Don't worry, the folks who operate nuclear power plants near Baltimore told us after a Japanese earthquake caused meltdowns and large radioactivity releases there.
We don't have severe earthquakes on the East Coast.
That proposition got tested Aug. 23, when the 5.8-magnitude quake centered in Virginia rattled buildings as far north as Toronto.
The closest nuclear plant to Baltimore is Exelon Corp.'s Peach Bottom facility on the Susquehanna River, 45 miles away. Peach Bottom is built to withstand ground movement equal to an earthquake registering 6.1 on the Richter scale, Exelon said in April, after the Japan catastrophe.
That sounds kind of close, even allowing for the logarithmic nature of the earthquake scale, in which each increment of 1.0 represents an order of magnitude. (A measurement of 6.0 represents shaking 10 times greater than that of a 5.0)
Exelon and Constellation Energy Nuclear Group, which owns the nuclear plant at Calvert Cliffs, about 75 miles south of Baltimore, play down the danger posed by last month's earthquake. Measurements at the earthquake's epicenter, company spokesmen say, don't represent what was going on at Peach Bottom or Calvert Cliffs.
But the plants' instruments showed significant ground movement, even if the readings were well within their published tolerances.
The Virginia earthquake and the Japan temblor have prompted a needed examination of safety at all U.S. nuclear plants, but especially at Peach Bottom, which has a design similar to that of the Fukushima reactors in Japan. Peach Bottom's two units are on a list of 27 reactors flagged by the Nuclear Regulatory Commission as possibly needing better anti-earthquake defenses, the Associated Press has reported.
"There's a great deal of uncertainty about the seismic resistance of any nuclear power plant," said Edwin Lyman, a physicist at the Union of Concerned Scientists. The organization doesn't oppose nuclear power but monitors the industry closely.
Earth movement at nuclear plants is measured in ground acceleration and is expressed as a portion of gravity.
Peach Bottom was designed to withstand ground acceleration of as much as 0.12G, said Exelon spokeswoman Judy Rader, The Aug. 23 earthquake produced ground movement of 0.011G at Peach Bottom, less than a tenth of its engineering limits and not even enough to shut down the plant, she said. (The ground acceleration scale is not logarithmic.)
Calvert Cliffs, too, continued running after the earthquake — unlike two reactors at Dominion Resources' North Anna plant in Virginia that automatically tripped off. Ground acceleration at Calvert Cliffs during the quake was 0.036G. The plant is designed to withstand ground acceleration of 0.15G, spokesman Mark Sullivan said.
But measuring ground movement seems to be an uncertain science. Like Peach Bottom, North Anna is designed to withstand 0.12G. Dominion told the Nuclear Regulatory Commission that ground acceleration at North Anna "may have exceeded plant standards," reported the Free Lance-Star of Fredericksburg, but it hadn't reported a figure as of late last week.
"It seems there is some uncertainty about even understanding the relationship of [quake] magnitude and peak ground acceleration — even when the quake is nearby," Lyman said.
There was no significant damage reported at North Anna.
Internal NRC documents obtained by the Union of Concerned Scientists a few months ago reveal doubts among the agency's staff about whether U.S. nuclear plants are sufficiently protected from earthquakes and terrorist attacks. Some new strategies to deal with accidents "have really not been reviewed to ensure that they will work," one NRC email said.
Peach Bottom's reliance on a nearby hydroelectric dam for emergency electricity to run critical cooling pumps is another a cause for concern, Lyman said: "In a large seismic event, you may not be able to count on backup power from hydroelectric."
(Calvert Cliffs has backup diesel generators inside earthquake- and flood-resistant buildings.)
The NRC recently revised its assessment of nuclear plant vulnerability to earthquakes. Tops on the list are Entergy's Indian Point units in New York, which have a one-in-10,000 chance per year of earthquake-induced damage to the nuclear core, according to the agency.
Peach Bottom is No. 34, with a one in 41,667 chance. Calvert Cliffs is No. 57, with a one in 83,333 probability. While the odds of catastrophe at either plant are very long, they're significantly shorter than they were before the agency's revisions.
"There is still a lot of uncertainty that makes me nervous," Lyman said.
Last week, in a note in the Federal Register, the NRC said "it is necessary to re-examine the level of conservatism in the determination of the original seismic design estimates" for all nuclear plants.
An earlier version of this story incorrectly named the owner of Indian Point nuclear plants in New York. The Sun regrets the error.