A comparative analysis of UO2 and MOX fuel behavior under reactivity initiated accident

Reactivity initiated accident (RIA) is one of the reactor accidents that limit the in-reactor performance of fuel especially at high burnup. In addition, according to recent experiments, RIA at high burnup can lead to fuel failure. In this paper, a comparative analysis was carried out for UO2 and Mixed Oxide (MOX) fuel behaviour under RIA as a function of burnup (0, 30, 60 MWd/kgM) and RIA type (realistic and severe) with use of the FRASM code. Comparison of the present analysis with experimental results gives the following three conclusions. First, under realistic RIA which can take place under reactor operating conditions, both UO2 and MOX fuels are intact. Second, under severe RIA which leads to local melting of fuel, there is a possibility that both UO2 and MOX fuel would fail. Third, UO2 fuel behaviour under RIA is more favorable than MOX fuel at beginning of life, while MOX fuel is more favorable at the burnups of 30 and 60 MWd/kgM. Fuel failure criterion applied to RIA, however, should be elaborated based on experimental data. (author)