The nuclear energy industry is dedicated to working closely with the NRC to take the most appropriate steps, guided by science and facts, to improve our facilities’ ability to withstand earthquakes that are stronger than any on record at nuclear plant locations.
November 2012
In the wake of the Fukushima Daiichi accident in Japan, the independent U.S. Nuclear Regulatory Commission issued recommendations that require America’s nuclear energy facilities be able to withstand extreme natural events that may occur in the region where they are located, including earthquakes. The nuclear energy industry is dedicated to working closely with the NRC to take the most appropriate steps, guided by science and facts, to improve our facilities’ ability to withstand earthquakes that are stronger than any on record at nuclear plant locations.
Nuclear energy facilities are designed and constructed to withstand the maximum expected earthquake in their areas—and then some. Companies that operate nuclear energy facilities are confident in the robustness of plant designs and built-in margins of safety to withstand earthquakes as much as twice as strong as those for which the facilities were designed.
Real-world experience here and in Japan demonstrates that nuclear energy facilities can remain safe, even if they experience the strongest quakes ever in their locales.
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Dominion’s North Anna reactors in Virginia safely withstood a 2011 earthquake that was the largest ever in the region. North Anna was further protected against earthquakes and other potential disasters in the early 1990s after the NRC requested new evaluations of earthquakes that are stronger than the plant was designed to withstand. Hundreds of detailed inspections and numerous tests by Dominion engineers and independent seismic experts showed that North Anna did not suffer any significant damage from the earthquake.
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There was no damage to safety systems at the Onagawa nuclear power plant, the nuclear energy facility closest to the epicenter of the magnitude 9 earthquake in Japan in 2011, according to a two-week evaluation of the site by global independent experts.
The industry is committed to continuous learning—checking and rechecking every safety measure to make sure nuclear energy facilities are prepared. The U.S. nuclear industry is continually researching seismic zones and making adjustments based on new data to provide superior protection against even the most extreme earthquakes.
Thirty years of research on seismic issues is driving updated models for protection against extreme ground motion. The industry will use that information as it responds to the recent NRC request for updated seismic hazard evaluations.
A 2005 NRC study found that earthquake hazard evaluations using new probabilistic methods produced larger ground motion estimates than previous evaluations for some plants in the central and eastern United States. The study prompted the agency to launch a study to better understand the safety margins for potential earthquakes at these plants. In January 2012, the NRC, the Electric Power Research Institute and the U.S. Department of Energy released a new seismic source model that will help nuclear energy facilities determine how to best prepare for extreme earthquakes. The industry also is updating its ground motion models based on new data.
Industry’s Recommended Approach
To meet the NRC and nuclear energy industry’s shared goal of further understanding seismic risks and enhancing the capability of each nuclear energy facility to withstand earthquakes, the industry is proposing an augmented approach to seismic protection at each reactor site. This approach will prioritize efforts to focus first on operations critical to maintaining electric power and reactor cooling capabilities during and after an earthquake. A longer-term follow-up will feature more comprehensive seismic probabilistic risk analyses to evaluate the effects of increased ground motion estimates.
By using this science-based approach, all companies will know more about the seismic characteristics near their facilities and will begin making changes soon, if needed, to reflect the new information. The industry believes this approach will result in tangible safety benefits in the short and long term, including:
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proactive, near-term seismic evaluations
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expedited confirmation of the most critical seismic protection capabilities (protecting water storage tanks, electrical power sources, etc.)
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immediate steps to implement measures that maintain power and reactor cooling capability, even during extreme events
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a comprehensive approach and framework for performing long-term seismic evaluations
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additional enhancements that address broader seismic mitigation capabilities once the data and expert resources are available.
Near-Term Safety Enhancements
The nuclear energy industry is developing an enhanced seismic protection strategy that exceeds current standards to ensure facilities are protected while additional data is analyzed and longer-term assessments are conducted.
The short-term work would include:
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developing updated, site-specific seismic hazard estimates using new, state-of-the-art methods
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evaluating the seismic margin of equipment critical to maintaining power and cooling and upgrading that equipment to provide additional protection against earthquakes, if needed
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completing a number of first-mover seismic probabilistic risk analyses to guide the other longer-term evaluations.
Longer-Term Safety Benefits
In the long-term, resources that are currently allocated to vital facility operations and other industry priorities will be available to study data and develop a framework to evaluate and enhance seismic safety capabilities. This augmented approach would ensure that qualified seismic experts are available to conduct appropriate studies and evaluations at each reactor site.
The long-term phase would include:
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completing comprehensive seismic probabilistic risk analyses
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performing updated seismic evaluations of spent fuel pools
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implementing additional equipment upgrades, if appropriate, to further enhance safety.
The NRC’s recommended timeline for completing seismic probabilistic risk analyses by 2017 is challenging because of the complexity of the analyses and the limited number of specialized technical experts who can perform the studies. Complications also could arise from coordinating availability of resources at facilities that are already committed to other critical operational activities and NRC directives.
The nuclear energy industry and NRC share the goal of enhancing safety during possible extreme earthquakes. The industry is committed to upgrading facilities to ensure more robust safety against a range of extreme natural threats in the near term while relying on facts and science to determine the specific path forward. The industry’s augmented approach should allow companies to make meaningful safety enhancements sooner while still developing seismic probabilistic risk analyses that could provide useful information for longer-term decisions.