YUCCA MOUNTAIN, Nev. -- For more than a decade, this mountain in the heart of the desolate Nevada desert has been promoted as the best spot to bury the country's mounting pile of nuclear waste.
But a recent discovery by federal researchers has cast doubt on the plan, providing ammunition for those who have long attacked the notion of creating a permanent nuclear waste dump at this site 100 miles northwest of Las Vegas.
The researchers have found that rainwater, which could dissolve nuclear waste, has seeped from the top of the mountain 800 feet into its innards, where the high-level waste would be stored, in just 40 years -- much faster than scientists had expected.
The finding, made by Energy Department researchers studying the site in a recently completed tunnel, raises the possibility that radiation would be spread into the environment much sooner than they had anticipated.
The state of Nevada argues that the discovery of the rainwater, which seeps through what are called fast-flow paths, presumed to be cracks in the rocks extending down from the surface, disqualifies the site.
But others, including those in the nuclear industry, say that the volume of water is minimal, no matter how fast it travels, and that the cracks might help, by concentrating the water flow in just a few spots, which builders of the burial caves would be able to avoid.
Scientists have always known that water would travel through the rock, but they had believed that the water would take hundreds or thousands of years to travel deep into the mountain, which would have sharply limited how fast radiation could spread.
The wastes would be dangerously radioactive for hundreds of thousands of years, physicists say, and would most likely reach humans through water, flowing underground through the wastes and eventually reaching the surface through springs or wells.
Scientists outside the government and many environmentalists have doubts about Yucca Mountain, and question whether enough can be known about any site to predict with confidence today how waste would behave thousands of years from now. But federal officials have assumed for years that the proper way to handle nuclear waste is to bury it, and since Congress picked Yucca Mountain as the leading candidate as a burial site, the Energy Department has spent more than $2.4 billion studying the mountain. If a repository here is approved, the department would be in charge of building it.
In a recent tour through the chilly, dusty tunnel, Susan Jones, the assistant manager for scientific programs on the project, said the evidence found so far was "not really enough to answer the question, but it raises questions."
"If we could figure out where and why it's happening, that would be helpful," Ms. Jones said of the fast-water seepage. "We're not particularly sure right now."
Ms. Jones said the department would continue its evaluation of the site and was planning to issue an interim report, or "viability assessment," in September 1998. A final decision on the site's suitability is still years away.
Climate was one reason Congress gave, more than a decade ago, for choosing Yucca Mountain as the leading candidate for the country's permanent nuclear waste storage. The area gets about six inches of rain a year, most of it evaporating before it seeps into the mountain. Because the area is so dry, it is sparsely settled, presenting a generally forbidding landscape, with place names to match. Yucca sits between Little Skull Mountain, just to the east, and the Funeral Mountains, one of the ranges adjacent to Death Valley, to the west.
Once Congress picked Yucca Mountain as a candidate for a nuclear dump, the Energy Department took on the task of evaluating the site. The most important part of this job, experts say, is understanding how water flows through the mountain because this helps scientists predict how waste will behave over the next 10,000 or 100,000 years.
By studying rock samples from the tunnel, which is at the level of the proposed site, the researchers have gained some idea how water travels from the mountaintop to where the waste would be stored. But they still are not sure how water travels from that level to the next 1,300 feet down to the water table. At that level the rock is saturated with water, which then flows horizontally over wide areas, eventually reaching wells and springs, and then humans. The water table rises and falls over long periods, but Government scientists say that in the last 2 million years it has not risen more than 300 feet above its current level.
The clue that rainwater reached the repository level in mere decades was fallout from nuclear bomb tests, which was found in the tunnel in the form of chlorine-36. Although Yucca Mountain is at the edge of the Nevada Test Site, where the government has detonated hundreds of bombs, the researchers say the chlorine-36 was not from those tests, but from nuclear tests conducted around the world over in the past few decades.
In addition to finding 40-year-old rainwater, the researchers also found water that fell as rain 5,000 to 20,000 years ago. That is what they had hoped to find to support the choice of Yucca Mountain, indicating that it took thousands of years for rainwater to travel that far.
At Los Alamos National Laboratory, part of the Energy Department, Dr. Andrew Wolfsberg, a hydrologist who is part of the team that discovered the chlorine-36, said the discovery would not doom the selection of Yucca Mountain. Even if the water was moving more quickly than expected, Wolfsberg said, it was not enough water to spread much waste.
And Steven Kraft of the Nuclear Energy institute, the trade association of the nuclear utilities, argued that even with the discovery, the mountain was still very dry.
"We're not talking about a faucet in your house that's running at 45 gallons per minute," Kraft said. "These are minuscule amounts dripping through the cracks."
But Steve Frishman, technical policy coordinator of Nevada's Agency for Nuclear Projects, said federal officials had long maintained that the mere existence of fast-flowing water would disqualify a site. And Frishman argued that the area was likely to get more rain over time, increasing the dangers.
"This area is about as dry as it has ever been or ever will be," Frishman said, pointing out that scientists predict that glaciers will once again cover large parts of North America in the next few thousand years, and that when that happens, rainfall here will be much heavier.
If the repository is built, water filtering down from above for the first few hundred years would be held at bay by the heat given off by the wastes, and so there would no danger of it corroding the waste and carrying it away at that point. Frishman said the water in the rock would behave like coffee in a percolator, turning to steam and bubbling up, then recondensing into water.
But as the radiation in the waste died down, the heat would, too, and the water would return. Over centuries or millennia, the water would make the containers holding the waste corrode, and then slowly dissolve the radioactive material, carrying some of it into the environment.
If the repository is built, the Energy Department says it would want to choose a packaging system for the waste that will corrode as slowly as possible. One test now under way in the tunnel is to heat blocks of rock and see how the water behaves and whether the rock chemistry changes, so that an appropriate packaging can be found.
The tunnel is huge, 25 feet in diameter, which the designers say was needed to assure adequate ventilation. But they acknowledged that even though the tunnel was built for study purposes, it is big enough to be a driveway for a repository.
The Energy Department plans to publish an environmental impact statement in 1999 and submit a site recommendation to the president in mid-2001. In 2002, the department would submit to the Nuclear Regulatory Commission, the agency that monitors civilian reactors, an application for a license to build the repository. If all goes well, it would begin accepting waste in 2010.
But holding to any schedule is unlikely. The 1982 Nuclear Waste Policy Act established the federal government's responsibility for finding a repository for the high-level waste from nuclear weapons plants and civilian power plants. The law called for opening a repository 16 years later, which would have meant in 1998. Although the official schedule now is for opening the site in 13 years, many experts think that Yucca Mountain is still at least 16 years away from opening, if, in fact, the site can be shown to be suitable.