and dried within the cask. Finally, it is preferred that the cavity have a top and a bottom, and that an inlet be located at or near the bottom of the cavity for supplying the non-reactive gas to the cavity and that an outlet for removing the wet non-reactive gas from the cavity be located at or near the top of the cavity. FIG. 1 illustrates a canister 20 that is suitable for use with the present invention. The present invention is not limited to specific canister geometries, structures, or dimensions and is applicable to any type of enclosure vessel used to transport, store, or hold radioactive elements. While the exemplified embodiment of the invention will be described in terms of its use to dry a canister of spent nuclear fuel (“SNF”), it will be appreciated by those skilled in the art that the systems and methods described herein can be used to dry radioactive waste in other forms and in a variety of different containment structures as desired. The canister 20 comprises a bottom plate 22 and a cylindrical wall 24 which forms a cavity 21. As used herein, the end 25 of the canister 20 that is closest to the bottom plate 22 will be referred to as the bottom of the canister 20 while the end 26 of the canister 20 that is furthest from the bottom plate 22 will be referred to as the top of the canister 20. The cavity 21 has a honeycomb grid 23 positioned therein. The honeycomb grid 23 comprises a plurality of rectangular boxes adapted to receive spent nuclear fuel (“SNF”) rods. The invention is not limited by the presence of the honeycomb grid. The canister 20 further comprises a drain pipe with an open bottom (not illustrated) located at or near the bottom of the canister 20 that provides a sealable passageway from outside of the canister 20 to the interior of the cavity 21. If desired, the drain opening can be located in the bottom plate 22 or near the bottom of the canister wall. The drain pipe can be opened or hermetically sealed using conventional plugs, drain valves, or welding procedures. As illustrated in FIG. 1, the canister 20 is empty (i.e. the cavity 21 does not have SNF rods placed in the honeycomb grid 23) and the top 26 of the canister 20 is open. In utilizing the canister 20 to transport and store SNF rods, the canister 20 is placed inside a transfer cask 10 (FIG. 2) while the canister 20 is open and empty. The open transfer cask 10, which is holding the open canister 20, is then submerged into a spent fuel pool which causes the volume of the cavity 21 to become filled with water. SNF rods that are removed from the nuclear reactor are then moved under water from the spent fuel pool and placed inside the cavity 21 of the canister 20. Preferably, a single bundle of SNF rods is placed in each rectangular box of the honeycomb grid 23. Once the cavity 21 is fully loaded with the SNF rods, the canister lid 27 (FIG. 2) is positioned atop the canister 20. The canister lid 27 has a plurality of sealable lid holes 28 that form a passageway into the cavity 21 from outside of the canister 20 when open. The transfer cask 10 (having the loaded canister 20 therein) is then lifted from the spent fuel pool by a crane and placed uprightly in a staging area (as shown in FIG. 2) so that the canister 20 can be properly prepared for dry-storage. This dry-storage preparation includes drying the interior of the canister 20 and sealing the lid 27 thereto. Referring now to FIG. 2 exclusively, when in the staging area, the canister 20 (containing the SNF rods and pool water) is within the transfer cask 10. Both the canister 20 and the transfer cask 10 are in an upright position. Once in the staging area, the drain pipe attached to the canister lid 27 (not illustrated) with a bottom opening at or near the bottom 25 of the canister 20 is used to expel the bulk water that is trapped in the cavity 21 of the canister 20 using a blowdown gas (usually helium or nitrogen). Despite draining the bulk water from the cavity 21, residual moisture remains in the cavity 21 and on the SNF rods. However, before the canister 20 can be permanently sealed and transported to a storage cask for long-term dry storage or transportation, it must be assured that that cavity 21 and the SNF rods contained therein are adequately dried. Because a low vapor pressure (“vP”) within a container indicates that a low level of moisture is present, the United States Nuclear Regulatory Commission (“NRC”) requires compliance to the 3 Torr or less vapor pressure (“vP”) specification within the cavity 21 of HLW containing casks. FIG. 3 is a schematic of an embodiment of a closed-loop drying system 300 capable of drying the cavity 21 to acceptable NRC levels without the need to intrusively measure the resulting vP within the cavity 21. Once the transfer cask 10, which is holding the canister 20, is positioned in the staging area and the bulk water is drained from the cavity 21, the drying system 300 is connected to the inlet 28 and outlet 29 of the canister 20 so as to form a closed-loop system. More specifically, the gas supply line 325 is fluidly connected to the inlet 28 of the canister 20 while the gas exhaust line 326 is fluidly connected to the outlet 29 of the canister 20. The inlet 28 and outlet 29 of the canister are mere holes in the canister 20. If desired, proper port connections, seals, and/or valves can be incorporated into the inlet and outlet 28, 29. The drying system 300 comprises a non-reactive gas reservoir 310, a supply pump 320, a flow rate valve 321, a dew point temperature hygrometer 330, a chiller 340, a recirculation pump 360, and a control system 350, which includes a suitably programmed microprocessor 351, a computer memory medium 352, a timer 353, and an alarm 370. While the illustrated embodiment of the drying system 300 is automated via the control system 350, neither the method nor system of the present invention is so limited. If desired, the functions carried out by the control system 350 can be carried out manually and/or omitted in some instances. The helium reservoir 320, the canister 20, and the chiller 340 are fluidly connected so that a non-reactive gas, such as helium, can flow through the closed-loop drying system 300 without escaping into the external environment. More specifically, the gas supply line 325 fluidly connects the helium reservoir 310 to the canister 20, the gas exhaust line 326 fluidly connects the canister 20 to the chiller 340, and the recirculation line 345 fluidly connects the chiller 340 to the helium reservoir 310, thereby forming a closed-loop gas circulation path. All of the gas lines 325, 326, and 345 can be formed of suitable tubing or piping. The piping and tubing can be constructed of flexible or non-flexible conduits. The conduits can be formed of any suitable material, such as metals, alloys, plastics, rubber, etc. All hermetic connections can be formed through the use of threaded connections, seals, ring clamps, an/or gaskets. The helium gas reservoir 310 is used to store helium gas. While helium gas is the preferred non-reactive vas for use in the present invention, any non-reactive gas can be used in conjunction with the system 300 and the operation thereof. For example, other suitable non-reactive gases include, without limitation, nitrogen, carbon-dioxide, light hydrocarbon gases such as methane, or any inert gas, including but not limited to noble gases (helium, argon, neon, radon, krypton and xenon). The supply pump 320 is operably coupled to the gas supply line 325. When activated, the supply pump 320 draws helium gas from the helium reservoir 310 and forces the helium gas into the cavity 21 of the canister 20 via the gas supply line 325. The helium gas continues to flow through the canister 20 and into the chiller 340 via the gas exhaust line 326. The recirculation pump 360 is operably coupled to the recirculation line 345. When activated, the recirculation pump 360 draws the helium vas that has been de-moisturized from the chiller 340 and forces the dry helium gas back into the helium reservoir 310 for further recirculation through the canister 20. While two pumps 320, 360 are illustrated as being incorporated into the drying system 300, the invention is not so limited and any number of pumps can be used. The exact number of pumps will be dictated on a case-by case design basis, considering such factors as flow rate requirements, pressure drops in the system, size of the system, and/or number of components in the system. The direction of the helium gas flow through system 300 is indicated by the arrows on the fluid lines. A flow rate valve 321 is operably coupled to the gas supply line downstream of the supply pump 320. The valve 321 is used to control the flow rate of the helium gas into and through the cavity 21 of the canister 20 and throughout the drying system 300. The valve 321 can be an adjustable flow rate valve. In other embodiments of the invention, the flow rate of the helium gas through the drying system 300 can be alternatively controlled by incorporating a mass flow rate controller. As with the pumps, any number of valves can be incorporated throughout the system 300 as desired. Moreover, the invention is not limited by any specific placement of the valve(s) or pump(s) along the closed-loop flow circuit. The dew-point temperature hygrometer 330 is operably coupled to the gas exhaust line 326 so that the dew-point temperature of the helium gas exiting the cavity of the canister 20 can be measured. Suitable means for dew point temperature measurement include direct moisture sensing devices, such as hygrometers, and other means, such as vas chromatography or mass spectroscopy. The hygrometer 330 preferably includes a digital signal in some embodiments. The dew point temperature hygrometer 330 repetitively measures the dew point temperature of the helium gas exiting the cavity 21. There is no requirement as to the sampling rate for repetitive measurements. For example, the dew point temperature hygrometer 330 can measure the dew point temperature of the helium gas multiple times per second or only once every few minutes. In some embodiments, the time intervals between repetitive measurements will be so small that the measurements will appear to be essentially continuous in nature. The time intervals will be determined on case-by case design basis, considering such factors as functionality requirements of the system and the flow rate of the helium gas. The inlet 342 of the chiller 340 is coupled to the vas exhaust line 326 while the outlet 343 is fluidly coupled to the recirculation line 345. The chiller 340 is provided to adequately de-moisturize the wet helium gas that exits the cavity 21 of the canister 20 so that the helium gas can be re-circulated back into the helium gas reservoir 320 for further use in the drying of the cavity 21. By sufficiently chilling the wetted helium gas that exits the cavity 21 of the canister 20, the water vapor in the helium gas will condense out of the helium gas in the chiller 340 and be removed via the drain 341 in liquid form. The exact temperature to which the wetted helium gas will be chilled will depend on the desired level of dryness. The greater the level of dryness desired, the lower the temperature. In one embodiment of the invention, it may be desirable to chill the wetted helium gas to a temperature of 25° F. or less. Once de-moisturized in the chiller 340, the dry helium gas will be re-circulated back into the reservoir 310 for further use. While the wetted helium gas is de-moisturized in the illustrated embodiment of the drying system 300 using a chiller 340, other de-moisturizing apparatus and methods can be used instead of or in addition to the chiller 340 if desired. For example, a condenser or freezer may be used. In another embodiment, the wetted helium gas may be exposed to a suitable desiccant, such as silica gel, that will absorb the water vapor from the wetted helium gas stream. The desiccant can be dried as necessary through heating, UV exposure, or other conventional drying process and subsequently reused. In embodiments of the present invention that do not re-circulate the helium gas, de-moisturizing the wetted helium gas will not be necessary. As such, the chiller 340 or other drying module will be omitted. The drying system 300 further comprises an automation system 350. The automation system 350 comprises a CPU 351, a computer memory medium 352, a timer 353, and an alarm 370. The CPU 351 is a suitable microprocessor based programmable logic controller, personal computer, or the like. The computer memory medium 352 can be a hard drive that comprises sufficient memory to store all of the necessary computer code, algorithms, and data necessary for the operation and functioning of the drying system 300, such as predetermined time, predetermined dew-pint temperature, desired chilling temperatures, flow rates, and the like. The timer 353 is a standard digitalized or internal computer timing mechanism. The alarm 370 can be a siren, a light, an LED, a display module, a speaker, or other device capable of generating audio and/or visual stimulus. While an alarm 370 is illustrated and described, any instrumentation, device, or apparatus that inform an operator that the drying system 300 has completed a drying process can be used. For example, a computer screen can simply indicate that the canister is dry via text or visuals. The CPU 351 includes various input/output ports used to provide connections to the various components 320, 321, 330, 340, 360, 370, 352, 353 of the drying system 300 that need to be controlled and/or communicated with. The CPU 351 is operably coupled to these components via electrical wires, fiber-optic lines, co-axial cables, or other data transmission lines. These connections are indicated by the dotted lines in FIG. 3. The CPU 351 can communicate with any and all of the various components of the drying system 300 to which it is operably connected in order to control the drying system 300, such as: (1) activating or deactivating the pumps 320, 360; (2) opening, closing, and/or adjusting the flow rate valve 321; (3) activating or deactivating the chiller 340; and (3) activating or deactivating the alarm 370. The CPU 351 (and/or the memory 352) is also programmed with the proper algorithms to receive data signals from the dew-point hygrometer 330, analyze the incoming data signals, compare the values represented by the incoming data signals to stored values and ranges, and track the time at which the values represented by the incoming data signals are at or below the stored values. The type of CPU used depends on the exact needs of the system in which it is incorporated. Referring to FIG. 4, a flowchart of an embodiment of a method of drying a cavity loaded with SNF according to an embodiment of the present invention is illustrated. The method will be described in relation to the drying system 300 of FIG. 3 for ease of description and understanding. However, the method is not limited to any specific structure or system, and can be carried out by other systems and/or apparatuses. At step 400, the cask 10 containing the SNF loaded canister 20 is positioned in a staging area after being removed from the cooling pool/pond. As discussed above, the cavity 21 of the canister 20 is filled with water from the pool at this time. The bulk water is drained from the cavity 21 of the canister 20 via a properly positioned drain, thereby completing step 400. Despite the bulk water being drained from the cavity 21 of the canister 20, the interior of the cavity 21 and the SNF are still moisture bearing and need further de-moisturization for long-term storage. In order to further dry the cavity 21 and the SNF, the drying system 300 is utilized. The canister 20 remains in the cask 10 during the drying operation. At step 410, the gas supply line 325 is fluidly coupled to the inlet 28 of the canister 20 while the gas exhaust line 326 is fluidly coupled to the outlet 29 of the canister 20. As a result, a closed-loop fluid circuit is formed in which the cavity 21 of the canister 20 forms a portion of the fluid circuit. Once the drying system 300 is properly hooked up to the canister 20, the answer to decision block 420 is YES and the operator activates the drying system 300. The drying system 300 can be activated manually by switching on the equipment or in an automated fashion by the CPU 351. When activated in an automated fashion, an operator will activate the drying system 300 by entering a system activation command into a user input device (not illustrated), such as a keyboard, computer, switch, button, or the like, which is operably coupled to the CPU 351. Upon receiving the associated system activation signal from the user input device, the CPU 351 sends the appropriate activation signals to the pumps 320, 360, the chiller 340, the hygrometer 330, and the flow rate valve 321. Activating, the supply pump 320 and the recirculation pump 360 results in the helium gas being drawn from the helium reservoir 310 and flowed through the closed-loop fluid circuit (which includes the gas supply line 325, the canister 20, the gas exhaust line 326, the chiller 340, and the recirculation line 345). The flow rate of the helium gas through the drying system 300 is controlled by the flow rate valve 321, which is preferably an adjustable valve. In one embodiment to the present invention, the CPU 351 opens the flow rate valve so that the helium gas flows through the canister 20 at a flow rate of approximately 400 lb/hr. However, the invention is not so limited and other flow rates can be used. The exact flow rate to be used in any particular drying operation will be determined on a case-by-case design basis, considering such factors as the open volume of the canister's cavity, the target dryness level within the canister's cavity, the initial moisture content within the canister's cavity, the moisture content of the helium gas maintained within the reservoir, desired number of hourly volume turnovers for the canister etc. The chiller 340 is also activated by the CPU 351 so that the wetted helium gas exiting the canister 20 can be de-moisturized prior to being re-circulated back into the helium reservoir 310. In one embodiment, the CPU 351 activates the chiller 340 so that the helium gas is chilled to a temperature of 25° F. or less. However, the chiller 340 can be used to cool the helium gas to any desired temperature that suitably de-moisturizes the helium gas. As discussed above, in some embodiments of the invention, other de-moisturizing apparatus, such as those that utilize a desiccant, can be used to dry the wetted helium gas instead of the chiller 340. Upon being activated, the supply pump 320 draws dry helium gas from the helium reservoir 310 and flows the dry helium gas into the wet cavity 21 of the canister 20 via the inlet 28. Upon entering the cavity 21, the dry helium gas absorbs water from the SNF and internal surfaces of the cavity 21 in the form of water vapor. The moisture laden helium gas then exits the cavity 21 via the outlet 29. As the wet helium gas exits the cavity 21, the hygrometer 330 repetitively measures its dew point temperature. As the hygrometer 330 measures the dew point temperature of the wetted helium gas, it generates data signals indicative of the measured dew point temperature values and transmits these data signals to the CPU 351 via the electrical connection, thereby completing step 440. Upon receiving the data signals indicative of the measured dew point temperature values, the CPU 351 compares the measured values to a predetermined dew point temperature value that is stored in the memory medium 352. Thus, step 450 is completed. The predetermined dew point temperature is selected so as to be indicative that the inside of the cavity 21 and the SNF is sufficiently dry for long term storage. In one embodiment, the predetermined dew point temperature is selected so as to correspond to a vapor pressure in the cavity 21 that is indicative of an acceptable level of dryness, such as for example 3 Torr or less. In such embodiments, the predetermined dew point temperature can be selected using either experimental or simulated correlations. Referring now to FIG. 5, an exemplary embodiment of how one selects the predetermined dew point temperature will be described. As can be seen from the curve delineated in FIG. 5, the water vapor pressure of gases, such as helium, correlates to a dew point temperature. Thus, using this curve, the predetermined dew point temperature can be determined once the target vapor pressure is known. For example, if the target vapor pressure is 3 Torr, this corresponds to a dew point, temperature of approximately 22.9° F. This position is indicated by point A on the curve. The target vapor pressure can be mandated by a government or other regulatory organization and can vary greatly. In some embodiments, it is preferable that the predetermined dew point temperature be in the range of approximately 20-26° F., and most preferably about 22.9° F. The invention, however, is not limited to any specific dew point value. The exact dew point temperature of the wetted helium gas that will correspond to an adequately dry state within the cavity 21 will be determined on a case-by-case basis, considering such factors as government regulations, mandated safety factors, the type of HLW being stored, the storage period, etc. Referring, back to FIG. 4, after the CPU 351 compares the measured dew point temperature to the predetermined dew point temperature, the CPU 351 then determines whether the measured dew point temperature is less than or equal to the predetermined dew point temperature, thus performing decision block 460. This comparison is performed for each signal received by the CPU 351. If the measured dew point temperature of the wetted helium gas exiting the canister is determined to be above the predetermined dew point temperature, the answer at decision block 460 is NO and the CPU 35 will continue to decision block 490. At decision block 490, the CPU 351 determines whether the timer 353 has been activated (which is done at step 470). If the timer 353 is activated, the answer at decision block 490 is YES and the CPU 351 deactivates the timer 353 and returns to step 440. If the timer 353 is not activated, the answer at decision block 490 is NO and the CPU 351 returns directly to step 440. Either way, if the measured dew point temperature of the wetted helium gas exiting the canister is determined to be above the predetermined dew point temperature, the drying system 300 continues to circulate the dry helium gas into and through the cavity 21 of the canister 20. However, if the measured dew point temperature of the wetted helium gas exiting the canister is determined to be at or below the predetermined dew point temperature, the answer at decision block 460 is YES and the CPU 351 will continue to step 470. At step 470 the CPU 351 activates/starts the timer 353. The timer 470 is programmed to run for a predetermined time. The selection and purpose of the predetermined time will be discussed in greater detail below. Once the timer is activated at step 470, the CPU 351 proceeds to decision block 480 to determine whether the timer 353 has expired whether the predetermined time has passed). If the answer at decision block 480 is NO, the CPU 351 returns to step 440 and the drying, system 300 continues to circulate helium gas through the cavity 21 of the canister 20 and repeat the operations of steps 440-470 until the predetermined time expires. In other words, the drying process continues until the measured dew point temperature of the wetted helium gas exiting the canister falls below (or equal to) the predetermined dew point temperature, and remains so for the predetermined time (without subsequently rising above the predetermined dew point temperature). By requiring that the measured dew point temperature of the wetted helium gas exiting the canister not only reach, but remain at or below the predetermined dew point temperature for the predetermined time, it is ensured that the cavity 21 and the SNF therein are sufficiently dried within an acceptable safety factor. This, along with the means for selecting the predetermined time, will now be described with respect to FIG. 6. Referring to FIG. 6, the affect on the dew point temperature that continuing the helium gas flow through the canister 20 over time is exemplified. The data in the graph was simulated assuming a dry helium flow rate of 400 lb/hr, a pressure of 50 psi, a moisture level of 1 mm Hg within the dry helium gas, a canister volume capacity of helium holdup of 10 lb, and an initial canister moisture level of 100 mm Hg. As can be seen from the graph, at time (“t”)=0.1 hours (i.e., 6 minutes), it can be estimated that the dew point temperature within the cavity 21 is at about 22.9° F. (which from FIG. 5 corresponds to a vapor pressure of about 3 Torr), indicated on the graph as point B. As the flow of helium gas through the cavity 21 is continued over time, the dew point temperature will continue to decrease until an equilibrium vapor pressure is reached, which in the graphed example is at about t=0.36 hours (i.e., about 22 min), indicated on the graph as point C. If desired, the flow of helium gas through the cavity can be further continued, but it will not result in any further significant decrease of the dew point temperature within the cavity 21. Taking points B and C as the points of reference, the predetermined time for this example is about 16 minutes (i.e., from 6 minutes to 22 minutes). However, if desired, the predetermined time can be less than or greater than 16 minutes for the example. The exact predetermined time for any situation will be determined on case-by-case design basis, considering such factors as open canister volume, flow rate, desired dryness within the cavity, desired or mandated safety factors, etc. In some embodiments of the invention, the predetermined time will preferably be in the range of 20 to 40 minutes, more preferably in the range of 25 to 35 minutes, and most preferably approximately 30 minutes. Referring back to FIG. 4, once the predetermined time expires, and the measured dew point temperature remains at or below the predetermined dew point temperature for the entire predetermined time, the CPU 351 arrives at decision block 480 again. However, the answer is now YES and the CPU 351 continues to step 510. At step 510, the CPU 351 generates shut down signals that are transmitted to the pumps 320, 360. Upon receiving the shutdown signals, the pumps 320, 360 are deactivated and the flow of helium gas through the drying system is ceased. Alternatively, the CPU 351 can cease the helium flow by dosing the valve 321. Once the pumps 320, 360 are deactivated, the CPU 351 generates and transmits an activation signal to the alarm 370, thereby completing step 520. Upon receiving the activation signal, the alarm 370 is activated. Depending, on the type of device that is used as the alarm 370, the response of the alarm 370 to the activation signal can vary greatly. However, it is preferred that the alarm's 370 response be some type of audio and/or visual stimuli that will inform the operator that the canister 20 is dry. For example, activation of the alarm 370 can generate a sound, display a visual representation on a computer screen, illuminate an LED or other light source, etc. Upon being informed by the alarm 370 that the cavity 21 of the canister 20 and the SNF is sufficiently dried, the operator disconnects the drying system from the canister 20 and seals the canister 20 for storage, thereby completing step 530. The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. As will be understood by those skilled in this art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Specifically, in some embodiments, the drying method of the invention can be carried out manually. In such an embodiment, the pumps and all other equipment will be activated/controlled manually. The readings by the hygrometer can be visually observed by the operator and the timing sequence operations can be performed manually. |
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description | The present invention relates to a control system for nuclear facilities, in which an auxiliary control device provided in the nuclear facilities actuates units to a safe side when a main control device provided in the nuclear facilities cannot control actuation of the units to the safe side due to a problem such as a common cause failure. Conventionally known is a reactor protection system in which, in a case where a nuclear facility is in an abnormal state of operation, a reactor trip and an engineered safety feature are actuated, in consideration of a common cause failure (common mode failure) on software(for example, refer to Patent Literature 1). This reactor protection system has two comparison logic processor modules, and the two comparison logic processor modules have different kinds of CPUs. One comparison logic processor module processes input data in a first processing order to output a trip state signal. The other comparison logic processor module processes input data in a second processing order, which is a reverse direction of the first processing order, to output a trip state signal. Accordingly, since the trip state signal can be output with the use of the other comparison logic processor module, which is different from the one comparison logic processor module, in this reactor protection system, this reactor protection system can exclude a common cause failure. Patent Literature 1: Japanese National Publication of International Patent Application No. 2004-529353 However, in a case where either one of the two comparison logic processor modules outputs a trip state signal by malfunction, the reactor protection system will shut down an operation of the nuclear reactor. Thus, when the operation of the nuclear reactor is shut down by malfunction, the nuclear facilities cannot be operated until the operation of the nuclear reactor is restored, and thus an operating rate of the nuclear facilities is lowered. An object of the present invention is to provide a control system for nuclear facilities enabling to restrict lowering of an operating rate of the nuclear facilities caused by malfunction. According to an aspect of the present invention, a control system for a nuclear facility includes: a detecting sensor provided in a nuclear facility and configured to output an abnormality detecting signal at the time of occurrence of an abnormality in the nuclear facility; a main control device for outputting a normal actuating signal when a unit is actuated normally in consequence of controlling the unit provided in the nuclear facility to a safe side based on the abnormality detecting signal; and an auxiliary control device, as an auxiliary of the main control device, for outputting an auxiliary actuating signal to actuate the unit to a safe side in a case where the auxiliary control device determines from output results of the abnormality detecting signal and the normal actuating signal that the unit is not actuated normally for the abnormality in the nuclear facility. The auxiliary control device includes: a NOT circuit connected to an output side of the main control device, and configured to invert input or no input of the normal actuating signal and output an inverted signal; and a first AND circuit configured to output the auxiliary actuating signal based on input or no input of the signal output from the NOT circuit and input or no input of the abnormality detecting signal. With this configuration, in a state in which the main control device is actuated normally, when an abnormality detecting signal is input in the main control device and the auxiliary control device from the detecting sensor, the main control device controls actuation of the unit provided in the nuclear facility to a safe side based on the abnormality detecting signal. The main control device outputs a normal actuating signal in a case where the main control device controls actuation of the unit to the safe side, and where this causes the unit to be actuated normally. At this time, the normal actuating signal is input in the auxiliary control device but passes through the NOT circuit, and thus the signal is not input in the first AND circuit. Accordingly, even when the abnormality detecting signal is input in the first AND circuit, the auxiliary actuating signal is not output from the first AND circuit. Consequently, when an abnormality occurs in the nuclear facility in a state in which the main control device is actuated normally (for example, in a state in which no common cause failure occurs), the main control device outputs the normal actuating signal, and thus the auxiliary control device can prevent the auxiliary actuating signal from being output from the first AND circuit. On the other hand, in a state in which the main control device is in a malfunction state (for example, in a state in which a common cause failure occurs), when an abnormality detecting signal is input in the main control device and the auxiliary control device from the detecting sensor, there is a case in which the normal actuating signal is not output from the main control device. At this time, the normal actuating signal is not input in the auxiliary control device but passes through the NOT circuit, and thus the signal is input in the first AND circuit. Accordingly, since the first AND circuit receives the signal from the NOT circuit and the abnormality detecting signal, the first AND circuit can output the auxiliary actuating signal. Consequently, the auxiliary control device can output the auxiliary actuating signal from the first AND circuit even when the main control device malfunctions, and thus the unit provided in the nuclear facility can be actuated to the safe side. Advantageously, in the control system for a nuclear facility, the auxiliary control device includes a delay circuit for delaying output of the abnormality detecting signal to the first AND circuit as much as predetermined time from reception of the abnormality detecting signal by the main control device to output of the normal actuating signal to the first AND circuit. With this configuration, the delay circuit can delay output of the abnormality detecting signal to the first AND circuit as much as the predetermined time until input of the normal actuating signal via the NOT circuit in the first AND circuit. That is, when the normal actuating signal is not input via the NOT circuit in the first AND circuit, this brings about a state in which the signal output from the NOT circuit is input in the first AND circuit. When the abnormality detecting signal is input in this state, the auxiliary actuating signal will be output from the first AND circuit. Accordingly, by providing the delay circuit, the abnormality detecting signal is input after the normal actuating signal is input via the NOT circuit in the first AND circuit. Accordingly, the first AND circuit can perform output or no output of the auxiliary actuating signal only when necessary by detecting input or no input of the abnormality detecting signal after detecting input or no input of the signal output from the NOT circuit. Advantageously, the control system for a nuclear facility further includes: a first manual manipulating unit configured to output an allowing signal allowing output of the auxiliary actuating signal by manual manipulation. The auxiliary control device further includes a second AND circuit configured to output the auxiliary actuating signal based on input or no input of the auxiliary actuating signal output from the first AND circuit and input or no input of the allowing signal. With this configuration, when the allowing signal is input in the second AND circuit by manual manipulation of the first manual manipulating unit, the second AND circuit can be in a state in which the auxiliary actuating signal can be output. On the other hand, when the allowing signal is not input in the second AND circuit by manual manipulation of the first manual manipulating unit, the second AND circuit can be in a state in which the auxiliary actuating signal cannot be output. Accordingly, an operator can control output or no output of the auxiliary actuating signal easily by manually manipulating the first manual manipulating unit as needed. Advantageously, the control system for a nuclear facility further includes: a second manual manipulating unit configured to output a manual actuating signal actuating the unit provided in the nuclear facility to a safe side by manual manipulation; and an OR circuit configured to output a second auxiliary actuating signal based on input or no input of the auxiliary actuating signal output from the second AND circuit and input or no input of the manual actuating signal. With this configuration, when at least either the manual actuating signal or the auxiliary actuating signal is input in the OR circuit, the OR circuit can output the second auxiliary actuating signal. Accordingly, since the operator can output the second auxiliary actuating signal easily by manually manipulating the second manual manipulating unit as needed, the unit can be actuated to a safe side by manual manipulation. Advantageously, in the control system for a nuclear facility, the nuclear facility includes a nuclear reactor having inside a core, a containment housing the nuclear reactor, and the unit. The unit includes a core damage preventing unit preventing damage of the core and a vessel breakage preventing unit preventing breakage of the containment, and the auxiliary control device outputs the auxiliary actuating signal to actuate the core damage preventing unit and the vessel breakage preventing unit to a safe side. With this configuration, since the auxiliary control device has only to output the auxiliary actuating signal that actuates the core damage preventing unit to a safe side and the auxiliary actuating signal that actuates the vessel breakage preventing unit to a safe side, the auxiliary control device can be configured to the minimum and can thus be configured simply. Advantageously, in the control system for a nuclear facility, the main control device includes a digital facility executing software on hardware, and the auxiliary control device is an analog facility configured by connecting respective junctions of electronic components by wires. With this configuration, since the main control device and the auxiliary control device can be configured differently, occurrence of a common cause failure can be restricted. Accordingly, even in a case where a common cause failure occurs in the digital facility of the main control device, the auxiliary control device can actuate the unit provided in the nuclear facility to a safe side at the time of occurrence of an abnormality in the nuclear facility. With the control system for a nuclear facility according to the present invention, in a case where the main control device is actuated normally, the unit provided in the nuclear facility is not actuated by the auxiliary control device. On the other hand, in a case where the main control device malfunctions due to a common cause failure or the like, the unit provided in the nuclear facility can be actuated by the auxiliary control device as needed. Accordingly, at the time of occurrence of an abnormality in the nuclear facility, the unit provided in the nuclear facility can be actuated to a safe side suitably by the main control device and the auxiliary control device. Also, in a case where the main control device is actuated normally, the unit provided in the nuclear facility will not be actuated by malfunction of the auxiliary control device, and thus lowering of an operating rate of the nuclear facility caused by malfunction can be restricted. Hereinafter, a control system for a nuclear facility according to the present invention will be described with reference to the attached drawings. It is to be noted that the present invention is not limited to the following embodiments. Also, components in the following embodiments include ones that are replaceable and practiced easily by a person skilled in the art or substantially identical ones. Embodiments FIG. 1 is a schematic view illustrating a nuclear facility controlled by a control system according to the present embodiment. A control system 40 for a nuclear facility 1 according to the present invention is adapted to control the nuclear facility 1 including a nuclear reactor 5, and a pressurized water reactor (PWR) is used as the nuclear reactor 5, for example. The nuclear facility 1 using this pressurized water reactor 5 includes a nuclear reactor cooling system 3 including the nuclear reactor 5 and a turbine system 4 performing heat exchange with the nuclear reactor cooling system 3, and a nuclear reactor coolant circulates in the nuclear reactor cooling system 3 while a secondary coolant circulates in the turbine system 4. The nuclear reactor cooling system 3 includes the nuclear reactor 5 and a steam generator 7 connected to the nuclear reactor 5 via coolant pipings 6a and 6b consisting of a cold leg 6a and a hot leg 6b. Also, a pressurizer 8 is interposed in the hot leg 6b while a coolant pump 9 is interposed in the cold leg 6a. The nuclear reactor 5, the coolant pipings 6a and 6b, the steam generator 7, the pressurizer 8, and the coolant pump 9 are housed in a containment 10. The nuclear reactor 5 is a pressurized water reactor as described above and is filled therein with the nuclear reactor coolant. In the nuclear reactor 5, multiple fuel assemblies 15 are housed, and multiple control rods 16 controlling nuclear fission of the fuel assemblies 15 are provided to enable insertion into the respective fuel assemblies 15. When the fuel assemblies 15 are subjected to nuclear fission while nuclear fission reactions are controlled by the control rods 16, heat energy is generated by this nuclear fission. The generated heat energy heats the nuclear reactor coolant, and the heated nuclear reactor coolant is sent to the steam generator 7 via the hot leg 6b. On the other hand, the nuclear reactor coolant sent from the steam generator 7 via the cold leg 6a flows in the nuclear reactor 5 and cools the inside of the nuclear reactor 5. The pressurizer 8 interposed in the hot leg 6b pressurizes the nuclear reactor coolant heated to a high temperature to restrict boiling of the nuclear reactor coolant. Also, the steam generator 7 causes the high-temperature and high-pressure nuclear reactor coolant to undergo heat exchange with the secondary coolant to evaporate the secondary coolant to generate steam and cool the high-temperature and high-pressure nuclear reactor coolant. The coolant pump 9 circulates the nuclear reactor coolant in the nuclear reactor cooling system 3. The coolant pump 9 sends the nuclear reactor coolant from the steam generator 7 via the cold leg 6a to the nuclear reactor 5 and sends the nuclear reactor coolant from the nuclear reactor 5 via the hot leg 6b to the steam generator 7. Here, a sequence of operations in the nuclear reactor cooling system 3 of the nuclear facility 1 will be described. When the nuclear reactor coolant is heated by heat energy generated by nuclear fission reactions in the nuclear reactor 5, the heated nuclear reactor coolant is sent to the steam generator 7 via the hot leg 6b by the coolant pump 9. The high-temperature nuclear reactor coolant passing through the hot leg 6b is pressurized by the pressurizer 8 to restrict boiling and flows in the steam generator 7 in a high-temperature and high-pressure state. The high-temperature and high-pressure nuclear reactor coolant flowing in the steam generator 7 is cooled by heat exchange with the secondary coolant, and the cooled nuclear reactor coolant is sent to the nuclear reactor 5 via the cold leg 6a by the coolant pump 9. The nuclear reactor 5 is cooled by the flow of the cooled nuclear reactor coolant in the nuclear reactor 5. That is, the nuclear reactor coolant circulates between the nuclear reactor 5 and the steam generator 7. Meanwhile, the nuclear reactor coolant is light water to be used as a coolant and a neutron moderator. The turbine system 4 includes a turbine 22 connected to the steam generator 7 via a steam pipe 21, a condenser 23 connected to the turbine 22, and a feed water pump 24 interposed in a feed water pipe 26 connecting the condenser 23 to the steam generator 7. To the turbine 22 is connected a generator 25. Here, a sequence of operations in the turbine system 4 of the nuclear facility 1 will be described. When steam flows in the turbine 22 via the steam pipe 21 from the steam generator 7, the turbine 22 is rotated. When the turbine 22 is rotated, the generator 25 connected to the turbine 22 generates electricity. Thereafter, steam flowing out of the turbine 22 flows in the condenser 23. The condenser 23 is provided therein with a cooling pipe 27, and one end of the cooling pipe 27 has connected to an intake pipe 28 taking cooling water (e.g., seawater) while the other end of the cooling pipe 27 has connected to a drain pipe 29 draining cooling water. The condenser 23 cools steam flowing from the turbine 22 by the cooling pipe 27 to turn the steam back to liquid. The secondary coolant as liquid is sent to the steam generator 7 via the feed water pipe 26 by the feed water pump 24. The secondary coolant sent to the steam generator 7 undergoes heat exchange with the nuclear reactor coolant in the steam generator 7 and becomes steam again. FIG. 2 is a configuration diagram of a control system for a nuclear facility according to the present embodiment. The nuclear facility 1 configured as above is provided with the control system 40 controlling actuation of respective units such as the aforementioned various pumps and not illustrated valves provided in the nuclear facility 1. This control system 40 includes a not illustrated central control facility, a not illustrated plant control facility, a safety protection system facility (main control device) 43, and a CCF countermeasure facility (auxiliary control device) 44. The central control facility is provided with a display unit displaying an operating state of the nuclear facility 1, a manipulating unit manipulating the nuclear facility 1, and the like, although these are not illustrated in figures. An operator operating the nuclear facility 1 visually recognizes the display unit to understand the operating state of the nuclear facility 1 and manipulates the manipulating unit as needed to operate the nuclear facility 1. The plant control facility controls operations of the nuclear reactor 5 and the respective units of the nuclear facility 1 based on a manipulating signal output from the manipulating unit of the central control facility. As illustrated in FIG. 2, the safety protection system facility 43 takes control so that the nuclear facility 1 may be shut down safely in a case where an abnormality occurs in the nuclear facility 1. The CCF countermeasure facility 44 is a backup facility assisting the safety protection system facility 43 and takes control so that the nuclear facility 1 may be shut down safely in a case where a problem such as a common cause failure (CCF) occurs in the safety protection system facility 43. The safety protection system facility 43 includes a plurality of control panels, some of the plurality of control panels are digital facilities in which computing units such as CPUs are built, and the digital facilities are facilities that can control safety protection systems of the nuclear facility 1 by executing various programs by the computing units. Meanwhile, the safety protection systems are functional systems functioning as stopping nuclear reactions of the nuclear reactor 5, cooling the nuclear facility 1, and preventing leakage of radioactive materials from the nuclear facility 1. The safety protection system facility 43 has high operational guarantee so as to be actuated reliably and be actuated even under a severe environment. To the safety protection system facility 43 are connected various detecting sensors 50 disposed in the nuclear facility 1, and the safety protection system facility 43 determines whether or not an abnormality occurs in the nuclear facility 1 based on an abnormality detecting signal obtained from each detecting sensor 50. In a case where the safety protection system facility 43 determines that an abnormality occurs in the nuclear facility 1, the safety protection system facility 43 outputs to each unit an actuating signal actuating the unit to a safe side and, in a case where the unit is actuated normally, outputs a normal actuating signal S1 to the CCF countermeasure facility 44. Here, the normal actuating signal S1 includes a nuclear reactor trip signal T for shutting down the nuclear reactor 5, an auxiliary feed water signal S for supplying the turbine 22 with the secondary coolant, and the like. The CCF countermeasure facility 44 is provided on the assumption of a case in which a common cause failure occurs in the safety protection system facility 43. The CCF countermeasure facility 44 is an analog facility, uses electric circuit parts such as switches and relays, and is configured by connecting respective junctions by electric wires. Here, the common cause failure is an event in which software used in each digital facility is not executed due to a common cause such as a bug. That is, in the present embodiment, the safety protection system facility 43 is a digital facility while the CCF countermeasure facility 44 is an analog facility to exclude a possibility of simultaneous failures of the safety protection system facility 43 and the CCF countermeasure facility 44 due to a common cause failure. To the CCF countermeasure facility 44 are connected the various detecting sensors 50 as well, and the CCF countermeasure facility 44 determines whether or not an abnormality occurs in the nuclear facility 1 based on an abnormality detecting signal obtained from each detecting sensor 50 in a similar manner to that of the safety protection system facility 43. In a case where the CCF countermeasure facility 44 determines that an abnormality occurs in the nuclear facility 1, the CCF countermeasure facility 44 outputs to each unit an auxiliary actuating signal S2 actuating the unit to a safe side. Meanwhile, the auxiliary actuating signal S2 includes a nuclear reactor trip signal T for shutting down the nuclear reactor 5, an auxiliary feed water signal S for supplying the turbine 22 with the secondary coolant, and the like, in a similar manner to that of the normal actuating signal S1. Also, the CCF countermeasure facility 44 includes an automatic control panel 52 enabling the auxiliary actuating signal S2 to be output automatically and a manual manipulating panel 53 enabling the auxiliary actuating signal S2 to be output manually. The automatic control panel 52 outputs to each unit the auxiliary actuating signal S2 actuating the unit to a safe side in a case where the automatic control panel 52 determines that an abnormality occurs in the nuclear facility 1 based on an abnormality detecting signal obtained from the detecting sensor 50. The manual manipulating panel 53 has a plurality of manipulating units (not illustrated) outputting various signals by manual manipulation. Examples of the plurality of manipulating units include a manipulating unit that enables the nuclear reactor trip signal T to be output and a manipulating unit that enables a trip allowing signal K1 that allows the automatic control panel 52, to output the nuclear reactor trip signal T, an auxiliary feed water allowing signal K2 that allows the automatic control panel 52 to output the auxiliary feed water signal S, and an alarm allowing signal K3 that allows the automatic control panel 52 to output an alarm. The automatic control panel 52 has a plurality of actuating circuits outputting various signals based on input abnormality detecting signals. The plurality of actuating circuits include a nuclear reactor trip circuit 60 outputting the nuclear reactor trip signal T, an auxiliary feed water activating circuit 61 outputting the auxiliary feed water signal S, and an alarm circuit 62 outputting an alarm, for example. The automatic control panel 52 also has a pressurizer pressure bistable 65 obtaining an abnormality detecting signal output from the detecting sensor 50 detecting pressure of the pressurizer 8 and a steam generator water level bistable 66 obtaining an abnormality detecting signal output from the detecting sensor 50 detecting water level of the steam generator 7, and the actuating circuits 60, 61, and 62 are connected to the pressurizer pressure bistable 65 or the steam generator water level bistable 66. The pressurizer pressure bistable 65 has low pressure bistables 65a and high pressure bistables 65b. The plurality of (2 in the present embodiment) low pressure bistables 65a are provided in accordance with the number of pressurizers 8 provided in the nuclear facility 1, and each low pressure bistable 65a outputs an abnormality detecting signal when a lower pressure value than a pre-set lowermost pressure value is obtained. The plurality of (2 in the present embodiment) high pressure bistables 65b are provided in accordance with the number of pressurizers 8 provided in the nuclear facility 1, and each high pressure bistable 65b outputs an abnormality detecting signal when a higher pressure value than a pre-set uppermost pressure value is obtained. The steam generator water level bistable 66 has low water level bistables 66a and high water level bistables 66b. The plurality of (4 in the present embodiment) low water level bistables 66a are provided in accordance with the number of steam generators 7 provided in the nuclear facility 1, and each low water level bistable 66a outputs an abnormality detecting signal when obtaining a lower water level value than a pre-set lowermost water level value. The plurality of (4 in the present embodiment) high water level bistables 66b are provided in accordance with the number of steam generators 7 provided in the nuclear facility 1, and each high water level bistable 66b outputs an abnormality detecting signal when a higher water level value than a pre-set uppermost water level value is obtained. The nuclear reactor trip circuit 60 has an AND circuit 70 connected to output sides of the low pressure bistables 65a, an AND circuit 71 connected to output sides of the high pressure bistables 65b, and a voting circuit 72 connected to output sides of the low water level bistables 66a. The nuclear reactor trip circuit 60 also has an OR circuit 73 connected to output sides of the AND circuit 70, the AND circuit 71, and the voting circuit 72, a delay circuit 74 connected to an output side of the OR circuit 73, a first AND circuit 75 connected to an output side of the delay circuit 74, and a NOT circuit 76 connected to an input side of the first AND circuit 75. When the AND circuit 70 receives abnormality detecting signals from the two low pressure bistables 65a, the AND circuit 70 outputs the abnormality detecting signal to the OR circuit 73. On the other hand, the AND circuit 70 outputs no abnormality detecting signal in a case where at least either one out of the two low pressure bistables 65a does not output an abnormality detecting signal. When the AND circuit 71 receives abnormality detecting signals from the two high pressure bistables 65b, the AND circuit 71 outputs the abnormality detecting signal to the OR circuit 73. On the other hand, the AND circuit 71 outputs no abnormality detecting signal in a case where at least either one out of the two high pressure bistables 65b does not output an abnormality detecting signal. When the voting circuit 72 receives abnormality detecting signals from three low water level bistables 66a out of the four low water level bistables 66a, the voting circuit 72 outputs the abnormality detecting signal to the OR circuit 73. On the other hand, the voting circuit 72 outputs no abnormality detecting signal in a case where at least three low water level bistables 66a do not output abnormality detecting signals. When the OR circuit 73 receives one or more abnormality detecting signals from at least one circuit out of the AND circuit 70, the AND circuit 71, and the voting circuit 72, the OR circuit 73 outputs the nuclear reactor trip signal T to the delay circuit 74. The NOT circuit 76 is connected at an input side thereof to the safety protection system facility 43. The NOT circuit 76 inverts the nuclear reactor trip signal T output from the safety protection system facility 43 and outputs the inverted signal to the first AND circuit 75. That is, when the nuclear reactor trip signal T is output from the safety protection system facility 43, the NOT circuit 76 does not output the signal to the first AND circuit 75. On the other hand, when no nuclear reactor trip signal T is output from the safety protection system facility 43, the NOT circuit 76 outputs the signal to the first AND circuit 75. When the first AND circuit 75 receives the signal from the NOT circuit 76 and receives the nuclear reactor trip signal T from the OR circuit 73, the first AND circuit 75 outputs the nuclear reactor trip signal T. On the other hand, the first AND circuit 75 outputs no nuclear reactor trip signal T when the NOT circuit 76 or the OR circuit 73 outputs no signal. The delay circuit 74 delays the nuclear reactor trip signal T to be output from the OR circuit 73 to the first AND circuit 75 as much as delay time from input of the abnormality detecting signal in the safety protection system facility 43 to input of the nuclear reactor trip signal T in the first AND circuit 75 via the NOT circuit 76. Also, the nuclear reactor trip circuit 60 has a latch circuit 78 connected to an output side of the first AND circuit 75 and an OR circuit 79 connected to an output side of the latch circuit 78. The latch circuit 78 has a latch OR circuit 81 connected to an output side of the first AND circuit 75 and a latch AND circuit (second AND circuit) 82 connected to an output side of the latch OR circuit 81. To an input side of the latch AND circuit 82 is connected the manual manipulating panel 53, and when the trip allowing signal K1 is input from the manual manipulating panel 53, the latch AND circuit 82 is in a state in which the nuclear reactor trip signal T can be output. To an output side of the latch AND circuit 82 is connected an input side of the latch OR circuit 81, and as long as the trip allowing signal K1 is input in the latch AND circuit 82, the latch AND circuit 82 is in a state in which the nuclear reactor trip signal T can be output. On the other hand, when the trip allowing signal K1 is not input from the manual manipulating panel 53, the latch AND circuit 82 cannot output the nuclear reactor trip signal T. To an input side of the OR circuit 79 is connected the manual manipulating panel 53, and when the nuclear reactor trip signal T is input from the manual manipulating panel 53, or when the nuclear reactor trip signal T is input from the latch circuit 78, the OR circuit 79 outputs the nuclear reactor trip signal T (second auxiliary actuating signal). Meanwhile, the nuclear reactor trip circuit 60 also functions as a turbine trip circuit enabling a turbine trip signal for shutting down the turbine 22 to be output and functions as a feed water isolation circuit enabling a feed water isolation signal for isolating a coolant circulating in the feed water pipe 26 in the containment 10 from the outside to be output. The auxiliary feed water activating circuit 61 has the aforementioned voting circuit 72, a delay circuit 84 connected to an output side of the voting circuit 72, a first AND circuit 85 connected to an output side of the delay circuit 84, and a NOT circuit 86 connected to an input side of the first AND circuit 85. The voting circuit 72 is shared with the nuclear reactor trip circuit 60. When the voting circuit 72 receives abnormality detecting signals from three low water level bistables 66a out of the four low water level bistables 66a, the voting circuit 72 outputs the auxiliary feed water signal S to the first AND circuit 85. On the other hand, the voting circuit 72 outputs no auxiliary feed water signal S in a case where at least three low water level bistables 66a do not output abnormality detecting signals. The NOT circuit 86 is connected at an input side thereof to the safety protection system facility 43. The NOT circuit 86 inverts the auxiliary feed water signal S output from the safety protection system facility 43 and outputs the inverted signal to the first AND circuit 85. That is, when the auxiliary feed water signal S is output from the safety protection system facility 43, the NOT circuit 86 does not output the signal to the first AND circuit 85. On the other hand, when no auxiliary feed water signal S is output from the safety protection system facility 43, the NOT circuit 86 outputs the signal to the first AND circuit 85. When the first AND circuit 85 receives the signal from the NOT circuit 86 and receives the auxiliary feed water signal S from the voting circuit 72, the first AND circuit 85 outputs the auxiliary feed water signal S. On the other hand, the first AND circuit 85 outputs no auxiliary feed water signal S when the NOT circuit 86 or the voting circuit 72 outputs no signal. The delay circuit 84 delays the auxiliary feed water signal S to be output from the voting circuit 72 to the first AND circuit 85 as much as delay time from input of the abnormality detecting signal in the safety protection system facility 43 to input of the auxiliary feed water signal S in the first AND circuit 85 via the NOT circuit 86. Also, the auxiliary feed water activating circuit 61 has a latch circuit 88 connected to an output side of the first AND circuit 85. The latch circuit 88 has a latch OR circuit 91 connected to an output side of the first AND circuit 85 and a latch AND circuit (second AND circuit) 92 connected to an output side of the latch OR circuit 91. To an input side of the latch AND circuit 92 is connected the manual manipulating panel 53, and when the auxiliary feed water allowing signal K2 is input from the manual manipulating panel 53, the latch AND circuit 92 is in a state in which the auxiliary feed water signal S can be output. An output side of the latch AND circuit 92 is connected to an input side of the latch OR circuit 91, and as long as the auxiliary feed water allowing signal K2 is input in the latch AND circuit 92, the latch AND circuit 92 is in a state in which the auxiliary feed water signal S can be output. On the other hand, when the auxiliary feed water allowing signal K2 is not input from the manual manipulating panel 53, the latch AND circuit 92 cannot output the auxiliary feed water signal S. The alarm circuit 62 has an OR circuit 95 connected to output sides of the high water level bistables 66b, a delay circuit 96 connected to an output side of the OR circuit 95, a latch circuit 97 connected to an output side of the delay circuit 96, a NOT circuit 98 connected to an input side of the latch circuit 97, and a second AND circuit 99 connected to an output side of the latch circuit 97. When the OR circuit 95 receives one or more abnormality detecting signals from at least one high water level bistable 66b out of the four high water level bistables 66b, the OR circuit 95 outputs an alarm signal A to the delay circuit 96. An input side of the NOT circuit 98 is connected to the safety protection system facility 43. The NOT circuit 98 inverts the nuclear reactor trip signal T output from the safety protection system facility 43 and outputs the inverted signal to the latch circuit 97. That is, when the nuclear reactor trip signal T is output from the safety protection system facility 43, the NOT circuit 98 does not output the signal to the latch circuit 97. On the other hand, when no nuclear reactor trip signal T is output from the safety protection system facility 43, the NOT circuit 98 outputs the signal to the latch circuit 97. The latch circuit 97 has a latch AND circuit (first AND circuit) 100 connected to an output side of the delay circuit 96 and a latch OR circuit 101 connected to an input side of the latch AND circuit 100. An input side of the latch OR circuit 101 is connected to the NOT circuit 98, and when the signal is input from the NOT circuit 98, the latch OR circuit 101 outputs the signal to the latch AND circuit 100. Input sides of the latch AND circuit 100 are connected to an output side of the latch OR circuit 101 and an output side of the delay circuit 96. When the latch AND circuit 100 receives the signal from the latch OR circuit 101 and receives the alarm signal A from the delay circuit 96, the latch AND circuit 100 outputs the alarm signal A to the second AND circuit 99. An input side of the second AND circuit 99 is connected to the manual manipulating panel 53, and when the alarm allowing signal K3 is input from the manual manipulating panel 53, the second AND circuit 99 outputs the alarm signal A. The delay circuit 96 delays the alarm signal A to be output from the OR circuit 95 to the latch AND circuit 100 as much as delay time from input of the abnormality detecting signal in the safety protection system facility 43 to input of the signal in the latch AND circuit 100 via the NOT circuit 98 and the latch OR circuit 101. Here, controlled targets of the safety protection system facility 43 and controlled targets of the CCF countermeasure facility 44 differ partially. Specifically, the controlled targets of the CCF countermeasure facility 44 are part of units preventing damage of a core of the nuclear reactor 5 and part of units preventing breakage of the containment 10 in the controlled targets of the safety protection system facility 43. That is, the CCF countermeasure facility 44 exerts a core damage preventing function preventing damage of the core and a vessel breakage preventing function preventing breakage of the vessel by outputting the auxiliary actuating signals S2 such as the nuclear reactor trip signal T and the auxiliary feed water signal S. FIG. 3 is a table which relates possible abnormal events that may occur in a nuclear facility to kinds of the core damage preventing function and the vessel breakage preventing function to be performed in accordance with the possible abnormal events. As illustrated in this table, the possible abnormal events include a transient event for a temperature or pressure of the coolant, rupture of a heat transfer tube provided in the steam generator 7 (SGTR), rupture of the steam pipe 21, rupture of the feed water pipe 26, and loss of the coolant by rupture (LOCA). Also, kinds of the core damage preventing function and the vessel breakage preventing function can be classified into three functions roughly: a function of stopping the nuclear facility 1, a function of cooling the nuclear facility 1, and a function of confining in the nuclear facility 1. The function of stopping the nuclear facility 1 includes a nuclear reactor trip function shutting down the nuclear reactor 5 and a turbine trip function shutting down the turbine 22. The function of cooling the nuclear facility 1 includes an auxiliary feed water function performing auxiliary feed water to the turbine system 4, an auxiliary feed water isolation function isolating auxiliary feed water supplied to the turbine system 4, a safety injection function injecting the coolant in the nuclear reactor cooling system 3, a function of letting out steam in the steam generator 7 of a main steam relief valve, and a function of letting out steam in the pressurizer 8 of a pressurizer relief valve. The function of confining in the nuclear facility 1 includes a main feed water isolation function isolating a coolant circulating in the feed water pipe 26 in the containment 10 from the outside, a main steam isolation function isolating a coolant circulating in the steam pipe 21 in the containment 10 from the outside, a containment vessel spray function spraying cooling water in the containment 10, and a containment vessel isolation function isolating the inside of the containment 10 from the outside. As illustrated in FIG. 3, the kinds of functions are classified into ones performed by the automatic control panel 52 of the CCF countermeasure facility 44, ones performed by the manual manipulating panel 53 of the CCF countermeasure facility 44, and ones performed by manual manipulation of units at sites at which the units are installed in accordance with the abnormal events. Here, ones performed by the automatic control panel 52 are ones having high occurrence frequency of the abnormal events and requiring early performance and are specifically expressed as a symbol A illustrated in FIG. 3. Ones performed by the manual manipulating panel 53 are ones having high occurrence frequency of the abnormal events but requiring no hasty manipulation and are specifically expressed as a symbol B illustrated in FIG. 3. Ones performed by manual manipulation of units at installation sites are ones having low occurrence frequency of the abnormal events but having great influences by the abnormal events and requiring manual manipulation and are specifically expressed as a symbol C illustrated in FIG. 3. With the above configuration, in a state in which the safety protection system facility 43 is actuated normally, when an abnormality detecting signal is input in the safety protection system facility 43 and the CCF countermeasure facility 44 from the detecting sensor 50, the safety protection system facility 43 outputs the normal actuating signal S1 in a case where the safety protection system facility 43 controls actuation of the respective units to a safe side, and where this causes the respective units to be actuated normally. At this time, the normal actuating signal S1 is input in the CCF countermeasure facility 44 but passes through the NOT circuit 76, 86, or 98, and thus the signal is not input in the first AND circuit 75, 85, or 100. Accordingly, even when the abnormality detecting signal is input in the first AND circuit 75, 85, or 100, the auxiliary actuating signal S2 is not output from the first AND circuit 75, 85, or 100. Consequently, when an abnormality occurs in the nuclear facility 1 in a state in which the safety protection system facility 43 is actuated normally, the safety protection system facility 43 outputs the normal actuating signal S1, and thus the CCF countermeasure facility 44 can prevent the auxiliary actuating signal S2 from being output from the first AND circuit 75, 85, or 100. On the other hand, in a state in which a CCF occurs in the safety protection system facility 43 as a digital facility (malfunction state), when an abnormality detecting signal is input in the safety protection system facility 43 and the CCF countermeasure facility 44 from the detecting sensor 50, there is a case in which the normal actuating signal S1 is not output from the safety protection system facility 43. At this time, the normal actuating signal S1 is not input in the CCF countermeasure facility 44 but passes through the NOT circuit 76, 86, or 98, and thus the signal is input in the first AND circuit 75, 85, or 100. Accordingly, when the CCF countermeasure facility 44 is actuated normally, and the abnormality detecting signal is input in the first AND circuit 75, 85, or 100, the first AND circuit 75, 85, or 100 receives the signal from the NOT circuit 76, 86, or 98 and the abnormality detecting signal, and thus the first AND circuit 75, 85, or 100 can output the auxiliary actuating signal S2. Consequently, in a case where the CCF countermeasure facility 44 is actuated normally, the CCF countermeasure facility 44 can output the auxiliary actuating signal S2 even when a CCF occurs in the safety protection system facility 43, and thus the units provided in the nuclear facility 1 can be actuated to the safe side. Also, since the delay circuits 74, 84, and 96 are provided, the abnormality detecting signal is input after the normal actuating signal S1 is input via the NOT circuit 76, 86, or 98 in the first AND circuit 75, 85, or 100. Accordingly, the first AND circuit 75, 85, or 100 can perform output or no output of the auxiliary actuating signal S2 by detecting input or no input of the abnormality detecting signal after detecting input or no input of the signal output from the NOT circuit 76, 86, or 98. Also, when the allowing signal K1, K2, or K3 is input in the second AND circuit 82, 92, or 99 by manual manipulation of the manual manipulating panel 53, the second AND circuit 82, 92, or 99 can be in a state in which the auxiliary actuating signal S2 can be output. On the other hand, when the allowing signal K1, K2, or K3 is not input in the second AND circuit 82, 92, or 99 by manual manipulation of the manual manipulating panel 53, the second AND circuit 82, 92, or 99 can be in a state in which the auxiliary actuating signal S2 cannot be output. Accordingly, an operator can control output or no output of the auxiliary actuating signal S2 easily by manually manipulating the manual manipulating panel 53 as needed. Also, when the nuclear reactor trip signal T is input in the OR circuit 79 by manual manipulation of the manual manipulating panel 53, the OR circuit 79 can output the nuclear reactor trip signal T (second auxiliary actuating signal). Accordingly, since the operator can output the nuclear reactor trip signal T easily by manually manipulating the manual manipulating panel 53 as needed, the units can be actuated to a safe side by manual manipulation. Also, since the CCF countermeasure facility 44 has only to output the auxiliary actuating signal S2 that actuates core damage preventing units to a safe side and the auxiliary actuating signal S2 that actuates vessel breakage preventing units to a safe side, the CCF countermeasure facility 44 can be configured to the minimum and can thus be configured simply. Also, since the safety protection system facility 43 includes the digital facilities while the CCF countermeasure facility 44 is the analog facility, occurrence of a failure by a common cause can be restricted. Accordingly, even in a case where a CCF occurs in the safety protection system facility 43, the CCF countermeasure facility 44 is actuated normally, and thus the units provided in the nuclear facility 1 can be actuated to a safe side at the time of occurrence of an abnormality in the nuclear facility 1. As described above, the control system for nuclear facilities according to the present invention is useful in nuclear facilities including a safety protection system facility and a CCF countermeasure facility and especially in a case where, at the time of occurrence of an abnormality, units provided in the nuclear facilities are activated to a safe side, and where, in a case where the safety protection system facility is actuated normally, the units are not activated to the safe side due to malfunction of the CCF countermeasure facility, thus to restrict lowering of an operating rate of the nuclear facilities. 1 nuclear facility 3 nuclear reactor cooling system 4 turbine system 5 nuclear reactor 7 steam generator 8 pressurizer 10 containment 15 fuel assembly 16 control rod 22 turbine 25 generator 40 control system 43 safety protection system facility 44 CCF countermeasure facility 50 detecting sensor 52 automatic control panel 53 manual manipulating panel 60 nuclear reactor trip circuit 61 auxiliary feed water activating circuit 62 alarm circuit 74 delay circuit of the nuclear reactor trip circuit 75 first AND circuit of the nuclear reactor trip circuit 76 NOT circuit of the nuclear reactor trip circuit 78 latch circuit of the nuclear reactor trip circuit 84 delay circuit of the auxiliary feed water activating circuit 85 first AND circuit of the auxiliary feed water activating circuit 86 NOT circuit of the auxiliary feed water activating circuit 88 latch circuit of the auxiliary feed water activating circuit 96 delay circuit of the alarm circuit 97 latch circuit of the alarm circuit 98 NOT circuit of the alarm circuit 99 second AND circuit of the alarm circuit S1 normal actuating signal S2 auxiliary actuating signal T nuclear reactor trip signal S auxiliary feed water signal A alarm signal K1 trip allowing signal K2 auxiliary feed water allowing signal K3 alarm allowing signal |
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description | This application is the national stage (Rule 371) of international application PCT/EP2015/068331 filed Aug. 10, 2015. The invention relates to a storage device for storing and/or transporting radioactive materials. More particularly, the invention relates to a storage device for transporting and/or storing, preferably irradiated, nuclear fuel assemblies. Such storage devices, also called storage «baskets» or «racks», have a plurality of cells inside which irradiated nuclear fuel assemblies are placed, for the transport and/or storage thereof. Fuel assemblies are in particular caused to be moved from the nuclear power plant, once they are no longer used as an energy source, to their storage or treatment site. This basket type is subjected to high temperatures. But, since mechanical characteristics of the structural elements making of the basket are degraded with temperature, it is necessary to remove the heat flux produced by the irradiated assemblies contained in the basket outwardly, in order to limit the temperature rise in the basket and thus ensure that the mechanical strength thereof is compatible with so-called free drop on undeformable target tests. In such baskets, peripheral partitions are attached to internal partitions by tightening screws extending mainly along the longitudinal direction of the internal partitions. The internal partitions are then in thermal contact with peripheral partitions substantially on the edge of the internal partitions. It is useful to increase the thermal contact area between the internal partitions and the peripheral partitions, in order to improve heat removal off the basket. The invention aims at solving at least partially the problems met in solutions of prior art. In this regard, one object of the invention is to provide a basket for transport and/or storage packaging of radioactive materials such as nuclear fuel assemblies. The basket comprises at least one internal partition and at least one peripheral partition. The peripheral partition is located sideways at the periphery of the internal partition. The internal partition comprises at least one wall having two opposite lateral surfaces. The internal partition delimits at least partially on either side of the same two cells intended to house radioactive materials, the peripheral partition participating with the internal partition in delimiting the cells. The peripheral partition comprises at least one housing accommodating one end of the at least one wall, the housing comprising two opposite lateral housing surfaces and a bottom bringing together both lateral housing surfaces. According to the invention, the basket comprises a tightening means configured to press at least one of the lateral wall surfaces against at least one of the lateral housing surfaces. The lateral contact of the at least one internal partition wall with at least one of the lateral surfaces of its housing provides an increase in the thermal contact area between the internal partition and the peripheral partition to which the internal partition is attached. As a result, there is a better heat removal off the basket and thus a decrease in the temperatures within the structural elements making it up. The mechanical strength of the basket is thus promoted by this improved heat removal. When the wall edge is also in thermal and mechanical contact with the housing bottom, heat removal off the basket is further increased. The invention can optionally include one or more of the following characteristics combined to each other or not. Depending on the type of radioactive material, the internal partition can comprise two parallel walls separated by a spacing, each of the walls having a lateral external surface and a lateral internal surface, at least one of the lateral internal/external surfaces being configured to be pressed against one of the lateral housing surfaces by the tightening means. When the internal partition end comprises two walls accommodated in two distinct separated housings, it is preferable that each of the lateral wall surfaces is in thermal and mechanical contact with one of the opposite lateral housing surfaces. Advantageously, the tightening means generates a pinching strain of the internal partition wall end between said lateral housing surface against which the wall is pressed, called a first pinching surface, and a second pinching surface facing the first pinching surface. The heat exchanges between the internal partition and the peripheral partition are increased when the internal partition is pinched. According to a particular embodiment, the end of the at least one wall is pinched in the housing, by being in mechanical contact with both lateral housing surfaces. According to an advantageous embodiment, the peripheral partition comprises an internal surface oriented inwardly of the basket and participating in delimiting the cells, the housing opening to the internal surface, such that at least one of the lateral housing surfaces is orthogonal to the internal surface. Preferably, a value ratio of a thickness of at least one wall to a length of wall lateral surface contact surface with one of the lateral housing surfaces, in a transverse cross-sectional plane of the basket, is between 0.2 and 1. A ratio equal to 1 remains advantageous when both lateral wall surfaces are in contact with the lateral housing surfaces. According to another advantageous embodiment, the internal partition is in mechanical contact with the peripheral partition on at least ¾ the height of the peripheral partition, preferably over substantially the entire height of the basket. According to another particular embodiment, the basket comprises a plurality of internal partitions formed by stacked interlaced structural elements. The tightening means preferably comprises a plurality of tightening elements spaced to each other along the height of the basket. The tightening elements are preferably configured each to exert a tightening force the value of which is independent of that of the other tightening elements. The plurality of tightening elements spaced along the height facilitates in particular a mechanical and thermal contact of the peripheral partition with an internal partition made as a single piece which extends substantially on the entire height of the basket. On the other hand, a plurality of tightening elements spaced from each other along the height of the basket is also interesting, when the internal partitions are formed by stacked interlaced structural elements. Indeed, the tightening elements thereby make it possible to compensate all the more easily for the possible differential expansions and possible manufacturing and assembly tolerances of the stacked interlaced structural elements. Advantageously, the tightening means is configured to be tightened/untightened from outside the basket. Basket assembly/disassembly operations are in particular facilitated. According to one particular embodiment, the tightening means comprises a screw and a nut configured to cooperate with the screw. Thereby, the tightening means is of a simple structure and can also be used to attach the internal partition to the peripheral partition. According to an advantageous embodiment, the tightening means comprises at least one jaw, the jaw being separation biased by the nut for pressing at least one of the lateral wall surfaces against at least one of the lateral housing surfaces. The tightening means preferably comprises at least one first tilted surface, the peripheral partition or the wall end comprising at least one second tilted surface complementary to the first tilted surface and configured to be supported on the first tilted surface. The increase in the tightening area facilitates lateral pressing of the wall in its housing. According to an advantageous embodiment, the tightening means comprises at least one elastic tightening element located in the spacing defined above, the elastic tightening element tending to press at least one of the lateral external surfaces against one of the lateral housing surfaces. The invention also relates to a pack for transporting and/or storing radioactive materials such as nuclear fuel assemblies, the pack comprising a packaging and a lid closing the packaging, the packaging housing a basket as defined above. The invention also relates to a method for assembling a basket as defined above, comprising, after a prior step of accommodating the wall end in its housing, a step of pressing at least one of the lateral wall surfaces against one of the lateral housing surfaces, such that the wall is located between the tightening means and the lateral housing surface against which the lateral wall surface is pressed. Identical, similar or equivalent parts of the different figures bear the same reference numerals so as to facilitate switching from one figure to the other. FIG. 1 represents a storage device 1 for irradiated nuclear fuel assemblies in a packaging (not represented) for transporting and/or storing fuel assemblies. The storage device 1 is called a basket in the following of the description. The basket 1 includes a head plate 3 and a bottom (not represented). In reference to FIGS. 1 and 2, the basket 1 comprises a plurality of adjacent cells 2, each of the latter extending along a longitudinal axis 4 of the basket. The cells 2 are of a square cross-section. They are each able to accommodate a square cross-section fuel assembly. However, the fuel assemblies and/or the cells 2 can also assume other shapes, such as a hexagonal shape. The cells 2 are provided so as to be juxtaposed to each other. They are made through a plurality of partitions 6, 8 and 10. The partitions 6, 8 and 10 are distributed into three distinct partition sets, respectively defined by a first set of internal partitions 6, a second set of internal partitions 8, as well as a set of peripheral partitions 10 radially located at the periphery of the internal partitions 6 and 8 with respect to the longitudinal axis 4 of the basket. The partitions 6, 8, 10 are common to several cells 2. In this regard, it is noted that the internal partitions 6, 8 generally participate in delimiting several cells 2 located on either side of the internal partition 6, 8 in question. The partitions 6, 8 comprise one or more walls 80, 82, 84 intended to separate the cells 2. These walls 80, 82, 84 have basically the shape of a plate. The internal walls 6, 8 are assembled to each other so as to be disposed in parallel and perpendicular to each other, in order to form square cross-section cells 2. The first internal partitions 6 are disposed in parallel to each other, in the same way as the second internal partitions 8 between them. Moreover, the first internal partitions 6 are assembled so as to be substantially perpendicular to the second internal walls 8. The peripheral partitions 10 are attached to the internal partitions 6, 8, so as to close the cells 2 at the periphery of the basket 1. In other words, the internal partitions 6, 8 make up at least three of the four planar lateral faces delimiting a cell 2. The internal surfaces 17 of the peripheral partitions 10 each form possibly one of the four planar lateral faces delimiting a cell 2. These internal surfaces 17 are oriented inwardly of the basket 1, as opposed to the external surfaces 19 of the peripheral partitions 10 which are located at the periphery of the basket 1 and which delimit the outside of the basket 1. The external surfaces 19 are preferably arcs of circles, so as to facilitate inserting/removing the basket 1 into/from the circular cavity of a packaging (not represented). In reference more specifically to the first embodiment, the internal partitions 6 and 8 are made as a single piece, each so as to extend on the entire length of the cell(s) 2 they define. In a similar way, the peripheral partitions 10 are made as a single piece, each so as to extend on the entire length of the cells 2 they define. In reference specifically to FIG. 2, the cells 2 are made through a plurality of structural assemblies 6a, 8a with notches and stacked along a stacking direction 11 parallel to the longitudinal axis 4 of the basket. The stacking direction 11 extends from the bottom of the storage device to a basket head plate. The stacking direction 11 is also called the basket height. The stack of parallel structural assemblies 6a, along a first direction 13, forms a first internal partition 6. The stack of parallel structural assemblies 8a, along a second direction 15, forms a second internal partition 8. The directions 11, 13 and 15 are orthogonal two by two. The notch structural assemblies 6a, 8a are thus perpendicularly interlaced. The structural assemblies 6a, 8a extend between at least two opposite peripheral partitions 10 to which they are attached. In the second embodiment, the peripheral partitions 10 are made as a single piece. Alternatively, it is quite contemplatable to provide that each peripheral partition 10 is made through a plurality of stacked structural assemblies. FIGS. 3 and 4 represent tightening of one of the internal partitions 6, 8 in a housing of a peripheral partition 10 of a basket 1, according to the first or the second embodiment. The internal partition 6, 8 comprises two parallel walls 82, 84 separated by a spacing. The walls 82, 84 are preferably identical. Each of the walls 82, 84 has a lateral external surface 81 and a lateral internal surface 85, such that the lateral external surface 81 and the lateral internal surface 85 are on either side of the wall 82, 84. The spacing e1 is held constant, for example by means of spacers (not represented) supported on the lateral internal surfaces 85, inside the spacing e1. The end of the internal partition 6, 8 is housed in a recess 101 which is made in the peripheral partition 10 and which comprises two housings 100 to house the partitions 82, 84. The end of each of the parallel walls 82, 84 of the internal partition 6, 8 is accommodated in one of the housings 100 of the peripheral partition 10. These housings 100 each comprise two opposite parallel lateral surfaces 102, 106. The lateral housing surfaces 102, 106 are gathered by a bottom 104. The housings 100 lead to an internal surface 17 of the peripheral partition 10, such that the lateral housing surfaces 102, 106 are orthogonal to the internal surface 17. The internal surface 17 and the internal partition 6, 8 delimit two contiguous cells 2, on either side of the internal partition 6, 8. The lateral external surface 81 of each of the walls 82, 84 is pressed against one of the lateral housing surfaces 102, 106 by a tightening means 9. The lateral external surfaces 81 have a shape complementary to the lateral housing surfaces 102, 106, so as to promote thermal contact of the internal partitions 6, 8 with the peripheral partitions 10. In the embodiment of FIG. 3, the lateral housing surfaces 102, 106 of an end of internal partition 6, 8 are parallel two by two. In reference more specifically to FIG. 4, the tightening means 9 comprises a plurality of tightening elements 90 spaced apart from each other along the height of the basket 1. Each tightening means 90 comprises a screw 92 and a nut 96 cooperating with the screw 92. The screws are housed in holes 91 of the peripheral partition 10, passing through the external surface 19. In this way, the tightening elements 90 can be screwed/unscrewed from outside the basket 1, by acting on the heads of screw 92. The nut 96 is located between two jaws 94, such that the jaws 94 are separation biased by the nut 96 and the screw 92 to press the lateral wall surfaces 81 against the lateral housing surfaces 102. More precisely, the nut 96 has two first tilted surfaces 97 and the peripheral wall 10 comprises, at each jaw 94, two second tilted surfaces 95 with a complementary shape to the first tilted surfaces 97. The first tilted and second tilted surfaces 95, 97 are intended to be supported on each other, so as to maximise the mechanical contact area between them and promote lateral tightening of the walls 82, 84 of internal partition 6, 8 in their housing 100. The tightening elements 90 can each exert a lateral tightening force F1 the value of which is independent of that of the other tightening elements 90, as a function of the tension exerted on the screw 92 and the nut 96. The tightening elements 90 thereby make it possible to compensate all the more readily for the possible differential expansions and possible manufacturing and assembly tolerances of the internal partitions 6, 8 and/or the peripheral partitions 10. To that end, independent tightening elements 90 spaced apart from each other along of the height of the basket 1 make it possible in particular to have a mechanical and thermal contact of the internal partition 6, 8 and the peripheral partition 10 over substantially the entire height of the basket 1, that is for example at least ¾ of the height of the peripheral partition 10. In the embodiment of FIGS. 3 and 4, the jaws 94 are formed as a single piece, in particular by extrusion, with the peripheral partition 10. The internal partition walls 82, 84 are thus in thermal contact with the peripheral wall 10, at least at both lateral opposite surfaces 102, 106 of the housing. The walls 82, 84 are thereby pinched in their housing 100. The first lateral surface 102 of the housing 100 then forms a first pinching surface of each wall 82, 84 and the second lateral surface 106 of the housing 100 forms a second pinching surface of this wall 82, 84. The internal partition 6, 8 and the tightening elements 90 are substantially symmetrical by a planar symmetry of a plane parallel to the walls 82, 84 and passing through the axis 93. In addition, the first tilted surfaces 97 are tilted to the external surface 19. The walls 82, 84 are thus each in contact with the bottom 104 of their respective housing 100. The tightening elements 90 of the embodiment of FIGS. 3 and 4 are the only means for attaching the internal partition 6, 8 to the peripheral partition 10. Alternatively, each jaw 94 could be formed as a single piece with one of the walls 82, 84 or attached to one of the walls 82, 84, so as to project from the rest of the wall lateral internal surface 85. These alternative embodiments have possibly the advantage of allowing a more ready machining of the jaws 94. On the other hand, the internal partition 6, 8 attached to the peripheral wall 10 and/or the tightening elements 90 could also have no planar symmetry. Further alternatively, the first tilted surfaces 97 could of course be of opposite tilts, that is move closer to each other towards the internal surface 17. By way of alternative, there could be a clearance between the edge of each of the walls 82, 84 and the housing bottom 104, enabling in particular possible differential expansions of the basket 1 and/or possible impacts undergone by the basket 1 along the direction 93 to be compensated for. However, the only thermal contact of the lateral external surfaces 81 with the housing surfaces 102 and possibly the thermal contact of the lateral internal surfaces 85 with the lateral surfaces 106 of the housing is generally sufficient to allow satisfactory thermal exchanges of the internal partitions 6, 8 with the peripheral partitions 10. To that end, it is generally sufficient that the value ratio of the thickness 107 of each of the walls 82, 84 to the length of the surface 105 of contact of its lateral external surface 81 with one of the lateral housing surfaces 102, 106, in the transverse cross-sectional plane of the basket 1 represented in FIG. 3 or in FIG. 8 and for example the transverse plane P of FIG. 2, is between 0.2 and 1. By way of further alternative, the basket 1 can comprise means for attaching (not represented) the internal partitions 6, 8 to the peripheral partitions 10, wherein the tightening means 9 is only used to press the wall(s) 80, 82, 84 against at least one of the lateral housing surfaces 102, 106, once the internal partition 6, 8 is at least partially attached to the peripheral partition 10. FIG. 5 represents an alternative embodiment of FIGS. 3 and 4, wherein the internal partition 6, 8 comprises a single wall 80. This single wall 80 comprises two opposite lateral external surfaces 81 and an edge 83 bringing together both these lateral surfaces. The recess 101 housing the end of the internal partition 6, 8 comprises a single housing 100 housing the end of the single wall 80. The edge 83 is located remote from the bottom 104 of the housing 100. The lateral external surfaces 81 of the internal partition 6, 8 are pressed against the lateral housing surfaces 102, 106 by a tightening element 9 comprising a single jaw 94. The jaw 94 is for example formed as a single piece by extrusion with the peripheral partition 10. This jaw 94 is tightened sideways against the wall 80 by a screw 92 cooperating with a nut 96 accommodated in a nut housing 99. The nut housing 99 leads to the internal surface 17, so as to be locally orthogonal to the internal surface 17. The alternative embodiment of FIG. 6 is distinguished from that of FIGS. 3 and 4 in that it comprises two tightening elements 90 in a transverse cross-sectional plane of the basket 1. On the other hand, the tightening elements 90 are accommodated at least partially in the housings 100, and the tightening elements 90 are free of jaws 94. The recess 101 accommodating the end of the internal partition 6, 8 comprises two housings 100 separated from each other by an intermediate wall 108 of the peripheral partition 10. Each of the walls 82, 84 is pinched between a first pinching surface formed by a lateral housing wall 106 and a second pinching surface 109 formed by the surface of contact of the nut 96 with the wall 82, 84 it tightens. The tightening elements 90 each comprise a screw 92 and a nut cooperating with the screw 92. The screw holes 91 lead to the housings 100 at the housing bottoms 104. The nuts 96 are located in the housings 100, by being supported by the external surface 81 of the wall 82, 84 along the second pinching surface 109. The nuts 96 carry the first tilted surfaces 97 and the second tilted surfaces 95 form the first lateral housing surfaces 102. The second tilted surfaces 95 are directly cut in the peripheral partition 10, so as to lead to the internal surface 17 forming an angle different from 90° with the internal surface 17. In a similar way to the embodiment of FIGS. 3 and 4, the screws 92 are tightened with a tightening force F2 oriented in the longitudinal direction of the internal partition 6, 8, that is in the first direction 13 or the second direction 15. The nuts 96 then exert directly a lateral tightening force F1 on the lateral external surfaces 81 of the wall 82, 84, so as to press the lateral internal surfaces 85 of the wall 82, 84 against the second lateral housing surfaces 106. The spacing e1 between the walls 82, 84 of the internal partitions is held constant by a transverse air gap 86 supported on the lateral internal surfaces 85 of the wall 82, 84 and by the portion of peripheral partition 10 located between the two contiguous housings 100. The alternative embodiment of FIG. 7 differs from the embodiment of FIG. 5 in that the tightening element 90 is at least partially in the housing 100, and in that the tightening element 90 comprises neither nut nor jaws. The recess 101 comprises a single housing 100 which houses partially the pusher 96, the wall 80 being pinched between a first pinching surface formed by the first lateral housing surface 102 and a second pinching surface 109 which is the surface of contact of the pusher 96 with the wall 80. The wall 80 comprises two opposite lateral external surfaces 81 gathered by an edge 83. The tightening element 90 comprises a screw 92 the head of which is accessible from outside the basket 1, and a pusher 96 intended to press one of the lateral external surfaces 81 against the first lateral housing surface 102. Because of the pusher 96, the other lateral external surface 81 of the wall is not in mechanical and thermal contact with the second lateral housing surface 106. The screw 92 is supported on the pusher 96 which is located at least partially in an indentation 99 of the peripheral partition 10, leading into the housing 100. The wall edge 83 is located remote from the housing bottom 104. FIG. 8 represents another alternative of the invention which is discriminated from the embodiment of FIGS. 3 and 4 in that the tightening elements 90 do not include a screw, a nut or a jaw. On the other hand, the tightening elements 90 are located remote from the peripheral partition 10. Finally, both walls 82, 84 of the internal partition 6, 8 are accommodated in a single housing 100. This single housing 100 forms the recess 101, both lateral external surfaces 81 of the walls 82, 84 being respectively pressed against the first lateral housing surface 102 and the second lateral housing surface 106. The end of the internal wall 6, 8 and the tightening element 90 are symmetric by planar symmetry passing through the axis 93. The tightening element 90 represented in this figure comprises an elastic tightening element 98 and a stress element 920 of the elastic tightening element 98, the stress element 920 also enabling the tightening element 98 to be held between the lateral internal surfaces 85. The elastic tightening element 98 takes for example the shape of a set of spring steel bent elastic washers. The set of washers is located in the spacing e1 and is supported by the lateral internal surfaces 81 it separation biases the one from each other. The lateral external surfaces 81 of the wall 82, 84 are thereby pressed against the lateral housing surfaces 102, 106, with a lateral force F1. The stress element 920 is intended to compress the elastic tightening element 98, so as to enable it to be inserted between the lateral internal surfaces 81 of the wall. On the other hand, the stress element 920 can also be used to bias the elastic tightening element 98 in separation, such that the elastic tightening element 98 moves the lateral internal surfaces 85 sufficiently away from each other to press the lateral external surfaces 81 against the lateral housing surfaces 102, 106. The basket 1 is assembled according to the method described below. The internal partitions 6, 8 are attached to each other beforehand so as to form the centre cells 2 of the basket. In the following, the peripheral partitions 10 are assembled to the internal partitions 6, 8, so as to close the peripheral cells 2 of the basket 1 sideways. The ends of the internal partitions 6, 8 are each housed in their respective recess 101, by pressing at least one of the lateral wall surfaces 81, 85 of the internal partition against at least one of the housing surfaces 102, 106 of the recess. A bottom and a head plate 3 contribute in holding all of the partitions of the basket 1, on either side of the height 11 of the basket, the head plate also enabling the basket to be handled. The method of assembling the internal partition 6, 8 with the peripheral partition 10 is now described in more detail in reference to FIGS. 3 to 8. Both opposite ends of the walls 80, 82, 84 of the internal partitions 6, 8 are first accommodated in their respective housings 100. The tightening means 9 located at one of the ends then presses at least one of the lateral surfaces 81, 85 of the wall 80, 82, 84 against at least one of the lateral housing surfaces 102, 106. The wall 80, 82, 84 is thereby located between this lateral housing surface 102, 106 and the tightening means 9. When the internal partition 6, 8 comprises two walls 82, 84, both these walls 82, 84 are first preferably accommodated both in their housing 100, before the tightening means 9 presses them against at least one of the lateral housing surfaces 102, 106. In addition, the internal partitions 6, 8 can be at least partially attached to the peripheral partitions 10, before the tightening means 9 ensures pressing of at least one of the lateral surfaces 81, 85 of at least one wall 80, 82, 84 against the corresponding lateral housing surface 102, 106. The walls 80, 82, 84 can possibly slide along the elongation direction of the internal partitions 6, 8, that is along the first direction 13 or along the second direction 15, before they are tightened against at least one of the lateral housing surfaces 102, 106 by the tightening means 9. This sliding enables for example possible differential expansions of the basket 1 to be compensated for and/or impacts undergone by the basket 1 to be accommodated. Of course, various modifications can be made by those skilled in the art to the invention just described without departing from the scope of the disclosure of the invention. |
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description | This invention relates to an improvement on a fuel compact used as a nuclear fuel in a nuclear reactor such as a high-temperature gas cooled reactor and formed by dispersing in a graphite matrix, coated fuel particles formed by coating minute balls (fuel kernels) of an oxide or a carbide of nuclear fuel material such as uranium or thorium with a thermal decomposition carbon layer, a silicon carbide layer, etc. and integrally molding them and a method of manufacturing such a fuel compact. A high-temperature gas cooled reactor is a nuclear reactor which can take out a gas such as a helium gas with peculiar high safety and very high outlet temperature because a reactor core structure containing a nuclear fuel is formed from graphite having large calorific capacity and good high temperature soundness and also a gas such as a helium gas which never causes a chemical reaction under high temperature is used as a coolant gas. Thus, the high temperature heat of about 900° C. from the high-temperature gas cooled reactor can be used in broad fields such as a hydrogen manufacture and a chemical plant as well as an electric power generation. (Coated Fuel Particles) In general, coated fuel particles of about 500 micrometer to 1000 micrometer diameter are used as the nuclear fuel for this high-temperature gas cooled reactor. The coated fuel particles are formed by coating with total four layers of first to fourth layers, the fuel kernels of about 350 micrometer to 650 micrometer diameter obtained by sintering a uranium dioxide, a thorium, etc. to the form of ceramics. Specifically, the coated layers are the following four layers. That is, the innermost first layer generally called a buffer layer is a layer which is formed of low-density thermal decomposition carbon (PyC) of a density of about 1 g/cm3 and serves to store a gas of a gas-like fission product (FP) and also to absorb swelling of the nuclear fuel. In general, the second layer applied onto this first layer is an inner thermal decomposition carbon (PyC) layer formed of high-density thermal decomposition carbon of a density of about 1.8 g/cm3 and serves to hold a gas-like fission product (FP) as a barrier of diffusion of the gas-like fission product (FP). The third layer called a silicon carbide (SiC) layer is formed of silicon carbide of a density of about 3.2 g/cm3 and serves to hold a solid-like fission product as a barrier of diffusion of the solid-like fission product and also serves as a main reinforcing member for the whole coated fuel particles. The outermost thermal decomposition carbon layer as the fourth layer is formed of high-density thermal decomposition carbon of a density of about 1.8 g/cm3 in the same manner as the second layer and serves to hold the strength of the whole coated fuel particles under irradiation by generating compression stress on the third silicon carbide layer by irradiation contraction and also to hold the gas-like fission product (FP). Such coated fuel particles are generally manufactured through the following processes. First, concretely explaining the production of the fuel kernel, a dropping undiluted solution is produced by adding and agitating pure water and a thickening agent to a uranyl nitrate undiluted solution formed by melting uranium oxide powder in a nitric acid. In this case, the thickening agent is added so that the liquid drop of the dropped uranyl nitrate undiluted solution becomes true ball-like form by its own surface tension during its dropping. A resin such as a polyvinyl alcohol resin which has a property of being solidified under alkali conditions, polyethylene glycols and metolose for example may be used as this thickening agent. Subsequently, after cooling the dropping undiluted solution prepared in such a way to a predetermined temperature and adjusting its viscosity, it is dropped into the ammonia solution by vibrating a dropping nozzle of thin diameter. In this case, the deformation of the liquid drop is prevented when it lands on the ammonia solution surface by blowing an ammonia gas upon the liquid drop in space where it drops until it lands there so as to gel the surface of the liquid drop. The undiluted solution dropped into the ammonia solution gets particles of heavy uranium acid ammonium by the full reaction of the uranyl nitrate with the ammonia in the ammonia solution. The particles of heavy uranium acid ammonium are roasted in the atmosphere to form uranium trioxide particles, which are further reduced and sintered to obtain the fuel kernels formed of high-density ceramics-like uranium dioxide. Since the diameter and the deviation from the spherical form of the thus obtained fuel kernels very substantially effect on the manufacture conditions in the subsequent coating process, the fuel kernels are fed to the coating process after their diameter is sorted by a sieve and their deviation from the spherical form is also sorted. Thereafter, in the coating process of the fuel kernels, the fuel kernels are loaded in a fluid bed and sequentially coated with the first through fourth layers by thermally decomposing the coating gases. In this case, the first low-density carbon layer is applied onto the fuel kernels by thermally decomposing an acetylene (C2H2) at about 1400° C. The second and fourth high-density thermal decomposition carbon layers are applied by thermally decomposing a propylene (C3H6) at about 1400° C. The third silicon carbide layer is formed by thermally decomposing a methyl-chorolosilane (CH3SiCl3) at about 1600° C. The thus manufactured coated fuel particles get over-coated particles by further applying graphite matrix material comprising graphite powder, a caking agent, etc. on the surface of the coated fuel particles. (Fuel Compact) In using the thus over-coated coated fuel particle as a fuel compact, after dispersing the coated fuel particles in a graphite matrix material, they are molded by press or by die into a solid type or a hollow type cylindrical body and then sintered to produce the fuel compact 10 of predetermined form shown in FIG. 7(A) (see JP 2000-284084A, for example). This fuel compact 10 is formed by integrally binding a plural of coated fuel particles 12 by softening a phenol resin contained in the graphite matrix material by heating dies or punches when the coated fuel particles 12 are compressed as shown in FIG. 8. (Loaded into a Reactor Core) The thus formed fuel compact 10 has two kinds of solid type cylindrical body and hollow type cylindrical body and, in either case, 1) a predetermined amount of fuel compacts are contained in a fuel sleeve (cylinder) of graphite with its top and bottom closed by plugs so as to form a fuel rod and the fuel rods are loaded directly into a plural of insertion openings of a hexagon pillar type graphite block of the high-temperature gas cooled reactor, or 2) the fuel compacts are loaded directly into the insertion openings of the hexagon pillar type graphite block. Finally, the hexagon pillar type graphite blocks are loaded as the fuel into the reactor core while they are superposed one step on another step in a honey cam arrangement. (Breakage of Fuel Compact) In this case, when the treatment of the fuel compacts 10, that is when they are loaded into the fuel sleeve or the graphite block is carried out, the fuel compact 10 mechanically contacts with the inner surface of the fuel sleeve or the graphite block to thereby apply an impact onto the fuel compact 10 whereby the corner 10b of the fuel compact 10 is possibly broken (see FIG. 7). In this manner, as a breakage arises in the fuel compact 10, a state of high temperature occurs within the high-temperature gas cooled reactor and therefore, when the fuel compact 10 is thermally expanded, the broken pieces thereof are held between the fuel compact 10 and the inner face of the fuel sleeve or the graphite block, which causes a high stress to occur in the place where the broken pieces are held, whereby the fuel compact 10, the fuel sleeve and the graphite block are damaged. In addition thereto, since a temperature difference arises due to a difference of cooling efficiency between the central part of the high-temperature cooling gas cooled reactor and the peripheral part thereof when the fuel compact is used in the reactor and therefore the central part of the high-temperature gas cooled reactor has a temperature higher than the peripheral part thereof, the central part of the high-temperature gas cooled reactor has thermal expansion larger than the peripheral part thereof, with the result that the fuel compact 10 tends to be deformed into a drum-like shape. The thus drum-shaped fuel compact 10 causes its corner 10b to mechanically contact with the inner surface of the fuel sleeve or the graphite block, which causes the fuel compact 10 to be possibly cracked. Thus, it is required to prevent such breakage of the fuel compact 10, but, in this case, it is also required to take a consideration of not damaging the coated fuel particles 12 by the stress when it is pressed. Accordingly, it is a principal object of the invention to provide a nuclear fuel compact adapted to prevent breakage of coated fuel particles and also to easily prevent breakage of the fuel compact, a fuel sleeve and a graphite block in an inexpensive manner. It is another object of the invention to provide a method for being able to easily and inexpensively manufacture a nuclear fuel compact adapted to prevent breakage of coated fuel particles and also to prevent breakage of the fuel compact, a fuel sleeve and a graphite block. In accordance with a first feature of the invention, there is provided a fuel compact formed by integrally molding coated fuel particles characterized by comprising a chamfer formed in its corner and said chamfer having plane or curved surface. In the fuel compact according to the first feature of the invention, the fuel compact may have the cylindrical form and the chamfer may be formed in the corner of the cylindrical fuel compact. Furthermore, the chamfer may be formed in each of the corners of the upper and lower ends of the cylindrical fuel compact. Moreover, in the fuel compact according to the first feature of the invention, in the case where the chamfer is in plane form, it may be of two or more stepped planes having different angles relative to an axial direction of the cylindrical fuel compact. Furthermore, in the case where the chamfer is in plane form, it is desirable that a thickness of the chamfer may be 0.10 mm or more, that the chamfering angle of the chamfer may fall within a range of 30° to 60° and that the upper limit of the thickness of the chamfer may have a value corresponding to the thickness in the state where the surface of the chamfer contacts with the periphery of the coated fuel particles. In addition thereto, in the case where the chamfering angle of the chamfers is other than 45°, the upper limit of the thickness of the chamfer preferably corresponds to a value corresponding to a larger value among two specified thicknesses of the chamfer in the state where the surface of the chamfer contacts with the periphery of the coated fuel particles. In the fuel compact according to the first feature of the invention, in the case where the chamfer is of curved shape, the upper limit of the thickness of the curved chamfer is set at the value where the curved chamfer contacts the outer peripheral face of the coated fuel particles. In accordance with the second feature of the invention, there is provided a method of manufacturing a fuel compact by integrally molding coated fuel particles by a die, characterized by forming a plane or curved taper in the corner of the die to thereby form plane or curved chamfer in the corner of the fuel compact. The plane taper may be of a single or multi-stepped plane form. In the method of manufacturing the fuel compact according to the second feature of the invention, the taper may be formed in the corner of the die by attaching a ring-like taper member having the taper surface onto the die. According to the first feature of the invention, since the chamfer is formed in the corner of the cylindrical fuel compact, the stress applied to the fuel compact decreases even though the fuel compact mechanically contacts with the surface of the fuel sleeve or the graphite block when it is handled or when it is thermally expanded and therefore the breakage of the fuel compact or the cracks in the fuel compact can be prevented, which causes the breakage of the fuel sleeve or the graphite block to be prevented. Especially, as the chamfer is of two stepped plane shape or curved shape, the thickness and the surface area of the chamfer can be larger and therefore the breakage of the fuel compact and the cracks in the fuel compact can be more effectively prevented in a preferable manner. As the thickness and the chamfering angle of the plane shaped chamfer may be adjusted appropriately or as the upper limit of the thickness of the curved chamfer is set at the value where the curved chamfer contacts the outer peripheral face of the coated fuel particles, the chamfer may have the shape corresponding to the shape of the coated fuel particles. This prevents stress from being unnaturally applied to the coated fuel particles when they are pressed even though the chamfer is formed and therefore the coated fuel particles are never broken. Thus, the strength of the fuel compact against the mechanical impact can be improved while the breakage of the coated fuel particles is prevented. According to the second feature of the invention, since the taper of plane form or curved form is formed at the corner of the mold to thereby form the chamfers at the corner of the cylindrical fuel compact, the breakage of the fuel compact which can be effectively prevented can be more easily manufactured. In this case, as the taper in the corner of the die may be formed by the ring-like taper member having the taper surface, the existing equipment can be utilized only by mounting the taper member onto the inside of the die without adding any large change, which allows the easier production of the fuel compact which is able to effectively prevent its breakage. Describing some forms where the invention is embodied with reference to accompanying drawings, FIG. 1 illustrates a nuclear fuel compact according to a first mode of embodiment of the invention and this fuel compact is formed by integrally molding a plural of over-coated particles 12 shown in FIG. 1(B) in an enlarged manner while thermally compressing them with a die shown in FIG. 2 either by press or by molding. Concretely explaining this, the fuel compact 10 may be manufactured by dispersing a predetermined amount of the coated fuel particles 12 into a graphite matrix comprising a graphite powder, a caking agent, etc., as to produce the over-coated particles 12, loading them in a metal die 1, as shown in FIG. 2 and then by compressing them by upper and lower metal punches 2A and 2B within the die 1. When the fuel compact 10 should be produced, the over-coated particles 12 may be heated by heating the die 1 and the punches 2 so that the phenol resin contained in the graphite matrix material within the over-coat layer 14 is softened whereby the graphite powder serves as a binder between the coated fuel particles 12, which causes the cylindrical fuel compact 10 shown in FIG. 1 to be formed. In FIG. 2, a reference numeral 3 designates a core rod for forming a hollow part of the cylindrical fuel compact 10, which may be provided if required. The die 1, the punches 2 and the core rod 3 may be formed of alloy tool steels, for example. The over-coated particles 12, before compressed, is provided with an overcoat layer 14 which is formed by coating the graphite matrix material of the graphite powder, the caking agent, etc. on the surface of the coated fuel particles 12 as shown in FIG. 1(B), which is already described. The overcoat layer 14 is formed, 1) in order to prevent the damage of the coated fuel particles 12A due to the pressure applied on press molding and 2) in order to prevent the thermal and mechanical damage of the coated fuel particles 12A on sintering by uniformly dispersing the coated fuel particles in the fuel compact 10 while the overcoat layer 14 is arranged between the adjacent coated fuel particles 12A. To this end, in general, the fuel compact 10 is formed by uniformly arranging the diameter of the over-coated particles 12A so that the coated fuel particles 12A may be uniformly dispersed. Although the overcoat layer 14 may be formed by dispersing the coated fuel particles 12A in the graphite matrix material comprising the graphite powder, the caking agent, etc., the thickness of the overcoat layer 14 can be adjusted to the proper value by setting the proper mesh size of a screen for sifting therethrough the coated fuel particles 12A having the overcoat layer 14 formed in the middle and last steps of the overcoat process and adjusting the time for the overcoat process. The fuel compact 10 of the invention has a plane chamfer 16 formed in the corner 10a of the cylindrical fuel compact 10, as shown in FIG. 1. As shown in FIG. 1(A), the chamfer 16 may be desirably formed over all the circumference of each of the upper and lower corners 10a of the cylindrical fuel compact 10. The chamfer 16 serves to reduce the stress applied to the fuel compact 10 because the mechanical impact applied to the corners 10a of the fuel compact 10 is distributed in comparison with the case where the load is locally applied to the edges 10b of the prior art fuel compact 10 shown in FIG. 7. Thus, the damage of the fuel compact 10 can be prevented and therefore the damage of the fuel sleeve and the graphite block, both of which are not shown, due to the removed pieces of the fuel compact 10 can be prevented. The chamfer 16 is fundamentally formed by mechanically cutting the upper and lower corners of the fuel compact 10 molded as shown in FIG. 7. In this case, the cutting process should be performed so that the coat layer of the coated fuel particles 12A is not damaged and therefore the range of thickness of the chamfer 16 is considerably important therefor. Instead of this mechanical working, the chamfer 16 may be formed by compression-processing the over-coated particles 12A by tapers 2a formed on the corners of the metal die such as the upper and lower punches 2A and 2B as shown in FIG. 2. The tapers 2a may be formed by attaching ring-like plane taper members 4 onto the upper and lower punches 2A and 2B, as shown in FIG. 2. As the fuel compact 10 is manufactured according to the method as shown in FIG. 2, the method of manufacturing the fuel compact according to the invention can be carried out just by attaching the taper members 4 onto the conventionally used punches 2A and 2B as shown in FIG. 8 without any large change applied to the punches 2A and 2B. In this manner, since the existing manufacturing equipment can be effectively used, the fuel compact 10 of the invention having the chamfers 16 can be manufactured easily and inexpensively. The taper members 4 may be attached onto the corners of the upper and lower punches 2A and 2B by setting the diameter of the taper members 4 to a value equal to the diameter of the upper and lower punches 2A and 2B. The thicknesses t and t′ (refer to FIG. 1 (B)) of the chamfer 16 may be desirably at least 0.10 mm or more. The damage of the fuel compact 10 can be fully prevented because the area of chamfer face of the chamfer 16 may get larger as the thicknesses t and t′ of the chamfer 16 get larger whereby the mechanical shock applied to the fuel compact 10 can be distributed so as to fully reduces the stress. In this invention, what is meant by the thickness t and t′ of the chamfer 16 is a distance from a position where one end face (the upper (or lower) face 10A or the side face 10B) of the fuel compact 10 is located to a position where the chamfer 16 intersects the other end face (the side face 10B or the upper (or lower) face 10A) in the chamfers 16 formed over the upper (or lower) face 10A and the side face 10B in the fuel compact 10 formed over the upper (or lower) face 10A and the side face 10B intersecting each other perpendicularly as shown in FIG. 1(B). In this manner, the thicknesses t and t′ of the chamfer 16 may be desirably set up to a value as large as possible in order to prevent the damage of the fuel compact 10. However, if the thicknesses t and t′ of the chamfer 16 would be set up to an excessively larger value, in case where the chamfer 16 is formed by mechanical working, the coat layer of the coated fuel particles 12A might be cut so as to adversely affect the irradiation action of the fuel compact and in case where the chamfer 16 is formed by the method of FIG. 2, the strength of the coated fuel particles 12A is adversely affected. Thus, the thickness should be preferably set within the range of value in which the fuel compact is not subject to such adverse affects. Also, if the chamfering angles θ and θ′ (see FIG. 1(B): the inclination angle of the chamfer 16 relative to the end face of the fuel compact 10: θ+θ′=90°) is set to more than the required value (if the other chamfering angle is set up to a smaller value), then the stress reduction function of the chamfers 16 will be reduced. To this end, the chamfering angles θ and θ′ (see FIG. 1(B) of the chamfer 16 may be set at a value which falls within a range of 30° to 60° and the upper limit of the thicknesses t and t′ of the chamfer 16 may desirably have a value corresponding to the thickness of the chamfer 16 when the chamfer 16 is deeply formed until the surface of the chamfer contacts with the peripheral face of the coated fuel particles 12 (see FIG. 1(C)). In the above-mentioned concrete example, if the thicknesses t and t′ of the chamfer 16 exceed the aforementioned upper limit, then chamfer 16 is formed so that a part of the coat layer of the coated fuel particles 12A is cut and therefore, the load will be excessively applied to the coated fuel particles 12A on compression of the over-coated coated fuel particles 12A, which causes the coated fuel particles 12A to be damaged and causes a undesirable state when the fission products are held. Especially, in the case where the chamfer 16 is formed by mechanical cutting while the thickness thereof exceed the upper limit, the coat layer of the coated fuel particles will be undesirably cut whereby there arises an inconvenience for the function of holding the fission products. Thus, it is required that the upper limit of the thicknesses t and t′ of the chamfer 16 should correspond at least to the thickness in the case where the surface of the chamfer is set at the position where it is superposed on the peripheral face of the coated fuel particles 12A and it is required that it is set up to the value not more than the above-mentioned thickness. This can improve the strength against the mechanical shock of the manufactured fuel compact 10 together with the prevention of the breakage of the coated fuel particles 12A having the overcoat layer 14. As shown in the illustrated form of embodiment, as the chamfering angle of the chamfer 16 is set up to 45°, both of the chamfering angles θ and θ′ get 45° and the thickness t from the upper face (or lower face) 10A of the fuel compact 10 gets equal to the thickness t′ from the side face 10B. On the other hand, as shown in FIGS. 3(A) and 3(B), if the chamfering angle of the chamfer 16 is set up to the value other than 45°, there will exist the chamfering angles θ and θ′ of different value (30° and 60°, for example) and as a result, the thicknesses of the chamfer 16 will be specified at the different value. More particularly, in the form of embodiment shown in FIG. 3(A), the thickness X1 from the upper surface 10A is different from the thickness X2 from the side face 10B and also in the form of embodiment shown in FIG. 3(B), the thickness Y1 from the upper surface 10A is different from the thickness Y2 from the side face 10B. In these case, among the thicknesses X1 or X2 (Y1 or Y2) of the chamfer 16 when the chamfer face contacts with the peripheral face of the coated fuel particles 12A, the larger value thereof is set at the upper limit and the thickness is set not to exceed beyond the upper limit. Furthermore particularly, the value of the thickness X1, which is a distance from the upper (lower) face 10A in the form of embodiment shown in FIG. 3(A) and the value of the thickness Y2, which is a distance from the side face 10B in the form of embodiment shown in FIG. 3(B) are set as the upper limit of the thicknesses of the chamfer 16, respectively so as not to exceed beyond the upper limit whereby the other thicknesses (X2 and Y1) necessarily get smaller than the thicknesses (X1 and Y2), respectively. Thus, the chamfer 16 never adversely affect the coated fuel particles 12A having the overcoat layer 14 whereby the damage of the coated fuel particles 12A having the overcoat layer 14 can be prevented. A modification of the first form of embodiment of the invention is illustrated in FIGS. 4(A) and 4(B) and in this modification, the chamfer 16 has two stepped plane form of different chamfering angles in the direction of an axis of the cylindrical fuel compact 10. In the illustrated embodiment, the chamfering angle θu of the first step (upper) plane chamfer portion 16U is set at a value smaller than the chamfering angle θd of the second step (lower) chamfer portion 16D. In this modification, the overcoat layer 14 may be cut as shown in FIG. 4(B) so that the chamfer 16 contacts with the coat layer of the coated fuel particles 12A in the same manner as in FIG. 1(C). According to this modification, since the thicknesses and the surface areas of the chamfer can be made larger than those of the single plane chamfers 16 shown in FIGS. 1 and 3, the damage and the crack of the fuel compact can be more effectively prevented in a desirable manner. The fuel compact 10 according to the second form of embodiment of the invention is illustrated in FIG. 5 and in this form of embodiment, the chamfer 16 has a curved form as shown in FIG. 5(B). In this manner, with the chamfer 16 having the curved form, the thickness t and the surface area of the chamfers 16 (see FIG. 5(B)) can be set at a value larger than those of the plane chamfer 16. In the example of FIG. 5(B), the curved chamfer 16 has a radius of the curved face R1 set so as to contact the outer face of the overcoat layer 14 on the coated fuel particles 12A (in this case, the radius of the curved face is equal to the radius of the overcoat layer 14). The curved chamfer 16 may have the larger radius and thickness of the curved face set by forming the chamfer 16 in the state where the overcoat layer 14 is cut as shown in FIG. 5(C), but in order to prevent the coat layer of the coated fuel particles 12A from being cut or damaged, the upper limit of the thickness of the curved face should be set at the value where the curved face of the chamfer 16 contacts the peripheral face of the coated fuel particles 12a (the peripheral face of the coat layer) as shown in FIG. 5(C). In this case, the radius of the curved face is indicated by R2 in FIG. 5(C). Thus, as the chamfers 16 have the thickness t of the curved face getting larger, the surface area of the chamfer 16 can be enlarged and therefore, since the stress applied to the fuel compact 10 decreases even though the fuel compact 10 mechanically contacts with the inner surface of the not shown fuel sleeve or graphite block when it is handled or when it is thermally expanded and therefore the breakage of the fuel compact 10 or the crack in the fuel compact 10 can be prevented, which causes the breakage of the fuel sleeve or the graphite block to be sufficiently prevented. Since the chamfer 16 has the curved form following the configuration of the coated fuel particles 12 even though the thickness of the curved face gets large to the upper limit, the stress is unnaturally never applied to the coated fuel particles 12A due to the chamfer 16 on pressing and therefore the coated fuel particles 12A are never broken, which improves the strength against the mechanical shock of the fuel compact 10 while the breakage of the coated fuel particles 12A is prevented. Furthermore, in case where the thickness of the curved face of the chamfer 16 does not reach the upper limit, the graphite matrix material will be interposed between the chamfer face and the coated fuel particles 12A, which causes a unnatural pressure to be applied to the coated fuel particles 12A due to the compression of the graphite matrix material on pressing to thereby possibly break the coated fuel particles 12A. In this manner, as the upper limit of the thickness of the curved surface of the chamfer 16 is so set that the coat layer of the coated fuel particles 12A is neither cut nor damaged, the thickness t of the chamfers 16 can be set up to the thickness of the value sufficiently as large as close to the radius of the coated fuel particles 12A while the stress applied to the coated fuel particles 12A is fully reduced so as to prevent the breakage of the coated fuel particles 12A whereby the mechanical strength of the fuel compact can be improved and the breakage of the fuel compact, the fuel sleeve and the graphite block can be sufficiently prevented. In the same manner as in the form of embodiment of FIG. 1, the chamfer 16 of the curved form can be also formed by mechanical working, but instead of it, it may be formed by providing curved face portions 2a on the corners of the die such as the upper and lower punches 2A and 2B, etc. and by compressing the coated fuel particles 12A having the overcoat layer 14 (that is the over-coated particles 12). In this case, in order to be able to effectively use the existing production equipment, this curved face portions 2a can be formed by attaching the taper-ring like taper members 4 having curved surface form onto the upper and lower punches 2A and 2B as shown in FIG. 6. Although some preferred embodiments of the invention have been described and illustrated with reference to the accompanying drawings, it will be understood by those skilled in the art that they are by way of examples, and that various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined only to the appended claims. |
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063273209 | abstract | An apparatus for succesively loading solid objects (19) into a tube (27), for instance, nuclear fuel pellets into a nuclear fuel tube, includes means (17) for feeding the objects towards one, open end (29) of the tube. A reduced pressure is induced between each solid object and the tube end prior to entry of the object into the tube. |
047088443 | summary | BACKGROUND OF THE INVENTION The present invention relates to assemblies for monitoring various operating parameters within a reactor core, including, in particular, the neutron flux distribution throughout the core and the core exit coolant temperature. During the operation of a nuclear reactor, it is necessary to constantly monitor a variety of operating parameters, including the neutron flux throughout the reactor core, the core exit coolant temperature, and the coolant level within the reactor pressure vessel. Heretofore, these operations have been performed by a variety of monitoring devices which extend through the reactor pressure vessel at various locations. Of course, each penetration of the reactor pressure vessel requires a high quality, reliable seal. Furthermore, it is common practice to utilize thermocouples for the various monitoring operations, particularly for monitoring the core exit coolant temperature. It is known that thermocouples are prone to failure and that their replacement is a difficult and time consuming operation. SUMMARY OF THE INVENTION It is an object of the present invention to reduce the number of locations at which the connections for such monitoring devices must pass through the pressure vessel of such a reactor. A further object of the invention is to reduce the frequency with which the thermocouples of such monitoring devices must be replaced. A further object of the invention is to provide an effective backup coolant level monitoring system for such reactors. Yet another object of the invention is to provide spare thermocouples which are installed at the same time as the primary thermocouples. The above and other objects are achieved, according to the present invention, by the provision of a combined in-core flux detector and thermocouple assembly for a nuclear reactor comprising: an outer tube which is sealed at its upper end; an inner tube disposed within, and extending along the length of, the outer tube; neutron detector means disposed within the inner tube; means connected to the neutron detector means for displacing the neutron detector means along the length of the inner tube; and a plurality of thermocouples disposed outside of the inner tube and enclosed within the outer tube. According to preferred embodiments of the invention, a group of the thermocouples enclosed within the outer tube are spaced apart along the length of the tubes and are electrically connected to constitute a backup coolant level monitoring system. Since the primary coolant level monitoring system utilized in many reactors is of the pressure sensitive type, a significant advantage of the present invention is that it provides a coolant level monitoring system operating according to a different principle so that any condition causing failure of one system is unlikely to simultaneously cause failure of the other system. According to a further feature of the invention, one of the thermocouples constitutes the normally operative core exit coolant temperature sensor, while a second one of the installed thermocouples is connected to take over this function if the normally operative coolant temperature thermocouple should fail. According to a particularly advantageous feature of this invention, all of the mechanical and electrical connections for the monitoring elements of the assembly can be brought out of the pressure vessel via a single passage which is preferably located in the vicinity of the bottom of that vessel. |
abstract | A remote seal connection includes an outer sleeve, configured to be inserted through a penetration in a wall and having an outer surface. A capillary is within the outer sleeve and carries a fluid configured to communicate a pressure from a remote seal to a pressure transmitter. A space is provided about the capillary and is positioned between the capillary and the outer sleeve. |
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claims | 1. An X-ray imaging apparatus comprising:a plurality of X-ray sources arranged two-dimensionally;an X-ray detector having a plurality of detecting elements two-dimensionally arranged facing said plurality of X-ray sources;an adjusting unit provided between said plurality of X-ray sources and said X-ray detector and configured to adjust an X-ray irradiation area of said plurality of X-ray sources; anda control unit configured to control said adjusting unit such that X-rays emitted from said plurality of X-ray sources irradiate different areas of an object,wherein said control unit has a plurality of modes of operation, comprising:a first mode for controlling said adjusting unit to shift the X-ray irradiation area; anda second mode for controlling said adjusting unit to change the angle of incidence of the X-ray. 2. The apparatus according to claim 1, wherein,in the first mode, said control unit controls said adjusting unit such that X-rays emitted from said plurality of X-ray sources irradiate different areas of an object; andin the second mode, said control unit controls said adjusting unit such that X-rays emitted from said plurality of X-ray sources irradiate the same area of an object from different directions at different timings, respectively. 3. The apparatus according to claim 1, wherein the X-rays emitted from said plurality of X-ray sources through said adjusting unit have the same direction. 4. The apparatus according to claim 3, wherein the size of the areas irradiated by the X-rays emitted from said plurality of X-ray sources are the same. 5. The apparatus according to claim 1, wherein said control unit selects one or more X-ray sources for emitting X-rays from among said plurality of X-ray sources in accordance with a given instruction. 6. The apparatus according to claim 1, wherein said control unit sequentially changes an X-ray source for emitting X-rays from among said plurality of X-ray sources. 7. The apparatus according to claim 1, further comprising a setting unit configured to set the distance from said plurality of X-ray sources to the object,wherein said control unit controls said adjusting unit such that X-rays emitted from said plurality of X-ray sources irradiate different areas of the object, respectively. 8. The apparatus according to claim 1, further comprising a support member for fixing said plurality of X-ray sources and said X-ray detector. 9. The apparatus according to claim 1, wherein said adjusting unit comprises an aperture mechanism for adjusting the size of openings corresponding to said plurality of X-ray sources, andwherein said control unit controls said adjusting unit so as to change the size of the openings to adjust the X-ray irradiation area. 10. The apparatus according to claim 1, wherein said adjusting unit comprises an aperture mechanism for adjusting the position of openings corresponding to said plurality of X-ray sources, andwherein said control unit controls said adjusting unit so as to change the position of the openings to adjust the X-ray irradiation area. 11. The apparatus according to claim 1, wherein said adjusting unit comprises an aperture mechanism for adjusting the size and/or position of openings corresponding to said plurality of X-ray sources, andwherein said control unit controls said adjusting unit so as to change the size and/or position of the openings to adjust the X-ray irradiation area. 12. The apparatus according to claim 2, wherein said control unit controls said adjusting unit and the plurality of X-ray sources such that X-rays emitted from said plurality of X-ray sources sequentially irradiate the same area of an object from different directions, in the second mode. 13. The apparatus according to claim 2, wherein said control unit can switch between the first mode and the second mode. 14. The apparatus according to claim 2, wherein the modes of operation of said control unit further comprise a third mode for controlling said adjusting unit and said plurality of X-ray sources such that X-rays emitted from said plurality of X-ray sources sequentially irradiate one of the different areas from different directions. 15. The apparatus according to claim 2, wherein the modes of operation of said control unit further comprise a fourth mode for controlling said adjusting unit and said plurality of X-ray sources such that X-rays emitted from said plurality of X-ray sources irradiate different areas of the object from one of the different directions. |
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041995392 | abstract | A method for monitoring and controlling the operation of a dual platen press used in the manufacture of nuclear fuel pellets is disclosed. The method comprises the steps of indicating the displacements of both platens and imposing the displacements of the platens on orthogonal axes such that the displacements jointly control the motion of a point which traces a lissajous figure representative of the displacement and relative velocity of the press platens. A second lissajous figure representing the desired platen movements and relative velocity may be superimposed on the first lissajous figure, differences between the first and second lissajous figures indicating deviations from the desired operation of the press. Alternately, a press operator may simply use the first lissajous figure constructed from the actual platen displacements to analyze the operation of the press. The completion of preselected portions of the first lissajous figure may be detected and used to trigger subsequent press operations. Mechanical, optical and electrical embodiments of devices for implementing the method are disclosed. |
063103532 | claims | 1. A mass spectrometer comprising: a source region; a shielded lens including at least two conducting electrodes; an analysis region; and a detector region; wherein said shielded lens produces and adjusts the position of a focal point of ions produced in said source region. an ion source region; a shielded lens; a flight region; and a detector region; wherein said source region, said shielded lens, said flight region and said detector region are positioned such that ions produced in said source region traverse through said shielded lens and said flight region to said detector region; and wherein said shielded lens produces and adjusts the position of focal point of said ions. 2. A mass spectrometer according to claim 1, wherein said shielded lens further comprises a conducting cylindrical electrode. 3. A mass spectrometer according to claim 2, wherein said cylindrical electrode has an axis which is coaxial with a path of said ions. 4. A mass spectrometer according to claim 2, wherein said conducting electrodes are conducting planar grids. 5. A mass spectrometer according to claim 4, wherein said cylindrical electrode is positioned between said conducting planar grids. 6. A mass spectrometer according to claim 4, wherein said planar grids are positioned perpendicular to said path of said ion beam. 7. A mass spectrometer according to claim 4, wherein said cylindrical electrode is electrically biased with respect to said planar grids to focus or defocus ions. 8. A mass spectrometer according to claim 4, wherein said planar grids have more than 8 wires per centimeter (20 wires per inch). 9. A mass spectrometer according to claim 4, wherein said grids have 8 wires per centimeter (twenty wires per inch). 10. A mass spectrometer according to claim 1, wherein said shielded lens comprised of at least two conducting cylindrical electrodes and at least one conducting planar grid. 11. A mass spectrometer according to claim 10, wherein said conducting cylindrical electrodes have an axis which corresponds to the nominal path of said ions. 12. A mass spectrometer according to claim 11, wherein a plane occupied by said planar grid is perpendicular to said axis. 13. A mass spectrometer according to claim 11, wherein said planar grid is positioned in a path of said ions. 14. A mass spectrometer according to claim 11, wherein said planar grid is positioned at an end of said conducting cylindrical electrodes. 15. A mass spectrometer according to claim 1, wherein said shielded lens comprises at least two planar conducting electrodes and at least two conducting planar grids. 16. A mass spectrometer according to claim 15, wherein said planar conducting electrodes are positioned parallel to each other. 17. A mass spectrometer according to claim 15, wherein said planar conducting electrodes are positioned such that said ions pass there between. 18. A mass spectrometer according to claim 15, wherein said planar grids are perpendicular to the path of said ions. 19. A mass spectrometer according to claim 15, wherein at least one of said planar grids is positioned at each end of said planar conducting electrodes. 20. A mass spectrometer according to claim 1, wherein said shielded lens comprises at least two pair of parallel planar conducting electrodes and at least one conducting planar grid. 21. A mass spectrometer according to claim 20, wherein each of said pair is positioned on opposite sides of the nominal path of said ions. 22. A mass spectrometer according to claim 20, wherein said planar grid is perpendicular to the nominal path of said ions. 23. An improved mass spectrometer according to claim 20, wherein said planar grid is positioned at one end of said two pair of planar conducting electrodes. 24. A mass spectrometer according to claim 1, wherein said analysis region comprises a quadrupole mass analyzer. 25. A mass spectrometer according to claim 1, wherein said analysis region comprises a time-of-flight mass analyzer. 26. A mass spectrometer according to claim 1, wherein said analysis region comprises an orthogonal time-of-flight mass analyzer. 27. A mass spectrometer according to claim 1, wherein said analysis region comprises a coaxial reflectron time-of-flight mass analyzer. 28. A mass spectrometer according to claim 1, wherein said analysis region comprises a tandem time-of-flight mass analyzer. 29. A mass spectrometer according to claim 1, wherein said analysis region comprises an ion trap mass analyzer. 30. A time-of-flight mass spectrometer comprising: 31. A time-of-flight mass spectrometer according to claim 30, wherein said flight region is a field free drift region. 32. A time-of-flight mass spectrometer according to claim 30, wherein said shielded lens further comprises a conducting cylindrical electrode. 33. A time-of-flight mass spectrometer according to claim 32, wherein said cylindrical electrode has an axis which is coaxial with a path of said ions. 34. A time-of-flight mass spectrometer according to claim 32, wherein said shielded lens further comprises conducting planar grids. 35. A time-of-flight mass spectrometer according to claim 34, wherein said cylindrical electrode is positioned between said conducting planar grids. 36. A time-of-flight mass spectrometer according to claim 35, wherein said planar grids are positioned perpendicular to said path of said ions. 37. A time-of-flight mass spectrometer according to claim 35, wherein said cylindrical electrode is electrically biased with respect to said planar grids to focus or defocus ions. 38. A time-of-flight mass spectrometer according to claim 35, wherein said planar grids have more than 8 wires per centimeter (20 wires per inch). 39. A time-of-flight mass spectrometer according to claim 35, wherein said planar grids have 8 wires per centimeter (twenty 24 wires per inch). 40. A time-of-flight mass spectrometer according to claim 32, wherein said shielded lens comprises at least two conducting cylindrical electrodes and at least one conducting planar grid. 41. A time-of-flight mass spectrometer according to claim 40, wherein said conducting cylindrical electrodes have an axis which corresponds to the nominal path of said ions. 42. A time-of-flight mass spectrometer according to claim 40, wherein a plane occupied by said planar grid is perpendicular to said axis. 43. A time-of-flight mass spectrometer according to claim 40, wherein said planar grid is positioned in a path of said ions. 44. A time-of-flight mass spectrometer according to claim 40, wherein said planar grid is positioned at an end of said conducting cylindrical electrodes. 45. A time-of-flight mass spectrometer according to claim 30, wherein said shielded lens comprises at least two planar conducting electrodes and at least two conducting planar grids. 46. A time-of-flight mass spectrometer according to claim 45, wherein said planar conducting electrodes are positioned parallel to each other. 47. A time-of-flight mass spectrometer according to claim 45, wherein said planar conducting electrodes are positioned such that said ions pass there between. 48. A time-of-flight mass spectrometer according to claim 45, wherein said planar grids are perpendicular to a path of said ions. 49. A time-of-flight mass spectrometer according to claim 45, wherein at least one of said planar grids is positioned at each end of said planar conducting electrodes. 50. A time-of-flight mass spectrometer according to claim 30, wherein said shielded lens comprises at least two pair of parallel planar conducting electrodes and at least one conducting planar grid. 51. A time-of-flight mass spectrometer according to claim 50, wherein each of said pair is positioned on opposite sides of the nominal path of said ions. 52. A time-of-flight mass spectrometer according to claim 50, wherein said planar grid is perpendicular to the nominal path of said ions. 53. A time-of-flight mass spectrometer according to claim 50, wherein said planar grid is positioned at one end of said two pair of planar conducting electrodes. |
051620960 | claims | 1. A system for detecting the presence of explosives in an object under observation by detection of a particular element, and the three-dimensional concentration of such particular element, at the different positions in the object, including, a cavity structure for receiving the object under observation, means in the cavity structure for providing thermal neutrons of high energy, neutron means disposed relative to the cavity structure for converting substantially all of the neutrons of high energy to thermal neutrons of low energy for interreaction with the object under observation in the cavity structure to obtain the production from the object of gamma rays representative of the presence and concentration of the particular element in the object, means for moving the object through the cavity structure, detectors disposed in the cavity structure and positioned relative to the thermal neutrons of low energy and the object for detecting the gamma rays to produce output signals indicative at each instant of such gamma rays, the neutron means and the detectors being disposed relative to one another to obtain the detection by the detectors at each instant of the gamma rays in a common plane transverse to the direction of movement of the object through the cavity structure, and means responsive to the output signals from the detectors at progressive instants of time in the common plane during the movement of the object through the cavity structure for processing such signals to indicate the presence, and the concentration on a three-dimensional basis, of the particular element in the object. the moving means includes a conveyor passing through the cavity structure and supporting the object under observation to move the object through the cavity structure and provide for the detection of the presence, and the concentration on a three-dimensional basis, of the particular element in the object at successive planes of the object, the successive planes being substantially parallel to the common plane and wherein the converting means are operative to provide for a retention of a portion of the neutrons of high energy to obtain the detection by the detectors of nitrogen in the explosives from the thermal neutrons of low energy and the detection by the detectors of hydrogen in the explosives from the neutrons of high energy. the object is a container and wherein the neutron means are disposed relative to the container in a common planar relationship to provide for the presence of the thermal neutrons in the contains and wherein the detectors are disposed relative to the container in the common planar relationship for receiving the gamma rays emanating from the container, the common planar relationship being substantially perpendicular to the direction of movement of the object through the cavity structure and wherein the cavity structure is defined by a plurality of walls having properties of slowing the neutrons of high energy in at least a portion of the range of such high energy and wherein means are disposed within the cavity structure for slowing the neutrons of the high energy in other portions of the range of such high energy. the detectors are disposed in a C-ring configuration, open at one end, in the common plane around the cavity structure and the neutron means are disposed in the open end of the C-ring configuration in the common plane to obtain the detection by the detectors of the presence of the particular element, and the concentration of the particular element at different positions, within the common plane to produce output signals representing the presence of the particular element in the object in such common plane and wherein the processing means process the signals produced at successive instants of time by the detectors in such common plane during the movement of the container through the cavity structure to indicate the presence, and the concentration at each position in the object on a three-dimensional basis, of the particular element in the object and wherein the converting means include premoderator means enveloping the neutron means and formed of a material for slowing the neutrons of high energy in a first range of such high energy, first moderator means disposed relative to the premoderator means, and formed of a material, for slowing the neutrons of high energy in a second range of such high energy and second moderator means disposed relative to the walls, and formed of a material, for slowing the neutrons of high energy in a third range of such high energy. the premoderator means is formed of a non-chlorinated hydrogenous material, the first moderator means is formed of heavy water and the second moderator means is formed of a carbonaceous material. an outer shield envelopes the second moderator means to prevent any stray neutrons from leaving the cavity structure. an outer shield envelopes the second moderator means to prevent any stray neutrons from leaving the cavity structure and wherein the outer shield is constructed of a hydrogenous material mixed with at least one of boron and lithium, wherein the wall members are formed of at least one of polyethylene and acrylic resin, wherein the premoderator means are formed of at least one of polyethylene and acrylic resin, wherein the first moderator means is formed of heavy water and wherein the second moderator means is formed from a material selected from the group consisting of graphite, polyethylene and acrylic resin. the detectors define a ring around the cavity structure to detect the presence and concentration of the particular element within a particular plane passing through the object under inspection to produce output signals representing such particular plane and wherein a shield member of a heavy metal envelopes the premoderator means to absorb unwanted gamma rays and prevent such rays from being directed to the inorganic detectors. the shield member being formed from a material selected from the group consisting of bismuth, lead, tungsten and depleted uranium. the detectors are disposed in the common plane relationship in a C-ring configuration, open at one end, with the neutron means disposed in the open end of the common plane of the C-ring configuration and wherein a shield member of a heavy metal is disposed relative to the premoderator means to absorb unwanted gamma rays and prevent such rays from being directed to the inorganic detectors. the detectors are disposed in a pair of common planes each having a C-ring configuration and wherein each C-ring configuration has an open end opposite the open end in the other C-ring configuration and wherein the pair of C-ring configurations are spaced from each other in the direction of movement of the object and wherein the neutron means are respectively disposed in the common plane in the open ends of the C-ring configurations and wherein means are disposed relative to the cavity structure for shielding individuals adjacent to the cavity structure from neutrons which pass through the cavity structure. the detectors are disposed relative to the object and the neutron means to detect the particular element in a plurality of successive spaced planes through the object in accordance with the movement of the object through the cavity structure to obtain a three-dimensional profile by the processing means of the presence, and the concentration at different positions on a three-dimensional basis, of the particular element in the object and wherein means are disposed relative to the cavity structure for shielding individuals adjacent to the cavity structure from neutrons which pass through the cavity structure and wherein such means are constructed of a hydrogenous material. the detectors in each of the C-ring configurations are disposed in oppositely positioned columns from the positioning of the detectors in the other C-ring configuration and each of the columns has parallel sets of the detectors and wherein the means for shielding individuals are formed from a material selected from the group consisting of borated paraffin, polyethylene, plexiglass and water mixed with a lithium compound. a cavity structure for receiving the particular object within the cavity structure, the cavity being defined by top and bottom walls and a pair of side walls, neutron means for producing neutrons of high energy within the cavity structure, means disposed relative to the cavity structure and the neutron means for converting substantially all of the neutrons of high energy to thermal neutrons of low energy to interact with the object in forming gamma rays of a particular energy, a plurality of detectors disposed within the cavity structure in a common plane to detect the gamma rays from the object of the particular energy, the plurality of detectors being disposed in an open C-ring configuration around the object to detect the concentration of the particular element in the object in the common plane passing through the object and the detectors during the movement of the object through the cavity structure, each detector producing output signals representative of the passage of the gamma rays from the object of the particular energy, the detectors being disposed adjacent the side walls and one of the top and bottom walls of the cavity structure, means for moving the object through the cavity structure, and means for processing the signals from the detectors to provide an indication of the profile of the concentration of the particular element at the different positions in the object. the moving means includes a conveyor means passing through the cavity structure and supporting the object to move through the cavity structure and to provide for the detection of the presence and concentration of the particular element in successive planes of the object parallel to the common plane and to provide a profile of the concentration of the particular element in the object at the different positions in the object and wherein the converting means include a plurality of means operative upon the neutrons of high energy from the neutron means in different portions of the range of high energy of the neutrons to convert such neutrons to thermal neutrons of low energy for detection by the detection means. the object is a container and wherein means are provided for processing the output signals from the detectors to provide the profile of the concentration of the particular element in the object at the different positions in the object and wherein the common plane is substantially perpendicular to the direction of movement of the object through the cavity structure and wherein the plurality of means in the converting means include premoderator means disposed relative to the neutrons of high energy to slow the neutrons of high energy in a first range of such high energy and moderator means disposed relative to the premoderator means to slow the neutrons of high energy in a second range of such high energy. computer means responsive to the output signals from the detectors for producing an alarm condition in response to a particular profile of the concentration of the particular element in the object at the different positions in the object and wherein the common plane is substantially perpendicular to the direction of movement of the object through the cavity structure and wherein the moderator means include first moderator means disposed relative to the premoderator means, and second moderator means disposed relative to the first moderator means, to respectively slow the neutrons of high energy in different portions of the range of such high energy. the detectors are formed into a C-ring configuration, open at one end, and the neutron means are disposed in the open end of the C-ring configuration and wherein the cavity structure is defined by walls having properties of slowing the neutrons of high energy in a particular range of such high energy. the plurality of detectors are defined by a spaced pair of C-ring configurations, each open at one end, having open ends opposite each other and separated from each other in the direction of movement of the object in the cavity structure and wherein the detectors in each of the C-ring configurations are in a common plane spaced from the detectors in the other C-ring configuration in the direction of movement of the object through the cavity structure and wherein the plurality of converting means include first means disposed relative to the neutron means to convert the neutrons of high energy in different portions of the range of high energy to thermal neutrons of low energy and second means disposed relative to the cavity structure to convert the neutrons in other portions of the range of high energy to the thermal neutrons of low energy. the first means include premoderator means disposed relative to the neutron means to convert the neutrons of high energy in a first one of different portions of the range of high energy to thermal neutrons of low energy and include moderator means disposed relative to the premoderator means to convert the neutrons of high energy in a second one of the different portions of the range of high energy to thermal neutrons of low energy. each of the spaced pair of C-shaped ring configuration is defined by parallel sets of individual detectors and wherein the premoderator means are formed of a non-chlorinated hydrocarbon material and the first moderator means are formed of heavy water and the second moderator means are formed of a carbonaceous material. shield means disposed relative to the second moderator means to prevent any stray neutrons from exiting the cavity structure. shield means disposed relative to the second moderator means to prevent any stray neutrons from exiting the cavity structure and wherein the shield means is constructed of a hydrogenous material mixed with at least one of boron and lithium. side structures and top and bottom structures are disposed in the cavity structure and wherein the detectors in one of the C-ring configurations are disposed in three of the top and bottom and side structures in the cavity structure and wherein the detectors in the other C-ring configuration are disposed in three of the top and bottom and side structures in the cavity structure and wherein the fourth one of the top and bottom and side structures in one of the C-ring configurations is opposite the fourth one of the top and bottom and side structures in the other C-ring configuration and wherein the C-ring configurations are substantially parallel to each other and substantially perpendicular to the direction of movement of the object through the cavity structure and wherein a shield member of a heavy metal is disposed relative to the converting means for absorbing unwanted gamma rays and wherein the heavy metal is selected from the group consisting of lead, bismuth, tungsten and depleted uranium. side and top and bottom structures are disposed in the cavity structure and wherein the detectors in one of the C-ring configurations are disposed in three of the top and bottom and side structures in the cavity structure and wherein the detectors in the other C-ring configuration are disposed in three of the top and bottom and side structures in the cavity structure and wherein the fourth one of the top and bottom and side structures in one of the open C-ring configurations is opposite to the fourth one of the top and bottom and side structures in the other open C-ring configuration and wherein the open C-ring configurations are substantially parallel to each other and substantially perpendicular to the direction of movement of the object through the cavity structure and wherein means are disposed relative to the second moderator means to prevent any stray neutrons from exiting the cavity structure. side structures and top and bottom structures are disposed in the cavity structure and wherein the detectors in one of the C-ring configurations are disposed in three of the top and bottom and side structures in the cavity structure and wherein the detectors in the other C-ring configuration are disposed in three of the top and bottom and side structures in the cavity structure and wherein the fourth one of the top and bottom and side structures in one of the open C-ring configurations is opposite to the fourth one of the top and bottom and side structures in the other open C-shaped configuration and wherein the open C-ring configurations are substantially parallel to each other and substantially perpendicular to the direction of movement of the object through the cavity structures and wherein shield means are disposed relative to the second moderator means to prevent any stray neutrons from exiting the cavity structure and wherein the shield means is constructed of a hydrogenous material mixed with at least one of boron and lithium. 2. The system of claim 1 wherein 3. The system of claim 1 wherein 4. The system of claim 1 wherein 5. The system of claim 4 wherein 6. The system of claim 4 wherein 7. The system of claim 4 wherein 8. The system of claim 4 wherein 9. The system of claim 8 additionally including 10. The system of claim 6 wherein 11. The system of claim 4 wherein 12. The system of claim 6 wherein 13. The system of claim 12 wherein 14. A detection system for producing a profile of the concentration of a particular element at the different positions in an object, including 15. The system of claim 14 wherein 16. The system of claim 14 wherein 17. The system of claim 16 additionally including 18. The system of claim 15 wherein 19. The system of claim 15 wherein 20. The system of claim 19 wherein 21. The system of claim 17 wherein 22. The system of claim 17 including 23. The system of claim 18 including 24. The system of claim 19 wherein 25. The system of claim 17 wherein 26. The system of claim 21 wherein |
claims | 1. An apparatus for storing radioactive waste comprising: a self-sealing bladder; a protective layer disposed on the bladder; a radiation barrier disposed on the protective layer; and an impact resistant layer disposed on the radiation barrier; wherein the self-sealing bladder is penetrated by an injector device and filled with the radioactive waste prior to the disposition of the protective layer, the radiation barrier and the impact resistant layer. 2. The apparatus of claim 1 , wherein the self-sealing bladder is made of a self-sealing polymeric material. claim 1 3. The apparatus of claim 1 , wherein the self-sealing bladder is made of a self-sealing rubber material. claim 1 4. The apparatus of claim 1 , wherein the radiation barrier is made of a lead-containing material. claim 1 5. The apparatus of claim 1 , wherein the impact resistant layer is made of a high impact polymeric material. claim 1 6. The apparatus of claim 1 , wherein the impact resistant layer is made of a rubber material. claim 1 7. The apparatus of claim 1 , wherein the radioactive waste is in a slurry form. claim 1 8. The apparatus of claim 1 , wherein the radioactive waste is in liquid form. claim 1 9. The apparatus of claim 1 , wherein the radioactive waste is in a paste-like form. claim 1 10. The apparatus of claim 1 , wherein the apparatus has a cylindrical shape. claim 1 11. The apparatus of claim 1 , wherein the apparatus has a spherical shape. claim 1 12. A method for storing radioactive waste in a container comprising the steps of: penetrating a self-sealing bladder and filling the self-sealing bladder with a radioactive material; coating the self-sealing bladder with a protective coating; coating the protective coating with a radioactive barrier coating; and coating the radioactive barrier coating with an impact resistant coating. |
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062263420 | claims | 1. A fuel assembly comprising: a plurality of elongated elements filled with nuclear fuel; and at least one component for retaining the elongated elements, wherein the at least one retaining component consists essentially of a ceramic material. 2. The fuel assembly according to claim 1, wherein the ceramic material is based on zirconium dioxide. 3. The fuel assembly according to claim 2, wherein the ceramic material comprises partially stabilized zirconium dioxide. 4. The fuel assembly according to claim 3, wherein the partially stabilized zirconium dioxide comprises magnesium oxide. 5. The fuel assembly according to claim 1, wherein the retaining component is a spacer, a bottom tie plate, or a top tie plate. 6. The fuel assembly, according to claim 5, wherein the spacer comprises internal springs formed in the ceramic material. |
041522052 | description | Referring now to the drawing and first, particularly, to FIG. 1 thereof, there is shown a pressurized water nuclear reactor wherein fuel assemblies 2 form the core of the pressurized water reactor and are disposed inside a pressure vessel 1, cooling water flowing through the fuel elements from the bottom to the top thereof in the manner represented by the arrows. One possible fuel element construction is shown in FIG. 2. The fuel element is formed of a framework made up of a head plate 4 and a base plate 4', as well as control rod guide tubes 5 connecting the head plate 4 and the base plate 4' to one another. At fuel rod positions, these control rod guide tubes extend through a number of mutually spaced superimposed spacer grids 3. In the view of FIG. 2, the mesh of the spacers are readily seen. The nuclear reactor fuel rods which pass through the latter have not been illustrated in the interest of greater clarity. These fuel rods, however, are held or supported in the individual mesh of the spacers for the purpose of centering and damping vibrations by means of resilient and rigid contact elements, the resilient contact elements usually engage the fuel rod in the middle of the spacer grid, the rigid contact elements or projections, on the other hand, engaging the fuel rod above and below this point; whence the name of the system: "three-point support". It has become known heretofore (note the Published Non-Prosecuted German Application cited hereinabove) to manufacture the spacer grids and the rigid as well as the resilient contact elements all of the same material i.e. a spring-elastic material. However, since such material has a relatively large neutron absorption cross section, proposals have been made earlier, as mentioned hereinabove, to make only the resilient parts out of this material. FIGS. 3 and 4 show the disposition of the contact elements 7 and 7' within the individual mesh of the spacers in two different structural forms of the grids, respectively, in square and octagonal geometry. In these figures, the fuel rods 6 are shown in circular outlines, the resilient contact elements 7 are shown as small rectangles, and the rigid contact projections 7' as semicircles. From this, it is readily apparent that a rigid contact element 7' is always disposed opposite a resilient contact element 7. This principle is obviously applicable also to other types of grid geometries, such as also that of the hereinafore cited Published Prosecuted German Application DT-AS 1,489,632. The additional FIGS. 5, 5a, 6, 7 and 7a show different possible embodiments of the resilient contact elements as well as the attachment thereof in the wall of the grid mesh of the spacer according to the invention. Like or corresponding parts are provided with the same reference characters in thes figures. Thus, each of FIGS. 5, 5a, 6, 7 and 7a shows a wall 31 of the spacer grid mesh, and a rectangular opening 32 intended for the insertion of a spring element 71, 72, 73, respectively, therein. The spring element 71 shown in FIGS. 5 and 5a in a side elevational, partly sectional view and in a front elevational view, respectively, and snapped into place with the wave-shaped part 71a thereof in the rectangular opening 32. The flat parts 71b and 71b' engage the mesh wall 31, an end 71c adjacent the flat part 71b being bent over. Through the suspension of the spring element or spring strip 71 in this manner, additional fastening reliability is obtained. The wave in the spring part 71a is such that, upon being subjected to pressure by a non-illustrated contacting fuel rod, applied in direction toward the mesh wall 31, this element section i.e. the spring part 71a, is lengthened, so that thereby the engagement between this element section 71a and the upper and lower edge portion of the mesh wall 31 defining the rectangular opening 32 is increased in the sense of strengthening the locking section, somewhat similar to the principle of a snap fastener. The spring element 72 shown in FIG. 6 in side elevational view has the same shape as that of FIG. 5 insofar as the wave-shaped or corrugated contact part 72a is concerned, and also the locking in the opening 32 is the same. The non-corrugated or non-wave-shaped spring portions adjoining both sides of the contact part 72a, however, are shaped to form contact projections 72b, which project into the adjacent mesh space and also engage a fuel rod therein. FIGS. 7 and 7a also show a partly sectional side elevational view and a front elevational view, respectively, of the spring element 73, which again, has a wave-shaped or corrugated part 73a, as well as two projections 73b. It is bent with an end portion 73c additionally over the upper edge of the web or suspended therefrom in this manner. In the region of the projections 73b, the spring element is made wider, note FIG. 7a, the width depending upon the required height of stamped-out projections 73b. The projections 73b are made in the form of cups in the instant embodiment of the invention, however, it is obvious that a simple folding of the spring strip material could also be provided for shaping these projections. In order to provide some idea of the order of magnitude of these spacer or spacer holder elements, it should be noted that the width of the sheet-metal webs 31 forming the mesh is about 30 mm; the rectangular opening 32 has approximately the dimensions 3.times.15 mm. The installation or assembly of the spring inserts 71, 72, 73 is very simple: the spring elements are forced sequentially into the respective openings 32 of the mesh walls in accordance with the construction shown in FIGS. 3 and 4. They are self-locking in this position, the holding forces being further reinforced by the elastic deformation of the spring parts 71a, 72a, 73a when the fuel rods are inserted during final assembly of the fuel element. In principle, this is achieved by providing for the length of the resilient or springy part to be somewhat greater than the length of the opening 32 and, thereby, a self-locking contact of the spring part in the mesh wall is provided. In contrast to the state of the art mentioned in the introduction hereto, trouble-free mounting of the spring elements with a minimum amount of material is achieved, and in addition, the possibility of forming rigid projections at the spring elements for the so-called three-point support of the fuel rods is provided. Obviously, variations can also be effected with regard to the waviness or corrugation of the spring part, just as it is also possible to make changes in the width thereof. |
abstract | The invention relates to a cooling apparatus (101) for a sample in an ion beam etching process, including, a sample stage (102) for arranging the sample, a coolant receptacle (120) containing a coolant, at least one thermal conduction element (106a, 106b) that connects the sample stage (102) to the coolant, a cooling finger (105) connected to the thermal conduction element (106a, 106b), the cooling finger (105) comprising a conduit (130, 131) through which coolant can flow and which is connectable to the coolant receptacle (120). The invention further relates to a method of adjusting the temperature of a sample in an ion beam etching process, including mounting a sample on a coolable sample stage (102), aligning the sample on the sample stage (102), and cooling the sample by coolant directed through a conduit (130, 131) of a cooling finger. |
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claims | 1. A system for providing multi-angular SPECT radiation sampling utilizing slant-angle collimation, said system comprising:a collimator positioned between a radiating mass within a patient and a radiation detector, said collimator being spaced apart from a translational path of the radiating mass at a predefined distance that defines a patient accommodation space;a plurality of apertures extending through said collimator, each of said apertures forming a passageway for radiation rays emanating from said radiating mass in a direction substantially aligned with a longitudinal axis of the respective passageway and thereby enabling the aligned radiation rays to strike said radiation detector;said plurality of passageways being arranged in a plurality of rows across said collimator and arranged so that said longitudinal axes of a first row of passageways are substantially parallel to each other and form a first angle with respect to a central plane of said collimator; anda second row of passageways being arranged so that said longitudinal axes of said second row of passageways are substantially parallel to each other and form a second angle with respect to said central plane of said collimator, where said second angle is different than said first angle. 2. The system as recited in claim 1, wherein said plurality of passageways further comprises:a third row of passageways being arranged so that said longitudinal axes of said third row of passageways are substantially parallel to each other and form a third angle with respect to said central plane of said collimator, where said third angle is different than said first and second angles. 3. The system as recited in claim 2, wherein each row of passageways contains a sufficient number of passageways arranged sufficiently close together to effectively form an elongate slot through said collimator. 4. The system as recited in claim 2, wherein said second angle is approximately one hundred and thirty-five degrees as measured clockwise from said central plane of said collimator to a respective third row passageway's longitudinal axis. 5. The system as recited in claim 2, wherein said first angle is approximately forty-five degrees as measured clockwise from said central plane of said collimator to a respective first row passageway's longitudinal axis. 6. The system as recited in claim 5, wherein said third angle is approximately ninety degrees as measured clockwise from said central plane of said collimator to a respective passageway's longitudinal axis. 7. The system as recited in claim 6, wherein said predefined distance at which said collimator is positioned from the translational path of said radiating mass is selected so that approximately one-half of a translating radiating mass is multi-angularly, SPECT radiation sampled through said collimator in a single translational pass of the radiating mass relative to said radiation detector. 8. The system as recited in claim 2, further comprising:said collimator being mounted on an instrument support assembly and said instrument support assembly being associated with a motive means for effecting longitudinal relative motion between said instrument support assembly and a patient for taking the multi-angular SPECT radiation sampling of the radiating mass in the patient utilizing the variously slant angled passageways and without requiring relative rotation between the patient and instrument support assembly. 9. The system as recited in claim 8, wherein said predefined distance at which said collimator is positioned from the translational path of said radiating mass is selected so that approximately one-half of the translating radiating mass is multi-angularly, SPECT radiation sampled through said collimator in a single translational pass of said radiating mass relative to said radiation detector. 10. The system as recited in claim 2, further comprising:said collimator being mounted on an instrument support assembly and said instrument support assembly being associated with a motive means for effecting exclusively longitudinal relative motion between said instrument support assembly and a patient for taking the multi-angular SPECT radiation sampling of the radiating mass in the patient utilizing the variously slant angled passageways and without requiring relative rotation between the patient and instrument support assembly. 11. The system as recited in claim 10, wherein said predefined distance at which said collimator is positioned from the translational path of said radiating mass is selected so that approximately one-half of the translating radiating mass is multi-angularly, SPECT radiation sampled through said collimator in a single translational pass of said radiating mass relative to said radiation detector. 12. The system as recited in claim 2, wherein said collimator and radiation detector are incorporated components in a first gamma camera that is aimed at the patient accommodation space, said first camera being mounted on an instrument support assembly configured for longitudinal relative motion with respect to said patient accommodation space for developing a first one pass, multi-angular SPECT radiation sampling of the radiating mass in the patient utilizing the variously slant angled passageways and without requiring relative rotation between said first camera and said patient accommodation space. 13. The system as recited in claim 12, wherein said predefined distance at which said collimator is positioned from the translational path of said radiating mass is selected so that approximately one-half of the translating radiating mass is multi-angularly, SPECT radiation sampled through said collimator in a single translational pass of said radiating mass relative to said radiation detector. 14. The system as recited in claim 12, wherein said first gamma camera is adjustably mounted for reconfiguration with respect to said patient accommodation space thereby enabling the development of a second, different perspective, one pass, multi-angular SPECT radiation sampling of the radiating mass in the patient. 15. The system as recited in claim 14, wherein the aim of said first gamma camera is offset approximately ninety degrees between said first and second perspective, one pass, multi-angular SPECT radiation sampling of the radiating mass in the patient. 16. The system as recited in claim 12, further comprising:a second gamma camera comprising a collimator and radiation detector, said second gamma camera being aimed at the patient accommodation space from a different perspective than said first gamma camera and thereby enabling the simultaneous development of two different perspective, one pass, multi-angular SPECT radiation samplings of the radiating mass in the patient. 17. The system as recited in claim 16, wherein said predefined distance at which said collimator is positioned from the translational path of said radiating mass is selected so that together with the configuration of the acute included angle at approximately forty-five degrees and the obtuse included angle at approximately one hundred and thirty-five degrees, approximately one-half of the translating radiating mass is multi-angularly, SPECT radiation sampled through said collimator in a single translational pass of said radiating mass relative to said radiation detector. 18. A system for providing multi-angular SPECT radiation sampling utilizing slant-angle collimation, said system comprising:a collimator positioned between a radiating mass within a patient and a radiation detector;a plurality of apertures extending through said collimator, each of said apertures forming a passageway for radiation rays emanating from said radiating mass in a direction substantially aligned with a longitudinal axis of the respective passageway and thereby enabling the aligned radiation rays to strike said radiation detector;said plurality of apertures being arranged in a plurality of rows, longitudinal axes of apertures of each row being substantially parallel to each other, longitudinal axes of a first row adjacent to one edge of said collimator forming an angle of approximately ninety degrees with longitudinal axes of a row adjacently to an opposite edge of said collimator. 19. A system for providing multi-angular SPECT radiation sampling utilizing slant-angle collimation, said system comprising:a collimator positioned between a radiating mass within a patient and a radiation detector;a plurality of apertures extending through said collimator, each of said apertures forming a passageway for radiation rays emanating from said radiating mass in a direction substantially aligned with a longitudinal axis of the respective passageway and thereby enabling the aligned radiation rays to strike said radiation detector;said plurality of apertures being arranged in a plurality of rows across said collimator, longitudinal axes of apertures of each row being substantially parallel to each other and pointing in a different direction than longitudinal axes of other rows. |
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summary | ||
summary | ||
052727424 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a typical nuclear fuel assembly 10. Fuel assembly 10 is generally comprised of a plurality of fuel rods 12, grid assemblies 14, guide tubes 16, lower end fitting 18, and upper end fitting 20. Fuel rods 12 are maintained in an array spaced apart by grid assemblies 14. Guide tubes 16 extend through grid assemblies 14 and are attached to lower end fitting 18 and upper end fitting 20 and, in addition to providing structural integrity to the entire assembly, also serve as guides for control rods not shown. Lower end fitting 18 and upper end fitting 20 provide structural and load bearing support to fuel assembly 10 and are also provided with openings therethrough to allow coolant to flow vertically through fuel assembly 10. FIG. 3 is a side sectional view of a prior art upper end fitting 20. Upper end fitting 20 is comprised of main body portion 22 that may be square or rectangular in section. The lower portion of main body portion 22 is rigidly attached to or may be integral with grillage or base 24. As seen more clearly in FIG. 1, the underside of base 24 is adapted for attachment to guide tubes 16. Pedestal 26 is attached to base 24 and extends upward therefrom to support control assembly 28. Spring retainer 30 is positioned inside main body portion 22 for movement therein and is provided with tabs 32 that are received in slots in main body portion 22. Spring retainer 30 thus serves to maintain helical spring 34 in its installed position in main body portion 22. FIG. 2 illustrates upper end fitting 36 of the present invention. Upper end fitting 36 is similar in basic construction to that of the prior art in FIG. 3 in that it is formed from main body portion 22, base 24, and a spring retainer 30. However, upper end fitting 36 is provided with a combined pedestal and holddown spring assembly 38. Leaf springs 40 are positioned adjacent each other such that the exterior radius of the springs are facing each other. Each leaf spring 40 is provided with a bore for receiving a bolt 42 therethrough. Nut 44 is threadably received on bolt 42 for holding leaf springs 40 together. Bolt 42 and nut 44 are sized so as to extend upwardly through a bore 46 in spring retainer 30 to the correct height to serve as a pedestal support for control assembly 28. Spring retainer 30 is free to move vertically in main body portion 22 and extends through slots therein. FIG. 4 illustrates the prior art upper end fitting 20 and upper end fitting 36 of the present invention as they appear in their installed position inside a nuclear reactor. Reactor internals 48 bear against the portion of spring retainers 30 that extend out of main body portion 22. This places the desired spring preload pressure on nuclear fuel assembly 10 to prevent unwanted movement caused by coolant flow during normal operations. Upper end fitting 36 causes less upward displacement of control assembly 28 than the prior art end fitting 20 at the time of installation and during irradiation growth of the assembly. During irradiation growth, base 24 is caused to move upward. In the prior art end fitting 20, pedestal 26 moves upward the same distance as base 24 and affects the vertical position of control assembly 28. In upper end fitting 36, the pedestal formed by bolt 42 and nut 44 do not move in proportion to that of base 24. The nut and bolt pedestal move approximately one-half the distance of base 24 as leaf springs 40 are flattened to a greater degree. The invention thus has much less effect on the vertical position of control assembly 28 than prior art end fitting 20. The length of the longer bolt and nut used to attach the springs together and form the pedestal assembly, as opposed to a shorter bolt and nut that would be used merely to attach the leaf springs together, results in added flexibility of the nut and bolt and provides a better structural connection for the spring assembly. 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. |
061954063 | summary | BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a pressurizer with a casing, in which at least one spray line ends. Such pressurizer are customary in a nuclear power plant with a pressurized water reactor. There, they are connected to a branch of a primary circuit which leads from a reactor. In the pressurizer, there is a spray system which is fed with water from a primary-circuit line that leads from a steam generator to the reactor. The water which is introduced through the spray system is therefore relatively cold as compared to the water which is situated inside the pressurizer. The spray system is generally closed off through the use of spray valves. The spray valves are only opened when an excessively high pressure is generated in the pressurizer, and the pressure in the pressurizer is lowered by praying-in relatively cold water. However, a valve cone of one of the spray valves may also have a small hole, so that some water is sprayed into the pressurizer continuously, even when the spray valve is closed. Heretofore, it has been customary to guide the spray lines into the interior of the pressurizer through a so-called spray lid, which is screwed onto a central flange on an upper dome of the pressurizer. To that end, the spray lines initially run upward from the primary circuit and then, after they have passed through a bend above the pressurizer, they run downward into the pressurizer. Heretofore, a so-called spray shroud has been necessary to ensure that the relatively cold water which is sprayed-in does not strike the hot wall of the pressurizer, which would lead to undesirable transient temperatures that would cause material fatigue. That spray shroud is a sheet-metal cylinder which is open at the top and bottom and is disposed concentrically inside the pressurizer. The water which is sprayed-in then strikes the inner wall surface of the sheet-metal cylinder, without coming into contact with the pressure-supporting casing wall. Spray lines are made from austenitic steel. Due to their small diameter, it is not possible for weld seams to be ground internally. Consequently, it is not possible to completely rule out fracture of a spray line. If a spray line breaks, expensive measures are needed to ensure that line parts which are thrust outward or an emerging jet of steam do not cause secondary damage in the power plant. Since the spray lines are guided downward into the pressurizer, at least the downwardly directed part of the spray lines empties when the spray valves are closed. Then, saturated steam from the pressurizer can penetrate into the spray lines and condense therein. The condensate then flows back into the pressurizer and makes room for fresh saturated steam. Therefore, according to the principle of conventional steam heating, at least the downwardly directed section of a spray line is continuously heated. Then, due to the temperature differences, feeding relatively cold water in when necessary may lead to material fatigue of the spray lines. If the spray valves are disposed above the pressurizer, the saturated steam also reaches the spray valves, where it can cause damage in the same way. Since the saturated steam inside the pressurizer is radioactive, there is also a risk of the spray lines as well as the spray valves being exposed to radiation. SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a pressurizer with a spray device, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, in which power-plant devices that are relevant to safety cannot be damaged by a fracturing spray line (causing line parts to strike outward or a jet of steam) and furthermore in which temperature fluctuation or radiation exposure does not impair the stability of any part of a spray line or of any spray valve. With the foregoing and other objects in view there is provided, in accordance with the invention, a pressurizer, comprising a casing having a wall and a lower region; a volume-compensation line leading from a hot system and ending in the casing; and a spray line only intended for cooling, the spray line leading from a cooler system, guided through the wall in the lower region, extended upward inside the casing and ending in the casing at a geodetically highest point of the spray line. In particular, this provides the advantage of exposing the spray line to only a minimal differential pressure with respect to its surroundings. Consequently, fracture of a spray line inside the pressurizer should not be expected. Even if a fracture were to occur, the minimal differential pressure means that there should be no expectation of any damaging movements of parts of the spray line which are to be attributed to a recoil. Simply because the spray line runs almost entirely inside the pressurizer, the risk of secondary damage caused by fracture of the line outside the pressurizer is minimized. The fact that the spray line ends at its geodetically highest point means that when the spray line is closed, it is no longer possible for any water to flow out of the spray line into the pressurizer. The spray line remains full of water until it is opened into the pressurizer. In particular, a spray valve disposed outside the pressurizer is also always full of water. It is therefore impossible for any saturated steam to penetrate into the spray line and to the spray valve, a phenomenon which would lead to temperature fluctuations. This provides the advantage of considerably reducing loads exerted on the spray system by temperature fluctuations as well as by exposure to radiation. Placing the spray line inside the pressurizer also provides the advantage of requiring only a few weld seams, at which it is not entirely possible to rule out a fracture of the line, on the relatively short portion of the spray line which still has to be situated outside the pressurizer. Inside the pressurizer, the spray line advantageously only has to have a relatively small wall thickness, since the differential pressure between the inside of the spray line and its surroundings is low. In accordance with another feature of the invention, the spray line has one or more spray nozzles in the region of its highest point. This provides good distribution of water which is fed into the pressurizer. In accordance with a further feature of the invention, a portion of the spray line which is provided with one or more spray nozzles is, for example, directed upward at an angle. In this way, the spray line remains full of water all the way to the spray nozzles when the spray valve is closed. However, it is ensured that the water is well distributed during spraying. In accordance with an added feature of the invention, the spray line is, for example, guided through the wall of a lower cylindrical part of the casing of the pressurizer at an oblique angle with respect to the wall. In accordance with an additional feature of the invention, the spray line is guided through the wall of a lower cylindrical part of the casing at right angles to the wall. In accordance with yet another feature of the invention, the spray line is guided through the wall of a dome-like part of the casing, which part closes off the casing at the bottom, at right angles to the wall. This latter embodiment provides the particular advantage that the largest possible section of the spray line runs inside the pressurizer, where the pressure line only has to withstand a slight pressure difference between the inside and the outside. Consequently, a small wall thickness of the line is sufficient over the longest possible distance of the spray line. The spray line is therefore particularly economical to produce. In accordance with a concomitant feature of the invention, the spray line is guided through the wall of the casing, where it forms a fixed point. This fixed point acts for the outer and inner parts of the line, resulting in the advantage that movements of one of the two parts of the spray line cannot be transmitted to the other part. Since the spray lines are made from austenitic material and the pressurizer is made from ferritic material, different thermal expansions may occur. This is true even if the pressurizer is lined with an austenitic material on the inside. In order to prevent damage as a result of different thermal expansions, the spray lines inside the pressurizer may be attached in such a way that it is possible for the spray lines to move relative to the pressurizer. The pressurizer according to the invention in particular provides the advantage of substantially ruling out damage to the spray lines, and consequently secondary damage caused by fractured spray lines as well. 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 pressurizer with a spray device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. |
claims | 1. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a current of coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel with the current of coolant flow being separated into streams which collide as said fluid flows to said outlet nozzles, and provided with a flow stabilizing member being lower than one of said outlet nozzles, said member being supported on or above a portion of the upper core plate that is not perforated for fluid flow, disposed in the vicinity of a core barrel in a region outside of said fuel region and positioned to separate said streams thereby preventing the streams from colliding to suppress temperature fluctuations of said coolant flow. 2. An internal structure of a nuclear reactor according to claim 1 , wherein said flow stabilizing member is disposed beneath an outlet of said outlet nozzle. claim 1 3. An internal structure of a nuclear reactor according to claim 2 , wherein said flow stabilizing member is disposed directly underneath a center portion of said outlet of said outlet nozzle. claim 2 4. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel, said upper plenum being shaped to define several separate streams for said coolant which collide; and a flow stabilizing member being lower than said outlet nozzle, said member being supported on or above a portion of the upper core plate that is not perforated for fluid flow, disposed in the vicinity of a core barrel in a region outside of said fuel region, wherein said flow stabilizing member is disposed at positions midway between said two adjacent outlet nozzles to prevent said separate streams from colliding to prevent temperature fluctuations of said coolant. 5. An internal structure of a nuclear reactor according to claim 4 , wherein said flow stabilizing member is dimensioned so that a top end thereof is positioned at a height level within a range from a position midway between an upper surface of said upper core plate and a lowermost portion of said outlet of said outlet nozzle to a position lower than said lowermost portion of said outlet. claim 4 6. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel, and provided with a flow stabilizing member being lower than said outlet nozzles, said coolant flowing along at least two streams which collide toward said outlet nozzles, said member being supported on or above a portion of the upper core plate that is not perforated for fluid flow, disposed in the vicinity of a core barrel in a region outside of said fuel region, wherein said flow stabilizing member is disposed directly underneath a center portion of said outlet of said outlet nozzle and dimensioned so that a top end thereof is positioned at a height level within a range from a position midway between an upper surface of said upper core plate and a lowermost portion of said outlet of said outlet nozzle to a position lower than said lowermost portion of said outlet to thereby prevent said streams from colliding. 7. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a current of coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel with the current of coolant flow being separated into streams which collide as said fluid flows to said outlet nozzles, and provided with a flow stabilizing member being lower than one of said outlet nozzles, said member being constructed to impede fluid flow therethrough, disposed in the vicinity of a core barrel in a region outside of said fuel region and positioned to separate said streams thereby preventing the streams from colliding to suppress temperature fluctuations of said coolant flow. 8. An internal structure of a nuclear reactor according to claim 7 , wherein said flow stabilizing member is disposed beneath an outlet of said outlet nozzle. claim 7 9. An internal structure of a nuclear reactor according to claim 8 , wherein said flow stabilizing member is disposed directly underneath a center portion of said outlet of said outlet nozzle. claim 8 10. The internal structure of a nuclear reactor according to claim 9 wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 9 11. The internal structure of a nuclear reactor according to claim 8 wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 8 12. The internal structure of a nuclear reactor according to claim 7 wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 7 13. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel, said upper plenum being shaped to define several separate streams for said coolant which collide; and a flow stabilizing member being lower than said outlet nozzle, said member being constructed to impede fluid flow therethrough, disposed in the vicinity of a core barrel in a region outside of said fuel region, wherein said flow stabilizing member is disposed at positions midway between said two adjacent outlet nozzles to prevent said separate streams from colliding to prevent temperature fluctuations of said coolant. 14. An internal structure of a nuclear reactor according to claim 13 , wherein said flow stabilizing member is dimensioned so that a top end thereof is positioned at a height level within a range from a position midway between an upper surface of said upper core plate and a lowermost portion of said outlet of said outlet nozzle to a position lower than said lowermost portion of said outlet. claim 13 15. The internal structure of a nuclear reactor according to claim 14 wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 14 16. The internal structure of a nuclear reactor according to claim 13 wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 13 17. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel, and provided with a flow stabilizing member being lower than said outlet nozzles, said coolant flowing along at least two streams which collide toward said outlet nozzles, said member being constructed to impede fluid flow therethrough, disposed in the vicinity of a core barrel in a region outside of said fuel region, wherein said flow stabilizing member is disposed directly underneath a center portion of said outlet of said outlet nozzle and dimensioned so that a top end thereof is positioned at a height level within a range from a position midway between an upper surface of said upper core plate and a lowermost portion of said outlet of said outlet nozzle to a position lower than said lowermost portion of said outlet to thereby prevent said streams from colliding. 18. The internal structure of a nuclear reactor according to claim 17 wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 17 |
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claims | 1. A nuclear plant, comprising:a containment;a pressure relief line communicating with said containment;a throttle device and a Venturi scrubber connected in series in said pressure relief line, said Venturi scrubber being disposed in a vessel with a washing liquid;said Venturi scrubber and said throttle device being dimensioned to establish, in the event of a critical depressurization of an air/vapor mixture flowing in said pressure relief line and through said throttle device, a flow velocity of the air/vapor mixture of more than 150 m/s in the Venturi scrubber. 2. The nuclear plant according to claim 1, wherein said Venturi scrubber and said throttle device are dimensioned to establish a flow velocity through said Venturi scrubber of more than 200 m/s. 3. The nuclear plant according to claim 1, wherein said Venturi scrubber comprises a multiplicity of Venturi tubes having outlets, a comparatively large number of said Venturi tubes are disposed with the respective said outlets above an intended setpoint level of the scrubbing liquid, and a comparatively small number of said Venturi tubes are disposed with an outlet direction directed downward. 4. The nuclear plant according to claim 3, wherein up to approximately 10% of said Venturi tubes are disposed with the outlet direction directed downward. 5. The nuclear plant according to claim 1, wherein said Venturi scrubber comprises a plurality of Venturi tubes having a throat cross-sectional area and an inlet cross-section area for the scrubbing liquid, and a ratio of said throat cross-sectional area to said inlet area is less than 10:1. 6. The nuclear plant according to claim 5, wherein said ratio is approximately 3:1. 7. The nuclear plant according to claim 1, wherein said Venturi scrubber comprises a plurality of substantially round Venturi tubes with a throat width of less than about 80 mm. 8. The nuclear plant according to claim 7, wherein said throat width of said Venturi tubes is less than about 40 mm. 9. The nuclear plant according to claim 1, wherein said Venturi scrubber comprises a plurality of substantially flat Venturi tubes with a throat width of less than about 100 mm. 10. The nuclear plant according to claim 1, wherein said Venturi scrubber comprises a plurality of Venturi tubes with a height to throat width ratio of more than 5. 11. The nuclear plant according to claim 1, wherein said Venturi scrubber comprises a plurality of Venturi tubes with a height to throat width ratio of more than 10. 12. The nuclear plant according to claim 1, which further comprises a washing liquid reservoir connected to said vessel on a scrubbing liquid side thereof. 13. The nuclear plant according to claim 1, which further comprises a feedback line connecting a scrubbing liquid side of said vessel to an interior of said containment. 14. The nuclear plant according to claim 13, wherein said feedback line is connected via said pressure relief line to the interior of said containment. 15. The nuclear plant according to claim 14, wherein said vessel is disposed geodetically lying at least approximately 5 m higher than an exit point of said pressure relief line from said containment. 16. The nuclear plant according to claim 15, wherein said vessel is disposed at least 10 m above said exit point. 17. The nuclear plant according to claim 1, wherein the washing liquid in said vessel has a pH of at least 9. 18. The nuclear plant according to claim 1, which further comprises, following said Venturi scrubber in a flow direction, a molecular sieve coated with silver compounds. 19. The nuclear plant according to claim 1, wherein said throttle device is integrated into said vessel. 20. A method for depressurizing a nuclear plant according to claim 1, which comprises subjecting the Venturi scrubber to a flow velocity of the medium carried in the pressure relief line of more than 150 m/s. 21. The nuclear plant according to claim 20, which comprises setting the flow velocity to more than 200 m/s. |
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048141380 | summary | The invention relates to a method for repairing a nuclear reactor fuel assembly by replacing a fuel rod of the fuel assembly filled with nuclear fuel and retained in a force-locking manner in a gap formed in a lattice-like spacer by means of a spring disposed in the gap, and a replacement rod for performing the method. A method of this type is known from German Published, Non-Prosecuted Application No. DE-OS 26 35 501. In this known method, a defective and irradiated fuel rod filled with nuclear fuel is removed from the nuclear reactor fuel assembly and replaced with a new replacement rod filled with nuclear fuel, which is inserted with a fuel rod changing tool into the gap in the lattice-like spacer in the nuclear reactor fuel assembly in which the defective fuel rod was located. However, this method cannot be used if the spring located in that particular gap of the lattice-like spacer has broken off or no longer has adequate spring force. In that case, neither the fuel rod originally located in that gap nor a replacement rod can be securely retained in the gap of the spacer of the nuclear reactor fuel assembly. However, as a rule the gap of the spacer of the nuclear reactor fuel assembly in which the spring for the force-locking retention of a fuel rod has broken or become unusable cannot merely be left unoccupied, because in the nuclear reactor, the space for the fuel rod missing from the nuclear reactor fuel assembly is filled with water, which changes the moderating action of the water in the nuclear reactor upon the neutrons located there. Furthermore, the missing fuel rod causes a change in the speed of the water flowing as coolant through the nuclear reactor, so that oscillation of the fuel rods still located in the nuclear reactor fuel assembly and consequent further damage to this fuel assembly cannot be precluded. In order to utilize the still considerable burnup potential present in the irradiated fuel rods of a nuclear reactor fuel assembly having a broken spring and located in a gap of the spacer, it is possible to move all of the irradiated fuel rods from the nuclear reactor fuel assembly and shift them into a new fuel assembly skeleton, thereby forming another fuel assembly. The skeleton is substantially formed of new spacers as well as a head and a base or foot piece, which are firmly connected to one another by means of control removal tubes which engage gaps in the spacers. However, this method is very time-consuming and accordingly entails high repair costs. A further factor is waste disposal costs for the irradiated skeleton of the old nuclear reactor fuel assembly. It is accordingly an object of the invention to provide a method for repairing a nuclear reactor fuel assembly and a replacement rod for performing the method, which overcomes the hereinafore-mentioned disadvantages of the heretoforeknown methods and devices of this general type and which makes it simpler and less expensive to repair a nuclear reactor fuel assembly in which the spring for the force-locking retention of a fuel rod in a gap of the spacer is unusable. With the foregoing and other objects in view there is provided, in accordance with the invention, in a nuclear reactor fuel assembly having a fuel rod filled with nuclear fuel retained in a gap formed in a lattice-like spacer by means of a spring disposed in the gap, a method for repairing the fuel assembly, which comprises replacing the fuel rod with a replacement rod, and retaining the replacement rod in the gap of the spacer with a retaining spring. In accordance with another mode of the invention, there is provided a method which comprises placing the retaining spring in a corner of the gap. The repair costs for the fuel assembly remain approximately the same as in the prior art repair method because of the use of the replacement rod. Nevertheless, the nuclear reactor fuel assembly does not have a vacant space where the fuel rod replaced by the replacement rod was located. With the objects of the invention in view, in a nuclear reactor fuel assembly having a fuel rod filled with nuclear fuel retained in a gap formed in a lattice-like spacer by means of a spring disposed in the gap, there is also provided a replacement rod for replacing the fuel rod, comprising a cladding tube having a shell with an opening formed therein, a sliding body movable inside the cladding tube in two longitudinal directions of the cladding tube, a slotted link disposed on the sliding body, a retaining spring guided in the slotted link and extending outwardly through the opening formed in the shell, and a locking device associated with the sliding body for displacing the spring radially outwardly upon movement of the sliding body in one longitudinal direction of the cladding tube so as to retain the replacement rod in the gap formed in the spacer and for displacing the spring radially inwardly upon movement of the sliding body in the other longitudinal direction of the cladding tube so as to release the replacement rod from the gap formed in the spacer. In accordance with a concomitant feature of the invention, the cladding tube has a protruding locking shoulder on the inside thereof, and there is provided an actuating rod with an outer shell surface displaceable inside the cladding tube for moving the sliding body, the locking device being in the form of a tongue spring with a given thickness and length disposed on the outer shell surface of the actuating rod, the tongue spring having two ends extending in the longitudinal direction of the actuating rod, one of the ends of the tongue spring facing in the direction of movement of the sliding body being secured on the actuating rod for expulsion of the retaining spring and the other of the ends of the tongue spring being spaced from the outer shell surface of the actuating rod for gripping the protruding locking shoulder from behind, a clamping sheath with a given length disposed inside the cladding tube, a protruding stop shoulder for the clamping sheath disposed inside the cladding tube and spaced apart from the locking shoulder by a given distance in the direction of movement of the sliding body for expulsion of the retaining spring, the clamping sheath being coaxially displaceable in the longitudinal direction of the cladding tube between the locking shoulder and the stop shoulder, the clamping sheath having an inner shell surface protruding beyond the locking shoulder in radial direction and being radially spaced apart from the actuating rod by a distance greater than the given thickness of the tongue spring, and the given distance between the locking shoulder and the stop shoulder being greater than the sum of the given length of the clamping sheath and the given length of the tongue spring in the longitudinal direction of the actuating rod. 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 method for repairing a nuclear reactor fuel assembly and a replacement rod for performing the method, 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. |
abstract | The present invention provides a gray rod control assembly for a nuclear reactor. The gray rod control assembly includes a spider assembly having a plurality of radial extending flukes and a plurality of gray rod assemblies coupled to the flukes of the spider assembly. Each of the gray rod assemblies includes an elongated tubular member, a first end plug, a second end plug, and a neutron absorber. The neutron absorber includes a matrix of refractory metal fabricated to be porous into which a metal or metal alloy is infused. The neutron absorber is distributed among a plurality of the gray rod assemblies. |
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claims | 1. A nuclear medicine imaging system comprising:a. a gantry,b. a detector attached to said gantry, having a gamma camera system and a collimator slot,c. a patient handling system, andd. a collimator server integrated into the patient handling system, holding a number of collimators,e. wherein the collimator is configured to:i. mount collimators into the collimator slot,ii. remove collimators from the collimator slot, andiii. store collimators. 2. The nuclear medicine imaging system of claim 1, wherein the collimator server further comprises:a. a number of drawers,b. each of the number of drawers being capable of holding one collimator, andc. each of the number of drawers having a front, each front capable of being opened. 3. The nuclear medicine imaging system of claim 1, further comprising:a. a collimator cart, includingi. a number of drawers,ii. each of the number of drawers being capable of holding one collimator, andiii. each of the number of drawers having a front, each front capable of being opened. 4. A method of mounting a collimator onto a detector of a nuclear medicine imaging system, comprising:a. aligning a collimator slot of a detector with a drawer of a collimator server that is integrated into a patient handling system,b. opening the drawer of the collimator server,c. lifting the collimator from the drawer of the collimator server to the collimator slot of the detector, andd. clamping the collimator into the collimator slot of the detector. 5. A method of removing a collimator from a detector of a nuclear medicine imaging system, comprising:a. aligning a collimator slot of a detector with a drawer of a collimator server that is integrated into a patient handling system,b. opening the drawer of the collimator server,c. unclamping the collimator from the collimator slot of the detector,d. lifting the collimator from the collimator slot of the detector drawer of the collimator server, ande. closing the drawer of the collimator server. 6. A method of mounting a collimator from a portable collimator cart having a plurality of vertically stacked drawers onto a detector of a nuclear medicine imaging system having a gantry on which said detector is supported, comprising:a. providing a collimator server integrated into a patient handling system of said nuclear medical imaging system,b. docking said collimator cart onto a docking mechanism of the nuclear medicine imaging system, wherein docking the cart positions the cart in lateral alignment with said detector such that said drawers are positioned to open in a direction toward said gantry,c. vertically aligning a collimator slot of a detector with a drawer of said collimator cart,d. opening the drawer of the collimator cart,e. lifting the collimator from the drawer of the collimator cart to the collimator slot of the detector, andf. clamping the collimator into the collimator slot of the detector. 7. The nuclear medicine imaging system of claim 3, wherein said collimator cart further comprises a plurality of wheels. 8. The nuclear medicine imaging system of claim 7, further comprising a docking aligner that aligns said collimator cart with said detector by forcing said wheels into a fixed position with respect to said gantry. |
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description | The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. By way of further background, and with reference initially to FIG. 1, in a capacitive circuit, the amount of power absorbed by a field developed within a dielectric is equal to the amount of the power returned to the circuit when the field collapses. Further, a capacitor will absorb power for one half of an applied AC cycle and return the power to the circuit during the next half of the cycle. By way of example, a DC charged capacitor is limited, because even by placing components in a fashion that orientates an electric field for generating thrust in one direction, no mater the relative polarity, a DC charged capacitive device can not operate as well as an AC powered capacitor because it can not make use of charging rates of change in voltage as easily as can an AC powered device. However, a pulsing DC is for all intents and purposes a regular direct current that will charge the capacitor and unless the capacitor dissipates that energy before the next pulse occurs, the capacitor will still have a residual charge that will remain until the next pulse. It has been discovered that a preferred effect occurs when the capacitor is initially charging, not when it is constantly charged as in a typical DC system. The charging time is associated with a drift velocity of charges. The DC device of the present invention operates with a constant charge rate that will, as the capacitor is increased in power, reach a saturation level of the capacitor and begin to create a leakage current. The leakage current will continue to build up until the device suffers a dielectric breakdown where arcing occurs, thus limiting the maximum energy that can be induced unto a DC device, significantly more than in a typical AC powered device. While an AC powered device can experience similar effects as does a DC powered device, its reversal of polarity and rate of cycles can take advantage of the superior thrust generated at the first few micro seconds of the charging time. This has the effect of generating more thrust with the same amount of energy input. As a result, higher power input levels can be reached without exceeding the rated power of the capacitor. The cycles reverse themselves before the maximum power rating is reached and a relative reversed polarity state compared to the previous cycle is induced. Since an AC cycle first charges the capacitor and then discharges it, followed by a relative polarity reversal, the capacitor can take full advantage of the best charging cycle frequency to power ratio and can thus generate a superior thrust effect. Charging and discharging time in a DC circuit is illustrated, by way of example, with reference to FIGS. 2 and 3. As illustrated, the charging of the capacitor is rapid at first, but slows down considerably as it reaches a full charge. The same holds true for the discharge rate. Reactance causes the slowing down in both cases, with the charges repelling each other during the charging and discharging process. Reactance is the resistance that charged particles experience as the capacitor charges. FIGS. 4 and 5 illustrate relationships of reactance Xc caused by capacitance and frequency in an AC powered capacitor, respectively. As frequency increases capacitance decreases. As frequency decreases, reactance increases without changing the structure of the capacitor. If we were to increase capacitance by changing the structure of the capacitor, and if we increase capacitance, the reactance decreases. If we decrease capacitance, reactance increases. As a result of the arrangement of capacitor plates, a polarity reversal has the same effect on both the positive and negative cycle and thus generates thrust at both sides of the cycle. With reference to FIG. 6, power being absorbed and returned to the circuit is illustrated within shaded areas under a positive and negative voltage cycle. The shaded areas above and below the baseline represent power that is absorbed by the capacitor. The solid curve line represents a current level rising and dropping as the AC cycles reach their peak to peak values. The dashed curve line represents voltage. Values for both the current and the voltage curve lines are dependent on a structure of the capacitor and a form of the power input. The amount of current that goes through a capacitor depends on the potential difference and the properties of that capacitor. However, in a capacitor, at any preselected AC potential difference, the current is greater at higher frequencies. As a result, an AC system, especially a capacitive as will herein be described in further detail, can use the charging time to its advantage as well as the polarity reversal cycle. Be reminded that the reversal of polarity in a cycle is always a positive energy input. Thus, positive and negative polarity will have the same effect, and can both take advantage of the above charging time effect. Also in a DC capacitor, the use of materials having a relatively low dielectric constant, the degree to which a material can resist flow of an electric charge, is effective in creating thrust because it is such a material through which currents will flow. In a DC system, this has the effect of charging the capacitor, while on the other hand, an AC current can travel through a material that normally DC could not, given the same amount of capacitance to hold the voltage, because of the charging time frequency advantage. Further, while a DC powered capacitor must use low rated dielectrics which limit the total capacitance, the AC powered devices can use high rated dielectrics and thus allow for extremely high rated capacitors to be made that can thus have even higher power ratings. This added to the charging time advantages results in a higher thrust without a significant increase in size of such capacitors, and thus devices. Since the AC device uses the energy more efficiently by generating thrust in the first moments of the charging cycle, then the same power (e.g. watts) yields more force. As illustrated with reference to FIG. 7, a device 10 of the present invention provides an engine 12, by way of example, for a vehicle 14 when employing the above described techniques, with such an engine being self-contained and carrying its own environment. Thus, the engine 14 can operate within the vehicle 14 without the need for direct exposure to the surrounding environment 16 through which the vehicle is moving. As a result, since the device 10 employing field propulsion can propel itself without exhausting any matter in the opposite direction of vehicle motion, it can propel itself without being exposed to the environment 16 through which it is moving. Such self-containment serves multiple purposes. First it makes the device 10 of the present invention safer by allowing the device to have a casing or housing 18 for operation of the device with minimum danger to users. Second the housing 18 is useful because it can be made into an RF or electromagnetic shield. Third, since the device 10 is electrical in nature, the housing 18 provides protection for the device against foreign objects or grounding contacts that could cause short circuits. The housing 18 also provides a convenient means from which to transfer propulsive forces created by the device 10 to the vehicle 14 such as a spacecraft, as herein described by way of example, automotive vehicles, marine vehicles, and aircraft. With reference to FIG. 8, one embodiment of the device 10 includes a plurality of engine cells 22 arranged about an axis 24 of the device. In the embodiment herein described, by way of example, the plurality of cells 22 are juxtaposed radially outward from the axis 24 and longitudinally along the axis. As illustrated with reference to FIG. 9, a preselected number of cells 22 will be arranged to meet the need for providing desired forces to be delivered, the more cells, the more power, the more thrust. As illustrated with reference to FIG. 10, the radial arrangement of cells 22 form a plate 26. Thus, with the formation of the plate 26, as desired, stacking of the plates will provide the desired size. Further, and as illustrated with reference to FIG. 11, neighboring plates will be supplied with opposing positive and negative charge, with the thrust directed toward the positive charge. As further illustrated with reference to FIG. 11, and again to FIGS. 8 and 9, the cells 22 are assembled circumferentially around and longitudinally along a core 28, which core extend to and, if desirable, beyond top and bottom surfaces 30, 32 of a cell assembly 34 formed therefrom. With the core 28, formed from a high dielectric material, a connection to a structure of the vehicle 14 can be made. The core material should preferably be made from a relatively strong material with a high dielectric constant, for facilitating construction of the device 10 and transferring of forces generated by the engine cells 22. As an alternative, and as earlier described with reference to FIG. 7, the device 10 is attached via the housing 18. Each cell 22, in a preferred embodiment herein described by way of example, includes a high dielectric 36 sandwiched between a conductive material forming an electrode 38 and a lower dielectric 40. Generally, the electrodes 38 will be formed from a copper sheet material, aluminum sheet material, and the like. The high dielectric 36 is preferably has similar dielectric properties as the core 28, for generally preventing current flow therethrough. While the lower dielectric 40 includes dielectric properties that permit current flow, and thus a field path therethrough. Preferably, the cell 22 is positioned with the electrode 38 placed to form a top of each cell, with the high dielectric 36 having a larger thickness than the lower dielectric 40, to further discourage an electric field path through the high dielectric, as herein illustrated. With reference again to FIGS. 9 and 11, each neighboring cell 22 is separated by a lower dielectric forming a channel 42. The channel 42 fills a gap between the cells 22 and functions as a circumferential spacer therebetween. Preferably, the material forming the channel 42 has similar dielectric properties and the lower dielectric 40 forming a part of the cell 22. In this way, the channel 42 and the lower dielectric 40 provide an electric field path shaping that is further formed around the high dielectric material 36, thus providing the desirable non-linear path for producing thrust. It is also preferred that the material used to form the housing 18 has similar dielectric properties as does the high dielectric 36. A bridge power conduit 44 is further provided at a plurality of locations within the channel 42 for carrying electrically conductive wire 46 from cell to cell, as illustrated with reference again to FIGS. 9 and 10. Material filling the conduit preferably includes similar dielectric properties as the high dielectric 36. The electrical wire 46 is connected to the electrodes 38 of cells 22 within one plate 26, as illustrated with reference again to FIG. 9, and alternatively by way of example, with reference to FIGS. 12 and 13. Preferably, the connection of the wire 46 is made at a generally central location of the electrode 38, with such connection of the wire 46 to each cell 22 within a plate 26 distributing energy evenly between all the electrodes in that plate. The electrical wire 46 is carried through a power input conduit 48 within each cell 22. In an alternate embodiment, and as illustrated with reference to FIG. 14, a staggered arrangement of plates 26 is provided, which arrangement serves to further increase non-linearity of the electric field, and therefore thrust. As a result, the device 10 of the present invention, generates a useful motive force using non-linear AC or DC electric fields applied between at least two electrodes divided by a dielectric. As earlier described, it is intended that the device 10 be preferably used with AC generated electric fields to take advantage of the charging time phenomenon to extract the maximum amount of force from the input energy field. Further, the materials that make up elements of the device 10 also serve the purpose of transferring a mechanical force of the device to a support 20 or directly to the vehicle 14, as illustrated again with reference to FIG. 7. With the formation of non-linear fields created by the above described structure for the device 10, the device can be used on the outside of a vehicle to create a propulsive force on the entire mass of the vehicle. The combined use of the internal engines 12 in combination with outer propulsion effect will produce a more efficient control of the vehicle 14. Further, the use of a vehicle skin 50 or outer hull for carrying the electrodes on a dielectric allows the entire vehicle to be used to create thrust. As herein described, by way of example, the use of the internal engine 14 allows the device 10 to induce lines of force to collapse towards an area where the engine is positioned, thus increasing the non-linearity of the field. By way of further detail regarding the preferred embodiment herein described by way of example, and with reference again to FIG. 11, the channels 42 and the lower dielectric 40 of the cell 22, as well as the high dielectric 36 improve performance of a set of neighboring plates 26 by increasing the amount of energy being used in a device and allowing that energy to generate a respective thrust without any increase in size. The channels 42 also increase the field effect by allowing the lines of force to be in a generally parallel arrangement, which, as is appreciated by one of skill in the art, increases the Lorentz force effect and therefore the field propulsion effect. The Lorentz force has been observed through experimentation as an important factor in the thrust generating phenomenon. The more parallel the lines of force are relative to each other, the larger the force effect for a given energy input. The Lorentz force is a recognized phenomenon that works partially by the forces generated between drift velocities of charges. The geometrical shape of the cell assembly 34, by way of example, cylindrical, circular, square, and the like, is not as important as what is done with the shape to optimize the drift velocity of the charges or energy input. The segmentation of the cells 22 for the device 10 as herein described, allows for control of the field by the variation of the potential of the cells and plates themselves and its intensity between the cells and plates, which is accomplished by an electronic control. Further, the routing of the wire 46 providing power lines to the respective plate 26 through the high dielectric material 36 serves the useful purpose of keeping arcing events to a minimum by distributing the energy over the plates and not at any one single wire point location. This prevents arcing at the leads and so maintains the needed power balance. Furthermore, the multi-port input to a plate 26, as described earlier with reference to FIG. 12, and shared connection of input, as illustrated with reference again to FIGS. 9 and 12, by way of example, are used to more equally distribute the energy. As earlier described with reference to FIG. 11, the dielectric material in the channel 42 is preferably of a relatively lower dielectric constant than the dielectric 36 on which the electrode 38 is placed to allow for a non-linear relationship to form between plates 26 and their respective electrodes. Further, there is a layer of dielectric material between the cells 22 created by the lower dielectric 40 of lower dielectric strength as for material in the channels 42. This allows the desirable formation of the non-linearity in the field. The plates 26 can be arranged so that the channels 42 are aligned with the next set of plates as earlier described with reference to FIG. 11, or staggered to cause a larger non-linearity effect, as earlier described with reference to FIG. 14. By the use of an electrical power source 52, constant DC and preferably pulsing DC, will provide a useful force generated by the field propulsion device 10 of the present invention, herein described. Further, as earlier described with reference to FIG. 6, taking advantage of the initial power increase within an AC supply of power provides yet further thrust from the device 10. With reference again to FIG. 7, for an alternate embodiment of the device 10, as herein described, it is expected that the teachings of the present invention will encourage use of a nose section 54 of the vehicle 14 to be segmented into sections as herein described for the device 10. An vehicle inner wall 56 will be made into a RF or electromagnetic shield without disturbing the thrust generating effect. The overall structure of the vehicle 14, like the cell 22, is made of a dielectric material on which electrode are positioned and through which the power is routed. The vehicle 14 will contain a main machinery bay 58 for housing key components. The outside walls of the bay are made from a dielectric material. The bottom wall 60 of the vehicle will be formed as yet another electrode, with the result that vehicle structure includes electrodes and dielectrics to generate thrust by the use of the field propulsion phenomenon, herein described for the present invention. Such a vehicle can then operate in any dielectric environment such as air or the vacuum of space. The internal engine 12 earlier described can then be used in conjunction with or as separate propulsion systems. The internal engine 14, unlike the engine formed form the structure of the vehicle can generate thrust in any environment because it is shielded from the environment through which the vehicle 12 is traveling. As illustrated with reference again to FIG. 7, an hydraulic system 62 is one example of a means of vectoring the engine 12 side to side to maneuver the vehicle 12. For the device 10 herein described with reference to FIG. 11, by way of example, generated a thrust in a direction as indicated by arrow 64. In contrast, the vehicle skin propulsion can provide a thrust vector by charging a section of its skin at higher potential relative to the other sections and thus generate more thrust from that section than from others. It is to be understood that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. |
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claims | 1. A transmission source loading apparatus for an imaging system utilizing a transmission source, comprising:a storage container for storing the transmission source; anda translation device, the translation device being adapted for advancing the transmission source from the storage container into a holder device for use of the imaging system, wherein the advancement of the transmission source is caused by a linear movement of the translation device without any rotational movement thereof. 2. The apparatus of claim 1, wherein an access door is located proximate to the storage container, the translation device being adapted for advancing at least a first portion of the transmission source into the holder device through an access port exposed by displacing the access door. 3. The apparatus of claim 2, wherein the translation device further includes:a drive assembly; anda source gripping device for retaining at least a second portion of the transmission source, the drive assembly being adapted for advancing the source gripping device to a loading point proximate to the access port. 4. The apparatus of claim 3, wherein the source gripping device includes:a housing;a first magnet portion fixed to the housing, the first magnet portion having a first magnetic holding force; andan electromagnet portion fixed to the housing, the electromagnet portion producing a second magnetic holding force when activated. 5. The apparatus of claim 4, wherein the holder device includes:a housing;a source receiving portion disposed in the housing; anda third magnet portion fixed to the housing, the third magnetic portion having a third magnetic holding force. 6. The apparatus of claim 5, wherein the third magnetic holding force is greater than the first magnetic holding force. 7. The apparatus of claim 6, wherein the holder device and source gripping device are adapted for alignment at the loading point such that when the at least first portion of the transmission source is advanced into the source receiving portion of the holder device, the third magnetic holding force being greater than the first magnetic holding force, the transmission source is retained by the source receiving portion of the holder device. 8. The apparatus of claim 5, wherein the first magnetic holding force and the second magnetic holding force combined are greater than the third magnetic holding force. 9. The apparatus of claim 8, wherein the holder device and source gripping device are adapted for alignment at the loading point such that when the transmission source is advanced into the source receiving portion of the holder device, the first magnetic holding force and the second magnetic holding force combined being greater than the third magnetic holding force, the transmission source is retained by the source gripping device. 10. The apparatus of claim 3, wherein the drive assembly includes:a carriage mounted on a lead screw, the carriage controllably translated along the lead screw by a control portion. 11. The apparatus of claim 10, wherein the control portion includes a servo motor. 12. The apparatus of claim 10, wherein the source gripping device is mounted on the carriage. 13. The apparatus of claim 3, wherein the source gripping device and at least a portion of the drive assembly are housed within the storage container. 14. The apparatus of claim 2, wherein the access door is coupled to a door drive assembly, the door drive assembly being adapted for displacing the access door to expose the access port. 15. The apparatus of claim 14, wherein the door drive assembly includes:a door mount fixed to the access door;a track assembly; anda control device being adapted for controllably displacing the door mounted along the track assembly. 16. The apparatus of claim 15, wherein the control device includes a pulley timing belt system coupled to the door mount for controllably displacing the access door. 17. The apparatus of claim 1, wherein the translation device is adapted for advancing the transmission source from the storage container into the holder device along a single axis of motion. 18. The apparatus of claim 1, wherein at least a portion of the translation device is housed within the storage container when the transmission source is in storage. 19. The apparatus of claim 1, wherein the translation device is engaged with the transmission source when the transmission source is in storage. 20. A transmission source loading apparatus for an imaging system utilizing a transmission source, comprising:means for storing the transmission source; andmeans for advancing the transmission source from the storage means into a means for rotating the transmission source for use of the imaging system, wherein the advancement of the transmission source is caused by a linear movement of the advancing means without any rotational movement thereof. 21. The apparatus of claim 20, wherein an access door is located proximate to the storage means, the means for advancing the transmission source being adapted for advancing at least a first portion of the transmission source into the means for rotating through an access port exposed by displacing the access door. 22. The apparatus of claim 20, wherein the means for advancing the transmission source is adapted for advancing the transmission source from the storage means into the holder means along a single axis of motion. 23. The apparatus of claim 20, wherein at least a portion of the advancing means is housed within the storage means when the transmission source is in storage. 24. The apparatus of claim 20, wherein the advancing means is engaged with the transmission source when the transmission source is in storage. |
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056087683 | claims | 1. An end plug for a fuel rod of a nuclear reactor fuel bundle assembly including upper and lower tie plates, the end plug comprising: an upper portion constructed of a first alloy material and including an exterior fuel rod receiving surface and a rapped hole in a lower end thereof; and a removable lower portion constructed of a second alloy material and including upper and lower threaded sections, said upper threaded section receivable within said tapped hole and said lower threaded section receivable within a correspondingly threaded hole in the lower tie plate. an upper portion constructed of a first alloy material and including an exterior partial length fuel rod receiving surface and a tapped hole in a lower end thereof; and a lower portion constructed of a second alloy material and including upper and lower threaded sections, said upper threaded section receivable within said tapped hole and said lower threaded section receivable within a tapped hole in the lower tie plate. a) providing an end plug for a lower end of said at least one partial length fuel rod comprising an upper portion constructed of a first alloy material and including an exterior fuel rod receiving surface and a tapped hole in a lower end thereof; and a lower portion constructed of a second alloy material and including upper and lower threaded sections, said upper threaded section receivable within said tapped hole and said lower threaded section receivable within a correspondingly threaded hole in the lower tie plate; b) rotating the fuel rod in a first direction to separate said fuel rod and the fuel rod end plug from the lower tie plate. 2. The end plug of claim 1 wherein said first alloy material is Zircaloy. 3. The end plug of claim 1 wherein said second alloy material is stainless steel. 4. The end plug of claim 2 wherein said second alloy material is stainless steel. 5. The end plug of claim 1 wherein said second material is harder than said first material. 6. The end plug of claim 1 wherein said upper and lower threaded sections are threaded in opposite directions. 7. In a fuel bundle assembly for a nuclear reactor having a plurality of fuel rods including a plurality of full length fuel rods extending between upper and lower tie plates and at least one partial length fuel rod extending between the lower tie plate and a spacer located between said upper and lower tie plates, the improvement comprising an end plug for at least said partial length fuel rod, said end plug secured between said partial length fuel rod and said lower tie plate, said end plug comprising: 8. The fuel bundle assembly of claim 7 wherein said first alloy material is Zircaloy. 9. The fuel bundle assembly of claim 7 wherein said second alloy material is stainless steel. 10. The fuel bundle assembly of claim 8 wherein said second alloy material is stainless steel. 11. The fuel bundle assembly of claim 7 wherein said second material is harder than said first material. 12. The fuel bundle assembly of claim 7 wherein said upper and lower threaded sections are threaded in opposite directions. 13. The fuel bundle assembly of claim 7 wherein respective ones of said end plugs are provided for said plurality of full length rods. 14. A method for removing a fuel rod from a fuel rod bundle assembly in a nuclear reactor, wherein the fuel rod bundle assembly includes a plurality of fuel rods including full length fuel rods extending between upper and lower tie plates and at least one partial length fuel rod extending upwardly from said lower tie plate, the method comprising the steps of: 15. The method of claim 14 wherein said upper and lower sections are threaded in opposite directions and wherein the method comprises an optional step of rotating the fuel rod in a second opposite direction to separate the fuel rod and the upper portion of the end plug from the lower portion of the end plug, leaving the latter in the lower tie plate. 16. The method of claim 14 wherein said first alloy material is Zircaloy. 17. The method of claim 14 wherein said second alloy material is stainless steel. 18. The method of claim 16 wherein said second alloy material is stainless steel. 19. The method of claim 14 wherein said second material is harder than said first material. 20. The method of claim 14 and including providing a respective one of said end plugs for each of said full length fuel rods. |
claims | 1. A passive cooling system of a nuclear power plant, the passive cooling system comprising:a steam generator in which steam is generated by heat exchange with a primary coolant system including a nuclear reactor;a cooling water storage tank storing cooling water therein;a water cooling heat exchanger disposed in the cooling water storage tank;an air cooling heat exchanger connected to the steam generator in parallel with the water cooling heat exchanger,wherein the air cooling heat exchanger is located outside of the cooling water storage tank;a divergence valve controllable to divert steam from the steam generator into both the water cooling heat exchanger and the air cooling heat exchanger,wherein the divergence valve controls the flow of steam generated in the steam generator which passes through the water cooling heat exchanger to be condensed by heat exchange with the cooling water,wherein the divergence valve controls the flow of steam generated in the steam generator which passes through the air cooling heat exchanger to be condensed by heat exchange with ambient air, andwherein the divergence valve includes an inlet, a first outlet, and a second outlet;a first pipe connecting an upper portion of the steam generator and the inlet of the divergence valve,wherein the first pipe allows steam generated in the steam generator to flow from the steam generator to the divergence valve;a second pipe connecting the first outlet of the divergence valve and an inlet of the water cooling heat exchanger,wherein the second pipe allows steam generated in the steam generator to flow from the first outlet of the divergence valve to the water cooling heat exchanger;a third pipe connecting the second outlet of the divergence valve and an inlet of the air cooling heat exchanger,wherein the third pipe allows steam generated in the steam generator to flow from the second outlet of the divergence valve to the air cooling heat exchanger;a fourth pipe connected to each of an outlet of the water cooling heat exchanger, an outlet of the air cooling heat exchanger, and a lower portion inlet of the steam generator,wherein the fourth pipe allows condensed steam to flow from the water cooling heat exchanger to the lower portion inlet of the steam generator,wherein the fourth pipe allows the condensed steam from the water cooling heat exchanger to be introduced in a liquid water state into the lower portion inlet of the steam generator,wherein the fourth pipe allows condensed steam to flow from the air cooling heat exchanger to the lower portion inlet of the steam generator, andwherein the fourth pipe allows the condensed steam from the air cooling heat exchanger to be introduced in a liquid water state into the lower portion inlet of the steam generator;a first open/close valve disposed in the second pipe,wherein the first open/close valve controls the flow of the steam passing through the second pipe;a second open/close valve disposed in the third pipe,wherein the second open/close valve controls the flow of the steam passing through the third pipe; anda cooling tower,wherein each of the cooling water storage tank, the water cooling heat exchanger, and the air cooling heat exchanger are located in the cooling tower. 2. The passive cooling system according to claim 1, wherein the water cooling heat exchanger and the air cooling heat exchanger are positioned above the steam generator such that the cooling water and the steam naturally circulate by gravity. 3. The passive cooling system according to claim 1, wherein the cooling tower having an air inlet in a lower portion thereof. |
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summary | ||
048658030 | abstract | A pressurized gas discharge system for the safety containment of a nuclear reactor includes a conduit structure connected to the containment and consisting of a plurality of modular conduit units which are flanged together end-to-end, each having flanged side openings with filter frame members including stainless steel fiber filter packs flanged thereto in end-to-end relationship. The filter packs extend fully across the frame members and have their circumferential edges clamped between the flanges of adjacent frame members so that in the clamped areas the filter packs are reduced in thickness to a fraction of their original thickness, the flanges having U-shaped members disposed on their faces such that the legs of the U-shaped member project toward the adjacent flange and provide two seal strips with the edges of the filter packs compressed therebetween. |
046541845 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention pertains to optimizing the magnetic field utilization factor, .beta., for toroidally confined plasmas such as those found in tokamak devices. Referring now to FIG. 1a, a tokamak plasma 10 is contained within an evacuated conductive shell or containment vessel 12. A vacuum region 14 is located between the outer plasma and inner containment vessel surfaces, respectively. A line 16 indicates the vertical centerline of the toroidal containment chamber 12. With reference to FIGS. 1a, 1b, the present invention provides increased magnetic field utilization factor, .beta., (averaged over the total plasma volume) by indenting the inboard side 11 of the poloidal minor cross section of tokamak plasma 10. As can be seen in FIG. 1, this identation deforms a previously circular or Dee-shaped plasma into a bean shape. In FIG. 1 aspect ratio is defined as R/a, the ratio of toroidal radius to poloidal radius; elongation of the plasma as b/a; and indentation as d/2a. The particular bean shape shown is for particular values: R/a=4.0, b/a=1.386, and d/2a=0.304. As will be shown later, this value of d/2a corresponds to the critical value for that aspect ratio and the plasma profiles defined in FIGS. 3a-3c. According to the present invention, bean shapes can exhibit strong local magnetic shear and short connection lengths and can, under certain modest conditions, make accessible the second region of stability against ballooning modes. Given the relation B=.gradient..phi..times..gradient..psi.+R.sub.o g.gradient..phi..ident..gradient..gamma..times..gradient..psi., J.times.B=.gradient.p, and .gradient..times.B=J, the Grad-Shafranov equation takes the form EQU .gradient..multidot.x.sup.-2 .gradient..psi.=J.multidot..gradient..phi.=-(p'+R.sub.o.sup.2 gg'/x.sup.2). (2) The poloidal flux within a surface of constant .psi. is 2.pi..psi., x is the major radius, .phi. is the azimuthal angle in the cylindrical coordinates (x, .phi., z), and primes denote differentiation with respect to .psi.. Equation (2) is solved by use of a flux coordinate code [J. DeLucia, S. C. Jardin, and A. M. M. Todd, J. Comput, Phys. 37, 183 (1980)] in the fixed-boundary mode, specifying the shape of the plasma boundary. The shape was given by the parametric "bean" equations: EQU x=x+.rho. cos .gamma., z=E.rho. sin .gamma., (3) where .rho.=A(1+B cost), .gamma.=C sint, and 0.ltoreq.t.ltoreq.2.pi. so that -C.ltoreq..gamma..ltoreq.C. Given A, B, C, and E the aspect ratio is fixed by the choice of x. The bean-shape of FIG. 1 is obtained by setting C=97.degree., and E=0.895, resulting in R/a=4.0, b/a=1.386, and d/2a=0.304. The indentation parameter, d/2a, is adjusted in part by changing C. The values of these parameters can be chosen to simulate the shapes a plasma will attain for a particular experiment. BALLONING STABILITY THEORY Ballooning Modes and Local Shear An important feature of conventionally shaped tokamak plasmas with circular or nearly circular cross sections is the beneficial averaged magnetic well which is formed as the result of the equilibrium shift of the magnetic axis. In a bean-shaped plasma, even at low pressure, a line or force spends most of its life at values of major radius smaller than the magnetic axis major radius. Because d1.about.xd.phi. and B.multidot.1/x, bean-shaping can easily make U.ident. d1/B smaller on the outer surfaces than on the magnetic axis. Together with finite shear, this feature tends to stabilize interchange modes which are constrained to be localized within a surface and constant along a field line. If this last constraint is relaxed, the plasma may be susceptible to ballooning where the perturbation can adjust itself to be large where the well is weak or nonexistent and to be small elsewhere. If the stabilizing effect of the magnetic field tension can be overcome by such a perturbation, then the plasma becomes unstable. These effects are contained in the ballooning equation [described in Dobrott D., Nelson, D. B., Greene, J. M., Glasser, A. H., Chance, and M. S., Frieman, E. A., Phys. Rev. Lett. 39 (1977) 943 and J. W. Connor, R. J. Hastie, and J. B. Taylor, Phys. Rev. Lett 40 (1978) 396]: ##EQU2## The first term in equation 4 represents the field tension, the second the potentially destabilizing combination of pressure gradient and magnetic curvature, and the third term stems from fluid inertia. A detailed study of this mode shows that the connection length and the local shear play important roles, Greene, J. M. and Chance, M. S., Nucl. Fusion 21 (1981) 453. As set forth in Green, J. M. and Johnson, J. L., Phys. Fluids 10 (1968) 729, the local shear can be written as ##EQU3## so that the local shear, S, is composed of an averaged global shear, q'(.psi.), and a residual oscillatory part. The solution of this equation is discussed in Dobrott, D., et al., and Connor, J. W., et al. cited earlier. In a conventional tokamak the residual part of the local shear S can be negative on the outer side (24 in FIG. 1) of the plasma major radius where the poloidal field is usually the strongest. It can, in fact, be so negative that S can vanish there, as shown in FIG. 2a which shows contours of equal shear for a tokamak plasma. This condition promotes ballooning instabilities because the vanishing of S is the condition that surfaces containing both B and .gradient..psi. exist and, thus, the local interchange of magnetic field lines can be most easily realized there. This phenomenon is difficult to prevent in the conventional tokamak. However, a strong outward shift of the magnetic axis can further strengthen the poloidal magnetic field on the outside and cause the vanishing points of S to move away from the destabilizing region. This shift may be realized by increasing the pressure, but the onset of the instability usually occurs before the stabilization due to local shear and/or shortened connection length takes place. Another route to stability, exploited here, is to indent the plasma at the inner major radius so that the effective shift of the axis is present even at low .beta.. Further increase of the pressure enhances the shift even more, then renders the plasma immune to the instability. Contours of constant local shear in the neighborhood of S=0 are shown in FIG. 2a for a moderately indented low-theoretically modelled plasma. There the local shear is zero or weak in the outer region of the plasma. Increasing the pressure at this indentation causes instability at about .beta..about.2.6%. A stronger indentation as shown in FIG. 2b causes the S=0 contour to move further out. In this case, even though the shear is still weak at low .beta. [FIG. 2(b)], an increase in pressure shown in FIG. 2(c) strengthens the local shear at large major radius, preserving stability by a self-healing process. Stabilization due to the shortened connection length of an indented plasma is also effective here. The strong poloidal field at the outside of the torus due to the indentation and finite pressure causes the magnetic field lines to move rapidly through the bad curvature region, spending longer at the tips of the bean where the normal curvature is favorable. As shown in FIG. 2d, there is a reduction of the dangerous region where the normal curvature is negative. Indentation and Accessibility to Very High-.beta.: The scenario for the application for this invention is depicted schematically in FIG. 4, which shows stable and unstable regions in a .beta..sub.av versus indentation diagram. In a conventional tokamak--one in which the indentation is low or non-existent--a plasma will remain stable to ballooning modes provided the beta lies below the threshold of the instability, curve A. At higher .beta. there is another threshold, curve B, above which the plasma can be stable again. This regime is generally called the second region of stability. The unstable region provides a barrier against operating a conventional tokamak at high beta. However, this barrier can be circumnavigated if the plasma is indented sufficiently to a critical indentation such that curves A and B intersect at point C in the figure. Starting at that value of the indentation, we see that accessibility to the second region of stability is achieved. Another way of looking at point C, is that this represents the point beyond which no ideal ballooning modes exist. Also, as can clearly be seen from FIG. 4, the first and second regions join for d/2a larger than the critical value. A possible regime of tokamak operation could be at point D. As a specific example, a study of the effect of bean-shaping has been carried out by examining, using numerical solutions to the aforementioned ballooning equation, the stability of a class of equilibria whose plasma surface shape in the poloidal cross section is parametrized by the formula in equation (3) EQU x(t)=x+.rho. cos .gamma., EQU z(t)=E.rho. sin .gamma., where .rho.=A(1+B cost), .gamma.=C sint, and 0.ltoreq.t.ltoreq.2.pi.. An example of this shape is given in FIG. 1 with A=1, B=0.6, C=97.degree., and E=0.895. The fixed boundary solutions of the Grad-Shafranov equation are computed from a flux-coordinate code operating in the mode in which we fix the safety factor, q(.psi.) and pressure profile p(.psi.). These are taken to be ##EQU4## and EQU p(y)=p.sub.o (1-y.sup.2).sup.2, (7) where 0.ltoreq.i.ltoreq.3 and y=.psi./.DELTA..psi., 2.pi..DELTA..psi. being the poloidal flux within the plasma. The coefficients q.sub.i are specified for this example such that q(0)=1.03, q(1)=4.2, q'(0)=0.84, q'(1)=9.0. The profiles for saftey factor, toroidal field, and pressure are shown in FIGS. 3a-3c respectively. Sequences of flux-conserving equilibria at fixed values of indentation are generated by varying the parameter p.sub.o. Each of these equilibria is examined for ballooning stability by solving Eq. (4). FIG. 5 shows the advantage of bean shaping in the stabilization process for a PBX-like tokamak with aspect ratios of 4, 7, and 10. Note that the unstable region is compressed with increasing aspect ratio. As shown in the figure, at low indentation an inorease of .beta..sub.av =2.intg.pdv/.intg.B.sup.2 dv=2p.sub.av /B.sup.2.sub.av (obtained by increasing p.sub.o) causes the plasma to become balloon unstable, but further increasing the pressure places the plasma in the so-called second stability regime. Moreover, if the indentation is large enough, the plasma can bypass completely the unstable region as the pressure is increased. Bean shaping thus provides an accessible path to the second region of stability for ballooning modes. For R/a=4, the critical indentation is 0.304, when R/a=7, critical indentation is 0.33, when R/a is 10, critical indentation is 0.35. Aspect Ratio Scaling The effect of varying the aspect ratio, R/a, is shown in FIG. 6 for a plasma with indentation fixed at d/2a=0.304 (C=97.degree.) and for the pressure profiles, p(.psi.), and the safety factor profiles, q(.psi.), cited in equations 6 and 7 above. There we see that while higher stable .beta. values in the first region are obtained with lower aspect ratios, the second regime becomes increasingly remote. At R/a=2 equilibria up to .beta..sub.av 80% are still unstable. As the aspect ratio is increased, the unstable region decreases making it appear more likely that operation above the ballooning limit should be possible. For this case, in which the indentation is still slightly smaller than the critical value, the unstable region does not vanish, as in FIG. 5, at least out to R/a.about.20, which is as far as present calculations have been performed. FIGS. 7a-7f illustrate some of the features of the current profile associated with the choice of q(0)=1.03, q(1)=4.2, q'(0)=0.84, q'(1)=9.0. Comparison of FIG. 7b with 7d indicates the variation with indentation at low .beta. (0.1%), while FIG. 7d and FIG. 7f (.beta..about.10%) illustrate the effect of varying .beta. at similar indentation. THE INTERNAL KINK MODE The use of bean-shaping (indentation) is also beneficial toward stabilizing the internal kinks for which n=1. Here n is the toroidal mode number in the Fourier decomposition of the plasma displacement: EQU F=F1,n expi (1.theta.-n.phi.). Calculations at Large Aspect Ratio In this first series of calculations the marginal stability contours for R/a=10 plasmas are compared with circular, elliptical, dee-shaped, and indented cross sections. The results are shown in FIG. 8. To produce FIG. 8, sequences of fixed boundary equilibria were generated with identical p and q profiles. The boundary shape was EQU X(.theta.)=R-B+(a+B cos .theta.) cos (.theta.+.delta. sin .theta.) EQU Z(.theta.)=E a sin .theta., (8) and FIG. 9 shows the cross sections of the four different shapes studied in FIG. 8. The calculations used p(y)=p.sub.o (1-y).sup.2.5, q(y)=q.sub.o +q.sub..beta. y.sup.2, with y.ident..psi./.DELTA..psi. as before. q.sub.o and q.sub..beta. were chosen such that q.sub.edge /q.sub.axis .about.2.5. Each member of the sequences so generated was then scaled to lower q values at fixed .beta. poloidal. This procedure generates a mesh of equilibria so that one can map out a region in the parameter space defined by q(0) and .epsilon..beta..sub.pol, as shown in FIG. 8. Here .epsilon. is the inverse aspect ratio and .beta..sub.pol in the .beta. of the plasma referred to the poloidal field. Each member of this mesh of equilibria was then analyzed by computer for stability to internal modes with n=1. The results of FIG. 8 demonstrate that shaping the plasma surface has a strong effect on the n=1 internal kink. For circular and elliptical plasmas, the n=1 mode can be unstable for a wide range of .epsilon..beta..sub.pol even without a q=1 surface inside the plasma. This is a pressure driven large wavelength ballooning-like mode. When q(0)<1, the mode becomes an internal kink. It is stabilized at sufficiently high .epsilon..beta..sub.pol. We note that ellipticity is destabilizing. The region of instability is seen to shrink considerably with the introduction of triangularity for the D-shaped plasma and the bean. Calculations for PBX Parameters Using sequences of equilibria generated above ("Indentation and Accessibility to very High-.beta.) with an aspect ratio of 4, the procedure described immediately above was followed to determine the explicit stabilizing effect of indentation as envisioned in the PBX experiment (Princeton Beta Experiment device located at the Princeton Plasma Physics Laboratory in Princeton, N.J.). The results are shown in FIG. 10, which shows regions of instability on the q.sub.o -.epsilon..beta.pol plane for several values of indentation. For comparison with FIG. 5, it is noted that the indentations chosen are all less than the first sequence of ballooning results at d/2a.congruent.0.1. The most unstable shape corresponds to a D-shaped plasma with essentially vertical inboard plasma surface. It is seen that even small indentations are quite stabilizing. The inset on FIG. 10 shows the variation of the height and width of the unstable region as a fuction of indentation. The critical indentation for complete stability to this mode is shown to be d/2a=0.1. Consistent with this, all equilibria shown explicitly on FIG. 4 are stable to the internal n=1 kink mode, even with q(0) as low as 1/2. The results of FIG. 10 were obtained with the flat pressure profile given above, which has p'(0)=0. While the internal kink stability boundary can be sensitive to the variation of plasma profiles, it is not believed that this choice is responsible for the stabilization, since the favorable effect of bean shaping was already seen in the calculations presented in the previous section which had finite p'(0). To be more specific with respect to PBX, this concept was tested on the most unstable shape of FIG. 10 (the Dee) by changing the pressure profile to p(y)=p.sub.o (1-y).sup.2, i.e., more peaked near the magnetic axis as compared with the profile described by equation 7. The results are shown in FIG. 11. As expected, this peaked profile is more unstable, especially when the q=1 surface is near the magnetic axis. Thus, while flattening the pressure profile certainly reduces the region of instability, indenting the cross section is the principal stabilizing ingredient. An example of a high-.beta. equilibrium (.about.10%) with typical parameters for the PBX experiment is shown in FIG. 12. Stability studies have shown that this configuration is stable against the internal (n=1) kink at least as high as .beta..about.20%, and against ballooning modes to .beta..about.9%. The values are in marked contrast with .beta..sub.c =1.4% (internal kink) and .beta..sub.c =2.7% (ballooning) previously reported by D. Johnson et al., Plasma Physics and Controlled Nuclear Fusion Research 1982, Vol. 1, IAEA, Vienna (1983) 1, for PDX circular high .beta./low q discharges. A convenient and efficient way to achieve the desired shaping of the poloidal cross-section of the plasma, including the inner side of the cross-section, is by energizing a pusher coil, or a set of pusher coils, located on or near the central plane and close to the plasma. Such a set of pusher coils is illustrated in FIG. 12, where this concept was applied to the PBX device at Princeton. The pusher coils work together with the other external coils for the tokamak to create the indented shape, but the pusher coils' proximity to the plasma makes their contribution to the shaping of the dominant one. The pusher coil current may also be programmed in time to achieve the amount of indentations appropriate to the instantaneous magnitude and profiles of the current and pressure. The above description of embodiments of the invention is given by way of example only and it should be understood that numerous modifications can be made therein without departing from the scope of the invention. |
summary | ||
046363505 | abstract | Control regulation and shutdown of gas-cooled, high-temperature nuclear reactors require precise adjustment of core reactivity through the use of absorber rods. Fine adjustment without permanent damage to the reactor core having a bed of spherical fuel elements is accomplished by a process and arrangement of the reactor such that two groups of absorber rods are independently controlled for insertion into the reactor cavity between the roof reflector and the bed of spherical fuel elements and into the fuel element bed itself. Adjustments can be made for rapid shutdown and/or complete shutdown as well as rapid shutdown required due to water or oil penetration into the reactor core. |
claims | 1. An X-ray differential phase contrast imaging device, comprising:an X-ray source for generating an X-ray beam;a source grating (G0) for generating a coherent X-ray beam from a non-coherent X-ray source (20);a collimator comprising slits for splitting the coherent X-ray beam into a plurality of fan-shaped X-ray beams for passing through an object;a phase grating (G1) for generating an interference pattern and an absorber grating (G2) for generating a Moiré pattern from the interference pattern arranged after the object;a line detector comprising detector lines for detecting the Moiré pattern generated by the phase grating (G1) and the absorber grating (G2) from the fan-shaped X-ray beams (28) passing through the object;wherein the X-ray source, source grating (G0), collimator, phase grating (G1), absorber grating (G2) and line detector are fixed to a common gantry and are movable with respect to the object, such that a number of interference patterns from different positions of the gantry are detectable for reconstructing a differential phase image of the object;wherein groups of grating lines and transparent areas (38) alternate with respect to each other in a direction perpendicular to the direction of the detector lines;wherein at least one grating (G0, G1, G2) of the source grating, the phase grating and the absorber grating comprises groups of grating lines and transparent areas between the groups of grating lines, and is movable with respect to the gantry, such thatin a first position of the source grating (G0) the X-ray beams pass through the grating lines and subsequently pass through the slits of the collimator and in a second position of the source grating (G0) the X-ray beams pass through the transparent areas and subsequently pass through the slits of the collimator, orin a first position at least one of the phase grating (G1) or the absorber grating (G2) the fan-shaped X-ray beams pass through the grating lines, and in a second position at least one of the phase grating (G1) or the absorber grating (G2) the fan-shaped X-ray beams pass through the transparent areas. 2. The imaging device of claim 1,wherein the groups of grating lines are equidistant and the transparent areas are equidistant. 3. The imaging device of claim 1,wherein the grating (G0, G1, G2) comprises a substrate transparent for X-rays and the transparent areas comprises areas on the substrate without metallization. 4. The imaging device of claim 3,wherein the grating lines are metal lines on the substrate; and/orwherein the grating lines are metal-filled trenches in the substrate; and/ orwherein the grating lines are trenches in the substrate. 5. The imaging device of claims claim 1, wherein the transparent areas (38) comprises holes in a substrate of the grating. 6. The imaging device of claim 1, further comprising:a motor for moving the grating (G1, G2) between the first position and the second position; anda controller for controlling the movement. 7. The imaging device claim 1,wherein the first position of the grating (G1, G2) is determined by a mechanical stopper. 8. The imaging device claim 1,wherein the first position of the grating (G1, G2) is determined by a position sensor. 9. The imaging device claim 1, further comprising:rails for guiding the grating. 10. The imaging device claim 1,wherein only the absorber grating (G2) has the transparent areas. 11. The imaging device claim 1,wherein the phase grating (G1) and the absorber grating (G2) have the transparent areas. 12. The imaging device of claim 11,wherein the phase grating (G1) and the absorber grating (G2) are movable independently from each other between the first position and the second position; and/orwherein the phase grating (G1) and the absorber grating (G2) are fixedly connected with each other and are movable together between the first position and the second position. 13. The imaging device claim 1, further comprising:a hinge for removing the source grating (G0) from the X-ray beam. 14. A method for acquiring differential phase image data and attenuation image data with the same device, the method comprising:moving a grating (G0, G1, G2) selected from a source grating, a phase grating and an absorber grating of the device in a first position, such that fan-shaped X-ray beams generated by a collimator pass through groups of grating lines on the grating (G0, G1, G2);acquiring differential phase image data by moving a gantry with the source grating (G0), phase grating (G1) and absorber grating (G2) and a line detector with respect to an object and by detecting X-rays passing through the object, the source grating (G0), phase grating (G1) and the absorber grating (G2) at a plurality of positions of the gantry;moving the grating (G0, G1, G2) in a second position, such that the fan-shaped X-ray beams pass through transparent areas on the grating (G0, G1, G2); andacquiring attenuation image data by moving the gantry with respect to the object and by detecting X-rays passing through the object at a plurality of positions of the gantrywherein in a first position of the source grating (G0) the X-ray beams pass through the grating lines and subsequently pass through the slits of the collimator and in a second position of the source grating (G0) the X-ray beams pass through the transparent areas and subsequently pass through the slits of the collimator, orin a first position at least one of the phase grating (G1) or the absorber grating (G2) the fan-shaped X-ray beams pass through the grating lines, and in a second position at least one of the phase grating (G1) or the absorber grating (G2) the fan-shaped X-ray beams pass through the transparent areas. 15. The method of claim 14, further comprising:calibrating the line detector, when the absorber grating (G2) and the phase grating (G1) are in the second position; andcalibrating the phase grating (G1) and the absorber grating (G2), when the phase grating (G1) and the absorber grating (G2) are in the first position and the source grating (G0) is in the second position. |
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claims | 1. An antiscatter grid including an electromagnetic coil array integrated with the antiscatter grid, wherein the electromagnetic coil array is registered with the antiscatter grid and wherein the electromagnetic coil array is configured to detect an electromagnetic field at the antiscatter grid. 2. The antiscatter grid of claim 1, wherein the electromagnetic coil array is in front of the antiscatter grid. 3. The antiscatter grid of claim 1, wherein the electromagnetic coil array is behind the antiscatter grid. 4. The antiscatter grid of claim 1, wherein the electromagnetic coil array is attached to the antiscatter grid. 5. The antiscatter grid of claim 1, wherein a portion of the electromagnetic coil array is transparent to x-rays. 6. The antiscatter grid of claim 1, wherein the electromagnetic coil array is a printed circuit board (PCB) electromagnetic coil array. 7. The antiscatter grid of claim 6, wherein the PCB electromagnetic coil array includes at least one electromagnetic coil. 8. The antiscatter grid of claim 6, wherein the PCB electromagnetic coil array includes a substrate and wherein the substrate is transparent to x-rays. 9. The antiscatter grid of claim 1, wherein the electromagnetic coil array is an electromagnetic receiver. 10. The antiscatter grid of claim 1, wherein the electromagnetic coil array is an electromagnetic transmitter. 11. The antiscatter grid of claim 1, wherein the electromagnetic coil array is an electromagnetic transceiver. 12. The antiscatter grid of claim 1, wherein the electromagnetic coil array includes at least one electromagnetic coil. 13. A method for detecting an electromagnetic field with an antiscatter grid, the method including:integrating an electromagnetic coil array with an antiscatter grid; anddetecting the electromagnetic field at the antiscatter grid with the integrated electromagnetic coil array, wherein the electromagnetic coil array is registered with the antiscatter grid. 14. The method of claim 13, wherein the electromagnetic coil array is in the field of view of the antiscatter grid. 15. The method of claim 13, wherein the electromagnetic coil array is a printed circuit board (PCB) electromagnetic coil array. 16. The method of claim 15, wherein the PCB electromagnetic coil array includes at least one electromagnetic coil. 17. The method of claim 13, wherein the electromagnetic coil array is an electromagnetic receiver. 18. The method of claim 13, wherein the electromagnetic coil array is an electromagnetic transceiver. 19. A method for using an electromagnetic coil array as an antiscatter grid, the method including:providing the electromagnetic coil array, wherein said electromagnetic coil array is printed circuit board (PCB) electromagnetic coil array with at least one track of said electromagnetic coil array etched into a PCB substrate material; andfiltering scattered x-rays with the electromagnetic coil array. 20. The method of claim 19, wherein the PCB electromagnetic coil array includes a substrate and at least one track, wherein the substrate is transparent to x-rays, and wherein the at least one track is opaque to x-rays. 21. A method for registering an electromagnetic coil array integrated with an antiscatter grid, the method including:positioning the antiscatter grid and the integrated electromagnetic coil array in an imaging system;acquiring an image of the antiscatter grid and the electromagnetic coil array; anddetermining that the electromagnetic coil array is registered with the antiscatter grid based at least in part on the image of the antiscatter grid and the electromagnetic coil array. 22. The method of claim 21, further including repositioning the antiscatter grid and the electromagnetic coil array in the imaging system. 23. The method of claim 21, wherein the determining step is based at least in part on the presence of a moire pattern in the acquired image. 24. The method of claim 21, wherein the determining step is based at least in part on the visibility of the electromagnetic coil array. 25. A printed circuit board (PCB) electromagnetic coil array integrated with an antiscatter grid, the PCB electromagnetic coil array configured to detect an electromagnetic field at the antiscatter grid. 26. A printed circuit board (PCB) electromagnetic coil array configured to function as an antiscatter grid wherein the PCB electromagnetic coil array includes a substrate and at least one track, wherein at least one track etched into the substrate PCB material. |
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description | The present application claims priority from Japanese Patent application serial no. 2012-285092, filed on Dec. 27, 2012, the content of which is hereby incorporated by reference into this application. Technical Field The present invention relates to a fuel assembly and, in particular, to a fuel assembly suitable for plying to a boiling water nuclear reactor. Background Art A plurality of fuel assemblies are loaded in a core of a boiling water nuclear reactor. Each fuel assembly has a fuel bundle disposed in a square tubular channel box. Each fuel bundle has a plurality of fuel rods in which a plurality of fuel pellets containing uranium are disposed, an upper tie plate which supports upper end portions of the fuel rods, a lower tie plate which supports lower end portions of the fuel rods, and a plurality of spacers, each of which maintains space among the fuel rods. One example of the fuel spacer is disclosed in Japanese Patent Laid-Open No. 62(1987)-105082. In general, these fuel spacers are disposed at predetermined intervals in the axial direction of the fuel assembly for the purpose of holding the fuel rods for preventing the fuel rods from bending or the like. In the boiling water nuclear reactor, cooling water boils in each fuel assembly loaded in the core of the reactor, and a part of the cooling water is converted into steam, and a gas-liquid two-phase flow containing the cooling water and steam goes up in the fuel assembly. The steam contained in the gas-liquid two-phase flow is separated from the cooling water by a steam-water separator and a steam dryer in the nuclear reactor. The separated steam is supplied from the nuclear reactor to a turbine connected to an electric generator. If a surface of the fuel rod is in a state of being covered with a liquid film of the cooling water in the core, heat removal from the fuel rod is soundly achieved. However, if the surface of the fuel rod is in a state of being in contact with steam constantly, heat removal from the fuel rod is carried out poorly, and as a result, the surface temperature of the fuel rod is increased. In order to prevent this increase in the surface temperature, it is necessary to bring the surface of the fuel rod to a state where the liquid film is present on the surface constantly. In an upper portion of the fuel assembly where the ratio of steam contained in the gas-liquid two-phase flow is increased, the liquid film is formed on each surface of the fuel rods, and a phenomenon called an annular-dispersed flow in which steam and liquid droplets are present occurs between the fuel rods. The gas-liquid two-phase flow goes up between the fuel rods while the adhesion of the liquid droplets in the steam to the liquid film on the surface of the fuel rod, and the scattering of the liquid droplets into the steam from the liquid film are repeated. In order to maintain the liquid film formed on the surface of the fuel rod, it is only necessary that the liquid droplets can actively adhere to the liquid film from the steam. As a result, it is possible to improve the thermal margin of the fuel assembly. The fuel spacers have a function of disturbing the flow of the gas-liquid two-phase flow going up a cooling water path formed between the fuel rods, and therefore, an effect of allowing the liquid droplets in the steam to adhere to the liquid film on the surface of the fuel rod is enhanced. However, the mechanism of disturbing the gas-liquid two-phase flow in the cooling water path by the fuel spacer causes a large pressure loss. This large pressure loss causes a decrease in the flow rate of the cooling water going up in the fuel assembly. The pressure loss of the fuel spacer is related to a projected area of the fuel spacer closing the cooling water path. Due to this, the thermal margin of the fuel assembly was tried to be improved by disturbing the flow of the gas-liquid two-phase flow in the fuel assembly while decreasing the pressure loss by decreasing the projected area of the fuel spacer to the cooling water path. Further, in the fuel assembly in which a part of the plurality of fuel rods are substituted with partial length fuel rods, the pressure loss of the fuel assembly is decreased by the use of the partial length fuel rods. By using the partial length fuel rods, a space where fuel rods are not present is formed on an upper side of the upper ends of the partial length fuel rods in the fuel assembly to decrease the pressure loss, and thus, the cooling water easily flows in the fuel assembly. However, the adoption of the partial length fuel rods increases the amount of liquid droplets flowing along with steam from the fuel assembly. In the fuel assembly described in Japanese Patent Laid-Open No. 2010-145232, partial length fuel rods are disposed in an outermost layer of a fuel rod array and an inner region which is a region on the inner side excluding a second layer from the inner surface of a channel box, and a partial fuel spacer having a size smaller than reference fuel spacers in the direction perpendicular to the center axis of the fuel assembly is disposed on the upper side of the upper ends of the partial length fuel rods in an inner region where these partial length fuel rods are disposed. The reference fuel spacers support all the fuel rods in the fuel assembly. On the other hand, the partial fuel spacer supports fuel rods, which are a part of all the fuel rods in the fuel assembly and are disposed in the inner region. The partial fuel spacer allows liquid droplets present in a space on the upper side of the partial length fuel rods to adhere to a liquid film on the surface of the fuel rod to decrease the amount of liquid droplets flowing out to the outside of the fuel assembly. Further, the increase in the pressure loss of the fuel assembly is minimized by disposing the partial fuel spacer. In the fuel assembly described in Japanese Patent Laid-Open No. 2001-318182, it is intended to increase the dry out margin of fuel rods and to decrease the pressure loss of the fuel assembly by supporting a plurality of fuel rods by two types of fuel spacers. These two types of fuel spacers are a fuel spacer having a low pressure loss and a fuel spacer having a large mixing effect. The latter fuel spacer includes blades for swirling cooling water attached to each grid plate in the vicinity of each intersection of the orthogonally provided grid plates. The former fuel spacer is not provided with such blades and achieves the decrease of a pressure loss. The fuel spacer having a low pressure loss and the fuel spacer having a large mixing effect are alternately arranged in the axial direction of the fuel assembly. Further, a water gap region (a region on the outer side of a channel box) in which saturated water is present is formed between the adjacent fuel assemblies loaded in the core, and a gas-liquid two-phase flow is present in the fuel assembly. Therefore, neutrons generated by nuclear fission of a fissile material in the fuel rods are easily moderated in the water gap region. Many of the neutrons causing nuclear fission of U-235 are supplied to the inside of the fuel assembly from the water gap region. As a result, the power in an outer peripheral portion in a cross section of the fuel assembly (a cross section in the direction perpendicular to the center axis of the fuel assembly) is increased. Since a thermal margin in this outer peripheral portion is not enough, in a fuel assembly of a general boiling water nuclear reactor, the uranium enrichment in the fuel rods disposed in the outer peripheral portion is lower than that in the fuel rods disposed in the inner side. In the cross section of each fuel assembly loaded in the core of a general boiling water nuclear reactor, the ratio of the average uranium enrichment in the outer peripheral portion in the cross section thereof to the average uranium enrichment in the cross section thereof is 0.9 or less. On the other hand, if the thermal margin of the fuel assembly can be ensured, the enrichment of the fissile material in the fuel assembly can be increased, and thus, the inventory of the fissile material can be increased. [Patent Literature 1] Japanese Patent Laid-Open No. 62(1987)-105082 [Patent Literature 2] Japanese Patent Laid-open No. 2010-145232 [Patent Literature 3] Japanese Patent Laid-Open No. 2001-318182 In the boiling water nuclear reactor, as described above, it is necessary to improve the thermal margin in an outer peripheral portion in the cross section of the fuel assembly in order to increase the inventory of a fissile material in the fuel assembly to be loaded in the core. At this time, it is considered acceptable not to improve the thermal margin in an inner region in the cross section of the fuel assembly. That is, by focusing on the outer peripheral portion in the cross section of the fuel assembly, there is a problem that the effect of improving the thermal margin is limited. The fuel assembly described in Japanese Patent Laid-Open No. 2010-145232 has a partial fuel spacer as described above. This partial fuel spacer is used along with a reference spacer by decreasing the pressure loss as much as possible. The partial fuel spacer described in Japanese Patent Laid-Open No. 2010-145232 has a small pressure loss, and plays a role in closing the cooling water path in the inner region in the cross section of the fuel assembly, and therefore, the flow rate of the cooling water in the outer peripheral portion can be increased. However, since the projected area of the partial fuel spacer for closing the cooling water path is small, the effect of increasing the flow rate of the cooling water in the outer peripheral portion is not enough. Further, the partial fuel spacer is disposed on the upper side of the upper ends of the partial length fuel rods in the axial direction of the fuel assembly. Since a region on the upper side of the upper ends of the partial length fuel rods is a region where an annular dispersed flow occurs, the disposition of the partial fuel spacer on the upper side of the upper ends of the partial length fuel rods is suitable for allowing liquid droplets in steam to adhere to the liquid film on the surface of the fuel rod. However, in the case where the partial fuel spacer is disposed on the upper side of the upper ends of the partial length fuel rods, an effect of increasing the flow rate of the cooling water flowing in the outer peripheral portion is decreased. An object of the present invention is to provide a fuel assembly, in which even in a case where inventory of a fissile material in fuel rods disposed in an outermost layer of a fuel rod array is increased, thermal margin of the fuel rods disposed in the outermost layer can be improved. A feature of the present invention for attaining the above object is a fuel assembly comprising a plurality of fuel rods containing a fissile material; a lower tie plate which supports each lower end portion of the fuel rods; an upper tie plate which holds each upper end portion of the fuel rods; a plurality of fuel spacers, each of which bundles the plurality of fuel rods; a channel box attached to the upper tie plate, extending toward the lower tie plate, and surrounding the plurality of fuel rods bundled by the fuel spacers; and a flow resistance member, which is disposed in an inner side of an outermost layer region of an array of the plurality of fuel rods in a cross section in a direction perpendicular to a center axis of the channel box, and through which coolant paths are formed, and which the fuel rods penetrate, wherein when the number of the fuel rods held by the flow resistance member is R, the number of all the fuel rods in the fuel assembly is A, and a projected area ratio C of projected area Sa of the flow resistance member from an upper tie plate side to projected area Sb of the fuel spacer which holds all the fuel rods in the fuel assembly from the upper tie plate side is defined by the following formula (1), the projected area ratio C is within a range of 1.5 to 5.2.C=(Sa/Sb)×(A/R) (1) Since the projected area Sa of the flow resistance member from the upper tie plate side is 1.5 to 5.2 times of the projected area Sb of the fuel spacer which holds all the fuel rods in the fuel assembly from the upper tie plate side, even in the case where inventory of a fissile material in fuel rods disposed in the outermost layer region is increased, the flow rate of coolant flowing in the outermost layer region at the upper tie plate side than the flow resistance member is increased. Thus, critical power ratio of the fuel rods disposed in the outermost layer region can be increased, and as a result, the thermal margin of the fuel rods disposed in the outermost layer region can be improved. According to the present invention, even in the case where inventory of a fissile material in fuel rods disposed in the outermost layer of a fuel rod array is increased, the thermal margin of the fuel rods disposed in the outermost layer can be improved. The inventors studied the improvement of burnup efficiency of a fissile material of a fuel assembly. As described above, since cooling water is present more in a water gap region on the outer side of the channel box than in the channel box, it is most efficient to burn a fissile material in the fuel rods disposed in the outermost layer adjacent to the channel box in the fuel rod array in the fuel assembly. In a case where the inventory of a fissile material is increased in the fuel rods disposed in the outermost layer, the thermal margin of these fuel rods is deteriorated. Therefore, measures for improving the thermal margin of the fuel rods disposed in the outermost layer were examined. The reason why the thermal margin of the fuel rods disposed in the outermost layer is decreased is because the liquid film present on the surfaces of the fuel rods is converted into steam due to a large amount of heat generation and the amount of water to cool the fuel rods is decreased. The inventors concluded that since the amount of cooling water in the outermost layer region of the fuel rod array in the fuel assembly can be increased by controlling the flow of the cooling water in the fuel assembly, the above problem can be solved by providing a flow resistance member in a central portion in the cross section of the fuel assembly. However, a fuel spacer disposed in the inside of the conventional fuel assembly acts as a flow resistance in a central portion in the cross section of this fuel assembly. That is, in the fuel assembly described in Japanese Patent Laid-open No. 2010-145232, the partial fuel spacer functions as a flow resistance member in a central portion in the cross section of the fuel assembly. On the other hand, since the fuel spacer is designed so as to decrease the flow resistance as much as possible, the effect of the fuel spacer as the flow resistance is small. Further, since the fuel spacer which does not hold all the fuel rods in the fuel assembly does not sufficiently play a role in holding the fuel rods, such a spacer is used as a supplementary member added to the fuel spacer which holds all the fuel rods in the fuel assembly having the present holding mechanism. This point is the same as in the present invention, however, an increase in pressure loss due to the addition of such a fuel spacer decreases the flow rate of cooling water in the fuel assembly, and thus the critical power is decreased. Unless an effect of increasing the critical power overtaking the decrease in the flow rate of cooling water due to an increase in resistance is obtained, it cannot be said that a true effect of increasing the critical power is obtained. In order to quantitatively show these effects, the inventors examined the critical power performance when the cross section (the projected area from the upper tie plate side of the fuel assembly) of the flow resistance member disposed in a central portion in the cross section of the fuel assembly was changed. The examination results will be described below. When this examination was performed, the following fuel assembly was assumed. First, in the case of using a square-shaped flow resistance member as shown in FIG. 1, in which the projected area from the upper tie plate side occupies about one-third of the projected area of a fuel spacer (for example, a fuel spacer 6 shown in FIG. 3), which holds all the fuel rods in the fuel assembly, from the upper tie plate side, the projected area of the reference fuel spacer is used as reference, and the projected area ratio C is defined as 1.0. Unless otherwise stated, the projected area described below refers to a projected area from the upper tie plate side. Further, as for the power of the fuel rods in the fuel assembly, a case where the relative power of the fuel rods disposed in the outermost layer in the fuel rod array is 1.2 was assumed. The relative power of the fuel rods disposed in the outermost layer in the fuel rod array being 1.2 can be achieved by increasing the average enrichment in the outermost layer of the fuel rod array as compared with the average enrichment in the cross section of the fuel assembly in a region filled with enriched uranium in the fuel assembly. Further, the increment of the pressure loss due to an increase in the projected area of the flow resistance member is treated as a decrement of the flow rate of the coolant. The critical power ratio indicated by a vertical axis shown in FIG. 4 shows the critical power ratio of the fuel assembly in a case where a flow resistance member having a projected area one-third of the projected area of the above-described reference fuel spacer is used. The projected area ratio C indicated by a horizontal axis shown in FIG. 4 is a rate of the projected area of the flow resistance member to the projected area of the reference fuel spacer, that is, the fuel spacer which holds all the fuel rods used in the fuel assembly including the flow resistance member. This projected area ratio C of the flow resistance member is defined by the formula (1).C=(Sa/Sb)×(A/R) (1) In the formula (1), Sa is the projected area of the flow resistance member, Sb is the projected area of the fuel spacer (reference fuel spacer) used in the fuel assembly to which the flow resistance member is applied, R is the number of the fuel rods held by the flow resistance member, and A is the number of all the fuel rods in the fuel assembly to which the flow resistance member is applied. FIG. 4 shows a change in the critical power ratio of the fuel assembly using the flow resistance member with respect to the projected area rate of the flow resistance member. In the case where the power of the fuel rods in the outermost layer of the fuel rod array of the fuel assembly is high, the amount of cooling water in the outermost layer of the fuel rod array can be increased by increasing the flow resistance in a central portion in the cross section of the fuel assembly and the critical power of the fuel rods disposed in the outermost layer is increased. In particular, when the projected area ratio of the flow resistance member is in a range of 1.5 to 5.2, the critical power is increased as compared with the conventional art. As a result, the inventory of a fissile material (for example, uranium-235) in the fuel rods disposed in the outermost layer can be increased within the range of the increment of the critical power, and thus, economic efficiency of fuel can be improved. Hereinafter, embodiments of the present invention reflecting the above examination results will be described. [Embodiment 1] A fuel assembly according to embodiment 1 which is a preferred embodiment of the present invention, applied to a boiling water nuclear reactor, will be described in detail with reference to FIGS. 1 to 3. A fuel assembly 1 according to the present embodiment is provided with a plurality of fuel rods 2, an upper tie plate 4, a lower tie plate 3, a plurality of fuel spacers 6, a plurality of water rods 5, a channel box 7, and a flow resistance member 15 (see FIG. 2). Each of the fuel rods 2 has a hermetically sealed fuel cladding (not shown) and this sealed fuel cladding is filled with a plurality of fuel pellets (not shown) each containing a fuel material. The plurality of fuel rods 2 include a plurality of fuel rods 2A and a plurality of partial length fuel rods 2B having a length shorter in the axial direction than the fuel rods 2A. The lower tie plate 3 supports a lower end portion of each of the fuel rods 2, and the upper tie plate 4 holds an upper end portion of each of the fuel rods 2A. These fuel rods 2 are disposed in an array of 10 rows and 10 columns in the cross section (the cross section in the direction perpendicular to the center axis of the fuel assembly, that is, the center axis of the channel box) of the fuel assembly 1. In a central portion in the cross section, two water rods 5, each of which has a cross-sectional area occupying a region capable of disposing four fuel rods 2, are disposed. Each water rod 5 is a water rod with a large diameter. The lower end portions of these water rods 5 are supported by the lower tie plate 3, and the upper end portions thereof are held by the upper tie plate 4. The plurality of fuel spacers 6 are disposed at predetermined intervals in the axial direction of the fuel assembly 1, and hold the fuel rods 2 and the water rods 5 such that a cooling water path through which cooling water flows is formed between the fuel rods 2 and between the fuel rod 2 and the water rod 5. The square tubular channel box 7 having a square-shaped cross section is attached to the upper tie plate 4 and extends toward the lower tie plate 3. The respective fuel rods 2 bundled by the fuel spacers 6 are disposed in the channel box 7. Incidentally, an outer width of the channel box 7 is about 15 cm, an outer diameter of the fuel rod 2 is about 1.0 cm, and an outer diameter of the water rod 5 is about 2.5 cm. The length of the region where the fuel pellets containing fissile uranium are filled in the fuel rod 2 according to the present embodiment, that is, a fuel effective length in the present embodiment is 3.8 m. When the fuel assembly 1 was loaded in the core of a boiling water nuclear reactor, one corner of the fuel assembly 1 is disposed facing a control rod which has a cross-shaped cross section. The channel box 7 is attached to the upper tie plate 4 by a channel fastener (not shown). The channel fastener has a function of maintaining a gap with a width required between the fuel assemblies 1 when the fuel assemblies 1 were loaded in the core, so that the control rod can be inserted between the fuel assemblies 1. Due to this, the channel fastener is attached to the upper tie plate 4 such that it is disposed at a corner of the fuel assembly facing the control rod. In other words, the corner portion facing the control rod CR of the fuel assembly 1 is a corner portion to which the channel fastener is attached. Each of the fuel pellets filled in each of the fuel rods 2 is produced by using uranium dioxide which is nuclear fuel material, and contains uranium-235 which is a fissile material. Each of the fuel spacers 6 disposed in the axial direction of the fuel assembly 1 is a ferrule-type fuel spacer, and includes a square-shaped band 7 having a plurality of spacer tabs 8 formed thereon, and ferrules 9 whose number is the same as that of the fuel rods 2 (see FIG. 3). Each of the ferrules 9 is a cylinder and are arranged in an array of 10 rows and 10 columns in the same manner as the fuel rods 2, and adjacent ferrules 9 are joined to each other by welding. The square-shaped band 7 is disposed surrounding the periphery of the ferrules 9 disposed in the outermost layer among the ferrules 9 arranged in a square grid of 10 rows and 10 columns, and joined to the ferrules 9 disposed in the outermost layer by welding. In each of the ferrules 9, two protrusions (fixing support members) 10 are formed at both end portions such that a part of the ferrule 9 is protruded inward. A spring member (elastic support member) 11 is provided across adjacent pair of ferrules 9 and attached thereto. In a central portion in the cross section of the fuel spacer 6, two water rod disposition regions 14, each of which occupies a region capable of disposing four ferrules 9, are formed. A bridge member 12 is provided every two adjacent ferrules 9 facing the water rod disposition region 14 and attached to a side surface of each ferrule 9. The spring member 13 serving as the elastic support member is attached to one bridge member 12 among the four bridge members 12 facing each of the water rod disposition regions 14. Each of the fuel spacers 6 is disposed in the channel box 7, and each of the spacer tabs 8 provided on the band 7 comes into contact with the inner surface of the channel box 7. Each of the fuel rods 2 arranged in an array of 10 rows and 10 columns is inserted one by one into each of the ferrules 9 of the fuel spacer 6, and supported by three support members including the two protrusions 10 formed in each ferrule 9 and the spring member 11 provided in each ferrule 9 disposed in the circumferential direction of the fuel rod 2. The plurality of partial length fuel rods 2B among the fuel rods 2 are disposed in a region (inner region) on the inner side of the respective fuel rods 2 annularly disposed in the shape of a square in the second layer from the channel box 7 toward the center axis of the fuel assembly 1 in the fuel rod array of 10 rows and 10 columns. These partial length fuel rods 2B are supported as described above by the other fuel spacers 6 except for the fuel spacer 6 disposed closest to the upper tie plate 4. Incidentally, the upper end portions of the partial length fuel rods 2B are not supported by the upper tie plate 4. All the fuel rods 2A are supported by all the fuel spacers 6. The two water rods 5 are separately inserted into the two water rod disposition regions 14 formed in each of the fuel spacers 6. Notches are attached to the outer surface of the water rod 5 at predetermined intervals in the axial direction of the water rod 5. Each of the notches protrudes in the radial direction of the water rod 5 from the outer surface of the water rod 5, and the number of the notches is the same as the total number of the fuel spacers 6 and the flow resistance member 15. Each of the fuel spacers 6 is supported by the water rods 5 by supporting one bridge member 12 facing one water rod disposition region 14 by the notches of the water rods 5 through a known method. Each of the water rods 5 disposed in each of the water rod disposition regions 14 is pressed against the other bridge member 12 by the spring member 13 to limit the movement in the direction perpendicular to the axis of the fuel assembly 1. The flow resistance member 15 will be described in detail with reference to FIG. 1. In the flow resistance member 15, a plurality of ferrules 9 are arranged in a square grid of 6 rows and 6 columns in a square-shaped band 20, and in the same manner as the fuel spacer 6, two water rod disposition regions 14A, each of which occupies a region capable of disposing four ferrules 9, are formed in the central portion in the cross section. The adjacent ferrules 9 are joined to each other by welding, and each of the ferrules 9 disposed in the outermost layer is joined to the band 20 by welding. In each of the ferrules 9, two protrusions 10 are formed in the circumferential direction in the same manner as the ferrules 9 of the fuel spacer 6, and a spring member 11 is provided across adjacent pair of ferrules 9 and attached thereto. A bridge member 12A is provided every two adjacent ferrules 9 facing the water rod disposition region 14A and attached to a side surface of each ferrule 9. A spring member 13A serving as the elastic support member is attached to one bridge member 12A among the four bridge members 12A facing each of the water rod disposition regions 14A. The flow resistance member 15 further includes a plurality of resistance members 16 and a plurality of resistance members 17. When the distance from the center of a given ferrule 9A to the center of a ferrule 9B which is adjacent to and comes into contact with the ferrule 9A is taken as 1, the distance from the center of the ferrule 9A to the center of a ferrule 9C which is adjacent to and comes into contact with the ferrule 9B in the direction orthogonal to the straight line connecting the center of the ferrule 9A to the center of the ferrule 9B is √2. The ferrule 9A and the ferrule 9C do not come into contact with each other, and a space is formed between the ferrule 9A and the ferrule 9C. In this manner in each first space (for example, a space formed between the ferrule 9A and the ferrule 9C) formed between two ferrules 9 adjacent to each other in the diagonal direction of the flow resistance member 15, that is, in the diagonal direction of the channel box 7, the resistance member 16 is disposed. Each of the resistance members 16 is a round plate-shaped member made of a zirconium alloy, and comes into contact with each side surface of the adjacent four ferrules 9 and is fixed by welding to the side surfaces of these ferrules 9. Each of the resistance members 17 is a round plate-shaped member made of a zirconium alloy, and is disposed in each second space formed by the band 20 and adjacent two ferrules 9 and comes into contact with the band 20 and these ferrules 9. The diameter of the resistance member 17 is smaller than that of the resistance member 16. The resistance member 17 disposed in the second space comes into contact with the side surface of each of the two ferrules 9 in contact with each other forming the second space and the inner surface of the band 20 and fixed thereto by welding. One flow resistance member 15 is disposed at a position closer to the lower tie plate 3 than the fuel spacer 6 disposed at a position closest to the upper tie plate 4 in the axial direction of the fuel assembly 1 and is disposed at a position of one end portion of the partial length fuel rod 2B opposite to the other end portion thereof held by the lower tie plate 3. The flow resistance member 15 is supported by the water rods 5 by supporting one bridge member 12A facing one water rod disposition region 14A by the notches of the water rods 5 through a known method in the same manner as the fuel spacer 6. Each of the water rods 5 disposed in each of the water rod disposition regions 14A is pressed against the other bridge member 12A by the spring member 13A to limit the movement in the direction perpendicular to the axis of the fuel assembly 1. Further, the flow resistance member 15 is disposed in an inner region which is on the inner side of each of the fuel rods 2A annularly disposed in the shape of a square in the second layer from the outside of the fuel rod array of 10 rows and 10 columns in the cross section of the fuel assembly 1, that is, on the inner side of the outermost layer of the fuel rod array of 10 rows and 10 columns. Each of the resistance members 16, each of which increases the flow resistance in a central portion in the cross section of the fuel assembly 1, and each of the resistance members 17 are disposed in the above-described inner region. Each of the ferrules 9 of the flow resistance member 15 is disposed directly above the other ferrules 9 disposed on the inner side of each of the ferrules 9 annularly disposed in the shape of a square in the second layer from the band 7 of the fuel spacer 6 disposed directly below the flow resistance member 15 toward the inner side. Each of the fuel rods 2A and 2B disposed in the inner region is inserted into each of the ferrules 9 of the flow resistance member 15. The projected area Sa of the flow resistance member 15 is Sa1 mm2, and the projected area Sb of the fuel spacer 6 which is a reference fuel spacer holding all the fuel rods 2 in the fuel assembly 1 is Sb1 mm2 (>Sa1 mm2). Further, the number R of the fuel rods 2 held by the flow resistance member 15 is 28, and the number A of all the fuel rods 2 in the fuel assembly 1 is 92. By substituting each of the values of these Sa, Sb, R, and A in the formula (1), the projected area ratio C (=(Sa1/Sb1)×(92/28)) of the flow resistance member 15 is obtained. This projected area ratio C is 2.0. The length of one side of the square-shaped band 20 of the flow resistance member 15 is 60% of the length of one side of the square-shaped band 7 of the fuel spacer 6, and the cross-sectional area of the flow resistance member 15 is about one-third of the cross-sectional area of the fuel spacer 6. In the fuel assembly 1 according to the present embodiment, the average enrichment in the cross-sectional area of the fuel assembly 1 is about 4.6 wt %, and the average enrichment in all the fuel rods 2A disposed in the outermost layer of the fuel rod array of 10 rows and 10 columns is about 5.6 wt %. In this manner, in the fuel assembly 1, the inventory of a fissile material in the outermost layer is increased. When operating a boiling water nuclear reactor having a core in which a plurality of fuel assemblies 1 are loaded, cooling water is supplied to the core and goes up in each of the fuel assemblies 1. The cooling water in the fuel assembly 1 is heated by heat generated by nuclear fission of uranium-235 which is a fissile material in the fuel rods 2 and a part of the cooling water is converted into steam. Then, a gas-liquid two-phase flow containing steam and cooling water goes up in the fuel assembly 1. The percentage of the steam contained in the gas-liquid two-phase flow is progressively increased toward the upper end portion in the fuel assembly. The flow of the gas-liquid two-phase flow having passed through the fuel spacer 6 disposed second from the upper tie plate 4 among all the fuel spacers 6 in the channel box 7 is divided into a gas-liquid two-phase flow flowing in each ferrule 9 of the flow resistance member 15 and a gas-liquid two-phase flow flowing in a region present between an inner surface of the channel box 7 and the band 20 of the flow resistance member 15. Since the pressure loss of the flow resistance member 15 provided with the resistance members 16 and 17 is increased, on the upper side of the flow resistance member 15, the flow rate of the gas-liquid two-phase flow per unit area flowing through an outer region (a region present between the inner surface of the channel box 7 and the band 20 of the flow resistance member 15), in which two layers of the fuel rods 2 disposed from the inner surface of the channel box 7 toward the inner side are disposed, is increased. Due to this, in each of the fuel rods 2 disposed in the outer region on the side closer to the upper tie plate 4 than the flow resistance member 15, the amount of the liquid film on the surface of these fuel rods 2 is increased and also the amount of liquid droplets in the steam adhering to the liquid film on the surface thereof is increased. As a result, cooling of each of the fuel rods 2 disposed in the outer region on the side closer to the upper tie plate 4 than the flow resistance member 15 is promoted, and the critical power of these fuel rods 2 is increased, and thus, the thermal margin is increased. The flow rate of the gas-liquid two-phase flow passing through each of the ferrules 9 of the flow resistance member 15 is decreased, however, a region on the side closer to the upper tie plate 4 than the upper ends of the partial length fuel rods 2B on the side of the flow resistance member 15, that is, a region directly above the upper ends of the partial length fuel rods 2B is a region where an annular dispersed flow increases, and the adhesion of liquid droplets present in the steam in this region to the liquid film on the surfaces of the fuel rods 2 in this region is promoted due to the action of the flow resistance member 15. Due to this, even in the region directly above the upper ends of the partial length fuel rods 2B, cooling of the fuel rods 2 is promoted. According to the present embodiment, since the projected area ratio of the flow resistance member 15 is 2.0, even if the average enrichment in each of the fuel rods disposed in the outermost layer of the fuel rod array is increased as compared with the average enrichment in the cross section of the fuel assembly 1, the thermal margin of each of the fuel rods 2 disposed in this outermost layer can be improved. In the present embodiment, the resistance members 16 and 17 are disposed in all the first and second spaces formed among the ferrules 9, however, a part of the resistance members 16 and 17 may be deleted as long as the projected area ratio of the flow resistance member 15 falls within the acceptable range of 1.5 to 5.2. The flow resistance member 15 may be disposed at any position in the axial direction of the fuel assembly 1 as long as it is in an enriched uranium region in the fuel assembly 1. However, in order to largely improve the thermal margin of the fuel rods 2 disposed in the outermost layer of the fuel rod array, it is preferred to dispose the flow resistance member 15 on the lower side of the upper end of the partial length fuel rod 2B. [Embodiment 2] A fuel assembly according to embodiment 2 which is another preferred embodiment of the present invention, applied to a boiling water nuclear reactor, will be described in detail with reference to FIG. 5. A fuel assembly according to the present embodiment has a structure that in the fuel assembly 1 of embodiment 1, the flow resistance member 15 is replaced with a flow resistance member 15A (see FIG. 5). The other structures of the fuel assembly according to the present embodiment are similar to the fuel assembly 1 according to embodiment 1. The flow resistance member 15A is a grid flow resistance member and has a structure in which bridge members 12A are attached to a plate member 22 which includes a plurality of resistance members 16A arranged substantially in a square grid of 7 rows and 7 columns and connection members 18 each connecting the adjacent resistance members 16A to each other. A plurality of connection members 18 are disposed so as to intersect at right angles to form a grid line in conjunction with the resistance members 16A which are a circular plate. Each of the circular resistance members 16A is disposed at each of the intersections of the grid lines of the flow resistance member 15A. Further, the plate member 22 of the flow resistance member 15A having a shape shown in FIG. 5 is formed by processing a plate material made of a zirconium alloy through press working. In the same manner as the flow resistance member 15, two water rod disposition regions 14A are formed in a central portion of the plate member 22 of the flow resistance member 15A. In each of the water rod disposition regions 14A, one bridge member 12A is disposed facing each of the water rod disposition regions 14A and attached to the plate member 22 of the flow resistance member 15A. A spring member 13A which presses a water rod 5 inserted into each of the water rod disposition regions 14A in the horizontal direction is attached to each of the bridge members 12A. In the flow resistance member 15A, a plurality of fuel rod insertion holes 21 are present and each of the fuel rod insertion holes 21 is formed such that it is surrounded by four resistance members 16A and the four connection members 18 connecting these four resistance members 16A. In the flow resistance member 15A, the resistance members 16A are disposed at the same positions as the resistance members 16 of the flow resistance member 15, and the diameter of the resistance member 16A is larger than that of the resistance member 16. The distance between the adjacent resistance members 16A in the diagonal direction of the flow resistance member 15A is slightly larger than the outer diameter of the fuel rod 2. Due to this, the projected area Sa of the flow resistance member 15A is Sa2 mm2, and is larger than that of the flow resistance member 15 used in embodiment 1 (Sa2 mm2>Sa1 mm2). The respective values of the projected area Sb of the fuel spacer 6 which is a reference fuel spacer, the number R of the fuel rods 2 held by the flow resistance member 15A, and the number A of all the fuel rods 2 in the fuel assembly according to the present embodiment are the same as in embodiment 1. As a result, the projected area ratio C of the flow resistance member 15A obtained according to the formula (1) (=(Sa2/Sb1)×(92/28)) is 3.0. One flow resistance member 15A is disposed in a channel box 7, and disposed at a position of upper end portions of partial length fuel rods 2B in the same manner as the flow resistance member 15 used in embodiment 1. The flow resistance member 15A is supported by water rods 5 inserted into the water rod disposition regions 14A in the same manner as the flow resistance member 15. A plurality of fuel rods 2A and a plurality of fuel rods 2B disposed in an inner region are inserted one by one into each of the fuel rod insertion holes 21. The outer surface of each of the fuel rods inserted into the fuel rod insertion holes 21 comes into contact with each of the resistance members 16A disposed around the fuel rod insertion holes 21. A path through which a gas-liquid two-phase flow flows is formed between the outer surface of the fuel rod 2 inserted into the fuel rod insertion hole 21 and the connection member 18. When operating a boiling water nuclear reactor in which the fuel assembly according to the present embodiment having the flow resistance member 15A is loaded in a core, in substantially the same manner as in the embodiment 1, the flow of the gas-liquid two-phase flow occurring in this fuel assembly is divided into a gas-liquid two-phase flow flowing in each of the fuel rod insertion holes 21 of the flow resistance member 15A and a gas-liquid two-phase flow flowing in a region present between an inner surface of the channel box 7 and the flow resistance member 15A. Since the pressure loss of the flow resistance member 15A provided with the resistance members 16A and the connection members 18 is increased, on the upper side of the flow resistance member 15A, the flow rate of the gas-liquid two-phase flow per unit area flowing through the above-described outer region is increased. Due to this, cooling of each of the fuel rods 2 disposed in the outer region on the upper side of the flow resistance member 15A is promoted, and the critical power of these fuel rods 2 is increased, and thus, the thermal margin is increased. The flow rate of the gas-liquid two-phase flow passing through each of the fuel rod insertion holes 21 of the flow resistance member 15A is decreased, however, also in a region just above the upper ends of the partial length fuel rods 2B, cooling of the fuel rods 2 is promoted in the same manner as in the first embodiment. According to the present embodiment, each effect generated in embodiment 1 can be obtained. Moreover, the flow resistance member 15A is simplified as compared with the flow resistance member 15 constituted by joining a plurality of ferrules 9, and thus, the production thereof is easy. [Embodiment 3] A fuel assembly according to embodiment 3 which is other preferred embodiment of the present invention, applied to a boiling water nuclear reactor will be described in detail with reference to FIGS. 6 and 7. A fuel assembly according to the present embodiment has a structure in which the flow resistance member 15 in the fuel assembly 1 according to embodiment 1 is replaced with a flow resistance member 15B (see FIG. 6). The other structures of the fuel assembly according to the present embodiment are similar to the fuel assembly 1 according to the embodiment 1. The flow resistance member 15B has a structure in which the resistance members 16 used in the flow resistance member 15 are provided for the fuel spacer 6. The structure of the flow resistance member 15B excluding the resistance members 16 is the same as that of the fuel spacer 6. Further, the position of each of the resistance members 16 disposed in the flow resistance member 15B is the same as that of each of the resistance members 16 disposed in the flow resistance member 15, and the resistance members 16 are present in the above-described inner region. The projected area Sa of the flow resistance member 15B is Sa3 mm2, and is larger than Sb1 mm2, which is the projected area Sb of the fuel spacer 6 serving as the reference fuel spacer, by the sum of the projected areas of the plurality of resistance members 16. Further, the number R of the fuel rods 2 held by the flow resistance member 15B is 92, and is the same as the number A of all the fuel rods 2 in the fuel assembly according to the present embodiment being 92. The projected area ratio C of the flow resistance member 15B used in the present embodiment obtained according to the formula (1) (=(Sa3/Sb1)×(92/92)) is about 2.0. One flow resistance member 15B is disposed in a channel box 7, and disposed at upper end portions of partial length fuel rods 2B in the axial direction of the fuel assembly in the same manner as the flow resistance member 15 used in the embodiment 1. Each of spacer tabs 8 formed on a band 7 of the flow resistance member 15B comes into contact with the inner surface of the channel box 7. The flow resistance member 15B is supported by water rods 5 inserted into water rod disposition regions 14A in the same manner as the flow resistance member 15. Each of the fuel rods 2 is inserted into each of the ferrules 9 of the flow resistance member 15B. When operating a boiling water nuclear reactor in which the fuel assembly according to the present embodiment having the flow resistance member 15B is loaded in a core, in substantially the same manner as in embodiment 1, the flow of the gas-liquid two-phase flow occurring in this fuel assembly is divided into a gas-liquid two-phase flow flowing in each of the ferrules 9 present in an inner region where the resistance members 16 of the flow resistance member 15B are disposed and a gas-liquid two-phase flow flowing in each of the ferrules 9 present in an outer region surrounding the inner region. Since the pressure loss in the inner region of the flow resistance member 15B is increased as compared with that in the outer region of the flow resistance member 15B due to the effect of the resistance members 16, on the upper side of the flow resistance member 15B, the flow rate of the gas-liquid two-phase flow per unit area flowing through the outer region is increased. Due to this, cooling of each of the fuel rods 2 disposed in the outer region on the upper side of the flow resistance member 15B is promoted, and the critical power of these fuel rods 2 is increased, and thus, the thermal margin is increased. The flow rate of the gas-liquid two-phase flow passing through each of the ferrules 9 in the inner region of the flow resistance member 15B is decreased, however, also in a region directly above the upper ends of the partial length fuel rods 2B, cooling of the fuel rods 2 is promoted in the same manner as in embodiment 1. According to the present embodiment, each effect obtained in embodiment 1 can be obtained. Since the flow resistance member 15B has a support mechanism for supporting all the fuel rods 2, it is possible to substitute the fuel spacer 6. [Embodiment 4] A fuel assembly according to embodiment 3 which is other preferred embodiment of the present invention, applied to a boiling water nuclear reactor will be described in detail with reference to FIGS. 8 and 9. A fuel assembly according to the present embodiment has a structure in which the flow resistance member 15B in the fuel assembly according to embodiment 3 is replaced with a flow resistance member 15C (see FIGS. 8 and 9). The other structures of the fuel assembly according to the present embodiment are similar to the fuel assembly according to embodiment 3. The flow resistance member 15C has a structure in which a part of the plurality of ferrules 9 in the flow resistance member 15B used in the embodiment 3 are replaced with a plurality of ferrules 9D. The other structure of the flow resistance member 15C is the same as that of the flow resistance member 15B. The height (the length in the axial direction of the fuel assembly) h2 of the ferrule 9 used in the flow resistance member 15C is the same as that of the ferrule 9 used in the flow resistance member 15B. In the flow resistance member 15C, eight ferrules 9 are disposed in the inner region. That is, eight ferrules 9 are present on the inner side of the position where twelve resistance members 16 are disposed on the outermost side among the resistance members 16 disposed in the inner region. The ferrules 9D are disposed surrounding a region where the ferrules 9 are disposed. Due to this, the ferrules of three layers from the band 7 toward the inner side are ferrules 9D. The height (the length in the axial direction of the fuel assembly) h1 of the ferrule 9D is lower than the height h2 of the ferrule 9 (h1<h2). As a result, the height of the band 7 according to the present embodiment is lower than that of the band 7 according to embodiment 1. In the present embodiment, in the same manner as embodiment 3, the resistance members 16 whose number and size are the same as in the case of the flow resistance member 15B are disposed in the inner region of the flow resistance member 15C, so that the projected area ratio C of the flow resistance member 15C is the same as that of the flow resistance member 15B, and is about 2.0. However, in the present embodiment, since the height h2 of the ferrule 9 disposed in the inner region of the flow resistance member 15C is higher than the height h1 of the ferrule 9D, the pressure loss of the ferrules 9 is larger than that of the ferrules 9D. Due to this, the pressure loss in the inner region of the flow resistance member 15C is larger than that in the outer region of the flow resistance member 15C by the action of the resistance members 16 and the ferrules 9. Moreover, a difference in pressure loss between in the inner region and in the outer region of the flow resistance member 15C is larger than that of the flow resistance member 15B. One flow resistance member 15C is disposed in a channel box 7, and disposed at upper end portions of partial length fuel rods 2B in the axial direction of the fuel assembly in the same manner as the flow resistance member 15 used in embodiment 1. The flow resistance member 15C is supported by water rods 5 inserted into water rod disposition regions 14A in the same manner as the flow resistance member 15. Each of the fuel rods 2 is inserted into each of the ferrules 9 and the ferrules 9D of the flow resistance member 15C. When operating a boiling water nuclear reactor in which the fuel assembly according to the present embodiment having the flow resistance member 15C is loaded in a core, in substantially the same manner as in embodiment 1, the flow of the gas-liquid two-phase flow occurring in this fuel assembly is divided into a gas-liquid two-phase flow flowing in each of the ferrules 9 present in an inner region where the resistance members 16 of the flow resistance member 15C are disposed and a gas-liquid two-phase flow flowing in each of the ferrules 9D present in an outer region surrounding the inner region. The flow rate of the gas-liquid two-phase flow per unit area flowing through the outer region of the flow resistance member 15C is increased as compared with the flow rate of the gas-liquid two-phase flow per unit area flowing through the outer region of the flow resistance member 15B. Due to this, cooling of each of the fuel rods 2 disposed in the outer region on the upper side of the flow resistance member 15C is promoted, and the critical power of these fuel rods 2 is increased, and thus, the thermal margin is increased. The flow rate of the gas-liquid two-phase flow passing through each of the ferrules 9 in the inner region of the flow resistance member 15C is decreased, however, also in a region directly above the upper ends of the partial length fuel rods 2B, cooling of the fuel rods 2 is promoted in the same manner as in embodiment 1. According to the present embodiment, the respective effects generated in embodiment 1 can be obtained. Since the height of the ferrule 9D disposed in the outer region is lower than that of the ferrule 9 according to embodiment 4, the pressure loss in the outer region can be decreased as compared with embodiment 3. [Embodiment 5] A fuel assembly according to embodiment 5 which is other preferred embodiment of the present invention, applied to a boiling water nuclear reactor will be described in detail with reference to FIG. 10. A fuel assembly according to the present embodiment has a structure in which in the fuel assembly according to embodiment 3, the flow resistance member 15B is replaced with a flow resistance member 15D (see FIG. 10). The other structure of the fuel assembly according to the present embodiment is the same as that of the fuel assembly according to embodiment 3. The flow resistance member 15D used in the present embodiment has a structure in which in the flow resistance member 15B used in embodiment 3, the constituent components (ferrules 9, resistance members 16, etc.) present in the inner region of the grid-shaped flow resistance member 15B are replaced with the flow resistance member 15A used in embodiment 2. The structure of the flow resistance member 15D excluding the flow resistance member 15A is the same as that of the fuel spacer 6. That is, in the flow resistance member 15D, ferrules 9 of two layers are disposed surrounding the flow resistance member 15A. Further, the flow resistance member 15A is present in the above-described inner region in the same manner as in embodiment 2. The projected area ratio C of the flow resistance member 15D is the same as that in the second embodiment and is 3.0. One flow resistance member 15D is disposed in a channel box 7, and disposed at upper end portions of partial length fuel rods 2B in the axial direction of the fuel assembly in the same manner as the flow resistance member 15 used in embodiment 1. The flow resistance member 15D is supported by water rods 5 inserted into water rod disposition regions 14A in the same manner as the flow resistance member 15. Each of the fuel rods 2 is inserted into each of the ferrules 9 of the flow resistance member 15D and the fuel rod insertion holes 21 of the flow resistance member 15A. When operating a boiling water nuclear reactor in which the fuel assembly according to the present embodiment having the flow resistance member 15D is loaded in a core, in substantially the same manner as in embodiment 1, the flow of the gas-liquid two-phase flow occurring in this fuel assembly is divided into a gas-liquid two-phase flow flowing in each of the fuel rod insertion holes 21 present in an inner region where the flow resistance member 15A is disposed and a gas-liquid two-phase flow flowing in each of the ferrules 9 present in an outer region surrounding the inner region. Since the pressure loss in the inner region of the flow resistance member 15D is increased as compared with that in the outer region of the flow resistance member 15D due to the effect of the flow resistance members 15A, on the upper side of the flow resistance member 15D, the flow rate of the gas-liquid two-phase flow per unit area flowing through the outer region is increased. Due to this, cooling of each of the fuel rods 2 disposed in the outer region on the upper side of the flow resistance member 15D is promoted, and the critical power of these fuel rods 2 is increased, and thus, the thermal margin is increased. The flow rate of the gas-liquid two-phase flow passing through each of the fuel rod insertion holes 21 of the flow resistance member 15A disposed in the inner region of the flow resistance member 15D is decreased, however, also in a region directly above the upper ends of the partial length fuel rods 2B, cooling of the fuel rods 2 is promoted in the same manner as in embodiment 1. According to the present embodiment, the respective effects generated in embodiment 1 can be obtained. In addition, according to the present embodiment, the following effects can be obtained. In order to increase the pressure loss, a grid-shaped configuration is effective, and on the contrary, a ferrule-type configuration is preferred in order to decrease the pressure loss. Therefore, in order to provide a difference in pressure loss between in the inner region and in the outer region in the cross section of the fuel assembly, by adopting the configuration of the flow resistance member 15D shown in FIG. 10, the thermal margin of the fuel rods 2 disposed in the outer region can be improved owing to a difference in flow resistance while substituting the fuel rod holding function of the fuel spacer. 1: fuel assembly, 2, 2A: fuel rod, 2B: partial length fuel rod, 3: lower tie plate, 4: upper tie plate, 5: water rod, 6: fuel spacer, 7: channel box, 9, 9A, 9B, 9C, 9D: ferrule, 12, 12A: bridge member, 14, 14A: water rod disposition region, 15, 15A, 15B, 15C, 15D: flow resistance member, 16, 17: resistance member, 21: fuel rod insertion hole, 22: plate member. |
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abstract | A radiographic apparatus is disclosed which controls a movement of a reciprocatingly moving grid so that the grid is not or less likely returned in the middle of exposure of an object to X rays. The probability that the object is still exposed to the X rays when the grid is moved in the vicinity of a turning point is thus substantially lowered. Therefore the probability that a resulting radiograph has no or less moire pattern due to the grid is substantially heightened. |
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abstract | A halide material, such as scintillator crystals of LaBr3:Ce and SrI2:Eu, with a passivation surface layer is disclosed. The surface layer comprises one or more halides of lower water solubility than the scintillator crystal that the surface layer covers. A method for making such a material is also disclosed. In certain aspects of the disclosure, a passivation layer is formed on a surface of a halide material such as a scintillator crystal of LaBr3:Ce of SrI2:Eu by fluorinating the surface with a fluorinating agent, such as F2 for LaBr3:Ce and HF for SrI2:Eu. |
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abstract | A radioisotope power source is disclosed. In one embodiment, the power source includes a dielectric liquid held within a vessel, a radioisotope material dissolved as an ionic salt within the dielectric liquid thereby forming an ionic salt solution, and a thermal-to-electric power conversion system configured to receive thermal heat generated from the decay of the radioisotope material and to generate electrical power. |
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claims | 1. A molten fuel nuclear reactor comprising:a reactor vessel defining a reactor core configured to contain molten nuclear fuel;a first heat exchanger arranged above and in fluid communication with the reactor core to receive nuclear fuel from the reactor core;a second heat exchanger arranged above the reactor core and in fluid communication with both the first heat exchanger and the reactor core to receive nuclear fuel from the first heat exchanger and deliver nuclear fuel to the reactor core,wherein nuclear fuel delivered to the reactor core is at a lower temperature than nuclear fuel received by the first heat exchanger; anda containment vessel surrounding the reactor vessel, the first heat exchanger, and the second heat exchanger;wherein the first heat exchanger includes a shell-and-tube heat exchanger and the second heat exchanger includes a separate shell-and-tube heat exchanger. 2. The molten fuel nuclear reactor of claim 1 further comprising:one or more impellers within the containment vessel configured to drive the flow of fuel through the reactor vessel, the first heat exchanger, and the second heat exchanger. 3. The molten fuel nuclear reactor of claim 1 further comprising:a neutron shield positioned between the reactor core and the first and second heat exchangers. 4. The molten fuel nuclear reactor of claim 1 further comprising:a reflector assembly surrounding at least a portion of the reactor vessel. 5. The molten fuel nuclear reactor of claim 1 further comprising:a reflector assembly within the reactor vessel and configured to be submerged within the nuclear fuel at a periphery of the reactor core during reactor operation. 6. The molten fuel nuclear reactor of claim 1 further comprising:one or more baffles affecting nuclear fuel flow in at least one of the reactor core, the first heat exchanger, and the second heat exchanger. 7. The molten fuel nuclear reactor of claim 1 further comprising:a plenum between a nuclear fuel outlet of the first heat exchanger and a nuclear fuel inlet of the second heat exchanger. 8. The molten fuel nuclear reactor of claim 1,wherein during reactor operation natural circulation drives the flow of nuclear fuel through the reactor vessel, the first heat exchanger, and the second heat exchanger,the natural circulation created by a temperature difference between fuel in the reactor core and the lower temperature fuel exiting the second heat exchanger. 9. The molten fuel nuclear reactor of claim 1, wherein the nuclear fuel is a salt of chloride, bromide, and/or fluoride. 10. The molten fuel nuclear reactor of claim 1, wherein the nuclear fuel contains one or more of uranium, plutonium, or thorium. |
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052672808 | abstract | Process for the conditioning or recycling of used ion cartridges.. The invention relates to a process for the treatment of ion cartridges or elements ensuring the treatment of contaminated waters of storage ponds or pools for nuclear reactor fuels. By cartridge transfer and suction means, said treatment consists of extracting the ion exchange resins contained in the cartridge.. When the resin has been extracted, a conditioning process makes it possible to decontaminate and then condition, independently of the resinous substance, the metal structure constituting the cartridge.. When the resin has been extracted, a recycling process makes it possible to clean the impurities from the metal structure and fill it again with new resin.. The invention has applications in the nuclear field and in particular in the field of treatment and conditioning of nuclear waste. |
043942695 | description | DETAILED DESCRIPTION The treated silica gel useful for the process of this invention can be prepared by soaking the gel in an aqueous solution of NaOH or LiOH for about 24 hours, after which the gel is filtered, air dried, washed with water, and again air dried. This treatment results in the adsorption of Na.sup.+, Li.sup.+, and OH.sup.- ions on the surface of the gel and increases the gel surface charge. Tests made by the inventors have shown that the capacity of the treated gel to clean TBP solvent increases with the amount of sodium or lithium adsorbed on the gel, the principal factor which determines the amount of the alkali metal adsorbed on the gel being the specific surface area of the latter. It is therefore preferable, so far as is practical while maintaining a desired flow rate through a column, to use a silica gel having a small particle size, and concomitantly a large surface area, to increase the gel adsorption capacity. A number of commercially available silica gels with mesh sizes up to 100-200 mesh have been effectively used in tests made by the inventors. The principal impurities removed from TBP solvent by the process of this invention are monobutyl phosphate, dibutyl phosphate, UO.sub.2.sup.2+, Pu.sup.4+, and fission products of plutonium and uranium complexed with monobutyl phosphate or dibutyl phosphate. Nitric acid is also removed from the TBP solution by the treated silica gel. Conventional adsorption column techniques are applicable for the process of the invention. One option for disposal of silica gel loaded with the above-named impurities by the process of the invention is to treat the gel as waste. For example, the loaded gel can be incorporated into glass bricks for convenient handling and storage. Another disposal option is to wash adsorbed impurities off the gel and then recycle it into further contact with contaminated TBP solution. Suitable solutions for eluting the gel are one containing 30% TBP and 70% hydrocarbon diluent, HNO.sub.3, and aqueous HNO.sub.3. Tri-2-ethylhexyl phosphate in a hydrocarbon diluent is being considered as an alternative to TBP for use in recovering uranium and plutonium from nitric acid nuclear fuel dissolving solutions. The mono-2-ethylhexyl phosphate and di-2-ethylhexyl phosphoric acid degradation products formed from this alternative extractant are extremely difficult to clean from the extractant by use of conventional sodium carbonate washing due to emulsion problems. However, the treated silica gel used in the process of this invention has been found to be effective for removing the mono-2-ethylhexyl phosphoric acid and the di-2-ethylhexyl phosphoric acid product from a tri-2-ethylhexyl phosphate and hydrocarbon diluent solution. The adsorption capacity of the treated gel for removing the last-named degradation products of tri-2-ethylhexyl phosphate is less than that of the gel for removing the degradation products of TBP because of the larger molecular size of the former compared to the latter. Use of the herein disclosed treated silica gel for removing contaminants from a solution of a hydrocarbon diluent and either tri-n-butyl phosphate or tri-2-ethylhexyl phosphate provides the following advantages: 1. The gel minimizes the problem of waste disposal associated with the sodium carbonate wash method of decontaminating a DBP solution. 2. The use of the gel eliminates the problems of gassing, emulsion, slow phase separations, formation of insoluble material at interfaces of phases, and entrainment between phases that occur when wash solutions are used for decontaminating extractant solutions. 3. The gel requires a much smaller storage volume than a wash liquid. 4. Wash methods require neutralization of acid in the extractant solution, which results in precipitation problems that are eliminated by use of the gel of the invention. Furthermore, the treated silica gel acts as a filter for the extractant solution so that other filters are not needed. 5. Treated silica gel is less subject to chemical and radiation damage than the macroreticular resins previously used as adsorbents for the contaminants in extractant solutions, and the gel can easily be eluted whereas macroreticular resins are eluted with difficulty. 6. The column flow rate usable with the method of this invention is at least twice that reported for hydrous titanium decontamination columns. 7. The use of treated silica gel for cleaning an extractant solution eliminates problems of toxicity and explosion that are involved with the use of hydrazine compounds as cleaning agents. 8. Lastly, the gel used in accordance with this invention is more effective for cleaning an extractant solvent than the wash or macroreticular cleaning means. The following test examples specifically illustrate the process of this invention. EXAMPLE I The following is a description of a solvent cleanup test using silica gel treated with LiOH in which silica gel column loading, elution, and regeneration are demonstrated. A batch of 6-16 mesh silica gel (Fisher Scientific Grade 05) was soaked for 24 h in a volume of 1.0 M NaOH solution such that 2 millimoles of LiOH were present in the solution per gram of silica gel. The gel was filtered, air dried, washed with a volume of water equal to the initial volume of LiOH solution, and again air dried. Analyses showed that the treated silica gel solids contained 250 mg of water and 7.3 mg of lithium per gram of gel. A 30% TBP approximately 70% hydrocarbon feed solvent containing 1.5.times.10.sup.-3 M UO.sub.2.sup.2+, 2.70.times.10.sup.-3 M dibutyl phosphate (DBP), approximately 3.0.times.10.sup.-4 M monobutyl phosphate (MBP), and slightly less than 5.times.10.sup.-3 M HNO.sub.3 was fed at a rate of 0.4 ml/min into a 1.0 cm diameter column containing 17.5 ml (15.7 g) of the above described pretreated silica gel at approximately 40.degree. C. Slight breakthrough of the DBP into the effluent began after 1250 ml of feed had passed through the column, and slight breakthrough of UO.sub.2.sup.2+ occurred after 1500 ml of feed had passed through. The column was drained after the UO.sub.2.sup.2+ began to break through and eluted with 150 ml of 0.25 M HNO.sub.3 aqueous solution at a 0.4 ml/min flow rate. It was found that 13 ml of the organic solvent which had adhered to the gel surface came off the column with the 150 ml of aqueous elution. At this point, the silica gel in the column was regenerated by a treatment in which each of two 25 ml volumes of 0.5 M LiOH were allowed to stand in the column for 4 h. Any DBP not eluted previously is eluted in this step. The column was drained, lightly dried with a stream of air, and filled with pure 30% TBP--70% normal paraffin hydrocarbon solvent (hereinafter referred to as NPH). The column was used in two additional loading, elution, and regeneration cycles similar to the above except that the elutions were with 100 ml volumes of 30% TBP, approximately 70% NPH, 0.6 M HNO.sub.3 solvent. The average loading on the silica gel column in the three cycles was approximately 0.19 millimoles of UO.sub.2.sup.2+ and 0.29 millimoles of DBP per gram dry weight of the silica gel. On the average approximately 98% of the UO.sub.2.sup.2+ and 92% DBP was eluted in each cycle. In the regeneration step, an average of approximately 1.0 millimole of lithium was adsorbed per gram of moist silica gel. This is approximately the quantity of lithium adsorbed per gram in the original preparation of the solid sorbent. EXAMPLE II The following is a description of a solvent cleanup test which is typical of several tests conducted using silica gel treated with sodium hydroxide (NaOH) solutions. A column the same size as in Example 1 was filled with 17.0 g of silica gel the same as Example 1 except that it was pretreated with NaOH solution instead of LiOH solution. The pretreated gel contained 236 mg of H.sub.2 O and 20.4 mg of sodium per gram of gel. A 30% TBP approximately 70% NPH feed solvent containing 4.6.times.10.sup.-3 M UO.sub.2.sup.2+, 8.0.times.10.sup.-3 M DBP, and less than 5.0.times.10.sup.-3 M HNO.sub.3 was fed into the column at 40.degree. C. at a rate of 0.3 ml/min. The UO.sub.2.sup.2+ and DBP effluent breakthrough curves are shown in the accompanying drawing. As can be seen, 400 ml of solvent was put through the column before there was significant breakthrough of the UO.sub.2.sup.2+ and DBP in the effluent. Average loading on the column amounted to 0.14 millimoles of UO.sub.2.sup.2+ and 0.23 millimoles of DBP per gram dry weight of the silica gel. It is estimated from extrapolation of the data in the drawing that 0.22 millimoles of UO.sub.2.sup.2+ and 0.31 millimoles of DBP would be loaded per gram dry weight of silica gel at 100% breakthrough of these constituents into the effluent. The approximate 26,000 liters of solvent used in processing one metric ton of nuclear fuel is estimated to contain approximately 26 mol each of UO.sub.2.sup.2+ and DBP. The estimated amount of sodium required to clean up 26,000 liters of such solvent using the silica gel method based on the above loading values would be approximately 3 kg. It has been estimated that 25 kg of sodium or approximately 100 kg of sodium nitrate is produced as waste using the sodium carbonate wash solvent cleanup method. Other tests were conducted identically to the above test except at faster feed flow rates. From these tests, it was shown that the capacity of the silica gel to load UO.sub.2.sup.2+ and DBP was unchanged at flow rates up to 1.1 ml/min. The capacity was decreased by approximately 40% at a rate of 1.7 ml/min. EXAMPLE III This is a description of tests to clean up irradiated solvent (30% TBP approximately 70% NPH). The test solvent had been used to extract uranium and plutonium from a dissolver solution of H. B. Robinson-2 reactor fuel. After the extractions, the loaded solvent was contacted with nitrous acid solution to remove easily stripped plutonium and with 0.01 M HNO.sub.3 solution to remove easily stripped uranium. In a process the stripped solvent at this point would be sent to solvent cleanup. The respective gross alpha and gross gamma activities retained in the stripped solvent were 4.8.times.10.sup.4 and 7.4.times.10.sup.3 c/m/ml and the respective DBP, UO.sub.2.sup.2+, and H.sup.+ concentrations were 3.times.10.sup.-4 M, 4.45.times.10.sup.-3 M, and 1.0.times.10.sup.-2 M. The alpha activity was primarily from .sup.239 Pu and the gamma activity primarily from fission product metal ions. A 270 ml volume of the stripped solvent was passed through a 1.0 cm diameter column containing 15 ml of silica gel (pretreated as described in Example II) at a rate of approximately 1.0 m/min. The gross alpha and gross gamma activities in the effluent solvent were decreased to less than 20 c/m/ml and less than 400 c/m/ml, respectively. The DBP concentration was decreased to 5.times.10.sup.-5 M and the MBP concentration was below the limits of detection (less than 1.times.10.sup.-5 M). Decontamination factors obtained for the solvent in the silica gel column are shown in Table 1. Decontamination factors for sodium and hydrazine carbonate equal volume wash tests are also shown. The gross alpha decontamination factor obtained by the column treatment was approximately 1200 times greater than that obtained in the wash tests. The gross gamma decontamination factor was only slightly greater in the column tests. TABLE I ______________________________________ Comparison of column tests.sup.a with aqueous wash tests.sup.b for solvent.sup.c cleanup Sodium Hydrazine Decontamination carbonate carbonate Silica gel treated factor 0.23 M 0.23 M with NaOH ______________________________________ Gross alpha.sup.d 2.0 1.9 2.4 .times. 10.sup.+3 Gross gamma 16.5 6.9 18 ______________________________________ .sup.a Column contained 15 ml of treated silica gel, flow rate = 1.3 ml/min/cm.sup.2 of column cross section surface area, temperature 40.degree. C. .sup.b Equal volume aqueousorganic equilibrations for 5 min, temperature 25.degree. C. .sup.c Solvent from tests using feed from H. B. Robinson fuel under LMFBR fuel processing conditions. .sup.d Gross alpha approximately 98% .sup.239 Pu and .sup.238 Pu. |
summary | ||
abstract | A radiation source for use in lithography. The radiation source comprising a pn-junction disposed on a substrate that can be reverse-biased to cause avalanche breakdown and emission of UV or DUV radiation by deceleration of electrons accelerated into an n-type region of the pn-junction. The radiation source can have a low operating voltage, a high switching speed, and provides great design freedom. High intensity can be provided, e.g., by the use of large or multiple sources. The pn-junction can be doped with impurities to increase emission of radiation at a desired frequency and increase the efficiency of the device. For protection, the pn-junction may be covered by a layer of transparent oxide. By reverse biasing the pn-junction with a potential difference at least 4V, radiation of wavelength 300 nm or less can be obtained. The pn-junction source of the present invention can replace conventional radiation sources and be using in connection with a mask/contrast device, or can be used to replace both the conventional radiation source and the mask/contrast device. |
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description | The following description is of the best mode presently contemplated for practicing the invention. This description is not to be taken in a limiting sense, but is made merely invention. The scope e invention should be ascertained with reference to the issued claims. In the description that follows, like numerals or reference characters will be used to refer to like parts or elements throughout. Referring now to the drawings, and more particularly to FIGS. 1, 2A and 2B, there is shown a commonly used conventional microelectronic package 10, which is a plastic package. FIG. 1 illustrates the package 10 with a spot shield attached. The packages are comprised of a die 20, which is composed of silicon or other semiconductor base. The die is generally attached to a die attach pad 18 for support. The die is then bonded with multiple lead wires 22, 24 to a lead frame with multiple leads 15, 16. This entire assembly is encased within a package 13 composed of suitable plastic material or other material such as ceramic. If thermal conductivity properties are important considerations, other materials such as ceramics are used, as shown in FIG. 3, these are more difficult to work with and can be conducting, necessitating an insulating feed through 25 to cover the leads 15, 16. A conventional method for shielding these packages is shown in FIG. 1, where a pair of shielding plates 30 and 31, usually made of a high Z material such as tantalum, is attached to the top and bottom portions of the package 13 respectively by a suitable adhesive (not shown). As shown in FIG. 3, another prior art technique relates to the use of integrated shielding technology, where the package itself, is part of the shielding. FIG. 3 shows the integrated shielding package 310 that also incorporates multiple die 320 and 321. The multiple die 320 and 321 on a die attach pad 318 employ multiple lead wires 322 and 324, together with a lead frame with multiple leads 315 and 316 and an insulating feed through 325, for a package 313. This type of package is called an MCM or Hybrid package. With multiple die within the package, the density of functions increases, while the overall weight required to accomplish the task is reduced. This type of packaging requires base members 340 and 341, which can be made of various shielding materials. For ionizing radiation, high Z materials can be used, enabling the package itself to become the radiation shielding. As shown in FIG. 4, the inventive method includes, as indicated in box 100, determining the inherent radiation tolerance of the die to be shielded. This test can be accomplished by a Cobalt-60 source or other penetrating irradiation source. Without the knowledge of what the inherent radiation tolerance is for the individual semiconductor device, the designer does not know how much or whether shielding is necessary. The next step as indicated at 102 involves determining the radiation spectrum and dose depth curve of the particular mission or radiation requirement of the application. For orbits around the earth, this is calculated using conventional radiation transport codes in conjunction with conventional radiation spectrum tables. The dose depth curve is generally represented as a total radiation dose versus thickness of equivalent aluminum shielding as shown in FIG. 5. Although not preferred, steps indicated at 100 and 102 can be omitted if the application is unknown and the designer desires only to enhance whatever the radiation tolerance of the integrated circuit to be protected. Knowing the inherent radiation tolerance of the integrated circuit device, as indicated at 100 and the dose depth curve as indicated at 102, the amount of shielding required can be determined to bring the integrated circuit device within tolerance as indicated at 104. Knowing the spectrum of radiation for the application, the layering of the inventive shielding material is tailored as hereinafter described in greater detail with reference to FIG. 8. High Z material is more effective at stopping electrons and Bremsstrahlung radiation, and less effective in stopping protons. Low Z material conversely is more effective at stopping protons and less effective at stopping electrons and Bremsstrahlung radiation. The next step, as indicated at 106, requires determining the form of the integrated circuit. For a prepackaged part, the amount of shielding is limited by the lead length on the bottom of the device, unless extenders are used. The most appropriate method of application of the inventive shielding composition is then determined as indicated at 108. The part is coated in a mold (not shown), using a dam (not shown), and the coating can be globbed, sprayed, injected or painted on. For die that are already mounted on the board (not shown), the methods mentioned above are effective, but to insure uniform radiation shielding, the bottom of the board underneath the part is also coated with the same thickness of the inventive shielding composition. The coating material is applied as indicated at 110 and then allowed to cure as indicated at 111. Temporary extenders are preferably used to provide thorough wetting throughout the binder. As an example, a preferred extender for epoxy is a high boiling point ketone. Additionally, by adjusting the properties of the binder, the bulk electrical properties of the shield composition is adjusted to be either insulating or conductive. Upon completion of coating the parts, testing is then performed electrically and mechanically, as indicated generally at 112. For space applications, the parts require space qualification testing. There are various different methods of application of the inventive shielding composition as contemplated by the invention and as indicated in FIGS. 5, 6, 7 and 8. However, the following examples are intended to be representative and not all inclusive of the possible application methods falling within the scope of the present invention. Referring now to FIG. 6, a coating method of the present invention is illustrated for a die 600 attached to a substrate 604. It should be understood that a multiple die device, such as the one shown in FIG. 3, may also be protected as will become apparent to those skilled in the art. The die is wire bonded at 606 and at 607 to lead frame devices 602 and 603, respectively, to complete electrical connections between the die and systems (not shown) outside of the package. A radiation shielding conformal coating composition is applied to the outside of the package 610. The package can then be applied to a board 615 or any other attachment system by any suitable conventional technique. The radiation shielding conformal coating composition 610 is applied uniformly on the outer surface of the package to insure uniform radiation protection in accordance with the present invention. The coating can be applied by injection molding, mold casting, spraying, globbing or brushing the material onto the part to be protected. Referring now to FIG. 7, another method,.of application according to the invention includes applying the radiation shielding conformal coating composition generally indicated at 709 to an integrated circuit device 700 previously attached to a board 730. The board 730 may have other devices such as a pair of devices 701 and 702 not requiring protection. The device 700 is attached to the board via wire bonds 720 and 721. The radiation shielding conformal coating composition 709 is then applied both on top of the device 700 at 711 and directly underneath the device 77 at 710 on the board 730. An area greater than the size of the device 700 is covered with radiation shielding conformal coating composition 710 on the bottom of the board 730. This is required to insure that the entire integrated circuit device is protected from radiation. The radiation shielding conformal coating composition 709 is applied by the same method as described in connection with the inventive method of FIG. 6. Referring now to FIG. 8, to enhance radiation shielding performance, multiple layers of the inventive radiation shielding conformal coating composition are applied. Using conventional codes such as NOVICE, different shielding layering are developed for each type of orbit. An optimum shielding geometry for a Geosynchronous Orbit is shown in FIG. 8. As shown in FIG. 8, in accordance with the present invention, a die 800 having an integrated circuit package 804 containing lead frame devices 802 and 803 is encased within a multiple layer radiation shielding composition generally indicated at 820, prior to mounting the shielded die to a board or substrate 815. The multiple layer shielding composition 820 comprises a layer of high Z particles 811 interposed between a pair of outer and inner layers of low Z particles 810 and 812. The low Z layer 812 is applied directly to the outer surface of the die 800 in accordance with the method described in connection with FIG. 6. Thereafter, the intermediate high Z layer 811 is then applied to the outer surface of the inner low Z layer 812. The outer low Z layer 810 is then applied to the outer surface of the intermediate high Z layer 811 to complete the shielding protection for the die 800. The shielded die 800 is then connected electrically and mounted to the board 815 by conventional techniques. The high Z material is effective in stopping electrons and Bremsstrahlung radiation, while the low Z material is more effective in stopping protons. A Geosynchronous orbit is dominated by trapped electrons, so it is preferable that the intermediate high Z layer 811, is thicker than the other two low Z layers. It will become apparent to those skilled in the art that the multiple layer coating method of the present invention can be used in connection with the protection of many different types and kinds of integrated circuit devices and the like. Additionally, the coating method can be applied by any method including, but not limited to, those described in connection with the method of FIG. 6. Referring to FIG. 9, there is shown a flexible shielding material, which is composed according to the present invention. The material 900 contains the inventive radiation shielding composition, and is flexible and pliable to serve as clothing for humans or gasket material for parts (not shown). The conformal coating material 900 includes a flexible binder such as latex. The material 900 is impregnated with a fabric such as a cloth woven material 910 for strength. The cloth material can be composed of conventional materials such as cotton or polyester. For extra strength, nonwoven fabric such as Kevlar or Teflon material can be used for the fabric. Considering now the inventive radiation shielding composition forming a part of the foregoing inventive methods and materials, the following examples of shielding compositions are given to aid in understanding the invention, but it is to be understood that the particular procedures, conditions and materials of these examples are not intended as limitations of the present invention. The tungsten powder serves as a high Z material for radiation shielding purposes. The epoxy serves as a binder to help adhere the composition to a surface, and the ketone is added as an extender. To formulate the inventive composition, the ingredients of Example I are mixed thoroughly, and then the mixture is applied to a part. The applied mixture is in the form of a paste, and is heated slowly at a suitable low temperature such as 40xc2x0 C. for about one hour to remove a substantial portion of the ketone extender without disrupting the integrity of the packed tungsten powder. The mixture is then heated at about 60xc2x0 C. for about 16 hours to retain the stability of the composition. The temperature is then increased to about 150xc2x0 C. for an additional period of time of about 0.5 hours. The resulting mixture has the desired consistency of a paste, and retains its stability due to the foregoing multiple heating phases. In general, the ingredients of the present Example can be adjusted to accommodate variations in the foregoing described inventive methods and applications. The shielding powder can be any suitable high Z radiation shielding powder such as osmium, iridium, platinum, tantalum and gold. In general, any high Z material may be employed having an atomic number of 50 and above. More preferably, the range of atomic numbers can be between 60 and 100, inclusive. The most preferred range of atomic numbers is between 73 and 79, inclusive. The shielding powder can also be a low Z material, such as the one mentioned in connection with the description of the inventive method of FIG. 8. The low Z shielding powder is preferably selected from the group consisting of copper, nickel, carbon, titanium, chromium, cobalt, boron, silicon, iron and nitrogen. In general, any suitable low Z material may be employed having an atomic number of 30 and below, but the most preferred group of low Z materials is selected from the group consisting of copper, nickel, carbon, iron, titanium, silicon and nitrogen. In general, the shielding powder can be any suitable material composed of a matrix of densely packed shielding particles. The preferred material is tungsten (Example 1) having a packing density of at least 150 grn per cubic inch. There can be between about 0.10 and about 0.50 parts by weight of a binder in the form of a suitable resin. The binder can be a urethane. The exact quantity of the binder determines the final density and strength of the shielding afforded by the inventive composition. A more preferred range of the binder is between about 0.13 and about 0.30. Also, in general, the extender assures complete wetting of the powders and adjusts the viscosity of the paste to suit the application method. This example of the inventive material may be used for the method described in connection with FIG. 9, wherein a fabric may be embedded therein for reinforcing purposes. Any suitable elastomer may be employed for the latex. As shown and described in the accompanying provisional patent application in Appendix A, there is described and shown a further and more detailed disclosure of the inventive methods and compositions. In the Appendix A, the inventive radiation shielding composition is identified by the trademark xe2x80x9cRADCOAT.xe2x80x9d. This invention provides additional ionizing radiation resistance to virtually any sensitive electronic device, with or without a package. Specifically, resistance to total dose ionizing radiation can be enhanced by adding shielding to any device without modification to Its form or function. Additional shielding, particularly under the device could be accommodated if lead lengths could be Increased. This invention utilizes a filled conformal coating in a versatile system that can apply high density material for localized shielding to many types of electronic components from exposed die to finished components mounted on a printed circuit board. It is suitable for low volume customized usage and does not require expensive tooling or equipment to implement The material is intended to provide easy application of a form of radiation shielding to existing electronic or other sensitive devices. The material developed here is essentially a (polymer or glassy) matrix highly loaded with dense (high specific gravity) particles. Tungsten (dispersed in epoxy) provides the most convenient, efficient and readily available radiologically dense material. Selection of the most appropriate combinations of particle sizes and shapes can increase the loading of the composite to provide the maximum density of the composite while retaining the workability of the paste prior to curing. Selection of the polymer can provide optimum adhesion of the particles to each other and to the component being shielded and influences the compatibility, workability and the mechanical and electrical properties of the composite. Some polymers allow the composite to be electrically insulating even at the high loading desired for maximum density. Spherical powders with a tap density of the order of 200 grams/cubic inch can produce composites with a specific gravity of 13 when mixed In the approximate ratio of 10 grams of powder to 0.15 grams of polymer. Fugitive solvents that are compatible with the chosen matrix can be added to ensure wetting of all the particles and satisfactory rheology of the paste. The rheology of the paste can be adjusted to suit the application (e.g. casting, molding, syringe or spray) and end use (e.g. bare die or mounted package). The polymer binder chemistry can also be varied to suit the application method. Lower density pastes can be used if thicker coatings can be tolerated. This widens the range of particle sizes and morphologies that can be incorporated into the paste. The additional polymer can be beneficial in terms of rheology, adhesion, electrical and thermo-mechanical properties. The insulating nature of the shielding paste can be enhanced by precoating the powders or by precoating the component. Allowing the insulating paste to completely cover the component including the leads can improve the level of shielding. Depending on the rheology of the paste, the coating material can be built up by spray or spatulation or if a lower viscosity paste is used, a dam can be placed around the device Until it has cured or solidified in place. The concept for RADCOAT(trademark) is based on RAD-PAK(copyright) and similar radiation hardening techniques which uses localized dense""shields around a sensitive (electronic) device. maximizing the density (specific gravity (S.G.)) of the shielding material, optimizes the efficiency of the shielding and minimizes the thickness and total mass of the shields. (Density and specific gravity are used interchangeably,. Density values used here have units of grams per cubic centimeter (gm/cc), specific gravity is numerically the same but has no units. The disadvantage to RAD-PAK(copyright) shielding is the package has to be individually designed and prefabricated for specific customized packages and applications and have to be prepared differently based on whether they are permanently brazed to the ceramic or soldered on as a lid. Long lead times and expensive customized tooling are a consequence of these requirements. They are not usually suited to attaching to finished devices. There is therefore a need for a material that would overcome these limitations The approach taken here is to use a thick film paste that would adhere to and conform to any device. Optimizing of the paste includes maximizing the content (mass) of the high xe2x80x9cZxe2x80x9d material in the paste to maximize the density of the resultant shield. (where xe2x80x9cZxe2x80x9d refers to the atomic number. In the xe2x80x9cArtxe2x80x9d, high Z refers to elements with atomic numbers greater than roughly 40.) The vehicle supports the high xe2x80x9cZxe2x80x9d powder and eventually bonds the mass in place on the package or device. The vehicle has to have other desirable properties which will be discussed later. The usual processing of refractory powdered metals involves high temperatures and pressures. Obviously this is not compatible with electronic devices so a different approach has to be taken. The most obvious way is to mix the powder in a liquid suspension that later hardens after application. Epoxy is a suitable medium. One problem is that it is usually difficult to add more than about 60 volume percent (v/o) of powder in the resin before it becomes xe2x80x98too dryxe2x80x99 or otherwise unmanageable. The effective density of such a composition would only be less than 12 grams/cc. The most promising shielding effectiveness lies with manipulating the xe2x80x98packing densityxe2x80x99 of the xe2x80x9chigh Zxe2x80x9d powder in the resin vehicle to maximize the final density of the composite. The technical paper entitled xe2x80x9cThe Advantage of Low Pressure Injection Moldingxe2x80x9d by Peter Shaffer in Materials Technologyxe2x80x94March/April 1993 is a guide in directing the development of high density pastes. Particularly relevant excerpts are reproduced below: The way to obtaining high particulate loadings is well known. Into an array of closely packed large particles is introduced a quantity of smaller ones of such size that they fit into the interstices between the larger ones. A small amount of an even finer fraction is introduced to fill these smaller voids, and so on, and so on with monosized spheres, the theoretical packing density in a close packed array is 74 v/o (volume percent). Perfect bimodal (to discrete sizes) packing yields a theoretical limit of 86 v/o, trimodal (three modes), 90 v/o. In practice the theoretical 74 v/o is never reached instead typical powder loadings, almost without regard for their composition, rarely exceed about 60 v/o. For an ideal four component packing system, the diameter ratios have been determined to be 316:36:7:1. This is frequently simplified to the rule of 7, each size differing from that of the next larger by a actor of seven The relative volume ratios were determined to be approximately 61:23:10:6. These determinations r made on near perfect-spheres of very narrow size ranges. Relatively Zings obtaining the high particle loadings is the easy part, making the system sufficiently fluid to flow is not The particles must be fully dispersed and all agglomerates broken into their individual crystallites. Their surfaces must be fully wetted by the fluid medium Finally, the suspension must be stabilized to prevent reagglomeration. The relative viscosities of a range of packing configurations have been calculated as shown in FIG. 1xe2x80x941. Further it has been demonstrated that at solute fractions over about 70 v/o, the viscosity should be expected to increase dramatically, even in systems having an infinite particle size distribution. In practice, most systems show greater tendencies to high viscosities and dilatancy than these calculations would suggest. A wide range of powders shapes are available, including spherical, crystalline and irregular. Some have high degrees of agglomeration, some have an inherently wide range of particle sizes some are fairly uniform in size. As expected, the coarser powders are better than the finer ones. Referring to FIG. 10, shown is a graph illustrating density variation with respect to percent by weight of Grade 50M spheroidal high. Z material. The best powder encountered was a fairly coarse spherical powder with a significant proportion of a range of finer powders. Binders appear to be interchangeable insofar as the resultant density of the composite (for a particular powder) is concerned. The nature of the binder does influence some other properties as will be discussed later. Epoxies, probably more thoroughly plasticized for fracture toughness may prove to be the best choice and are likely to be NASA approved for the proposed end use. Thermoplastic and thermosetting formulations are often available which adds to the versatility of the system and can be changed to suit the method of application. Preliminary results show that the density/radiation protection performance is not dependent on the binder chemistry. Therefore, any superior resin system can be substituted at any time. Latex appeared to have the best overall properties as far as preparation, application and cured properties are concerned. While latex may not be the material of choice since it contains ammonia and water in the uncured state, a suitable synthetic material that is similar in consistency and behavior could be used that would be acceptable for contact with electronic devices. The best results so far from simple mixing of selected powder and resin (with the aid of a fugitive wetting agent) has been a S.G of 13.1 with 10 grams of powder mixed with 0.15 grams of epoxy resin. If the composite had been fully dense, there would have been 79 v/o of metal in the composite and the S.G would have been 15.5. Approximately 12 v/o of voids must therefore be present to account for the measured density value. This powder loading of about 67 v/o resulting from a rather crude manual mixing technique is quite good since the literature cited earlier indicated that it difficult to routinely exceed 60 v/o. Another consideration has to be the electrical properties of the material since it may be in intimate contact with a wire bonded bare die or a package with exposed leads. The high loadings of metallic powder is expected to result in a conductive material from extensive particle to particle contacts, but the epoxyxe2x80x94and latexxe2x80x94based composites have high resistances The siliconexe2x80x94based composites were highly conductive. If the binder completely wets the xe2x80x9chigh Zxe2x80x9d particles then the lowest free energy state for each particle would be surrounded by a thin film of liquid. This insulating film isolates the xe2x80x9chigh Z particles and results in a non-conductive composite. (Externally applied pressure could disrupt this insulating film and force particle to particle contacts). Contact angles greater than zero would result in agglomeration of the particles and conductive paths and this may account for the conductivity of the siliconexe2x80x94based composites. The xe2x80x9chigh Zxe2x80x9d powders can be individually coated to ensure that no particle to particle contacts could occur which would compromise the insulating properties of the composite. Larger particle sizes which make the denser composites can be coated with thin layers of an insulator without seriously degrading the density of the particles. Suitable rheology needs to be maintained while maximizing the particle content of the uncured paste. The easiest application is to pour the paste over the device. A better method would involve putting a dam around the to contain the shape and maintain the appropriate shielding thicknesses. However, not all PWAs requiring shielding may allow the use of dams. Syringe application is another method. A lower solids paste with a fast evaporating solvent constituent might allow a syringe to be used. Such a formulation, may also allow spraying to be used to build up to the required thickness and shape in the same manner gunite is applied. RAD-COAT(trademark) can be applied to parts on a board, chip-on boards, and to the individual prepackaged or unpackaged components for ionizing radiation shielding. While particular embodiments of the present invention have been disclosed, it is to be understood that various different modifications are possible and are contemplated within the true spirit and scope of the appended claims. There is no intention, therefore, of limitations to the exact abstract or disclosure herein presented. |
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055815928 | summary | CROSS-REFERENCE TO RELATED APPLICATION This application is related to the following copending application which is commonly assigned and is incorporated herein by reference: R. Guida et al., "Method for Fabricating an Anti-scatter X-ray Grid Device for Medical Diagnostic Radiography," U.S. application Ser. No. (attorney docket number RD-24,116), filed concurrently herewith. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to the field of diagnostic radiography and, more particularly, to an anti-scatter grid capable of yielding high resolution, high contrast radiographic images. 2. Description of the Related Art During medical diagnostic radiography processes, x-radiation impinges upon a patient. Some of the x-radiation becomes absorbed by the patient's body, and the remainder of the x-radiation penetrates through the body. The o differential absorption of the x-radiation permits the formation of a radiographic image on a photosensitive film. Of the x-rays that pass through the body, primary radiation travels unimpeded and directly along the path from which the x-rays were originally emitted from the source. Scattered radiation is that which passes through the body, is scattered by the body elements, and thus travels at an angle from the original path. Both primary and scattered radiation will expose a photosensitive film, but scattered radiation, by nature of its trajectory, reduces the contrast (sharpness) of the projected image. In conventional posterior/anterior chest x-ray examinations, for example, about sixty percent of the radiation that penetrates through the body can be in the form of scattered radiation and thus impart a significant loss of image contrast. Therefore, it is desirable to filter out as much of the scattered radiation as possible. One embodiment for filtering scattered radiation includes an anti-scatter grid which is interposed between the body and the photosensitive film. Scattered radiation impinges upon absorbent (opaque) material in the grid and becomes absorbed. Also absorbed by the absorbing material, however, is a portion of the primary radiation. The radiographic imaging arrangement of this embodiment provides higher contrast radiographs by virtue of the elimination of the scattered radiation, but necessitates an increase in radiation dosage to the patient in order to properly expose the photographic element. The increased radiation requirement results in part because the scattered radiation no longer constitutes part of the imaging x-ray beam, and in part because as much as 30% or more of the primary beam impinges upon the absorbing material in the grid and itself becomes filtered out (i.e. absorbed). The increased radiation required for the exposure can be a factor of seven (7) or more, i.e., the patient can receive seven times the x-radiation dose when the grid is used as a part of the radiographic system. Because high doses of x-radiation pose a health hazard to the exposed individual, there has been a continual need to reduce the amount of x-radiation a patient receives during the course of a radiographic examination. Many conventional grids use thin lead strips as the x-ray absorber and either aluminum strips or fiber composite strips as transparent interspace material. Conventional manufacturing processes consist of tediously laminating individual strips of the absorber material and non-absorber interspace material by laboriously gluing together alternate layers of the strips until thousands of such alternating layers comprise a stack. Furthermore, to fabricate a focused grid, the individual layers must be placed in a precise manner so as to position them at a slight angle to each other such that each layer is fixedly focused to a convergent line: the x-ray source. After the composite of strips is assembled into a stack, it must then be cut and carefully machined along its major faces to the required grid thickness that may be as thin as only 0.5 millimeters, the fragile composite then being, for example, 40 cm by 40 cm by 0.5 mm in dimension and very difficult to handle. If the stack has survived the machining and handling processes, the stack must further be laminated with sufficiently strong materials so as to reinforce the fragile grid assembly and provide enough mechanical strength for use in the field. Accidental banging, bending, or dropping of such grids can cause internal damage, i.e., delamination of the layers which cannot be repaired, rendering the grid completely useless. A significant parameter in the grid design is the grid ratio, which is defined as the ratio between the height of the x-ray absorbing strips and the distance between them. The ratios typically range from 4:1 to 16:1. Because a value of about 0.050 mm lead thickness is a practical lower limit imposed by current manufacturing limitations, i.e., it being extremely difficult to handle strips at this thickness or thinner, a grid with a ratio of 4:1 with a line rate of 60 lines per centimeter demands that the interspace material be 0.12 mm in thickness and results in a grid that is only 0.5 mm thick. Because of the manufacturing limitations, the lead strips in these grids are generally too wide and, consequently, yield a large cross-sectional area that undesirably absorbs as much as 30% or more of the primary radiation. Furthermore, the thick strips result in an undesirable shadow-image cast onto the film. To obliterate the shadows, it becomes necessary to provide a mechanical means for moving the grid during the exposure period. This motion of the grid causes lateral decentering and can consequently result in absorption of an additional 20% of the primary radiation. Thus the use of wide absorber strips requires a significant increase in patient dosage to compensate this drawback. SUMMARY OF THE INVENTION Accordingly, an object of an embodiment of the invention is to provide a robust anti-scatter grid with a high line rate so that it is not necessary to move the grid during an x-radiation exposure period. Another object of an embodiment of the present invention is to provide a grid with uniform lines and spaces capable of absorbing less primary radiation than conventional grids and thus permitting a reduction in the x-radiation necessary to properly expose the photosensitive element. Another object of an embodiment of the present invention is to provide a grid that is focused to the source of the x-radiation and capable of improving image contrast. Briefly, according to an embodiment of the present invention, an anti-scatter x-ray grid for medical diagnostic radiography comprises a substrate having channels therein and including material that is substantially non-absorbent of x-radiation; and absorbing material in the channels including material that is substantially absorbent of x-radiation. In a preferred embodiment, the substrate comprises material capable of remaining stable at the melting temperature of the absorbing material. One substrate material and absorbing material combination which has been found to be particularly advantageous is a plastic substrate and a lead-bismuth alloy absorbing material. |
043127088 | abstract | The reactor stud hole plug unit comprises a compression plate, a mandrel, an elastomeric seal ring adapted to be compressed during movement of the mandrel relative to the compression plate and a nut threaded to the mandrel to hold the unit in assembled relationship. The compression plate includes an annular rim spaced inward of the peripheral edge. The compression plate rests on the reactor wall surrounding the hole to be plugged with the rim extending into the hole. The mandrel which has a centrally threaded stud extending through the compression plate includes an upper cylindrical section and a lower cylindrical section of larger cross section with the two cylindrical sections being joined by a frustoconical section. The seal ring which has a rectangular cross section is dimensioned to snugly fit about the cylindrical upper section of the mandrel and to engage the compression plate rim in aligned relationship. Tightening of the nut draws the mandrel into the compression plate causing the ring seal to deform and fill the available space between the components of the plug unit and the wall of the hole. |
abstract | A nuclear reactor fuel assembly includes a plurality of fuel rods, a plurality of guide channels, two nozzles, one of which has a bearing plate with openings, elements for the detachable connection of the nozzles to the guide channels, a detachable connection locking device and locking device fasteners. The elements for the detachable connection of the nozzles to the guide channels have a cross-section size greater than the size of openings in the nozzle bearing plate. |
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