Simulation tools and approaches for the compliance with performance-based ECCS cladding acceptance criteria (10 CFR50.46c)

The Nuclear Regulatory Commission (NRC) is currently considering a revision of the requirements in 10 CFR 50.46C, rules, focused on the ECCS rule in LOCA scenarios. The new approach modifies the analysis strategy in order to take into account also the effects of the burn-up rate. The maximum temperature and the oxidation of the cladding must be casted as function of the fuel exposure in order to find the limiting conditions in the history of the reactor, with its different design and different reloading patterns. This new analysis requires new tools and capabilities in order to have reasonable computational times and good accuracy, taking in account the dynamic phenomena of multi-physics systems. In order to perform such analysis, a rigorous Probabilistic Risk Assessment (PRA) strategy needs to be employed. This work is a proof of concept for illustrating a new proposed approach that will be required in the next years, in order to face the challenges posed by the new rule.