A model for fission gas release and gaseous swelling of the uranium dioxide fuel coupled with the FALCON code

A comprehensive model GRSW-A was developed to analyse the processes of fission gas release, gaseous swelling and microstructural evolutions in the uranium dioxide fuel during base irradiation and under transient conditions. The GRSW-A analysis incorporates a number of models published in open literature, as well as some original models that were already published by the authors elsewhere. Consequently, only the most prominent aspects of GRSW-A and its coupling with the FALCON fuel behaviour analysis and licensing code are described in this paper. The analysis of fuel behaviour in the REGATE experiment is presented, which includes the base irradiation of the fuel segment in a PWR to a burn-up of about 50 MWd/kgU, which was followed by a power ramp in the SILOE research reactor. Besides, the generalized data on fission gas release (FGR) in PWR fuel during the base irradiation up to a burn-up of about 70 MWd/kgU is interpreted using coupled FALCON and GRSW-A. Moreover, a mechanistic interpretation of the published data for pellet swelling during the base irradiation up to a burn-up of 100 MWd/kgU is put forward. In all the cases, the coupled FALCON/GRSW-A analysis has shown the improved prediction capability compared to the original FALCON MOD01, which is achieved due to the account for the mutual effect of thermal and, in particular, high-burn-up-assisted mechanisms of fission gas release and swelling under steady-state and transient conditions.