Storing Nuclear Waste/The Yucca Mountain site. Arid climate and geology bring DOE to one Nevada crest

Yucca Mountain is a lonely, nondescript wrinkle in the Nevada desert. To the east of its 700-foot crest lies the sprawling Nevada Test Site (NTS), where the US Department of Energy (DOE) tests nuclear weapons deep underground.

The test site's presence and the geology of this spot have made Yucca Mountain the unlikely focus of political controversy: It has become one of three preferred locations for the nation's first burial site for highly radioactive waste from commercial nuclear reactors in the United States.

The NTS has proved of particular interest because of its desert climate. Donald L. Vieth, the director of the waste program at DOE's Las Vegas office, explains why.

The concept of geological disposal, he says, is to turn highly radioactive reactor waste into a solid. Then you bury it 1,000 to 3,000 feet underground.

To guard against the possibility that a river might expose the waste by cutting a thousand-foot deep canyon there over the next millennia or that a fault might rupture it, you look for geologically stable formations that have lasted for millions of years -- and, as far as anybody can tell, will last for millions more.

Once such a formation is found, ``that leaves only one way for the waste to get out: groundwater,'' Mr. Vieth says. Over time, everything dissolves in water. So the aridity of the Nevada desert, combined with the fact that the water table is extremely deep so a repository can be sited above it, represents Yucca Mountain's chief virtue.

The rock beneath the mountain is tuff, formed from volcanic ash. Depending on the temperature when it formed and the pressures it has been exposed to since, tuff varies in consistency from a soft chalk that crumbles in the hand to a concrete-like rock as strong as granite.

Of the six inches of annual rainfall, the DOE estimates that only a few millimeters escape evaporation or desert plants to seep down through the layers of tuff. The layers are laced with a complex network of cracking and faulting.

Although they admit there is a lot they don't know yet, the energy researchers figure that very little of this water would find its way to the repository site 1,700 feet below. And much of what did would be vaporized by the heat from the radioactive-waste canisters.

On the other hand, Yucca Mountain has a major drawback: earthquakes. According to the US Geological Survey, the spot is subject to significant quakes every 90 years or so.

According to the DOE, such temblors would not harm the repository tunnels but could damage surface structures. A bigger question is whether future quakes might alter the water table or create new potential pathways for the radioactive material to escape to the groundwater 500 feet below.

``This is a hard issue to handle,'' Vieth acknowledges.

Less investigation has been lavished on Yucca Mountain than on the candidate site in Hanford, Wash. As a result, there is more uncertainty. A key unknown is the time it takes water to flow through the dry layers of rock between the repository location and the water table. This is a vital point: Water flow times from the site to the accessible environment must be greater than 10,000 years. DOE estimates that water travels through this unsaturated zone only inches per year but acknowledges that considerable work must be done to support this contention.

It is a point on which Robert Loux, director of Nevada's Nuclear Waste Project Office, attacks the DOE vigorously.

In the draft environmental assessment (EA) on Yucca Mountain, the DOE analysis assumed that the water travels through the pores of the rock, rather than through the fractures. Some of the state's consultants feel that flow through the fractures would be fast enough to disqualify the site under the DOE guidelines.

This is one example of the department failing to apply ``appropriate conservatism,'' Mr. Loux charges.

``The point of the EA is to evaluate the existing information on the sites. People seem to forget that this is not the final word. We have five more years of work,'' replies the DOE's Vieth.

But the EAs are supposed to form the basis by which three sites are selected for site characterization. This involves sinking a large shaft on the site and mining tunnels to thoroughly evaluate the geology of the site. The process is estimated to cost $500 million per site.

The state considers DOE work so suspect that it has demanded federal subsidies to conduct its own studies. But the DOE has refused. So Nevada and Washington state have challenged this decision in court.

Loux's critical tone reflects the controversy that has developed over the project.

Gov. Richard Bryan (D) turned up the political thermostat earlier this year by declaring that, if it were up to him, he would veto the project. Other state Democrats have fallen quickly in line, perhaps recognizing, as some political analysts have pointed out, that the issue might unite the state's normally divided Democrats.

Key GOP leaders quickly counterattacked. US Sen. Chic Hecht (R), whom Governor Bryan is considered likely to oppose in 1988, has taken the lead. While not willing to support the project outright, Senator Hecht branded Bryan's stand as premature.

He added that the governor's position had already cost the state a $12-million NTS project and had jeopardized Nevada's chances for a piece of the multibillion-dollar Strategic Defense Initiative research pie.

It is unclear whether the issue has touched the Nevada public deeply: Only a handful of people turned out for public hearings on the subject held in February.

Critics of the Yucca Mountain site come mainly from the ranks of opponents to the test site and the US nuclear weapons program. Bill Vincent, the Las Vegas spokesman for Citizen's Alert, says, ``DOE's operation of the test site has been so bad that we can't trust them to operate a repository safely.''

He says transportation is his main concern. This priority is unique to Nevada. It appears directly related to the proximity of Las Vegas 100 miles away and its dependence on tourism.

``I start with the presumption that high-level waste is not compatible with tourism,'' says US Rep. Harry Reid (D). ``We spend millions of dollars to get people to come to our state. If we have one accident, even if no one is hurt, it would be headline news.''

Fourth of five articles. Next: The runner-up sites.