Development of Probabilistic Safety Assessment Considering Slope Collapse by Earthquake

In Japan, a part of nuclear power plants is surrounded by the land slope. In such a nuclear power plant, it is necessary to evaluate the stability of the slope under the deterministic seismic condition, and to ascertain that the plant is kept in a safe condition even if collapse of the slope might occur due to earthquakes. A probabilistic safety assessment methodology considering the slope collapse (Slope PSA) has been developed as a part of seismic PSA at Japan Nuclear Energy Safety Organization (JNES). This method consists of slope collapse hazard evaluation, fragility evaluation (evaluation of secondary influences on nuclear facilities) and system reliability analysis. In the slope collapse hazard evaluation, probabilities of slope stability, failure modes, collapse behavior, rock reach area and shock force to nuclear facility are analyzed and calculated. This report describes the slope collapse hazard evaluation procedure and sample calculations for a model slope, and also results of parametric studies for the rock block behavior analysis. (authors)