Suggestions to Enhance the Crush Strength of a LWR Spacer Grid Assembly

A spacer grid is one of the most important structural components in a LWR fuel assembly. The spacer grid, which supports nuclear fuel rods laterally and vertically with a friction grip, is an interconnected array of slotted grid straps welded at the intersections to form an eggcrate structure. Dimples and springs are stamped into each grid strap to support the fuel rods. Zircaloy is prevailing as the material for a spacer grid because of its low neutron absorption characteristic and its extensive successful in-reactor use. The primary considerations are to provide a Zircaloy spacer grid with a crush strength sufficient to resist design basis loads, without significantly increasing the pressure drop across the reactor core. A Zircaloy grid strap's thickness and height have generally been considered as the main design variables in order to meet the above considerations. However, since the above design variables for a spacer grid assembly are very closely related with the pressure drop of a coolant, their application to a spacer grid design is significantly restrictive. Therefore, it could be very helpful for designing a spacer grid assembly, if new design variables are deduced without affecting the pressure drop of a coolant so much. In this study, new design variables to enhance the crush strength of a spacer grid assembly are deduced and their validity is confirmed by applying them to a spacer grid design and performing a crush strength test and a finite element analysis