SURROGATE-BASED OPTIMIZATION MODEL OF BEST-REPRESENTATIVITY SODIUM FAST REACTOR SEVERE CORE ACCIDENT REACTIVITY EFFECTS IN THE ZEPHYR CRITICAL FACILITY

This project deals with original representativity studies of local reactivity effects in a fast lattice during severe core accident in Sodium-cooled Fast Reactor aiming to implement new experimental programs in the French ZEPHYR project of new critical facility. This representativity study is based on sensitivity analysis of reactivity coefficients and local flux distribution in case of degradation of the ASTRID inner core. SCA sequence, e.g., voiding, fuel meltdown etc., potentially has pronounced influence on the neutronic characteristics of the fast reactor’s core and can lead to prompt recriticality. To predict the core behaviour during such disruptions, it is necessary to develop accurate and reliable computational and experimental tools and methodologies. The assessment of reactivity behaviour that represents different stages of the disrupted core configurations is one of the challenges assigned to ZEPHYR and requires a new way of performing measurements in critical assemblies. The project is carried out in both assembly and core levels. Recent results indicate that it is possible to identify high representativity experimental configurations using surrogate-based approaches for a 2-step optimization strategy.