Two-step two-stage fission gas release model

A two-step two-stage model is developed in this study on the basis of the recent theoretical model. This model incorporates a two-step burn-up factor in the two-stage diffusion processes in the grain lattice and at the grain boundary during the fission gas release. In-pile data sets available in FRAPCON-3 code are used to validate the model. Results show that the predictions are in better agreement with the experimental measurements than those of any other models built in the code over the entire burn-up range up to 75 000 MWd/MTU.