Nuclear power output in Texas is set to double with the first steps taken in a proposed expansion yesterday. The two-reactor Comanche Peak nuclear power plant near Glen Rose would expand to four reactors under a federal application that Dallas-based Luminant filed Friday.

The proposed expansion of the Somervell County plant, about 75 miles southwest of Dallas, is part of a nationwide push for nuclear power, which backers hail as clean energy but many environmentalists oppose because of safety and waste concerns. Getting US Nuclear Regulatory Commission approval and building the new reactors could take 10 years and cost from $10.2 billion to $17 billion, according to industry estimates.

Luminant, the generating arm of Energy Future Holdings Corp, which was created in the private buyout of TXU, said it formed a joint venture with reactor vendor Mitsubishi Heavy Industries (MHI), which could take a 12 per cent share. The new reactors would be built using MHI's 1,700-megawatt, US-Advanced Pressurized Water Reactor (US-APWR) design.

"The US-APWR is the right technology, MHI is the right partner and this joint development is the right commercial focus for our team," said Mike Blevins, Luminant executive vice president and chief nuclear officer. "This is an important step forward into expanding the use of safe, dependable, clean nuclear power here in Texas."

"This joint venture will enhance the relationship between both companies, but more importantly, the construction and operation of the US-APWR at Comanche Peak will help ease the growing demand for electricity in the State of Texas," said Hiroshi Inoue, executive officer and senior vice president of MHI's nuclear energy systems headquarters.

Luminant selected MHI's US-APWR as its technology of choice in March 2007, following an extensive evaluation of prospective nuclear generating technologies. MHI established Mitsubishi Nuclear Energy Systems as a wholly owned subsidiary in Washington, DC, in July 2006, to introduce the US-APWR to the US market.

MHI submitted an application to have the US-APWR design certified by the NRC in December 2007; that application is currently under NRC review. Mitsubishi Corporation, an MHI partner, is also supporting this project.

The US-APWR has a larger core, new automatic safety systems and other advanced design elements. MHI built the existing 23 pressurised-water reactors operating in Japan and has a 24th under construction. MHI also provides a wide range of maintenance services to the plants once they are in operation.

Comanche Peak's power output would more than double. The two existing reactors, operating since the early 1990s, have a combined output of 2,300 megawatts. The new reactors would produce a combined 3,400 megawatts, which Luminant said would serve 1.8 million average homes. Power grid managers say Texas will need 15,600 additional megawatts in 10 years if old gas or coal plants shut down.

Luminant filed a 7,500-page combined operating license application with the NRC that would authorize both construction and operation of the new reactors. Under formerly separate processes, the existing plant took 21 years to build.

Company officials announced the filing Friday before about 150 employees and civic leaders in a ceremony overlooking the two existing reactors. The filing capped two years of advance work.

"It's a big day for our company and a big day for the state of Texas," said John Young, chief executive of Energy Future Holdings. Luminant and MHI will seek official support for financing from the US and Japanese governments. Luminant has submitted a loan guarantee application form to the US Department of Energy and is finalizing Phase I application information for submittal in accordance with the established guidelines.

Awareness of the environmental effects of fossil fuel power - from local air pollution to global warming - has boosted the US nuclear industry, which went decades without starting new plants due to the public's safety concerns and investor reluctance.

Many environmentalists say safety concerns remain, and they note that the federal government has not provided a permanent repository for reactors' spent fuel rods, which are far more radioactive and dangerous at the end of their useful lives than when new.

This month the NRC began a three-year licensing review of US Energy Department plans to put high-level waste inside Yucca Mountain, Nevada. "Nuclear power is neither safe nor clean," said Ken Kramer, executive director of the Sierra Club's Texas chapter. "From our perspective, you could get pretty far down the road with greater efficiency."