WWER-1000 shutdown probabilistic risk assessment: An introductory insight

The probabilistic risk assessment has become an essential part of every plant's safety/risk analysis. In the past, regulations and safety assessments of nuclear power plants were traditionally concentrated on full power operation. However, because of the events that might potentially occur during low power and shutdown modes, the assessment of risk at these operational modes is now gaining more importance. In this paper, we concentrate on the initiating events as well as the sequence of events that lead to reactor core damage during the low power and shutdown operation modes of a typical WWER-1000 nuclear reactor, a Russian designed PWR. The accident scenarios and safety functions along with the front-line systems are discussed. Finally, event trees for the most important groups of initiating events and fault trees are developed