Combustion Engineering, Inc.

Westinghouse Electric Company LLC

Patrick A Perrotti

William J Bryan

Zeses E Karoutas

Stephen C Hatfield

Paul F Joffre

Richard P Broders

Lawrence V Corsetti

Michael L Martin

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.

Fuel assembly and associated grid for nuclear reactor

A metal component (10) having non-uniform material characteristics which cause the component to undergo differential growth upon exposure to a neutron flux, and a process for producing such a component. The invention is useful for making metal components for use in nuclear reactors, particularly fuel assembly cantilever grid springs (12). By cold working a portion (40) of a cantilever spring on the convex side of the curved region of the spring, a spring can be provided which has a smaller reduction in preload upon exposure to radiation than a conventional cantilever spring.

Nuclear reactor grid strip cantilever spring with nonuniform material

A method for sputter coating the inside surface (30) of a fuel assembly tubular component (10) such as a control rod guide tube (200) with wear or corrosion resistant material. The steps include supporting the component tube in a fixture (12,14) and supporting a source tube (100,300) of e.g., wear resistant material, coaxially within the component tube, thereby defining a cylindrical annulus (24) between the tubes. The annular space is evacuated and backfilled with an inert working gas (26) such as argon, to a pressure sufficient to sustain a plasma discharge. The component tube is positively biased (36) as an anode, and the source tube is negatively biased (34) as a cathode, such that a plasma of the working gas is established in the annular space. A circumferential magnetic field is generated around the source tube to confine and shape the plasma whereby the source tube is bombarded with ions from the plasma substantially uniformly over the length of the source tube. Wear resistant material is thereby sputtered substantially uniformly from the source tube onto the inside surface of the component tube, to form a coating thereon.

Fuel assembly sputtering process

A method for sputtering coating the inside surface of a fuel assembly tubular component (10,200,400,700) with absorber material such as a burnable poison or getter. The steps include supporting the e.g., cladding tube (10) in a fixture (12,14) and supporting a source tube (100) of e.g., burnable poison material coaxially within the cladding tube, thereby defining a cylindrical annulus (24) between the tubes. The annular space is evacuated and backfilled with an inert working gas (26) such as argon, to a pressure sufficient to sustain a plasma discharge. The cladding tube is positively biased (36) as an anode, and the source tube is negatively biased (34) as a cathode, such that a plasma of the working gas is established in the annular space. A circumferential magnetic field is generated around the source tube to confine and shape the plasma whereby the source tube is bombarded with ions from the plasma substantially uniformly over the length of the source tube. Burnable poison material is thereby sputtered substantially uniformly from the source tube onto the inside surface of the cladding tube, to form a burnable poison coating thereon.

Sputtering process burnable poison coating

A nuclear fuel assembly grid (1) has a plurality of flat strips (10,12) that are orthogonally interlaced along vertical slots (38,60) through their upper or lower edges and welded together to form an egg crate-like array of four-walled cells (14) for receiving respective fuel rods (16), each cell including springs (20,30) and arches (32,34) projecting from the walls for contacting and supporting a respective fuel rod in the interior of the cell. At least some of the cells having flow deflection vanes (36,56) projecting integrally from a cell wall into the interior of the cell without contacting the fuel rod. Preferably, the vane is bent along a bend line (52) that is parallel to the upper edge (24) of the strip, into the interior of the cell, thereby forming an angle of between about 15 degrees and 30 degrees relative to the plane defined by the body, or plate portion of the strip.

Inverted vane mixing grid

The laser beam welding of a spacer grid assembly is accomplished by dividing a laser beam (21) into at least two beam segments (37). These beam segments (37) are then routed around the mixing vanes (31) and focused below the vanes (31). The focus and coincidence (34) of the beam segments (37) may be moved down along the intersection to provide an elongated smaller diameter weld. The spacer grid assembly of the present invention has an improved Departure from Nucleate Boiling performance, increased strength against buckling, and a reduced detrimental effect on the coolant flow.

Split beam laser welding system

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.

Spacer grid assembly fixture

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.

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Newington, CT, United States of America

Patrick A Perrotti