Abstract: A fuel assembly for a nuclear reactor that employs dissimilar materials for the fuel assembly grid and the control rod guide thimbles. The guide thimbles are secured to the grid employing a through grid cell sleeve that is welded to the grid and spot weld rings that are secured over the sleeve and welded directly to the guide tube through windows in the sleeve.

Abstract: A bi-alloy spacer grid (BASG) is provided with grid straps and springs made using different zirconium alloys. The grid straps are made from a relatively low growth zirconium alloy, and the springs are made from a relatively high growth zirconium alloy. The springs are coupled to the grid straps by welding, mechanical interference, or secondary forming in place. When subjected to irradiation, the springs grow relative to the grid straps thereby maintaining contact with the fuel rod cladding, while the grid straps resist growth to maintain structural stability of the entire fuel assembly. The optimized balance of the high growth springs and low growth grid straps mitigates the formation of gaps between the fuel rods and grid support structures). The growth properties of the grid straps and springs may be further controlled through optional different fabrication processes.

Abstract: A spacer grid having tunable mixing vanes for optimizing coolant flow is provided for a nuclear fuel assembly. The mixing vanes include an upper piece and a lower piece, which are coupled to a middle ligament that is coupled to the top or downstream portion of one or more of the grid straps forming the spacer grid. The upper piece, lower piece, and middle ligament are bent, rotated, and/or twisted into various positions to more effectively mix the coolant and affect the coolant's flow as it moves upwards through the fuel assembly. For example, in one embodiment, the mixing vane has an “S” shape wherein the middle ligament is positioned parallel to the longitudinal axes of the fuel rods of the fuel assembly, the upper piece bends towards one of the fuel rods, and the lower piece bends away from the fuel rod. In this manner, optimized even and sustained mixing of the coolant is provided.

Abstract: A bi-alloy spacer grid (BASG) is provided with grid straps and springs made using different zirconium alloys. The grid straps are made from a relatively low growth zirconium alloy, and the springs are made from a relatively high growth zirconium alloy. The springs are coupled to the grid straps by welding, mechanical interference, or secondary forming in place. When subjected to irradiation, the springs grow relative to the grid straps thereby maintaining contact with the fuel rod cladding, while the grid straps resist growth to maintain structural stability of the entire fuel assembly. The optimized balance of the high growth springs and low growth grid straps mitigates the formation of gaps between the fuel rods and grid support structures). The growth properties of the grid straps and springs may be further controlled through optional different fabrication processes.

Abstract: A spacer grid having tunable mixing vanes for optimizing coolant flow is provided for a nuclear fuel assembly. The mixing vanes include an upper piece and a lower piece, which are coupled to a middle ligament that is coupled to the top or downstream portion of one or more of the grid straps forming the spacer grid. The upper piece, lower piece, and middle ligament are bent, rotated, and/or twisted into various positions to more effectively mix the coolant and affect the coolant's flow as it moves upwards through the fuel assembly. For example, in one embodiment, the mixing vane has an “S” shape wherein the middle ligament is positioned parallel to the longitudinal axes of the fuel rods of the fuel assembly, the upper piece bends towards one of the fuel rods, and the lower piece bends away from the fuel rod. In this manner, optimized even and sustained mixing of the coolant is provided.

Abstract: A four point contact grid for a nuclear fuel assembly, that is structured to engage at least one generally cylindrical fuel rod. The four point contact grid includes a plurality of elongated, generally flat straps including a first set of straps and a second set of straps, each strap having a plurality of cell portions. The straps are divided into a first set and a second set. The first set of straps are disposed in a spaced parallel relation to each other. The second set of straps are also disposed in a spaced parallel relation to each other and are generally perpendicular to the first set of straps. The first set of straps and second set of straps are coupled to each other thereby forming a plurality of generally square cells. Each strap cell portion has at least one protrusion. Each the strap cell portion further has only a single protrusion extending into each cell. Each the protrusion is either an elongated spring or an elongated dimple.