Research items regarding seismic residual risk evaluation

The seismic design review guideline for light water nuclear reactors has been revised in September 2006. In this guideline, nuclear utilities are requested to perform evaluation of the seismic residual risk due to ground motions exceeding the design basis ground motion 'Ss', which is redefined according to the revised guideline, by seismic PSA method, as well as performing seismic re-evaluation by conventional deterministic method. In response to this, JNES has developed seismic PSA models that can cover all the domestic BWR and PWR plants to support the regulatory review by NISA. In addition to this, multi-units site PSA models for level 1 and 3 have been being developed, considering concurrent failures of systems, structures and components among adjacent multi-units in the same site, in order to evaluate concurrent core damage frequency and associated radiological effects to the environment. Tsunami PSA models have been being developed as well, however, considering the occurrence of the severe accidents at the Fukushima Dai-ichi Power Station after the great earthquake and Tsunami on March 11 2011, works for developing PSA models for seismic event with accompanied Tsunami events have also been commenced in 2011. (author)