Abstract: A support grid for a nuclear fuel assembly, the nuclear fuel assembly including a generally cylindrical fuel rod with a diameter, wherein the support grid includes a frame assembly having a plurality of generally circular cells and a plurality of helical frame members. The helical frame members are disposed in the cells and are structured to contact the cell as well as a fuel rod. The helical fuel rod contact portion may have a variable pitch.

Abstract: A nuclear fuel assembly grid having a torpedo-shaped mixing vane assembly supported at each intersection of the grid straps that surrounds a fuel rod support location. The torpedo-shaped stem supports mixing vanes that extend over each of the fuel rod support locations.

Abstract: A nuclear fuel assembly grid having a torpedo-shaped mixing vane assembly supported at each intersection of the grid straps that surrounds a fuel rod support location. The torpedo-shaped stem supports mixing vanes that extend over each of the fuel rod support locations.

Abstract: A support grid for a nuclear fuel assembly, the nuclear fuel assembly including a generally cylindrical fuel rod with a diameter, wherein the support grid includes a frame assembly having a plurality of generally circular cells and a plurality of helical frame members. The helical frame members are disposed in the cells and are structured to contact the cell as well as a fuel rod. The helical fuel rod contact portion may have a variable pitch.

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 crud-resistant nuclear fuel element cladding in which the axial locations that experience nucleate boiling during reactor full power operation are highly polished so that the maximum size of any surface defect on the highly polished surface is approximately 0.1 microns. The remainder of the cladding surface remains unpolished so that crud is more evenly redistributed over the entire fuel cladding surface to limit the thickness of the crud that is formed to less than 35 microns.

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 nuclear fuel rod spacer grid is formed of slottedly interlocked sets of flat strips. One set of strips is formed with integral coplanar tab portions which have one or more edge portions bent at angles to form integral mixing vanes.

Abstract: A flow deflector grid (10) for a nuclear fuel assembly, comprising a plurality of metal strips (12,14) which intersect in a regular array to form an egg-crate type lattice, which defines a plurality of coolant flow channels (16). Each channel has sidewalls (42,44) defined by the strips, a height dimension defined by the height of the strips, a plurality of corners (46) defined by the strip intersections (26), a channel central axis parallel to the height dimension, and a flow cross section normal to the channel axis for coaxially receiving a fuel rod (18) spaced within the channel sidewalls. A unitary flow deflector member (30) is attached to and situated in the corner of each channel so as to be cradled between first and second sidewalls.

Abstract: 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.

Abstract: Pressurized water reactor fuel bundles (10) have a cast lower end fitting (20) which provides reduced pressure drop because nozzles (24) are of polygonal (rectangular or square) cross-section and the flow entrance wall portion (32) is a parabolic shape which merges into a wall portion (30) parallel to the flow direction. The parabolic shape of portion (32) and fillets (24a) at the nozzle (24) corners also give an improved draft to the casting. Pressure drop reduction was substantially greater than standard calculations indicated would be obtained.

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.