Abstract: A detection apparatus is usable to detect the neutron absorption capability of a control element of a nuclear installation and includes a neutron radiograph apparatus and a robot apparatus. The neutron radiograph apparatus includes a neutron emission source of variable strength, a detector array, a mask apparatus and a positioning robot all under the control of a central processor and data acquisition unit. The neutron emission source is advantageously switchable between an ON state and OFF state with variable source strength in the ON state, which avoids any need for shielding beyond placing the neutron emission source in an inspection pool at the nuclear plant site including but not limited to the spent fuel or shipping cask laydown pools. The neutron emission source is situated at one side of a wing of the control element and generates a neutron stream, the detector array is situated on an opposite side of a wing, and the neutron emission source and detector array are robotically advanced along the wing.

Abstract: A fuel rod for a nuclear reactor, including a cladding tube having a first end with an annular end face, a second end with an annular end face, and a cylindrical body portion extending therebetween, and a first tube end plug including a front portion, an annular lip with an annular end face, and a substantially straight cylindrical body portion extending therebetween, wherein the surface area of the annular end face of the first end of the cladding tube and the annular end face of the annular lip of the first tube end plug are substantially equal, and the annular end face of the first end of the cladding tube and the annular end face of the annular lip of the first tube end plug are connected by a resistance pressure weld.

Abstract: Device and method for checking fuel rods with IFBA, their zirconium diboride coating. The device includes a variable magnetic field generator and a magnetic field pickup device, arranged in the vicinity of the rod, as well as a control system for comparing both fields in order to measure the electric conductivity of the rod. The method includes the steps of: arranging the rod to be measured between the generator and the pickup device; generation of a variable magnetic field in the generator; picking-up of the magnetic field; comparison between the generated magnetic field and the picked-up one in order to quantify the electric conductivity of the rod; if the electric conductivity differs from a reference value, consider the rod for checking or recycling.

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: 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: 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 having a lower tip absorber material which exhibits substantially lower irradiation induced swelling than a second absorber material which extends above the lower tip absorber material. The lower tip absorber material having a substantially lower reactivity worth than the second absorber material, extends from a lower end plug of the control rod to an elevation just above a dashpot in a thimble guide tube in a nuclear fuel assembly when the control rod is fully inserted within the thimble guide tube.

Abstract: The invention regards a neutron absorbing component (1) and a method for manufacturing a neutron absorbing component. The neutron absorbing component comprises a core (2) consisting of a first material, a layer (3) consisting of a second material. The layer encloses a least partly the core and is adapted to protect the core from an outer surrounding. The first material has a higher neutron absorption capability than the second material. The neutron absorbing component is manufactured by sintering in such a way that an intermediate layer (4) is formed between the core and the layer. The intermediate layer has a material gradient that comprises a decrease of the concentration of the first material from the core to the layer and an increase of the concentration of the second material from core to the layer.

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 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: Parameters DAOPX (=AOP?AOX) and DAOIX (=AOI?AOX) are calculated based on axial offsets of the power distribution (AOX and AO1). A movement control of a control rod is then performed in such a manner that a plot point of a trajectory of the parameter DAOPX and the DAOIX is induced toward the major axis of an ellipse drawn by the trajectory, based on the parameters (DAOPX and DAOIX) and allowable ranges (DAOPX—L and DAOIX—L) obtained in advance. With this configuration, the xenon oscillation is suppressed by controlling the xenon oscillation in a simultaneous manner simply by controlling an axial power distribution in a reactor by a simple operation with a clear purpose.

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: 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 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. The first region is disposed in an upper end portion and a lower end portion of the structure element, respectively.

Abstract: A polarized neutron guide for separating neutrons into polarized neutrons while minimizing loss of the neutrons is provided. The polarized neutron guide includes a body, the first space and the second space, and a neutron separation space. The body includes super mirrors coated with a neutron-reflective thin film and the first and second spaces are formed by the first plate inside the body. The neutron separation space is formed by the second plate disposed at the entry of the first space and the third plate disposed at the entry of the second space. Spin-up polarized neutrons and spin-down polarized neutrons are simultaneously separated and transferred in the first and second spaces, respectively. Therefore, with minimum loss of the neutrons, the spin-up polarized neutrons and the spin-down polarized neutrons are effectively separated and collected.

Abstract: The present invention relates to a control rod blade for a boiling water reactor. The control rod blade comprises a plurality of channels, which are arranged to receive an absorber material, a free edge portion with a recess, which comprises outlets for said channels, and a cover element , which is arranged to be attached by means of at least one welding operation such that it seals at least a part of said recess . Furthermore, the control rod blade comprises a profile element , which, before said welding operation of the cover element is performed, is arranged to be applied against a bottom surface in the recess in a position such that the profile element covers the outlets of said channels.

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 rod for a nuclear reactor having a rod cladding defining an internal volume, the rod cladding having an upper end and a lower end, an upper end fitting positioned in the upper end of the rod cladding, a rod internal arrangement configured in the internal volume of the rod cladding, an absorber rod lower end cap positioned at the lower end of the rod cladding, the lower end cap having an upper surface and a lower surface, a stack support with a stack support upper end and a stack support lower end, the stack support lower end placed in contact with the upper surface of the lower end cap, the stack support upper end configured to support the rod internal arrangement, and an annulus of material configured around the stack support and contacting the upper surface of the lower end cap.

Abstract: A control cluster for a pressurized water nuclear reactor comprising a bundle of neutron-absorbing rods each of which comprises a metal tube called cladding which is sealed off by a top end plug at its top end and by a bottom end plug at its bottom end and has a support, or spider, of radiating shape to which the absorber rods are attached through their upper end plugs, characterized in that the cladding of at least some of the absorber rods is weld-free hafnium tubes, the top end plugs of the absorber rods having hafnium cladding being of titanium-based alloy and being welded to the top end part of the hafnium cladding of the absorber rod, the bottom end plugs being of massive hafnium and being welded to the bottom.

Abstract: An advanced gray rod control assembly (GRCA) is 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, a substantially pure silver neutron-absorber disposed within the tubular member, and a support tube surrounding the neutron-absorber within the tubular member to resist silver-swelling. Delta-power of the reactor is improved by minimizing the exposed surface area of the absorber and distributing it among all of the rods of the GRCA.

Abstract: A tie rod having a cruciform cross section is provided with steps for fixing sheaths at tips of cruciform arms of the tie rod; the tips of each of sheaths are fitted onto the steps of the tie rod, each of the sheaths having a U-shaped cross section; and each of the sheaths is fixed to the tie rod by performing a laser welding using a YAG laser beam or a CO2 laser beam with the sheath being fitted onto the tie rod to achieve a continuous weld of at least a part of the tie rod in a longitudinal direction thereof. An axial center position of the beam is shifted from an end face position of the step of the tie rod at least toward an axis center of the tie rod.

Abstract: A control rod (2) for boiling water reactor comprising four absorber blades (6, 7, 8, 9) which form an orthogonal cross with a cruciform centre (10). The width of the absorber blades coincides with the radial direction of the control rod and the length of the absorber blades coincides with the axial direction of the control rod. Each one of the absorber blades comprises an absorber material distributed in the longitudinal direction, whereby a mean value of the quantity of absorber material per unit of length of the control rod is smaller in the upper part of the control rod than in the lower part thereof. Each one of the absorber blades comprises in its upper part (15) an inner part arranged radially inside an outer part, where the outer part is provided with absorber material whereas the inner part lacks absorber material, whereby said inner part in at least some portion constitutes at least one-fourth of the width of the absorber blade.

Abstract: A control rod for a BWR according to the present invention comprises a first unit composed of a tie rod, a handle mounted on an axially upper portion of the tie rod and a lower support member or falling speed limiter mounted on a axially lower portion of the tie rod; and a second unit composed of a sheath containing therein reactivity control material, an upper end plate mounted on an axially upper portion of the sheath and a lower end plate mounted on an axially lower portion of the sheath, wherein an upper portion of the upper end plate is fixed to the handle, a lower portion of the lower end plate is fixed to the lower support member or falling speed limiter, whereby the control rod is constructed as a joined body of the first unit and the second unit.

Abstract: A method for manufacturing a control rod of a nuclear reactor, the control rod having a blade including neutron absorbers and a sheath, a tie rod for fixing the blade, a handle and a lower-blade fixed to the tie rod and the blade. The method includes a first step for cutting weep holes for water to cool the neutron absorbers in the sheath and cutting a periphery of the sheath, a second step for bending the sheath cut in the first step to a C-shape, a third step for inserting the neutron absorbers in a bent portion of the sheath formed by bending in the second step, a fourth step for successively welding the blade to the tie rod, the blade to the handle and the blade to the lower-blade, and a fifth step for finishing portions welded in the fourth step.

Abstract: A control rod for a nuclear reactor has a structure which is capable of suppressing expansion of a reduced-diameter portion of a neutron absorber in a radial direction under shocks applied upon every stepwise driving of a control rod cluster and which can ensure integrity of a cladding tube over an extended period. The control rod includes a cladding tube closed hermetically at both ends thereof by a top end plug and a bottom end plug, respectively, a neutron absorber loaded into the cladding tube and includes a reduced-diameter portion having a smaller diameter than the other portion, the reduced-diameter portion being disposed at the bottom end plug side of the control rod, and a hold-down spring for pressing the neutron absorber downwardly against the bottom end plug. A sleeve is disposed within an annular space defined between an outer peripheral surface of the reduced-diameter portion and an inner peripheral surface of the cladding tube.

Abstract: The absorber rod comprises cladding (12) of stainless steel closed by plugs (14, 16) and containing a column of absorber pellets (24) e.g. of boron carbide. It also has an end bar (26) of hafnium secured to the bottom plug by a purely mechanical connection.

Abstract: A boiling water type nuclear reactor core, in which a plurality of fuel assemblies, each enclosed in a channel box, are loaded and a plurality of control rods, each having control blades, are arranged between the channel boxes. Long blade control rods, each having control rod blades which extend in four directions, are arranged between channel boxes on diagonals of square bundle regions each formed by a plurality of fuel assemblies, and short blade control rods, each having a control rod blade length of about half of the width of one of the square bundle regions, are arranged between the channel boxes in the center of each of the square bundle regions.

Abstract: The invention relates to a control rod for a boiling water reactor. The control rod comprises a top piece and a bottom piece between which an absorber part is arranged. The absorber part comprises a central part (4) and four absorber blades (3) extending from the central part (4). The absorber part comprises a channel (10) which comprises the central part and which extends along the length of the whole absorber part. The channel is surrounded by walls of a neutron-absorbing material with a long service life, for example hafnium. The channel is at least partially filled with a moderator, for example light water. During the manufacture the absorber part has undergone a heat treatment such that the hafnium alloy has been completely or partially transformed from &agr;-phase to &bgr;-phase and thereafter been rapidly cooled to &agr;-phase.

Abstract: A transfer device for moving a poison rod assembly between fuel cells in a nuclear fuel storage facility coupleable to an overhead crane. The poison rod assembly has a plurality of poison rods disposed in rows. The device includes an elongated outer member, an inner member, and a gripper assembly supported by the inner member. The inner member is slidably disposed within the elongated outer member. The overhead crane is coupled to the inner member for sliding said inner member between an upper position and a lower position. An interlock assembly selectively couples the inner member and elongated outer member. Thus, moving the crane, which is coupled to the inner member either moves the inner member relative to the elongated outer member when the interlock is not engaged, or, moves both the inner member and the elongated outer member when the interlock is engaged.

Abstract: A control rod for a nuclear reactor has a structure which is capable of suppressing expansion of a reduced-diameter portion of a neutron absorber in a radial direction under shocks applied upon every stepwise driving of a control rod cluster and which can ensure integrity of a cladding tube over an extended period. The control rod includes a cladding tube closed hermetically at both ends thereof by a top end plug and a bottom end plug, respectively, a neutron absorber loaded into the cladding tube and includes a reduced-diameter portion having a smaller diameter than the other portion, the reduced-diameter portion being disposed at the bottom end plug side of the control rod, and a hold-down spring for pressing the neutron absorber downwardly against the bottom end plug. A sleeve is disposed within an annular space defined between an outer peripheral surface of the reduced-diameter portion and an inner peripheral surface of the cladding tube.

Abstract: A control rod for a nuclear reactor is composed of a center structural member, a plurality of wings each composed of a sheath member of long plate structure having a U-shaped cross section and secured to the center structural member, a front end structural member secured to a front end side of the wing in a wing inserting direction in a reactor core, a terminal end structural member secured to a terminal end side of the wing, a plurality of integral type neutron absorbing elements each having a plate structure accommodated in each of the sheaths in a row in a longitudinal direction thereof and each being formed in plate shape by integrating one or more neutron absorbing plates, and a plurality of load supporting members for supporting weights of the integral type neutron absorbing elements.

Abstract: A cylindrical thin-wall sleeve including an SiC fiber-reinforced SiC composite material (SiC/SiC), which has a porosity of 40% or less and a wall thickness of 5 mm or less.

Abstract: A hermaphroditic absorber exploits the inherent spatial change in the neutron spectrum within a lumped poison mass in a thermal reactor neutron flux field. The hermaphroditic absorber (poison mass) incorporates two types of absorbers, the first being a strong thermal absorber near the surface of the mass, and the second being a strong resonant absorber in the interior of the poison mass. The outer regions of the poison mass are comprised of a strong “1/v” thermal absorber, and the inner region of the poison mass is comprised of a resonance absorber. This resonance absorber more appropriately exploits the hardened characteristics of the neutron spectrum within the absorber mass by selectively absorbing the epi-thermal neutrons. The creation of the hermaphroditic poison mass permits an increase in the control material worth while maintaining the external dimension of the structure containing the control material, such as a BWR control rod.

Abstract: A boiling water type nuclear reactor core, in which a plurality of fuel assemblies, each enclosed in a channel box, are loaded and a plurality of control rods, each having control blades, are arranged between the channel boxes. Latitudinal long blade control rods, each having control rod blades which extend latitudinally in four directions, are arranged between channel boxes on diagonals of square bundle regions each formed by a plurality of fuel assemblies, and latitudinal short blade control rods, each having control rod blades which extend latitudinally in four directions with each control rod blade having a latitudinal length of about half of the width of one of the square bundle regions, are arranged between the channel boxes in the center of each of the square bundle regions. The long blade control rods have a latitudinal blade length which is about twice as long as the latitudinal blade length of the short blade control rods.

Abstract: There is provided a reactor control rod which is capable of suppressing an excessive frictional force acting on passive state oxide films formed on the surfaces of neutron absorber elements, and also reducing the possibility to cause electrochemical problems, and a method of manufacturing the same. The reactor control rod comprises a wing having a sheath which has a substantially U-shaped cross-section. A top end structure is secured to a longitudinal top end of the sheath. A bottom end structure is secured to a longitudinal bottom end of the sheath. An opening portion of the sheath is secured to a central structure. A neutron absorber element is made of neutron absorbing material. The neutron absorber element is charged in the sheath. A supporting rod through hole is formed in the neutron absorber element, so as to penetrate the neutron absorber element. A supporting rod fitting hole is formed in the sheath. A load supporting rod is inserted into the supporting rod through hole.

Abstract: A control rod for a nuclear reactor is composed of a center structural member, a plurality of wings each composed of a sheath member of long plate structure having a U-shaped cross section and secured to the center structural member, a front end structural member secured to a front end side of the wing in a wing inserting direction in a reactor core, a terminal end structural member secured to a terminal end side of the wing, a plurality of integral type neutron absorbing elements each having a plate structure accommodated in each of the sheaths in a row in a longitudinal direction thereof and each being formed in plate shape by integrating one or more neutron absorbing plates, and a plurality of load supporting members for supporting weights of the integral type neutron absorbing elements.

Abstract: Seed-blanket type nuclear reactor cores are employed to burn thorium fuel with conventional reactor fuels, including nonproliferative enriched uranium, and weapons or reactor grade plutonium. In a first embodiment, the core is completely nonproliferative in that neither the reactor fuel, nor the generated waste material, can be used to manufacture nuclear weapons. In a second embodiment of the invention, the core is employed to burn large amounts of weapons grade plutonium with the thorium, and provides a convenient mechanism by which stockpiled weapons grade plutonium can be destroyed and converted into electrical energy. The cores of both embodiments are comprised of a plurality of seed-blanket unit fuel assemblies which have centrally located seed regions that are surrounded by annular blanket regions. The seed regions contain the uranium or plutonium fuel rods, while the blanket regions contain thorium fuel rods.

Abstract: A control rod includes four panels in cruciform section each containing a plurality of absorber tubes. The absorber tubes are mounted between upper and lower mounting structures having generally T-shaped slots opening toward one another. The absorber tubes have generally T-shaped end plugs for reception in the slots. The slots and end plugs are configured to permit limited axial movement of each absorber tube relative to the control rod and to adjacent tubes. The absorber tubes are maintained in tension during all nuclear operations including during a scram.

Abstract: The control cluster is usable for power regulation and for load following. It comprises a spider from which are suspended rods containing a column of neutron-absorbing material. The neutron-absorbing material in at least some rods is stainless steel in lower part of the rod and, in an upper part of the rod having a length equal to 20 and 40% of the height of the column of absorbing material, another material exhibiting an interference neutron absorption which is much higher than that of stainless steel, for instance Ag-In-Cd.

Abstract: A control cluster for a water cooled and moderated nuclear reactor, comprises a spider and rods suspended from the spider. Each rod contains neutron-absorbing material. In a lower portion of each rod, the material is a metal neutron absorber. In an upper portion, it is a stack of pellets of boron carbide B.sub.4 C. In a middle fraction occupying a height lying in the range 35% to 45% of the total height, it is zirconium diboride ZrB.sub.2 isotopically enriched in boron 10 or hafnium diboride HfB2.

Abstract: The control rod for a nuclear reactor includes a plurality of wings each having segments of neutron absorbing material exposed along the length of the rod. During refueling, the segments of neutron absorbing material are rearranged within the control rod and the control rod is reinserted into the reactor core. By rearranging the segments, optimum use of the depletion capacity of each segment is effected, maximizing the number of cycles for which the control rod may be used.

Abstract: The control rod includes a plurality of elongated tubes containing neutron-absorbing material in a planar array to form wings on opposite sides of a central axis of the control rod. Each tube is formed with a plurality of protuberances in excess of four such that the tubes can be welded to adjacent tubes with the weld lines disposed inwardly of the side surfaces of the wings to improve the flexibility of the control rod. The wings of each planar array have connecting elements of each other planar array thereof, enabling lateral movement of the planar arrays of wings relative to one another to further enhance flexibility and movement of the control rod between the fuel channels of the nuclear core.

Abstract: A control rod for a nuclear reactor incorporates a plurality of neutron absorber tubes containing neutron absorbing materials. The absorber tubes are substantially rectangular inside and outside, each tube containing at least one axial stack of substantially round neutron absorbing material segments or capsules.

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 condition sin closely packed fuel storage racks.

Abstract: A replacement rod for insertion into a nuclear fuel assembly to replace a fuel rod containing a neutron absorbing, fissile fuel, includes Hafnium sufficient to substantially replace the neutron absorption capacity of the fuel rod. The replacement rod also includes a non-fissile second material that is commonly used for structures in nuclear fuel assemblies. The second material is preferably selected from the group consisting of a stainless steel, a zirconium alloy and zirconium. In one embodiment, the Hafnium is fabricated into a cylindrically-shaped rodlet, or core, and the second material is fabricated into an annulus around the core. Alternatively, the Hafnium and the second material are each distributed about uniformly throughout a cylindrical volume of the replacement rod. Refurbishing nuclear fuel assemblies by replacing damaged fuel rods with replacement rods according to the invention obtains an improved peaking factor over prior art methods.

Abstract: A generally cruciform-shaped control rod for a nuclear reactor is formed by vertical stiffeners laterally spaced one from the other and interconnected by horizontal stiffeners at their ends defining discrete compartments in each wing of the cruciform-shaped control rod. Sheathing overlies the stiffeners to seal each of the compartments from its surrounding environment. Neutron-absorbing material, such as boron carbide and/or hafnium tubes, are disposed in each compartment. Each wing is secured to a generally cruciform central tie rod formed of planar plates superposed one over the other alternately at right angles with the outer edges of the plates welded to the inner edges of the wings, affording structural support to the control rod.

Abstract: A flux trap neutron absorber arrangement for use in a fuel storage body between a pair of fuel storage cans which receive and store nuclear fuel assemblies includes separate pockets spaced from one another and extending vertically along and attached to the exterior of each of the adjacent side walls of adjacent spaced storage cans, an elongated flat plate of a thermal neutron absorber material mounted in each pocket, the plates of thermal neutron absorber material being likewise spaced from one another and defining a fast neutron slow-down region therebetween, a slab of a metal hydride disposed in the fast neutron slow-down region between the plates of thermal neutron absorber material and the separate pockets on the adjacent side walls, a canister containing the slab of the metal hydride being disposed in the fast neutron slow-down region, the canister being connected to at least one of the adjacent side walls of the adjacent storage cans.

Abstract: In a control rod for nuclear reactors with elongated channels for boron carbide or other neutron-absorbing material which swells upon neutron irradiation, the neutron-absorbing material (20a), in at least some of the channels (18b), is provided with projecting portions (20a') or arranged in a casing with portions projecting towards the channel walls. Further, the projecting portions are adapted to form between them and the channel walls unfilled spaces (40) for taking up swelling neutron-absorbing material.

Abstract: In the field of commercial nuclear reactors, there is an increasing demand for long-life control blades in order to meet the requirements of higher economy and reduction in the disposal of radioactive wastes. A control blade proposed by the invention stands a long use by virtue of the use of a long-life neutron absorber which is typically made of hafnium. Despite the use of hafnium which has a large specific weight (13.3 g/cm.sup.3), the size, shape and weight of the control blade are substantially the same as those of conventional control blades which employ boron carbides B.sub.4 C as the neutron absorber, so that the control blade can be back-fitted in existing boiling water reactors without difficulty.