Approach to Assess Influence of Earthquake-Induced Slope Collapse on Nuclear Power Plant Facilities

As a result of the disaster of nuclear power plant caused by the 2011 off the pacific coast of Tohoku Earthquake, establishment of a method to estimate the influence of slopes on the seismic safety of nuclear facilities has become necessary. The creation of such a method can yield important information regarding potential risk as well as risk management regarding seismic safety. The existing guidelines used to evaluate landslide risk provide guidance for landslide zoning as well as how landslide risk can be reduced and avoided. According to these guidelines, either people or houses are typically used as targets of risk evaluation. Particularly, for a specific slope, it is necessary to evaluate the damage of the potentially affected structures quantitatively and systematically. Therefore, the definition and basic assessment procedure of three limit states (stability limit, reachable limit and damage limit) are herein described. Furthermore, an evaluation case for a slope model describes the influence of slope collapse due to an earthquake. In this case, the fragility curves, as well as the occurrence probability for each limit state are described and an evaluation example is provided. Regarding new ideas and methods to evaluate the conditional reachable probability and the conditional damage probability as well as a method to evaluate the total probability of all three limit states are proposed. From the results obtained in our example case, it is found that systematical assessment of the risk information of facilities damaged due to slope collapse is useful, and is made possible via numerical analysis.