All of TVA's electric power transmission lines in Alabama and almost all in Mississippi were taken out by Wednesday's storms.
The storms also forced the Browns Ferry Nuclear Plant onto diesel backup power and into emergency and automatic cold shutdown of its reactors.
Bill McCollum, chief operating officer of the Tennessee Valley Authority, said Thursday it could be weeks before power can be restored to all of the utility's 300,000 Alabama and Mississippi customers.
"With the level of damage we have, it will be - we hope it will be days until we get most of the customers back on - but it will be weeks before we've fully repaired all of the damage," he said.
The plant produces about 3,400 megawatts of power, about 10 percent of TVA's total output.
McCollum said the reactors, now being cooled by backup diesel power, are safe. The pools that hold the reactors' spent radioactive fuel rods also are being cooled by backup diesel power, he said.
A tornado that touched down at Widows Creek Fossil Plant in Stevenson, Ala., also damaged transmission equipment and lines, taking several out of service.
Transmission lines are the monster power cables that carry electricity from power plants to distributors such as EPB and Huntsville Utilities.
Now those utilities, along with a number of large industries that are wired directly to TVA transmission lines, will not have power until the lines are repaired, McCollum said.
At the Scottsboro Electric Power Board in Scottsboro, Ala., a recorded message of frustration greets callers: "We are experiencing an extended outage. We do not have any power coming from TVA. Until they restore our power, we cannot restore your services. We are sorry for the inconvenience."
James B. Sandlin, manager of the Scottsboro utility distributor, said he thinks the company's 8,500 customers are "mostly patient."
The Jackson County town dodged a bullet on tornado damage, and most of Scottsboro's downed power lines were restored Wednesday. But then TVA lost power.
"We're at the mercy of TVA," Sandlin said.
Browns Ferry concerns
Sandy Kurtz, an anti-nuclear activist and co-founder of the Bellefonte Efficiency and Sustainability Team, said her group is pleased that the diesel generators kicked in as they should at Browns Ferry, but she still finds the event troubling.
"It reminds us of Fukushima," she said, referring to the Fukushima Dai-ichi nuclear plant in Japan, which has had radiation leaks since an earthquake and resulting tsunami crippled its cooling systems in March.
"This power outage and reactor shutdown is yet one more example of the ongoing and unnecessary risks associated with nuclear power," Kurtz said.
The loss of the transmission lines also caused Browns Ferry Nuclear Plant to lose power. When the plant generates power, it uses some of its electricity to power itself, and the excess is sent out on the transmission lines. When the transmission lines can't take power away from the plant, it causes the reactors to shut down, according to TVA officials.
When that happened, TVA declared a "notification of unusual event" after the normal and alternate power supplies for essential equipment at Browns Ferry were unavailable for more than 15 minutes, according to TVA officials. The notification is the lowest of the four levels of nuclear plant emergency classifications required by the Nuclear Regulatory Commission.
NRC spokesman said Ken Clark said all three reactors at the plant are in safe shutdown, and the NRC has four Browns Ferry resident inspectors who are overseeing the shutdown and repair.
TVA has a two-week supply of diesel fuel and is bringing in more, Clark said.
Seven of the diesel generators started as they should, he said. One was in scheduled maintenance but already may have been returned to service, he said.
The generators are in a safe concrete building next to the reactor building, Clark said. The fuel is stored underground.
The only transmission line TVA didn't lose at the plant is not large enough alone to operate and cool the plant. McCollum said it is being used to light plant buildings.