Evaluating the Seismic Diversity and Robustness of Nuclear Power Plants

The occurrence of common cause failures poses a critical threat to the seismic safety of nuclear power plants. The installation of diverse components such as isolation systems is believed to be a promising strategy to avoid such failures, especially in the context of disasters such as the Fukushima accident. Although the effectiveness of implementing diverse components in enhancing the seismic safety has been qualitatively evaluated, a quantitative examination considering the system reliability has not been performed yet. Therefore, in this study, a method to quantitatively evaluate the effectiveness of diverse components in preventing failures was developed. The definitions of the seismic diversity and robustness in different domains were examined. Subsequently, the proposed approach was used to evaluate the effectiveness of the seismic diversity strategy on enhancing the system reliability at 11 sites in Japan. Moreover, the seismic robustness of the system was assessed. The results indicated that the optimal constitution of diverse components depends on the seismic environment at each site, and the seismic diversity is a more effective strategy compared to that of multiplicity to ensure the seismic safety of nuclear power plants.