Abstract: A dynamic neutron reflector assembly for a “breed-and-burn” fast reactor incrementally adjusts neutron spectrum and reactivity in a reactor core. The composition of materials in the dynamic neutron reflector may be adjusted to change neutron reflectivity levels, or to introduce neutron moderating or absorption characteristics. The dynamic neutron reflector may contain a flowing reflecting liquid of adjustable volume and/or density. Submergible members may be selectively inserted into the flowing reflecting liquid to alter its volume and introduce other neutron modifying effects such as moderation or absorption. Selective insertion of the submergible members allows for concentration of the neutron modifying effects in a selected portion of the reactor core. The flowing reflecting liquid may also act as a secondary coolant circuit by exchanging heat with the molten fuel salt.

Abstract: A nuclear power generation system being safe and easily controlled by load following. The nuclear power generation system has a nuclear reactor employing a load following control method. The reactor includes: a fuel assembly reactor core having metallic fuel containing at least one selected from uranium-235, uranium-238 and plutonium-239; a reactor vessel containing the reactor core; metallic sodium loaded into the reactor vessel and heated by the reactor core; and a neutron reflector for achieving criticality in the reactor core with effective multiplication factor of neutrons emitted from the reactor core being maintained at or above about 1. The neutron reflector is coupled to spring or spiral metallic members and utilizing heat deformation in the metallic members due to the temperature in coolant metallic sodium to control the fast neutron reflection efficiency of the neutron reflector.

Abstract: A fuel element has a ratio of area of fissionable nuclear fuel in a cross-section of the tubular fuel element perpendicular to the longitudinal axis to total area of the interior volume in the cross-section of the tubular fuel element that varies with position along the longitudinal axis. The ratio can vary with position along the longitudinal axis between a minimum of 0.30 and a maximum of 1.0. Increasing the ratio above and below the peak burn-up location associated with conventional systems reduces the peak burn-up and flattens and shifts the burn-up distribution, which is preferably Gaussian. The longitudinal variation can be implemented in fuel assemblies using fuel bodies, such as pellets, rods or annuli, or fuel in the form of metal sponge and meaningfully increases efficiency of fuel utilization.

Abstract: A method of shutting down a nuclear reactor may include compressing a scram gas that is in fluid communication with a scram accumulator. The scram accumulator defines a chamber therein and contains bellows within the chamber. The bellows are configured to hold a scram liquid in isolation of the scram gas. The scram gas exerts a compressive force on the bellows in a form of stored energy. The method may additionally include releasing the stored energy in response to a scram signal such that the scram gas expands into the chamber of the scram accumulator to compress the bellows and expel the scram liquid from the scram accumulator to insert control rods into a core of the nuclear reactor.

Abstract: A compact nuclear power generation system includes a reactor (3) comprising a core (2) which uses metal fuel containing either or both of uranium-235/238 and plutonium-239. A reactor vessel (1) houses the core (2). Metal sodium primary coolant (8) is heated by the core (2). A neutron reflector (9) maintains the effective multiplication factor of neutrons emitted from the core (2) at approximately one or more to bring the core into a critical state. The neutron reflector is movable from a lower part towards an upper part of the core. The heated metal sodium is supplied to a main heat exchanger (15) which is located outside the reactor. A secondary coolant of supercritical carbon dioxide, which circulates through the main heat exchanger, is in heat exchange with the heated metal sodium. The heated secondary coolant drives a turbine (20). A power generator (21) can be operated by the driven turbine.

Abstract: A pressurized water nuclear reactor (PWR) includes a once through steam generator (OTSG) disposed in a generally cylindrical pressure vessel and a divider plate spaced apart from the open end of a central riser. A sealing portion of the pressure vessel and the divider plate define an integral pressurizer volume that is separated by the divider plate from the remaining interior volume of the pressure vessel. An internal control rod drive mechanism (CRDM) has all mechanical and electromagnetomotive components including at least a motor and a lead screw disposed inside the pressure vessel. Optionally CRDM units are staggered at two or more different levels such that no two neighboring CRDM units are at the same level. Internal primary coolant pumps have all mechanical and electromagnetomotive components including at least a motor and at least one impeller disposed inside the pressure vessel. Optionally, the pumps and/or CRDM are arranged below the OTSG.

Abstract: A traveling wave nuclear fission reactor, fuel assembly, and a method of controlling burnup therein. In a traveling wave nuclear fission reactor, a nuclear fission reactor fuel assembly comprises a plurality of nuclear fission fuel rods that are exposed to a deflagration wave burnfront that, in turn, travels through the fuel rods. The excess reactivity is controlled by a plurality of movable neutron absorber structures that are selectively inserted into and withdrawn from the fuel assembly in order to control the excess reactivity and thus the location, speed and shape of the burnfront. Controlling location, speed and shape of the burnfront manages neutron fluence seen by fuel assembly structural materials in order to reduce risk of temperature and irradiation damage to the structural materials.

Abstract: A control rod grasped by a hook of a grasping equipment is moved down and is positioned at an upper end of a hollow piston of a control rod drive mechanism (CRD) in a state that the control rod is fully withdrawn from a core. Furthermore, the hook is inserted into an opening of a handle of the control rod. The hook is lifted up so as to make contact with the handle. The control rod grasped by the grasping equipment is rotated by a grasping equipment rotation apparatus. A state that gaps formed between joint convexities in a coupling socket of the control rod are positioned right above coupling spud convexities of the hollow piston occurs. At this time, the control rod falls by its own weight and the coupling spud convexities pass through the gaps. A grasping equipment movement apparatus suppresses the falling speed of the control rod. The control rod is rotated at 90° and the control rod and CRD are connected.

Abstract: The invention relates to a neutron reflector block. The neutron reflector block comprises a first portion and a second portion. The first portion has a first end face and oppositely located intermediate shoulders which are spaced from the first end face. The first end face and the intermediate shoulders are bounded by spaced side faces and spaced upper and lower faces. The second portion protrudes from the first portion between the intermediate shoulders and has spaced side faces and spaced upper and lower faces. The second portion side faces are more narrowly spaced relative to the first portion side faces. The second portion also has a second end face located oppositely to the first end face.

Abstract: A reactor core is immersed in a liquid metal coolant in a core barrel of a liquid metal cooled reactor. The reactor core includes a plurality of fuel assemblies contained in the core barrel, a neutron absorber that absorbs a neutron in the reactor core, and a neutron moderator that moderates a neutron therein so as to control a reactivity of the reactor core. The neutron absorber and the neutron moderator constitute a mixture contained in reactivity control assemblies of the reactor core in the liquid metal coolant prior to immersion of the reactor core. The neutron moderator is composed of zirconium hydride.

Abstract: The present invention relates to tubular elements, such as fuel assembly tubes, which are designed to be used in high pressure and high temperature water in nuclear reactors, such as pressurized water nuclear reactors. In particular, the present invention relates to a method of improving wear resistance and corrosion resistance by depositing a protective coating having a depth of from about 5 to about 25 ?m on the surface of the tubular elements. The coating is provided by nitriding the tubular element at a temperature of from about 400° C. to about 440° C. The nitridation of the tubular element can be carried out for a duration of from about 12 hours to about 40 hours.

Abstract: A fast reactor performing reflector control to control reactivity of the core by moving a neutron reflector in the vertical direction, including: a core fuel assembly; a neutron absorption assembly in the middle of the core fuel assembly; a reflector assembly at the circumference of the core fuel assembly; plural inner neutron shields at the circumference of the reflector assembly; a cylindrical core barrel surrounding entirety of the plural neutron shields; and a drive mechanism controlling the reflector. The reflector assembly includes: a reflector element that reflects neutrons from the core fuel assembly towards the core; a cavity section, arranged thereabove, that permits leakage of neutrons to outside the core; a linkage mechanism that links the reflector element and the cavity section; a guide tube that defines a space for removal/insertion of these; and a connecting section that connects the drive mechanism and the cavity section.

Abstract: A method for controlling a nuclear reactor is disclosed. The method includes providing a moderator zone in a core of the nuclear reactor, providing a fuel in the moderator zone, and providing one or more housings, each having a cavity, adjacent to the fuel. The method also includes allowing movement of a moderator between the moderator zone and the cavity of the one or more housings at a lower portion of the one or more housings. The method further includes confining moderator in the cavity of the one or more housings at an upper portion of the one or more housings.

Abstract: The invention concerns a control rod configured for a nuclear power light water reactor of the BWR or PWR kind. The control rod contains absorber material. At least 50%, with respect to weight, of the absorber material that is in the control rod is in the form of hafnium hydride. The invention also concerns the use of such a control rod during operation in a nuclear power light water reactor of the BWR or PWR kind.

Abstract: A method for controlling a nuclear reactor is disclosed. The method includes providing a moderator zone in a core of the nuclear reactor, providing a fuel in the moderator zone, and providing one or more housings, each having a cavity, adjacent to the fuel. The method also includes allowing movement of a moderator between the moderator zone and the cavity of the one or more housings at a lower portion of the one or more housings. The method further includes confining moderator in the cavity of the one or more housings at an upper portion of the one or more housings.

Abstract: A fast reactor having a reactivity control reflector has a reactor vessel in which a coolant is accommodated, a reactor core which is installed in the reactor vessel and dipped with the coolant, and a reflector installed outside of the reactor core so as to be movable in a vertical direction for controlling the reactivity of the reactor core. The reflector of the fast reactor has a lower neutron reflecting portion having a neutron reflection capability higher than that of the coolant and an upper cavity portion located above the neutron reflecting portion and having a neutron reflection capability lower than that of the coolant. The cavity portion is composed of a plurality of cylindrical hermetically-sealed vessels.

Abstract: In a nuclear reactor in which a primary coolant is contained, the primary coolant moves upwardly from the core by an operation thereof. An annular steam generator is arranged in an upper side of the core into which the upwardly moving primary coolant flows and transfers heat in the primary coolant into water therein to generate a steam. A passage structure defines a coolant passage for the primary coolant to an outside of the core. The heat-transferred primary coolant in the annular steam generator flows downwardly in the coolant passage so as to flow into the core, thereby moving upwardly. A reactor vessel is arranged to surround the coolant passage so as to contain the core, the annular steam generator and the passage means therein.

Abstract: A pressurized water nuclear reactor (PWR) includes a once through steam generator (OTSG) disposed in a generally cylindrical pressure vessel and a divider plate spaced apart from the open end of a central riser. A sealing portion of the pressure vessel and the divider plate define an integral pressurizer volume that is separated by the divider plate from the remaining interior volume of the pressure vessel. An internal control rod drive mechanism (CRDM) has all mechanical and electromagnetomotive components including at least a motor and a lead screw disposed inside the pressure vessel. Optionally CRDM units are staggered at two or more different levels such that no two neighboring CRDM units are at the same level. Internal primary coolant pumps have all mechanical and electromagnetomotive components including at least a motor and at least one impeller disposed inside the pressure vessel. Optionally, the pumps and/or CRDM are arranged below the OTSG.

Abstract: A fast reactor having a reflector control system is provided which decreases the change in reactivity of the reactor core with time without performing control of a reflector lifting speed and that of a water flow rate. The above fast reactor has a liquid metal coolant, a reactor core immersed therein, and a neutron reflector which is provided outside the reactor core and which is moved in a vertical direction for adjusting leakage of neutrons therefrom for controlling the reactivity of the reactor core. The neutron reflector described above is gradually moved in an upward direction with the change in reactivity caused by fuel burn-up, and at least a part of a lower region of the neutron reflector is a high reflection region having a high neutron reflection ability as compared to that of the other region. The high reflection region is located from the bottom to a place between one fourth and one half of the height of the neutron reflector from the bottom end thereof.

Abstract: A nuclear reactor comprises a fuel rod into which nuclear fuel is enclosed and a control rod that controls nuclear reactions of the nuclear fuel. A concentration of a neutron absorber in a primary coolant at a full power operation of the nuclear reactor, when an operation of the nuclear reactor is started, is set equal to or lower than a value that is obtained by adding a predetermined value to a value obtained by subtracting a concentration of the neutron absorber that is required for maintaining a cold shutdown state of the nuclear reactor when an operation of the nuclear reactor is started from a concentration of the neutron absorber that is required for maintaining cold shutdown of the nuclear reactor when an operation of the nuclear reactor is completed.

Abstract: In order to stably control a nuclear reactor in a short time, so as not to enter an unstable region that is determined by the relationship between the reactor pressure, the reactor power and the subcooling of the core inlet coolant at start-up time, the nuclear reactor system comprises: an power control apparatus for generating a control rod operation signal for operating a control rod, based on the reactor water temperature change rate; a feed water control apparatus for generating a feed water flow rate signal and a discharge water flow rate signals based on the reactor water level signal; and a process computer for performing overall control of the power control apparatus and the feed water control apparatus, wherein the feed water control apparatus has the reactor water temperature change rate setting section for adjusting the reactor water temperature change rate set value based on the variation of the reactor water level signal.

Abstract: In a nuclear reactor in which a primary coolant is contained, the primary coolant moves upwardly from the core by an operation thereof. An annular steam generator is arranged in an upper side of the core into which the upwardly moving primary coolant flows and transfers heat in the primary coolant into water therein to generate a steam. A passage structure defines a coolant passage for the primary coolant to an outside of the core. The heat-transferred primary coolant in the annular steam generator flows downwardly in the coolant passage so as to flow into the core, thereby moving upwardly. A reactor vessel is arranged to surround the coolant passage so as to contain the core, the annular steam generator and the passage means therein.

Abstract: Disclosed embodiments include nuclear fission reactor cores, nuclear fission reactors, methods of operating a nuclear fission reactor, and methods of managing excess reactivity in a nuclear fission reactor.

Abstract: Illustrative embodiments provide a reactivity control assembly for a nuclear fission reactor, a reactivity control system for a nuclear fission reactor having a fast neutron spectrum, a nuclear fission traveling wave reactor having a fast neutron spectrum, a method of controlling reactivity in a nuclear fission reactor having a fast neutron spectrum, methods of operating a nuclear fission traveling wave reactor having a fast neutron spectrum, a system for controlling reactivity in a nuclear fission reactor having a fast neutron spectrum, a method of determining an application of a controllably movable rod, a system for determining an application of a controllably movable rod, and a computer program product for determining an application of a controllably movable rod.

Abstract: A fast reactor having a reflector control system is provided which decreases the change in reactivity of the reactor core with time without performing control of a reflector lifting speed and that of a water flow rate. The above fast reactor has a liquid metal coolant, a reactor core immersed therein, and a neutron reflector which is provided outside the reactor core and which is moved in a vertical direction for adjusting leakage of neutrons therefrom for controlling the reactivity of the reactor core. The neutron reflector described above is gradually moved in an upward direction with the change in reactivity caused by fuel burn-up, and at least a part of a lower region of the neutron reflector is a high reflection region having a high neutron reflection ability as compared to that of the other region. The high reflection region is located from the bottom to a place between one fourth and one half of the height of the neutron reflector from the bottom end thereof.

Abstract: A control rod grasped by a hook of a grasping equipment is moved down and is positioned at an upper end of a hollow piston of a control rod drive mechanism (CRD) in a state that the control rod is fully withdrawn from a core. Furthermore, the hook is inserted into an opening of a handle of the control rod. The hook is lifted up so as to make contact with the handle. The control rod grasped by the grasping equipment is rotated by a grasping equipment rotation apparatus. A state that gaps formed between joint convexities in a coupling socket of the control rod are positioned right above coupling spud convexities of the hollow piston occurs. At this time, the control rod falls by its own weight and the coupling spud convexities pass through the gaps. A grasping equipment movement apparatus suppresses the falling speed of the control rod. The control rod is rotated at 90° and the control rod and CRD are connected.

Abstract: A fast reactor having a reflector control system is provided which decreases the change in reactivity of the reactor core with time without controlling a reflector lifting speed and a water flow rate. The fast reactor has a neutron reflector provided outside the reactor core and which is moved in a vertical direction for adjusting neutron leakage to control the reactivity of the reactor core. The neutron reflector is moved in an upward direction with the change in reactivity caused by fuel burn-up. At least a part of a lower region of the neutron reflector may be a region having a high neutron reflection ability as compared to that of the other region. The high reflection region is located at the bottom of the neutron reflector and extends from between one fourth and one half of the height of the neutron reflector.

Abstract: A traveling wave nuclear fission reactor, fuel assembly, and a method of controlling burnup therein. In a traveling wave nuclear fission reactor, a nuclear fission reactor fuel assembly comprises a plurality of nuclear fission fuel rods that are exposed to a deflagration wave burnfront that, in turn, travels through the fuel rods. The excess reactivity is controlled by a plurality of movable neutron absorber structures that are selectively inserted into and withdrawn from the fuel assembly in order to control the excess reactivity and thus the location, speed and shape of the burnfront. Controlling location, speed and shape of the burnfront manages neutron fluence seen by fuel assembly structural materials in order to reduce risk of temperature and irradiation damage to the structural materials.

Abstract: A traveling wave nuclear fission reactor, fuel assembly, and a method of controlling burnup therein. In a traveling wave nuclear fission reactor, a nuclear fission reactor fuel assembly comprises a plurality of nuclear fission fuel rods that are exposed to a deflagration wave burnfront that, in turn, travels through the fuel rods. The excess reactivity is controlled by a plurality of movable neutron absorber structures that are selectively inserted into and withdrawn from the fuel assembly in order to control the excess reactivity and thus the location, speed and shape of the burnfront. Controlling location, speed and shape of the burnfront manages neutron fluence seen by fuel assembly structural materials in order to reduce risk of temperature and irradiation damage to the structural materials.

Abstract: In a reflector-controlled fast reactor in which neutron reflectors disposed outside a rector core, immersed in a primary coolant, are moved vertically to thereby adjust leakage of neutrons from the reactor core and control reactivity of the rector core, a region, which is located around the reactor core and in which the neutron reflectors move, is surrounded by a material inferior to the primary coolant in terms of neutron reflection capability.

Abstract: A fast reactor having a reflector control system is provided which decreases the change in reactivity of the reactor core with time without controlling reflector lifting speed and a water flow rate. The reactor has a liquid metal coolant, a reactor core immersed therein, and a neutron reflector provided outside the core and is moved in a vertical direction for adjusting leakage of neutrons therefrom for controlling the reactivity of the core. The reflector described above is gradually moved in an upward direction with the change in reactivity caused by fuel burn-up, and at least a part of a lower region of the reflector is a high reflection region having a high neutron reflection ability as compared to that of the other region. The high reflection region is located between the bottom and one fourth and one half of the height of the neutron reflector.

Abstract: A fast reactor 1 controlled with a reflector comprises: a reactor vessel 7 accommodating therein a coolant 5; a reactor core 2 disposed in the reactor vessel 7 and immersed in the coolant 5; and a reflector 4 that vertically moves for adjusting leakage of neutrons generated from the reactor core 2 to control a reactivity of the reactor core 2, the reflector 4 including a neutron reflecting part 4a disposed on an outside of the reactor core 2 in a vertically movable manner, the neutron reflecting part 4a having a neutron reflecting ability higher than that of the coolant 5, and a cavity part 4b positioned above the neutron reflecting part 4a, the cavity part 4b having a neutron reflecting ability lower than that of the coolant 5. The neutron reflecting part 4a is formed of a plurality of metal plates 37 that are stacked on each other. Each of the metal plates 37 has a plurality of coolant channels 36 through which the coolant 5 flows.

Abstract: A fast reactor has a reactivity control assembly including a reactor shutdown rod of a backup reactor shutdown system and neutron absorbers to suppress the initial surplus reactivity, a reactor shutdown rod drive mechanism for releasing the reactor shutdown rod and units of neutron absorber drive mechanism capable of moving the respective neutron absorbers up and down. The reactor shutdown rod and the neutron absorbers are arranged in a wrapper tube. The reactor shutdown rod drive mechanism causes an inner extension tube to fall and release the reactor shutdown rod by means of a gripper section at the lowermost end of an outer extension tube by turning off the power supply to a holding magnet at the time of scram. Each of the units of neutron absorber drive mechanism has a dual tube type drive shaft including an outer extension shaft and an inner extension shaft. When grasping the neutron absorbers, the outer extension shaft is pulled up to allow both of the extension shafts to be inserted.

Abstract: In a nuclear reactor in which a primary coolant is contained, the primary coolant moves upwardly from the core by an operation thereof. An annular steam generator is arranged in an upper side of the core into which the upwardly moving primary coolant flows and transfers heat in the primary coolant into water therein to generate a steam. A passage structure defines a coolant passage for the primary coolant to an outside of the core. The heat-transferred primary coolant in the annular steam generator flows downwardly in the coolant passage so as to flow into the core, thereby moving upwardly. A reactor vessel is arranged to surround the coolant passage so as to contain the core, the annular steam generator and the passage means therein.

Abstract: In a nuclear reactor in which a primary coolant is contained, the primary coolant moves upwardly from the core by an operation thereof. An annular steam generator is arranged in an upper side of the core into which the upwardly moving primary coolant flows and transfers heat in the primary coolant into water therein to generate a steam. A passage structure defines a coolant passage for the primary coolant to an outside of the core. The heat-transferred primary coolant in the annular steam generator flows downwardly in the coolant passage so as to flow into the core, thereby moving upwardly. A reactor vessel is arranged to surround the coolant passage so as to contain the core, the annular steam generator and the passage means therein.

Abstract: An instrumented capsule for nuclear fuel irradiation tests in research reactors includes an outer shell; a rod tip assembly assembled to a lower end plate of the shell, thus absorbing impact; fuel rod assemblies supported in the shell by means of support tubes and housing therein, sintered fuel bodies and in-capsule instruments, such as thermocouples and self-powered neutron detectors (SPND); a protective tube connected to the upper end plate and protecting instrument control cables; and a guide pipe connected to the inclined extension part of a junction tree and guiding the instrument control cables to a control unit provided outside the reactor.

Abstract: A reactivity control rod adapted to be used in a reactor core of a fast reactor and disposed at a substantially central portion of the reactor core for controlling a reactivity therein. The reactivity control rod includes a wrapper tube surrounded by a plurality of fuel rods in a reactor core, and a plurality of neutron absorber rods arranged in the wrapper tube. At least one of the plurality of neutron absorber rods includes a cladding tube and a mixture filled in the cladding tube. The mixture is composed of a neutron absorber that absorbs a neutron and a neutron moderator that moderates the neutron.

Abstract: The present invention relates to a control rod blade for a boiling water reactor. The control rod blade (2) comprises a free edge portion with a recess (7) which comprises a plurality of outlets, arranged in a row, for channels (3), which are arranged to receive an absorber material (10) and a cover element (4) arranged to be attached along at least a section of the edge portion. The cover element (4) comprises a cover portion (12) arranged to seal the opening of the recess (7) and a support portion (13) arranged to, in a mounted state, abut a bottom surface in the recess (7) and to allow the formation of at least a passage (16) between the outlets of the channel (3) in the recess (7).

Abstract: An absorber body arranged to absorb radiation in a nuclear energy arrangement. The absorber body comprises more than one area with a locally reduced thickness.

Abstract: A sealed submersible electric motor driven centrifugal primary cooling fluid pump is entirely submersible in the electron beam tube cooling system of an X-Ray system incorporates a heat exchanger in the pump, wherein primary cooling fluid (oil or other high dielectric strength fluid) that is pumped in the sealed pump through an annular primary fluid passage therein is cooled by secondary cooling fluid flowing through an annular passage wrapped around the primary fluid annular passage over the length of the primary fluid annular passage, providing a compact unit of pump and heat exchanger.

Abstract: In a nuclear reactor in which a primary coolant is contained, the primary coolant moves upwardly from the core by an operation thereof. An annular steam generator is arranged in an upper side of the core into which the upwardly moving primary coolant flows and transfers heat in the primary coolant into water therein to generate a steam. A passage structure defines a coolant passage for the primary coolant to an outside of the core. The heat-transferred primary coolant in the annular steam generator flows downwardly in the coolant passage so as to flow into the core, thereby moving upwardly. A reactor vessel is arranged to surround the coolant passage so as to contain the core, the annular steam generator and the passage means therein.

Abstract: A method for compensating a rod position indication system for non-linearity comprises the steps of applying an excitation current to a primary of a sensor for inducing a generally linear voltage that is representative of the position of a control rod on a secondary of the sensor. The excitation current includes a first frequency which is sufficient to provide the generally linear output for the sensor. The excitation current is then modified to include a second frequency which is sufficient for providing the generally linear output when the first frequency is insufficient to provide the generally linear output.

Abstract: A neutron absorbing apparatus which includes two adjacent neutron absorbing plates and a mounting assembly with latching means configured to be easily secured to fuel assemblies while the fuel assemblies remain under water in a fuel storage rack, thereby eliminating the need to remove the fuel assemblies or the fuel storage rack for installation. The two neutron absorbing plates are positioned orthogonally to form a chevron cross section which can be placed about the fuel assemblies by insertion in the existing space between the fuel assemblies and the cell walls of a fuel storage rack. A prescribed orientation of the chevron configured neutron absorbing plate in the cells of the fuel storage rack together with the selected use of a single neutron absorbing plate economically provides sufficient neutron absorption in all radial directions about the fuel assemblies to maintain safe storage conditions in closely packed fuel storage racks.

Abstract: A fast reactor comprises a core composed of nuclear fuel, a core barrel surrounding an outer periphery of the core, an annular reflector surrounding an outer periphery of the core barrel, a partition wall structure surrounding an outer periphery of the annular reflector and supporting the core barrel by a supporting structure arranged radially of the fast reactor, the partition wall structure constituting an inner wall of a coolant passage for a primary coolant, a neutron shield surrounding an outer periphery of the partition wall structure and disposed in the coolant passage, a reactor vessel surrounding an outer periphery of the neutron shield and having an inner wall constituting an outer wall of the coolant passage, and a guard vessel surrounding an outer periphery of the reactor vessel.

Abstract: In a field of commercial nuclear reactors, a control blade, which is inserted into and withdrawn from the core of a nuclear reactor so as to start/shut-down the operation thereof and to control the reactor power, must have soundness, high reactivity and long life. The control blade for nuclear reactors is arranged to prevent swelling of a neutron absorber so as to improve the soundness. Furthermore, even if the swelling takes place, the soundness of the control blade can be maintained. The control blade is arranged to prevent the swelling phenomenon in such a manner that boron exhibiting excellent neutron absorbing performance absorbs hydrogen which is produced as a result of reactions with the neutrons. The control blade for nuclear reactors has an upper structure member, a lower structure member, a central tie member disposed between the upper and lower structure members, a plurality of wings connected to each other by the central tie member, and neutron absorber enclosed in the wing.

Abstract: A nuclear reactor plant is provided in which the reactor coolant system contains a dissolved solution of enriched boric acid. The boron-10 to boron-11 atomic isotope ratio of the enriched boric acid solution is greater than 30:70 at the start of the reactor core cycle. The nuclear reactor plant design provides for minimal mixing between the reactor coolant solution containing the enriched boric acid solution and the natural boric acid solution used during refueling operations.

Abstract: A method for affecting neutron spectral shift in a reactor core includes providing a liquid poison in a hollow control blade extending into the core, displacing the liquid poison with a first fluid for obtaining a hard neutron spectra during a beginning interval of the core fuel cycle for converting fuel, and then increasing moderating ratio for obtaining a soft neutron spectra during an end interval of the cycle for burning the converted fuel. An exemplary apparatus for practicing the method displaces the liquid poison in the control blade with the first fluid for obtaining the hard neutron spectra. The first fluid may be either replaced, displaced, or added to by a second fluid having a second moderating ratio for obtaining the soft neutron spectra.

Abstract: The invention relates to a nuclear reactor with improved efficiency.The nuclear reactor comprises a massive partition (18) of material reflecting high energy neutrons at the circumference of the core (7) of the reactor, two layers (19 and 20) of material absorbing low energy neutrons and containing fertile material arranged one at the lower part and one at the upper part of the core (7) and an assembly of neutron energy spectrum variation rods (27). The rods (27) are associated with mechanisms permitting them to be either fully inserted into the core (7), or fully extracted. These rods (27) consist of a material absorbing low energy neutrons and permit a shift of the neutron spectrum towards the high energies.The invention is particularly applicable to pressurized water nuclear reactors.

Abstract: An assembly for controlling the release of neutrons in a nuclear reactor having the core split into two halves. A disk assembly formed from at least two circular disks is positioned substantially at the center of and coaxially with the core halves. Each disk is machined with an identical surface hole pattern such that rotation of one disk relative to the other causes the hole pattern to open or close. The disks may be formed from neutron absorbing material or moderator material. The holes may be provided with fissile material inserts to enhance reactivity when in the open position. A drive motor mounted adjacent the reactor and drive shaft operatively engaged between the drive motor and disks is used to rotate the disks.

Abstract: A gas cooled high temperature reactor with a core of preferably spherical fuel elements enclosed by a graphite roof and a side and bottom reflector. In order to minimize environmental contamination by fission products, even upon (hypothetical) core overheating accidents, the upper part of the roof reflector incorporates volatile iodine and cesium iodide, suitable metal atoms or molecules of the compounds of these metals bonded into the cracked binder material of the graphite. The dilution of the doping material must be high enough (from 1:100 to 1:10,000), so that the substances (for example alkaline earth metals or rare earths) are present as individual atoms or molecules. The iodine is chemically bound to the doping atoms, and iodide formed in this matter is retained in the cracked binder material. Molecules of high temperature oxides may also be incorporated.