Abstract: A marked reduction in the pressure drop of cooling liquid through a grid spacer of a nuclear fuel assembly is attained by convexly contouring the upstream (usually the lower) edges of the grid members. Preferably, they are made streamlined or semicylindrical. This can be done by first beveling and then etching them, by directing a stream of mixture of abrasive and an organic polymer against them, or by traversing an electron or laser beam along them at a power and velocity such as to cause local melting. A lesser improvement is secured by beveling alone. A still further improvement can be obtained by also tapering the downstream (usually upper) edges.

Abstract: In a BWR fuel assembly, fuel rod spacers are disposed in desired axial positions along the fuel rods by a plurality of yieldably-resilient arcuate-shaped leaf springs. Some of the springs are disposed between an interior side of the fuel assembly outer channel and exterior sides of the spacers, whereas others are disposed between an exterior side of a central water cross and the exterior sides of the spacers. The springs thus contact the spacers and either the channel or water cross and exert sufficient contacting force thereon to maintain the spacers substantially stationary in the desired axial positions along the fuel rods. The springs extend generally parallel to the axial direction of the fuel rods and are spaced apart from one another in a direction generally transverse to such fuel rod axial direction. Each spring can be fixedly attached at one end to the spacer or clipped on an edge of the spacer.

Abstract: A nuclear reactor fuel assembly for accommodating mutually parallel rods disposed side by side therein includes a spacer formed of two mutually parallel grid sections having sides, each of the grid sections including outer straps flatly facing the rods at which the grid sections are interconnected, each of the grid sections including main sleeves being positioned like positions of the same color in rows and columns disposed at right angles to each other on a chess board leaving a free intermediate position between each two occupied positions, the main sleeves dividing the grid sections into grid mesh openings at the positions each able to receive a respective rod therein, each main sleeve in one of the grid sections having edges and being aligned with a main sleeve in the other grid section forming pairs of main sleeves, connecting straps each interconnecting the main sleeves of a pair of main sleeves forming contact springs for rods, each of the connecting straps having a width being smaller than the circumf

Abstract: A grid for supporting and spacing nuclear fuel rods, particularly at the nodes of a triangular array, has a peripheral frame of regular polygonal, typically hexagonal, shape and at least two beds of wires spaced in the longitudinal direction of the fuel assembly. Each bed has at least two series of mutually parallel wires secured to said frame at the end thereof, the wires of a same one of said series being parallel to two opposed side of said frame and all said wires defining passages for said fuel elements.

Abstract: In a nuclear reactor fuel element for receiving mutually parallel rods, the improvement includes a rectangular grid-shaped spacer including planar webs crossing and facing the rods defining grid mesh openings receiving the rods, the webs including two outer webs forming an outer corner of the spacer and defining a corner grid mesh opening at the outer corner, the outer corner having an outward curve being curved in a direction parallel to the longitudinal direction of the rods, the outer webs having edges at the curve transverse to the rods being drawn inward toward the rods in the corner grid mesh opening forming a bevel in longitudinal direction of the rod.

Abstract: A double lock joint structure is used in a reconstitutable fuel assembly for attaching the adapter plate of the assembly top nozzle in releasable locking engagement upon the upper end portions of the assembly guide thimbles. The joint structure includes axially extending slots defined in each guide thimble upper end portion permitting inward elastic collapse thereof to a compressed position and outward elastic return thereof to an expanded position. The joint structure also includes axially spaced upper and lower annular bulges formed in the upper end portion. The upper annular bulge has an outside diametric size greater than the inside diametric size of the adapter plate passageway when the guide thimble upper end portion is at its expanded position and less than the inside diametric size of the adapter plate passageway when the upper end portion is collapsed to its compressed position allowing insertion and withdrawal of the upper end portion into and from the adapter plate passageway.

Abstract: The invention relates to a spacer arranged to retain and fix elongated fuel rods into bundles insertable into a nuclear reactor fuel assembly, said spacer being of a zirconium alloy having a low neutron absorption. To counteract play and hence wear in case of increasing burnup when the springs relax and the rod diameter is reduced by shrinkage, the spacer is made with different textures in the springs (2, 3) and the surrounding structure (1, 6). The difference in texture gives the springs a great axial irradiation growth and the surrounding structure a small axial irradiation growth, which contributes to a remaining deflection tendency of the springs in relation to the surrounding structure during the life of the fuel assembly.

Abstract: Vertical and axial movement of fuel rods relative to grid spacers in a fuel bundle of a BWR or PWR nuclear reactor is prevented by use of sleeves welded to various vertical positions upon a fuel rod, whereby the sleeves have horizontally and vertically oriented windows and slots for engaging protrusions and corner springs, respectively, located in the openings for receiving fuel rods of the grid spacers.

Abstract: A fuel assembly has a fuel spacer consisting of a water rod having an outer diameter greater than that of fuel rods and a large number of circular sleeves into which the fuel rods are inserted. The fuel spacer has four bridge members. Both ends of these bridge members are fitted to two of eight circular sleeves which are adjacent one another in the diagonal direction of the fuel spacer. Both ends of each bridge member are bent so that its center projects outwardly away from the water rod.

Abstract: A fuel assembly has a plurality of elongated fuel rods, a plurality of grid structures axially spaced from one another along the fuel rods between opposite ends thereof and supporting the fuel rods in a side-by-side spaced array, and a pair of tie plates disposed at the respective opposite ends of the fuel rods. Each of the fuel rods has a pair of end plugs sealing opposite ends thereof, with at least the end plug at one of the opposite ends of each fuel rod having an extension member thereon which extends axially outward from the end plug and is of a diameter less than that of the fuel rod. At least one of the tie plates has a plurality of holes defined by endless sidewalls formed therethrough between opposite sides of the tie plate and in an array which matches that of the fuel rods.

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 nuclear reactor fuel assembly having a grid-shaped spacer for retaining fuel rods, the spacer includes four flat, sheet metal outer straps disposed on edge at right angles to the fuel rods defining corners of the spacer, inner sheet metal straps disposed within the outer sheet metal straps, the inner straps include two given inner straps each being transverse to one of two respective given outer straps at a corner of the spacer dividing the spacer into meshes for fuel rods including a corner mesh at a corner of the spacer and two other meshes laterally adjacent the corner mesh, a contact spring for a fuel rod disposed in the corner mesh, the contact spring having two end parts each being locked in a respective recess formed in one of the given inner straps locking the contact spring to one of the given outer straps, the recesses starting from an end edge of the one given inner strap parallel to the fuel rods, two extended arms in the corner mesh each being integral with a respective one of the end parts and

Abstract: A nuclear fuel assembly comprises two end pieces connected by guide tubes. Grids are distributed along the guide tubes and define passages distributed according to a regular pattern. Some of the passages receive the tubes. Other passages retain fuel elements parallel to the tubes. Individual sleeves containing a burnable poison are carried by the tubes, each in a space bounded by one grid on one side, by an other grid or an end piece on the other side. The length of the sleeves is selected for allowing differential thermal expansion of the tubes and grids. One end of each sleeve may be secured to lugs of an associated grid.

Abstract: The present invention relates to a method and to an apparatus for producing nuclear reactor structures, such as spacing grids, by pulse laser welding.The grid is placed in a tight enclosure and having thin plates, which intersect one another, so as to define a certain number of crosspieces. By means of a laser source positioned externally of the enclosure, each of the ends of the crosspieces is fixed and optionally the crosspieces are welded along the intersections of the plates.Application to the construction of zirconium alloy spacing grids.

Abstract: A plurality of independent cells having a regular octagonal or circular cross section are arranged in the form of a lattice. Cross-sectionally square independent cells are substituted for two octagonal or circular cells in the central portion of the lattice arrangement. These two square independent cells are so formed that each side of the cells has the largest possible length when the cells are placed among the adjacent cells having a regular octagonal or circular cross section. Spacer support rods serving also as water rods are inserted into the square cells in such a fuel spacer, which consists of a combination of cells having a regular octagonal or circular cross section and cells having a square cross section as mentioned above, to form a fuel assembly.

Abstract: A nuclear reactor fuel assembly spacer grid having grid straps and a first type of spring clip. The grid straps define standard cells enclosing fuel rods and thimble cells enclosing control rod guide thimbles. The spring clip is bent to widthwise encircle a grid strap and has its two ends welded together. The first type of spring clip is used at a location on a grid strap having a standard cell and an adjacent thimble cell. The spring clip has a spring portion compressibly contacting the fuel rod in the standard cell. The spring clip also has a pair of separated flat portions straddling the control rod guide thimble in the thimble cell so as not to interfere with the guide thimble. The spring clip is made of a material having good radiation stress relaxation properties.

Abstract: Spacer for centering fuel rods of fuel assemblies in water-cooled nuclear reactors, including a grid of sheet metal webs formed of a zirconium alloy and being disposed on edge, rigid bumps formed from at least some of the webs for contacting a fuel rod, at least some of the webs having relatively wide cutouts and relatively narrow lateral slots formed therein, and resilient contact elements formed of chrome nickel steel and having a head part, a base part, a resilient band connecting the head and base parts together into one piece and a bent-out point formed on the resilient band for contacting a fuel rod, the head and base parts of the contact element being insertable into the cutouts and movable into a locked position in the lateral slots formed in the webs.

Abstract: In a fuel assembly for a nuclear reactor a fuel element spacer formed of an array of laterally positioned cojoined tubular ferrules each providing a passage for one of the fuel elements, the elements being laterally supported in the ferrules between laterally oriented spring members and oppositely positioned rigid stops, the wall thickness of the ferrules being relatively large and the height of the ferrules being relatively small to reduce hydride concentration in the ferrule material while maintaining relatively low flow resistance.

Abstract: In a nuclear fuel assembly spacer providing passages for fuel rods or other elongated elements, a spring component of H-shape including a pair of spaced spring members of hairpin-like configuration connected by a retaining strap wherein an arched side of one of the spring members projects into one of the passages and the arched side of the other of the spring members projects into an adjacent one of the passages for resilient engagement with the fuel rods or other elongated elements extending through the passages.

Abstract: A spacer for use in a fuel assembly of a nuclear reactor having thin, full-height divider members, slender spring members and laterally oriented rigid stops and wherein the total amount of spacer material, the amount of high neutron cross section material, the projected area of the spacer structure and changes in cross section area of the spacer structure are minimized whereby neutron absorption by the spacer and coolant flow resistance through the spacer are minimized.

Abstract: In a fuel assembly for a nuclear reactor a fuel element spacer formed of an array of laterally positioned cojoined tubular ferrules each providing a passage for one of the fuel elements, the elements being laterally supported in the ferrules between slender spring members and laterally oriented rigid stops.

Abstract: A nuclear reactor fuel assembly spacer grid. The grid straps form an egg crate configuration creating standard cells to enclose the fuel rods. The standard cells have at least one of their straps with an integral spring portion extending into the standard cell and pushing against the fuel rod. A distinct backup spring is positioned transverse to and behind each of the spring portions of the straps and is positioned so as not to touch the fuel rods. The straps are made of a material having a low neutron capture cross-section while the backup spring is made of a material having good radiation stress relaxation properties.

Abstract: The present invention relates to a spacer grating for fuel element in a nuclear reactor of the PWR type, said grating being constituted by intersecting plates. Over the greater part of the walls equipped with springs, double springs comprise two active parts on either side of the wall on which the double spring is placed, allowing the symmetrical action of this spring on two different pencils inside two adjacent cells. On the other walls equipped with springs, single springs comprise one active part only, disposed in one of the two cells separated by the wall on which is placed the spring of which the other part is not capable of coming into contact with a fuel pencil. The invention is particularly applicable to the manufacture of fuel assemblies in nuclear reactors of the PWR type.

Abstract: The present invention relates to a device for fixing a spring to a spacing grid for fuel elements of nuclear reactors.This device is characterized in that it is constituted by two retaining bridges (8) for the spring (6) made in one of the thin metal sheets constituting the grid and maintaining the spring (6) against said sheet. Two other bridges (10) located outside the bridges (8) constitute abutments for stopping the translation of the spring (6). A double stamping (12) made in the thin metal sheet at the approaches of each retaining bridge (8) constitute a precise translation guide for the spring (6).Application to the spacing grids of fuel elements of nuclear reactors.

Abstract: Advantage is taken of the non-uniform axial neutron flux density distribution in a nuclear reactor core by using fuel rod spacers of low neutron absorption in high neutron flux density regions and fuel rod spacers of low coolant flow resistance in the lower neutron flux density regions of the core, this spacer combination also providing higher fuel bundle thermal limits.

Abstract: A spacer grid for fuel assemblies in a water reactor is provided. The grid shell is shaped so that a pressing in Zircaloy can be made. Cross members in a lattice in the shell provide spacing for the fuel pins of the fuel assembly. Each fuel pin has its own cell in the lattice, and at least some of the joints between the members comprise two attachment points spaced along one of the members at a single intersection.

Abstract: A fuel assembly for a nuclear reactor including a plurality of fuel rods held in spaced, parallel position between upper and lower tie plates and retained in lateral position by intermediate spacers and having a water tube in lieu of a fuel element in one or more of the rod positions, the water tubes having an outside diameter greater than that of the fuel rods and the spacer springs in the spacer cells of the water tubes being modified to accommodate the larger diameter of the water tubes.

Abstract: A nuclear fuel assembly including a guide tube sleeve having tabs projecting outwardly from the sleeve to modify coolant flow.

Abstract: Spacer for fuel rods assembled into a fuel assembly for nuclear reactors formed of a grid structure of sheetmetal webs passing edgewise perpendicularly through one another including resilient and rigid contact elements fastened to the sheetmetal webs, each of the fuel rods being supportable by two diagonally opposing three-point contact systems, each of the systems being formed of one of the resilient contact elements and two of the rigid contact elements, the one resilient contact element being centrally disposed, as viewed in axial direction, and the two rigid contact elements being oppositely disposed and being ring-shaped.