Constellation Energy has pulled its nuclear power plant in Calvert County off a short list of potential sites for a new nuclear reactor but said a joint venture it formed this week would strongly consider building another reactor at the facility.

The Calvert Cliffs nuclear power plant, 50 miles southeast of Washington, was one of six plants that an energy consortium had considered for the site of what could be the first nuclear energy reactor built in the United States in 30 years. The consortium, NuStart Energy Development LLC, had planned to select two locations by Oct. 1 and apply to the U.S. Nuclear Regulatory Commission for licenses to build and operate a reactor at each of them.

But this week, Constellation announced a joint venture with Areva, a French-owned nuclear company, to develop and operate a type of reactor different from what the NuStart consortium is considering. The Baltimore-based company said Calvert Cliffs was, therefore, "no longer appropriate" as a potential site for a NuStart reactor.

Michael J. Wallace, president of Constellation's Generation Group, said Calvert Cliffs was still an attractive site for its new joint venture, UniStar Nuclear, which will consider building reactors at plants owned by other companies.

"Our interest in Calvert Cliffs as a viable site is undiminished," he said.

He said the partnership planned to select sites for a reactor by September 2006. Construction would begin by 2010, and units would go online by 2015.

But Jim Riccio, a nuclear policy analyst with the environmental group Greenpeace, said it could take much longer for the Areva reactor design to receive federal approval. He also doubted that it would ever be economically feasible for the partnership to build a nuclear unit.

"They are not going to break ground any time soon on this," he said.

Staff researchers Bobbye Pratt and Richard Drezen contributed to this report.