Due to higher earthquake risk in the region, the U.S. Nuclear Regulatory Commission is requiring three Pennsylvania nuclear reactors to conduct in-depth reassessments of their ability to withstand larger earth tremors.
FirstEnergy's Beaver Valley Units 1 and 2, in Shippingport, Beaver County, and Exelon's Three Mile Island Unit 1, south of Harrisburg in Dauphin County, are among nine commercial nuclear reactors in the eastern U.S. and two dozen nationwide that must conduct the re-evaluations and issue reports to the NRC by the end of the year.
"Based on the latest seismic data, the risk of earth movement is higher in the region, and more testing and analysis is warranted," said Neil Sheehan, an NRC spokesman. "That doesn't mean the plants are unsafe. Earth movement is still a low probability event there, but they have to do further evaluation of what the risks would be."
The initial seismic reviews at all 100 of the nation's commercial nuclear reactors were ordered by the NRC in 2012 based on the U.S. Geological Survey's updated 2008 national seismic risk assessment, and following the massive earthquake off the coast of Japan in March 2011, which triggered a tsunami that severely damaged the Fukushima nuclear reactor.
The 2008 USGS seismic risk assessment showed more of an earthquake risk in Pennsylvania and other Mid-Atlantic states than was previously understood, Mr. Sheehan said.
"Because of the new data available from the USGS, we have a greater understanding of where faults are, and some areas could be prone to more earth activity," he said.
Jennifer Young, a FirstEnergy spokeswoman, said the Beaver Valley Units 1 and 2 were built in the 1970s and designed to withstand the seismic risks known at the time, plus a margin of protection beyond that.
"The new ground motion levels by the USGS are slightly above what [Beaver Valley] was designed for," Ms. Young said. "But we expect there won't be any need for major modifications. We may find a need for some enhancements, but we don't expect to find any big, new need. The plants are very robust and well designed to have more than sufficient protections."
She said the seismic risks in the northeast region have increased more than in other regions of the nation, mainly because of new higher seismic risk models for an earthquake centered hundreds of miles away in the New Madrid Seismic Zone, along the borders of Missouri, Arkansas and Tennessee.
That fault spawned big earthquakes in December 1811, January 1812 and February 1812 that caused widespread devastation. Estimates say the quakes would have registered between magnitude 7.5 and 7.7. By comparison, the 1906 San Francisco earthquake that killed 3,000 people and leveled 80 percent of the city had an estimated magnitude of 7.8.
Mark Petersen, USGS project chief of the 2008 National Seismic Hazard Maps in Golden, Co., said new ground motion records and additional geological studies of the New Madrid fault show higher recurrence rates than previously thought.
"Because of what happened with the New Madrid in 1811-1812," he said, "we're more worried about big earthquakes in those areas in the future."
He said new USGS seismic risk maps are due out in September and are expected to show slightly higher seismic risks than the 2008 maps.
Don Hopey: email@example.com or 412-263-1983.