Application of Large Event Tree/Small Fault Tree Approach in Evaluation of MNPP Feedwater Lines Large Break Accident

The principle of large event tree/small fault tree approach,the gist and rule for small event classification,and the establishing rule and modularization of large event tree are introduced.The dominant contributors to the core damage and the weakness of the system were identified through studying the Probability Safety Assessment（PSA） by large event tree/small fault tree approach for the feedwater lines large break accident of MNPP in full power condition.The result of application indicates that the approach is with the advantage of directly representing the relativity between the support system and front system and estimating the importance of the support system.