抄録
The Severe Accident (SA) leading to core melt had not been considered to occur in Japanese Nuclear Power Plants (NPPs) because various kinds of countermeasures were adopted for the first through third layers of Defense in Depth (DiD). The direct cause of Fukushima Daiichi accident was considered to be the loss of all AC powers caused by an unexpected huge tsunami, but the insufficient measures for the fourth and fifth layer of DiD was pointed out as a lessons learned of Fukushima Daiichi accident. From this viewpoint, foreign NPP investigations have been performed by JANSI in order to gather and analyze information how foreign NPPs are taking SA countermeasures. Before Fukushima Daiichi accident, SA countermeasures adopted in Japanese NPPs were far behind from the advanced foreign NPPs, but nowadays we think that SA countermeasures in Japanese NPPs have caught up and have reached almost the same level as advanced foreign NPPs. Moreover, JANSI is going to study additional SA countermeasures as voluntary basis for the safety improvement of Japanese NPPs based on SRS-46 and foreign NPPs investigations.
