This will be the first hearing under a Democratic-controlled Congress after the proposed nuclear repository received mostly friendly handling from Republicans during much of Bush's presidency. Both Yucca supporters and opponents are anticipating a new era of debate.

Michael Mariotte, executive director of the Nuclear Information and Research Service, a watchdog group, expects the hearing to showcase more critical oversight while hinting at the nuclear policies of a Democratic White House.

Democratic presidential contender Sen. Hillary Clinton of New York called for the hearing to investigate the administration's delay in releasing radiation-exposure standards, among other issues.

Clinton serves on the Senate Environment and Public Works Committee, but she might not be the only presidential contender in attendance at its hearing Wednesday: There is talk that Republican Sen. John McCain of Arizona might stop by . And Democratic Sen. Barack Obama of Illinois will submit questions to the panel.

The industry thinks the hearing could offer a venue to clarify the candidates' positions on nuclear power, which is rebounding with about 30 new nuclear plants on tap. Congress also is debating $50 billion in federal loan guarantees.

That said, Democrats are already being criticized for loading the hearing's witness table with anti-Yucca forces. "It's probably going to be more of a Halloween freak show," one nuclear industry representative scoffed.

As the Energy Department makes a final push to get its application to the Nuclear Regulatory Commission before the June 30 deadline, vital issues remain that the committee is poised to address.

After years of hearings, inch-thick reports and several legal battles, the debate comes back to one of the most personal subjects of all: cancer.

Just how much cancer-causing radiation should be allowed to come from the tons of spent nuclear fuel that the federal government wants to store in perpetuity at Yucca, 90 miles northwest of Las Vegas?

Is a risk of 1 in 1,700 people dying from cancer from the repository acceptable, as has been proposed? How about 1 in 70, as is suggested for the future? What about 1 in 13?

Yucca Mountain raises many specters for Nevadans, including the prospect of thousands of shipments of nuclear waste traveling to the state in what critics fear could become a "mobile Chernobyl" or target of terrorist hijacking.

Once buried, the radioactive waste could pollute ground water used for drinking and livestock for generations to come.

Nevadans have reason to be skeptical of government assurances that the site will be safe. This is the state that lived through the atomic age of above-ground nuclear tests at the Nevada Test Site, and the health problems that have resulted, including higher cancer rates among Test Site workers and downwinders .

Keeping a promise of safety for the next 1 million years seems impossible.

When the federal officials started discussing the cancer-causing potential from Yucca, they proposed a 1 in 1,700 cancer fatality risk for the first 10,000 years - meaning one in every 1,700 people exposed throughout their lifetime to radiation primarily from the aquifers across the site had a risk of dying of cancer.

A federal court threw out that standard as not tough enough. Even though that level of exposure is used by the Environmental Protection Agency as a general rule, the court said the agency needs to account for a future when the waste will be its most toxic, about 100,000 years from now.

So the agency offered a new risk assessment: 1 in 1,700 for the first 10,000 years, then 1 in 70 for the years after that. It used the median, rather than the mean, as required by Congress and the courts, meaning half the people would be exposed to higher doses. Those getting the most exposure would face a cancer death risk of 1 in 13, said Arjun Makhijani, president of the Institute for Energy and Environmental Research, who has argued against the standard.

Makhijani said the risk is even greater for women, making it "a little like Russian roulette."

"All of these risks we would consider unacceptable."

The process has stalled and a final version of the dose levels is being reviewed by the White House's Office of Management and Budget.

Clinton, speaking to Nevada reporters this summer, announced her intentions to call the Senate hearing to shed light on the "great deal of confusion and stonewalling by the administration."

Nevada's lead attorney fighting the dump, Joseph R. Egan, is among many who think the delay is an orchestrated attempt by the Bush administration to dodge a Nevada lawsuit before the June deadline if the state finds the new cancer standards unacceptable.

"We're pretty cynical about the process and for good reason," Egan said. "We think they're deliberately holding out."

However the Energy Department has said it can move forward with its June application without the radiation-exposure standards.

The Energy Department's latest report on Yucca Mountain shows that it thinks there will be far less exposure to cancer-causing radiation than is currently allowed under the EPA's existing guidelines - less than 1 percent of allowable limits in most cases.

Yucca Mountain is already 20 years behind schedule, with its new opening date estimated in 2017 or beyond.

The nuclear industry, which once said Yucca was vital to its efforts to build new power plants as part of the Bush administration's nuclear renaissance, now sees the dump as one piece of a plan that includes keeping waste in interim storage at nuclear plants, as is done now.

"Yucca Mountain isn't a silver bullet," said John Keeley, a spokesman for the Nuclear Energy Institute, the leading industry trade group. "The good news is because of the success of interim storage, we're not looking at a crisis situation."

The cancer issue is only one of the many debates that probably will play out over the next several months as Democrats take the lead and the June deadline looms.

In many ways, the conversation about how to use a Yucca repository might be just beginning.

Nils Diaz, the former chairman of the Nuclear Regulatory Commission, said last week he thinks Yucca will be used in some capacity.

But, he said, "I believe we will first determine if there are better alternatives to storing fuel at Yucca Mountain."