The Nuclear Regulatory Commission is widely expected to approve on Thursday a construction and operating license for new nuclear power reactors for the first time since 1978, giving Southern Co. the green light to build two new units at its existing Vogtle site in Georgia.

Southern, which filed its license application in March 2008, said it expects the project to cost $13.3 billion. It will use Toshiba’s AP1000 reactors, the design of which the NRC certified in December, and it hopes to bring them online in 2016 and 2017.

The new reactors, however, are no longer seen as the start of what the industry once predicted would be a nuclear renaissance. Virtually all of the 31 plants that had been proposed by 2009 have been shelved as a result of cheap natural gas, high construction costs, weak electricity demand and safety concerns following the Fukushima Daiichi disaster in Japan.

Ten anti-nuclear groups have vowed to file suit against the NRC if it approves the license as expected. They said they would argue that the agency broke the law by failing to consider the full lessons of the Fukushima disaster, in which a string of four reactors were badly damaged in an earthquake and tsunami.

Southern, whose Georgia Power subsidiary owns 45.7 percent of the project, has already spent $4 billion preparing the site and doing preliminary construction 26 miles southeast of Augusta.

It has been able to keep pushing ahead in part because the Energy Department in February 2010 approved $8.3 billion in loan guarantees for the new reactors, saving Southern and its partners hundreds of millions of dollars in financing costs, one of the biggest expenses of building nuclear power plants. Critics say that the Obama administration underestimated the risk of default, cost overruns and delays.

Moreover, in Georgia, utilities can pass along costs to ratepayers while construction is still in progress. In most states, utilities can only start charging ratepayers for a power plant once the plant is operating. Georgia ratepayers paid $233 million in 2011 and this year will pay $258 million to cover part of Southern’s costs. Additional amounts will be passed along in later years, averaging $8.74 a month for a typical customer, according to Southern spokesman Mark Williams.

The Vogtle project “survives only because Georgia regulators have agreed to make the customers pay for it regardless of the fact that its power is likely to be three times as expensive as other realistic combinations of alternatives,” said Peter Bradford, a former NRC commissioner and critic of many nuclear projects.

Williams said Georgia Power would be able to charge customers $1.7 billion of the company’s $6.1 billion in costs before the plants come online.

The last nuclear reactor built in the United States is the Tennessee Valley Authority’s Watts Bar plant, which was started in 1973, suspended in 1988, then completed in 1996. A second unit was never completed because electricity consumption grew less than expected, according to the TVA.

Applications for new reactors dropped off in 1978 for financial reasons, and then the Three Mile Island accident in 1979 dealt a further blow to nuclear power expansion. Instead, federal regulators have extended licenses for 71 of the nation’s 104 nuclear power plants. Today, nuclear power provides 20 percent of U.S. electricity, but many plants will reach the end of their license extensions over the next two to three decades.

Marc de Croisset, an analyst for FBR Capital Markets, said that an NRC approval for Vogtle could mean rapid approval for other new units, including two that the utility Scana has proposed to build in South Carolina, another state that allows costs to be passed along to ratepayers during construction.

“This marks the beginning of a riskier phase of the construction process,” de Croisset wrote recently. “The utility industry will be watching for any cost overruns and other mishaps. How well construction progresses could spur further nuclear builds or potentially bring the nuclear renaissance to a standstill, particularly given the backdrop of low natural gas prices.”

Others were more skeptical about the future for nuclear power. “New nuclear power is an economic meltdown waiting to happen and the American taxpayer is on the hook for the financial fallout,” said Jim Riccio, a spokesman for Greenpeace. He said taxpayers were helping “to build new nuclear reactors that corporations would never risk building themselves.”