Experimental Investigations on In-Vessel Corium Retention through Inherent Gap Cooling Mechanisms

Abstract

In-vessel retention (IVR) of corium is considered as one of the most attractive severe accident management strategies in that the success of the IVR can considerably reduce the concerns about containment failure and associated risks. Among the various measures to attain the IVR, inherent gap cooling through the in-vessel flooding is very useful since it requires no additional engineering features for the IVR. In this study, simulant melt experiments using thermite melt (Al₂O₃/Fe or Al₂O₃ only) were performed to technically validate the concept of in-vessel gap cooling. The experimental results indicate that a gap could form between the debris and the vessel lower head which could be attributed to the difference of materials between the debris and the vessel, the existence of water inside the lower plenum and the internal pressure load. The heat removal capacity in the gap was determined by the possibility of a water in-gression into the gap. In the case of a small gap size, effective heat removal to the extent of the vessel bottom could not be achieved due to the difficulties of water ingression induced by the counter current flow limits (CCFL). Therefore, for an application of the in-vessel gap cooling concept to the real accident sequences, the regime for an effective gap cooling should be mapped according to the relocated melt mass and the gap size.

KEYWORDS:

• in-vessel retention
• gap cooling
• counter current flow limits