大規模システムの安全性評価(<特集>大規模システムの安全性)

抄録

This paper introduces the basic concept of Probalilistic Risk Assessment (PRA) , which evaluates the safety of large-scale systems. Firstly, the use of probability concept in the design of technical system is briefly reviewed, and then the concept of risk is defined. Then, PRA procedure is reviewed which is composed of risk analysis and risk assessment. Risk analysis obtains accident sequences and estimates their probabilities and effects using Event Tree Analysis and Fault Tree Analysis. Risk assessment examines whether the risk analysys result satisfies the risk acceptance level. If the risk acceptance level is not achieved, some measure must be taken to reduce the risk. PRA continues until the risk acceptance is achieved. Human plays an important role not only in the safety assessment, but also in accident sequences leading to system failure. Finally, the human-related problems in PRA are discussed from three viewpoints: the definition and evaluation of probability, the risk acceptance, and human error analysis.