Modeling volatile fission products transport into the Germinal V2 fuel performance code by coupling to thermochemical software

International audienceWithin the PLEIADES simulation platform co-developed by CEA, EDF and FRAMATOME, GERMINAL is the fuel performance code devoted to the in-pile behaviour of mixed oxide fuel pins for Sodium-cooled Fast Reactors. The feedback on such fuel elements, based on experimental observations mainly acquired during PHeNIX french reactor operation, shows that a layer of volatile fission products, called JOG for Joint Oxyde-Gaine, is formed between the fuel pellet and the clad for a burn-up of 6 to 8 %FIMA. At higher burnup, the volatile fission products compounds can react with the cladding material components (Fe, Ni, Cr), corroding the inner wall of the clad.Thus, it is important to improve our chemical modeling of the uranium and plutonium mixed oxide fuel behavior under typical irradiation conditions. For that purpose, the thermochemical code ANGE (close to SOLGASMIX) and, more recently, the OpenCalphad (OC) software, have been integrated into the GERMINAL V2 fuel performance code. The main motivations for choosing OpenCalphad are first its ability to use efficient models and its compatibility with the TAF-ID database.Coupled simulations have been performed on French reactor PHeNIX fuel pins irradiated to different burnup both with ANGE + TBASE using a description based on the Lindemer and Brynestad one, and OpenCalphad + TAF-ID using the description of Gueneau et al. for the modeling of the fuel with its fission products in solution.The calculation results show quite good qualitative agreement with post-irradiation observations regarding the JOG thickness evaluations and the fuel pellet chemical composition. Nevertheless, the simulations are strongly dependent on the volatile fission products release rate as well as on the oxygen content considered in the calculations. Thus, in near future, it will be important to focus on these aspects in order to confirm our evaluations