TVA's tricky job of cutting two holes in the roof of a Sequoyah Nuclear Plant reactor to extract and replace four steam generators has come to a safe end, according to officials.
Tennessee Valley Authority announced Friday that the plant's Unit 2 reactor is making electricity again after the three-month job was completed seven days early.
The work -- along with regular refueling and maintenance -- also came in under the projected $376 million budget, according to TVA spokesman Ray Golden.
Now TVA will move ahead with a plan to ask the Nuclear Regulatory Commission to extend TVA's operating license for Sequoyah by as much as 20 more years, he said.
Currently, the Soddy-Daisy plant's two reactors are licensed until 2020 and 2021.
Everything about the generator replacement job, termed by TVA's chief nuclear officer, Preston Swafford, as "a complex feat of design, engineering and skilled craftsmanship," was massive -- from its safety precautions to its largest-in-the-world crane.
"I'm extremely proud of the nuclear professionals who worked tirelessly to manage this outage at Sequoyah Unit 2 safely, with careful attention to costs and schedule, all while continuing to operate Unit 1 at 100 percent power," Swafford said.
The new generators -- like the old ones -- work in tandem with the 30-year-old pressurized water reactor to make electricity. They were built into the reactor at a time when the nuclear industry believed a reactor's working lifespan was 30 to 40 years.
To ensure the public's safety when the radiation containment building's top was peeled back by robots wielding massive high-pressure water sprays, TVA covered the roof with custom tents to catch any dust that might escape the water spray.
The water drained from the containment roof cutting process was run through eight filtration tanks and monitored thoroughly before being released into the river.
And the scrapped generators were sealed for decades of storage in monitored and seismically qualified, thick concrete bunkers on the plant site, according to Marie Gillman, generator replacement project supervisor.
Similar generator replacements have occurred at 39 other nuclear plants across the country, including Sequoyah's Unit 1 in 2003 and Watts Bar in 2006, Golden said.
But in other locales, not all were successful.
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 were 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.
In 2012 at San Onofre Nuclear Plant in California, a replacement resulted in dust damaging equipment and has led to an extended shutdown.
But Golden said planning began for these generator replacements about a decade ago, and site preparation here about two years ago with a team dedicated specifically to this task.
Including Sequoyah's normal plant personnel, contractors and temporary workers, there were nearly 3,000 people involved in the generator replacements and reactor refueling.
About 1,300 temporary workers were dedicated to the steam generator work, which required about 1 million work hours -- all completed without a single lost-time incident, Golden said.
Additionally, about 1,000 temporary workers supported the refueling and maintenance of Unit 2.
Sequoyah Unit 2 is one of six nuclear reactors operated by TVA at three nuclear power plants. About 30 percent of Tennessee Valley electricity is generated in nuclear plants.