Multi-objective-based seismic fragility relocation for a Korean nuclear power plant

An optimal risk-informed seismic fragility relocation is proposed for structures, systems, and components (SSCs) of nuclear power plants (NPPs) that mitigates the core damage risk of the NPP and raises the cost performance. The proposed approach employs a seismic probabilistic safety assessment technique to effectively distribute seismic fragilities of SSCs from the perspective of overall plant risk. The main objectives of the optimal seismic fragility relocation are to mitigate the core damage risk and minimize the total cost for the SSCs of the NPP. To deal with such conflicting purposes, a genetic algorithm-based multi-objective optimization scheme is adopted. This approach systematically obtains a set of Pareto optimal solutions that are neither inferior nor superior to each other. The process for choosing the most appropriate seismic fragility distribution plan from the optimal front of Pareto solutions is also discussed with an emphasis on the study of the uncertainty quantification on such optimal Pareto solutions. As an example for such an optimal fragility relocation study, this study considers a typical type of Korean NPP. The numerical results confirm that the proposed approach provides diverse optimal seismic fragility relocation plans which can effectively reduce the core damage risk as well as the cost compared to the current fragility distribution of this example NPP. Finally, the best optimal alternatives for the fragility relocation are selected based on the Pareto optimal solution's robustness of performances against their perturbations.