A kinetic rate theory modelling of fission gas release and fuel swelling for UN fuels

Fission gas behavior and fuel swelling have always been an important issue for nitride fuels. In this paper, a mechanistic fission gas behavior model of nitride fuels has been established using the kinetic rate theory, based on the fuel temperature distribution input provided by a finite element computational platform. The fission gas release and fuel swelling of the nitride fuels were simulated in details and the simulation results were compared with experimental data from open literature. Using the established model, previous diffusion coefficients of Xe gas in nitride fuels derived by earlier works were analyzed, and a new diffusion coefficient suitable for simulation of nitride fuels was proposed. A parameter sensitivity analysis was carried out for the two important parameters in the rate theory simulation of fission gas behavior, the nucleation factor and the resolution coefficient. Suitable values for both parameters for nitride fuels were determined, and their influence on fission gas behavior and fuel swelling were assessed. In addition, a bimodal distribution for bubble size was observed and the underlying physics driving factor was determined to be the gas bubble resolution.