WASHINGTON — New York Sen. Hillary Clinton and Illinois Sen. Barack Obama on Wednesday declared themselves flatly opposed to building a nuclear waste repository in Nevada, a clear indication that the 2008 presidential election could end a 25-year effort to build the controversial dump.

Clinton delivered her opposition in person and Obama by letter as the Senate Environment and Public Works Committee held its first hearing on Yucca Mountain since Democrats took over Congress in January.

Sen. Barbara Boxer, D-Calif., the panel's chair, said she had scheduled the hearing at the request of Clinton, the front-runner for the Democratic presidential nomination, who has been campaigning in Nevada on the issue. The state caucuses are Jan. 19.

Congress has been planning for an underground repository to hold spent fuel from commercial power plants and waste from defense plants since 1982. Yucca Mountain was selected as the site, and Congress voted to reaffirm that as recently as 2002, over the objections of Nevadans.

Critics charge that moving spent fuel from more than 100 commercial nuclear plants to Yucca Mountain — 100 miles from Las Vegas — would be a huge health and safety risk. They charge that the site leaks, is in an active earthquake zone and is being proposed for licensing by the Nuclear Regulatory Commission next year when its design is only 35 percent complete.

"You can't go ahead and build a house when its design is only 35 percent complete," Boxer charged at the hearing.

But witnesses for the Energy Department, the Environmental Protection Agency and the Nuclear Regulatory Commission said that submission of an application for a construction license doesn't require that every detail be mapped out.

Michael Weber, head of the NRC's nuclear material safety unit, said the process for Yucca Mountain is about the same as the one the agency followed in licensing nuclear power plants.

About the only agreement among witnesses and senators was that it's safe to keep spent fuel in storage at the power plants for a century or longer. The federal government was supposed to start accepting the waste at Yucca Mountain in 1998. But when that deadline passed with the repository in doubt, the NRC ordered plants to construct areas to hold the waste in dry casks.

Federal taxpayers are picking up the tab for that, at a cost of about $7 billion through 2017 - the best guess for when the repository might start accepting waste, assuming no problems arise.

Clinton made clear Wednesday that if she's elected president, she will halt the project.

"Yucca Mountain is not the answer," she declared. "We need to get it right. It's time to move on from Yucca Mountain. I believe we need to start over."

Obama said as much in a letter to Boxer and Senate Majority Leader Harry Reid, D-Nev.

"The selection of Yucca Mountain has failed," Obama said.

Reid needed no convincing. He's always opposed the dump, saying it was forced onto the state when its Senate delegation was new and weak.

So where should the waste go?

"Leave it where it is," Reid said. "It’s safe for 100 years. Maybe then we can do something."

But some lawmakers, such as Sen. Larry Craig, R-Idaho, said abandoning Yucca Mountain would be to abandon the promise of nuclear power as the country tries to cut greenhouse gas emissions from coal-burning generating plants to curb global warming.

"If we don’t go with Yucca Mountain, we are stuck with coal-fired generation," agreed Sen. Jim DeMint, R-S.C.

After the hearing, Edward Sprout, director of the nuclear waste program at the Energy Department, said the arguments against Yucca Mountain are bogus, including those over the EPA's slowness in writing radiation emission standards that would govern the site.

Under the model the Energy Department has developed for Yucca Mountain, the peak releases won't occur for 200,000 years and then would expose someone living 11 miles away to about the same level of radiation that he or she would encounter on a round-trip flight across the country, Sprout said.

As to the politics, Sprout said: "What happens in the elections and the next administration I have no control over."

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(c) 2007, McClatchy-Tribune Information Services.