The worst case scenario including melt-down of reactor core components has been recognized as one of the safety issues. Without any counter measure, this may lead to penetration of RPV (Reactor Pressure Vessel) due to significant thermal loads caused by the relocation of molten core debris into the lower plenum. The present paper shows applicability of ERVC (External Reactor Vessel Cooling), aimed at limiting radiological releases by adopting the in-vessel retention concept, under core melting conditions. Systematic numerical analyses were carried out by taking into account diverse melting progress mechanisms, properties and amounts of molten debris, and damage models. Consequences of the thermal loads under assumed core melting conditions, such as the critical locations and time to reach penetration of the RPV lower plenum, were compared as a part of sensitivity analyses. Also, influences of each parameter were examined and technical findings from the assessment were discussed to demonstrate effectiveness of the ERVC for severe accident mitigation features of new power plants.

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