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New Earthquake Computer Model - Seismic Risk : Nation's Nuclear Reactors
The News - Current Events
January 31, 2012
earthquake risk

Research suggests the risks posed to the nation's nuclear reactors may have been underestimated and therefore could be worse than the power plants were designed to withstand.

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.  [sciam]

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.

 
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