Southern Co., the biggest U.S. power producer, is seeking permission from the federal government to build two additional nuclear reactors and almost double output at its Vogtle site in Georgia.

The company is proposing to add two 1,150-megawatt reactors to the two-unit site about 20 miles south of Augusta. Atlanta-based Southern's application was the first of two submitted Monday to the U.S. Nuclear Regulatory Commission. South Carolina-based SCANA Corp. said it also filed an application.

"We expect demand for electricity in the Southeast, specifically in Georgia, to increase significantly by 2015 and beyond," Barnie Beasley, president of Southern's nuclear unit, said in a statement. "Nuclear power is a safe, reliable, cost-effective power source that has a low impact on the environment."

The commission has said it expects by the end of 2010 to receive applications for as many as 33 new reactors in the United States. There are 104 operating reactors in the United States, and nuclear units provided 19 percent of the nation's electricity in 2006, according to the Energy Information Administration.

SCANA's and Southern's applications mark the first time the commission has received more than one in a single day. Neither company has made a final decision on whether to build reactors.

Rising costs and debates over who will take on the risk of building reactors has led to some delays and cancellations.

Warren Buffett's MidAmerican Energy Holdings Co. said in January it was canceling plans for an Idaho reactor because of economic concerns.

In another case, "the cost and commercial terms associated with the construction of new nuclear units has emerged over the past few months as perhaps the biggest remaining obstacle to the 'nuclear renaissance' in the United States," NRG Energy Inc. said in a March 25 statement.

Southern informed Georgia regulators in December that it would need more time to deliver cost estimates for new units at Vogtle, after it had pressed for an expedited bidding process for new power plant proposals that could serve demand in 2016.

Southern and SCANA have submitted the eighth and ninth applications, respectively, seeking permission for new U.S. reactors.

Prior to last year, the commission had not received a new license request in nearly 30 years.

"It is further indication these companies are seriously considering building new nuclear," Mitch Singer, spokesman for the Washington-based Nuclear Energy Institute, which represents plant owners and vendors, said in a telephone interview.