Nuclear regulators said Thursday they want the operators of all 104 U.S. commercial reactors to conduct new assessments of their facilities' vulnerability to earthquake damage.
The decision was motivated by the increased awareness that seismic risks may have been underestimated by nuclear-power industry and regulators in the past, especially for the central and eastern U.S.
A draft requirement for the new assessments, released Thursday for public comment by the U.S Nuclear Regulatory Commission, has been in the works for six years, but gained urgency with the nuclear accident at Japan's Fukushima Daiichi nuclear installation in March and smaller earthquakes in Virginia in the past two weeks that sidelined two reactors.
On Thursday, a 3.4-magnitude aftershock was felt at the North Anna nuclear power station, which was shut down Aug. 23 after suffering damage from a 5.8-magnitude earthquake, the biggest in Virginia in more than a century. Owner Dominion Resources Inc. recently told the NRC that it believed the initial quake might have exceeded the level for which the nuclear plant was designed.
The Nuclear Energy Institute, a trade group that represents owners of nuclear plants, said it was analyzing the NRC proposal and would respond by Oct. 31, the public comment deadline.
In the late 1990s, the NRC told plant owners to take a fresh look at seismic issues. In a 2002 report, the NRC said that almost all plant owners reported "no plant vulnerabilities" beyond those already taken into account when plants were built.
In 2005, the NRC said that applications for new reactors—often proposed for the same sites as existing reactors—included earthquake-risk assessments that were worse than previously understood in several cases, and suggested some existing plants could be in jeopardy.
At that time, the NRC stepped up efforts to develop a better seismic risk model for the central and eastern U.S., working with the U.S. Geological Survey and the Electric Power Research Institute in Palo Alto, Calif. A new model is expected to be available next year that utilities would use in their new assessments.
Thursday's proposal would give plant operators up to two years to finish their work. It is expected to be a difficult task, because it will require plant operators to get intricate details on many components and systems not previously analyzed in such great depth.
Once the NRC has updated seismic reports in hand, the agency will decide whether to order upgrades. The effort to enact those changes, however, could be hampered by a federal requirement that any costly upgrades be justified by commensurate, tangible improvements in safety. Since earthquakes are hard to predict, that could become contentious.
Thursday's proposed rule comes in the midst of continuing analysis of earthquake damage at the North Anna plant. This week, the NRC said the quake, centered nearby, shifted several 110-ton casks that store used fuel.
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