Phase-field simulation of recrystallization and calculation of the effective thermal conductivity of polycrystalline UO2

Abstract

During the operational lifespan of uranium dioxide (UO2) fuel, the emergence of a specific process termed recrystallization may transpire. The influence of recrystallization on the thermal conductivity of the fuel holds paramount significance, bearing direct implications for both safety and economic considerations. In the current investigation, a phase-field model incorporating an explicit nucleation model for recrystallized grains was formulated to study the formation and growth of recrystallized grains within polycrystalline UO2. The simulations conducted in this study revealed that the kinetics of recrystallization adhered to the empirical equation, and the observed variation in grain size during recrystallization exhibited concordance with experimental data. To elucidate the variation in thermal conductivity during recrystallization, a thermal conductivity model based on the microstructure generated through phase-field simulations was employed. The relationship between grain boundary (GB) thermal resistance and phase-field simulation parameters has been determined through empirical formulas. The simulated values of thermal conductivity during recrystallization demonstrated a commendable agreement with empirical functions. By comparing the computational results of thermal conductivity with or without recrystallization, it is proven that recrystallization is beneficial to the effective thermal conductivity because the increase in thermal conductivity due to the elimination of defects by recrystallization exceeds the decrease in thermal conductivity due to the introduction of large area GBs.