Steam rises from the cooling tower of the single operating reactor at TVA's Watts Bar Nuclear Plant in Spring City, Tenn.

Federal regulators have granted another nine-month extension of TVA's construction permit for the oft-delayed Watts Bar Nuclear Power Plant to give TVA a cushion in meeting its targeted completion of the plant's second reactor.

The U.S. Nuclear Regulatory Commission said Friday it approved the extension after assessing work being done at the plant. NRC spokesman Roger Hannah said the construction permit is one of the last of its type -- the only other is at TVA's Bellefonte Nuclear Plant -- since new plants started today come under a single construction and operating license.

The NRC is ready to accept TVA's application next year to operate the Unit 2 reactor by the end of 2015, Hannah said.

Construction of Watts Bar began in 1974 but has been repeatedly delayed because of changes in TVA's power demand and construction delays in trying to complete the twin-reactor plant. The Unit 1 reactor at Watts Bar was completed in 1996 at a cost of more than $6 billion and TVA projects the total cost for the second reactor to be even higher.

TVA suspended work on Unit 2 in 1988 and resumed work in 2007 when the utility projected it could complete the reactor in five years at an additonal cost of $2.5 billion, excluding interest expenses. TVA now expects to have the unit done in 2015 at an additonal cost of about $4 billion to $4.5 billion. TVA had already spent several billion dollars on Unit 2 before work was suspended.

"When we first decided to continue construction on Unit 2 back in 2007, we had originally targeted a completion date in 2012," TVA spokesman Jim Hopson said. "There are risks, no doubt, in any type of large-scale construction project like this, but we believe we've got the organizational structure, the right managers, plus we've got a lot of oversight that will allow us to address any problems that may come up."

Much of the heavy lifting on Watts Bar's second unit is already done, he said, with most of the remaining work comprising "system completion," he said. That helped NRC give the project a clean bill of health as far as environmental issues, a ruling that was "not unexpected, but certainly a pleasure to see coming in."

TVA Bill Johnson told Tennessee Valley Authority directors last week that the physical plant work on the Unit 2 reactor is about 80 percent complete and over 95 percent of the work presented for inspection is meeting quality control requirements. TVA employees and contractors at Watts Bar also have completed more than 22.9 million hours without a lost time incident at Watts Bar.

TVA expects to begin pumping water into the reactor in the spring of 2014 and to test component parts by December 2014, Johnson said.

"We're on tract for commercial operation by December 2015," he said."Watts Bar Unit 2 will add 1,150 megawatts of energy to the system and move us closer to a cleaner, more balanced generating mix."

Johnson outlined a vision to the TVA board last week to generate 40 percent of TVA's power using nuclear power, 20 percent with coal, 20 percent using natural gas with the rest a combination of hydroelectric and renewable energy. Currently, the agency produces closer to 30 percent of its power from nuclear sources, with coal taking the lead at 38 percent, natural gas in third place with 15 to 20 percent, with the rest coming from hydro and renewable sources.

In a financial report released this week, TVA said its six nuclear units operated from 73.7 percent up to 97 percent of the time during the past fiscal year, depending upon the fuel loading and repair work done at each reactor in the past year.

Sequoyah Unit 2 operated the least because TVA installed four new steam generators in Unit 2, which Johnson said was "the high point of the year" for TVA.

"This was a three-month effort staffed by almost 3,000 workers," said Johnson, who said the project was done safely and efficiently.

Contact Dave Flessner at dflessner@timesfreepress.com or Ellis Smith at esmith@timesfreepress.com