Abstract: A control rod for a nuclear fuel assembly is described herein that includes a neutron absorbing material having a melting point greater than 1500° C. that does not form a eutectic with a melting point less than 1500° C., and may further include a cladding material having a melting point greater than 1500° C. The cladding material is selected from the group consisting of silicon carbide, zirconium, a zirconium alloy, tungsten, and molybdenum. The absorbing material is selected from the group consisting of Gd2O3, Ir, B4C, Re, and Hf. The metal cladding or the absorbing material may be coated with an anti-oxidation coating of Cr with or without a Nb intermediate layer.

Abstract: An energy transportation and grid support system utilizes at least one transportable containment module capable of storing thermal or chemical energy typically produced from renewable or geothermal sources and providing connectivity with energy conversion equipment typically located in a land or sea-based operating facility. The system includes circuitry to hookup to an adjacent electricity grid for the provision of grid support and/or piping to move thermal energy typically used to drive steam turbines generating ? electricity. The operating facility also includes a communication arrangement to link with and exchange operations control data with a grid or heating operator and the energy transportation operator. The invention is directed to both apparatus and method for the energy transportation and grid support system.

Abstract: A fuel rod for a nuclear fission reactor is disclosed and claimed. The fuel rod includes an elongate hollow cladding configured to retain a nuclear fuel therein. The cladding includes an elongate hollow tube. Fiber layers are positioned around the outside surface of the tube or within the tube forming an integral part thereof. Both the tube and the fibers are formed of a ceramic material. A fuel assembly including a plurality of such fuel rods is also disclosed and claimed.

Abstract: A nuclear reactor control rod with SiC fiber reinforced structure comprises wing sections and a central joint section. Each of the wing sections is a flat plate spreading axially and radially, and includes storage tubes and a wing surface structural member. The storage tubes are arranged in parallel in a flat plane and contain a neutron absorbing member containing the neutron absorbing material. The wing surface structural member is formed by molding of SiC/SiC composite material as to cover surfaces of the storage tubes and formed to have an outward shape of a flat plate. The central joint section and storage tubes are made of SiC/SiC composite material. The central joint section bundles the wing sections together at center. The storage tubes are bundled together with fibers made of SiC or a textile made of SiC.

Abstract: Disclosed is a method for treating an absorber pin, wherein the pin comprises a cladding in which a sintered boron carbide-based material having cracks is located, the material having porosity less than 1% of the volume of the material, the cracks containing sodium and at least one radioactive material. The method includes contacting the material with a treatment reaction mixture including carbon dioxide and water, in such a manner that the production of sodium carbonate and the expansion thereof cause the opening of cracks and of the sheath from at least one slit provided in the sheath as well as the propagation of the treatment process within the material. The process overcomes the physical-chemical properties of a sintered boron carbide-based material as much as possible. These properties prevent an easy treatment of the sodium and radioactive material contained in the cracks of the material.

Abstract: A method and apparatus for a fret resistant fuel rod for a Boiling Water Reactor (BWR) nuclear fuel bundle. An applied material entrained with fret resistant particles is melted or otherwise fused to a melted, thin layer of the fuel rod cladding. The applied material is made of a material that is chemically compatible with the fuel rod cladding, allowing the fret resistant particles to be captured in the thin layer of re-solidified cladding material to produce an effective and resilient fret resistant layer on an outer layer of the cladding.

Abstract: Methods of forming at least a portion of a neutron absorber include combining a first material and a second material to form a compound, reducing the compound into a plurality of particles, mixing the plurality of particles with a third material, and pressing the mixture of the plurality of particles and the third material. One or more components of neutron absorbers may be formed by such methods. Neutron absorbers may include a composite material including an intermetallic compound comprising hafnium aluminide and a matrix material comprising pure aluminum.

Abstract: The present invention relates to a nuclear reactor, in particular a pool-type nuclear reactor cooled with liquid metal (for example, a heavy metal such as lead or lead-bismuth eutectic) or with sodium or molten salts, having a core formed by a bundle of fuel elements and immersed in a primary fluid circulating between the core and at least one heat exchanger; the fuel elements extend along respective parallel longitudinal axes and have respective bottom active parts immersed in the primary fluid to constitute the core, and respective service parts that extend at the top from the active parts and emerge from the primary fluid; the fuel elements are mechanically supported via respective top end heads anchored to supporting structures and can be operated via handling machines.

Abstract: In a control rod having a plurality of elongated members for absorbing neutrons within a nuclear reactor to control a nuclear reaction, each elongated member may include a cylindrical inner capsule configured to contain neutron absorbing material therein. The elongated member may also include an absorber tube enclosing the cylindrical inner capsule, the absorber tube having an outer surface configured with a plurality of generally flat, planar sides between adjacent rounded corners.

Abstract: Nuclear reactor systems and methods are described having many unique features tailored to address the special conditions and needs of emerging markets. The fast neutron spectrum nuclear reactor system may include a reactor having a reactor tank. A reactor core may be located within the reactor tank. The reactor core may include a fuel column of metal or cermet fuel using liquid sodium as a heat transfer medium. A pump may circulate the liquid sodium through a heat exchanger. The system may include a balance of plant with no nuclear safety function. The reactor may be modular, and may produce approximately 100 MWe.

Abstract: A control rod for a boiling water reactor is provided with a structure element having mutually-perpendicular four blades. The four blades have a neutron absorber-filling region that neutron absorber is held, respectively. In the structure element, a plurality of regions formed in an axial direction of the control rod include a first region having a first cross-section that forms a first united cruciform cross-section of the four blades connected one another, a second region having a second cross-section that has each separated cross-section of the four blades, and a third region having a third cross-section that has a second united cross-section of continuous two blades of the four blades, disposed in a diametrically opposite direction and facing each other and each separated cross-section of remaining two blades of the four blades, disposed perpendicularly to the continuous two blades.

Abstract: In a cooling structure and a cooling method for a control rod drive mechanism and in a nuclear reactor, a housing (59) in which magnetic jacks are housed is fixed to an upper portion of a reactor vessel (41), and an air intake unit (102) that takes cooling air into the housing (59), a first exhaust duct (104) that is arranged side by side with the air intake unit (102) in a circumferential direction of the housing (59), into which cooling air in the housing (59) is suctioned through a first inlet (109) at a lower portion thereof, and that guides the cooling air upward, a second exhaust duct (105) that is disposed below the air intake unit (102), into which cooling air in the housing (59) is suctioned through a second inlet (110), and that guides the cooling air to the first exhaust duct (104), and a discharging unit (111) that is formed at an upper portion of the housing (59) and discharges cooling air in the first exhaust duct (104) to the exterior are provided.

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: A precursor formulation of a silicon carbide material that includes a ceramic material and a boron-11 compound. The ceramic material may include silicon and carbon and, optionally, oxygen, nitrogen, titanium, zirconium, aluminum, or mixtures thereof. The boron-11 compound may be a boron-11 isotope of boron oxide, boron hydride, boron hydroxide, boron carbide, boron nitride, boron trichloride, boron trifluoride, boron metal, or mixtures thereof. A material for use in a nuclear reactor component is also disclosed, as are such components, as well as a method of producing the material.

Abstract: A control rod for nuclear reactors includes four wings including neutron absorbers containing hafnium, a front end structural member which has a cross shape in cross section and includes brackets bonded to the leading ends of the wings, and a terminal end structural member which has a cross shape in cross section and includes brackets bonded to the tailing ends of the wings. The four wings are bonded to a wing-bonding member including a cross-shaped center shaft so as to form a cross shape. The front end structural member and the wing-bonding member are made of a zirconium alloy. The wings include neutron-absorbing plates having neutron-absorbing portions and each have an outer surface which is opposed to a fuel assembly and at which a hafnium-zircaloy composite member covered with zircaloy is disposed. The neutron-absorbing plates are opposed to each other with trap spaces disposed therebetween.

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 control rod for nuclear reactors includes four wings including neutron absorbers containing hafnium, a front end structural member which has a cross shape in cross section and includes brackets bonded to the leading ends of the wings, and a terminal end structural member which has a cross shape in cross section and includes brackets bonded to the tailing ends of the wings. The four wings are bonded to a wing-bonding member including a cross-shaped center shaft so as to form a cross shape. The front end structural member and the wing-bonding member are made of a zirconium alloy. The wings include neutron-absorbing plates having neutron-absorbing portions and each have an outer surface which is opposed to a fuel assembly and at which a hafnium-zircaloy composite member covered with zircaloy is disposed. The neutron-absorbing plates are opposed to each other with trap spaces disposed therebetween.

Abstract: A neutron absorbing insert for use in a fuel rack and method of manufacturing the same. In ones aspect, the invention is a neutron absorbing apparatus comprising: a plate structure having a first wall and a second wall that is non-coplanar to the first wall; the first and second walls being formed by a single panel of a metal matrix composite having neutron absorbing particulate reinforcement that is bent into the non-coplanar arrangement along a crease; and a plurality of spaced-apart holes formed into the single panel along the crease prior to bending.

Abstract: A nuclear reactor having a liquid metal or molten salt coolant in a riser space 130?, has a cylindrical containment vessel 134 with a reactor vessel 120?, at least two lobes 121, preferably three to nine lobes 121, each lobe 121 interconnected with the other lobe(s) and each containing a fast reactor core, 116?, 116?, 116? and 116??.

Abstract: Example embodiments are directed to methods and apparatuses for generating desired isotopes within water rods of nuclear fuel assemblies. Example methods may include selecting a desired irradiation target based on the target's properties, loading the target into a target rod based on irradiation target and fuel assembly properties, exposing the target rod to neutron flux, and/or harvesting isotopes produced from the irradiation target from the target rod. Example embodiment target rods may house one or more irradiation targets of varying types and phases. Example embodiment securing devices include a ledge collar and/or bushing that support target rods within a water rod and permit moderator/coolant flow through the water rod. Other example embodiment securing devices include one or more washers with one or more apertures drilled therein to hold one or more example embodiment target rods in a water rod while permitting coolant/moderator to flow through the water rod.

Abstract: A control rod drive (CRD) tube, its manufacture, and installation in a pressurized water reactor (PWR) is disclosed. The control rod drive tube includes a tube body adapted to penetrate an aperture in the RPV head and an offset flange formed around a circumference of the tube body at a predetermined location along its length. The offset flange increases circumferentially from a first point along the circumference of the tube body to a second point along the circumference of the tube body.

Abstract: A control rod drive mechanism according to the present invention includes a cylindrical guide tube having a latch hole, a hollow piston coupled to the control rod and freely moving up and down within the guide tube, a latch provided in the hollow piston so as to freely swing and freely engaging with and disengaging from the latch hole of the guide tube, and a spring locking the latch to the latch hole of the guide tube. Further, an elevating member having a latch guide which can come into contact with the latch is provided so as to freely move up and down within the guide tube. Further, the latch includes a guide surface coming into contact with the latch guide of the elevating member, and the latch guide includes a guide roller coming into contact with the guide surface of the latch.

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.

Abstract: An advanced gray rod control assembly (GRCA) for a nuclear reactor. The GRCA provides controlled insertion of gray rod assemblies into the reactor, thereby controlling the rate of power produced by the reactor and providing reactivity control at full power. Each gray rod assembly includes an elongated tubular member, a primary neutron-absorber disposed within the tubular member said neutron-absorber comprising an absorber material, preferably tungsten, having a 2200 m/s neutron absorption microscopic capture cross-section of from 10 to 30 barns. An internal support tube can be positioned between the primary absorber and the tubular member as a secondary absorber to enhance neutron absorption, absorber depletion, assembly weight, and assembly heat transfer characteristics.

Abstract: A control rod spider assembly connection between a connecting finger and a rodlet. An upper end plug of the rodlet is secured to the inner bore of the hollow connecting finger with a mating one of a right hand or left hand thread interfacing between the interior of the bore and the circumference of the rodlet. The upper end of the rodlet is captured by a second fastener mechanism having the other of the right hand or the left hand thread. The second fastener mechanism is anchored to one or both of the connecting finger or the upper end plug to secure the connection.

Abstract: A neutron reactor includes a neutron shield which is disposed outside a nuclear reactor core and adapted to absorb neutrons leaking from the core. The neutron shield includes a plurality of containers each of which contains a powdered neutron absorbing material and which are stacked with one another in a vertical direction, and a cladding tube which houses the containers. The neutron absorbing material is composed of B4C powder.

Abstract: An electromagnet comprises a plurality of nested freestanding electrically insulating former layers, and electrically conductive wire wrapped around the outsides of the freestanding electrically insulating former layers to define a multilayer electrical coil in which adjacent layers of the multilayer electrical coil are spaced apart by intervening freestanding electrically insulating former layers. Electrically energizing the multilayer electrical coil generates a magnetic field inside the multilayer electrical coil. In some embodiments the electrically conductive wire is bare wire not having electrical insulation. In some embodiments the former layers comprise a ceramic material. In some such embodiments the electromagnet further comprises a ferromagnetic core disposed inside the multilayer electrical coil. An electric motor employing such an electromagnet as a stator pole is also disclosed.

Abstract: An apparatus or system that may incorporate a single component to connect the control rod blade to the control rod drive system (CRD) of a Nordic-type of BWR. The apparatus or system may eliminate the need of using multiple components to connect the control rod blade with the CRD.

Abstract: A maintenance/repair device for reactor internal structure 6 of the present invention includes a device body 6a configured to be fixed on a reactor internal structure 49. Connected to the device body 6a is a welding-part repair mechanism 6b configured to repair a welding part 49a of the reactor internal structure 49. Thus, a welding part 2a of the reactor internal structure 49 can be repaired by the welding-part repair mechanism 6b, while the device body 6a is fixed on the reactor internal structure 49.

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 control rod for a pressurized-water nuclear reactor contains an absorber rod which is arranged in a casing tube. At least in a lower section, the absorber rod is provided with at least one recess which takes up at most a portion of the circumferential surface of this section. This reduces problems associated with an expansion in the volume of the absorber rod.

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.

Abstract: A compressed powder composite (CPC) material for absorbing neutrons emitted from spent nuclear fuel thereby preventing the initiation of a chain reaction. The CPC material is typically provided as a substantially insoluble cylindrical pellet that is highly resistant to corrosion and is not subject to the failure modes associated with the alloy materials typically used in neutron absorption materials. The pellet preferably includes a dendritic nickel powder substantially uniformly mixed with a neutron absorber powder material, preferably boron carbide. Tubes filled with CPC materials, such tubes for replacing control roads so that a spent nuclear fuel assembly may be disposed of substantially indefinitely.

Abstract: A control rod for a pressurized-water nuclear reactor contains an absorber rod which is arranged in a casing tube. At least in a lower section, the absorber rod is provided with at least one recess which takes up at most a portion of the circumferential surface of this section. This reduces problems associated with an expansion in the volume of the absorber rod.

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: A control rod has four blades, each of which has a rectangular cross section in a plane perpendicular to an axis of the control rod, disposed so as to form a cross-shaped cross section in the plane perpendicular to the axis. The blades include a plurality of aligned square tubes having a square cross section in a plane perpendicular to the axis and including a neutron absorber filling hole filled with neutron absorber, frame plates disposed parallel to the aligned square tubes in a direction perpendicular to a width direction of the blade, and on one side end and another side end of the blade in the width direction, respectively, and cover plates disposed along the width direction and sandwiching the aligned square tubes. Each blade has the aligned square tubes, the frame plates and the cover plates joined together as a single-piece construction by Hot Isostatic Pressing diffusion bonding.

Abstract: A high-temperature gas reactor control rod is provided that does not degrade the joining state between the control rod elements even when stress is applied thereto, and that can improve the safety of the high temperature gas reactor remarkably by improving the heat resistance thereof. The high-temperature gas reactor control rod has a plurality of control rod elements (1) each having a neutron absorber (7) between an outer cylinder (9) and an inner cylinder (8) that form a double cylindrical tubular shape, the control rod elements (1) joined to each other in a vertical direction, characterized by: a columnar support member (2) for supporting at least the neutron absorber (7), disposed in the inner cylinder (8); and joining means for joining to another control rod element (1), provided at least one of upper and lower ends of the support member (2).

Abstract: A conduction cooled neutron absorber may include a metal matrix composite that comprises a metal having a thermal neutron cross-section of at least about 50 barns and a metal having a thermal conductivity of at least about 1 W/cm·K. Apparatus for providing a neutron flux having a high fast-to-thermal neutron ratio may include a source of neutrons that produces fast neutrons and thermal neutrons. A neutron absorber positioned adjacent the neutron source absorbs at least some of the thermal neutrons so that a region adjacent the neutron absorber has a fast-to-thermal neutron ratio of at least about 15. A coolant in thermal contact with the neutron absorber removes heat from the neutron absorber.

Abstract: A core of a light water reactor having a plurality of fuel assemblies, which are loaded in said core, having nuclear fuel material containing a plurality of isotopes of transuranium nuclides, an upper blanket zone, a lower blanket zone, and a fissile zone, in which the transuranium nuclides are contained, disposed between the upper blanket zone and the lower blanket zone, wherein a ratio of Pu-239 in all the transuranium nuclides contained in the loaded fuel assembly is in a range of 40 to 60% when burnup of the fuel assembly is 0, sum of a height of the lower blanket zone and a height of the upper blanket zone is in a range of 250 to 600 mm, and the height of said lower blanket zone is in a range of 1.6 to 12 times the height of the upper blanket zone.

Abstract: An embodiment of the present invention takes the form of an apparatus or system that may incorporate a single component to connect the control rod blade to the control rod drive system (CRD) of a Nordic-type of BWR. An embodiment of the present invention may eliminate the need of using multiple components to connect the control rod blade with the CRD.

Abstract: A control rod includes a tie-rod, a handle mounted to an upper end portion of the tie-rod, either a connector plate or a fall velocity limiter mounted to a lower end portion of the tie-rod, sheaths having a U-shaped cross-section, welded intermittently to the tie-rod at a plurality of locations in the axial direction of the tie-rod, and having an upper end welded to the handle and a lower end welded to either the connector plate or the fall velocity limiter, and a neutron absorbing member disposed inside each of the sheaths. An upper end of a weld portion located at uppermost position in an axial direction of the tie-rod among a plurality of weld portions between the tie-rod and the sheath is disposed at a position within a range between 0.8 and 13% of total axial length Ls of the sheath below an upper end of the sheath.

Abstract: A control rod includes a tie-rod, a handle mounted to an upper end portion of the tie-rod, either a connector plate or a fall velocity limiter mounted to a lower end portion of the tie-rod, sheaths having a U-shaped cross-section, welded intermittently to the tie-rod at a plurality of locations in the axial direction of the tie-rod, and having an upper end welded to the handle and a lower end welded to either the connector plate or the fall velocity limiter, and a neutron absorbing member disposed inside each of the sheaths. An upper end of a weld portion located at uppermost position in an axial direction of the tie-rod among a plurality of weld portions between the tie-rod and the sheath is disposed at a position within a range between 0.8 and 13% of total axial length Ls of the sheath below an upper end of the sheath.

Abstract: A neutron absorbing insert for use in a fuel rack and method of manufacturing the same. In ones aspect, the invention is a neutron absorbing apparatus for insertion into a fuel rack comprising: a sleeve having a first wall and a second wall, the first and second walls forming a chevron shape; and the first and second wall being a single panel of a metal matrix composite having neutron absorbing particulate reinforcement bent into the chevron shape along a crease.

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: Methods of forming at least a portion of a neutron absorber include combining a first material and a second material to form a compound, reducing the compound into a plurality of particles, mixing the plurality of particles with a third material, and pressing the mixture of the plurality of particles and the third material. One or more components of neutron absorbers may be formed by such methods. Neutron absorbers may include a composite material including an intermetallic compound comprising hafnium aluminide and a matrix material comprising pure aluminum.

Abstract: A method of and a system for evaluating constraint functions for improving nuclear reactor performance involve generating an operational solution for a nuclear reactor using a constraint to account for a problem with the operation of the nuclear reactor. The problem is based at least in part on channel deformation criteria.

Abstract: The present invention provides a gray rod control assembly (GRCA) containing an improved neutron absorber comprised of a porous matrix of refractory metal infused with a neutron absorbing metal or metal alloy for a nuclear reactor. The reactor has a plurality of fuel assemblies, each including numerous elongated fuel rods supported in an organized array by substantially transverse support grids, and a plurality of guide thimbles disposed through the support grids and along the fuel rods. The GRCA includes a spider assembly structured to provide controlled insertion of gray rod assemblies within the thimbles of the fuel assembly, thereby controlling the rate of power produced by the reactor. Each gray rod assembly includes an elongated tubular member, a first end plug, a second end plug and the improved neutron-absorber disposed within the tubular member.

Abstract: A fast reactor including a reactivity control assembly including a reactor shutdown rod and neutron absorbers, a reactor shutdown rod drive mechanism, and units of neutron absorber drive mechanism. The reactor shutdown rod drive mechanism causes an inner extension tube to fall and release the reactor shutdown rod by a gripper section by turning off the power supply to a holding magnet at the time of scram. When grasping the neutron absorbers, an outer extension shaft is pulled up to allow both of the extension shafts to be inserted. After the outer extension tube gets to a handling head section of the neutron absorber, the outer extension shaft is pushed down to grasp the neutron absorber externally by latch fingers of the gripper section so that the neutron absorber can be moved up and down.

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 nuclear fuel assembly having a tube-in-tube control rod guide tube design that incorporates an end plug that extends axially upward to an elevation above the lower most grid where it is sealed at its upper end to the lower end of the control rod guide tube. The guide tube lower end plug has a threaded recess in its upper surface that mates with a corresponding dashpot end plug threaded extension that is formed as an insert in the lower end of the guide tube. A hole formed through the outer wall of the guide tube end plug at the elevation of the lower portion of the recess provides a positive inspection port for assuring the proper seating of the dashpot. A method of manufacture of such a fuel assembly is also disclosed.