Sodium-cooled fast reactor and related multiphase flow phenomena, 4; Assessment of molten fuel-sodium interactions in severe accidents

Matsuba, Kenichi  

SFRs have the characteristic that reactivity is introduced when coolant boiling or movement of core constituents occurs within the core. Therefore, in the event of a severe accident involving core meltdown, there is a possibility of recriticality leading to mechanical energy release. To avoid this possibility, a safety design involves installing flow paths within the core to rapidly discharge molten fuel from the core, as well as a core catcher at the bottom of the reactor vessel to retain it. It is believed that molten fuel discharged outside the core interacts with sodium, and as a result of this molten fuel-sodium interaction, the molten fuel solidifies into fine particles and accumulates on the core catcher. This paper presents the current status of assessment of molten fuel-sodium interactions in severe accidents.