New spacer grid to enhance mechanical/structural performance

A spacer grid (SG), which supports nuclear fuel rods (FRs) laterally and vertically with a friction grip, is one of the most important structural components in a PWR fuel. The forms of the grid straps and spring form are known to be closely related with the SG crush strength and the integrity of FR support, respectively. In this study, a new SG form and its manufacturing technology were suggested for enhancing the integrity of the FR support and the SG crush strength by using a systematic optimization technique without significantly increasing the pressure drop across the reactor core. Finite element (FE) analysis and crush strength tests on the new SG form were carried out to check the performance enhancement compared with commercial SGs. According to the results, it is estimated that the actual critical load enhancement of the SG is approximately up to 30%, and the actual contact area, when an FR is inserted into an SG cell, is more than double for the new SG form. And also, some design variables that affect the SG crush strength were classified and their effects on the crush strength were investigated by an FE analysis and a crush strength test. (author)