* What: Steam generator replacement
* How: With 380-foot crane
* When: The next 90 days
* Where: Soddy-Daisy
* Cost: $360 million
TVA is about to peel the top off a reactor at Sequoyah Nuclear Plant.
That's literally what the Tennessee Valley Authority's $360 million project to replace the Unit 2 steam generators will entail.
And everything about the three-month job is massive - from safety precautions to quell public concerns to the largest crane in the world, which had to be constructed onsite.
"The planning work started about a decade ago, and we're now at the site preparation stage that began in the past year or two with a team dedicated specifically to this task," said TVA spokesman Ray Golden.
TVA is replacing four original generators that work in tandem with the 30-year-old pressurized water reactor to make electricity.
Because they were built into the plant from the ground up, TVA must cut the top off the reactor's concrete containment building to get the old ones out and the new ones in.
To do that contractors will use a hydroblaster - a high-pressure water jet.
Then with the giant crane they will lift out, one at a time, each 345-ton generator. Then the crane will lift the similarly hefty replacement generators and gingerly set them inside to be rewelded into place.
Both Golden and frequent TVA critic David Lochbaum, nuclear project director of the Union of Concerned Scientists, say the process should not present contamination concerns for the public.
There could be some radioactive dust released, but it would be expected to be well below safety standards, Lochbaum said.
How big is big?
Generator refits such as this one have been done at dozens of other nuclear plants around the country -- including Sequoyah's Unit 1 in 2003 and Watts Bar in 2006, Golden said.
The biggest concern is more of economics rather than safety, as the industry claims every day a nuclear reactor is idled costs a utility $1 million in revenues.
Golden said TVA is planning to complete the generator replacement and normal refueling in 80 to 90 days.
There have been some problems at other plants.
In 2009 at Crystal River Nuclear Plant in Florida, workers creating the containment wall opening discovered an unexpected crack, or separation, inside the concrete wall and a gap between the outer 10 inches of concrete and the inner concrete. The steel liner, which was intact and undamaged, and the 32-inches of concrete outside the steel liner also was intact. But the plant is still shut down.
In 2010 at Three Mile Island Nuclear Plant in Pennsylvania, a radiation leak during a similar operation resulted in 150 workers being sent home.
At San Onofre Nuclear Plant in California, a replacement this year resulted in dust damaging equipment that led to an extended shutdown after the plant restarted.
But Golden said TVA expects no problems, and anticipates improved efficiency at the plant when the new generators are in place.
"We'll be about the 40th reactor site to undergo generator replacement," he said.
Already two giant cranes are beginning to lift construction material to and from the top of the Unit 2 containment building in Soddy-Daisy.
The largest crane is 380 feet tall.
"It took 175 tractor-trailer loads of equipment to erect it," Golden said.
The shorter crane, at 322 feet, is hardly small.
The two machines have a weighty task.
The large one will make about 22 heavy lifts. Each of the four generators it will remove from the reactor's containment building weigh 345 tons.
"To give that some perspective, that's the equivalent of about 345 VW Beetles," Golden said.