Evaluating Risks of Multi-unit Nuclear Sites: Insights and Considerations

Probabilistic safety assessment (PSA) is a valuable tool for evaluating the safety of nuclear power plants (NPPs). With the advent of evolutionary small modular reactors (SMRs) and the potential for multi-unit nuclear sites, it becomes essential to develop a comprehensive PSA approach that considers the hazards and safety challenges specific to such installations. The current paper provides a critical synthesis of the existing PSA methodologies and expands upon them by introducing a multi-unit PSA (MUPSA) framework designed to address the complex risks associated with multi-unit NPP sites. Recognizing the limitations of current PSA practices, this paper delves into the unique challenges posed by the proximity of units and the potential for cascading events. The paper lays out foundational assumptions for MUPSA, emphasizing the need for a holistic approach that captures the intricacies of multi-unit dependencies and shared system responses. A structured MUPSA model is proposed that integrates these considerations, offering a step-by-step approach that enhances the predictive capability of safety assessments in a multi-unit context. Practical considerations for implementing the MUPSA model are discussed, highlighting how this model can be adapted to real-world scenarios and contribute to the refinement of safety protocols. In conclusion, the paper underscores the contributions of the MUPSA framework to the broader field of nuclear safety and risk assessment, providing a pathway for more robust safety management in the burgeoning landscape of complex multi-unit nuclear installations. The insights presented in this paper aim to contribute to the safe deployment and operation of multi-unit nuclear sites and support the licensing of evolutionary SMRs.