Method of Analyzing Criteria for Primary Containment Vessel Venting and Protective Measures for Public Risk Reduction

Abstract

Primary containment vessel (PCV) venting is one of the mitigating measures for severe accidents (SAs) on nuclear power plants. To prevent PCV failure, PCV venting will be conducted through judgement by responsible persons when the plant reaches relevant SA conditions. From the viewpoint of public safety, the judgement should be performed considering progress in public evacuation. This study is carried out to investigate effective PCV venting criteria in terms of public risk reduction and to propose protection measures against a delay in public evacuation caused by adverse conditions. To quantify the degree of judgement on PCV venting, the analysis method used here considers fuzzy inference, which makes it possible to formalize human reasoning. The analysis links both the thermal-hydraulic progression during an SA and protection measures to the discussion on interfaces between defense-in-depth levels 4 (control of SA conditions) and 5 (mitigation of a radiological consequence).