Workers inspecting the reactor containment building at the North Anna nuclear plant in Mineral, Va., after a quake last summer. The temblor proved stronger than the plant was designed to withstand, causing minor cosmetic damage and unhooking the plant from the electric grid.
With the release of a computer model of all known geologic faults east of Denver, nearly all of the nuclear power plants in the United States are about to embark on a broad re-evaluation of their vulnerability to earthquakes. The new mapping is the first major update of the fault situation for plants since 1989.
The map has been in preparation since 2008, well before the earthquake and tsunami that caused three meltdowns at Fukushima Daiichi in Japan last March or the quake near Mineral, Va., last summer that shook a twin-reactor plant beyond the degree expected. Still, those events have lent urgency to the effort to assess the American plants’ ability to withstand quakes.
The new study does not calculate the risk of damage from an earthquake or even specify how much ground motion is likely at the reactor sites. That work is left to the plants’ owners, supervised by the Nuclear Regulatory Commission.
The industry began to realize after the Fukushima disaster that engineers did not have a strong understanding of which structures and systems at the plants were most vulnerable.
The quake in Mineral, Va., caused only cosmetic damage to Dominion’s plant, known as North Anna, even though the ground motion exceeded what the plant was designed to withstand. But the plant did lose access to power from the grid, a safety concern, when a tall ceramic insulator holding up a power cable broke after the shaking started.
“The model is the first step,’’ Scott Brunell, a spokesman for the Nuclear Regulatory Commission, said of the map. “We’re not going to be at the point of knowing whether plants have to do anything else for some time.’’
In 2007, the commission made a preliminary determination that 27 of 96 reactors in the central and eastern United States might need improvements to withstand earthquakes. In 2004, the United States Geological Survey said that the eastern United States was more likely to see major earthquakes than had previously been estimated, although that report was not specific to nuclear plants.
Plant owners will have to determine if the data released on Tuesday indicates that a quake will produce ground movement beyond what designers expected; after that, they will determine what if anything is likely to fail and what damage that might cause.
The computer model, which uses information from every known earthquake from 1568 to 2008, was developed by the Electric Power Research Institute, a nonprofit utility consortium, with help from the Department of Energy and the Nuclear Regulatory Commission.
Jeffrey F. Hamel, an earthquake expert at the research institute, said that analyzing the geology of the eastern and central United States was different from analyzing that of the West because the East is “a stable continental region.”
In the West, he noted, faults occur at the boundaries between tectonic plates, those great chunks of the earth’s crust. In the East, “intra-plate” faults cause quakes. “This is very challenging,” he said. “It’s hard to characterize intra-plate quakes.’’
Not everyone is pleased with the route that the commission is taking when it comes to future construction. David Lochbaum, a reactor expert with the Union of Concerned Scientists, said that the agency had already approved sites for new reactors and designs for new reactors based on computer analyses of earthquake hazards.
If considerable study is needed on the quake vulnerability of existing reactors, he argues, the uncertainty surrounding the soundness of future plants must be even greater. “How can we know more about the reactors that haven’t been built than the ones that have been built?’’ he said.