The outage, which begins Monday, was planned to allow for replacement of the four steam generators in Unit 2.
“TVA typically does their outages in the spring and fall when there is a low load on the grid, so there won’t be a challenge to the grid because the other units will be up and running,” Sequoyah operations manager Sean Connors said.
Two types of power are delivered from the plant: 500,000-watt power and 161,000-watt power.
The 161,000-watt power is relayed to Cleveland and Bradley County. The 500,000-watt power is sent as close as Chattanooga and as far away as Nashville.
Officials emphasized none of these areas will experience a drop in service during the outage.
“This is a really important outage for Sequoyah,” site vice president John Carlin said. “We use outages to really improve our reliability and really improve our margins. It is a time for us to replace new fuel into the reactor.
“It’s a time we take advantage of doing some very extensive maintenance and doing some very extensive modification to the plant. … The most reliable plants are the safest plants,” he said.
The plant produces enough power for 1.3 million people, according to Carlin.
Personnel at Sequoyah stressed there is not a problem with the current steam generators, but they are being replaced before they begin to degrade and affect the plant’s operations.
“One of the reasons we’re replacing the steam generators is to increase our margins and safety,” Carlin said. “They are going to increase the reliability of the station.”
The outage will be run on a well-planned schedule. Mike Scaggs, senior vice president of Nuclear Construction, said this schedule is calculated down to the minute to ensure the replacement of the steam generators is successful. The process is being carefully planned in the outage control center within the Sequoyah plant.
“The steam generator replacement is really just … a statement of our commitment to keeping our nuclear fleet safe,” Scaggs said. “The purpose of replacing the steam generators is before [they] become degraded and not performing the way they need to perform, we replace them so we don’t cut into the margin of quality or safety too deeply.”
Scaggs said personnel are continually admonished that if they do not understand something, stop and ask questions.
More than 1,000 people are involved to the outage project, Scaggs said.
“This is a monumental effort that’s been in the works for many years at TVA,” Carlin said.
Models and computer images have been created for many of the moving parts of the project to plan out each step of the process.
“Any time we can practice something … we work really, really hard on doing that,” outage project manager Marie Gillman said. “We do mock-ups of all the welding, we do mock-ups of the cutting. We do mock-ups of making sure that everything is clean and pristine when we are finished.”
The new steam generators were made in Korea and ordered in 2007, Gillman said.
The new generators have been on the site for a year in preparation for the planned outage.
Gillman said how long the process takes, from ordering to receiving the steam generators, depends on the demand because only a few places in the world can supply such a massive undertaking.
Altogether the four steam generators cost $90 million. Each generator is 70-feet tall and weighs 345 tons. The generators are housed in a concrete cylinder building.
To replace the generators, part of the top of the current building will be cut off using a water blast of 20,000 pounds of pressure to cut the 3-foot thick concrete. Each generator is surrounded by a concrete chamber within the concrete cylinder, which will also have the top cut off. Before a steam generator is removed, it is drained of all the water used in the process before any lines to the generator are cut.
Noise from cutting the cylinder building will be heard for about a five-mile radius during the process. The cutting will last about five days.
Plant manager Paul Simmons said residents in Soddy-Daisy and Lakesite, the towns nearest the plant, have been warned about the noise. The sound has been compared to a 747 airliner sitting on a runway with its engines roaring.
However, the project at Sequoyah will also bring revenue to the area because of the specialized teams staying nearby for the duration of the outage, Carlin said.
The planned outage will start on Monday and will run though the end of the year.
“Obviously our goal is to make it shorter rather than longer,” Carlin said.
The goal is to have the project completed in 90 days.
Weather can be a factor in the process and can delay the completion time.
One of the largest cranes in the world, developed in Sweden, will be used to lift the empty steam generators from their current home to the new holding building. The generators will remain there until the plant is decommissioned. At that time, they will be hauled away in one piece for proper disposal or will be cut up on site and remain at the facility, Gillman said.
Gillman said many utilities choose to leave the steam generators on-site.
Scaggs said the crane was delivered in kit form in more than 170 tractor-trailer loads. He said the crane takes 30 days to assemble.
Steam generator replacements have been successfully completed in the past. Scaggs said this is the third such replacement for TVA.
The steam generators for Sequoyah Unit 1 were replaced in 2003. These steam generators are stored on site in a concrete building and monitored on a monthly basis to check for radon levels. The steam generators being replaced in this outage will be bolted to the floor in an identical building, Scaggs said. The building is designed to withstand any inclement weather such as tornadoes, and is also designed to withstand earthquakes.
“We ensure that there is no potential for anything to impact either the employees or the public,” Carlin said.
Other nuclear power plants across the country have replaced steam generators in the past. Scaggs said knowledge from these previous projects is being applied to the Sequoyah Unit 2 replacements.
In addition to replacing the four steam generators for Unit 2, the plant will also be replacing one of its turbines. The turbine works much like a water wheel to produce energy but instead of water it uses steam, Simmons said.