WASHINGTON -- Sen. Patty Murray, D-Wash., repeatedly asked Energy Secretary Steven Chu if he could show any scientific basis for terminating Yucca Mountain, Nev., as the nation's nuclear repository during a congressional hearing Thursday.

Other knowledge and other conditions e-volved that made Yucca Mountain in-creasingly not look "like an ideal choice," Chu answered initially at an Energy Appropriations Subcommittee hearing. He was looking down, the ease with which he had answered previous questions in the hearing gone.

But was there scientific evidence, Murray pressed.

"It was an unfolding of issues that continued," Chu said, adding that President Obama made very clear that it's not an option.

But was there scientific evidence behind that decision, Murray asked again.

She came to the hearing "very dismayed" that a day earlier the Department of Energy had filed to permanently withdraw the licensing application for Yucca Mountain, which was planned to hold high-level radioactive waste and irradiated fuel from the Hanford nuclear reservation.

"Over the last 30 years, Congress, independent studies and previous administrations have all pointed to, voted for and funded Yucca Mountain as the nation's best option for a nuclear repository," Murray said.

"And in concert with those decisions, billions of dollars and countless work hours have been spent at Hanford and nuclear waste sites across the country in an effort to treat and package nuclear waste that will be sent there," she said. "Without a repository, those sites and the communities that support them have been left in limbo."

There have been changes since work began on Yucca Mountain, including a Supreme Court ruling that the repository must protect the environment from the waste not just for 10,000 years, but a million years, Chu said.

Radioactive dating has shown that other sites, like salt domes, have been inherently stable for longer than a million years, he said. That's very different than Yucca Mountain, which has deep fissures that would be saturated with water if climate changes, he said.

In addition, the salt in salt domes would ooze around the waste, making the disposal permanent, he said.

It's the sort of issue that will be considered by the newly named blue ribbon commission that will study options for disposal of nuclear weapons waste and options for the nation's used commercial nuclear fuel, he said.

Murray responded that less-studied options could prove to have problems as they are investigated to the extent that Yucca Mountain has been.

"We can't just unilaterally take one site out of the equation," she said.

She also asked Chu if any communities near former nuclear weapon sites, including the Tri-Cities, had been consulted in the DOE decision to terminate Yucca Mountain.

They had not, Chu said, but DOE has a legal obligation to remove high-level radioactive waste that it takes very seriously. The blue ribbon commission will be making suggestions, possibly including changes in legislation, that "will allow for a comprehensive, sensible approach to the back-end of the fuel cycle," he said.

"I don't believe science can say Yucca Mountain is the ideal site given what we know today and what can be developed in the next 50 years," he said.

Murray also questioned Chu about the Obama administration's proposed Hanford budget for fiscal 2011. It includes a $50 million shortfall for ground water cleanup and protection, she said.

"These budgets aren't put together just by wishing or magic," she said. "DOE works with the regulators, they work with communities, they agree on milestones."

The proposed budget is adequate to meet legal obligations, Chu said, adding that he consistently has supported DOE's environmental cleanup program.

Chu had the last word, pointing out that some of DOE's large environmental cleanup projects have a troubling history of falling behind schedule and exceeding their budgets.