Development of the methods to change the fault tree logic structure according to the changing conditions of a system in a one top PSA model

Korea Atomic Energy Research Institute (KAERI) has developed two methods to handle the problems when a one top PSA model used in a risk monitor was developed that could not match the structure of house trees. These two methods are (1) the development of a special gate called a ‘condition gate’ and (2) the implementation of an If-Then-Else (ITE) logic in the PSA model structure. The proposed methods were applied to an example case, e.g., the station blackout (SBO) accident sequences of a one top PSA model. It was demonstrated that these methods could properly handle the complex condition changes of a system during the SBO accident sequences by using the proposed methods.