The Department of Energy is proposing doubling the size of a national nuclear waste repository it plans to build deep below an ancient volcanic ridge in the Nevada desert.

Citing ongoing production of waste at nuclear power plants around the country, the Energy Department has revealed plans to entomb almost 150,000 tons of highly radioactive waste at Yucca Mountain.

Nevada's senators and a state official said Friday they doubt Congress would revise a law that caps the Yucca Mountain project at 77,000 tons of radioactive waste, and will balk at a price tag that now tops $77 billion.

"If they think they are going to get more money for an irresponsible plan to ship nuclear waste across the country and into Nevada's backyard, they're dreaming," Democratic Majority Leader Harry Reid said.

Bob Loux, head of the Nevada Agency for Nuclear Projects and the state's chief anti-Yucca administrator, branded an environmental study outlining the proposal as "invalid and likely illegal.''

He said it went beyond Congressional authorization under the Nuclear Waste Policy Act of 1982, and sought exemptions from transportation regulations and hazardous waste laws.

The release of the environmental study, which triggers a 90-day public comment period, came as the Energy Department ramps up efforts to meet a self-imposed June 30 deadline to submit an application to the Nuclear Regulatory Commission for a license to operate the repository in tunnels 1,000 feet below the desert surface.

On Thursday, project chief Edward F. "Ward" Sproat III, in testimony before the House Budget Committee, raised the projected cost of the project to more than $77 billion, or about 35 percent more than the $57.5 billion the Energy Department projected in 2001.

Energy Department spokesman Allen Benson in Las Vegas said the revised figure reflected an "update" of an environmental study that Congress relied upon in 2002 when it picked the site 90 miles northwest of Las Vegas to bury the nation's commercial, military and research nuclear waste.

"It reflects the new repository design," Benson said, calling it "prudent and wise" to analyze a larger repository to contain waste being generated by 121 reactors in 39 states.

The federal government is mandated by law to dispose of the nation's nuclear waste, and the Energy Department was supposed to open the Nevada site by 1998. But the Yucca Mountain project has been slowed by lawsuits, quality control concerns and funding shortfalls.

Project officials have pushed back the target date for opening to 2017 or later.

Nevada's congressional delegation is united in opposition to the project, and Tory Mazzola, spokesman for Sen. John Ensign, R-Nev., called passage of any bill increasing the storage limit "unlikely.''

"This is just another example of DOE's attempt to move this project forward, but objective observers aren't so sure," Mazzola said.

The environmental study makes crucial projections on radiation emissions, and airs plans for transporting and burying waste that scientists say will remain radioactive for millions of years.

The study predicts "no adverse health effects to individuals" from radiation levels of up to 0.24 millirem per year measured 11 miles from the site for the first 10,000 years and no more than 2.3 millirem per year after 10,000 years.

By comparison, a chest X-ray exposes a patient to 10 millirem while a mammogram results in a 30 millirem exposure.

The projected emissions would be well below a standard proposed by the federal Environmental Protection Agency after a federal court in 2004 threw out an earlier radiation standard.

The study calls for utilities operating nuclear power plants to be responsible for loading and sealing waste "transport, aging and disposal" canisters at sites in 39 states around the country. The canisters would be shipped by rail and remain sealed during handling and entombment at Yucca Mountain.

Another environmental study issued Thursday identifies the so-called "Caliente Corridor" as the preferred route across Nevada for the Energy Department to build a railroad to the Yucca Mountain site.