Abstract
Severe accident analysis was performed for a station blackout (TBU) sequence in a typical BWR-5 plant with modified Mark-II type containment by MAAP5.01 code. Core heatup, degradation and relocation processes, reactor vessel failure and resultant impact on the containment including hydrogen production were investigated. Sensitivity analysis focusing on direct contact heating (DCH), which affect on the consequence of TBU sequence, was also performed. If extensive DCH does not occur in the TBU sequence, failure of the containment vessel can be postponed. On the other hand, concrete ablation at a floor and a side wall inside the pedestal due to molten core - concrete interaction (MCCI) significantly increases, because a large amount of debris with high temperature stays inside the pedestal.
