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Regulators say flood barriers may not protect TVA's nuclear plants

9:36 AM, Jan 26, 2012   |    comments
The cooling towers at TVA's Sequoyah Nuclear Plant in Soddy-Daisy rise above the trees near a residential neighborhood / AP
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By Anne Paine, The Tennessean

Sand baskets that the Tennessee Valley Authority installed at dams to protect its nuclear plants from a worst-case flood could fail, according to a federal nuclear oversight group.

The Nuclear Regulatory Commission said the baskets are not capable of standing up to the impact of debris barreling down the Tennessee River in a massive flood.

"There is potential for this debris to damage the baskets or push the individual baskets apart, causing a breach," an NRC letter dated Wednesday to TVA says. "There would be no time to repair the baskets because the flood would already be in progress."

Still, the baskets are considered adequate for the short term.

The sand-filled, wire mesh baskets were placed around Cherokee, Fort Loudon, Tellico and Watts Bar dams and earthen embankments to raise them a few feet after it was determined.

Ray Golden, a TVA spokesman, said the letter about the sand baskets, which are considered a temporary measure, had just been received.

"We'll have to evaluate the NRC's response to us and determine what the next steps are," he said.

The electric power producer had told the NRC in 2010 that a project to resolve flooding concerns would extend into 2016 with dam modifications handled by the U.S. Army Corps of Engineers. Lack of federal funds is expected to cause more delay.

The NRC says the baskets will have to do for now.

"It's acceptable as a temporary fix," said NRC spokesman Joey Ledford.

Browns Ferry, 100 miles south of Nashville, and Watts Bar, 60 miles southwest of Knoxville, are considered to have enough safety margin.

"It's Sequoyah that might have the most problems," he said, referring to the nuclear plant about 20 miles northeast of Chattanooga.

"We're talking basically historic floods. There's a lot of safety factors already in play. I'm sure if there were any danger of flooding, plants would be shut down and secured."

At Sequoyah, diesel generators and spent fuel pool cooling pumps could be affected, the letter said. Having backup power and keeping highly radioactive waste cool at plants are critical and were the major reason for a disaster that began last year after an earthquake and tsunami at the Fukushima nuclear complex in Japan.

"We believe the plant is safe," Golden said. "If there is an opportunity to make it safer, we will pursue it."

While the chances of the worst-case flood as envisioned is "extremely remote," TVA wants to ensure against all possibilities, he said.

The problem that the dams, as originally built, would not withstand what is classified as a "probable maximum flood" came to light as TVA did preliminary work toward completing Bellefonte Nuclear Plant about 110 miles southeast of Nashville.

NRC cited the power producer with three violations in 2008 for shortcomings that included an inability to provide the flood calculations done when it first won approval to build its riverside nuclear plants.

TVA officials found when redoing estimates using newer diagnostic tools that the worst-case flood could be higher than anticipated, and decided to use sand baskets for a quick, temporary patch.

The NRC letter requested TVA to provide a status update at least once a year on its work.

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