On improving seismic risk and cost for nuclear energy facility based on multi-objective optimization considering seismic correlation

Currently, the system, structure, and component (SSC) seismic design and seismic probabilistic safety assessment (SPSA) process for the nuclear energy facility are performed individually, thus seismic risk reduction and cost efficiency cannot be pursued. Accordingly, this study proposes a method to determine the seismic design margin of SSCs of nuclear research reactor (RR) by minimizing seismic risk and cost simultaneously. To concurrently minimize the two conflicting goals of risk and cost, a multi-objective optimization (MOO) method is introduced. Also, such a method includes considering seismic correlations between SSCs for the accurate risk assessment. An improved sampling-based seismic risk assessment technique is proposed and combined with the MOO method to efficiently consider the seismic correlation between SSCs. As a result, Pareto-optimal solutions which minimized the seismic risk and cost of the existing RR were derived by applying the proposed method. These optimal solutions reduced up to 25% in seismic risk or up to 30% in cost compared to the existing one. Also, the proposed sampling-based risk method secured efficiency compared to the existing method. Consequently, the novelty of this study lies in the development of a method for determining the seismic margin of the SSC design based on the multi-objective optimization technique combined with the enhanced SPSA, and the improvement of costs and risks to the existing RR.