What: Steam generator replacement
How: With 380-foot crane, hydroblaster and more than 2,000 workers
When: Beginning early Monday
Where: Sequoyah Nuclear Plant in Soddy-Daisy
Cost: $360 million
In the coming week, a remote-controlled robot will begin a continuous run around what looks like a miniature train track suspended over the domed top of Sequoyah Nuclear Plant's Unit 2 reactor.
The robot will hold a hydroblaster cutting machine that, with 20,000 pounds per square inch of water pressue, will grind through three feet of concrete to make two 45-by-20-foot holes in the top of the containment building over the reactor.
The noise — described as "like a 737 sitting at the end of the runway" — will be continuous for four or five days and nights.
And it will be audible for about five miles.
Tennessee Valley Authority's nuclear construction chief Mike Skaggs and Sequoyah site Vice President John Carlin said they know the noise and the presence of the world's largest crane towering 370 feet above the plant to lift out four massive generators and lifting in four more may prompt concern and even irritation from neighbors.
But supplanting the 30-year-old generators is necessary.
"We're replacing them so we don't cut too deeply into the margin of safety and performance," he said.
Carlin said the noisy part of the 90-day plant outage and generator replacement project is just a fraction of the $360 million effort.
"This is a very, very major project," Carlin said.
When it is complete and the plant returns to operation, TVA will ask the Nuclear Regulatory Commission to extend Sequoyah's operating licenses at its two reactors for another 20 years.
Now the reactors are licensed until 2020 and 2021.
"It's a very detailed assessment that will be reviewed by both the American Council on Reactor Safety and the Nuclear Regulatory Commission," Carlin said.
Sequoyah has a room dedicated as an "outage control center."
For the next three months, that outage control center will essentially become the project war room.
Here and for the next three months, TVA officials will watch -- via close-circuit camera and computer screen -- every aspect of the project that has been 10 years in planning, Carlin said.
First the plant will be shut down, the fuel removed and the generator water level will be lowered. Once the roof is cut and the metal plate ceiling of the generator room is lifted, then first one then another of the four generators will be lifted by the giant crane. Each 30-year-old generator -- and its replacement -- is 70 feet tall and weighs 345 tons.
Each new generator -- made in South Korea at a cost of $22.5 million -- must fit back into place perfectly and be rewelded.
In the outage control center, plant and project managers can watch remotely and "coach" workers, making sure no one gets too much exposure as they work to cut and reweld pipes in the containment area.
Marie Gillman, generator replacement project supervisor, said 1,100 people have been dedicated to the project, and both the workers and the public should be safe.
She pointed to several work area "mock ups" where workers and contractors have been "practicing" cuts and reattachments on real-sized equipment so that when the work will be done in the containment building, workers won't be performing the operation for the first time.
She said the water drained from the containment roof cutting process will be run through eight different filtration tanks and monitored thoroughly before being released into the river.
Tents will cover the roof to catch any dust that might escape the water, she said.
And the scrapped generators will be sealed and stored in monitored and seismically qualified, thick concrete bunkers on the plant site.
Generator refits such as this one have been done at 40 other nuclear plants around the country -- including Sequoyah's Unit 1 in 2003 and Watts Bar in 2006, Golden said.
And lessons from those refits indicate plant economics have been more at risk than the public, as the industry claims every day a nuclear reactor is idled costs a utility $1 million in revenues.
At Sequoyah, officials said the 90-day clock will begin ticking on Monday.
But Scaggs made it clear that if questions arise, work will stop until safe and sure answers are determined.
"That schedule has got the logic of what we need to do to protect our staff and the health and safety of the valley," he said.
Pam Sohn has been reporting or editing Chattanooga news for 25 years. A Walden’s Ridge native, she began her journalism career with a 10-year stint at the Anniston (Ala.) Star. She came to the Chattanooga Times Free Press in 1999 after working at the Chattanooga Times for 14 years. She has been a city editor, Sunday editor, wire editor, projects team leader and assistant lifestyle editor. As a reporter, she also has covered the police, ...