Analytic method to break logical loops automatically in PSA

In Probabilistic Safety Assessment (PSA), when the fault trees of support systems are merged, logical loops are generated due to the mutual dependencies of support systems. KAERI (Korea Atomic Energy Research Institute) has developed a method to break such logical loops automatically. The developed method provides the criteria to identify parts of the fault trees that cause the logical loops. Using a top-down approach, the logic of fault tree is expanded. During the expansion, the terms that cause the logical loops are identified based on the given criteria and are deleted automatically. By using the above procedure, we will get the new logic of fault trees without the logical loops. This method is implemented in KIRAP (KAERI Integrated Reliability Analysis Package) and tested for sample cases. The results obtained by the developed method are compared to ones obtained by the conventional method that has been used previously to break the logical loops in PSA.