Top event probability evaluation of a fault tree having circular logics by using Monte Carlo method

The current quantification method using minimal cut set generation in a PSA (Probabilistic Safety Assessment) uses several approximations for practical reasons. The Monte Carlo approach can be used as a supplementary means to verify the results of the minimal cut set approach. A new quantification algorithm using Monte Carlo sampling has been developed to handle a fault tree having circular logic. As a pilot application, two event trees of loss of off-site power and station blackout for a nuclear power plant have been quantified using the presented algorithm, which shows large conservatism in the conventional fault tree quantification method.