Multi-Scale Modeling of Fission Gas Evolution in UO2

Fission gases in uranium dioxide (UO2) nuclear fuels, of which Xe is one of the most prominent, influence fuel performance during reactor operation and have implications for accident scenarios. Their behavior, including the nucleation and growth of fission gas bubbles, is a multiscale problem. We use a multiscale modeling approach to understand the behavior of Xe in UO2 as a function of microstructure by considering the effect of different types of grain boundaries on the evolution of Xe. Using density functional theory we calculate the activation energies for Xe diffusion in UO2 plus or minus x and we determine the interaction of Xe with different types of grain boundaries in UO2 using molecular statics. These results are then input into amesoscale model that predicts the evolution of Xe as a function of microstructure containing different distributions of grain boundaries. We find that the evolution of Xe depends significantly on the microstructure.