Development direction of design earthquake evaluation methodology for nuclear power plant sites considering the Gyeongju earthquake on September 12, 2016

Abstract:

The design earthquake (DE) of nuclear power plant (NPP) sites in South Korea is determined by considering the maximum ground motions expected at sites through geological and seismological characteristic evaluation within a radius of 320 km and detailed geological survey within a radius of 8 km from sites. The DE is evaluated in a deterministic way according to 10 CFR Appendix A to Part 100 U.S. Federal Act, a foreign regulation subject to the Nuclear Safety and Security Commission (NSSC) Notice No. 2017-15. In addition, the Korea Institute of Nuclear Safety (KINS) has required operators to conduct a probabilistic seismic hazard analysis to assess the effects of uncertainties accompanied in DE.

Meanwhile, the U.S. revised Federal Regulations in 1997 to allow the DE to be determined in a probabilistic way, and it has been applied to commercial NPP sites since 1997. To this end, the U.S. Nuclear Regulatory Commission issued the regulatory guide 1.208 to provide a performance-based approach to define the site-specific earthquake ground motion. Therefore, it is necessary to proactively review the domestic applicability of such a procedure to properly prepare for international trends.

Most of recent major earthquakes in Korea, such as M_L 5.8 Gyeongju earthquake (GE) on September 12, 2016, have occurred at faults that are not exposed to the surface area, and ordinary surface geological surveys alone have difficulties in identifying causative faults of such events. The NSSC is carrying out a project of 'Seismic source characterization of 2016 GE and re-evaluation of seismic safety regulation of NPP sites' from 2017 to 2021. The goal of the project is to predict the magnitude of the maximum earthquake potential and then to evaluate the maximum ground motions at nearby NPP sites. The KINS particpates in the sub-project to identify the applicability of the performance-based site-specific earthquake ground motion to domestic NPP sites and to study the DE evaluation considering the characteristics of causative faults of recent major earthquakes in South Korea. Through this, the DE evaluation methodology for NPP sites and related technical standards will be upgraded and revised.

This work was funded by the Korea Foundation of Nuclear Safety (No. 1705010-0420-SB130 and 1805020-0320-SB110).