Modeling of high burnup UO$_2$ fuel pulverizaiton

Abstract

In this study, the effect of grain boundary segregation of fission products on the grain boundary cohesive energy of uranium dioxide was analyzed using first principles calculations. Using the calculation results, a model was developed to predict the high burnup fuel pulverization phenomenon. The grain boundary segregation tendency of zirconium, molybdenum, cesium, and xenon was investigated, and the effect of grain boundary segregation of the elements on the grain boundary cohesive energy was analyzed. As a result of the calculations, it was confirmed that the grain boundary segregation of xenon effectively lowers the grain boundary cohesive energy, and the grain boundary cohesive energy according to the area concentration of xenon on various types of uranium dioxide grain boundary was calculated. A high burnup uranium dioxide fuel pulverization model was implemented in FRAPCON 4.0/FRAPTRAN 2.0, a nuclear fuel analysis code, using a two-stage fission gas diffusion model and the grain boundary cohesive energy according to the calculated xenon area concentration. It was confirmed that the implemented model predicts the actual nuclear fuel pulverization phenomenon with very high accuracy. The developed model can be used for safety analysis of nuclear reactors loaded with high burnup nuclear fuel and licensing to increase the maximum burnup limit of nuclear reactors.