Modeling Fission Gas Release and Bubble Evolution in UO2 for Engineering Fuel Rod Analysis

We present model developments for fission gas behavior and application to integral fuel rod simulations with the BISON fuel performance code. First, we give an overview of a physics-based engineering model of fission gas behavior developed in recent years and available in BISON. The model includes the fundamental physical processes of intra-granular bubble evolution and swelling coupled to gas atom diffusion, bubble evolution and swelling at grain boundaries, fission gas release due to grain-boundary bubble interconnection and micro-cracking during transients. Second, we present recent BISON simulations of LWR fuel rod irradiation tests including power ramps from the Risø-3 experiment. Calculations are compared to post-irradiation experimental data of fission gas release, xenon radial distributions in the fuel, and cladding diameter profiles. These new results extend the experimental validation base of the fission gas model for integral fuel rod simulations.