Abstract: A new spring design for a strap employed in a grid of a nuclear reactor fuel assembly includes a pair of ligaments that each connect with the free portion of the retention plate. The ligaments each are equally spaced a certain distant from the termination of the slots within the strap body. The spring additionally includes a spring contact plate that is wider than the connections of the spring ligaments with the free portion to increase the surface area with which the spring contact plate is in contact with and retains the fuel rod, and thus reduces the contact stresses therebetween. The spring contact plate additionally includes an embossed spring contact member protruding outwardly therefrom reduces the frictional stresses on the fuel rod when it is inserted into and removed from the cell and during vibration of the fuel rod and/or the strap.

Abstract: An improved support grid of a nuclear reactor fuel assembly is described. The support grid has a plurality of first and second straps which are assembled so as to form an eggcrate structure defining grid cells in a square arrangement. The support grid includes a plurality of mixing vanes integrally formed on a side edge of the first and second straps adjacent to an area where the straps cross. The mixing vanes slanted to be adjacent to a fuel rod are each shaped to show no welding apertures formed therein in their horizontal planes of projection thereby maximizing the coolant impinging area to agitate and swirl a coolant flow.

Abstract: A nuclear fuel spacer grid, fabricated by intersecting a plurality of grid strips and used for placing and supporting a plurality of elongated fuel rods within a nuclear fuel assembly, is disclosed. The spacer grid of this invention has a plurality of dimple vanes on its grid strips. The dimple vanes are designed to guide the coolant from one cell to neighboring cells of the spacer grid, thus accomplishing a desired coolant mixing effect and increasing the thermal allowance of the fuel rods and accomplishing a high performance fuel assembly. The spacer grid also has a multi-spring structure, consist in of one arc-shaped main spring and two bow-shaped sub-springs. The main spring directly supports the fuel rod within the spacer grid, while the sub-springs have the same radius of curvature as that of the external surface of the fuel rod and effectively support the fuel rod when the main spring fails to support the fuel rod.

Abstract: A fuel assembly for a nuclear reactor is described, the fuel assembly including: a plurality of fuel pins (12) extending substantially parallel to the axis of the assembly and to each other; at least two structural grids spaced apart from each other, the grids being in contact with said fuel pins (12) and maintaining said fuel pins substantially mutually parallel and preventing contact therebetween, wherein the fuel assembly further comprises at least one mixing grid (50) situated intermediate said at least two structural grids, the fuel assembly being characterized in that said mixing grid (50) is positioned and fixedly located out of substantial contact with said fuel pins (12), the mixing grid also having turbulence inducing means (61) to promote turbulence in a coolant (62) flowing through said fuel assembly in use and in that the mixing grid is formed from sheet metal wherein the plane of the metal sheet from which the mixing grid is formed lies in a plane which is transverse to the axis of the fuel pin

Abstract: A fuel assembly spacer grid including swirl deflectors respectively arranged at interconnections between interconnecting longitudinally and laterally-extending straps on upper ends of the interconnecting straps adapted to support fuel elements of a nuclear fuel assembly. Each of the swirl deflectors has four vanes bent to have an air vane shape. By virtue of this configuration, an improvement in the efficiency of the spacer grid cooling the fuel elements. The spacer grid also includes springs each configured to generate not only a main spring force caused by a displacement of the spring occurring when the spring comes into contact with a fuel element placed in a reactor core, but also an additional spring force caused by hydraulic pressure applied to the spring. Each spring, which is in a fixed state at one end thereof, has a free bent portion at the other end.

Abstract: A fuel assembly (1) comprising a plurality of elongated elements (3) filled with nuclear fuel and at least one component (5, 6, 7) for retaining the elongated elements (3), wherein the retaining component (5, 6, 7) is completely or partly made of a ceramic material.

Abstract: A spacer grid with H-springs for use in a nuclear reactor fuel assembly is disclosed. In the spacer grid, two sets of intersectional grid strips are arranged in sets at an angle to each other prior to being encircled by a plurality of perimeter strips, thus forming a plurality of four-walled cells individually placing and supporting an elongated fuel rod therein. A plurality of regularly spaced openings are formed on each of the grid strips and perimeter strips at portions corresponding to the cells. An H-shaped spring is set in each of the openings and has a specifically curved rib capable of being brought into conformal surface contact with a fuel rod placed in each of the cells. The H-shaped spring thus elastically supports the fuel rod. Two positioning dimples are provided on each of the strips at positions above and below each of the openings.

Abstract: An upper hold-down spring structure for a nuclear reactor fuel assembly. A hold down spring 20 mounted on an upper surface of an upper nozzle 11 of a fuel assembly for a pressurized water reactor is composed of an upper plate spring 21 having plastic spring characteristics and a lower plate spring 23, base ends of which are fixed with a fastening bolt 18 at a common position. The upper spring 21 and the lower spring 23 are made of precipitation hardened nickel base alloy and the thickness of the springs are determined so as to keep the stresses generated less sensitive to stress corrosion cracking.

Abstract: A support grid for laterally maintaining the relative position of elongated fuel elements within a fuel assembly for use within a core of a nuclear reactor. The grid is formed in the shape of a lattice with the intersecting lattice members defining a plurality of cells, most of which respectively support the nuclear fuel elements. The remaining cells support nuclear control rod guide tubes and instrumentation thimbles. The cells supporting the nuclear fuel elements are provided with diagonally positioned springs on two adjacent walls. The springs support the fuel elements against dimples which protrude from the opposite cell walls. The adjacent, diagonal springs in each fuel element cell are inclined in opposite directions. The springs are formed from narrow, parallel slits in the cell wall that terminate along a line parallel to the line of intersection with the adjacent wall. The spring slits continue along that parallel line in a direction away from the spring to increase its flexure.

Abstract: In a reactor core, there is charged a number of fuel assemblies composed of a channel box and a fuel bundle disposed therein, in which fuel rods adjacent to each other are arranged so as to provide a triangular shape and a ratio of a coolant channel cross section to a fuel cross section is set to be 1 or less.

Abstract: A nested sleeve grid restraint system and a method for making a nested sleeve grid restraint system are disclosed. The nested sleeve grid restraint system comprises an insert tube installed in and secured to the intermediate spacer grid and concentrically around a fuel assembly instrumentation tube, the insert tube having ends extending from the intermediate spacer grid, respectively, above and below the intermediate spacer grid; two spacer sleeves, each having flared ends; the spacer sleeves each being fitted concentrically around the fuel assembly instrumentation tube, respectively, above and below the intermediate spacer grid; the flared ends of the spacer sleeves fitting over the ends of the insert tube extending above and below the intermediate space grid whereby the insert tube nests in the spacer sleeves.

Abstract: A spacer for retaining and positioning elongated elements at one or a plurality of levels in a nuclear reactor fuel assembly comprises a grid structure of joined-together sleeve cells. A coolant is adapted to flow upwards through the fuel assembly. The majority of the sleeve cells are provided with an upstream edge with a waveform. The edge is waveformed in such a way that the upwardly flowing coolant first encounters a peak of the wave which is disposed between the joints of the sleeves and thereafter a valley of the wave which is disposed at the joints of the sleeves. The peaks are arranged closer to a center of the sleeve cell than the valleys. Between the peaks and valleys, oblique edges are formed.

Abstract: The ferrule spacer includes a ferrule having an elongated slot with a pair of tabs projecting laterally into the slot. An elongated spring has opposite ends bearing against the interior wall of the ferrule and flats overlying the tabs along the outside of the ferrule. The mid-span portion of the spring projects in a central aperture between the ferrule tabs for biased bearing engagement against the fuel rod. The fuel rod is maintained against oppositely disposed stops formed on the ferrule. The spring is inserted and removed from the inside of the ferrule.

Abstract: A spacer for a nuclear reactor fuel assembly includes sheet metal webs which intersect one another on edge and form grid meshes. A leaf spring projects from a sheet metal web in a grid mesh and is assigned to a bearing boss for the force-locking holding of a rod in the grid mesh. The leaf spring is attached to the sheet metal web at a leaf edge extending in the longitudinal direction of the rod. In order to avoid fretting in a nuclear reactor, a perforation is formed in the leaf spring and has a contour that narrows toward the sheet metal web to which the leaf spring is attached.

Abstract: A protection flap provided on mixing vanes of structural or mid-span mixer grids in order to eliminate or substantially reduce fretting of fuel rods retained by such grids. The flap is an extension or addition of vane material bent upwardly so as to be substantially parallel to the longitudinal axis of the fuel rod being retained. The flap provides a smooth, vertical surface against which the fuel rod contacts in case of vibration, bowing or shifting.

Abstract: The spacer comprises a plurality of strips interleaved with one another to form an eggcrate-type pattern defining essentially rectilinear cells for each fuel rod. Each strip includes a central body portion with cantilevered loop spring-like projections extending to opposite sides, with spring contact portions projecting inwardly. Stops are provided along each of the central body regions of the strips intermediate the loop springs that project to the opposite side of the strip. Adjoining walls have loop spring portions for biasing the rod into engagement with opposing stops whereby each fuel rod is supported at six contact points, i.e., four spring contact points and two hard stop contacts opposite the paired spring contacts.

Abstract: The spacer for a nuclear fuel bundle includes unit cells having upper and lower, generally octagonally shaped walls connected one to the other by spring leg portions along sides thereof 90.degree. apart. The walls also carry stops in opposition to the sides of the walls to which the spring leg portions are connected. By orienting the cells in the spacer such that the majority of the cells have their stops lying toward one side of the spacer, the fuel bundle can be disposed in a horizontal position on the one side of the spacers. In that manner, the dead load of the fuel rods and spacers is borne by the stops along the underside of each spacer without substantially loading the springs of the spacer cells.

Abstract: In a nuclear reactor fuel bundle assembly having a plurality of fuel rods and a non-round water rod extending between upper and lower tie plates, and having at least one fuel rod spacer located along the non-round water rod, an improvement which includes cooperating components on the fuel rod spacer and on the water rod for permitting movement of the spacer along the water rod to a desired axial location and for thereafter preventing further axial movement of the spacer in at least one of two opposite axial directions, the cooperating components including at least one spring on one of the spacer and the water rod.

Abstract: A spacer for a nuclear fuel bundle comprises a plurality of discrete, generally cylindrical ferrules, with each ferrule having a pair of circumferentially spaced fuel rod contacting portions along one side of the ferrule and three superposed openings in the ferrule along an opposite side thereof. A leaf spring having opposite end projecting portions and a central projecting portion is disposed between adjacent ferrules with the end projecting portions and the central portion disposed within the openings of the ferrule. The central portion includes a boss projecting inwardly for engagement against the fuel rod in one ferrule and the end projections contain bosses projecting inwardly and spaced from the fuel rod of the one ferrule. The end projections bear against an adjacent ferrule. The spring is captured between the two ferrules and contacts the ferrules at a plurality of laterally and vertically spaced contact points so that the spring is stabilized against flow-induced vibration.

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: An arrangement of fuel rod support members having dimples and springs is presented to prevent abrasive wear of the fuel rods caused by bouncing of the fuel rods against the supporting members caused by vibrations in a diagonal direction of the support grids. The supporting members are disposed such that dimples are respectively provided on one pair of adjacent walls located on one side of the vibrational direction while springs are respectively provided on adjacent walls located on the opposite side of the vibrational direction.

Abstract: A method of repairing a nuclear fuel rod assembly having a damaged fuel rod and/or a damaged spacer cell.

Abstract: With an arrangement that the axial distance from the upper end of a first opening area to the upper end of the second opening area is equal to the axial distance from the upper end of a first coupling member to the upper end of a second coupling member, when a spring member is moved upwardly relative to round cells, the upper end of the second coupling member comes into contact with the upper end of the second opening area, and the spring members receives upwardly acting forces from fuel elements. The spring member is thereby prevented from inclining with respect to flow of a coolant. Simultaneously, the upper end of the first coupling member contacts the upper end of the first opening area, and the spring member is stably held in a condition where it is aligned with the direction of the coolant flow.

Abstract: A spacer includes a plurality of ferrules welded to one another to form a structural integral matrix for locating fuel rods in a fuel bundle. Each ferrule has a pair of stops along one side of the ferrule and a central opening along its opposite side. An elongated flat spring having openings straddling a central cross-piece is disposed along an outer edge of the ferrule with the spring openings receiving band portions of the ferrule above and below the opening through the ferrule. The intermediate cross-piece bears against an adjoining ferrule whereby the end portions of the spring bear against the rod in the one ferrule, biasing it against the opposite stops. Thus ferrule/spring construction reduces the quantity of material of the ferrule, thereby improving performance without sacrificing structural integrity.

Abstract: A spacer for retaining nuclear fuel rods in laterally spaced relation to one another includes first and second sets of spacer strips extending in mutually perpendicular diagonal directions relative to a generally rectilinear peripheral spacer band. The strips have linearly extending sections with adjacent sections angularly related to one another and meeting at apices. The sections of each strip alternately intersect a diagonal line across the spacer with the apices alternately located on opposite sides of the diagonal line. Alternate apices have springs projecting to one side of the strip for engaging fuel rods and apices between the alternate apices have stops projecting on opposite sides of the strip for engaging the fuel rods. Slots are provided in the strips enabling intermeshing of the strips with one another to define discrete cells peripherally encompassing and retaining fuel rods within the spacer.

Abstract: A grid-shaped spacer includes a sheet-metal web having a web aperture formed therein defining two spaced mutually opposite aperture edges. The aperture edges oppose an elongation of an elongate spring which is curved about a direction transverse to its own longitudinal direction and which has a tab that engages through the web aperture at each of two spring ends. At least one of the tabs is snapped into a notch formed in one of the spring edges opposing the elongation of the spring.

Abstract: A nuclear fuel assembly for a pressurized water reactor having lower and upper tie plates, guide tubes, spacer grids, an instrumentation tube, and extended fuel rods which extend to the lower tie plate and which are spaced radially and supported along the guide tubes by the spacer grids, at least one of the extended fuel rods having at a lower end a fuel rod lower end cap secured by a first spring within an aperture in the lower tie plate and which exerts a lateral force against the lower end cap. The upper tie plate further includes a fuel rod support housing which extends down over the upper end of the at least one of the extended fuel rods and has a second spring positioned in a bore in the fuel rod support housing which exerts a lateral force on the upper end of the extended fuel rod positioned within the bore in the fuel rod support housing.

Abstract: A fixturing tool includes a sleeve having a central region with a circular axial opening and four leaf springs projecting from each of the opposite ends of the central region. The central region is cruciform in cross-section with arcuate side walls between the projections of the cruciform. Unit cells are arranged on a base having openings corresponding in location to the centers of the unit cells in their final assembly in a spacer for a nuclear fuel rod bundle. Fixturing devices are freely and loosely disposed within the unit cells and pins are partially inserted through the fixturing devices to expand the leaf springs to engage the unit cells. Once the cells with fixturing devices and partially inserted pins are centered over the base openings, the pins are advanced into the openings in the base to accurately align each unit cell relative to one another to enable final welding of adjacent cells to one another.

Abstract: A critical power enhancement system is provided for a pressurized fuel channel type nuclear reactor comprising a plurality of fuel bundles contained in a fuel channel and containing a plurality of fuel elements horizontally oriented within the fuel channel. The system comprises at least one appendage strategically located on each of certain fuel elements along its length and projecting outwardly from the surface of the fuel element. The appendages generate turbulence in the coolant flowing at locations along the length of the fuel bundle, where the critical heat flux is most likely to occur. The presence of the appendages suppress the occurrence of the critical heat flux in the fuel bundle thereby increasing the safety limit on the maximum power that can be produced by the reactor.

Abstract: A fuel assembly comprises a plurality of fuel rods, tie plates for holding both ends of these fuel rods, and spacers which support these fuel rods. The spacer comprises a plurality of cells into which the fuel rods are inserted respectively, the adjacent cells being joined to each other at axial ends thereof, whereby a space between these cells being held or retained, and a plurality of loop springs held respectively on the cells. Each of the loop springs has a pair of resilient members which are located within the pair of adjacent cells and which urge the fuel rods in a radial direction, and a pair of connections which connect axial ends of the resilient members to each other. Each of the connections have a passage through which coolant flows axially and which is defined by a closed peripheral wall. The closed peripheral wall is not uniform in thickness. The pair of adjacent cells have at axial end portions of peripheral walls openings for accommodating or receiving the connections of the loop spring.

Abstract: A boiling water reactor fuel assembly having a lowered fuel rod support plate and increased fuel rod length while restraining the fuel rods against lateral vibration.

Abstract: A unitary one-piece lower tie plate grid has a lower portion and an upper portion for supporting the fuel rods. The lower tie plate grid includes cylindrical boss portions extending upwardly from the lower grid portion and arranged in square matrices for receiving the lower end plugs of the fuel rods. Web portions extending upwardly from the lower tie plate portion interconnect the boss portions along the sides of the matrices. The lower grid portion includes a plurality of openings which open into the flow spaces defined by the convex portions of the bosses and the webs within each square matrix of the upper portion of the tie plate. Coolant flows through the openings into the flow spaces for further flow upwardly about the fuel rods. The openings are radiussed adjacent their lower ends and have tapered divergent walls opening into the flow spaces. In another form, the openings have a step intermediate the upper and lower surfaces of the lower grid portion to define a minimum cross-sectional flow area.

Abstract: Disclosed is a grid structure for supporting fuel rods in a nuclear reactor. The grid structure is formed of a plurality of interconnected thin metal grid straps that are welded or brazed together to provide a structural network of interconnected open grid cells, similar to an "egg crate divider". The grid straps are provided at regular intervals, corresponding to the width of a grid cell, with pairs of spaced, substantially horizontal, slotted spring-like projections and a substantially X-shaped spring-like projection vertically intermediate the horizontal projections. The spring-like projections are designed to support and hold the fuel rods within the grid cells under both balanced and unbalanced forces acting on the fuel rod assembly while it is in service, surrounded by coolant in the nuclear reactor.

Abstract: A nuclear fuel rod spacer grid is formed of slottedly interlocked sets of flat strips. One set of strips is formed with integral coplanar tab portions which have one or more edge portions bent at angles to form integral mixing vanes.

Abstract: A nuclear fuel assembly for a boiling water reactor having a spacer grid for positioning and retaining the fuel rods. The spacer grid comprising an upper grid structure and a lower grid structure. Each grid structure comprises a first set of grid strips and a second set of grid strips which intersect to form in each grid structure a lattice of rectangular and square shaped cells through which the fuel rods extend and which act against the fuel rods within the cells. The lattice in each of the upper grid structure and the lower grid structure being the same. The upper grid structure and the lower grid structure being oriented relative to one another so that each of the rectangular and square shaped cells in the upper grid structure is superimposed on a corresponding one of the rectangular and square shaped cells in the lower grid structure so as to act cooperatively against and provide support to a fuel rod on four sides of the fuel rod.

Abstract: A fuel assembly includes a cluster of mutually parallel fuel rods. A fuel assembly channel laterally surrounds the cluster of fuel rods and has a substantially rectangular cross section and flat channel walls. Grid-like spacers having meshes formed therein each receive a respective one of the fuel rods for guiding the fuel rods in a plurality of axial positions. At least one support spring laterally supports each respective one of the fuel rods in the mesh guiding the fuel rod. Each of the spacers have inner ribs being aligned parallel to the fuel rods and outer peripheral ribs opposite the channel walls. At least some of the inner ribs are fastened to the peripheral ribs, and the outer peripheral ribs are joined together only by the inner ribs.

Abstract: A grid structure is presented in which grid cells are formed by orthogonally intersecting straps prefitted in the longitudinal direction with a plurality of slitted spring frame members. Therefore, when the straps are assembled, the spring frame members are also orthogonally intersected. The spring frame members are made of Inconel and provided with welding tabs while the straps are made of zircalloy and provided with their own welding tabs. Therefore, welding can be performed to firmly join the spring frame members to each other while the straps can also be welded firmly to weld the like metals. The spring sections are thus firmly joined and attached to the straps which are firmly joined. The grid of this configuration thus provides an excellent service life without the losing The fuel rod retaining power, which would result from neutron radiation and thermal damages on holding devices made of zircalloy.

Abstract: A hexagonal grid is comprised of castled strips which are (a) bent into a zigzag form, and (b) interleaved with one another so that half-height bridge segments, which extend between and are integral with adjacent full-height castle segments, are placed in edge-to-edge contact so that they align with one another. This forms a grid with no double thickness portions. During fabrication the strips are sandwiched between slotted top and bottom plates. These plates are formed with access openings at sites where three segments intersect and through which welding is carried out. Relatively long spring features are only formed in full-height castle segments. The absence of these features in the half-height bridge segments allows the overall height of the grid to be minimized.

Abstract: Spacers (10) with a cell-formed lattice-work for retaining parallel elongated elements such as fuel rods (5) into a bundle in a nuclear reactor fuel assembly are arranged in a suitable spaced relationship to each other along the bundle, and the cells are formed from tubular sleeves (1). Each one of these sleeves (1) offers a passage for one of the elements in order to fix the elements in relation to each other. Substantially half the number of sleeves (1) in a spacer (10), distributed evenly over the cross section of the bundle, are located in a first plane across the bundle and are joined to each other inside a first frame (11) surrounding the bundle, thereby forming a lattice of sleeves (1) and gaps (13). The remaining sleeves (1) of the spacer (10) are joined together inside a second frame (12) surrounding the bundle and are located in a second plane, separate from the first plane, across the bundle.

Abstract: A method of manufacturing fuel channels made of zirconium-based alloy by combining heat treatment, warm forming and thermal sizing. Fuel channel strip material is heated to a temperature which initiates the transformation from a hexagonal close-packed to a body-centered cubic crystallographic phase and then quenched at a rate which initiates transformation to a hexagonal close-packed crystallographic phase having a texture factor f.sub.L =0.28-0.38. The heat-treated strips are formed into fuel channel components by bending at an elevated temperature sufficient to increase the ductility of the strip material. After the fuel channel components are welded together, the fuel channel is annealed by thermal sizing.

Abstract: An all Zircaloy spacer having integral springs and single metallic layer spacer thickness between fuel rods is disclosed. Each spacer cell includes upper and lower octagonal crowns. These octagonal crowns have a full panel height adjoining the defined sub-channel volume between fuel rods and half panel heights adjoining adjacent cells. The crowns at opposite ends of each octagonal spacer cell are designed to interleave to form a single wall thickness of the spacer material. Accordingly, half wall heights at one crown are defined toward the spacer cell while half wall heights at the other crown end are defined away from the spacer cell. By inverting and adjoining the respective spacer cells at their respective crowns, the crowns form upper and lower crown matrices holding adjoining cells of the spacer together. From two adjacent sides of the four sub-channel adjacent full height sides, cell legs extend between the crowns with upper and lower stops immediately adjacent the crowns.

Abstract: A metal component (10) having non-uniform material characteristics which cause the component to undergo differential growth upon exposure to a neutron flux, and a process for producing such a component. The invention is useful for making metal components for use in nuclear reactors, particularly fuel assembly cantilever grid springs (12). By cold working a portion (40) of a cantilever spring on the convex side of the curved region of the spring, a spring can be provided which has a smaller reduction in preload upon exposure to radiation than a conventional cantilever spring.

Abstract: A rectilinear sectioned water rod--preferably of square cross-section--is provided with horizontal grooves for keying to bands on the inner, water rod surrounding aperture of spacers. Each spacer is constructed preferably of Inconel and includes a specialized inner band for keying to the water rod. The inner spacer member includes an upper surrounding band, a lower surrounding band, and four connecting vertical members--one positioned at each corner of the water rod. Two adjacent vertical members are bent inward to contact one side of the water rod at spaced apart points on the corners of the water rod. The remaining two adjacent vertical members are bent inward to contact the remaining two corners at single points on each vertical member.

Abstract: A mixer grid for a nuclear reactor fuel assembly has a plurality of strips arranged in interlocking rows and columns defining a plurality of cells. A stopper is fixed to each corner of each cell for both directing coolant flow, providing coolant mixing and providing a smooth contact surface for the fuel rod. The stopper is either cone-shaped or cylindrical for directing and channeling coolant flow. The stopper also has a smooth, flat chamfered surface for contacting the fuel rod and minimizing damage upon the shifting of the fuel rod. The grid is attached to the nuclear reactor fuel assembly by using guide cells comprising a plurality of support arches for welding to the nuclear reactor fuel assembly.

Abstract: A grid strip (10) for a fuel rod support grid of a nuclear fuel assembly is cold-formed from a flat annealed plate having length, height, and width dimensions. A plurality of slots (12,14) extend along the height dimension at regular intervals along the length dimension, thereby defining successive cell walls (16,18,20) between successive slots along the length dimension. Each cell wall has upper, central, and lower regions (28,30,32) along the height dimension, each region including a substantially flat base area (34,36,38) and fuel rod support structure (22,24,26) projecting integrally from the base area along the width dimension of the strip. The support structure in each of the upper and lower regions includes a relatively stiff, arched stop (22,26) which projects in a first direction and the support structure in the central region includes a relatively soft, arched spring (24) which projects in a second direction opposite the first direction.

Abstract: A gridlike spacer for fuel assemblies having rods in a bundle, includes polygonal grid meshes having ribs intersecting at corners and extending transversely to the rod bundle between the rods of the rod bundle. The ribs have lateral surfaces facing the rods penetrating the meshes. Springs each protrude diagonally into at least one corner of a respective one of at least a majority of the grid meshes. Each of the springs has a middle part for laterally supporting a given rod penetrating the respective mesh. The middle part is a cylinder segment curved convexly about an axis of curvature at right angles to the rod bundle. Each of the springs has two spring ends adjoining one another in the direction of the rod bundle. The middle part changes over at the spring ends with a convex curvature into two legs being approximately parallel to the rod bundle. The legs are supported at least on the lateral surface of one of the ribs facing toward the given rod.

Abstract: The grids (14) of a nuclear fuel assembly (10) include an outer strip, or perimeter plate (100), having outwardly projecting formations (104,106) spaced from the side edges (110) of the internal grid strips (108), for resiliently absorbing lateral forces before such forces are transferred directly to the internal strips. The load dissipating feature of the present invention can be enhanced by providing orifices (552) in the substantially flat, central region (502) of each perimeter plate. This produces an hydraulic damping effect that can be pre-established by selecting the orifice sizes for a given set of impact load conditions.

Abstract: A nuclear fuel assembly grid (100) made from a plurality of interlaced corrugated metal strips (102-116) forming an egg-crate configuration so as to define plurality of four-walled cells (118) for receiving respective individual fuel rods (120). The spaced apart vertical bend lines (160,162) of the currugation define vertices (130,132) and consecutive body panels (164,166) which alternate generally inwardly and outwardly between consecutive bend lines. A vertical slot (168) extending from one of the strip upper or lower edges (176) into each panel midway between consecutive bend lines, and overlapping a slot from an interlaced strip to form an hourglass-shaped cell having opposed convex walls and opposed concave walls and four 90 degree corners (150). Spring (148) and stop (153) structure projects from each wall of a cell, for centering and supporting the fuel rod within the cell.

Abstract: Fuel assembly including deflector vanes for deflecting a component of a fluid stream flowing past such fuel assembly. The fuel assembly comprises a lattice member having rhombic-shaped rod cells and generally rhombic-shaped thimble cells therethrough. A plurality of parallel fuel rods extend through respective ones of the rod cells and a plurality of parallel control rod guide thimble tubes extend through respective ones of the thimble cells. A plurality of deflector vanes are associated with each rod cell and are integrally attached thereto on the upstream edge of each rod cell. Each deflector vane extends above its associated rod cell and curvilinearly protrudes partially over the rod cell for deflecting a component of the fluid stream onto the exterior surface of the fuel rod that extends through the rod cell.

Abstract: A fuel assembly supporting structure for a nuclear reactor fuel assembly which comprises a two-way shape-memory alloy. A shape-memory alloy is selected which has an overall transition temperature range substantially above atmospheric temperature and substantially below a temperature experienced by the shape-memory alloy under reactor operating conditions. By using a shape-memory alloy in the design, the support structure assumes a first configuration for securely supporting one or a plurality of nuclear reactor components at a temperature above the overall transition temperature range and assumes a second configuration for loosely engaging the reactor components below the transition temperature range.