US Patent 7623612 Bi-alloy spacer grid and associated methods

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.