2018 | AFC ACCOMPLISHMENTS 169 Accomplishments: During FY17, effort was focused on applying Bayesian calibration techniques to the zirconium redistribution model. This was completed utilizing the best available metallic fuel models in BISON and EBR-II data to assess the viability of the models. Failure to match the species redistribution profile across different datasets led us the conclusion that either the underlying BISON models are providing the wrong state variables, or the zirconium redistribution model is missing or masking physics relevant to species redistribution. Following this, FY18 focused on improving the BISON simulations through robustness improvements and development of a new swelling model, as well as improvements to the zirconium redistribution model through implementation of a fully consistent phase diagram. Although the currently implemented swelling model has already been identified as a weak spot in metallic fuels modeling in BISON, the difficulty in developing a predictive model, a problem shared across all non-empirical fission gas models, has Figure 1. Example results from the new fission gas swelling and release model.