Case studies for evaluating conditional probabilities of external explosions

Abstract

Abstract In recent years international experience has shown that external hazards can be safety significant contributors to the risk for nuclear power plants because such hazards have the potential to reduce simultaneously the level of redundancy by damaging redundant systems. Therefore, effective protections against external hazards have to be accurately assessed applying deterministic, probabilistic or combined methodologies. With respect to the external hazard “explosion” – two different types of risky situations for the plant under consideration have to be investigated: the explosive material is available as a stationary source in the neighbourhood of the plant or the explosive material is mobile (i. e. by ships, rails or trucks). In the latter case, the situation changes with the varying distances. Moreover, the transport way could be a straight line or a bent which also has to be addressed in the calculations. Methods which can be applied to evaluate the probability of occurrence of an external explosion event are, e. g., fault tree analyses, event tree analyses and Monte Carlo simulations. Two case studies applying Monte Carlo simulations for assessing the probability of occurrence of external explosion events, given an accident with creation of an explosive gas cloud, are presented.