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Nuclear Regulatory Commission says accident models could be amiss

By Mike M. Ahlers, CNN
updated 8:23 PM EST, Fri February 17, 2012
STORY HIGHLIGHTS
  • The models may underestimate how much nuclear fuel would heat up during system failures
  • The commission is asking 11 U.S. nuclear power plants for more information
  • There is no immediate threat to public safety

Washington (CNN) -- The Nuclear Regulatory Commission has asked 11 nuclear power plants for information about the computer models they use to test different accident scenarios, saying those models may underestimate how much nuclear fuel will heat up during cooling system failures.

There is no immediate threat to public safety, said NRC spokesman Scott Burnell, but the commission said an error in the computer models may conceal a problem that could impact public safety in a disaster, such as a major earthquake that destroys the plant's main cooling water conduit.

The NRC's review could result in some nuclear plants being ordered to "dial back" their power-generating capacity to meet safety standards, Burnell said.

At issue is a phenomenon known as "thermal conductivity degradation," or TCD, the NRC said. TCD refers to the fact that nuclear fuel loses its capacity to transfer heat as it ages.

The NRC said it is concerned that some computer models may not account for TCD.

If the plants are not considering TCD, the possibility exists that fuel rods could heat up 100 degrees more than anticipated in an accident scenario, exceeding the 2,200-degree limit considered safe, the NRC said. That could damage the fuel rods' outer layer, leading to reactor damage, the NRC said.

"We need information from a few nuclear power plant licensees to maintain assurance that they can continue to operate safely with sufficient margin," Eric Leeds, director of the NRC's Office of Nuclear Reactor Regulation, said in a statement.

The NRC is seeking information from 11 nuclear power plants, all with the pressurized water reactor design. They are: Beaver Valley 1 and 2 in Pennsylvania, Braidwood 2 and Byron 2 in Illinois, Catawba 1 and 2 in South Carolina, Donald C. Cook 1 and 2 in Michigan, Kewaunee in Wisconsin, and McGuire 1 and 2 in North Carolina.

The plants have until March 19 to provide the information to the NRC staff.

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