Progress on Modelling the Thermo-Mechanical Performance of Accident-Tolerant Fuels

This paper discusses the work of CIEMAT to extend and validate fuel performance codes for the simulation of advanced technology fuels (ATFs). An in-house extension of the FRAP-family codes to FeCrAl cladding and Cr-doped UO2 fuel is described. The fission gas release and the pellet-cladding mechanical interaction of Cr-doped UO2 during irradiation have been assessed against experimental data. In addition, the ballooning response of FeCrAl under loss-of-coolant accident (LOCA) conditions has been evaluated, taking Zircaloy-4 as a reference material to emphasize major behavioural differences. The simulation of Cr-doped UO2 fuel under reactor conditions has revealed that the fission gas release is highly sensitive to the pre-processing of input data. Moreover, accounting for the enhanced viscoplasticity of Cr-doped UO2 is essential in accurately describing pellet-cladding mechanical interaction during power ramps; otherwise, the cladding deformation will be overestimated. As for the LOCA scenario, the superior mechanical strength of FeCrAl entails a delay in the prediction of the burst time, as well as a reduced balloon size. This work has been carried out under the IAEA/CRP ATF-TS framework.