Tornadoes put nuclear plant out of service

The plant and its three reactors are safely cooled down, but electricity lines that take power to and from the facility will have to be repaired, said Tennessee Valley Authority spokesman Ray Golden.

Emergency diesel generators are providing part of the power needed for cooling the reactors and pools that hold highly radioactive nuclear waste. Part is coming from offsite.

"At no time was the plant or the public in any danger," Golden said.

"The plant is safely shut down and cooled down and will stay in that status until the transmission system has been restored enough to receive power."

That could take "a number of days, if not weeks," he said.

Since 5 p.m. April 27, Browns Ferry, near Athens, Ala., has been declared in a low-level emergency state by the Nuclear Regulatory Commission. This issue is that it's having to operate on backup diesel generators.

The emergency classification should be dropped when one more offsite power line that is connected to the facility is restored. That was expected soon, Golden said.

Browns Ferry has General Electric reactors and nuclear waste pools similar to those found at the troubled Fukushima nuclear complex in Japan, where explosions occurred and radioactive materials have been released after power was lost following an earthquake and tsunami.

The waste pools, kept filled with water for cooling and to shield workers from radioactivity, are high in the reactor buildings under a tin roof in Japan and at Browns Ferry. Critics have said for years that the setup is vulnerable to terrorist attacks and power loss, which could shut down the cooling system.

The highly radioactive used fuel can be hot enough to boil the water off in the pools if cooling water is not kept circulating. Radioactive releases and even fires can result. The backups failed at the Japan plant, and officials say it appears at least some of the waste was exposed to the air.

TVA officials have said that they believe the water from the tsunami knocked out the backup generators in Japan and that TVA has more redundancies built into its system.

It's adding more, including diesel-driven fire trucks, Golden said. A total of about $15 million has been proposed since the Fukushima disaster for several projects, with almost half for moving more of the used fuel out of pools and into dry cask storage.

Many experts say the concrete and steel casks, which don't require power or cooling water, are more secure.

The storms also knocked out large blocks of TVA's siren system that is intended in an emergency to alert residents and businesses within 10 miles of its nuclear plants.

About 70 out of 100 sirens around the Browns Ferry plant failed, but most were operating again, Golden said.

At TVA's Sequoyah Nuclear Plant, about 20 miles northeast of Chattanooga, 30 of 100 quit functioning. Most of those have been restored, too, he said.

The number of homes and businesses without power had been reduced from a high of 677,000 to 152,000 as of May 2, he said.

Outages come as a result of damaged TVA lines and also a smaller, extensive network of locally owned distributor lines.

The shutdown of Browns Ferry should not cause a financial strain for TVA and its ratepayers, Golden said. The outages resulted in less power needed.

TVA, an independent federal agency that receives no tax dollars, sells power to distributors throughout Tennessee and parts of six other states.