Qualitative Risk Analysis of Primary Containment Vessel Venting using STAMP/STPA

Abstract

Primary Containment Vessel (PCV) venting is one of the measures for mitigating severe accidents in a nuclear power plant. To prevent PCV failure, the PCV venting is conducted as judged by an authorized person in a plant when the plant reaches relevant severe accident conditions. From the viewpoint of public safety, the judgement should be performed with cooperation among relevant organizations such as the plant site, cabinet, regulator, and local government, considering the evacuation of residents. In this study, a system risk analysis is qualitatively performed to identify the hazard causal factors of PCV venting, focusing on interactions among systems including organizations using the System Theoretic Accident Model and Processes/System-Theoretic Process Analysis (STAMP/STPA), which assumes the accidents involve a complex and dynamic “process” and focuses on the interactions among humans, machines, and the environment. It is identified that STPA helps to find the broad interactions among organizations responsible for PCV venting, which has the potential to lead to an accident.