Development of level 2 PSA methodology for sodium-cooled fast reactors, 5; Development of technical basis for the protected loss of heat sink

Tobita, Yoshiharu; Yamano, Hidemasa  

As part of level-2 PSA methodology development for sodium cooled fast reactors, the phenomenological event tree for the Protected Loss of Heat Sink (PLOHS) is constructed for JSFR (Japan Sodium-cooled Fast Reactor). The early stage of PLOHS accident, where the heating of coolant, coolant boiling and uncovering of core occur, is analyzed by the ARGO code. The event progression in the subsequent core degradation phase, where the meltdown of core and the power transient by re-criticality occurs, is analyzed by the APPLOHS and SIMMER-III codes. The dominant factors, which affect the event progression in PLOHS, are recognized through these analyses and by considering the phenomenological event progression. The event tree of PLOHS is developed assigning these dominant factors as the headings. For each of the headings, available information for judgment of branching probability are reviewed and integrated as database for level-2 PSA.