Potential Uses of Seismic PSA for Risk Management of NPPs - A Review of Recent Studies at JAEA

Aiming at contributing to the discussions on the use of seismic PSA for risk management of nuclear power plants, this paper reviews three recent studies made at the Japan Atomic Energy Agency(JAEA) in the field of ageing management, accident management and emergency planning. The first study is the development of component reliability analysis procedure considering seismic conditions conducted as part of the material degradation and ageing management research program. In order to contribute to ageing management strategies, JAEA developed a procedure that combines the probabilistic fracture mechanics analysis code with seismic hazard analysis. The second and third studies were performed as part of the research program on seismic risk management. The second study is on the core damage sequences and frequencies of two BWR units of same design located in the same site. This study indicated that the cross connection of emergency electric power between two units, which has been implemented as part of accident management procedures in Japan on the basis of internal event PSA, might be quite effective also for seismic conditions if credit can be taken on the fragility of connection system. The third study is on the damage to the road and buildings in the vicinity of an NPP caused by earthquake motions. This study suggested that, in emergency planning for NPPs, the reference earthquake motions for efficient estimation of the damages to the society could be determined from a level 1 seismic PSA as those of seismic motion intensity that contributes most to the core damage frequency. This paper gives an over view of these studies and technical issues to be studied for extending the uses of seismic PSA for these new fields. (authors)