An assessment methodology for in-vessel corium retention by external reactor vessel cooling during severe accidents in PWRs

A consistent probabilistic approach is proposed to evaluate the feasibility of in-vessel retention of the molten corium through external reactor vessel cooling (IVR-ERVC) during severe accidents of pressurized water reactors (PWRs). By combining the results of Level-1 probabilistic safety assessment, a critical heat flux correlation, and wall heat flux distributions calculated by a severe accident code with appropriate adjustment, we can reasonably predict the overall success probability of the IVR-ERVC from the viewpoint of thermal failure. The practicability of the proposed approach is illustrated with a preliminary application to the Korean Standard Nuclear Power Plant. This paper also discusses future developmental needs for more reliable assessment.