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 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: In a fuel bundle assembly (B) for a nuclear reactor wherein a plurality of fuel rods (R) and at least one water rod (W) extend between an upper tie plate and a lower tie plate, an improvement includes a fixed connection between the water rod (W) and the lower tie plate (L), the fixed connection including a threaded lower end plug of the water rod and a threaded hole in a boss formed in the lower tie plate adapted to receive the threaded lower end plug, the threaded lower end plug (50) formed with a diametrical slot (54) therein and the boss (56) formed with a pair of slots (60, 62) extending from opposite sides of the hole such that the diametrical slot (54) and the pair of slots (60, 62) are alignable when the threaded lower end plug (50) is threaded into the boss (56); and a key (64) insertable within the aligned slots to thereby fix the water rod against rotational movement.

Abstract: The lower tie plate grid includes cylindrical bosses and webs interconnecting the bosses for supporting nuclear fuel rods and defining flow channels through the grid for flowing coolant upwardly about the fuel rods. The grid includes shaped body members having flow openings, the members being disposed in each of the flow channels. In one form, the members define with the side walls of the bosses and webs a debris retention zone. In another form, sets of generally parallel, laterally spaced bars are disposed at discrete elevations in the flow channels. The bars are orthogonally related to one another whereby the effective debris catching area is defined by the openings through the crossed bars in plan, while the coolant flow area comprises essentially the space between each set of bars.

Abstract: An improved method for assembling bundles of nuclear fuel rods which reduces damage to the fuel cladding surface as the fuel rods are passed through an array of spacers. In particular, the invention prevents or greatly reduces the severity of longitudinal scratches on the fuel rods. The method uses thin-walled metallic tubes having a wall thickness of 0.003 to 0.006 inch and a yield strength in excess of 140,000 psi. The predetermined tube thickness ensures that the tube remains elastic. The tube deflects the cell springs when inserted in the spacer cells and reduces the load exerted on the fuel rods.

Abstract: A fuel bundle and lower tie plate assembly for a nuclear reactor includes a plurality of fuel rods supported between an upper tie plate and a lower tie plate assembly. The lower tie plate assembly includes an upper grid portion and a lower body portion, the upper grid portion having a plurality of fuel rod supporting bosses interconnected by a plurality of webs thus forming flow openings between the bosses. The body portion includes an inlet nozzle and a peripheral wall extending between the bottom nozzle and the upper grid portion to define a flow volume therein. A debris catcher is located within the flow volume and includes a pair of superposed plates, the plates each having a plurality of holes of substantially the same size, shape and pitch, but wherein the holes of one of the pair of plates are offset from the holes of the other of the pair of plates by one half the hole pitch.

Abstract: A spacer for use with a fuel bundle in a nuclear reactor includes a matrix of ferrules for surrounding individual fuel rods within a bundle; a band surrounding the matrix and defining a peripheral wall of the spacer, the band having an upper edge; and a plurality of laterally spaced flow tabs extending upwardly from the upper edge, each flow tab having a lower substantially vertical portion and an upper inclined portion extending away from the vertical portion. The vertical portion and the inclined portion are formed with centrally located creases which define reverse bends in the upper and lower portions of the tab.

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 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 divergent side walls downstream of a throat area to define a flow venturi.

Abstract: Spring assemblies are employed in adjoining ferrules of a spacer in a nuclear fuel bundle to bias the fuel rods against stops and hence position the fuel rods in the spacer. The spring assemblies in one form include back-to-back spring bodies having central leaves with forward projections extending through rectilinear openings in adjacent ferrules to engage fuel rods to bias the rods against stops at the opposite sides of the ferrules. Outer pairs of leaves straddle the central leaf and project rearwardly and join the spring bodies one with the other whereby the central leaves, end portions of the springs connected to the central and outer leaves, and the outer leaves act as paired springs in series, providing a low spring constant. In another form, a single spring body has a central leaf with a projection extending through an aperture of a ferrule to bias the fuel rod. The outer leaves bear against the outer surface of the adjoining ferrule.

Abstract: In a boiling water reactor fuel bundle, a three dimensional debris catching grid construction is placed within the flow volume defined by the lower tie plate assembly between the inlet nozzle and upper fuel rod supporting grid. A perforated plate is utilized having round holes as small consistent with the prevention of inadvertent closure due crudding and a hole pitch consistent with mechanical integrity requirements. The perforated plate is placed in a three dimensional construction such as a dome, cylinder, pyramid, inverted pyramid or corrugated construction spanning the flow volume of the lower tie plate assembly. As a consequence of this three dimensional grid construction, the total flow through area of the perforations in the metal plate does not introduce appreciable pressure drop in the lower tie plate assembly between the inlet nozzle and the rod supporting grid.

Abstract: A fuel bundle assembly for a nuclear reactor, wherein a plurality of fuel rods and at least one water rod extend between an upper tie plate and a lower tie plate, includes upper end plugs secured to a pair of water rods and having axial cut-out portions defined by upper and lower shoulders. A latching mechanism for securing the pair of water rods to the upper tie plate includes a latch bar mounted on an upper surface of the upper tie plate and rotatable into and out of the cut-out portions in the end plugs when the end plugs extend above the upper surface of the tie plate upon installation of the upper tie plate on the fuel bundle assembly. A locking pin is provided which prevents the latch bar from being accidentally unlocked.

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: Leaf-type springs are inserted into slots in an upper tie plate of a nuclear fuel assembly and bear against interior surfaces of the fuel channel to center the upper tie plate within the fuel channel. More robust similarly configured leaf springs are secured in slots in the upper tie plate and are cantilevered for bearing engagement through slots in the fuel assembly channel against the reactor top guide to bias the fuel assemblies toward the control rod. To mount each spring to the upper tie plate, the base of each leaf spring includes a central beam and a pair of outermost beams spaced from the central beam, all beams lying in a common plane. Laterally outwardly directed tabs are provided on the lower ends of the outer beams. Stops are provided intermediate the ends of the outer beams. By inserting the unstressed, unloaded base of the springs into the slots, the outer beams are displaced inwardly into a stressed condition.

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 arranged in square matrices for receiving the lower end plugs of the fuel rods. Web portions 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 lower flow openings into the flow spaces for further flow upwardly about the fuel rods. The openings are defined by the convex lower portions of the bosses and webs, as well as projections which extend laterally inwardly from the convex surfaces of the lower boss portions toward a central region in the middle of the square matrix.

Abstract: A two part lower tie plate assembly is disclosed for use with a fuel bundle of a boiling water nuclear reactor. The two parts include a rod supporting grid section and nozzle section. Both the rod supporting grid section and the nozzle section are constructed asymmetrically. The rod supporting grid section contains one half of the total offset required for a D lattice lower tie plate and the nozzle section contains one half of the total offset required for a D lattice lower tie plate. When a D lattice lower tie plate is required, assembly occurs so that the offsets are additive. When a C lattice lower tie plate is required, assembly occurs that the offsets are subtractive. Assembly of the lower tie plate is provided be either bolting or welding. There results on single rod supporting grid and nozzle section components capable of assembly to fit either a C or a D lattice.

Abstract: A debris catching arrangement is disclosed for incorporation within the flow plenum up stream or below the rod supporting grid of the lower tie plate assembly. The device is preferably placed within the lower tie plate flow plenum between the fuel bundle inlet orifice and the rod supporting grid structure supporting the fuel rods; alternate placement can include any inlet channel upstream of the fuel rods including the fuel support casting. The disclosed debris catching designs include successive side-by-side coil springs placed in layers across the tie plate plenum. Preferably, the respective tie plates are placed in alternating directions with a first layer of springs oriented at 90.degree. to an alternate and underlying layer of springs. Multiple layers of such springs are used with four layers being preferred. At their respective crossing points, the springs of adjacent layers are joined--as by welding--with the result that the filter is a solid unitary mass.

Abstract: An apparatus for loading nuclear fuel rods through spacer grid cells of a fuel bundle includes a handle having at least one elongate clip joined thereto, and a flexible tubular sleeve joined to the clip. The clip rigidly supports the sleeve along its longitudinal axis while allowing the sleeve to unfurl perpendicularly thereto for disassembly from a fuel rod. In several embodiments of the invention, the clip may include a slot for bridging adjacent grid cells during assembly, or the clip may be removably fixedly joined to the handle for allowing easy replacement of the sleeves.

Abstract: In a boiling water reactor fuel bundle, a three dimensional debris catching grid construction is placed within the flow volume defined by the lower tie plate assembly between the inlet nozzle and upper fuel rod supporting grid. A perforated plate is utilized having round holes as small consistent with the prevention of inadvertent closure due crudding and a hole pitch consistent with mechanical integrity requirements. The perforated plate is placed in a three dimensional construction such as a dome, cylinder, pyramid, inverted pyramid or corrugated construction spanning the flow volume of the lower tie plate assembly. As a consequence of this three dimensional grid construction, the total flow through area of the perforations in the metal plate does not introduce appreciable pressure drop in the lower tie plate assembly between the inlet nozzle and the rod supporting grid.

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.