Abstract: An improved grid for use in a fuel assembly of a nuclear reactor includes a plurality of straps that are interconnected with one another in a lattice fashion to define a plurality of cells, with the straps being configured to include a plurality of relatively more compliant springs and a plurality of relatively less compliant dimples, whereby each cell includes only one pair of springs and one pair of dimples disposed therein. The springs and dimples are contoured to engage a fuel rod or a thimble tube disposed within the cell. Each spring directly confronts one of the dimples to provide confronting pairs of features that engage the fuel rods or thimble tubes, with each cell including two pairs of confronting features. The ligaments of the springs and dimples extend in a direction generally perpendicular to the direction of coolant flow through the reactor in order to minimize pressure drop.

Abstract: An improved grid for use in a fuel assembly of a nuclear reactor includes a plurality of straps that are interconnected with one another in a lattice fashion to define a plurality of cells, with the straps being configured to include a plurality of relatively more compliant springs and a plurality of relatively less compliant dimples, whereby each cell includes only one pair of springs and one pair of dimples disposed therein. The springs and dimples are contoured to engage a fuel rod or a thimble tube disposed within the cell. Each spring directly confronts one of the dimples to provide confronting pairs of features that engage the fuel rods or thimble tubes, with each cell including two pairs of confronting features. The ligaments of the springs and dimples extend in a direction generally perpendicular to the direction of coolant flow through the reactor in order to minimize pressure drop.

Abstract: A system for performing laser welding comprises an optical lens for receiving an incoming laser beam and for dividing the laser beam into a number of different beam segments. The top surface is defined by a number of different surfaces for respectively dividing the laser beam into the number of beam segments. The optical lens has a convex bottom surface for focusing and directing the beam segments onto a respective number of welding locations. Preferably, the laser welding system is used to simultaneously perform five welds on an improved spacer grid assembly which has a cylindrical member located at each intersection of the spacer strips. By simultaneously performing the five requisite welds, the welding time is significantly reduced. Also, the welding process is simplified since the system only has to be in one position to perform all of the welds at each intersection.

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: A retainer is for retaining a grid on a fuel assembly. The retainer has at least one aperture at one end thereof for receiving a shoulder on a guide control tube and legs on the other end thereof for welding to the grid. The one end of the retainer is captured between the shoulder and a surface on the bottom nozzle of the fuel assembly when the guide tube is attached to the bottom nozzle. The retainer reduces the rotation of the guide tube resulting from torquing of the screws which connect the guide tube to the bottom nozzle thereby increasing the integrity of the 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 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: A fuel assembly has a spring detent spacer grid of intersecting strips for capturing and retaining deleterious debris carried by reactor coolant before it enters the active region of a fuel assembly. A plurality of fuel end caps are peripherally grooved to receive springs projecting from the strips. The end caps are thus captured by springs and debris is wedged and trapped on opposite sides of the strip and against the end caps by pairs of adjacent integral leaves projecting from the stips intermediate and substantially symmetrically arranged about their intersections.

Abstract: Integral vanes 4 with optimized size, shape and bend angles maximize coolant mixing and fuel rod 12 heat transfer downstream. Recessed weld nuggets 5 with no vane cutout are optimized for size, strength and corrosion resistance. Staggered arches 20',22' and springs 20,22 minimize turbulence and reduce grid pressure drop and promote coolant mixing. Crowned arches 20',22' and springs 20,22 decrease scoring of fuel rods 12 and are sized to minimize turbulence and pressure drop. Minimum cutouts in unslotted section of grid strip 46,46' give 15-20% strength increase. Intermediate weld and tapered end slots 48 give 15% strength increase. Ribbed and round dimple stiffeners 38,39 on outer strips increase buckling resistance, reduce handling damage and spreads accidental loading. Outer strips 32 are optimized for strength, handling, turbulence generation and pressure drop. They also divert enough flow to interior of fuel assembly to match thermal power distribution and eliminate fuel rod corrosion concerns.

Abstract: A solid or hollow replacement rod 40 for use in a pressurized water reactor (PWR) fuel assembly 10 inserts into cells of the spacer grids 18, 20 and 22 past mixing vanes 32, without damaging them, because of its asymmetric tip 42 formed by chamfer 54 and elongated curved surface 52 and its offset "x" formed by the bowed end section 44.

Abstract: A fuel element support grid for supporting a plurality of nuclear fuel elements intermediate their ends has at least some of the pairs of intersecting and slottedly interlocked strips including pairs of intersecting integral fluid flow directing vanes along at least one adjacent edge of each of the strips of the pair. Welds attach the pair of vanes to each other thereby providing welded attachment of the strips. The welds may be at the intersection of the vanes remote from their areas of integral attachment to their respective strips or they may be adjacent to their areas of integral attachment to their respective strips. The strips may be bent to provide the strip function and the arch function within the same stream engaging profile as the strip alone presents.

Abstract: An upper end fitting 14 of a nuclear fuel assembly is provided at two of its opposite corners with spring retention caps 12 having a hook-like structrue defined by an inwardly directed flange 50 engaging a slot 56 in the top nozzle or end fitting 14. The spring packs 20 are retained within the spring retention caps 12 even if one or both spring retention screws 34 break and both the broken screw portions and the springs are maintained in operative position by the cap 12 until reconstitution.

Abstract: A fuel element support grid for supporting a plurality of nuclear fuel elements intermediate their ends has at least some of the pairs of intersecting and slottedly interlocked strips including pairs of intersecting integral fluid flow directing vanes along at least one adjacent edge of each of the strips of the pair. Welds attach the pair of vanes to each other thereby providing welded attachment of the strips. The welds may be at the intersection of the vanes remote from their areas of integral attachment to their respective strips or they may be adjacent to their areas of integral attachment to their respective strips.