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 debris catching strainer grid for capturing and retaining deleterious debris carried by reactor coolant before it enters the active region of a fuel assembly and creates fuel rod cladding damage has a plurality of fuel end cap compartments defined by pairs of first and second intersecting and slottedly interlocked grid-forming strips attached to a perimeter member and to each other. The end cap compartments defined by strips including vertical rows of integral leaves on opposite sides of the strip or by pairs of adjacent integral leaves intermediate their intersections. In the latter case, each leaf of the pair of leaves is the mirror image of the other leaf of the pair with an asymmetric shape with the greatest distance of projection out of the plane of the strip remote from the midpoint of the strips between their intersections.

Abstract: The present invention is directed to a method for increasing the wear and corrosion resistance of zirconium and zirconium alloys by ion implantation. In particular the present invention is directed to the ion implantation of nitrogen and/or carbon for the purpose of increasing wear resistance; and the ion implantation of arsenic, carbon, chromium, nitrogen, tin, phosphorus or combinations thereof for the purpose of increasing the corrosion resistance.

Abstract: A neutron streaming shield comprising a plurality of wire mesh baskets, each basket located between two adjacent vessel nozzles, the total area of the nozzles and baskets being sufficient to intercept any streaming neutrons. The baskets are substantially filled with a multiplicity of randomly packed lumps of a neutron attenuating material, preferably a borated-hydrogenated-argillaceous media. Since the basket is somewhat flexible, it can be inserted in the annulus above the nozzles and then filled with the lumped material, forming a plurality of barriers to compliment the attenuating affect of the nozzles, such that any streaming neutrons will be stopped either by the nozzles or the lumped material in the baskets.

Abstract: Repaired fluid conveying tubes are tested for leaks by isolating the repaired region from the remainder of the tube and then pressurizing the isolated region with a suitable gas. The isolation is accomplished by axial compression of one or a pair of seals which expand radially when subjected to axial force.

Abstract: Nuclear fuel assemblies having square cross-sections mount tubes at each corner, the tubes containing springs which are extended through apertures in the tube walls when actuated by solid rods extended down into the tubes by the weight of the upper guide structure of the nuclear vessel in which the fuel assemblies are mounted. The springs, extended from strategically located positions along the length of the tubes, engage the surface of adjacent fuel assemblies to dimensionally stabilize the fuel assemblies relative to each other and the vessel in which they are mounted.

Abstract: A method for testing the clad integrity of a nuclear fuel rod, comprising the first step of fabricating a sealed fuel rod with a wad of electrically conducting material mounted therein. The material is of a type that undergoes a permanent change in electrical conductivity when exposed to water. The next step is to establish an eddy current signal characteristic of the moisture-free rod. The rod is then loaded into the core as part of a fuel assembly. After the producing power, the assembly is removed for inspection, and an eddy current signal is again obtained from the rod. The eddy current signals are compared to determine whether inleakage of moisture has oxidized or otherwise altered the conductivity of the wad enough to significantly change the characteristic signal.

Abstract: An improved nuclear fuel assembly in which the lowermost grid is located close to the lower end fitting of the assembly, and a conventional Zircaloy-clad fuel rod is fitted with a stainless steel tip having a bevelled notch thereon for engaging resilient means on the grid within about one inch (2.5 cm) from the lower tip of the fuel rod. The notch mechanically restrains the fuel rod from lifting upwards during reactor operation, yet is shallow enough to permit removal of the fuel rod in the event reconstitution is required. The stainless steel tip is mechanically secured to the Zircaloy end cap of the fuel rod, and is located in a low importance flux region of the core so that the higher neutron poison absorption cross section of stainless steel is of little consequence. Since the lowermost grid secures each fuel rod within one inch of the lower end of the rod, there is little likelihood that the coolant flowing over the lower ends of the fuel rods will induce significant vibrations.

Abstract: A reconstitutable nuclear fuel assembly is improved by the placement of a wear sleeve within the control rod guide tube and below the removable guide tube post. The improvement comprises the guide tube having an internal ledge at its upper end from which a flanged, thin-walled metal cylindrical sleeve is suspended. The cylinder is expanded into firm contact with the inner wall of the guide tube over substantially the entire length of the cylinder. The friction fit provided by the firm contact prevents the sleeve from being pushed upward by the flow of coolant through the tube, while the flange and ledge prevent any downward movement of the sleeve in the tube. The flange on the ledge is located in spaced vertical alignment with the lowermost internal portion of the post. Thus, as the sleeve thermally expands it moves upward into the space.

Abstract: A fuel assembly having a lower end fitting and a spidered actuating rod interacting therewith for holding the assembly down on the core support stand against the upward flow of coolant. Locking means and bracing means for interacting with projections on the support stand are carried by the lower end fitting and are actuated by the movement of the actuating rod operated from above the top of the assembly. The locking means include weak springs mounted near some but not all of the end fitting posts, for engaging the support stand. Stiff springs are mounted internal to the other posts, for uring the posts against adjacent support stand projections to provide a bracing for the locking means as the spider portion of the actuating rod presses against the locking spring. The angle and spring rate per unit length of the bracing spring are preset to assure a fairly constant locking force during the life of the assembly.

Abstract: A fuel assembly having a lower end fitting and actuating means interacting therewith for holding the assembly down on the core support stand against the upward flow of coolant. Locking means for interacting with projections on the support stand are carried by the lower end fitting and are actuated by the movement of an actuating rod operated from above the top of the assembly. In one embodiment of the invention the downward movement of the actuating rod forces a latched spring to move outward into locking engagement with a shoulder on the support stand projections. In another embodiment, the actuating rod is rotated to effect the locking between the end fitting and the projection.

Abstract: A bimetallic spacer means designed to be cooperatively associated with a nuclear fuel assembly and operative to resist the occurrence of in-reactor bowing of the nuclear fuel assembly. The subject bimetallic spacer means in accord with one embodiment of the invention includes a member formed, at least principally, of zircaloy to which are attached a plurality of stainless steel strips. The latter stainless steel strips are located on the external surface of the zircaloy member and with the major axis of each of the plurality of stainless steel strips extending substantially perpendicular to the major axis of the zircaloy member.

Abstract: An earthquake resistant apparatus for storing nuclear fuel within a water-filled pool wherein a structural grid which supports the fuel is in turn supported by cables from an upper elevation. The grid is located below the water level and spaced from the walls of the pool an amount, preferably at least equal to the anticipated earthquake displacement. The grid is located below the water level a sufficient depth for radiation shielding during fuel handling and storage, and tension members are preferably ten times the design earthquake displacement. A horizontal baffle is located around the periphery of the pool at an elevation above the grid.

Abstract: A wear sleeve for a guide tube in a nuclear fuel assembly, and a method of installing the sleeve. The sleeve is an elongated metal cylinder having an upper portion adapted to be suspended from the upper end of the guide tube, and a lower portion adapted to be permanently deformed into interference fit with the walls of the guide tube whereby the sleeve may be secured against vertical movement. The method of installing the sleeve includes the steps of suspending the sleeve from the upper end of the guide tube, then expanding a selected lower surface of the sleeve until the sleeve is permanently deformed, whereby an interference fit between the sleeve and tube is formed.

Abstract: An alignment system is provided for nuclear fuel assemblies in a nuclear core. The core support structure of the nuclear reactor includes upwardly pointing alignment pins arranged in a square grid and engage peripheral depressions formed in the lateral periphery of the lower ends of each of the fuel assemblies of the core. In a preferred embodiment, the depressions are located at the corners of the fuel assemblies so that each depression includes one-quarter of a cylindrical void. Accordingly, each fuel assembly is positioned and aligned by one-quarter of four separate alignment pins which engage the fuel assemblies at their lower exterior corners.

Abstract: A nuclear reactor control rod containing a stack of B.sub.4 C absorber pellets in which the pellets in the lower end have a radius smaller than that of the other pellets and are wrapped with a sleeve having a linear compressibility sufficient to accommodate exposure-induced radial expansion of the end pellets without producing excessive clad strain and having a thermal conductivity sufficient to keep the centerline temperature of the end pellets below the melting point of B.sub.4 C. One such sleeve material is a type 347 stainless steel having 22.5% theoretical density.

Abstract: A fuel assembly for a nuclear reactor wherein the fuel element receiving and supporting grid is comprised of a first metal, the guide tubes which pass through the grid assembly are comprised of a second metal and the grid is supported on the guide tubes by means of expanded sleeves located intermediate the grid and guide tubes. The fuel assembly is fabricated by inserting the sleeves, of initial outer diameter commensurate with the guide tube outer diameters, through the holes in the grid assembly provided for the guide tubes and thereafter expanding the sleeves radially outwardly along their entire length such that the guide tubes can subsequently be passed through the sleeves. The step of radial expansion, as a result of windows provided in the sleeves having dimensions commensurate with the geometry of the grid, mechanically captures the grid and simultaneously preloads the sleeve against the grid whereby relative motion between the grid and guide tube will be precluded.

Abstract: An alignment system is provided for nuclear fuel assemblies in a nuclear core. The core support structure of the nuclear reactor includes upwardly pointing alignment pins arranged in a square grid and engage peripheral depressions formed in the lateral periphery of the lower ends of each of the fuel assemblies of the core. In a preferred embodiment, the depressions are located at the corners of the fuel assemblies so that each depression includes one-quarter of a cylindrical void. Accordingly, each fuel assembly is positioned and aligned by one-quarter of four separate alignment pins which engage the fuel assemblies at their lower exterior corners.

Abstract: .Iadd.A nuclear reactor with control rods in channels between fuel assemblies wherein the fuel assemblies incorporate guide rods which protrude outwardly into the control rod channels to prevent the control rods from engaging the fuel elements. The guide rods also extend back into the fuel assembly such that they are relatively rigid members. The guide rods are tied to the fuel assembly end or support plates and serve as structural members which are supported independently of the fuel element. Fuel element spacing and support means may be attached to the guide rods..Iaddend.