Application of probabilistic techniques to seismic risk analysis on the Diablo Canyon Plant

The principal purpose of this study was to make an assessment of potential risks to the public from earthquake-caused accidents at the Diablo Canyon Nuclear Power Plant. Since large earthquakes are relatively rare events at any given location and nuclear power plants are required to be designed to high standards of strength, such studies deal inevitably with small probabilities determined from combinations of rare events. Some of the methods used in the study were based on those used in the Reactor Safety Study, a recent comprehensive study conducted by the Nuclear Regulatory Commission for nuclear plants of the Diablo Canyon type. In this study, which was specifically devoted to risks from earthquakes, all the data and conditions used were based on those applicable to the Diablo Canyon Plant and site characteristics. Among other results, it was found that even when considering the impact on the plant of accelerations well in excess of the maximum which the NRC has asked the company to consider, the risk to the health and safety of the public caused by possible earthquake damage to the plant was found to be extremely remote. As an illustration, the probability of an individual in the closest community to the site being exposed to as much as 25 Rem of radiation to the whole body is only about one in seven million per year