Effects of recrystallization on fission gas behavior in U₃Si₂ fuel at LWR temperature: A combination of phase-field method and rate theory

The not well-known fission gas behavior of U₃Si₂ under light water reactor (LWR) conditions is a key limitation for its application as accident tolerant fuel (ATF) in commercial LWRs. In this paper, we developed a rate theory calculation model based on the kinetic rate theory framework originally developed in the GRASS-SST code, modified by the phase-field method, to investigate the influence of grain size on fission gas behavior in U₃Si₂ fuel under LWR conditions. The phase=field model examines microstructural development, specifically, evolution in grain size, in U₃Si₂ fuel. This model is then incorporated into the rate theory framework to analyze fission gas release and the retained fission gas bubble areal fraction during irradiation. The integration of these mesoscale models enhances our understanding of the impact of grain size evolution on fission gas behavior. The simulations of fission gas release show good agreement with post-irradiation examination (PIE) data, providing validation to the model and insights into the varying retained fission gas behavior observed in different regions of irradiated fuel pellet.