U.S. nuclear power companies will be directed to reassess their reactors' vulnerability to an elevated threat from earthquakes east of the Rockies, using new computer models and seismic data released today by an industry and government project.
The Central and Eastern U.S. Seismic Model incorporates four years of research triggered by estimates that earthquake hazards centered in New Madrid, Mo.; Charleston, S.C.; and other fault areas could be worse than current nuclear reactors were designed to withstand.
The Nuclear Regulatory Commission ordered the review in 2005, concluding that while U.S. reactors remained safe, the possibility of increased seismic threats required more investigation.
The industry-backed Electric Power Research Institute (EPRI), the NRC and the Energy Department collaborated in preparing the new model and data, working with the U.S. Geological Survey, the Defense Nuclear Facility Safety Board and industry and academic experts. The new data replace models from 1998 and 1999.
The new model will enable plant operators to make site-specific estimates of the maximum ground forces likely to hit their sites during earthquakes, and then to calculate the likelihood that their reactors could be safely shut down, said Jeffrey Hamel, EPRI's manager on the project. The study's $7 million cost was shared by EPRI, DOE and the NRC. Reactors in the western United States will have to perform similar site-specific assessments, EPRI said.
Hamel said the updates are likely to identify increased hazards, but that will be only the first step in determining whether reactor upgrades are required.
Mandatory information requests in March
"We expect that the new model will result in a higher likelihood of a given ground motion compared to calculations done with previous models," he said. "You can't draw the conclusion from A to B that the risk has gone up at a nuclear plant. You have to take all that hazard information, those calculations, then transfer them to the site. Then the site-specific design and safety features have to be factored into an overall calculation to understand where it stacks up."
The NRC is expected to issue the new mandatory information requests in March. Drafts of the request are circulating in the industry now. It may be a year or more before the new seismic studies are completed, and if any plant retrofits are required, those actions would take more time, the NRC said.
The need to update seismic risks at U.S. reactors has been recognized for more than a decade; however, the NRC concluded that the uncertainties about the hazards did not pose a threat to public health that would require immediate action. The agency concluded in 2010, "Operating nuclear power plants are safe. The Safety/Risk Assessment confirms that the overall seismic risk estimates remain small for operating nuclear power plants and the current seismic design provides a safety margin."
With that qualification, the NRC began a new review of seismic hazards in 2005, entitled Generic Issue 199. It was far along when Japan was devastated by a magnitude-9.0 earthquake and tsunami last March, which resulted in a nuclear disaster at the Fukushiima Daiichi power complex. The GI-199 review was adopted as one of the NRC's post-Fukushima actions, and the NRC now will follow a stricter regulatory approach in evaluating industry responses that the earlier review called for, NRC spokesman Scott Burnell said.
The new study includes an extended "earthquake catalog," chronicling the history of earthquakes east of the Rockies between 1569 and 2008. The earlier study had covered the period from 1627 to 1985, Hamel said.
The North Anna experience
In addition to making advanced calculations of earthquake hazards from geological data and measurements of recent quakes, researchers searched old church and newspaper records for evidence of seismic events centuries ago, Hamel said. "Chimneys knocked down, church bells ringing [on their own]: Those kinds of observations in history are correlated to an intensity scale" to estimate their magnitude, he said.
The model was tested on seven sites selected because of their geological and seismic significance, Hamel said. They are not nuclear power plant sites. They are in central Illinois near New Madrid, Mo.; Chattanooga, Tenn.; Houston; Jackson, Miss.; Manchester, N.H.; Savannah, Ga.; and Topeka, Kan. The model will confirm increases in seismic hazards there, Hamel said.
The new model, with data through 2008, does not include the magnitude-5.8 earthquake in central Virginia last Aug. 12, which tripped the reactors at Dominion's North Anna nuclear plant. Ground motion at the site during the earthquake "exceeded levels for which the plant was originally licensed," Dominion noted. The NRC concluded that "safety system functions were maintained" and "reviews of the plant equipment, systems and structures did not reveal significant damage."
"North Anna experienced an earthquake larger than it was designed for, but the reason it came out so well is its owner voluntarily upgraded its seismic protection when they knew about the hazard in the early '90s," said David Lochbaum, director of the nuclear safety project for the Union of Concerned Scientists, in an interview last year with "Frontline."
The NRC had requested the industry to conduct seismic inspections in the 1990s, and the NRC summed up that effort in 2002, saying that 70 percent of the plants proposed improvements as a result of their seismic reviews. But the follow-through was left to the plant operators. The NRC noted that "in most cases, plants have not reported completion of these improvements to the NRC."
"The NRC didn't require owners like [those] of North Anna and others to fix it," Lochbaum said. "But that was a billion-dollar asset that could become a billion-dollar liability if you don't protect it, so North Anna's owners voluntarily upgraded its seismic protection." Owners of two dozen reactors have not done the same, and have not yet been required to, he added. "They're relying more on luck than they should be."
Correction: The 1998 and 1999 models that the new computer models and seismic data are replacing were incorrectly identified as EPRI's in an earlier version.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500