Degraded core relocation in Sodium-cooled Fast Reactor severe accident $-$ particle-size debris flow

International audienceIn the context of improved safety requirements for generation IV Sodium-cooled Fast Reactors (SFR), an innovative severe accident mitigation scenario is being investigated. The mitigation strategy consists of transfer tubes (DCS-M-TT) and a core catcher. The transfer tubes are dedicated to discharge molten fissile materials from the core center region and guide them towards the core catcher where long-term cooling and sub-critical state are assured. The physical phenomena occurring during the discharge via DCS-M-TT is introduced in this paper. The current demonstration of the mitigation strategy is based on best-estimate calculations with the reference computer code SIMMER. Previous analyses showed that the material discharge via DCS-M-TT can be efficient to avoid re-criticalities and prevent large mechanical energy release. However, uncertainties of SIMMER approach are identified on the relocation process related to a possible particle-size debris accumulation and blockage formation inside the transfer tube. It is believed to originate from the particle treatment in the code. Thus, a review of particulate flow modelling is summarized in this work. The first validation and verification on particle flow treatment in SIMMER is presented. Recommendations for reactor calculations and first orientations for future RandD are highlighted