A method to improve cutset probability calculation in probabilistic safety assessment of nuclear power plants

In order to calculate the more accurate top event probability from cutsets or minimal cut sets (MCSs) than the conventional method that adopts the rare event approximation (REA) or min cut upper bound (MCUB) calculation, advanced cutset upper bound estimator (ACUBE) software had been developed several years ago and shortly became a vital tool for calculating the accurate core damage frequency of nuclear power plants in probabilistic safety assessment (PSA). Usually, the whole cutsets in the industry PSA models cannot be converted into a Binary decision diagram (BDD) due to the limited computational memory. So, the ACUBE selects the major cutsets whose probabilities are larger than the others, and then converts the major cutsets into a BDD in order to calculate more accurate top event probability from cutsets. This study (1) suggests when and where the ACUBE should be employed by predicting the amount of overestimation of the top event probability depending on the cutset structure, (2) explains the details of the ACUBE algorithm, and (3) demonstrates the efficiency of the ACUBE by calculating the top event probability of some PSA cutsets. (C) 2014 Elsevier Ltd. All rights reserved.