Development of a FT modeling method for initiating event frequency estimation

We developed a Fault Tree (FT) modeling method to estimate the initiating event frequency by reflecting a systems' configuration change and to handle it directly in the Core Damage Frequency (CDF) FT. In the case of obtaining the initiating event frequency through the FT analysis, we have used a complicated estimation process in the existing Probabilistic Safety Assessment (PSA) as follows: Estimating the each initiating event frequency through the FT analysis and, Putting the initiating event frequency estimated into the FT for CDF and, Estimating the CDF frequency through the quantification of CDF FT However, this means that it is necessary to perform several quantifications to obtain the initiating event frequency in case that a systems' configuration change. A component failure related to the initiating event is modeled in duplicate in the fault tree for the initiating event frequency estimation and for the CDF estimation. Therefore, we might have a problem with the estimation of the importance for the component because we quantify separately these two fault trees. Thus, in this paper, we propose a method to quantify the fault tree for the initiating event frequency and the CDF simultaneously