Development of a fission gas release and swelling model for sodium-cooled fast reactor fuels

[Display omitted] •GRESS code is developed for analyzing fission gas release and swelling in SFR.•Grain size and gas bubble diameter exhibit rapid variations within a specific range of fuel temperature.•The relatively minimal variation in grain size and gas bubble diameter at higher fuel temperatures result in a decrease in gas bubble swelling.•FGR and intragranular gas bubble swelling increase over time during transient operation.•The results demonstrate the coupling and interaction of fission gas behavior with each other. In order to simulate the behaviors of Fission Gas Release (FGR) and swelling for Sodium-cooled Fast Reactor (SFR) under normal and transient conditions, a Gas RElease and Swelling Simulations (GRESS) code is developed using COMSOL Multiphysics. GRESS is mainly based on a previous model called the Operational Gas RElease and Swelling (OGRES) model, in which the FGR and swelling are primarily related to burnup, time and temperature. GRESS assumed that there is a spherical grain at the fuel pellet. The grain is presented by a 2D axisymmetric geometry in COMSOL Multiphysics. Fission gas atom generation, gas atom diffusion, gas atom diffusion into the bubble, bubble resolution, gas bubble nucleation, gas bubble migration to the grain boundary, bubble pressure, gas bubble swelling, grain growth, oxygen to metal atomic ratio, fuel porosity, fuel thermal conductivity, heat generation rate, pore velocity, pore concentration, plutonium migration and so on are considered in GRESS code. The output results include grain size, gas bubble diameter, gas bubble concentration, the amount of gas atoms per bubble, gas atom diffusion coefficient, bubble diffusion coefficient, surface diffusion coefficient (varying with temperature), FGR (varying with time), and swelling (varying with time and radius). The comparison of the results with other modeling outcomes and experiments is performed, which shows a good agreement.