A systematic framework to investigate the coverage of abnormal operating procedures in nuclear power plants

It is evident that the reliability of complex socio-technical systems, such as NPPs (nuclear power plants), is very critical for public safety. For this reason, the DID (defense-in-depth) concept has been adopted as a core principle to ensure the operational safety of NPPs. Regarding this, the provisioning of AOPs (abnormal operating procedures) is essential for implementing the DID concept. Unfortunately, since most AOPs were developed based on operational experience, it is not easy to investigate their coverage in a systematic manner. Therefore, in this study, a framework to identify the coverage of AOPs is proposed based on a SPV (single point vulnerability) model. As for the initial validation of the suggested framework, the coverage of OPR1000 (optimized power reactor 1000 MWe) units operating in the Rep. of Korea is analyzed. As a result, it is revealed that their coverage is about 63%. In addition, it is confirmed that one of the component failures distinguished from the proposed framework actually triggered an unexpected reactor trip event in an OPR1000 unit. Therefore, it is possible to expect that the proposed framework can be used as a practical tool to enhance the coverage of AOPs.