Abstract: A neutron capture therapy system, including a beam shaping assembly, and a vacuum tube and at least one cooling device. The beam shaping assembly includes a beam inlet, an accommodating cavity accommodating the vacuum tube, a moderator adjacent to an end portion of the accommodation cavity, a reflector surrounding the moderator, and a radiation shield and a beam outlet arranged in the beam shaping assembly. An end portion of the vacuum tube is provided with a target. The cooling device undergoes a nuclear reaction with a charged particle beam incident from the beam inlet to produce neutrons. The moderator decelerates the neutrons produced by the target to an epithermal neutron energy region. The reflector leads deviating neutrons back to the moderator. At least one accommodating pipeline accommodating the cooling device is arranged in the beam shaping assembly. A filler is filled between the cooling device and the accommodating pipeline.

Abstract: A mitigation assembly for a nuclear reactor including a box with an upper portion forming the head of the assembly housing an upper neutron shielding device, including a head including removable lock and a slug installed free to move in translation relative over a given travel distance, the lock being configured such that locking/unlocking between the head and the box can be made by displacement of the slug with an extraction grab with its pawls attached in the slug. The lower part of the upper neutron shielding device includes a cone-shaped sealing block with the tip of the cone oriented downwards, cooperating with a cone-shaped internal surface of the box, a sealing device being formed between the two, the assembly created forming a removable sealing plug.

Abstract: A fuel channel for a nuclear power boiling water reactor is configured to include a bundle of fuel rods with nuclear fuel. The fuel channel is made of a sheet material and has a plurality of sides which have an elongated shape and which are connected to each other such that a corner with an elongated shape is formed where two adjacent sides meet. In one or more corners, the sheet materials from the two adjacent sides overlap with each other such that there is a corner region with double sheet material consisting of the overlapping sheet material from one of the two sides and the overlapping sheet material from the other of the two sides.

Abstract: A truss-reinforced spacer grid and a method of manufacturing the same are provided, in which truss members having a small diameter are woven to form a truss structure surrounded by an external plate, and the truss structure is joined to the external plate to thereby improve the strength of the mechanical structure. The truss-reinforced spacer grid includes a truss structure in which horizontal trusses formed by horizontally weaving a plurality of truss members are vertically disposed at regular intervals, and an external plate is joined with ends of the horizontal trusses and surrounds the truss structure.

Abstract: A fuel assembly for a pressurized-water reactor includes fuel rods held in cells of spacers, control rod guide tubes, and a headpiece and a foot piece, by which it is fixed to upper and lower core grids, respectively. A spacer having a first part, which lies on a radially outer side with respect to a longitudinal center axis of the fuel assembly, and a second part, which lies on a radially inner side and is completely surrounded by the first part are included to reduce the size of gaps between fuel assemblies. The second part is formed of Zircaloy. The first part is made of a metallic material, and when compared to the Zircaloy of the second part, has a lower growth in the radial direction, caused by neutron radiation and a higher coefficient of thermal expansion.

Abstract: A high energy absorption top nozzle for a nuclear fuel assembly that employs an elongated upper tubular housing and an elongated lower tubular housing slidable within the upper tubular housing. The upper and lower housings are biased away from each other by a plurality of longitudinally extending springs that are restrained by a longitudinally moveable piston whose upward travel is limited within the upper housing. The energy imparted to the nozzle by a control rod scram is mostly absorbed by the springs and the hydraulic affect of the piston within the nozzle.

Abstract: Apparatus for the determination of radiation induced growth due to burnup of a nuclear reactor fuel assembly in a reactor core.

Abstract: A new design concept of boiling water reactor fuel rod is disclosed. The new design is characterized by an upward shift in the location of the fuel pellet stack inside the fuel cladding. The resulting axial power shift upward decreases two-phase and total pressure drop and has a stabilizing effect. A device for affecting such fuel pellet displacement is a crushable tube placed under the fuel pellet stack, which also helps to mitigate fuel-clad mechanical interaction and reduces the likelihood of clad failure.

Abstract: The present invention relates to a fuel assembly with a substantially square cross section for a light-water reactor. The light-water reactor comprises a plurality of fuel rods extending between a top tie plate and a bottom tie plate. A fuel rod comprises a cladding tube which surrounds a column with fissionable material. According to one aspect of the invention, at least one fuel rod is provided with an axial gap in the fissionable material. Around this axial gap, the mass of the material is greater than the mass of the material in the main part of the cladding tube.

Abstract: The invention relates to a fuel assembly (1) and a spacer (7) for a nuclear reactor wherein the spacer comprises a plurality of cells (9) for retaining and mutually fixing parallel elongated elements (3, 8) extending through the cells to form a bundle in the fuel assembly. The cells are tubular and internally provided with four elongated, non-independently resilient supports (10), formed in the sleeve material, or with two elongated, non-independently resilient supports (10), formed in the sleeve material, and two independently resilient supports (16), wherein the supports are intended to provide an all-sided positioning of the elongated element. (FIG.

Abstract: A fuel assembly for a boiling water reactor includes a cluster of mutually parallel fuel rods. A fuel assembly channel laterally surrounds the cluster of fuel rods and has open upper and lower ends. A top plate covers the upper open end of the fuel assembly channel and has coolant outlets formed therein. A foot part is assembled from a plurality of individual parts and includes a cast transitional piece having a lower end with an inlet opening formed therein and an upper edge inserted into the open lower end of the fuel assembly channel. The transitional piece defines and surrounds a flow channel widening upward in funnel-like fashion from the inlet opening. The foot part also includes a base plate being disposed at and welded to the upper edge of the transitional piece. The base plate covers the open lower end of the fuel assembly channel and has coolant inlets formed therein.

Abstract: A method and a device for controlling the coolant flow to the fuel rods (1) in the fuel assembly of a pressurized-water reactor, fuel assembly including an elongated bundle of control rod guide tubes and fuel rods (1) which is arranged between a top nozzle and a bottom nozzle. The bundle is retained by spacers (2) supported by the control rod guide tubes and the top and bottom nozzles are provided with a plurality of openings for the coolant flow. According to the invention, the coolant flow along the fuel rods (1) of a fuel assembly which is under low load is reduced by the insertion of special, or the activation of existing, throttle or guide members (10,11,12,13,16) on the spacers (2) or on the fuel rods (1) between the spacers (2) such that the coolant flow is diverted to one or more adjacent fuel assemblies.

Abstract: A spring design particularly suitable for use in the core of a nuclear reactor includes one surface having a first material oriented in a longitudinal direction, and another surface having a second material oriented in a transverse direction. The respective surfaces exhibit different amounts of irraditation induced strain.

Abstract: A zirconium based alloy plate of low irradiation growth, containing not more than 5 wt % Sn and/or not more 5 wt % Nb, and the balance Zr of not less than 90 wt %. The alloy plate has a texture that <0001> orientation (Fr value) with respect to direction perpendicular to the surface of the plate ranges from 0.20 to 0.50. This alloy plate is effective in being used to form a fuel channel box. Also a fuel assembly using this channel box is provided in which the crystal orientation of the zirconium alloy is made random by a heat treatment. Specifically, by the heat treatment, the Fr, Ft, and Fl values thereof are set to 0.25 to 0.50, 0.25 to 0.36, and 0.25 to 0.36, respectively.

Abstract: A fuel assembly has a top nozzle which includes a lower adapter plate and a plurality of guide structures thereon. The lower adapter plate has a peripheral edge. The guide structures are attached to and extend upwardly from the lower adapter plate at locations spaced inwardly from the peripheral edge of the lower adapter plate so as to separate the lower adapter plate into an interior portion extending between interior sides of the guide structures and mountable to the guide thimbles and a peripheral portion extending about exterior sides of the guide structures. The guide structures define a plurality of vertical guide slots.

Abstract: A fuel containment containing nuclear fuel rods of a fuel assembly which will be loaded into a reactor core of a fast breeder reactor is formed narrow in width at middle portion of vertical direction and long in length of vertical direction. And as being used in the reactor core, the middle portion of vertical direction of the fuel containment, wherein both of heat generation and swelling are larger than that of other portion, expands more than other portion, but undesirable contact with adjacent fuel assemblies can be avoided as the middle portion is previously formed narrow. Moreover, the other portions, wherein expansion of the fuel containment and undesirable contact with adjacent fuel assemblies are barely caused, are formed previously wide in width by enlarging the coolant flow path of the fuel containment, whereby pressure drop of coolant of coolant used in the reactor core can be reduced.

Abstract: A double enclosure top nozzle subassembly for a nuclear fuel assembly includes an upper structure having a top plate and an outer depending peripheral sidewall enclosure, a lower structure having a lower adapter plate and an inner upstanding peripheral sidewall enclosure disposed below the top plate and within the outer sidewall enclosure. The outer and inner sidewall enclosures are slidably movable relative to one another as the top plate moves toward and away from adapter plate. A plurality of resiliently-yieldable biasing devices, such as leaf springs extend between and engage the top plate and lower adapter plate. Interengagable structure on the lower and upper edges of the respective outer and inner sidewall enclosures limit movement of the top plate and lower adapter plate away from one another so as to retain the outer and inner sidewall enclosures in sliding contacting relationship together.

Abstract: A fuel assembly includes an array of fuel rods and guide thimbles disposed in laterally spaced relation to one another. The guide thimbles have upper ends extending above the upper ends of the fuel rods. The fuel assembly also includes a top nozzle defined solely by a flat rectangular adapter plate having a main central portion and a peripheral portion surrounding and merging with the main central portion. The main central portion of the adapter plate has a plurality of attachment holes receiving the upper ends of guide thimbles for attachment of the adapter plate upon the guide thimble upper ends in spaced relation above the fuel rod upper ends. A first sest of holes are defined through one pair of diagonal corners of the adapter plate for use in attaching sets of spring assemblies directly to and upon the adapter plate for alignment along the peripheral portions thereof.

Abstract: An apparatus for controlling the flow of coolant through a nuclear fuel assembly, in which a coolant flow restrictor 26 having longitudinal ducts 30 is provided with plug members 48, 49, 50 of different lengths. The plug members 48, 49, 50 are moved longitudinally by the effect of neutron induced growth on an actuating member 60. A connecting member 53 converts the growth of the actuating member 60 into a longitudinal movement of the plug members 48, 49, 50 so that they are progressively withdrawn from the flow restrictor 26 to increase the flow of coolant through the flow restrictor 26.

Abstract: A fuel assembly has a top nozzle which includes a lower adapter plate and a plurality of guide structures thereon. The lower plate has a periphery bounding an interior thereof mounted by guide thimbles. The guide structures are attached to and extend along the periphery of lower plate and upwardly therefrom. The top nozzle also includes upper hold-down plate and a plurality of leaf spring assemblies. The upper plate is mounted to the guide structures for slidable movement relative thereto such that the upper plate can move toward and away from the interior of the lower plate within the space bounded by the guide structures as the upper plate slidably moves along the guide structures. The leaf spring assemblies are interposed between and engaged with the lower and upper plates so as to yieldably support the upper plate in spaced relation above the lower plate and bias the upper plate for movement away from the lower plate.

Abstract: An improved lower tie plate having increased fluid flow resistance is disclosed for use in a boiling water nuclear reactor. The fuel bundle includes the lower tie plate, an upper tie plate, and a plurality of fuel rods supported therebetween in vertical upstanding relation, with the fuel rods surrounded by a square sectioned channel. In the preferred embodiment, some of the upper fuel rods are of partial length. The surrounding channel confines the fluid flow through the fuel bundles between the tie plates for the extraction of heat from the fuel rods undergoing a fission reaction. The lower tie plate includes a first group of apertures for the support of the fuel rods to selected positions in the 9x9 matrix; appropriate numbers of these apertures are threaded for tying the upper and lower tie plates together with tie rods. The matrix is interrupted at larger apertures for the support of moderator containing water rods.

Abstract: In a BWR- or PWR-type nuclear reactor, the fuel rods in the fuel assembly are cooled by a coolant flow which is pumped through the fuel core. Depending on the degree of burnup of the fuel rods, the coolant flow to the fuel assemblies may need to be changed for the cooling to be matched to local need. To control coolant flow on the basis of the degree of burnup of the fuel rods, the irradiation growth of elongated elements in the fuel assembly has been utilized.

Abstract: An expandable top nozzle subassembly for a nuclear fuel assembly includes an upper structure having a top plate and a depending peripheral sidewall enclosure, a lower adapter plate disposed below the top plate and within the enclosure with the adapter plate and sidewall enclosure being slidably movable relative to one another so as to move the top plate toward and away from adapter plate, and a plurality of resiliently-yieldable biasing devices extending between and engaging the top plate and lower adapter plate. Interengagable structure on a lower edge of the enclosure and on a peripheral edge of the adapter plate capture and retain the adapter plate within the enclosure upon movement of the enclosure relative to the adapter plate which moves the top plate away from the adapter plate.

Abstract: To provide intrinsic reactor safety, the fuel sub-assemblies of a nuclear reactor core are provided with reactivity control mechanisms operable, in response to temperature rises above desired limits, to interact with adjacent fuel sub-assemblies and effect radial dilation of the core in order to reduce reactivity. Various embodiments are disclosed in which differential thermal expansion of an operating device or devices (34; 40; 42, 44, 46; 50) is translated into radially outward displacement of a lever or levers (28) for contact with neighbouring sub-assemblies.

Abstract: The invention relates to a fuel assembly for a nuclear reactor comprising a bundle of longitudinal fuel rods which are insertable into the fuel assembly and held together by spacers (1), consisting of cells, arranged along the bundle. The wall of the fuel assembly towards the bundle of fuel rods is provided with a number of first locking members (5) arranged in the longitudial direction of the wall, and the spacers (1) are provided with a second locking member. The second locking member comprises at least two interconnected rods (3), one rod consisting of material having a low coefficient of thermal expansion and the other rod consisting of material having a high coefficient of thermal expansion. These rods have been adapted, in dependence on the temperature in the reactor in operation, to bring the second locking member into engagement with the first locking members (5) and to release the same when the reactor is shutdown.

Abstract: A nuclear fuel assembly comprises a bundle of elongated fuel rods distributed at nodes of a regular lattice and a structure for retaining said fuel rods. The structure has a lower end piece, and upper end pieces, tie rods connecting said end pieces and grids distributed along the tie rods for maintaining the fuel rods at the nodes. The structure consists of two substructures slidable with respect to each other in the direction of the fuel rods. Springs located between the two substructures spread apart the two end pieces for respective abutment against a lower core plate and an upper core plate.

Abstract: A device for relieving thermally induced stresses developed in a nuclear fuel assembly during reactor heatup is disclosed herein. The device generally comprises a stress relieving fastener capable of connecting a fuel assembly top nozzle, which may be stainless steel, to a threaded stud, which may be Zircaloy. The stud is attached to a fuel assembly channel. The fastener includes a threaded nut having a deformable portion for relieving thermally induced stresses developed in the stud by the differential thermal expansion of the top nozzle and stud. In a first embodiment of the nut, the deformable portion comprises a circumferential, deformable ridge which is substantially recessed from the marginal edge of the nut and which is disposed on the bottom most surface of the nut. The ridge contacts the top nozzle when the nut threadedly engages the stud. A second embodiment of the nut is similar to the first embodiment except that the deformable ridge is disposed flush with the marginal edge of the nut.

Abstract: Spacer grids for a nuclear fuel assembly are arranged in superadjacent groups having grid springs and opposing dimples which contact a fuel rod passing through a cell of the spacer grid with a selected spring force. As fabricated, the lowermost grid exerts the greatest initial spring force on the rod; intermediate grids exert a smaller spring force; and the uppermost grid exerts yet a lower spring force. The fuel rod is supported laterally while it is permitted to age expand axially with little axial compression resulting from the spring forces of the springs and dimples, whereby bowing of the rod is diminished.

Abstract: A modular component nuclear fuel assembly design in which sub-assembly fuel modules are joined together to form an integral fuel assembly. The invention permits a defective or damaged fuel assembly to be reconstituted from new sub-assembly fuel modules thereby facilitating quick repair. By using sub-assembly fuel modules, the invention allows for modular enrichment and/or burnup variations within a fuel assembly and permits tailoring of reactivity and/or fuel burnup within the core thereby enhancing fuel management and utilization and enabling peaking factors to be reduced. The sub-assembly fuel module design permits easy access to interior fuel rods thereby affording an increased fuel rod surveillance capability and further permits advanced fuel design to be incorporated into a reactor core with a minimum of risk.

Abstract: A fuel assembly for use at non-control rod locations of a nuclear reactor core includes top and bottom nozzles and longitudinal structural members extending between and attached to the nozzles for forming an integral unitary structure. One or more of the structural members includes an elongated hollow cladding tube extending between the top and bottom nozzles and end plugs secured to opposite ends of the tube for hermetically sealing and attaching the tube to the top and bottom nozzles. The improvements in the structural member relate to features for reducing fuel assembly bow. Such features relate to a quantity of thermal or irradiation-induced creep resistant material and pretensioning means positioned within the tube. The creep resistant material is a ceramic material in stacked pellet form and coated with a burnable adsorber material.

Abstract: A fuel assembly includes top and bottom nozzles, elongated hollow control rod guide thimbles extending longitudinally between and rigidly interconnecting the top and bottom nozzles such that together they form a rigid structural skeleton of the fuel assembly, transverse grids being supported on the guide thimbles at axially spaced locations therealong between the top and bottom nozzles, fuel rods extending through and being supported by the grids between the top and bottom nozzles so as to extend in generally side-by-side spaced relation to one another and to the guide thimbles, and elongated solid tie rods extending longitudinally between the top and bottom nozzles and through and rigidly interconnected with the grids so as to extend in generally side-by-side spaced relation to one another, to the fuel rods and to the guide thimbles so as to bolster the stiffness of the structural skeleton of the fuel assembly.

Abstract: A method of straightening an irradiated fuel assembly having a plurality of control rod guide thimbles in which some of the guide thimbles are bowed and thus greater in length than other of the guide thimbles comprises the steps of determining the length adjustments required for shortening the respective bowed guide thimbles in order to make their respective lengths generally the same as the other guide thimbles, and then forming expansions in the bowed guide thimbles so as to shorten their respective lengths by the amounts of the length adjustments. Usually, a plurality of expansions are made in most of the bowed guide thimbles at spaced locations between opposite ends thereof. Some of the expansions differ in the amount of shortening from other of the expansions. Also, the total amount of shortening of the bowed guide thimbles is controlled by the number of the expansions and the amount of shortening which results from each expansion.

Abstract: Zirconium alloy or Zircaloy grid straps in a fuel assembly grid have predetermined texture (or grain orientation) to offset stress relaxation which occurs upon irradiation of the grid. Particularly, by providing "f-factor" values of the material greater in generally orthogonal, longitudinal directions of the straps than in the strap height direction, the grid strap material will undergo irradiation shrinkage in the longitudinal directions which will serve to offset stress relaxation and maintain sufficient spring force on the fuel rods extending through the cells formed by the grid straps.

Abstract: A fuel assembly for a boiling water reactor has a bundle of fuel rods consisting of a top tie plate and a bottom part which, together with a plurality of fuel rods, constitutes a rigid unit. The fuel rod bundle is surrounded by a fuel channel (1), to which there is attached a fixing member (2) cast in stainless steel. The fixing member (2) is attached to a vertical projection (3), extending from the top tie plate, by means of a bolt (4) which is loaded with a tensile force and a sleeve (10) which is loaded with a compressive force and which surrounds the bolt and is arranged in the fixing member, the coefficients of thermal expansion of the bolt and the sleeve being less than that of the fixing member.

Abstract: A flow channel-to-nozzle attachment for a nuclear fuel assembly wherein the flow channel and nozzle are formed of material having different thermal coefficients of expansion, the attachment comprising tapered bars secured to the lower inner ends of the channel which bars are fitted into similarly tapered grooves in the adjacent outer surfaces of the nozzle, the angle of taper being selected such that the tapered bars move more or less deeply into the grooves in the nozzle with temperature changes without bending or stressing the lower end of the channel.

Abstract: A fuel assembly, particularly advantageous for use with a BWR, wherein the fuel bundle is adapted to be inserted into an envelope formed from a flow channel and a lower nozzle assembly. The fuel bundle is essentially axially symmetrical having identical top and bottom tie plates. Within the fuel bundle, alternate fission gas plenums are disposed at the top and bottom of the bundle respectively.During the refueling operation, the fuel bundle is removed from the reactor core, axially inverted and reinserted into the core for continued burn up. The invention takes advantage of the reactivity increase possible in a BWR when a partially burned fuel bundle is inverted.

Abstract: A nuclear fuel assembly, particularly advantageous for use in a pressurized water reactor, wherein each alternate fuel rod in the assembly is positioned with its fission gas plenum zone at the top of the assembly and the intervening alternate fuel rods are positioned with their fission gas plenum zones at the bottom of the assembly. All of the fuel rods are preferably axially coextensive. An axial blanket region may be formed by providing the fuel zone of each fuel rod with a small zone of natural or depleted uranium at a part of the fuel zone furthest from the fission gas plenum zone. A method of effectively lengthening the active length of a nuclear fuel assembly is also described.

Abstract: The invention relates to a method for producing an assembly, as well as to an assembly produced by this method.The foot of the assembly is butt welded to the hexagonal tube prior to the introduction of the bundle of rods into the latter. This introduction takes place in the vertical direction using a jack which passes through the foot of the assembly. The upper neutron protection is then fixed by pressing the tube into recesses. Finally, the vacuum producing system and the plug are fitted in the foot.Application to assemblies for fast neutron nuclear reactors.

Abstract: A nuclear fuel assembly for high utilization of the nuclear fuel is disclosed. Alternate fuel rod assemblies are axially shifted relative to each other to create zones of high hydrogen-to-uranium ratios at the ends of the core for high utilization of the fuel at the core ends. Each fuel rod assembly comprises separate upper and lower fuel rods. The axial shift provides intermeshing of the separation between axially aligned fuel rods at the core center. Seed blankets are located at the ends of the core and lower enriched sections are located at the core center during beginning of core life. After a specified amount of fuel depletion from reactor operation, the upper and lower rods are interchanged and an opposite axial shift is employed. The high utilization fuel assembly provides for burnup gradient utilization, axial blanket utilization, plutonium production and burnup, axial power flattening, and less use of enriched uranium.

Abstract: Water-cooled nuclear reactor fuel assembly of the type comprising two end pieces, respectively an upper end piece and a lower end piece, said end pieces having openings for the circulation of the light cooling water, the spacing grids made from a single metal have a relaxation effect under irradiation and are constituted by two groups of perpendicular plates, said grids defining cavities, each of which is traversed either by a fuel rod, or by a connecting rod, said spacing grids being distributed along the connecting rods, the walls of each cavity having bearing members for holding in place the fuel rods, wherein the fuel rods are jointed to an end piece and wherein means are provided for maintaining the group of grids against one of the upper or lower end plates, both during the operation of the reactor and when it is shut down.

Abstract: A nuclear fuel assembly includes and upper yoke, a base, an elongated, outer flow channel disposed substantially along the entire length of the fuel assembly and an elongated, internal, central water cross, formed by four, elongated metal angles, that divides the nuclear fuel assembly into four, separate, elongated fuel sections and that provides a centrally disposed path for the flow of subcooled neutron moderator along the length of the fuel assembly. A separate fuel bundle is located in each of the four fuel sections and includes an upper tie plate, a lower tie plate and a plurality of elongated fuel rods disposed therebetween. Preferably, each upper tie plate is formed from a plurality of interconnected thin metal bars and includes an elongated, axially extending pin that is received by the upper yoke of the fuel assembly for restraining lateral motion of the fuel bundle while permitting axial movement of the fuel bundle with respect to the outer flow channel.

Abstract: A fuel assembly for a boiling water reactor comprises a plurality of fuel rods (2, 2'), which constitute four partial bundles and are surrounded by a fuel channel system (1) comprising one partial tube for each partial bundle. Each of the four partial bundles rests on a bottom tie plate (19) and is positioned with respect to the others by means of a common top tie plate (31), which is provided with a lifting loop (33) which is sufficiently strong to be able to lift the four partial bundles simultaneously, a major part of the lifting force being transmitted to said bottom tie plates via a plurality of supporting fuel rods (2').

Abstract: A fuel assembly which comprises a plurality of subassemblies of fuel rods (12), which are each enclosed in a corresponding wall system (1), is provided at its upper end with a horizontal distribution channel (22, 32), extending along the periphery, which upon emergency cooling receives sprinkling water and distributes this among the different subassemblies.

Abstract: The present invention relates to an anti-fly-off device for the fuel element of a nuclear reactor.This device, which is applicable to a nuclear reactor, comprises a plurality of sheathed fuel elements kept parallel to one another by a system of spacing grids and a stucture, independent of the fuel elements and formed by two parallel plates, namely an upper plate and a lower plate, between which extend brace rods regularly distributed among the system of fuel elements, whereby at least certain of these brace rods are surrounded by grid sleeves. A casing introduced into the grid sleeves of the lower grid around the brace rods and fixed by its lower end to the lower plate has at its upper end an outer shoulder which, with an appropriate clearance, blocks the upward displacement of the grid sleeve.

Abstract: An upper tie plate assembly for a nuclear reactor includes the usual tie plate having holes to receive the tie rod of the fuel assembly. A lower side member is welded to each side of the tie plate and there is a spring seat at each corner, connected to the lower side members. An upper side member parallels each lower side member at a higher elevation. At an intermediate elevation, there are leaf springs paralleling the side members, with their ends received within spring seats provided at the corners of the plate. Sliders are mounted on the upper side members and engage the midpoints of the upper surfaces of the springs. As the fuel assembly expands, the sliders, which engage an upper core plate of the reactor, deflect the springs from their normal, upperwardly bowed position, through a flattened position, to a downwardly bowed position. The ends of the springs are mounted within the spring seats in such a manner that they are free to accommodate extension of the springs.