NRC sets seismic priorities

The US Nuclear Regulatory Commission (NRC) has drawn up a list of 21 reactor sites in central and eastern USA that must carry out in-depth analyses of updated earthquake risks as a matter of priority. The regulator says that all are considered safe for continued operation in the meantime.

The NRC has been reviewing updated earthquake hazard information submitted by the 60 reactor sites in the central and eastern region as part of its implementation of lessons learned from the 2011 Fukushima accident in Japan, which was triggered by an earthquake and the subsequent tsunami that far exceeded the design specifications of the plant. Using existing information, operating plant sites have re-evaluated the likely effects of earthquakes on their site. Of the 60 sites, NRC says 16 have demonstrated that their original plant designs would account for the updated hazards and require no further action.

Based on the findings of its review, the NRC has now set two priority lists for the completion of follow-on work to carry out detailed risk analyses based on the re-evaluations. The first list of 10 sites has been given until June 2017 to submit their detailed risk analyses, while the second list of 11 sites has a deadline of December 2019. All 21 sites on the priority lists have also been given until the end of this year to complete an "expedited approach" review to ensure that the plants' systems and key components, particularly cooling systems, could ensure a safe shutdown if an earthquake were to occur at a higher seismic ground motion than allowed for in their original design.

The NRC is still deciding whether a further 23 sites in the central and eastern regions, including TVA's unfinished Bellefonte site, will also require a detailed risk evaluation. Those plants have also been given until December to complete an expedited approach assessment, but if the NRC rules they need to submit an in-depth risk analysis they will have until December 2020 to do so.

Each plant's recalculated hazard has been compared to the ground movement allowed for in the plant's original design process, and the NRC says the submittals show that the plants have "substantial safety margin above their designs' anticipated hazards". Eric Leeds, director of the NRC’s Office of Nuclear Reactor Regulation, said the regulator remained confident that all the plants could continue operating safely while detailed analysis and any identified actions are carried out. "If a plant’s new hazard exceeds the original design, the plant has to do a detailed analysis to determine any changes in accident risk from a quake. Plants must also do shorter-term work to see if they should enhance key safety equipment,” he said.

Similar re-evaluations are being completed for the three nuclear power plants in the more geologically complex western USA (Palo Verde in Arizona, Columbia Generating Station in Washington, and Diablo Canyon in California).

Researched and written
by World Nuclear News