Development of evaluation methodology to enhance cavity flooding strategy on operating PWR power plant

•The knowledge and technical understandings on the corium cooling mechanisms especially including the corium behaviors in pre-flooded cavity have been much improved.•The sensitivity analysis was performed for the corium coolability, and it was confirmed that the identification of the required amount of water for flooding can provide higher confidence for BMT-prevention strategy.•Estimation methodology to enhanced cavity flooding strategy was proposed in this paper. To mitigate the concrete ablation by the relocated molten corium in cavity, the decay heat from molten corium should be removed sufficiently to prevent BMT by flooding the cavity. In practical aspect, the negative effects of this cavity flooding strategy, such as threats of the containment over-pressurization and the steam explosion, may compete with the effectiveness of the strategy itself at the real accident situation. According to recent researches, the understanding the cavity corium behaviors has been advanced and it can be utilized in improving the cavity-flooding strategy, and based on this consideration, the evaluation methodology to enhance cavity flooding strategy was proposed in this study. The main idea is how to materialize the technical aspects of the enhanced ex-vessel corium coolability into the existing cavity flooding strategy together with minimizing the negative effects. Application of this evaluation methodology can provide an optimal way to prevent BMT more effectively.