Severe accident studies on the efficiency of mitigation devices in a SFR core with SIMMER code

Sodium-cooled Fast Reactors (SFR) are investigated as future Generation IV reactor concepts. In SFR, the core configuration is not most reactive during nominal operation, its geometry change or coolant voiding can induce a reactivity insertion. Within these considerations, mitigation devices should be implemented into in order to limit thermal energy released fuel severe accident and thereby possibility mechanical loadings of structure when vaporized materials expand. Complementary safety called Transfer Tubes (TT) studied French concept an effective measure accidents reach final safe state, even case failure all shutdown systems including passive rods. More precisely TT, with their upper part located above core, cross support linked catcher zone situated main vessel bottom. Their purpose extract fissile from secondly favor transfer molten region damage. The discharge out necessary lower reactivity, relocation enable stabilization, sub-criticality cooling. An extensive work on calculations phenomena identification related through TT was performed. These studies represent outcome performed 2014–2019, collaboration Japanese JAEA MFBR Framatome framework SFR project carried by CEA. Calculations were mechanistic calculation code SIMMER results presented this paper. Firstly, whole unprotected loss flow (ULOF) sequence calculated code. From calculations, power evolution set boundary conditions for more detailed model six assemblies around TT. This used focus key check impact design parameter local bottom restriction inside way.