Fuzzy probability based event tree analysis for calculating core damage frequency in nuclear power plant probabilistic safety assessment

Probabilistic Safety Assessment (PSA) is an established approach to evaluate safety and performances of nuclear power plants (NPPs). It consists of coupled fault tree analysis (FTA) and event tree analysis (ETA). FTA is used to graphically model possible failure scenarios of the evaluated safety systems and quantify their occurence likelihoods. Meanwhile, ETA is used to graphically show event sequences leading to core damage and quantify their frequencies. Fuzzy concept has been introduced and integrated into FTA to deal with uncertainties raised in basic event reliability evaluation when related historical failure data is limited, such as fuzzy probability – based fault tree analysis (FPFTA). To be coupled with ETA, uncertainties modeled in FPFTA need to be propagated into the quantification of core damage frequency (CDF). The motivation of this study is how to propagate uncertainties raised in FPFTA into the quantification of CDF in NPP PSA. Therefore, the objective of this study is to develop a fuzzy probability – based event tree analysis (FPETA) to assess CDF in NPP PSA. An illustrative case study is provided to demonstrate the feasibility and the applicability of the proposed FPETA. The results have confirmed that proposed FPETA could be used as a reasonable alternative for conventional ETA to quantify CDF when probability distributions are not available. Furthermore, the results also demonstrate that the proposed FPETA can be coupled with FPFTA in NPP PSA.