Evaluation of core disruptive accident for JSFR to achieve in-vessel retention, 2; Early-discharge phase

Kamiyama, Kenji  ; Tobita, Yoshiharu; Toyooka, Junichi  ; Konishi, Kensuke ; Yamano, Hidemasa   

Event sequences of the core melting progression during ULOF event were considered and evaluated based on databases both of in-pile and of out of-pile experiments. The ULOF is an representative unsuccessful operation of active and passive reactor shutdown systems in the loss of flow case in sodium-cooled fast reactors. It was concluded that formation of the large-scale molten-fuel pool, which will lead severe power excursion, can be avoided and therefore mechanical failure of the reactor vessel can be avoided, since the molten fuel is discharged from the core region during the early stage of core melting progression by introduction of the fuel assembly with inner duct structure (FAIDUS).