Georgia Power will pay approximately $6.4 billion to Westinghouse Electric to build its share of two proposed 1,100-megawatt nuclear reactors at the utility's Vogtle plant south of Augusta, the utility said Wednesday.

If approved, the plants promise customers higher power bills starting in 2018 . Customers would pay an additional $12 a month on a typical 1,000 kilowatt-hour bill, the company said. That amount is expected to decline over time, the company said.

The $6.4 billion projection represents Georgia Power's 45.7 percent ownership of Vogtle. The plant's other co-owners — Oglethorpe Power, Municipal Electric Authority of Georgia and Dalton Utilities — will also pay for their part of the project. The other co-owners are currently negotiating how much they will each pay Westinghouse.

Georgia Power officials said they did not want to speculate on the total price tag because of a number of variables.

"Their costs are different than ours," said Oscar Harper, Georgia Power's vice president of resource planning.

The projection comes with several caveats, Georgia Power officials said. They leave flexibility for budget overruns, adjustments for fluctuations in the prices of steel or other materials, and contractors' performance bonuses that are tied to meeting certain milestones.

The company may ask the state Public Service Commission if it could start collecting money to pay for the nuclear plants before they are built. This pay-as-you-go-plan would mean consumers ultimately would pay less because they limit the effects of inflation and possible interest rate increases over the long run.

Harper said the company would consider that and other financing options in August.

Westinghouse would build two reactors using a new AP1000 design that is modified from previous models. Utility officials tout its simpler design and enhanced safety features.

The first reactor is expected to start producing electricity in 2016. The second, in 2017. Vogtle is already home to two reactors that began operating in the late 1980s. Besides Vogtle, Georgia Power operates the Hatch nuclear plant in southeastern Georgia near Baxley.

Nuclear power is making a comeback in the United States as the nation tries to lessen its dependence on natural gas and foreign oil as well as cut back on carbon emissions and other pollutants. Based on the state's expected growth, Georgia Power says it needs to add more than 7,000 megawatts of capacity and that nuclear energy is essential to achieving that goal.

While several utilities have hinted at building nuclear reactors, few have actually committed to doing so. To spur the building of nuclear plants, the federal government has put in place tax breaks and is considering offering loan guarantees and other forms of insurance against regulatory delays and cost overruns. Georgia Power is considering applying for these but has not yet, Harper said.

"We're well positioned for each of them," he said.

Georgia Power submitted its agreement with Westinghouse to the PSC last month but did not disclose the cost figure until Wednesday. Any independent power producers that wanted to submit rival bids for plants powered by nuclear, coal or natural gas to meet Georgia's future demand, had to do so by May 1.

No other bids were submitted, a PSC spokesman said. Still, an independent evaluator at the PSC must review the company's plans. They also must receive federal approvals before they are built.

Neill Herring, a lobbyist for environmental groups, said there are less-expensive ways to provide large amounts of electricity and curb carbon emissions.

"You can get a lot more bang for your buck in spending money in other ways, if want all you want to do is reduce carbon," said Herring, who opposes nuclear plants because they are very expensive.