The accident in Japan on March 2011 was caused by a natural event (i.e., earthquake, and the induced tsunami) which was far more severe than the design basis for the Fukushima Dai-ichi nuclear power plant. The reactor cores of Dai-ichi unit 1 through 3 have been degraded due to the long term station blackout (SBO). Actually, a nuclear power plant is able to prevent the core damage despite the SBO event occurs, called “coping capability” or “coping time”.
In this paper, the SBO coping capability is assessed for Qinshan II unit 3 based on the following: 1) reactor coolant inventory, 2) condensate inventory for decay heat removal, 3) class 1E battery capacity, 4) compressed air, 5) effects of loss of ventilation, 6) containment isolation. As a result, the SBO event tree is suggested to be updated and a few vulnerabilities have been identified and some modifications are proposed.