(A) study on the influence diagrams for the application to containment performance analysis

Abstract

Influence diagrams have been applied to containment performance analysis of Young-Gwang 3\&4 in an effort to explicitly display the dependencies between events and to treat operator intervention more generally. This study has been initiated to remove the three major drawbacks of the current event tree methodology: 1) Event tree cannot express dependency between events explicitly. 2) Accident Progression Event Tree (APET) cannot represent entire containment system. 3) It is difficult to consider operator intervention with event tree. To resolve these problems, a new approach, i.e., influence diagrams, are proposed. In the present work, the applicability of the influence diagrams have been demonstrated to YGN 3\&4 containment performance analysis and an assessment of accident management strategies. To show that the results of the application of influence diagrams are reasonable, results are compared with that of YGN 3\&4 IPE. Both results are in good agreement. In addition, influence diagrams are used to assess two accident management strategies: 1) RCS depressurization, 2) cavity flooding. Cavity flooding has a favorable effect to late containment failure and basemat melt-through, and depressurization of RCS is good for steam generator tube rupture. However, early containment failure probability is worse in both cases. As a result of the present study, it is shown that influence diagrams can be applied to the containment performance analysis.