Considerations for Implementing Earthquake Response Guidelines to Nuclear Power Plants

For the first time in Korea, four units of the Wolsung NPPs have experienced a manual shutdown due to the 2016 Gyeongju earthquake of M5.8 because the peak ground acceleration (PGA) of the ground motions that were recorded at the plant site during the earthquake exceeded the OBE acceleration. Based on this experience in Korea, the Nuclear Safety and Security Commission (NSSC) has decided to revise an earthquake reporting system. A direction of implementation is discussed in this paper. The revised plant response guidelines to an earthquake require a rapid decision-making. The OBE exceedance should be evaluated within two hours and a manual shutdown of the plant should be determined within four hours following an earthquake. To satisfy these requirements, it is recommended that adequate and plant-specific technical information be provided for operators and on-site personnel to estimate the physical conditions of vulnerable SSCs and determine if a shutdown of the plant is required.