The Watts Bar Unit 2 reactor began producing electricity for the first time on Friday, the Tennessee Valley Authority said.

The plant is officially synced to the grid and licensed reactor operators have begun an initial test run of generation components, a major milestone for the first completed nuclear power plant in the United States this century.

TVA Chief Nuclear Officer Joe Grimes called Friday's achievement “another major step in fully integrating Watts Bar Unit 2 as the seventh operating unit in TVA's nuclear fleet.”

Plant operators expect to power up slowly while conducting “full plant testing" of systems and controls at increasing reactor power levels up to 100 percent. There is no specific target date for that process to be completed. TVA said it would be later this summer that the 1,500 megawatt plant would be producing at 100 percent.

In the meantime, tests powering up and down will be repeated several times. The unit, fully operational, is expected to provide power – combined with the Watts Bar Unit 1 reactor -- for as many as 1.3 million homes.

The photo shows reactor operator Eric Silvers in the Unit 2 control room with his eye on the plant monitor reading 49 megawatts of output.