Assessment of hydrogen risk under containment severe challenge status

Sanmen nuclear power plant is the first third-generation plant based on passive design. Assessment of hydrogen risk under containment severe challenge status (SCST) according to Sanmen severe accident management guidelines (SAMG) in operation is needed. Plant model including the primary system, containment and engineered safety features is built with integration accident analysis code. An accident sequence induced by 2 inch break at hot leg combined with engineered safety features unavailable is studied, which generates over 100% active core Zr oxidation hydrogen generation. Due to the failure of containment water cooling, inert containment environment occurs, resulting in coexistence of containment overpressure challenge and hydrogen challenge, known as containment severe challenge status. The comparison of only operating severe challenge guideline-2 (SCG-2) and operating SCG-2 and SCG-3 based on SAMG is investigated. The result shows that the preferred means to start or shut off containment water cooling system based on SCG-2 and SCG-3 can mitigate the containment overpressure challenge and hydrogen risk. (authors)