The 500-foot-tall cooling tower, narrow at the middle to create a draft, is intended to handle 410,000 gallons of water a minute. It is still sturdy, but dark and weathered and streaked with yellow-green moss.

Other parts are more modern. The turbines, which convert steam from the reactor to mechanical energy that is turned into electricity, were replaced before they were ever used because newer designs are more efficient and durable.

Not everyone is convinced that finishing the job is a good idea.

The underlying difficulty, according to S. David Freeman, whom President Jimmy Carter appointed to chair the T.V.A. in 1977, and who tried to shut many of the nuclear projects, is that the agency’s executives are “nuke-aholics.”

“They’re addicted to nuclear power,” said Mr. Freeman, the author of a book that argues that renewable energy can meet nearly all electricity needs. He said that when he joined the T.V.A. board, “they were telling me Watts Bar was 90 percent finished, but a few years later it was 84 percent finished.”

Stephen A. Smith, executive director of the Southern Alliance for Clean Energy, is another skeptic. “There are elements of T.V.A. that are drawn to nuclear like a moth to the flame,” he said. “And the reality is T.V.A. has been burned very, very badly by nuclear power over the years.”

The contractors lowballed the price to build it in 1970 and again in 2006, Mr. Smith said. “To make it like new, they’re pulling out equipment that has never operated, and replacing it with new equipment,” he said. For people who pay electric bills, he added, “this has been a disaster.”

For the same money being spent to finish Watts Bar 2, the agency could have improved efficiency and reduced demand by more power than the reactor will produce, he argued. But his group has given up trying to stop it; now the alliance is trying to block the restart of yet another nuclear plant project abandoned years ago, Bellefonte 1.