Cooling towers let off steam at the Sequoyah Nuclear Plant.

The Tennessee Valley Authority began refueling the Unit 2 reactor at the Sequoyah Nuclear Plant Unit today after TVA completed 438 consecutive days of operation.

"Every 18 months, one of the Sequoyah units is taken offline so fuel can be replaced and maintenance can be safely performed on key equipment and systems," Sequoyah Vice President John Carlin said. "Sequoyah's Unit 1 will continue to safely operate and generate electricity during the Unit 2 refueling.

More than 600 contractor workers will supplement Sequoyah's employees during the refueling outage. The project will involve more than 150,000 work-hours until the outage is completed.

At full capacity, Sequoyah's 1,160-megawatt Unit 1 and 1,160-megawatt Unit 2 combined produce enough electricity for more than 1.3 million homes. TVA also operates three units at the Browns Ferry Nuclear Plant in Athens, Ala., and one unit at the Watts Bar Nuclear Plant near Spring City, Tenn., where a second unit is scheduled for completion in late 2015.