Modelling Fission Gas Behaviour with the BISON Fuel Performance Code

The fission gas behavior model included in INL’s fuel performance code BISON is being continually extended and improved. In the present contribution, we give an account of the most recent developments and results on modelling fission gas behaviour in uranium dioxide fuel for BISON. Recent developments include (i) a physically based model for intra-granular behaviour including bubble evolution, (ii) an improved numerical algorithm (called PolyPole-1) for the computation of intra-granular gas diffusion to grain boundaries and (iii) a transient model that accounts for the effect of fuel micro-cracking in fission gas release (FGR). This transient model has been validated to fuel rod power ramp experiments and more recently, also applied in BISON simulations of reactivity-initiated accident (RIA) experiments. We present our newly obtained FGR results from RIA simulations. These initial results indicate that, while traditional models are unable to reproduce a significant increase in FGR during the short duration of a RIA event, the transient model in BISON properly predicts the high FGR observed during RIAs.