By Scott DiSavino April 30 (Reuters) - U.S. regulators have signed off on an environmental review for two new nuclear reactors that Progress Energy Inc hopes to build at Levy County on Florida's west coast. The U.S. Nuclear Regulatory Commission (NRC) said in a release on Friday the NRC staff and the U.S. Army Corps of Engineers completed the final environmental impact statement for Levy's combined construction and operating licenses (COL). Before the U.S. Nuclear Regulatory Commission (NRC) can approve of the 2,200-megawatt (MW) project, the NRC said its staff must complete a safety review and its judicial arm must decide on a challenge of the staff's environmental review by environmental groups. Progress Energy, a North Carolina-based power company, has said the NRC could issue a license for Levy in early 2013. Progress estimated the total cost of the Levy plant at $17 billion to $22 billion, including about $3 billion needed for transmission infrastructure, with the first unit expected to enter service in 2021 and the second 18 months later. Progress said it planned to include joint owners in the Levy project, but has yet to announce any joint owners. Progress in January 2011 agreed to a $13.7 billion merger with neighboring North Carolina-based power company Duke Energy. Progress applied with the NRC in July 2008 to build and operate two Westinghouse Electric AP1000 reactors at Levy. Westinghouse is majority owned by Japanese multinational Toshiba Corp. The AP1000 is a 1,100-MW pressurized-water reactor design. The Levy plant is on the west coast of Florida near Progress' 860-MW Crystal River nuclear power plant. Crystal River has been off line since September 2009 when a refueling and power up-rate began. During the upgrade, workers discovered a gap in the concrete containment dome, which was opened to install new steam generators. Crystal River was originally expected to restart in April 2011 but Progress said last summer the unit would not restart until 2014. The company has estimated the cost of repairing the containment structure at between $900 million and $1.3 billion. AP1000 MOST POPULAR The AP1000 reactor design planned for Levy is the most popular design in the United States, claiming 12 of the 20 reactors under development or construction in the country. The NRC certified the AP1000 in December 2011 and there are four AP1000s under construction in the United States - two at Southern Co's Vogtle nuclear plant in Georgia and two at Scana Corp's Summer nuclear plant in South Carolina. The two reactors at Vogtle will cost Southern and partners about $14 billion and enter service in 2016 and 2017. The two reactors at Summer will cost Scana and partners over $9 billion and enter service in 2017 and 2018. The utilities have said the difference in cost depends on several factors including whether the reactors are at a greenfield site like Levy and the cost of transmission lines. Despite the so-called nuclear renaissance, the four new units at Vogtle and Summer will likely be the only new reactors built in the United States by 2020. The Tennessee Valley Authority, meanwhile, expects to finish an older reactor over the next few years at the Watts Bar nuclear plant in Tennessee that the government-owned power company started working on in the 1970s, stopped work in the 1980s, and restarted in the 2000s. Several factors have stalled the nuclear renaissance that observers predicted a decade ago when fossil fuel prices were high and the U.S. government was expected to cap carbon dioxide emissions to combat global warming. Low natural gas prices have kept electricity prices low, making it economically difficult for energy companies to build anything but natural gas-fired power plants without state-sponsored programs such as those in Georgia, South Caroline and Florida, that guarantee nuclear builders will recover costs. New nuclear construction also slowed after the nuclear accident at the Fukushima nuclear plant in Japan last year. Other factors include weak growth in power demand and growing use of energy efficiency and conservation programs.