Under Revised Quake Estimates, Dozens of Nuclear Reactors Face Costly Safety Analyses

Owners of at least two dozen nuclear reactors across the United States have told the Nuclear Regulatory Commission that they cannot show that their reactors would withstand the most severe earthquake that revised estimates say they might face.

The earthquake reassessment has been a mixed bag; it showed that in many locations, the chance of an earthquake in which the ground shakes relatively slowly — the most damaging kind — was smaller than previously estimated.  High-frequency earthquakes, in which the shaking back and forth happens more than 10 times per second, was higher for some locations.  Those high-frequency quakes do not threaten big components, but some engineers say they can cause electric switches to change position, among other problems.

A second Entergy plant, Pilgrim, in Plymouth, Mass., will also require more analysis, Mr. Drake said.  Two industry experts said that across the central and eastern United States, plants at 24 sites reported that the new earthquake threat was larger than what they were designed to face.  The commission has not released a total yet.

Under Revised Quake Estimates, Dozens of Nuclear Reactors Face Costly Safety Analyses