ATLANTA --- Georgia Power filed a plan Friday that, if approved by state regulators, would nearly double the output of nuclear power at Plant Vogtle and could lead to one of the largest wood-burning biomass power plants in the country.

In a filing with the Public Services Commission, Georgia Power said adding two 1,100-megawatt nuclear reactors to the two existing reactors at Plant Vogtle would add $12 to customers' bills when the reactors come online in 2018.

The company estimates the units would save customers between $2 billion and $6.5 billion in generation costs during their lifetime when compared with similarly sized coal-powered units, and between $1 billion and $6.5 billion when compared with a natural gas-fired plant.

The expansion is estimated to cost about $14 billion, with Georgia Power paying 45.7 percent of the cost. Three other utilities -- Oglethorpe Power Corp., Municipal Electric Authority of Georgia and Dalton Utilities -- will pick up the rest of the tab.

The filing includes a request that regulators allow Georgia Power to add construction costs to customers' bills before work begins, which the company estimates could reduce construction costs by as much as 30 percent.

The Public Services Commission is expected to make a decision in March 2009, but the plan will need the go-ahead from the U.S. Nuclear Regulatory Commission.

Opponents to the expansion say new reactors aren't needed and that the amount of water the reactors would draw from the Savannah River, estimated at 70 million to 80 million gallons a day, is ill-timed given the drought.

Environmental lobbyist Neil Herring said Georgia Power could buy additional capacity from out-of-state power companies at the Plant Scherer nuclear power plant near Macon, Ga.

"We could have plenty of low-cost power available instantly," Mr. Herring said.

He also said allowing the company to charge for construction before the reactors are in use gives little incentive for preventing cost overruns.