A Study of probabilistic risk assessment methodology of external hazard combinations; Identification of hazard combination impacts on air-cooling decay heat removal system

Okano, Yasushi; Nishino, Hiroyuki  ; Yamano, Hidemasa   ; Kurisaka, Kenichi 

A sodium-cooled fast reactor uses the ambient air as an ultimate heat sink to remove decay heat, thus meteorological phenomena can potentially pose risks to the reactor. If a rare and intense external hazard occurs concurrently with another external hazard, it would affect the systems (i.e. air cooler of decay heat removal system). In this study, a new scheme of screening of the external hazard combinations was proposed. The authors classified simultaneous or sequential combinational hazards, and identified associated potential effects in terms of hazard duration and sequential order. As a result, this study identified scenarios of the external hazard combinations of preceding rare and intense external hazard with an following additional external hazard.