Abstract: A fuel assembly for a boiling water reactor includes an elongated box extending between a top part and a bottom part, having box walls with flat outer surfaces defining a polygonal outer cross section with rounded corners, an interior and a longitudinal axis. A bundle of fuel rods is disposed in the box and aligned parallel to one another and to the longitudinal axis of the box. The fuel rods are disposed beside one another in rows parallel to the box walls. The box walls have reinforcements protruding into the interior in the vicinity of the rounded corners defining a relatively increased wall thickness, and the box walls have a relatively reduced wall thickness between the reinforcements.

Abstract: A fuel assembly (1) for a nuclear reactor of pressurized-water type with a number of fuel rods (2) retained into a bundle by means of spacers (3) between a top nozzle (4) and a bottom nozzle (5) which includes a plurality of openings for a coolant flow to the fuel rods (2). A partial fuel box (7) is providing at at least the lower part of the fuel assembly and extending from the bottom nozzle (5) and at least up past the lowermost ordinary spacer (3) of the bundle.

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: There is provided a method of manufacturing a grid for a nuclear fuel assembly, the grid having at least two crossed sets of mutually parallel plates which define cells, some of which receive guide tubes and others receive fuel rods, the plates being provided with boss means for limiting the amount of movement available to the rods relative to the nodes of a regular array. The plates are formed with bosses projecting radially inwardly into each cell for receiving a fuel rod by such an amount that they define a passage having a size at least equal to a minimum diameter of the fuel rods. Then the bosses are deformed radially outwardly for imparting to each passage a predetermined radial size, slightly higher than that of one fuel rod and determined by a gauge.

Abstract: An improved spacer is disclosed which contains an Inconel grid and a Zircaloy surrounding band. The Inconel grid can be fabricated from the extremely thin and highly elastic spring metal utilizing a modification of a prior art cell construction that includes paired inwardly bent vertical spring legs with cantilevered and rod encircling upper and lower arm pairs The spring legs extend at spaced apart locations between the upper and lower arm pairs and have a medial spring rod contacting portion for biasing the rods into stops on the rod encircling arm pairs. The springs at the upper and lower ends are provided with spring dimple stops to prevent over stressing of the spring during assembly or handling of the fuel bundle into which the spacer is incorporated. The rod encircling arm pairs have an offset from center where the two arms meet at their distal ends to complete encirclement of the rods. This offset from center enables the cells to be fastened in cell pairs at their respective embracing arms.

Abstract: A fuel assembly of a pressurized water nuclear reactor includes at least two fuel rods, respectively, having a cladding tube of given outer and inner diameters and pellets of given outer diameter received in the cladding tube, the fuel rods being disposed in the fuel assembly at a given mutual spacing of center points thereof, a ratio of the given mutual spacing of the center points of the fuel rods to the outer diameter of the cladding tube being in a range between 1.35 and 1.37.

Abstract: A nuclear reactor core assembly includes a support plate having a plurality of inlets for channeling water to a core lattice fixedly joined thereto. The lattice includes a plurality of flow channels, each including a respective separately removable fuel bundle. In a preferred embodiment, the core lattice includes a plurality of flow dividers joined together for allowing unrestrained expansion and contraction thereof, and which prevent crossflow of water therebetween.

Abstract: Grid strips for a nuclear fuel assembly grid have elongated weld tabs. The weld tabs are bent against the strips along the intersection with an adjacent orthogonal strip. The tabs are dimensioned and positioned to initially extend substantially the entire length of the intersection of two grid strips. The tabs are then melted during the welding process.

Abstract: A swirl vane is disclosed for addition to a spring metal grid spacer utilized with a conventional nuclear boiling water nuclear reactor. The spring metal spacer includes a matrix of fuel rod containing cells. Each cell has at least one spring leg and at least two fuel rod encircling arms. The spring leg functions to bias a fuel rod contained within the cell at the spacer to one side of the cell. The two rod encircling arms define stops against which the fuel rods are biased. The cells themselves are welded into a unitary matrix and preferably surrounded by a metallic band. The improved swirl vane of this invention includes an "I" shaped spring steel strip. This strip includes top and bottom tabs for engaging the respective top and bottom grid structure of the spacer. The "I" shaped strip is then twisted to provide the swirl vane surface, this twisting being preferably slightly less than or greater than the total twisting required.

Abstract: To provide quality assurance inspection of the dimensional characteristics of cells to be incorporated in spacers utilized in nuclear fuel bundles to establish critical spacings between fuel rods, a cell is placed in a fixture dimensioned to gauge the outer dimensions of the cell. A fuel rod-simulating pin is then inserted through the cell to rest on fuel rod-positioning stops formed on the cell. "Go, no go" feeler gauges then check the dimensions of the gaps between the fixture and pin.

Abstract: The additional mixing grid has no belt and comprises at least two sets of crossed plates that are fixed to each other at their cross-points, the plates being fitted with fins for stirring the coolant, and delimiting cells, some for receiving guide tubes and the others for receiving fuel rods. Each plate is provided, on each of the faces of those internal cells that receive the rods, with bosses that project sufficiently little to leave radial clearance for the rods passing through the cells and the projection of the bosses is proportioned relative to the projection of the fins so that in the event of bending vibration the rods come into contact with the bosses without reaching the fins, the lengths of the plates being such that the footprint of the additional grid is less than the footprint of the polygon constituting the virtual envelope of the rods.

Abstract: A fuel assembly for a nuclear reactor is provided with a number of parallel fuel rods, which are retained by means of spacers (2), and guide tubes (3) between the fuel rods. The guide tubes (3) are also attached to the spacers (2) as well as to a top nozzle and a bottom nozzle (4, 5). The guide tubes (3) are provided, at least at the spacers (2), with external threads (7) for improved fixing to the spacers.

Abstract: A mixing grid for use in a pressurized reactor comprises at least two sets of crossed fixed together at their cross-points, delimiting cells, some for receiving fuel rods and the others for receiving guide tubes, the plates being provided with coolant stirring fins extending the plates downstream and disposed to deflect the coolant transversely to its general flow direction, each plate being provided with abutment means projecting inwardly from each of the faces of the cells for receiving fuel rods, thereby delimiting a passage that is larger than the size of the rods but small enough to prevent a rod contained in the cell coming into contact with the fins. In each wall the abutment means comprise two portions of plate that are cut out and deformed into a scoop-shape, and that are offset relative to each other in the coolant flow direction, with the scoops projecting in opposite directions and tending to cause coolant to pass from one cell to another.

Abstract: In a nuclear fuel bundle for a boiling water reactor, the prior art suggested concept of tapered fuel rods forming the bundle array is disclosed in a practical design including a fuel bundle and an improved associated spacer utilized in the upper two phase region of the fuel bundle. A tapered fuel rod is utilized having a large diameter bottom tube for holding corresponding large diameter fuel pellets at the fuel rod bottom, a smaller diameter top tube for holding correspondingly smaller diameter pellets at the top of the fuel rod, and a bell reducer situated between the large diameter lower fuel tube and the smaller diameter upper fuel tube. This bell reducer tapers from the large outside diameter of the lower fuel tube and the smaller outside fuel diameter of the upper fuel tube and forms a smooth transition between the large and small diameter sections of the fuel rod. An improved fuel rod spacer is disclosed for use with the upper and smaller tube portions of the fuel rods.

Abstract: A grid for use on a PWR fuel element comprises a belt of hexagonal shape and three sets of plates secured to the belt. The plates in each set are mutually parallel and are at an angle of 120.degree. with the plates of the two other sets. All plates have the same length and have a 120.degree. bend in their middle. Each plate is parallel to two successive faces of the belt.

Abstract: A fuel bundle having spacers optimally deployed is disclosed wherein the distance between the spacers varies along the length of the fuel bundle. The fuel bundle has a dense fuel rod array (preferably in the range of 10.times.10). It includes at least one part length rod extending from the lower tie plate toward but not to the upper tie plate, which part length rod terminates at a spacer and defines under the upper tie plate overlying the end of the spacer a vent volume for the preferential venting of vapor moderator (steam) from the fuel bundle. A vertical spatial distribution of the spacers is disclosed in which the bottom spacers in the single phase region of the fuel bundle are relatively closely vertically spaced and the upper spacers are relatively more distantly vertically spaced one from another.

Abstract: There is disclosed a grid in a nuclear fuel assembly for supporting fuel rods and thimbles, which includes a plurality of elongated straps intersecting perpendicularly with each other to define a plurality of first grid cells for supporting the fuel rods and a plurality of second grid cells for supporting the thimbles. Each grid cell has a prescribed intervening distance defined between the opposed straps. A cylindrical sleeve is arranged on at least one of the opposite ends of the strap portions defining the second grid cell and has an inner diameter generally identical to the intervening distance. There is provided an engaging unit for securing each sleeve to the strap portions. The engaging unit includes at least one first engaging portion provided on the strap portions and at least one second engaging portion provided on the sleeve. The first and second engaging portions are held in resilient engagement with each other.

Abstract: A fuel assembly for a boiling water reactor includes an elongated case having an interior and inner surfaces. A base part has inlet openings discharging into the interior of the case for coolant flowing in a given flow direction and a head part has outlet openings leading out of the interior of the case for the coolant flowing in the given flow direction. Mutually parallel fuel rods containing nuclear fuel are disposed in the case between the base and head parts. The inner surfaces of the case have a profile with a rectilinear alignment as seen in the given flow direction and flow trippers extending transversely to the alignment in the form of bulges protruding inward in the given flow direction. Each of the bulges has a sloped surface facing toward the coolant with an impact surface substantially perpendicular to the given flow direction.

Abstract: Bottom end fuel assembly reconstitution is permitted by elimination of weld of Inconel lower grid perimeter strip to stainless steel lower end fitting. Slots in 2 or 3 sides of L.E. Fitting capture ribbed sections of grid perimeter strip, locking screws hold L.E. Fitting in position on guide thimbles. Grids lip on perimeter strip is interlocked by sliding in L.E. Fitting groove.

Abstract: A strip (16) for an eggcrate-type nuclear fuel assembly grid (10), in which the fuel rod support springs (30,36) are formed by beams (75,77) and a connecting arch (78). More particularly, the strip has a substantially flat body (56), upper and lower edges (84,86) defining the strip vertical height, and opposed side edges (80) defining the length of the body. The fuel rod support structure (30) projects transversely from the body and comprises a plurality of spring members spaced apart in the longitudinal direction along the body, each spring member having a pedestal portion (75,77) resiliently supported by the body and a contact portion (78) integrally formed on and projecting from the pedestal portion. The pedestal portion preferably includes a beam integrally constrained at both ends by the body. By integrally fixing the ends, the spring member can be considerably smaller and produce the same force for a given deflection as a conventional grid.

Abstract: There is disclosed a grid in a nuclear fuel assembly for supporting fuel rods and thimbles, which includes a plurality of elongated straps intersecting perpendicularly with each other to define a plurality of grid cells. A plurality of engaging units are provided on the grid cells for supporting thimbles, respectively. Each engaging unit includes at least one engaging member provided on at least one of the opposite ends of the straps of the grid cell and defining an engaging portion. A plurality of cylindrical sleeves are arranged in the grid cells for supporting thimbles, respectively. Each sleeve has at least one engaging projection associated with the engaging portion of the engaging member. The engaging projection of the sleeve and the engaging portion of the engaging member are formed such that when the sleeve is turned circumferentially, the engaging projection is held in engagement with the engaging portion.

Abstract: A spacer for a fuel bundle is disclosed in which a grid type construction provides an approximation to a traditional ferrule spacer. First and second sets of diagonally extending strips of Zircaloy are utilized extending along opposite diagonals across a square sectioned spacer. One set of strips is disposed in a first parallel array along a first diagonal, with each strip of the set being spaced from other strips of the set at rod width spaced intervals along the second and remaining diagonal. The other set of strips is disposed in a second parallel array along an second diagonal, with each strip of the set being spaced from the other strips of the set at rod width spaced intervals along the first diagonal.

Abstract: Herein disclosed is a reactor core including a plurality of fuel assemblies having a plurality of fuel rods. In a central region of the transverse section of the fuel assembly, a plurality of fuel rods are arranged in the form of a square lattice. In the peripheral region surrounding the central region, a plurality of fuel rods are arranged in the form of triangular lattice. The pitch of the fuel rods arranged in the square lattice form is equal to that of the fuel rods arranged in the triangular lattice form. With the arrangement of the fuel rods in the triangular lattice form in the peripheral region, the ratio of the moderator to the fuel of the peripheral region is smaller than that of the central region. As a result, the local power peaking drops. Since the arrangement of the fuel rods is partially in the triangular lattice form, the pitch of the fuel rods can be increased to augment the MCPR.

Abstract: A grid key and method for keying exterior grid cells in a nuclear fuel assembly. The grid key has a main body portion having first and second ends and is bent at approximately a 45 degree angle near the first end. Two tabs extend outward from the first end at a right angle to the main body portion to define a T-shape. The T-shaped end is inserted into the window of the exterior grid strip such that the top of the T-shape is parallel to the longitudinal axis of the grid assembly. The main body portion is then rotated 90 degrees to position the top of the T-shaped end to be perpendicular to the longitudinal axis of the grid assembly and behind the exterior grid strip. The main body portion is then pulled away from the exterior grid strip in a vertical rotating motion, causing the top of the T-shaped end to pull the exterior grid strip away from the center of the cell defined by the grid assembly.

Abstract: A method and apparatus for assembling an egg-crate type grid (10) by orthogonally interengaging slots (30,32) cut transversely into one longitudinal edge of each of a plurality of metal strips (12,14). A first plurality of strips (14) is supported on their lower unslotted edges in north-south orientation so that the strips are uniformly spaced apart in parallel in the east-west direction with all the slots (32) oriented upwardly on the upper edge. The slotted upper edges (26) of adjacent north-south strips are then spread farther apart in the east west direction while maintaining the lower edges (28) at said uniform spacing. The lower, slotted edges (24) of a second plurality of east-west oriented strips are interengaged with the north-south strips while the selected portions of the upper edges of the north-south strips are spread. The upper edges of the first plurality of strips are then returned to the unspread orientation.

Abstract: A fuel assembly in the form of an elongated channel having several corners is connected to a coolant intended to flow through the channel. A bundle of similarly elongated fuel rods, retained by a plurality of spacers, is arranged in the channel, and arranged in the upper part of the fuel assembly, at least between a pair of spacers, is a sleeve formed of a sheet around the bundle. The sleeve has an external shape which conforms closely to the walls of the fuel assembly and is perforated by a large number of openings, the total surface of which is at least as large as the sheet surface remaining on one side of the sleeve.

Abstract: A fuel assembly for a pressurized water reactor includes fuel assembly edges and a fuel assembly interior. A bundle of mutually parallel fuel rods with cladding tubes each contain nuclear fuel. A given number of guide tubes are provided for control rods. A support structure includes an upper end with a fuel assembly head, a lower end with a fuel assembly foot, and a plurality of spacers disposed perpendicular to the fuel rods. The spacers have a uniform grid structure with edge meshes formed therein at the fuel assembly edges and inner meshes formed therein in the fuel assembly interior. Each of the inner meshes are surrounded by four respective immediately adjacent meshes each having the same area and each containing a respective one of the guide or cladding tubes or an instrumentation tube.

Abstract: A bracing grid suitable for use in a light water reactor has a plurality of mutually intersecting sets of plates defining cells which receive fuel rods. The plates carry springs for retaining the rods by friction. Each spring is formed has a U legs located each on one side of a plate, the branch being for contact on the elements in two mutually adjacent cells separated by the plate. The two legs are connected by a loop straddling the plate and are connected to each other by a weld at the base of the loop, through a window formed through the plate. The legs of each spring are also mutually connected by mechanical locking means which retain the two legs with respect to each other and with respect to the respective plate.

Abstract: The invention relates to a fuel assembly in the form of an elongated channel having several corners. The channel is connected to a coolant intended to flow through the channel. A bundle of similarly elongated fuel rods, retained by a plurality of spacers (8), is arranged in the channel. The spacer (8) has an outer frame which is provided all around with a plurality of windows (10). According to the invention, deflection fins (9) are placed in said window and are so directed that cooling water flowing along the wall of the fuel assembly is diverted in a direction towards the center of the channel to improve the cooling for those fuel rods which are located in this region.

Abstract: An improved spacer is disclosed which contains an Inconel grid and a Zircaloy surrounding band. The Inconel grid can be fabricated from the extremely thin and highly elastic spring metal utilizing a modification of a prior art cell construction that includes paired inwardly bent vertical spring legs with cantilevered and rod encircling upper and lower arm pairs. The spring legs extend at spaced apart locations between the upper and lower arm pairs and have a medial spring rod contacting portion for biasing the rods into stops on the rod encircling arm pairs. The springs at the upper and lower ends are provided with spring dimple stops to prevent over stressing of the spring during assembly or handling of the fuel bundle into which the spacer is incorporated. The rod encircling arm pairs have an offset from center where the two arms meet at their distal ends to complete encirclement of the rods. This offset from center enables the cells to be fastened in cell pairs at their respective embracing arms.

Abstract: A spring-and-spacer assembly for maintaining fuel rods upright in a fuel assembly of a nuclear reactor core is provided. The spring is in the form of a continuous loop with first and second legs having mid-leg rod-contact regions. Bend regions are positioned on each side of each contact region extending toward the interior of the loop spring. In most positions, the spring is used to load two adjacent fuel rods. In configurations in which there is an unpaired fuel rod, a plate having a tab for contacting the spring is provided. The spring provides the desired force, such as about 2.5 pounds per fuel rod, in a small rod-to-rod spacing of less than about 0.14 inches.

Abstract: A spring-and-spacer assembly for maintaining fuel rods in a upright preferred position in a fuel assembly of a nuclear reactor core is provided. The spring has a leg portion and two loop portions, one at each end of the leg. Each loop engages an ear formed in a ferrule of the spacer. Each loop contains a dimple which contacts an ear of the ferrule. The central leg portion has a dimple, or a projection, which contacts a fuel rod and biases the fuel rod against stops. The spring load is transmitted to the ferrule ears by the dimples in the spring loops. Preferably, the spring rotates about the dimple when flexed, contributing to spring flexibility. The high spring flexibility permits use of the spring in connection with small rod-to-rod spacing fuel assemblies. This construction permits providing a low-mass, low-surface area spring, in turn providing for low neutron absorption and low flow obstruction.

Abstract: A grid key and method for keying exterior grid cells in a nuclear fuel assembly. The grid key has a main body portion having first and second ends and is bent at approximately a 45 degree angle near the first end. Two tabs extend outward from the first end at a right angle to the main body portion to define a T-shape. The T-shape end is inserted into the window of the exterior grid strip such that the top of the T-shape is parallel to the longitudinal axis of the grid assembly. The main body portion is then rotated 90 degrees to position the top of the T-shaped end to be perpendicular to the longitudinal axis of the grid assembly and behind the exterior grid strip. The main body portion is then pulled away from the exterior grid strip in a vertical rotating motion, causing the top of the T-shaped end to pull the exterior grid strip away from the center of the cell defined by the grid assembly.

Abstract: An improved spacer and method of making a spacer is disclosed for use in a nuclear fuel bundle wherein a plurality of fuel rods enclosed within a channel are maintained in parallel side-by-side relation by a plurality of the spacers. Each spacer is placed within the fuel bundle at selected elevations between upper and lower tie plates. The improved spacer is a member of the class of spacers wherein solid strips of material are welded at interstitially placed tube members between the fuel rods to form the continuous spacer grid. The improvement constitutes forming separate upper and lower reduced section grids from separate, normally aligned, first and second parallel sets of grid members. One grid is formed for the top of the spacer; the remaining grid is formed for the bottom of the spacer. Tube members placed interstitially between the fuel rods are used to interconnect the grids.

Abstract: A debris screen for a fuel assembly for a reactor to which coolant fluid is supplied comprises a substantially planar plate member having an array of coollant openings extending through the plate member dimensioned to trap at least a portion of debris particles carried by the coolant; and a skirt member enclosing the periphery of the plate member; each of the coolant flow openings having a coolant entry region at a lower surface, a coolant exit region at an upper surface and a coolant flow path extending between the entry and exit regions, the flow path including an intermediate segment laterally offset from the entry and exit regions to cause coolant to change direction of flow in the intermediate segment and thereby prevent at least a portion of the debris particles from passing through the plate members.

Abstract: A nuclear power plant has a water or liquid sodium coolant and a metallic component having surfaces coming into contact with the coolant. A coating is disposed on the surfaces of the metallic component, such as fuel rod cladding tubes or spacer grids. The coating is formed of titanium carbide (TiC), titanium nitride (TiN), zirconium nitride (ZrN), chromium carbide (CrC), titanium aluminum vanadium nitride (TiAlVN), tantalum nitride (TaN), zirconium carbide (ZrC), or tungsten carbide (WC).

Abstract: A nuclear fuel support grid 10' of egg-crate structure has wave defining strips 12a, 12b, 12c, 12d defined by bends 16' inclined from the vertical and opposing cantilevered springs 18' with inclined spring bases 20' opposing them for support of fuel rods 22 intermediate their ends. The "inclined waves" defined by inclined surfaces formed by bends 16' and spring bases 20' of cantilevered springs 18' provide lateral components to the coolant flow in patterns which enhance DNB and corrosion behavior.

Abstract: A zirconium alloy for use in spacer grids for nuclear reactor fuel claddings, which consists essentially of, on a weight percent basis,2.5 to 10% Nb,0.01 to 1.5% of one or more components selected from the group consisting of Y and rare earth elements and oxides thereof,0.05 to 1% of one or more optional element selected from the group consisting of Fe, Cr, Mo and V, andthe remainder Zr and incidental impurities.

Abstract: A nuclear fuel assembly support grid includes a multiplicity of spring structures for engaging fuel rods extending through the cells of the grid. Each spring structure is formed on each cell wall section to form a matrix of fuel rod receiving cells in the grid. Each spring structure is composed of a pair of spaced apart upper and lower opposite outer portions being integrally attached at their outer ends to the respective wall section, and a middle portion disposed between in laterally spaced relation from the outer portions and integrally connected at its outer ends with respective inner ends of the outer portions. The integrally-connected outer and middle portions are defined by a pair of generally U-shaped slots formed in a reverse interlocking relation to one another in the wall section of the one cell.

Abstract: The spacer-grid comprises at least one single-piece plate (1) through which extend a group of openings (2) at least a part of which constitutes an even network of passages (2) for the fuel rods and the guide tubes of the fuel assembly. The spacer-grid may be formed by one single-piece plate (1) of great thickness or by the association of a plurality of parallel single-piece plates interconnected by an outer girdle element.

Abstract: A nuclear fuel assembly grid includes a multiplicity of dimple and spring structures for engaging fuel rods extending through the cells of the grid. Each of the dimple and spring structures have a pair of outer portions and a middle portion with opposite lengthwise edges thereon. The edges of the middle portions of the dimple structures and the outer and middle portions of the spring structures have one-sided chamfers defined thereon, whereas the edges of the outer portions of the dimple structures have double-sided chamfers defined thereon. The one-sided chamfers are longer than the double-sided chamfers.

Abstract: A zirconium alloy sheet containing 2 to 3% of niobium is cooled at a controlled and moderate rate to the .alpha.+.beta. state. Plates (2, 2') are cut from the cooled sheet and cold-formed. The grid (1) is assembled from the plates (2, 2') which are welded together and the completed grid is then returned to the .alpha. phase by heating at a temperature of between 400.degree. and 550.degree. C. for a period of ten to thirty hours.

Abstract: An improved nuclear fuel assembly (10) of the type having a plurality of intersecting metal strips (14) welded at the strip intersections (32). At least some of the strips (16a, 18a) have nonlinear upper or lower edges (32a, 44a) at the intersections such that some of the intersection welds (34) at the strip upper or lower edges are at different elevations (34b) relative to intersection welds at other upper or lower edges (34a, 34c, 34d).

Abstract: An inproved grid (16) for a nuclear fuel assembly (10), having a plurality of externally projecting, integrally formed anti-bowing springs (50) spaced about the grid perimeter plate (26), for interacting with flat surfaces (52') on the opposite grids (16') of adjacent assemblies (10'). The anti-bowing springs (50) are horizontally separated along each grid (26) in periodic alternation with substantially flat portions (52) of the perimeter plate (26). Preferably, each grid has a plurality of primary anti-bowing springs (70) that project a distance at least equal to the nominal gap (g) between assemblies, and a plurality of secondary anti-bowing springs (72) that are stiffer but project less than the primary springs. Also, backup springs (74) are disclosed as integrally formed ridges adjacent to the anti-bowing springs. The interaction of each grid (16) with its neighbor (16') "tightens" the core during power operation and provides an anti-bowing effect.

Abstract: A nuclear fuel assembly grid includes a multiplicity of spring structures for engaging fuel rods extending through the cells of the grid. Each spring structure is formed on each cell wall section to form a matrix of fuel rod receiving cells in the grid. Each spring structure is composed of a pair of spaced apart upper and lower opposite outer portions being integrally attached at their outer ends to the respective wall section, and a middle portion disposed between and integrally connected at its outer ends with respective inner ends of the upper and lower outer portions. The upper and lower outer portions extend in alignment with one another and in generally diagonal relation to the direction of the central longitudinal axis of the one cell between upper and lower portions of the wall section. The middle portion which contacts the fuel rod extends in generally transverse relation to the direction of the central longitudinal axis of the one cell.

Abstract: A nuclear fuel assembly grid comprising an improved outer grid strap wherein abutting outer grid strap segments are joined at a point of intersection with an inner grid strap. The normally preformed weld where the inner strap fork tines extend through the outer grid strap thereby fixedly bonds the outer grid strap segments together.

Abstract: Disclosed is a fuel assembly comprises a plurality of cylindrical fuel rods with a plurality of fuel pellets sealed therein, a plurality of small units each having a predetermined number of the fuel rods bundled spaced with a fixed intercentral distance and being arranged in such a manner that the intercentral distance between the component fuel rods falling on the mutually juxtaposed sides of the adjacent small units is larger than the intercentral distance between the adjacent fuel rods in the small units, and at least one water rod near the center of a cluster of the plurality of the small units.

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 fuel assembly for nuclear reactors comprising a skeleton having two end pieces connected together by elongate elements and several grids spaced apart along the guide tubes and forming cells for holding a bundle of fuel elements in position at the nodes of a regular lattice. The grids comprise median grids adapted for resisting lateral shocks and having fins for creating turbulences in the flow of the coolant along the assembly, bottom grids without fins and ensuring the cross bracing of the elements and top grids with fins and ensuring cross bracing of the elements, the top and bottom grids imposing on the coolant a pressure loss lower than the median grids.

Abstract: A channel box and/or a spacer of a fuel assembly is a welded construction and made of a Zr-Nb-Sn alloy comprising 0.5-2.2 wt % Nb, 0.5-1.5 wt % Sn contained so as to satisfy the relation of Sn(wt %) 22.times.Nb(wt %)--3.0, and balance Zr or a Zr-Nb-Sn-Mo alloy comprising 0.5-2.2 wt % Nb, 0.5-1.5 wt % Sn contained so as to satisfy the relation of Sn(wt %).gtoreq.2.times.Nb(wt %)--0.3, 0.1-0.8 wt % Mo, and balance Zr. The welded portion, its heat affected zone and the unwelded portion of the channel box and/or the spacer have substantially the whole equilibrium phase structure.