Updated Earthquake Risk Assessment Required at Nuclear Plants

By TAMMY WEBBER | February 4, 2012

Nuclear plants throughout the central and eastern United States must be reassessed within four years to determine how well they might withstand earthquakes, including plants in Illinois and Iowa where new geological data suggest earthquakes could be more frequent and intense than previously believed, the Nuclear Regulatory Commission said.

The commission this week released an updated seismic risk model that plant operators must use to recalculate risks. The model has been in development for four years but took on a greater urgency after last year’s nuclear disaster in Japan following an earthquake and tsunami, said Viktoria Mitlyng, a Lisle, Ill.-based spokeswoman for the NRC.

Exelon Energy, which operates Illinois’ 11 nuclear reactors, believes it will take three to five years to complete studies for all of its plants before determining whether any need upgrades, but “would not expect to incur significant costs as a result,” said spokesman Marshall Murphy. He said the company’s units already are designed to withstand an earthquake of 6.0 to 6.9 on the Richter scale.

Murphy said the plants also are built to withstand “variety of other significant natural events and … are constructed in a safe manner in which there are numerous redundant safety systems in place.”

Exelon’s Dresden Nuclear Power Plant, about 65 miles southwest of Chicago, and NextEra Energy’s Duane Arnold Energy Center, just north of Cedar Rapids, Iowa, are in areas where scientists believe that seismic risk is slightly greater than indicated by past data, Mitlyng said.

Both also use Mark I boiling-water reactors, which are the same model as the Fukushima Daiichi plant that failed in Japan, a design that has been a concern to some environmentalists and scientists in this country.

David Lochbaum, director of the nuclear safety project for Union of Concerned Scientists, said spent fuel rods at those plants are stored above and outside of the reactor containment chamber instead of at ground level, and systems used to cool the rods were not built to withstand earthquakes. He said the assumption when the plants were built was that the rods would be shipped off-site for burial. But that didn’t happen after a U.S. plan to bury spent rods in Nevada’s Yucca Mountain was stalled.

If the storage area or piping were to rupture, it might be more difficult to keep the rods covered with water, which is required to protect them “because they’re up in the attic,” Lochbaum said, adding that, “I don’t want to imply that Dresden is a house of cards.”

Exelon officials have said all their reactors are safe.

A spokeswoman for the Arkansas Nuclear One plant near Russellville, Ark., said officials will review the new seismic model to determine if upgrades are needed, but the plant doesn’t anticipate major changes. She said the plant was designed and built to withstand the largest earthquake historically reported in the area, plus a margin of safety.

“Our original design is pretty solid,” Gregory said. “We feel like we’re safe today and we’ll be safe tomorrow, but we constantly reevaluate our processes.”

However, Gregory cautioned that it’s too early to tell whether the plant, which is operated by Entergy, will have to make any tweaks based on the new seismic model.

“The challenge is going to be simply meshing this with the time expectations that the regulator has,” said Steve Kerekes, a spokesman for the Nuclear Energy Institute, a Washington-based policy group. “It’s not going to be a surprise to them because this is an issue that’s been percolating for many years now.”

In Kansas, Jenny Hageman, spokeswoman for the Wolf Creek Nuclear plant, said it’s unclear if there will be a change in risk for Wolf Creek, about 90 miles southwest of Kansas City. She said Wolf Creek is designed to withstand an earthquake equivalent to the maximum potential earthquake in the region, with an additional safety margin.

“Wolf Creek will use the information from the new seismic model in evaluating seismic hazards as part of our ongoing efforts to incorporate lessons learned from events at the Fukushima Daiichi nuclear power plant,” Hageman said.

Scott Bond, manager of nuclear development for Ameren Missouri, also did not anticipate major changes in risk for the company’s Callaway Nuclear Generating Station in central Missouri.

“What we would stress here is really this is not associated with Fukushima,” Bond said. “This was ongoing. It really is just part of the constant reexamination of nuclear safety by the industry and the regulators.”

The Associated Press reported in September that the NRC believed a fourth of America’s reactors might need modifications to make them safer in the event of an earthquake. The report, based on a preliminary AP analysis of government data, came after the largest earthquake to hit Virginia in 117 years appeared to exceed what the North Anna nuclear power plant was built to sustain. The plant northwest of Richmond was shut down for three months after the Aug. 23 quake caused peak ground movement about twice the level for which the plant was designed.

(Associated Press Reporters Jeannie Nuss in Arkansas and Maria Sudekum in Missouri contributed to this report.)

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