The plant-specific uncertainty analysis for an ex-vessel steam explosion-induced pressure load using a TEXAS–SAUNA coupled system

An ex-vessel steam explosion has been considered as one of the most challenging severe accident phenomena to the integrity of the reactor cavity and containment of a nuclear power plant, owing to its rapid and dynamic characteristics. The purpose of this paper is to provide plant-specific uncertainty analysis results on the ex-vessel steam explosion-induced pressure loads, which can be used as key input to assess the conditional failure probability if the fragility structures of interest is provided. The APR1400, a two-loop pressurized water reactor, has been selected as a reference plant for an uncertainty analysis. For this purpose, a comprehensive uncertainty analysis has been performed for key thermal–hydraulic conditions of the reactor pressure vessel and cavity, which can highly influence on these pressure loads, with the help of a coupling of a steam explosion analysis code (TEXAS-V) with a sampling-based uncertainty quantification code (SAUNA). To get a more robust conclusion based on the analysis results, various sensitivity analyses have been applied to both probability types (e.g., normal and uniform PDF) and sampling schemes (e.g., random and Latin Hypercube sampling). Key contributors (i.e., physical and model parameters) to the underlying pressure loads have been determined by assessing the six currently available types of importance measures.