Containment severe accident management strategies for PWR plants in Japan

Five Japanese PWR utilities have conducted the joint studies on containment severe accident management for PWR plants in Japan. The utilities have discussed the severe accident management strategies for 4 typical PWR plants from the view of in-house safety activities. Knowledge obtained from the results of PSA and severe accident studies has been systematically investigated, and the event sequences leading to core damage or containment vessel (CV) failure were classified into several categories. Then, the accident management strategies against the dominant sequences were specified. The dominant physical events leading to CV failure were classified into 9 categories. Four candidates for accident element measures against those events were selected, and their effectiveness, feasibility and influences on existing safety functions have been identified: CV cooling by natural convection, water injection into CV, forced depressurization of primary system, controlled burning of hydrogen (applied only for the plants with ice condenser CV)