The Nuclear Regulatory Commission (NRC) on Tuesday urged owners of 62 nuclear power plants in the Central and Eastern U.S.—facilities housing 96 of the nation’s 104 commercial nuclear reactors—to reevaluate seismic hazards using a new seismic model and information from a recent report.
The Central and Eastern United States Seismic Source Characterization for Nuclear Facilities model and report released on Tuesday culminates a four-year $7 million effort by the NRC, the Department of Energy, and the Electric Power Research Institute (EPRI). It essentially replaces previous seismic source models used by industry and government since the late 1980s, the NRC said, and it would also be used to license 22 potential new nuclear sites in the region that encompasses portions of the U.S. east of longitude 105 degrees West.
Project participants collected and analyzed an expanded data set, including historical earthquake and geological data for the entire study region, from 1568 through 2008 to develop the new model. “The model can be used to calculate the likelihood of various levels of earthquake-caused ground motions,” the NRC said in a statement.
“Calculations with the new model are expected to result in a higher likelihood of a given ground motion compared to calculations done using previous models. These calculations, however, are not equivalent to a nuclear power plant’s overall risk. Plant operators must combine the information from the new model with a plant’s design and safety features to determine site-specific risks.”
Sample calculations using the new seismic model indicated that the largest predicted “ground motions” could occur in the vicinity of repeated large magnitude earthquake sources, such as such as New Madrid, Mo., and Charleston, S.C., the NRC warned. Other sources are Charlevoix (lower St. Lawrence); Cheraw Fault (High Plains in southeastern Colorado); Meers Fault (southwestern Oklahoma); Reelfoot Rift–Marianna (Marianna, Ark., 47 miles southwest of Memphis, Tenn.); Reelfoot Rift–Commerce Fault Zone (Tamms, Ill., to Qulin, Mo.); and Wabash Valley (Indiana and Illinois).
Though the Central and Eastern United States Seismic Source Characterization Project was part of NRC efforts to implement lessons learned from the 2011 Fukushima nuclear disaster, according to EPRI documents, the project was begun long before, in April 2008. The model does not take into account the August 2011 East Coast earthquake. “Should the model be updated again, the August 2011 Virginia earthquake will be included,” EPRI says.
However, it noted, “Because the range of uncertainties have been included in the model, it is unlikely that new earth sciences information will fall outside of that range. For example, the Virginia earthquake occurred within a region that had been recognized from past seismicity as being capable of future earthquakes (the region is called the ‘Central Virginia Seismic Zone’) and the size of the earthquake was smaller than the maximum earthquake magnitudes assessed for this region.”
The Central and Eastern U.S. is considered a stable continental region, EPRI adds, which is why the regional model could be applied to the nuclear reactors and facilities in this region. “Sites in the western United States will need to develop site-specific seismic source characterization models for their use,” it says.
Sources: POWERnews, NRC, EPRI