U.S. NUCLEAR REGULATORY COMMISSION RESPONSE TO SEISMIC HAZARD AT OPERATING NUCLEAR POWER FACILITIES IN THE UNITED STATES FOLLOWING EVENTS AT FUKUSHIMA DAI-ICHI (Invited Presentation)

The Nuclear Regulatory Commission (NRC) established the Near-Term Task Force in response to the earthquake and subsequent tsunami that resulted in the accident at the Fukushima Dai-ichi Nuclear Power Plant and identified three recommendations related to seismic hazards at operating nuclear power facilities. Recommendation 2.1 (R2.1) requires a licensee to reevaluate seismic hazards based on present-day NRC requirements and guidance. To address R2.1, licensees in the western US (WUS) are performing Senior Seismic Hazard Analysis Committee (SSHAC) Level 3 analyses. The SSHAC process should incorporate any new pertinent geologic data that are available in addition to collection of new geologic data. Central and eastern US (CEUS) licensees will reevaluate the seismic hazard using the regional SSHAC-based CEUS seismic source characterization model. CEUS licensees are not required to collect or incorporate new geologic data. All licensees will calculate ground motion response spectra to compare to the existing safe shutdown earthquake ground motion for their plants. Based on results of this comparison, further risk assessments using either seismic margins analysis or probabilistic risk assessment may be needed. The NRC is working with industry to develop guidance for certain screening, prioritization and implementation issues related to seismic reevaluations and will endorse industry guidance or issue its own, as necessary. Recommendation 2.2 (R2.2) is a proposed rulemaking requiring licensees to reevaluate new and significant external hazard data every 10 years and determine how the data should be used. The NRC is also reviewing background information and assessing international experiences to support the technical basis for this rulemaking. Recommendation 2.3 (R2.3) requires licensees to perform seismic walkdowns of their plants. The NRC worked in cooperation with industry to develop walkdown procedures that will address equipment anchorages, the potential for adverse equipment interactions during an earthquake, and assess recent changes or updates to the facilities. The NRC will use the results of R2.1 and R2.3 to both inform the R2.2 rulemaking and determine whether the design basis hazards or protection features need to be updated to ensure adequate protection against the reevaluated hazards.