Development of integrated FEPs for safety case scenario development

To establish a deep disposal repository for high-level radioactive waste, it is crucial to develop a safety case, which is comprehensive evidence and arguments supporting the safety of a nuclear facility or activity. The development of safety cases is achieved by creating scenarios based on a comprehensive understanding of the disposal system. Scenarios are developed using Features, Events, and Processes (FEP) and must follow the rules of comprehensiveness, systematic approach, transparency, and traceability (rules for the scenario). Also, scenarios have to be developed in a way that the stakeholders understand the whole development process clearly. In this study, an intermediate step was introduced for the high-level radioactive waste management program to strengthen the rules for the scenario. An intermediate step was established through the integration of FEP. For integrating FEPs, we classified 268 NEA International FEPs into six classifications concerning the relationships between each FEP to scenario and safety objectives. Finally, we selected Repository system evolution FEPs as the target for integration because they can result in significant changes in system performance.